Design of an Ultra Wideband Radio Front-End for Multi-band Communications

Department of Science and Technology Institutionen för teknik och naturvetenskap

Linköpings universitet Linköpings universitet

SE-601 74 Norrköping, Sweden 601 74 Norrköping

Examensarbete

LITH-ITN-PR-07/001--SE

Design of an Ultra Wideband

Radio Front-End for Multi-band

Communications

José Luis Alcaraz González

LITH-ITN-PR-07/001--SE

Design of an Ultra Wideband

Radio Front-End for Multi-band

Communications

Examensarbete utfört i Elektronikdesign

vid Linköpings Tekniska Högskola, Campus

Norrköping

José Luis Alcaraz González

Handledare Magnus Karlsson

Examinator Shaofang Gong

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Institutionen för teknik och naturvetenskap Department of Science and Technology

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LITH-ITN-PR-07/001--SE

Design of an Ultra Wideband Radio Front-End for Multi-band Communications José Luis Alcaraz González

As things stand today, the application of multiband systems with a variety of frequency band combinations is accelerating. The new generation of wireless communication devices includes many utilities that use different standards. This project deals with design of a single antenna module for different standards, i.e., to design an ultra-wideband antenna together with frequency multiplexer. The thesis focuses on the wideband antenna design. In

principle, the module must be able to work with GPS, GSM, UMTS, ZigBee, Bluetooth and Wi-Fi in the 1.5-2.5 GHz band.

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Design of an Ultra Wideband

Radio Front-End for Multi-band

Communications

A Master’s thesis work by

José Luis Alcaraz González

2007-09-11

Department of Science and Technology

Norrköping

i

Abstract

Application of multiband systems with a variety of frequency band combinations is accelerating since the communication capacity is increasing and new functions like GPS or Bluetooth are being added. It is expected, therefore, that all the handsets will probably become compatible with multibands in the near future. In such multiband systems, a multiband antenna is definitely one of the key devices since it is compatible with all the frequency bands without resort to multiple antennas as is usual in today´s practices. This project deals with design of a single antenna module for different standards, i.e., to design an ultra-wideband antenna together with frequency multiplexer. The thesis focuses on the wideband antenna design. In principle, the module must be able to work with GPS, GSM, UMTS, ZigBee, Bluetooth and Wi-Fi in the 1.5-2.5 GHz band.

The antenna type chosen was the dipole antenna and it was implemented using a four metal layer PCB structure wich includes a flexible material. Two different shapes were used for the dipole, square and circular. The design process is mainly carried out in two steps. In the first step dimensions of the antennas were calculated and some results were verified in Linecalc. Then, in the second step, dimensions were experimentally tuned until simulation results fulfilled the demands of the design specifications. Evaluation was done by looking at impedance bandwidth and radiation characteristics. Simulation results showed that with perfect circular discs a correct adaptation could not be obtained in the specificated frequency band and because of this an improved circular discs antenna was designed. With this new design a good result was obtained, the voltage standing wave ratio was under 3 in the whole band. With the rectangular antenna a good result was also obtained, too. In both cases, the worst behaviour was in the middle of the bandwidth.

The multiplexer structure came from a theorical design. Initial transmission line parameters were calculated in Linecalc and filters are implemented with the ADS tool. Finally, the design is experimentally tuned until good simulations results were obtained. The network insertion loss is under 2.3 dB between input port and all output ports and isolation behavior between all the different ports is satisfactory.

In the end, the complete Multi-band Front-end was simulated using both antennas obtaining good behaviour for isolation and return loss parameters.

In conclusion, a planar ultra wide-band front-end for GPS, GSM, UMTS, Bluetooth, WiFi, and ZigBee standards in the 1.5-2.5 GHz band using planar dipole antenna and microstrips has been designed with good simulation results.

ii

Acknowledgements

I would like to express my gratitude to the following people for treating me so kindly, they have supported me in countless ways during the last few months:

Professor Shaofang Gong, for his guidance, support and for giving me the opportunity to develope my Thesis work in his group at Linköping Universitet.

My supervisor, Magnus Karlsson, for his help with ADS and for all the time he has dedicated to me.

Pär Håkansson and Allan Huynh, for their help the first days in Sweden.

Mutaz Hamed Hussien Hamed Hussien Khairi, Johan Nordlander and other diploma workers in the group, for their support.

My friends here in Sweden, Nacho, Maikel, Juanbe, Luis, Fleur, Nacho N., Víctor, Eva, Lorena and all the others for their friendship during all these months.

The spanish friends who came to visit me, Manu, Sisco, Marga, Marta, Carlos, Quique and Diego. They brought me pieces of Spain to make things easier all these months when i was far from home.

Last but not least, I would like to thank deeply my beloved family with special thanks to my parents, my brother and my girlfriend, Ana. Thank you for your encouragement.

iii

List of Abbreviations

3G Third Generation

3GPP 3rd Generation Partnership Project

ADS Advanced Design System

BPSK Binary Phase Shift Keying

CCA Clear Channel Assessment

CCK Complementary Code Keying

CEPT Conférence européenne des administrations des postes et

des télécommunications

CDMA Code Division Multiple Access

CSMA/CA Carrier Sense Multiple Access with Collision Detection

DSSS Direct Spread Spectrum Modulation

DBPSK Differential Binary Phase Shift Keying

DQPSK Differential Quadrature Phase Shift Keying

ETSI European Telecommunications Standards Institute

FDMA Frequency Division Multiple Access

FDD Frequency Division Duplexing

FHSS Frequency Hopping Spread Spectrum

GSM Global System for Mobile Communications

GPS Global Position System

ITU International Telecommunication Union

IEEE Institute of Electrical and Electronics Engineers

ISM Industrial, Scientific and Medical

MAC Medium Access Control

OFDM Orthogonal Frequency Division Multiplexing

O-QPSK Offset Quadrature Phase-Shift keying

PDA Personal Digital Assistant

PCB Printed Circuit Board

iv

LR-WPAN Low Rate Wireless Personal Area Network

TDMA Time Division Multiple Access

TEM Transverse Electromagnetic

UMTS Universal Mobile Telecommunications System

UHF Ultra High Frequency

VSWR Voltage Standing Wave Ratio

Wi-Fi Wireless Fidelity

WCDMA Wideband Code Division Multiple Access

WLAN Wireless Local Area Network

WPAN Wireless Personal Area Network

vii

List of Figures

Fig. 2.1. Entire front-end system

Fig. 2.2. Trilateration in two dimensions

Fig. 2.3. Positioning principle in three dimensions Fig. 2.4. WiFi network

Fig. 2.5. Bluetooth piconets Fig. 2.6. Two port network Fig. 3.1. PCB cross-section Fig. 3.2. PCB Upper view

Fig. 3.3. Front and cross-section of the balun structure. Fig. 3.4. Reference Antenna dimesions

Fig. 3.5. Reference Antenna layout Fig. 3.6. Reference antenna VSWR Fig. 3.7. Rectangular Antenna design

Fig. 3.8. Rectangular Antenna dimensioning Fig. 3.9. Rectangular antenna balun dimensions Fig. 3.10. Balun layout for the rectangular antenna

Fig. 3.11. Forward transmission simulation for the rectangular antenna balun Fig. 3.12. Rectangular antenna balun balance

Fig. 3.13. Rectangular antenna balun phase angle

Fig. 3.14. Rectangular Antenna + balun schematic Fig. 3.15. Rectangular Antenna + balun VSWR

Fig. 3.16. Circular disc antenna design

Fig. 3.17. Circular Disc Antenna Dimensioning Fig. 3.18. Circular disc antenna balun dimensioning Fig. 3.19. Balun layout for the circular disc antenna

Fig. 3.20. Forward Transmission simulation for circular disc antenna balun Fig. 3.21. Circular disc antenna balun balance

Fig. 3.22. Circular disc antenna balun phase angle

Fig. 3.23. Circular Antenna directly connected to Balun schematic Fig. 3.24. Circular Antenna directly connected to Balun VSWR

Fig. 3.25. Circular disc Antenna +Balun schematic Fig. 3.26. Impossible Matching with circular antenna Fig. 3.27. Disc antenna Improved design

Fig. 3.28. Improved design dimensioning

Fig. 3.29. Improved antenna +Balun schematic Fig. 3.30. Improved antenna +Balun VSWR

Fig. 3.31. Multiplexer structure

Fig. 3.32. Fourth-order bandpass filter of coupled line Fig. 3.33. Coupled section

viii Fig. 3.35. GSM&GPS filter simulation

Fig. 3.36. Wifi&Zigbee&Bluetooth filter simulation Fig. 3.37. Filters comparison

Fig. 3.38. Multiplexer schematic

Fig. 3.39. Simulation of forward transmision for the three subbands Fig. 3.40. Multiplexer Return Loss

Fig. 3.41. Multiplexer Isolation

Fig. 3.42. Schematic for the entire Multi-band front-end using the rectangular antenna Fig. 3.43. Multi-band front-end Return Loss with Rectangular Antenna

Fig. 3.44. Multi-band front-end Isolation with Rectangular Antenna

Fig. 3.45. Schematic for the entire Multi-band front-end using improved disc antenna Fig. 3.46. Multi-band front-end Return Loss with Improved disc Antenna

Fig. 3.47. Multi-band front-end Isolation with Improved disc Antenna Fig. 4.1 Balun layout sent to manufacturer

Fig .4.2 Balun layout layers

Fig. 4.3 Rectangular antenna layout sent to manufacturer Fig. 4.4 Improved disc antenna layout sent to manufacturer

Fig. 5.1. VSWR comparison between Dipole, Square and Improved Disc Antenna Fig. 5.2. VSWR comparison between Square and Improved disc antenna with balun Fig. A.1. Absolute Fields Reference Antenna (1.57GHz)

Fig. A.2. Abolute Fields Reference Antenna (2GHz) Fig. A.3. Absolute Fields Reference Antenna (2.4GHz) Fig. A.4. Power Reference Antenna (1.57GHz)

Fig. A.5. Power Reference Antenna (2GHz) Fig. A.6. Power Reference Antenna (2.4GHz)

Fig. B.1. Absolute Fields Rectangular Antenna (1.57GHz) Fig. B.2. Absolte Fields Rectangular Antenna (2GHz) Fig. B.3. Absolute Fields Rectangular Antenna (2.4GHz) Fig. B.4. Power Rectangular Antenna (1.57GHz)

Fig. B.5. Power Rectangular Antenna (2GHz) Fig. B.6. Power Rectangular Antenna (2.4GHz)

Fig. C.1. Absolute Fields Circular Disc Antenna (1.57GHz) Fig. C.2. Absolute Fields Circular Disc Antenna (2GHz) Fig. C.3. Absolute Fields Circular Disc Antenna (2.4GHz) Fig. C.4. Absolute Fields Improved Disc Antenna (1.57GHz) Fig. C.5. Absolute Fields Improved Disc Antenna (2GHz) Fig. C.6. Absolute Fields Improved Disc Antenna (2.4GHz) Fig. C.7. Power Circular Disc Antenna (1.57GHz)

Fig. C.8. Power Circular Disc Antenna (2GHz) Fig. C.9. Power Circular Disc Antenna (2.4GHz) Fig. C.10. Power Improved Disc Antenna(1.57GHz) Fig. C.11. Power Improved Disc Antenna(2GHz) Fig. C.12. Power Improved Disc Antenna(2.4GHz)

ix Fig. D.1. Reference antenna plot of currents

Fig. D.2. Reference antenna far field plot for different frequencies Fig. D.3. Rectangular antenna plot of currents

Fig. D.4. Rectangular antenna far field plot for different frequencies Fig. D.5. Circular disc antenna plot of currents

Fig. D.6. Circular disc antenna far field plot for different frequencies Fig. D.7. Improved disc antenna plot of currents

x

List of Tables

Tab. 2.1. GSM bands Tab. 2.2. UMTS bands

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1 Introduction

1.1 Background

The progress of wireless communication equipment is ever accelerating toward implementation of the ubiquitous society, placing more importance to the antenna technologies day by day.

As handsets improve in compactness and functions in recent years, antennas for these equipment have come under the spotlight, transforming their longstanding impression of “an accessory for wireless communications equipment” into “a key device for wireless communication.”

As things stand today, the application of multiband systems with a variety of frequency band combinations is accelerating. The new generation of wireless communication devices includes many utilities that use different standards like GSM (Global System for Mobile Communications), GPS (Global Position System), Bluetooth, etc.

GPS, for example, has become increasingly popular and the common GPS navigators will become another integrated function in mobile phones.

Nowadays only independent modular solutions for the reception of this kind of standards exist. To implement a single module of reception for different standards requires a more complex design, specially the front-end part, because to cober with very large bandwith is needed.

1.2 Purpose

The purpose of the thesis work is to design an ultra wideband radio front-end able to work with GPS, GSM, UMTS (universal Mobile Telecommunications System), ZigBee, Bluetooth and Wi-Fi (Wireless Fidelity) . This means to design an ultra wideband antenna with low losses in the whole range of the involved frequency spectrum and a multiplexer network.

1.3 Method

The theoretical background of antennas and microwaves was given in many courses in my university of origin in Spain. The design and simulation tool used is Advanced Design System 2004 (ADS) from Agilent Technologies Inc. More knowledge of wideband antenna was obtained by reading selected literature.

The dimensions of the antennas were calculated and some results were verified in Linecalc (a tool included in ADS), suitable for transmission line calculations. They were experimentally tuned until simulations results fulfilled the demands of the design specifications.

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1.4 Limitations

In the thesis work only antennas and baluns are manufacturated. The multiplexer network was not manufacturated because there was not enough time. So the complete multi-band front-end is only tested by simulation with ADS.

The antennas prototypes were not measured because PCB foundry has problem to deliver the PCBs. Another student, Erika Tejedor Royo, will do all the measurements in her thesis work.

1.5 Structure of the report

The first chapter of the report briefly covers the necessary theory. In the next chapter one can see the design process and simulation results. Following, some discussions about results is made. The last part contains the conclusion and some ideas for future work.

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2 Theory

2.1 Standard Specifications

The front-end system shown in Fig. 2.1 must be able to receive the following standards: GPS, GSM, UMTS, Wi-Fi, Bluetooth and ZigBee. Therefore, first of all, a very important thing to define my complete design is to do a summary about frequencies, bandwithds and other physical aspects of these standards.

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2.1.1 GPS

GPS is a space-based radio navigation system, managed by the US Air Force for the government of the United States of America. Initially intented for military use, the first satellite was launched in 1978 and the system was operational in 1993. Today, parts of the information from the system are readily available to the general public, creating a large market for devices using the GPS signals for positioning or for obtaining a precise time reference.

The basic idea behind GPS is rather straightforward; knowing the distance to objects with known positions, and applying well-known methods of trilateration will give the requested position information. The objects with known position are the GPS satellites. The distances to the satellites, called pseudoranges, are calculated using the fact that distance = c × (satellite time - receiver time ), where c is the speed of the electromagnetic wave. Trilateration in two dimensions require the distances to at least three known objects, see Fig. 2.2.

Fig. 2.2. Trilateration in two dimensions Fig. 2.3. Positioning principle in three dimensions

This means that position information in three dimensions would require at least four satellites. However, since it is known that the surface of the Earth is beneath the satellites, one solution can be discarded and only three satellites are needed. The GPS system is made up of 24 “geosincronized” satellites.

All satellite vehicles support transmission of data on two different frequencies, called L1 and L2. These signals use carrier wave frequency of 1575.42 MHz and 1227.60 MHz, respectively. Both these signals are modulated using a non-public ranging code meant for authorised – i.e. military – users only. L1, however, is also modulated using a publicly available ranging code known as the Coarse Acquisition (C/A) code. The C/A codes consist of a stream of 1023 binary digits that repeat themselves every 1 ms. Each satellite vehicle is assigned its own, ever repeating C/A code, which thereby uniquely identifies the satellite. The modulation

process is Direct Sequence Spread Spectrum – Code Division Multiple Access (DSSS-CDMA). The L1 carrier uses Binary Phase Shift Keying (BPSK) to carry 50 bit/s of data.

Assuming line-of-sight, the GPS specification states that the minimum signal strength at ground level is -130 dBm (which corresponds to -160 dBW). The L1 signal is Right Hand Circularly Polarised (RHCP) and its bandwith is 8 MHz [1571.42-1579.42] MHz [1][2][3].

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2.1.2 GSM

The Global System for Mobile communications was previously well-known as “Group Special Mobile”. It consists of a world-wide standard for digital mobile telephones. The standard was created by the CEPT and later developed by ETSI for the European cell telephones, with the intention to develop a world-wide norm. The standard is open, non proprietor and evolutionary. It is the predominant standard in Europe, as well as in the rest of the world.

The radio links of the system are duplex, using two different frequencies. One for the uplink, from the phone to the station, and the other for the downlink, from the station to the phone. Every pair of frequencies is a radio channel. Table 2.1 shows the bands:

Tab. 2.1. GSM bands

European triband phones typically cover the 900, 1800 and 1900 MHz bands giving good coverage in Europe and allowing limited use in North America, while North American tri-band phones utilize 850, 1800 and 1900 for wide-spread North American service but limited world-wide use. A new addition has been the quad- band phone, supporting all four major GSM frequency groups, allowing for widespread usage globally, including in North America.

Since radio spectrum is a limited resource shared by all users, a method must be utilized to divide up the bandwidth among as many users as possible. The method chosen by GSM is a combination of Time and Frequency Division Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the total 25MHz bandwidth into 124 carrier frequencies of 200Khz bandwidth. One or more carrier frequencies are then assigned to each base station. Each of these carrier frequencies is then divided in time, using TDMA scheme, into eight time slots. One time slot is used for transmission by the mobile and one for reception. They are separated in time so that the mobile unit does not receive and transmit at the same time, a fact that simplifies the electronics.

GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 5.6 and 13 kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called Half Rate (5.6 kbit/s) and Full Rate (13 kbit/s). These used a system based upon linear predictive coding (LPC). In addition to being efficient with bit rates, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal [4][5].

UPLINK DOWNLINK GSM 900 124 radiochannels 890-915 MHz 935-960 MHz

E-GSM 49 radiochannels 880-890 MHz 925-935 MHz

GSM 1800 374 radiochannels 1710-1785 MHz 1805-1880 MHz

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2.1.3 UMTS

Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile phone technologies. The currently most common form using Wideband-CDMA (W-CDMA) as the underlying air interace, is standasdized by the 3GPP, and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems. To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard which it was designed to succeed.

The radio links are duplex as GSM standard.Those are the UMTS bands:

Tab. 2.2. UMTS bands

Radio interface uses the Frequency Division/Wide Code Division Multiple Acces (FDD/WCDMA). It is a multiplex technique based on CDMA (Code Division Multiple Access). It consists of using a different digital code for each user. These codes are shared by the emitter and receiver. The difference between WCDMA and CDMA is that in WDCMA codes with a speed much greater than the signal to transmit are used. In the transmitter the code is used to transform the user signal into a broadband signal (expanded spectrum). And in the receiver the code is used to separate the different communications which share the same carrier.

The implementation of W-CDMA was a technical challenge because of its complexity and versatility. The complexity of W-CDMA systems can be viewed from different angles: the complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. In W-CDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. UMTS networks need to support all current second generation services and numerous new applications and services.

Main advantages that this one system contributes are: more spectral efficiency; total reusability of the frequencies, faster transmission speed (from 114 Kbps to 2 Mbps) and greater security.

The bit modulation used is QPSK (QuadraturePhase Shift Keying). One of its main advantages is that it offers the same efficiency of power, using half of bandwidth, which is a very important thing in the satellite data transmission [6][7].

UPLINK DOWNLINK

1920-1980 Mhz 2110-2170 Mhz

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2.1.4 WLAN (IEEE 802.11)

The Wireless Local Area Network (WLAN) IEEE 802.11b/g/a also known by the brand Wi-Fi, denotes a set of standards developed by Working Group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802).

A Wi-Fi enabled device such as a PC, cell phone or PDA can connect to the Internet when within the range of a wireless network connected to the Internet. The area covered by one or several interconnected access points is called a hotspot. Hotspots can cover as little as a single room or as much as many square miles covered by overlapping access points (see Fig. 2.4).

Fig.2.4. WiFi network

Wi-Fi allows LANs to be deployed without cabling for client devices, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs. Wi-Fi has become widespread in corporate infrastructures, which also helps with the deployment of RFID technology that can piggyback on Wi-Fi. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.

Concretly, IEEE 802.11b and 802.11g standards use the 2.4 GHz band wich is included in this diploma work specification. Those standards use DSSS (Direct-Sequence Spread Spectrum) as radio frequency modulation, with each channel being 22 MHz wide, allowing up to three evenly-distributed channels to be used simultaneously without overlapping each other. IEEE 802.11b uses CSMA/CA (Carrier Sense Multiple Access with Collision Detection) as media access method and CCK (Complementary Code Keying) as its modulation technique, wich is a variation of CDMA. The hardware of IEEE 802.11g is compatible with 802.11b. The modulation scheme used in this standard is OFDM, CCK or DBPSK/DQPSK+DSSS depending on the data rates [10][11][12][13].

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2.1.5 Bluetooth

Bluetooth is a radio standard and communication protocol primarily designed for low power consumption, with a short range (power-class-dependent: 1 metre, 10 metres, 100 m) based on low-cost transceiver microchips in each device. Bluetooth wireless technology intended to replace cables connecting portable and/or fixed devices while maintaining high levels of security.

A fundamental Bluetooth strengh is the ability to simultaneously handle both data and voice transmissions. This enables users to enjoy variety of innovative solutions such as a hands-free headset for voice calls, printing and fax capabilities, and synchronizing PDA, laptop, and mobile phone applications to name a few.

Bluetooth uses FHSS and splits the 2.4 GHz (2400-2483.5MHz) ISM (Industrial, scientific and medical) unlicensed band into 79 channels of 1 MHz each. Bluetooth devices hop among the 79 channels 1600 times per second in a pseudo-random pattern (spread spectrum, frequency hopping, full-duplex signal at nominal rate of 1600 hops/sec). This system combat interference and fading.

Connected Bluetooth devices are grouped into networks called piconets (Fig. 2.5); each piconet contains one master and up to seven active slaves. The channel-hopping sequence of each piconet is derived from master's clock. All the slave devices must remain synchronized with this clock.

Fig.2.5. Bluetooth piconets

RF operation uses a shaped, binary frequency modulation to minimize transceivers complexity and the bit rate is 1 Mbps (Basic Rate) or, with Enhanced Data Rate, a gross air bit rate of 2 or 3Mb/s. Most commonly used radio is Class 2 and uses 2.5 mW of power [8][9][14].

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2.1.6 Zigbee

Zigbee is an open and global standard for Wireless Sensor Networks (WSN). The first version v1.0 was ratified in December 2004 by the Zigbee alliance that is an association of several companies. The standard is a part of the Low Rate Wireless Personal Area Network(LR-WPAN) for communication at short distance. The aim of the standard is to define low cost, low power effect, wireless networks for short range and imbedded applications. The purpose is that products based on Zigbee will, independent of implementer and manufacturer, produce interoperable, low cost and highly usable devices.

ZigBee is built up on the IEEE 802.15.4-2003 standard that describes the PHY layer and the MAC layer for LR-WPAN. These networks are focused on small devices used at short range for low data rate with low power consumption and low device cost. This standard defines a robust radio device. Choosing a channel for transmission is made by a method called Clear Channel Assessment (CCA). The method finds a free channel for transmission though scan the radio spectrum. The CCA methos uses a Carrier Sense Multiple Acces with Collision Avoidance (CSMA-CA) algorithm.The assigment of this algorithm is to assess if a channel is used and to find a channel for transmission. The standard IEEE 802.15.4 defines two hardware plattforms. One descries the 2.4 GHz spectrum and the others the 868/915 MHz spectrum. The lower band uses different modulation techniques and lower data rate than the upper band. The rest of the report applies only for the 2.4 GHz band.

Tab. 2.3. ZigBee frequency bands.

In the 2.4 GHz band sixteen channels are defined; each channel occupies 3 MHz and channels are centered 5 MHz from each other, giving a 2MHz gap between pairs of channels. Channels are assigned as follows:

Fc=2045+5(n-11)in MHz, for n=11,12,….,26

An ortogonal modulation Offset Quadrature Phase-Shift keying (O-QPSK) that transmit four bits per symbol is used [9][15][16].

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2.2 Ultra-wideband Antenna

Application of multiband systems with a variety of frequency band combinations is accelerating since the communication capacity is increasing and new functions are being added including GPS (1.57 GHz) and Bluetooth (2.4 GHz). It is expected, therefore, that all the handsets will probably become compatible with multibands in the near future. In such multiband systems, a multiband antenna is definitely one of the key devices since it is compatible with all the frequency bands without resort to multiple antennas [19].

Broadband planar antennas are the newest generation of antennas boasting the attractive features required, such as low profile, light-weight, low cost and ease of integration into arrays, to make them ideal components of modern communication systems.

Some interesting planar antenna for wireless communication devices are:

• Planar inverted-F antennas (PIFAs)

• Very-low-profile monopoles (bent, folded)

• Printed monopole/dipole antennas

• Metal-plate antennas (constructed using line-cutting or stamping)

• Slot antennas (stamped from metal or integrated with system ground plane)

• Folded dipole antenna

These antennas have an optimal behaviour in the wireless communication bands including the global system for mobile communications (GSM; 890-960 MHz), the digital communication system (DCS; 1710-1880 MHz), the personal communication system (PCS; 1850-1990 MHz) and. universal mobile telecommunication system (UMTS; 1920-2170 MHz). Also in wireless local area network (WLAN) system in the 2.4 GHz (IEEE 802.11b; 2400-2484 MHz) and 5.2 GHz (IEEE 802.11a; 5150-5350 MHz) bands. Ultra-wide band (3.1~10.6 GHz) must be included too [20].

In general, the antennas for broadband communication systems should have sufficiently broad operating bandwidths for impedance matching and high-gain radiation in desired directions. Theoretically, frequency independent antennas, can also be applied to broad band design. A typical design is the self-complementary periodic structures, such as planar periodic slot antennas, bidirectional log-periodical antennas, log-log-periodical dipole arrays, two/four-arm log spiral antennas, and conical log-spiral antennas. However, for the log-periodic antennas, frequency-dependant changes in their phase centers severely distort the waveforms of radiated pulses. Biconical antennas are earliest antennas used in wireless systems constructed by Sir Oliver Lodge in 1897, as mentioned by John D. Kraus. They featured relatively stable phase centers with broad well-matched bandwidths due to the excitation of TEM (Transverse ElectroMagnetic) modes. Following that, many

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diverse variations of biconical antennas such as finite biconical antennas, discone antennas, and single-cone with resistive loadings are formed and optimized for broad impedance bandwidths. The cylindrical antennas with resistive loading also feature broadband impedance characteristics. However, the antennas mentioned above are seldom used in portable devices due to their bulky size or directional radiation-although they are widely used in electromagnetic measurements. Alternatively, planar monopoles(dipoles) or disc antennas have been proposed because of their broad bandwidths and small size. The earliest planar dipole may be the Brown-Woodward bowtie antenna, wich is a simple and planar version of a conical antenna.

It is well known that the infinite biconical antennas can be considered as an infinite uniform transmission line, wich can radiate a dominant TEM. Thus, this structure features a frequency independent impedance response. However, in engineering, a finite biconical antenna and single cone with a ground plane are of more practical interest, as shown in Fig. 2.6a and Fig. 2.6b; they are analogous to a terminated transmission line with frequency-dependent reflection at its ends. Therefore, the structures have a limited well-matched impedance bandwidth but a stable phase center within the bandwidth. The biconical antennas can be asymmetrical with the cones of different geometries.

Fig. 2.6. Conical antennas

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Triangular planar monopoles, the flat version of the biconical antennas, were first presented for broadband applications ( see Fig. 2.7a). One of the poles can be replaced with an electrically large conducting plate acting as a ground plane (see Fig. 2.7b). Furthermore, the two poles of the antenna can be of different shapes. In order to integrate the antenna into RF circuits, the antennas can be readly printed onto a printed circuit board(PCB) [21].

(a) (b) Fig. 2.7. Planar antennas

The optimization of the shape of the planar antenna, especially the shape of the bottom portion of the antenna, can improve the impedance bandwidth by achieving smooth impedance transition. By optimizing the location of the feed point, the impedance bandwidth of the antenna will be further widened because the input impedance is varied with the location of the feed point [25]. By means of electromagnetic coupling between the radiator and feeding strip, good impedance matching can be achieved over a broad bandwidth [26].

Planar monopoles of other shapes are capable of providing broad band-widths. Fig. 2.8 demonstrate the typical circular planar monopole wich also obtain broadband characteristics due to the smooth transition between the radiator and feeding strip. From the dipole compromising two elliptical radiators, it is clear that the aperture between the radiators forms a transmission structure similar to a planar waveguide.

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In addition, the wideband antennas printed on PCBs are more practical to implement. The antennas can be easily integrated into other RF circuits. Basically, the planar radiators are etched onto the dielectric substrate of the PCBs. For monopoles, the ground plane may be coplanar with the radiators or under the dielectric substrate. The ground plane may be modified to enchance the bandwidth. The radiators can be fed by a microstrip line and coaxial cable.

It should be noted that the planar monopole or dipole antennas feature broad impedance bandwidth but some what suffer high cross-polarization radiation levels. The large lateral size and/or asymetric geometry of the planar radiaton. Fortunately, the purity of the polarization issue is not critical, particulary for the antennas used for portable devices [21].

2.3 Important Parameters

In this section the most important parameters considered in the design are widely explained. Those parameters are VSWR and the S-Parameters.

2.3.1 S-Parameters

Scattering parameter or more commonly referred as S-parameter representation plays an important role in RF systems regarding measurement and technical documentation.

This importance is due to the fact that normal system characterisations like open or short-circuit measurements can no longer be accomplished as it is done in a low frequency application. Measurement methods for low-frequency systems usually strive to measure the total voltage or current as a function of frequency. At high frequencies good measurement results using these methods are very hard to achieve. Instead the S-parameters were developed, which are defined as the ratio of normalised power waves and are easier to measure.

Fig. 2.9 shows two different two port representations, the left one shows the definition for voltage and current and the right one shows the normalised incident power wave an and normalised reflected power wave bn.

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The normalised power waves are defined as follows:

Where Zo is the characteristic impedance of the two-port network. S-parameters

are determined by measuring the magnitude and the phase of the incident, reflected and transmitted voltage waves.

Depending on which port that is terminated different S-parameters for a two-port network can be found.

Conditions a1 = 0 and a2 = 0 mean that no power waves are returned to the

network at either port 1 or port 2. This can only be accomplished when the connected transmission lines are terminated into their characteristic impedance. To clarify the meaning of S-parameters it can be said that S11 and S22 specify how much

of the incident signal is reflected at port 1 and port 2, respectively. S21 and S12

specify how much of the incident wave that pass through the device from port 1 to port 2 and from port 2 to port 1, respectively [17].

If a logarithmic magnitud is used, we obtain the return loss, fordward transmission and isolation.

Forward Transmission = |20 log10|S21||dB

Return Loss = |20 log10|S11||dB

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2.3.2 VSWR

In the design proces, the most important parameter simulated for the antenna improvement is the VSWR (Voltage standing wave ratio) at different frequencies (other simulation results are shown in appendix). VSWR is a measure of how well a load is impedance-matched to a source. Impedance matching means the maximum power transfer from source to load.

To understand this parameter we need to understand the reflection coefficient wich is what we read from a Smith chart. A reflection coefficient magnitude of zero is a perfect match, a value of one is perfect reflection. The symbol for reflection coefficient is uppercase Greek letter gamma ( ). Note that the reflection coefficient is a vector, so it includes an angle. Unlike VSWR, the reflection coefficient can distinguish between short and open circuits. A short circuit has a value of -1 (1 at an angle of 180 degrees), while an open circuit is one at an angle of 0 degrees. Quite often we refer to only the magnitude of the reflection coefficient. The symbol for this is the lower case Greek letter .

The return loss of a load is merely the magnitude of the reflection coefficient expressed in decibels. The correct equation for return loss is:

Return loss = -20 x log [mag( )]

Below are the equations that convert between VSWR, reflection coefficient and return loss (as well as mismatch loss) [17][18]:

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3 Design and Simulation Result

The antennas design process is mainly carried out in two steps. In the first step dimensions of the antennas were calculated and some results were verified in Linecalc. Then, in the second step, dimensions were experimentally tuned until simulation results fulfilled the demands of the design specifications.

The multiplexer structure comes from a theorical design. Some transmission line parameters are calculated in Linecalc and filters are implemented with the ADS tool too. Finally, the design is experimentally tuned until good simulations results were obtained.

3.1 Specification

The specification of the antenna was given at the start of the project. The antenna should be used in the frequency band 1.5-2.5 GHz and be matched at 50 Ω. In this frequency range the following standards are covered: GPS, UMTS, GSM, WiFi, Bluetooth and ZigBee. The specification of the design are:

• Frequency band: 1.5-2.5 GHz

• VSWR<3

The design will be implemented using a four metal layer PCB structure wich includes a flexible material. In Fig. 3.1 a cross section of the design is shown where all layers are illustrated.

Fig. 3.1. PCB cross-section Rigid (NH9326) Rigid (NH9326) Flex Polymite cond con2 Gnd Bottom

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Fig. 3.2 shows the design upper vision where the rigid and flexible parts are differentiated. The rigid part is composed by the balun and the flexible part by the antenna.

Fig. 3.2. PCB Upper view

Like in all the microwaves circuits, in broad band planar antennas the choice of substrate material can affect the overall performance drastically. When designing RF circuits in general it is desirable to control parameters that affect signal loss, which occurs either through impedance missmatch or dielectric loss. The substrate can add to impedance missmatch in transmission lines due to differences in the thickness of the dielectric. This thickness affects the spacing between signal trace and the groundplane thus changing the characteristic impedance (Zo) of the

transmission line, which induces signal reflections. Dielectric losses are caused by the conductance between traces and the groundplane, due to the Loss Tangent (tg δ), which indicates how much of the propagating signal is lost to the dielectric. Besides good properties it is also important that these properties are stable, as high variations in these properties will cause even worse effects than what is gained from that material. Knowledge about these parameters is a good step towards a stable design

[24].

Those are the parameters for both substrates, Rigid(NH9326) and Flexible(Flex Polymite):

• substrate height: 0.2 mm.

• Relative permittivity: 3.25

• Dissipation factor: 0.004

• Conductor thickness:0.03mm

The only design restriction is the minimum line width and separation, which is 0.113mm. This measure is taken from the PCB manufacturer design rules

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3.2 Antennas

The antenna design has followed two ways, i.e, the circular antenna design and the rectangular antenna design. Also a simple dipole antenna simulation has been carried out to use it as a reference.

Antenna structure and dimension come from Planar Antennas article [21] and differential disc dipole antenna design from Magnus Karlson [22]. Dimensioning has been scaled for my frequency range and a later improvement based on experiment and repeated simulations has been made. The antenna size in general is around λ/2 for all the designs. Where λ is obtained from a frequency that is within the frequency range specificated and gives a good result in the simulation for the rest of frequencies that includes this frequency range.

After the antenna, a balun is designed. Balun is an abbreviation of balanced to unbalanced, wich implies that the signal path is transformed from balanced to unbalanced or vice versa. The purpose of the balun in this design is to transform a single-ended output to differential outputs. The signal is split into two paths and hence the attenuation of the measured output signal will be at least 3 dB lower than the input signal. A balun can be done in several ways. In this diploma work a four layer structure including two broadside coupled microstrips is used (see Fig. 3.1).

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3.2.1 Dipole Antenna (Reference Antenna)

The reference antenna is the most simple antenna structure, a λ/2 dipole. Fig. 3.4 shows an example of dipole antenna dimensions for 1.4GHz. This antenna is only simulated to have an evidence that with this kind of structure it is impossible to make a wideband design. In Fig. 3.5 the layout made in ADS can be seen.

Fig. 3.4. Reference Antenna dimesions

Fig. 3.5. Reference Antenna layout

Fig. 3.6 shows VSWR simulation at different frequencies. This result shows that it is impossible to obtain one wideband antenna with this design type, the curve under 3 is too narrow. Therefore, it is unnecessary to continue the study of this kind of structure. For aditional simulation see appendix A and D.

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3.2.2 Rectangular Antenna

Fig. 3.7 shows the most important experimentally steps in the antenna dimensioning.

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The design starts from two regular quadrilaterals (λ/4 side) (see Fig. 3.7a). The λ chosed comes from the circular antenna design wich was made first. Lower spacing gives better feed-line impedance matching. Due to this reason the minimun space permitted by the manufacturer between lines is used. With this structure shown in Fig. 3.7a the result is not so good, specially for the upper band. In the next designs, it is tested to narrow the structure. First, lateral sides are narrowed (Fig. 3.7b) and then upper sides (Fig. 3.7c). The result improves a lot when the antenna is narrowed by the upper sides until the shape shown in Fig. 3.7c where the upper side is narrowed 6mm. Some lenghts and widths are tested for the feed lines.

Finally, Fig. 3.7d shows the structure with the best VSWR simulation. The Antenna is the same as Fig. 3.7c but the feed-lines are 2mm shortter. This result is very good, most of the specificated band is under 1.5. In Fig. 3.8 the dimensions for the better rectangular antenna design are shown. For additional simulation results see appendix B which contais graphs of abolute fields and power (Gain, Directivity, Effective Area, Efficiency, Radiated Powerfor) for 1.57, 2 and 2.4 GHz. Efficiency above 95% at the three frequencies can be seen. Appendix D contains various 3-D graphs.

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Next step is to design a balun with a correct matching to the rectangular antenna designed. In Fig. 3.9 the resulting dimensioning for the balun can be seen. The layout made with ADS is shown in Fig. 3.10

Fig. 3.9 Rectangular antenna balun dimensions

. Fig. 3.10. Balun layout for the rectangular antenna.

In the next pictures, the correct behaviour of the Balun is shown. First of all, Fig. 3.11 shows a correct forward transmission simulation in our frequency range. Insertion loss round 0.75 dB, variation within the frequency band 1.5-2.5 GHz ~0.5 dB.

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Using a single ended simulation, the Fig. 3.12 shows a good balance and Fig. 3.13 a correct phase angle(180 degrees) between the two branches. The red curve is one branch and the blue curve is the other.

Fig. 3.12. Rectangular antenna balun balance Fig. 3.13. Rectangular antenna balun phase angle

Finally, Fig. 3.15 shows a good VSWR simulation for the antenna together the balun (Fig. 3.14), because all the bandwidth is under 3 as the specfication say. A very good matching can be seen in the downer and the upper parts of the bandwidth wich are under 2, on the other hand, in the middle band the VSWR is round 3.

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3.2.3 Disc Antenna

3.2.3.1

Circular Disc Antenna

In Fig. 3.16 some experimentally steps for the circular disc antenna dimensioning are shown.

- 25 -

The design starts from two perfect circular discs (diameter λ/4) togheter with the feed lines (see Fig. 3.16a). In order to calculate λ to minimize size a frequency of the high part of the band it is used. The first evolution shown (Fig. 3.16b) turns out to increase the disc diameters, to shorten the feed lines from and to apply a slight cut in the inner ends of the circles. A great improvement can be appreciated in the VSWR(Fig. 3.16b). Finally, testing with frequencies of the lowest part of the band to calculate the disc diameters, the design although is increased in size improves a lot its result.(Fig. 3.16c).

Last improvement consists of reducing the feed lines width to half (Fig. 3.16d). The VSWR resulting from the simulation is so good. All the curve is under 1.5, the behavior is very constant throughout all the specificated band. The dimensions of the best design can be seen in Fig. 3.17.

Fig. 3.17. Circular Disc Antenna Dimensioning

For additional simulation results see appendix C and D. Appendix C contais graphs of abolute fields and power (Gain, Directivity, Effective Area, Efficiency, Radiated Powerfor) for 1.57, 2 and 2.4 GHz. Efficiency above 95% at the three frequencies can be seen. Appendix D contains various 3-D graphs.

- 26 -

As in the rectangular antenna, the following step is to design a balun with a correct matching to the antenna, so that all the set provides a good result. The balun used in this design is the same as the rectangular antenna design. The only difference is that the ends are slightly shortter. Exactly, 2 mm each end(see, Fig. 3.18). Next the layout picture for this balun is shown in Fig. 3.19.

Fig. 3.20 shows a correct forward transmission, wich is very similar to the rectangular antenna balun. Insertion loss round 0.75 db and a variation within the frequency band of 0.5dB.

Fig. 3.18. Circular disc antenna balun dimensioning

Fig. 3.19. Balun layout for the circular disc antenna

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As Fig. 3.21 and Fig. 3.22 show, using a single ended simulation, we can see that the balance and the phase angle between the two branches (blue and red curves) are correct. If a simulation connecting virtually balun and the antenna is made ( see Fig. 3.23 a correct VSWR (see Fig. 3.24) is obtained.

Fig. 3.21. Circualr disc antenna balun balance Fig. 3.22. Circular disc antenna balun phase angle

Fig. 3.23. Circular Antenna directly connected Fig. 3.24 Circular Antenna directly connected

to Balun schematic to Balun VSWR

The problem is that antenna and balun must be physically connected, and for a real design we need some space between the antenna and balun.That means that it’s necessary to extend the feed line of the antenna. Fig. 3.26 shows several VSWR simulations using different feed lines with diverse widths and lenghts. It becomes evident in the curves that a correct adaptation between antenna and balun cannot be obtained with this type of design.

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15mm

20 mm

3.2.3.2

Improved Design

To solve the problems of the circular disc antenna an improved design was made. In Fig. 3.27 the different steps in the design can be seen.

Fig. 3.27. Disc antenna Improved design

(a) (b) (c) (d) 96.6 mm 96.6 mm 96.6 mm 96.6mm 24 mm 15 mm 15 mm 20 mm

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Starting off3.16d structure, a piece of the inferior part of antenna is cutted with the objective of being able to connect balun without extending the feed lines(see Fig. 3.27a). The changes in VSWR aren’t practically appreciable. In following steps the inferior ends of discs are cleared (Fig. 3.27b) and the feed lines are extended by the inner part (see Fig. 3.27c). As final design (Fig. 3.27d), a narrower antenna than the perfect disc antenna is obtained. VSWR are quite similar. In the corresponding frequency range the curves moves around 1.25. Fig. 3.28 shows the dimensions of the circular antenna improved design.

Fig. 3.28. Improved design dimensioning

For additional simulation results see appendix. Appendix B contais graphs of abolute fields and power (Gain, Directivity, Effective Area, Efficiency, Radiated Powerfor) for 1.57, 2 and 2.4 GHz. Efficiency above 95% at the three frequencies can be seen. Appendix C contains various 3-D graphs.

The balun used in this design is the same as the circular disc antenna design (see Fig. 3.18). In this case, the simulation of the joint antenna-balun gives a correct result for the VSWR. As Fig. 3.30 shows, the curve is all the time under 3db.

Fig. 3.29. Improved antenna +Balun schematic Fig. 3.30. Improved antenna +Balun VSWR

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3.3 Frequency Multiplexer Network

With the purpose of separating frequencies in which the different standards work from the rest of the band for their processed work, a multiplexer network is designed. In the present chapter, a possible design of the network as an example is specified.

The design consists of a triplexor that will divide the band in three subbands. First of these subdivisions corresponds to the GPS band, the following corresponds to a band shared by GSM and UMTS and finally the high part correspons to a band shared by WiFi, Zigbee and Bluetooth.

The structure designed is a triplexer. It is realized with microstrip technology and is based in [23]. The triplexer consist of three series quarter-wavelenght transmission lines, three bandpass filters, and three transmission lines for tuning of the filter impedance. The series transmission lines provide a high impedance at the respective frequency band. The filter tuning lines optimizes the stop band impedance of each filter providing a high stop band impedance in the neighboring bands. Fig. 3.31 shows the structure of the proposed triplexer.

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3.3.1 Filters

In order to carry out the design of the multiplex network, first thing is to design the necessary filters starting off specifications exposed in the project first section.

The filters will be designed and simulated with the ADS support. The type of filters that will be used are convencional coupled line bandpass filters (Fig. 3.32).

Characteristics of this kind of filters depend on several parameters, the most important parameter is length (l) in the coupled region, the spacing (S) between the couplings and the line width (W) (see Fig. 3.33).

Fig. 3.32. Fourth-order bandpass filter of coupled line Fig. 3.33. Coupled section

The length of the coupled regions is expected to be some were around λ/4 of the desired center frequency. Spacing has most impact on the attenuation while width and length have a larger impact on the behaviour regarding to the centre frequency, impedance and ripple within the passband but it is the combination that matters. The order of the filter depends on how many coupled regions are used. Higher order fillters have steeper slopes but the drawback is that attenuation within the passband becomes larger.

Designing the filter in ADS was done by using a design guide for passive circuits with microstrip lines. Choosing a desired filter type, edge-coupled filter in this case, filter order and/or desired pass- and stop-bands the program generates a good starting point for a design in schematic. The first thing to check on the generated design is that all physical dimensions pass the design restriction. The multiplexer won’t be manufactured, so layout part will be skipped [17][24].

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3.3.1.1

Filter for GPS

The central frequency of this standard is 1575,42 MHz and the bandwidth used is 8MHz. A 5th order bandpass filter is used. The parameters for this first filter are the following ones:

Lower Pass-Band Edge: 1.55GHz Upper Pass-Band Edge:1.6GHz Lower Stop-Band Edge:1.5GHz Upper Stop-Band Edge:1.65GHz Ripple:3db Attenuation Stop-Band Edge: 20db Fig. 3.34 shows diferent S-parameters resulting from the simulation. At the center frequency the Return Loss (S11) is -29db, in S21 simulation a pass-band with

2.3 dB of attenuation can be seen. The other parameters show a good behaviour too. In the pass-band a lineal phase and a constant module can be seen. Also the specification for the stop-band is fulfilled.

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3.3.1.2

Filter for GSM&UMTS

Within the diverse frequencies that standard GSM uses, design includes GSM 1800, Uplink:1710-1785 MHz // Downlnk:1805-1880 MHz and GSM 1900, Uplink:1850-1910MHz // Downlink:1930-1990MHz.

On the other hand, frequencies of UMTS standard are: Uplink:1920-1980 MHz // Downlink:2110-2170 MHz.

In conclusion, parameters of this second filter will be:

Lower Pass-Band Edge: 1.7GHz Upper Pass-Band Edge:2.2GHz Lower Stop-Band Edge:1.69GHz Upper Stop-Band Edge:2.23GHz Ripple:3db Attenuation Stop-Band Edge: 20db Fig. 3.35 shows different S-parameters resulting from the simulation. At the center frequency the Return Loss (S11) is round -40db. In S21 simulation a pass-band

with a very small attenuation is observed, only 0.5 dB. In the pass-band a lineal phase and a constant module can be seen. Also the stop-band shows a good behaviour.

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3.3.1.3

Filter for WiFi&Zigbee&Bluetooth

Zigbee, Bluetooh and Wifi (802.11b y 802.11g) work in the same frequency 2.4GHz. Wifi standard uses the bigger bandwidth, from 2.4 to 2.485 GHz, 85MHz.

Therefore, design parameters for this filter are the following ones:

Lower Pass-Band Edge: 2.3GHz Upper Pass-Band Edge:2.45GHz Lower Stop-Band Edge:2.25GHz Upper Stop-Band Edge:2.6GHz Ripple:3db Attenuation Stop-Band Edge: 20db In Fig. 3.36 S-parameters resulting from the simulation are showed. The attenuation in the pass-band is round 1.75 dB. At the center frequency the Return Loss (S11) is round -25db. In the pass-band a constant module and a lineal phase

can be seen. Also the specification for the stop-band is fulfilled.

- 35 -

Finally, a comparison of the three filters forward transmission simulation is shown in Fig. 3.37. It can be clearly observed that as specification said GSM and UMTS filter pass-band is much more wider than the others. The band-pass attenuation in this filter is under 1dB, that is a very good result. The other filters maintain a correct operation in their band-pass too. Both with attenuation under 2.3 dB.

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3.3.2 Complete Multiplexer Structure

In the next schematic (Fig. 3.48.), the whole parameters used in the multiplexer design are shown. The three series quarter-wavelenght transmission lines made from lenghts of 9, 7 and 31.5 mm, the three bandpass filters specified in section 3.3.1, and three transmission lines for tuning of the filter impedance made from lenghts of 30, 2 and 2 mm. Both kind of transmission lines, the quarter-wavelenght and the tunning ones, are 0.55 width. In the picture, the substrate parameters are shown, too.

The series transmission lines provide a high impedance at the respective frequency band and the tunning transmission lines optimizes the stop band impedance of each filter providing a high stop band impedance in the neighboring bands.

- 37 - 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 1.0 3.0 -30 -20 -10 -40 0 freq, GHz d B (S (2 ,2 )) d B (S (3 ,3 )) d B (S (4 ,4 )) 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 1.0 3.0 -200 -150 -100 -50 -250 0 freq, GHz d B (S (3 ,2 )) d B (S (3 ,4 )) d B (S (2 ,4 ))

Fig. 3.39 shows the simulation results for the three sub-bands forward transmission of the triplexer. The three pass-bands can be appreciated. In the three cases insertion loss is under 2.5 db. In the next figures, return loss and isolation for ports 2, 3,4 are shown. A good behavior in the return loss curves can be appreciated (Fig. 3.40), the minimums of the curves are round the filters center frecuencies. The isolation curves are good too.The worst isolation case is between port 3 and port 4, around -25db (Fig. 3.41).

Fig. 3.39. Simulation of forward transmision for the three subbands.

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3.4 Complete Multi-band Front-end

3.4.1 Using Rectangular Antenna

In Fig. 3.42 the schematic for the entire Multi-band front-end using the rectangular antenna can be seen. The output port of the balun is connected to input port of the multiplexer. In the design proces the antenna was matched at 50Ω that means that ideally simulations might be the same as in section 3.3.2.

- 39 - 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 1.0 3.0 -175 -150 -125 -100 -75 -50 -25 -200 0 freq, GHz d B (S (2 ,1 )) d B (S (3 ,2 )) d B (S (3 ,1 )) 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 1.0 3.0 -30 -25 -20 -15 -10 -5 -35 0 freq, GHz d B (S (1 ,1 )) d B (S (2 ,2 )) d B (S (3 ,3 ))

The isolation and return loss curves are shown in Fig. 3.43 and Fig. 3.44. In general, a good behavior in the return loss curves can be appreciated, the minimums of the curves are round the filters center frecuencies except in the port 2 where a small desviation can be seen. The isolation curves are good. The worst isolation case is between port 3 and port 2, around -25db.

Fig. 3.43. Multi-band front-end Return Loss Fig. 3.44. Multi-band front-end Isolation

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3.4.2 Using Improved Disc Antenna

Fig. 3.45 shows the schematic for the entire Multi-band front-end using the improved disc antenna.

- 41 - 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 1.0 3.0 -175 -150 -125 -100 -75 -50 -25 -200 0 freq, GHz d B (S (2 ,1 )) d B (S (3 ,2 )) d B (S (3 ,1 )) 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 1.0 3.0 -30 -25 -20 -15 -10 -5 -35 0 freq, GHz d B (S (1 ,1 )) d B (S (2 ,2 )) d B (S (3 ,3 ))

In Fig. 3.46 and Fig. 3.47 the isolation and return loss curves are shown respectively. No important differencies with the multi-band front-end using the rectangular antenna can be notified. The worst isolation case is again 25 dB between port 2 and 3.

Fig. 3.46. Multi-band front-end Return Loss Fig. 3.47. Multi-band front-end Isolation

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4 PCB-fabrication

Four prototypes will be manufacturated, the rectangular antenna, the improved disc antenna with and the baluns separated for independent measurement. The measurement will be carried out by Erika Tejedor Royo in her future Master Thesis.

Fig. 4.1 shows the rectangular antenna balun layout sent to the manufacturer. The feed lines are adapted to be able to incorporate the connectors. Next the different layers separately are showed.

The characteristics for conductor 1, conductor 2, bottom and ground are detailed in section 3.1. The pink discontinuous line(rigid) delimits the rigid part of the structure. The green discontinuous line(Mill) delimits the whole PCB structure.

At least 5 vias between λ/2 lenght must be included in the balun to block nondesireble radiations. The vias for the connectors must be included too.

Fig. 4.1. Balun layout sent to manufacturer

Fig. 4.2. Balun layout layers

(a) Conductor 1 (b) Coductor 2

(c) Ground (d) Bottom

- 43 -

Fig. 4.3 and Fig. 4.4 show the rectangular antenna design and improved disc antenna design layouts sent to the manufacturer. Vias can be appreciatted in the bottom of the Balun structure. The mill is 1mm close to the rigid part because of the manufacturer tools specification.

Fig. 4.3. Rectangular antenna layout sent to manufacturer

Fig. 4.4. Improved disc antenna layout sent to manufacturer

For the Improved disc antenna balun (see Fig. 4.4) a curved ending must be added in order to be able to put the SMA connector (Fig. 4.5).