DESIGN AND FABRICATION OF A MICRO-STRIP ANTENNA FOR WI-MAX APPLICATIONS

DESIGN AND FABRICATION OF

A MICRO-STRIP ANTENNA FOR

WI-MAX APPLICATIONS

Tulha Moaiz Yazdani

Munawar Islam

This thesis is presented as part of Degree of Master of Science in Electrical Engineering

Blekinge Institute of Technology

October 2008

Blekinge Institute of Technology School of Engineering

U

Abstract

Worldwide Interoperability for Microwave Access (Wi-Max) is a

broadband technology enabling the delivery of last mile (final leg of delivering

connectivity from a communication provider to customer) wireless broadband

access (alternative to cable and DSL). It should be easy to deploy and cheaper

to user compared to other technologies. Wi-Max could potentially erase the

suburban and rural blackout areas with no broadband Internet access by using

an antenna with high gain and reasonable bandwidth

Microstrip patch antennas are very popular among Local Area Network

(LAN), Metropolitan Area Network (MAN), Wide Area Network (WAN)

technologies due to their advantages such as light weight, low volume, low cost,

compatibility with integrated circuits and easy to install on rigid surface.

The aim is to design and fabricate a Microstrip antenna operating at

3.5GHz to achieve maximum bandwidth for Wi-Max applications. The

transmission line model is used for analysis. S-parameters (

S11

and

S21

) are

measured for the fabricated Microstrip antenna using network analyzer in a lab

environment.

The fabricated single patch antenna brings out greater bandwidth than

conventional high frequency patch antenna. The developed antenna also is

found to have reasonable gain.

U

Acknowledgement

It is a great pleasure to express our deep and sincere gratitude to

our supervisor Dr. Mats Pettersson, Ph.D, Senior Lecturer of Blekinge

Institute of Technology. Whose extreme patience made this

dissertation possible His wide knowledge and his logical way of

thinking have been great value for us. He provided us always

energetic and devoted supervision and guidance throughout the thesis

work. He always very much cooperative and helped us whenever we

needed, in spite of his busy schedule.

We would also like to thanks our colleagues for whom we have

regard, and wish to extend our warmest thanks to all those who have

helped us with our work.

And finally special dedication to our families whom help and

support for us in these years. We simply could not done it without

them and hope that someday we can make it up to them.

Chapter 1 Wireless communication Technology

1.1 Introduction

1.2 History

1.3 Basic Communication System

1.4 Different Mobiles Generation

1.5 WLAN

(Wireless Local Area Network)

1.6 Bluetooth

1.7 Wi-Max

1.8

Importance of Antenna in Wireless System

1.9

Future of Wireless Technology

Chapter 2 Antenna Essentials

2.1

Antenna Definition

2.2

Antenna Radiation

2.3

Friis Transmission Equation

2.4

Radiation Field Region around Antenna

2.5

Antenna Parameters

2.6

Far Field Radiation from Hertzian dipole

Chapter 3 Microstrip Patch Antenna

3.1

Introduction

3.2

Feeding Methods

3.3

Comparison of Different Feed Methods

3.4

Methods of Analysis

3.5

Bandwidth & Quality Factor of Microstrip Antenna

3.6

Advantages & Disadvantages

Chapter 4 Result and Measurement

4.1

Design Procedure

4.2

Measurement and Result

4.3

Conclusion

- vii -

CDMA

Code Division Multiple Access

EDGE

Enhanced Data for GSM Evolution

FCC

Federal Communication Commission

FR-4

Flame Resistance-4

GSM

Global Systems for Mobile

iDEN

integrated Digital Enhanced Network

IEEE

Institute of Electrical and Electronic Engineering

ISM

Industrial, Scientific and Medical

LAN

Local Area Network

MAN

Metropolitan Area Network

MBWA Mobile

Broadband Wireless Access

MMIC

Monolithic Microwave Integrated Circuit

NLOS

Non Line of Sight

OFDM

Orthogonal Frequency Division Multiplexing

PAN

Personal Area Network

PCMCIA Personal Computer Memory Card International Association

PDA

Personal Digital Assistance

R.L

Return Loss

SCDMA Synchronous

CDMA

SMA

Sub Miniature version A

TACS

Total Access Communication System

UMTS

Universal Mobile Telecommunication System

VoIP

Voice over Internet Protocol

WAN

Wide Area Network

WCDMA Wideband

CDMA

WiDEN

Wideband iDEN

WLAN

Wireless Local Area Network

Chapter 1

Wireless Communication

1.1 Introduction

Telecommunication is assisted transmission of signals over a distance for the purpose of communication. In early time this may involve the use of smoke signals, drums, semaphore (an apparatus for conveying information by means of visual signals, as a light whose position may be changed), flags or heliograph (a device for signaling by means of a movable mirror that reflects beam of light, esp. sunlight, to a distance). In modern times, telecommunication typically involves the use of electronic transmitters such as the telephone, television, radio or computer[1]. Radio or wireless communication means to transfer information over long or short distance without using any wires. Million of people exchange information every day using pager, cellular, telephones, laptops, various types of personal digital assistants (PDAS) and other wireless communication product [2]. The thesis aims to design an antenna model using IEEE given frequency band and to determine its various parameters, that how we can improve it using the frequency of 3.5GHz.

This thesis investigates the use and design of a rectangular patch antenna having a thin metallic strip placed a fraction of wavelength above the ground surface with coaxial feed system. This antenna is found to be suitable for IEEE 802.16d Wi-Max application.

1.2 History

Guglielmo Marconi invented the wireless Technology in 1896 (The actual invention of radio communications more properly should be attributed to Nikola Tesla, who gave a public demonstration in 1893. Marconi’s patents were overturned in favor of Tesla in 1943[ENGE00]) [3]. In 1901 Guglielmo Marconi sent telegraphic signals across the Atlantic Ocean from Cornwall to St.Johan’s Newfoundland, it covers a distance of 1800 miles. His invention allowed two parties to communicate by sending each other alphanumeric characters encoded in an analog signal [3].

Over the last century, wireless technologies have led towards the radio, television, Paging system, Cordless phone, Mobile telephone, Satellite and wireless networks. This advancement in wireless communication is widely deployed and used through out the world in last four decades [4].

The first practical standard of cellular communication named first Generation (1G) was deployed and used in 1980. 1G uses the analog signal for communication of voice calls only. In the beginning of nineteen’s century this standard changed to digital second Generation (2G) and to the end of nineteen’s century it was still digital but better bandwidth and good quality of signal in third Generation (3G), Now a days industries are working on fourth Generation (4G) [5].

1.3 Basic Communication System

The block diagram of communication system is shown below,

Fig: 1.1 Block diagram of digital communication system [7] I. The input data which can be any shape like voice, video, images.

II. The input data is applied to the channel encoder, this portion changing the data into very suitable manners like A-D converter and then transmit the data.

III. Channel is actually a medium (wired or wireless) between transmitter and receiver. In channel part there are two inputs one is coming from transmitter and other is channel noise (unwanted signal or information is called noise). Thus the resultant data at the output of channel is altered.

IV. The altered data at the output of channel is received by the receiver. The received data is decoded to reconstruct an original data transmitted by transmitter.

V. Finally the reconstructed data is forward to the destination. 1.3.1 Concept of Cellular System

A cellular telephone system provides a wireless connection to the Public Switch Telephone Network (PSTN) for any user location within the radio range of the system [8].The limited capacity of the first mobile radio-telephone services was related to the spectrum used, not much sharing and a lot of bandwidth dedicated to a single call [9]. It provided the good coverage but impossible to reuse the same frequency due to interference. The cellular concept addressed many of the shortcomings of first mobile telephones like frequency reuse and wasted spectrum allocated to a single user.

In 1968 Bell Labs proposed the cellular telephone concept to the Federal Communications Commission (FCC). Then it was approved, it used the spectrum frequency of 845MHz to 870-890MHz band [9].

In 1960 to 1970’s Bell working on mobile system give the concept of dividing the coverage area into small cells, each of reused portions of spectrum. This leads to greater system infrastructure. It is the hexagon [4] geometry cell shape.

Fig: 1.3 Frequency Reuse in cellular Networks [4]

In above Fig 1.3 shows cellular frequency reuse concept. Cells with the same letter use the same set of frequencies. A cell cluster is outlined in bold and replicated over the coverage area. In the example, cluster size, N, is equal to seven, and the frequency reuse factor is 1/7 since each cell contains one-seventh of the total number of available channels [4].

FCC finally allocated the 40MHz spectrum in the 800MHz band, where a signal channels occupies 30 KHz bandwidth for Advance Mobile Phone System (AMPS) [10]. Cellular system is widely popular across the world due to its portability, flexibility, quality, bandwidth, and specially user friendly.

1.4 Different Mobiles Generation

1.4.1 First Generation

Advanced Mobile Phone System (AMPS) is a first generation cellular technology. AMPS is a analog mobile phone system standard developed by the BELL Labs, and officially introduced in the America in 1983 and Australia in 1987.AMPS uses separate frequencies or channels for each conversation. The anatomy of each channel is composed of two frequencies 416 of these are in the 824-849MHz range for transmissions from mobile stations to base stations, paired with 416 frequencies in the 869-894MHz range of transmissions from base stations to the mobile stations. Each cell site will use subset of these channels and must use a different set than neighboring cells to avoid interference. This significantly reduces the number of channels available at each site in real world systems [11].

1.4.2 Second Generation 2G

a. GSM

It supports 8 time slotted users for each 200 KHz radio channels. It uses the 890-915MHz for uplink and 935-960MHz for downlink.

b. Interim Standard (IS-136)

It is also known as North American Digital Cellular or US digital Cellular. It supports three time slotted users for each 30KHz radio channel and it is a popular choice for carrier in North America. It uses the frequency band of 824-894MHz and also using the channels scheme of TDMA [4].

c. Pacific Digital Cellular (PDC)

It is a Japanese technique which is same as the AMPS engaging 50 million people. It also uses the TDMA scheme.

d. Interim Standard 95(IS-95)

It relates to second generation technique which is known as Code Division Multiple Access (CDMA). It is based on Direct Sequence CDMA multiple access. Thus multiple users simultaneously share the same channel (Channel Spacing is 1.25 MHz). [4]. CDMA is widely used in all over the world.

1.4.3 Second Generation 2.5G [4]

The 2.5 technology is used for high speed data rate needed for web browsing; email traffic, mobile commerce and location based mobile services. The 2.5G technology also supports the popular web browsing which is called the Wireless Application Protocol (WAP).

Following are the standard of 2.5Generation, a. High Speed Circuit Switch Data (HSCSD)

It provides the consecutive time slots in order to obtain the high speed data rate. It increases the data rate of 14,400bps as compared to the original of 9,600bps in GSM specification. It is ideal for dedicated Internet streaming and web browsing. It provides the 200 KHz channels bandwidth.

b. General Packet Radio System (GPRS)

It is suitable for non real time Internet usage, including emails, faxes and web browsing where user downloads high data and also upload on internet. As compare to the HSCSD it supports more users in sense of burst manners. GPRS handset work on GPRS network at 171.2Kbps, it also uses the TDMA scheme and its channel bandwidth is 200 KHz.

c. Enhanced Data Rate for GSM (EDGE)

It used for both GSM and IS-136 operators and it is also connecting technology of 3G high speed data access. Handsets work on EDGE network at 384Kbps. The channel bandwidth is 200 KHz.

1.4.4 Third Generation

a. Wideband Code division Multiple Access (W-CDMA)

It is a high speed transmission protocol with air interface of 3G network Freedom for Mobile Multimedia Access (FOMA). It uses the 5MHz bandwidth. Multiple type of handover used between the different cells [12].

b. Universal Mobile Telecommunication System (UMTS)

UMTS air interface uses Time division duplex spectrum between uplink and downlink. It is more flexible because the usage of available spectrum according to traffic pattern [13]. UMTS is used to provide the internet on the mobile which is enhance form of the Wi-Max standard.

c. High Speed Packet Access (HSPA)

It is used to increase or enhance the performance of existing UMTS protocols [14]. HSPA family comprise of High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA).

This network is basically an enhancement of 3G in 3.5G. It increases the performance by using the Adaptive Modulation and Coding (AMC).

1.4.5 Comparison of 3G Wireless

Table 1.1

3G wireless comparison Technology Generation Connection

Type Theoretical Max Kbps Carrier Max Kbps Typical Throughput Kbps GSM 1G Circuit  9.6  CDMA 2G Circuit  14.4  GSM GPRS Class 6 2.5G Packet 64.4 40.6 15-30 GSM GPRS Class 10 2.5G Packet 86.2 54.2 20-40 GSM GPRS Class 12* 2.5G Packet 86.2 54.2 20-40 CDMA 1×RTT 2.75G Packet 307 153 60-80 GSM Edge Class 2 2.75G Packet 118 118 40-80 GSM Edge Class 10 2.75G Packet 237 237 80-160 GSM Edge Class 12** 2.75G Packet 237 237 80-160 UMTS(W-CDMA) 3G Packet 384 384 200-300 1×EVDO(CD MA 2000) 3G Packet >2000 >2000 300-500

HSDPA 3G Packet >2000 >2000 TBA

1.4.5 Fourth Generation (4G)

Fourth generation is IP based wireless systems which support voice, data and video streaming. In 4th generation especially High speed global internet Access is provided. It is basically high speed; high capacity and low cost services with improved security. It also focuses on the Quality of service. In 4G generation more focus on bandwidth efficiency because the service provide to last mile (final leg of delivering connectivity from a communication provider to customer) with high data rate.

All the technologies use in 4th generation is base on special standard of IEEE, like 802.11 for WLAN, 802.15 for Bluetooth, 802.11g for Wi-Fi, Wi-Max 802.16, and other like WCDMA, Hyper Lane etc.

1.5 Wireless Local Area Network (WLAN)

The IEEE 802.11 working group was founded in 1987 and actually it standardized in 1997 and to define the specification for wireless LAN. It is enable a local network of computers to exchange the data or other information by radio waves. 1.5.1 IEEE Standard of WLAN

a. IEEE 802.11

It’s operated at frequency of 2.4 or 5GHz and achieves the high data rate of 24 to 54Mbps. It uses the Frequency Hoping Spread Spectrum (FHSS) modulation technique. It use for low power transmission range in 10 to 100 meter. It is basically use in offices, buildings and Campus.

b. IEEE802.11b

It is an extension of 802.1, it use the frequency of 2.4GHz. It handles the data rate up to 11Mbps. It uses the modulation technique of direct sequence spread spectrum (DSS).

c. IEEE 802.11g

It uses the 2.4GHz frequency band. Its bandwidth is 54Mbps and uses the frequency technique of Orthogonal Frequency Division Multiplexing (OFDM). It has less electromagnetic interference. Its range is up to 100meter. It carries the more data than the 802.11b.The basic infrastructure of WLAN is shown in Fig 1.4.

Wired Network

Access point

Basic Service Set

Extended Service Set

1.5.2 Wireless Fidelity (Wi-Fi)

The term Wi-Fi was created by an organization called the Wi-Fi Alliance, which oversees tests that certify product Interoperability. Wi-Fi uses the specification of 802.11 family. Wi-Fi follows all the flavors of WLAN specification. Wi-Fi is use in many places like schools, offices, homes. Its special feature is use in hot spot like airports, hotels, fast food places where people can access the network easily [15].

Because Wi-Fi uses all the bands of WLAN, there is frequency jump between different bands. It provides to minimize the interference and multiple devices use for same wireless connection simultaneously.

Wi-Fi also provides the wireless ad-hoc network. In ad-hoc network all devices connected wirelessly and create a new network.

Fig: 1.5 Wi-Fi based Architecture [20] The communication process is given as,

A computer’s wireless adapter translates data into a radio signal and transmits through antenna. A wireless router receives signal and decodes it and sends the decoded information to internet using a wired medium.

1.5.3 Comparison of different 802.11 Standards Table 1.2

Wireless LAN Throughput by IEEE Standard IEEE WLAN

Standard

Over-the-Air (OTA) Estimates

Media Access Control Layer, Service Access Point (MAC SAP) Estimates

802.11b 11Mbps 5Mbps 802.11g 54Mbps 25Mbps (when .11b is not _present) 802.11a 54Mbps 25Mbps

802.11n 200+ Mbps 100Mbps

Comparison of different 802.11 transfers rates [17]

1.6 Bluetooth

Bluetooth is basically an IEEE standard of 802.15 [6]. It use for small distance transmission of data. Bluetooth is founded by special interest group (Ericsson, Nokia, and Intel IBM Toshiba) responsible for its standard. It uses the Industrial, Scientific and Medical (ISM) frequency band of 2.4GHz. Frequency jumps is 1600 hops/s and switching time for transmission and reception is 220 micro second. Bluetooth is designed for low power consumption, with short range depending on the power class. 1.6.1 Comparison of different Bluetooth Classes

Table 1.3

Bluetooth different classes

Class Max. Permitted Power mW

(dBm)

Range (Approximated)

Class 1 100mW (20dBm) ~100 meter

Class 2 2.5mW (4 dBm) ~10 meter

Class 3 1 mW (0dBm) ~1 meter

Comparison of different power classes [6]

In Bluetooth [3] two or more devices are communicated in pico nets. At most 10 Pico nets can accommodate in same Bluetooth radio. It provides connectivity between mobile and other devices.

Each Pico net has only single master. All communication takes place with master. Master in one Pico net can be slave of another Pico net. Active slave is use for transmit and receive data. Parked slave not take too much power, most of the time it is in sleeping position. It just wakeup and check the new data.

1.6.2 Bluetooth Usage Model

Blue tooth usage model describe how Bluetooth can be used. For each usage model there is one or more corresponding profiles defining protocol layers and functions to be used.

The Bluetooth usage model comprises of a. Internet Bridge

Describe how a mobile phone or cordless modem provides a PC with dial up networking capabilities without the need of physical connection to the PC.

b. Three in One Phone

Describe how a telephone handset may connect to three different service providers.

c. Ultimate headset

Defines how a Bluetooth equipped wireless headset can be connected, to act as a remote unit’s audio input and output interface.

d. File Transfer

This usage model offers the capability to transfer data objects from one Bluetooth device to another. Files, entire folders, directories and streaming media formats are supported in this usage model.

e. Synchronization

It provides the mean of automatic synchronization between for instance a desktop PC, a portable PC, a mobile phone and a note book.

1.7 Wi-Max

Wi-Max is the Worldwide Interoperability for Microwave access, its aim to provide wireless data over a long distance in variety of ways. It based on IEEE 802.16 standard. It is also called the wireless metropolitan area network. Wi-Max is standard based technology enabling delivery of last mile and as an alternative to wired broadband like cable and Digital Subscriber Line (DSL) [16]. Wi-Max would operate similar to the Wi-Fi but at high speed and greater distance and greater number of user can use this technology. Wi-Max technology is incorporated in mobile, Laptop and Personal digital assistance (PDAs).

1.7.1 Different Families members of Wi-Max [16], [18] a. IEEE 802.16

It was the first standard of Wi-Max which was introduced in 2001 and is used as the backhaul (Transporting traffic between distributed sites) link. The frequency range is 10-66GHz. Wi-Max use single carrier modulation technique.

b. IEEE 802.16 2004

This is based on 802.16-2004 version of the IEEE 802.16 standard and on ETSI Hiper MAN. It uses Orthogonal Frequency Division Multiplexing (OFDM) and supports fixed and nomadic access in Line of Sight (LOS) and Non Line of Sight (NLOS) environments. 802.16-2004 were focused on fixed and nomadic applications in the 2-11GHz frequencies.

c. IEEE 802.16e/IEEE 802.16

It was introduced in first on 2005. In this version for mobile users which provide the High bandwidth, handover and network architecture and also the cell reselection. This feature of Wi-Max compete all the standard of cellular. Modulation technique is use for this standard is OFDM.

1.7.2 Comparison of different 802.16 standards Table 1.4 IEEE 802.16 standard

IEEE 602.16 IEEE 802.16-2004 IEEE 802.16e

Completed December 2001 May 2004 Est.Mid-2005

Spectrum 10-66GHz 2-11GHz 2-6GHz

Application Backhaul Wireless DSL & Backhaul Mobile Internet Channel

Condition Line of sight only Non-Line of sight Non-Line of sight Bit Rate 32-134Mbps at 28-MHz Canalization Up to 75 Mbps at 20-MHz Canalization Up to 15 Mbps at 5-MHz Canalization Modulation QPSK,16QAM &64QAM OFDM 256,OFDM 2048QPSK, 16QAM,64QAM Same as 802.16d,Scalable OFDMA Channel Bandwidth 20,25 & 28MHz Selectable Channel Bandwidth between 1.5 &

20MHz

Same as 802.16d

Comparison of Different Wi-Max standard [19]

Wi-Max basic architecture is just like a cellular system using the Base station that covers the area. The 802.16 is a point to multipoint protocol, [38] where multiple subscribers can access the same radio platform by using the multiplexing method. It is a connection oriented system where it uses the star and mesh topology in physical layer.

Fig: 1.7 Basic Architecture of Wi-Max [32]

The IEEE 802.16 extension, rectified in January 2003, use a frequency band of 2-11GHz, enabling a non line-of-sight connections [32]. This wide spectrum presently includes both licensed and unlicensed bands. Wi-Max towers are similar to the cellular telephone where they are directly connected to the internet service providers with high speed wired connection. Two towers can also connected by using LOS to each other refer as backhaul, where single tower can cover the area up to 3000 square miles. This constitutes a major breakthrough in wireless broadband access, allowing operators to connect more customers to single tower and thereby substantially reduce service cost.

1.7.3 Some Advantages of Wi-Max technology a. Easy to Deployment

For large coverage and capacity of networks .Operators can rapidly deploy their networks today and easily scale to meet the growing demands of tomorrow. b. Optimized Mobility

It provides to enable the mobile devices and optimizes handover [33]. c. Network Scalability

It enables new types of transport networks such as metro Ethernet, [33] and Point –to-Point for backhaul.

d. Quality of Service (QoS)

1.7.4 Some Disadvantages of Wi-Max technology a. Range

The typical range with standard equipment is on the order of tens of meters. To obtain a additional for a larger structure repeaters or additional access point must be deployed leads to costly solution.

b. Reliability

Wireless signals are subject to wide variety of interference and complex propagation effects that are beyond the control network administrator.

1.8 Importance of Antenna in Wireless System

An antenna is a metallic structure, which converts electromagnetic waves into electrical currents and vice versa. In wireless communication system same antennas used for both transmission and reception. Antenna is one of the most important elements in wireless communication system [36].

A common way to characterize the performance of an antenna is radiation pattern which is graphical representation of radiation properties of an antenna as a function of space coordinates. The simplest pattern is produced by an idealize antenna known as isotropic antenna (is a point in space that radiates power in all direction equally).

1.8.1 Antennas Types a. Wire Antennas

Wire antennas are familiar to the layman because they are seen virtually every where on automobiles, buildings, ships, aircraft and so on [22]. These are various shapes of wire antennas such as straight (dipole), loop, and helix.

Fig: 1.8 Dipole Wire Antenna [22] b. Aperture Antennas

Aperture antennas are very useful for aircraft and spacecraft applications, because they can be very conveniently flush-mounted on the skin of the aircraft or spacecraft [22]. These are different types such as Pyramidal horn, Conical horn and Rectangular waveguide.

c. Microstrip Antennas

Microstrip antennas consist of a metallic patch on a ground substrate. The metallic patch can take many different configurations like rectangular, circular, Dipole etc. These antennas can be mounted on the surface of high-performance aircraft, spacecraft, satellite, missile, cars, and even handheld mobile telephones [22]. They are discussed in more detail in chapter 3.

Fig: 1.10 Rectangular Microstrip patch Antenna [22] d. Array Antennas

The arrangement of the array may be such that the radiation from the elements adds up to give a radiation maximum in a particular direction or direction, minimum in others, or otherwise as desired [22]. They are the different types such as Yagi-Uda array, Microstrip patch array, Slotted-waveguide array and Aperture array.

Fig: 1.11 Aperture Array Antenna [22] e. Reflector Antennas

Because of the need to communication over great distance, sophisticated forms of antennas had to be used in order to transmit and receive signals that had to travel millions of miles. A common antenna form for such application is a parabolic reflector [22]. The diameter of this antenna is as large as 305 m. Such large dimensions are needed to achieve the high gain required to transmit or receive signals after millions of miles of travel.

f. Lenz Antennas

Lenz antennas can be used in most of the same applications as are the parabolic reflectors, especially at higher frequencies. By proper shaping the geometrical configuration and choosing the appropriate material of the lenses, they can transfer various forms of divergent energy into plane waves [22].

Fig: 1.13 Lenz antenna with index of refraction n >1 [22]

1.9 Future of Wireless Technology

Wireless Communication industry is growing day by day. Main focus of this technology is to provide the maximum data for each user. IEEE and ITU-R are responsible for wireless standardization.

1.9.1 Mobile Broad Band Wireless Access (MBWA)

It is the Mobile Broadband Wireless Access of IEEE 802.20 standard is one possible future of wireless technology. Main purpose of this standard is a formal specification for packet –based air interface designed for IP-based services [34]. Following are the key feature of this technology

• IP roaming & handoff (at more than 1 Mbps) • New MAC and PHY with IP and adaptive antennas

• Optimized for full mobility up to vacuolar speeds of 250km/h • Operates in Licensed Bands (below 3.5GHz)

Chapter 2

Antenna Fundamentals

2.1 Antenna Definition

Antenna is transducers (it converts one from of energy in to another) that transmit or receive electromagnetic waves (has electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation) [39].

2.2 Antenna Radiation

E

Source Transmission Line Antenna Free space wave

Fig: 2.1 Antenna Radiations [22]

2.3 Friis Transmission Equation

It gives the power transmitted from one antenna to another in an idealized condition.

(Өr, Φr)

(Өt, Φt)

R

Fig: 2.2 Transmitting and receiving antenna for Friis transmission equation [22]

The Friis transmission equation is given as,

(

) (

)

2 2 2 2 1 1 , , 4 r cdt cdr t r t t t r r r t r t P e e D D P .P R P πλ θ φ θ φ ⎛ ⎞ ⎛ ⎞ ⎛ _{⎞ ⎜ ⎟} ⎜ ⎟ ⎜ _{⎟ ⎜ ⎟} ⎝ ⎠ ⎝ _{⎠ ⎝ ⎠} = − Γ − Γ

(

2.1

)

where Are transmitter and receiver conduction, dielectric efficiency respectively, ,

, cdt cdr e e

t

Γ Γ are transmission coefficient of transmit and receive antenna _r respectively,D_t(θ φ_t, )_t is the directivity of transmit antenna andD_r( , )θ φ_{r r} is a directivity of receive antenna in direction of

(

θ_r,Φ_r

)

,Pt and Pr polarization vector of transmitting and receiving antennas respectively, taken in appropriate direction [40]

The simplest form of Friis equation is given by considering two antennas one transmitting and other is receiving then ratio of power received by the receiving antenna to the power transmitted by transmitting antenna is given as [40]

2 4 r t r t P G G P R λ π ⎛ = _⎜ ⎝ ⎠ ⎞ ⎟

( )

2.2

where λ is a Wavelength, R is a distance between two antennas, the received power Pr (delivered to the receiver load), transmitting power Pt [22], Gr receiving antenna gain and Gt transmitting antenna gain.

2.4 Radiation Field Region around Antenna

The space surrounding a antenna can be divided in to three regions [22] that is, • Reactive Near Field Region

Fig: 2.3 Field Region Around antenna [22] 2.4.1 Reactive Near Field Region

The near field is that part of radiated field (electromagnetic radiation has a electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation) [41] nearest to the antenna.

The reactive energy oscillates towards and away from antenna, appearing as a reactance hence in this field region reactive filed dominates. The outer most boundaries for this region is at a distance

3

1 0.62 /

R = D λ

( )

2.3

whereR is the Distance from antenna, D is the Largest dimension of antenna and λ is ₁ the Wavelength

2.4.2 Radiating Near Field Region (Fresnel Region)

Radiation field dominates as compared to reactive near field region. This region is between reactive near field and far field region. The outermost boundary for this region is at distance

2

2 2 /

R = D λ

( )

2.4

whereR is the Distance from Antenna surface, D is the Dimension of Antenna and λ ₂ is the Wavelength

2.4.3 Far Field Region (Fraunhofer Region) 2

2 2 /

R = D λ

( )

2.5

radial distance in this region. The region beyond radiating near field is far field region.

2.5 Antenna Parameters

2.5.1 Radiation Pattern

It is defined by “radiation pattern is the representation of graph which describes the radiation properties of antenna as a function of space coordinate” [22]. The radiation pattern of antenna includes [22]

1. Power flux density 2. Field strength 3. Directivity

4. Radiation Intensity 5. Polarization

Radiation pattern are described with reference to isotropic antenna (that radiates equally in all direction). Plot of directional antenna is shown in figure below [22], typically has a more power in particular direction as compared to isotropic antenna (radiates in all direction)

Null Back Lobe

Minor Lobes

Side Lobe

HPBW

Fig: 2.4 Radiation pattern of directional antenna [22] • Half Power Beamwidth

In a plane containing the direction of maximum of beam, the angle between two direction in which the radiation intensity is one half value of beam [22]. • Main Lobe

Lobe having maximum radiation in particular direction. • Side Lobe

Lobes other than main lobe is called side lobe. These lobes are unwanted and degrade the antenna performance.

• Back Lobe

2.5.2 Directivity

Measure of a maximum power density radiated by the practical antenna relative to the power density radiated by an ideal isotropic antenna (that radiates equally in all direction) [22]

Ratio of radiation intensity in given direction from antenna to radiation intensity averged overall directions.

4 i U D U P U π = =

( )

2.6

D = directivity of the antenna (Dimenshionless) U= radiaion intensity of the antenna

Ui = radiaion intensity of an isotropic source P= total power radiated

Directivity of antenna is generally expressed in dBi (logrithmic unit relative to the gain of isotropic antenna). Antenna having a narrow main lobe would have better directivity and vice versa.

2.5.3 Input Impedence

Impedence of antenna is given as [22] R +jX

in in in

Z =

( )

2.7

in

Z = antenna impedence of teminals in

R = antenna resistance at terminals in

X = antenna reactance at terminals(represent the power stored in near field of

antena) Rin consist of two component Rr (radiation resistance) and RL (load resistance) and is given as

Rin=Rr+RL

( )

2.8

2.5.4 Voltage Standing Wave Ratio (VSWR)

Source generates the signal towards antenna, some waves are reflected back to source along with travelling waves. These constructive and destructive waves create standing waves. A pattern is shown below Fig 2.5 [22].

VSWR is given as [22] 1 1 VSWR= + Γ − Γ

( )

2.9 r in i in V Z Z V Z Z − Γ = = + s s

)

(

2.10 where Γ is a Reflection coefficient, Vr is amplitude of reflected wave and Vi is a amplitude of incident wave

VSWR is basically a measure of impedance mismatch between transmitter and antenna. Higher the voltage standing wave ratio (VSWR) greater the mismatch and vice versa.

According to maximum power transfer theorem maximum power can be transferred only if impedance of transmitter is complex conjugate of impedance of antenna.

Zin=Z∗s

(

2.11

)

Where,

in in in

Z =R + jX Antenna input impedance

s s in

Z =R + jX Characteristic impedance of transmission line

2.5.5 Antenna Efficiency

Antenna efficiency describes how actively an antenna is working. Losses occurs within the antenna are due to reflections (mismatch between transmission and antenna) and I2R losses (conduction and dielectric). The total antenna efficiency is given by [22]

eo=e e er c d

(

2.12

)

Where eo is a total antenna efficiency, er = (1-|Ґ2|) reflection efficiency, ec is a conduction efficiency and ed is a dielectric efficiency.

Antenna radiation efficiency (is a ratio of actual power radiated to the power applied at the input terminal) is given as

r cd c d r L R e e e R R = = +

(

2.13

)

the total antenna efficiency is given as

eo=e er cd=ecd

(

1− Γ2

)

(

2.14

)

2.5.6 Antenna Gain

Gain of antenna is product of efficiency and directivity when efficiency is 100% then gain is equal to directivity. When direction is not stated power gain is normally taken in direction of maximum radiation.

Gain is given by [22]

(

)

( )

in

radiation intensity U θ,

Gain 4π 4π

total input accepted power P

φ

= =

(

(

2.162.16

)

)

The relative gain is given as The relative gain is given as

( )

(

( )

)

(

)

in 4π U θ, Gain

P lossless isotropic source

φ

=

(

2.17

)

2.5.7 Polarization

Polarization is a property of transverse waves (a moving wave that consist of oscillations occurring perpendicular to the direction of energy transfer) which describes the orientation of the oscillations in the plane perpendicular to the wave’s direction of travel. Waves which vibrate in one plane only referred to as polarized waves. The most common type of polarization include linear (horizontal / vertical) circular (right hand / left hand polarization) and elliptical where linear and circular are special cases of elliptical polarization [24].

• Linear Polarization

A time harmonic wave is said to be linearly polarized in space if electric field vector at that given point always directed along straight line.

-1 1

00

• Circular Polarization

A time harmonic wave is said to be circularly polarized in space if electric field vector at that given point traces a circle.

Fig: 2.7 Circular Polarizations [23] • Elliptical Polarization

Elliptically polarized electromagnetic wave consists of two electromagnetic waves that are linearly polarized and having unequal amplitudes but has the same frequency. In result a wave with electric vector that both rotates and changes its magnitude. An elliptical shape can be traced out by the tip of electric field vector and therefore it is referred to as elliptical polarization [28].

2.5.8 Bandwidth

Bandwidth is defined as a range of frequencies. It can also be defined as a difference between the upper and lower frequencies[43].

Bandwidth of broadband antenna can be defined as a ratio of upper to lower frequencies .

Bandwidth of narrrow band antenna can also be expressed as percentage of frequency difference over center frequency can be given as [26]

( )

% H L 100 narrowband C f f BW f ⎡ − ⎤ = ⎢ ⎥ ⎣ ⎦

(

2.18

)

where fH is a upper frequency, fL is a lower frequency and fC is a center frequency.

2.6 Far Field Radiation from Hertzian Dipole

Fig: 2.9 Spherical Coordinate System for Antenna Analysis [22]

Far field radiation from a Hertzian dipole (is a theoretical dipole antenna that consists of infinitesimally small current source in free space, although a true Hertzian dipole cannot physically exist a best approximation to the length of Hertzian dipole is L<λ/50)[44] is easily described with the help of spherical coordinate system [22] as shown in Figure 2.4.

The angle θ denotes the elevation angle and angle Φ denotes the azimuth angle. The x-z plane basically showing elevation E-plane (Φ=0) where the electric field vector is in maximum range conversely x-y plane representing the azimuth H-plane (θ=Pi/2) where the magnetic field containing the direction of maximum radiation.

( )

0 2 sin 1 1 1 4 jkr kI Le E j r jkr kr θ η θ π − ⎡ ⎤ = ⎢ + ⎥ ⎢ ⎥ ⎣ − ⎦

(

2.19

)

0 2 cos 1 1 2 jkr r I Le E r j θ η π − _⎡ = _⎢ ⎣ kr⎦ ⎤ + _⎥

(

2.20

)

0 sin ₁ 1 4 jkr kI Le H j r φ θ π − _⎡ = _⎢ ⎣ jkr⎦ ⎤ + _⎥

(

2.21

)

0 r H =

(

2.22

)

0 Hθ =

(

2.23

)

0 Eφ =

(

2.24

)

where η is the intrinsic free space impedance, k is the 2 /π λ wave propagation constant, r is the radius for spherical coordinate system,I is the uniform current and ₀ L is the length of the dipole

By considering the far field, the term r2 can be neglected then equation can be written as 0 _sin 4 jkr kI Le E j r θ η _π θ − =

(

2.25

)

0 sin 4 jkr kI Le H j r φ θ π − =

(

2.26

)

0 r E =

(

2.27

)

The above equation 2.7 and 2.8 is showing that E(θ) and H(Φ) are non zero field and transverse(perpendicular) to each other. The direction of E, H and r from a right handed set such that poynting vector is in r direction and indicates the direction of propagation of electromagnetic waves. The time average poynting vector is written as [22] 1 [ ] 2 av ∗ = W Re Ε× Η _{(Watts m )/} 2

E and H are peak values of electric and magnetic field.

The average power radiated by antenna can be written as [22]

ds is the vector differential surface (

rad _rad

P =

_w

∫∫

W ds (Watts)

(

2.29

)

1 2

ds= ± ×dl dlJJG JJG)

rad is the magnitude of the time varying poynting vector (Watts/m2).

Chapter 3

Microstrip Patch Antenna

3.1 Introduction

In high performance aircraft, spacecraft, satellite and missile application, where size, weight, cost, performance, ease of installation and aerodynamic profile are constraint this type of low profile antennas may required [22]. Microstrip patch antenna also very popular in the field of Mobile communication. Patch antennas are usually used within the frequency range of 2-11GHz. A basic architecture of Micro strip patch antenna shown below Fig 3.1 [23].

Patch Dielectric Substrate Ground Plane L t h W

Fig: 3.1 Microstrip Patch Antenna Diagram structure [23]

A microstrip antenna is basically consists of radiating patch, dielectric substrate, feed and ground plane. Patch and ground plane made of material such as copper or gold.

Fig: 3.2 Different types of patches [22]

During the fabrication of antenna, height of the dielectric substrate between the patch and ground plane is very much critical, because it effects on the efficiency of the antenna. On the other hand by increasing the height of substrate surface wave are introduced. These surface waves are undesirable. Surface waves travel within the substrate and scattered on the edges of patch which cause poor polarization called the firings effect, which we will discuss later.

3.1.1 Rectangular Microstrip Patch

Microstrip patch antenna consists of radiating patch, dielectric substrate, ground plane and feed technique. Radiating patch placed a small fraction of wavelength above the ground plane and separated by the dielectric substrate. The radiating patch can be of any material however we are using FR-4 (PCB). Most of the commonly used antennas have a feed point where we get impedance of 50 or 75ohm. Microstrip patch antennas are fed at 50ohm.

3.1.2 Patch Dimension

In rectangular patch, the height (h) of the dielectric substrate is usually defined between the range of 0.003λ0 ≤ h ≥ 0.05λ0. The length of patch is taken in range of

λ0/3 < L < λ0/2.The width is taken in between the range of λ0/2 < L < λ0. Patch is

selected to be thin that is in range of t<< λ0 (where “t’’ is the patch thickness).The

dielectric constant of substrate (Єr) normally in the range of 2.2≤Єr≤12. [22] Where

3.2 Feeding Methods

In Microstrip patch antenna, there are various type of feed methods are use, these methods are categorized in two main types, these are the Contacting and non Contacting.

a. Contacting

In contacting method technique, RF power is directly applied to the patch through BNC connector. The contacting feed methods are Microstrip Feed Line and Coaxial Probe.

b. Non-Contacting

In non Contacting method the power has given through coupling. It depends on the Aperture Coupled Feed and Proximity Coupled Feed.

The four most popular techniques are • Microstrip Line Feed

• Coaxial Probe • Aperture Coupling • Proximity Coupling 3.2.1 Microstrip Line Feed

Microstrip Feed Line is depending on the conducting strip. In this technique a conducting strip directly connected to the patch which is smaller in dimension as compare to patch. It is very easy to fabricate, very simple in modeling and match with characteristic impedance 50Ω or 75Ω. This can achieve by properly controlling the inset position. A model of Microstrip Line Feed shown in Fig 3.3 [22]

Microstrip feed Patch

Substrate

Ground plane

Fig: 3.3 Microstrip Feed Line [23] 3.2.2 Coaxial Feed

plane. It has many advantages as compare to others, like it is easy to fabricate and match. It has low spurious radiation. On other hand it has narrow bandwidth and difficult to model especially in the thick substrate where we need to drill at hole, fix the connector and soldering the cable with great care [22]. A typical model of Coaxial Feed is shown in Fig 3.4 [23]

Fig: 3.4 Coaxial Feed [23] 3.2.3 Aperture Coupled Feed

Aperture Coupled feed is more complex and more difficult to fabricate as compare to others. It consist of two substrates which separated by ground plane. On bottom side of the lower substrate there is a microstrip fed line whose energy is coupled to the patch through slot on the ground plane. High dielectric material is used for bottom substrate and thick and low dielectric constant material for the top substrate. In this design the substrate electrical parameters, feed line width and specially slot size and position can be use to optimize the design. It has the spurious radiation where on the other side it provides the narrow bandwidth [22], [30]. A model of Aperture Coupled is shown in Fig 3.5 [23]

3.2.4 Proximity coupled Feed

In Proximity Coupled Feed method two dielectric substrates are used such that the feed line is between the two substrates and radiating patch is on top of the upper substrate. Its fabrication is not easy as compare to other feed techniques. The length of the feeding stub and the width to line ratio of the patch can be used to control the match point. Advantage of this feed is that it almost eliminates spurious radiation and provides high bandwidth (as high as 13%) [22], due to overall increase in the thickness of the microstrip patch antenna. This scheme also provides choice between two different dielectric medium, one for the patch and one for the feed line to optimize the individual performance [22]. A basic model shown Fig 3.6 [23]

Fig: 3.6 Proximity Coupled Feed [23]

3.3 Comparison of Different feed Methods

Table 3.1

Comparison of Different Feed Techniques Microstrip

Line Feed Coaxial Feed

Aperture Coupled Feed

Proximity Coupled Feed

Spurious more more less Minimum

Reliability better poor due to

soldering good Good

Ease of fabrication easy soldering and drilling needed alignment

required Alignment required Impedance

matching easy easy easy Easy

Bandwidth (achieved with

impedance matching)

2-5% 2-5% 2-5% 12%

3.4 Method of Analysis

There are three methods are use for analysis the data. • Transmission Line Model

• Cavity Model • Full wave Model

Transmission line model is most popular and easy to use. It gives the good physical insight but it is less accurate and it is more difficult to model for coupling. If we compare the Transmission line model with cavity model, it is more accurate but more complex. The full wave models are extremely accurate, arbitrary shaped elements and coupling. But it is more complex and gives less physical insight as compare to other [25].

3.4.1 Transmission Line Model

Transmission line model is the simplest of all and give good physical insight but it is less accurate. It is easy to fabricate the antenna model by using transmission line. In this model a fring effect is created at the edges of the patch which cause radiation, the fring effect is discussed as,

a. Frings Effect

Fringe is an effect which is situated on the edge or away from the centre of something. Fringing effect is also explained as the amount of fringing is a function of the dimensions of the patch and height of the substrate [22]. Due to limitation of patch dimensions, fields at the edges of patch produce fringing effect. For principle of E-Plan fring effect is the function of the ratio of the length of the patch L to the height h of the substrate (L/h) and Єr of substrate. In figure 3.7 typical electrical fields lines are situated within the substrate and some in air [24].

Fig: 3.7 Electric field line [22]

1 2 1 1 1 2 2 r r reff h W ε ε ε = + + − ⎡_⎢ + ⎤_⎥− ⎣ ⎦

( )

3.1

In order to operate the transmission line model in the fundamental (TM10)

mode, the length of the patch should be slightly less than λ/2 where λ is the wavelength in the dielectric medium and is equal to λ0/√Єreff where λ0 is the free space

wavelength.

Radiating Slots

Ground

_Plane

L

Patch

W

E

V

E

H

E

_V

E

H

Patch

GroundPlane

h

L

L

Fig: 3.8Transmission Line Model [22], [23]

In above Figure 3.8 it shows that frings effect is created at the edges of the patch. To fabricate the antenna by using the transmission line model, we should calculate the following things, first of all specify the resonant frequency, length, width and height of substrate. We use the following formulas for calculation [22],

1. Effective Patch Width (W)

(

2

)

2 o r 1 c W f ε = × +

( )

3.2

where c is the velocity of light,fo is the Resonant frequency and εr is the dielectric constant

2. Effective Dielectric Constant (εreff) 1 2 1 1 1 2 2 r r reff h W ε ε ε = + + − ⎡_⎢ + ⎤_⎥− ⎣ ⎦

( )

3.3

3. Frings factor (∆L)

(

)

(

)

0.3 0.264 0.412 0.258 0.8 reff reff W h L h W h ε ε ⎛ ⎞ + _⎜ + _⎟ ⎝ Δ = ⎛ ⎞ − _⎜ + _⎟ ⎝ ⎠ ⎠

_{( )}

3.4

4. Effective length (Leff)

2 eff o reff c L f ε =

( )

3.5 5. Length 2 eff L L= − Δ L

( )

3.6 3.4.2 Cavity Model

Transmission Line Model is easy to use but it has some discrepancy. Cavity model is more accurate as compare to transmission line model. In cavity model it is difficult to find out the amplitude of the electric and magnetic field if the microstrip antenna treated only as cavity [22].

In Cavity model the interior region of dielectric substrate is model as a cavity bounded by electric walls on the top and bottom. The substrate should be very thin; it is just like a normal patch. A typical diagram of cavity model is shown Fig 3.9 [25]

Fig: 3.9 Charge distribution & Current density creations on microstrip patch [25]

So it is very difficult to measure the absolute amplitude of the electric and magnetic fields if microstrip antenna treated only as a cavity. By treating the walls of cavity, as well as material in it is lossless, it would not radiate and its input impedance will be purely reactive. If the material is lossless, the cavity will not radiate its input impedance is reactive [26]. To account it for radiation, there should need to find out

the loss mechanism which is described by introducing the effective loss tangent. After defining the loss tangent it behave like an antenna where loss tangent is reciprocal to Q-factor. 1 T eff Q δ =

( )

3.7

QT =Antenna quality factor

Cavity model has the capability to deal with normalize fields within the dielectric substrate. It has a advantage to deals with field variation along the radiating patches.

3.4.3 Full wave Model

The full wave model is more accurate as compare to other like cavity and Transmission Line models. The Method of moment describes the solution in form of an integral and it can be used to handle arbitrary shapes [25]. In full wave model surface current are used to model the microstrip patch and the volume polarization currents are used to model the fields in the dielectric slab. It versatile and can be treat single elements, finite and infinite arrays, stacked elements, arbitrary elements and coupling. It has been shown by how an integral equation is obtained for these unknown currents and by using the method of moments, this electric field integral equations are converted into matrix equations which can be solved by various techniques of algebra to provide the good results [29].

3.5 Bandwidth & Quality Factor of Microstrip Antenna

The main limitation factor of microstrip patch antenna is the narrow bandwidth. But we can improve the bandwidth by using the different feeding technique method. We can improve the bandwidth approximately 35% by increase the thickness of dielectric substrate and dielectric constant is taken lower value [25]. An other method to improve the bandwidth of patch antenna is to create the array of more patches by adding more layers.

3.5.1 Q-factor

Q-factor is a figure of merit that is represented the losses of antenna. These losses are the radiation, coduction, dielectric and surface wave losses.

1 1 1 1 1 t rad c d s Q =Q +Q +Q +Qw

( )

3.8 Where, is the total quality factor, is the quality factor due to radiation losses,

is the quality factor due to conduction losses, is the quality factor due to dielectric losses and

t

Q Qrad

c

Q Qd

sw

Q is the Quality factor due to surface waves.

However fractional bandwidth of antenna in inversely proportional to the total quality factor QT, here a trade off required between Bandwidth and Q-factor (quality

Relationship between bandwidth and Q-factor 1 o T f f Q Δ =

( )

3.9

3.6 Advantages & Disadvantage

Microstrip patch antennas are increasing in popularity for use in wireless applications due to their low profile structure. Therefore they are extremely compatible for embedded antennas in handled wireless devices such as cellular phones, pagers, Wireless routers etc. These are also use in for aircraft, spacecraft, and satellite and missile applications [25]. Some of their advantages are given below:

• Light weight and Low volume

• Support both, linear as well as circular polarization • Low fabrication cost and ease of fabrication

• Mechanically robust specially on rigid surface

• Can be easily integrated with microwave integrated circuit (MICs) Microstrip antenna has some major disadvantage like,

• Narrow Bandwidth • Low efficiency • Low power

Chapter 4

Design, Measurement and Result

4.1 Design Procedure

Due to high frequency and impedance matching, Microstrip patch antenna is very famous in wireless communication.

In our design Mirostrip antenna consist of radiating patch and ground plane. Patch and ground plane are connected to each other with a thin wire. Microstrip patch antenna is used for both linear and circular polarization but we are focusing on linear polarization. Because we are fabricating this antenna for Wi-Max application at operating frequency 3.5GHz, We can increase our bandwidth in different ways. One method is to change the substrate height (up to certain threshold) to get more bandwidth. Another, antenna bandwidth (using transmission line model) can be improved by increasing the substrate thickness or height (we choose air as a substrate with dielectric constant 1). The problem of this solution is as the substrate height increases surface waves are introduced. Surface waves travel within the substrate and scattered at bends of the radiating patch which interns degrade the antenna performance. However to accommodate this factor and air dielectric substrate is used which has the dielectric constant is 1 and by using air substrate surface waves are not excited easily. Hence, it is critical to justify the height where larger bandwidth can be achieved with reasonable amount of gain.

4.1.1 Different Parameters

These are the parameters which is very important to fabricate the Mirostrip Patch Antenna.

a. Resonant Frequency

Resonant frequency of this antenna is chosen 3.5GHz. Because we are fabricating Wi-Max application the resonant frequency is chosen from IEEE 802.16 span of 2-11GHz.

b. Dielectric Substrate

We are choosing the Air Dielectric substrate which has the value of dielectric constant 1 in order to get better efficiency.

c. Height of Substrate

Height of substrate is chosen 4mm in-between the ground plane and radiating patch.

4.1.2 Calculation of Patch Dimension

As we mention in chapter 3 we are using the Transmission Line model [22] for calculation of patch Dimension.

a. Input Parameters

• Dielectric Constant (εr) = 1

• Height of Patch above ground plane = 4mm 1. Calculation of Patch Width

1 2 2 r o c W f ε = +

where c is the velocity of light, fo is the resonant frequency and εr is the dielectric constant

(

)

(

)

8 9 3 10 / 1 1 2 3.5 10 2 m s W HZ × = + × 0.043 cm W =

So calculated width is,

43 mm

W =

2. Calculation of effective Dielectric Constant (

ε

reff) 1 2 1 1 1 12 2 2 r r reff h W ε ε ε = + + − ⎡_⎢ + ⎤_⎥− ⎣ ⎦

where εreff is the effective dielectric constant, εr is the dielectric constant of substrate, h is the height of dielectric substrate and W is the width of the patch

1 2 1 1 1 1 4 1 12 2 2 43 reff ε − + − ⎡ ⎤ = + _⎢ + _⎥ ⎣ ⎦ εreff = 1

3. Calculation of Frings factor (∆L)

The mathematical calculation gives the frings effect as under Δ =L 2.75 mm

4. Calculation of effective Length (Leff) 2 eff o reff c L f ε =

(

)

8 9 3 10 / 2 3.5 10 1 eff m s L = × × So, calculated effective length is,

Leff =43 mm `

5. Calculate the total length

L L= eff − Δ2 L L=43 2 2.75−

(

)

So after the subtracting the frings effect of both side from effective length, we found total length is, (it is slightly greater but we will take round figure)

L=37 mm

4.1.3 Calculation of Ground Plane (Lg and Wg)

The size of ground plane should be greater than the patch. The ground plan can be infinite but due to physical constraints this is not possible. The ground plane to the underside of any such printed circuit will increase the gain of this antenna [29].

But on other side this may adversely affect the overall bandwidth of the structure. For this design a reasonable large ground plane is determined consisting of square pattern of 120mm.

4.1.4 Patch Model & Feed Point Location (Xf ,Yf)

Microstrip patch antenna is fabricated by using a PCB board with copper on one side and plastic on the other. The patch is cut according to the calculated values 37*37* 4mm (L*W*H). After that we locate a feed point on the patch. The true feed point is given by 50Ω impedance matching.

Fig: 4.1 Fabricated Antenna Model

4.2 Measurement and Result

We use the network Analyzer for measuring the different parameters of the Microstrip Patch antenna. We will calculate the, S11 parameters and S21 Parameters on

the operating frequency of 3.5GHz. 4.2.1 S11 Parameters

a. Return Loss

Fig: 4.2 Graph shows return Loss

Above graph shown the return loss of -21.53dB which is actually the good, ideally return loss should be RL ≥ -9.5dB.

b. Bandwidth

The range of frequencies where by using this range an antenna performance can be determined to specific standard [22]

We were selecting the Resonant frequency of 3.5GHz but in graph it shown 3.04GHz where we can get better bandwidth. It means we are getting 0.46GHz less in our actually bandwidth. Here is many factors can involve to getting lower frequency, like due to inductance and capacitance effect in BNC connector and also it can be happened due to dimension cut less in actual calculation.

Table 4.1

Different result on different resonant frequencies Resonant Frequency (GHz) Return Loss (dB) Bandwidth (MHz) 3.05 -12.872 150 3.04 -19.472 69

Antenna

3.08 -28.781 11

The height of a substrate (air) directly affects the bandwidth and due to the many other factors like inductance and capacitance effect in BNC connectors we get 3.04GHz center frequency.

At the center frequency of 3.04GHz a reasonable bandwidth is achieved with return losses of -19.472dB. Table 4.1 shows that as the return loss increases, the bandwidth gets narrower and narrower.

c. Impedance

Fig: 4.4 Smith chart of Impedance

4.2.2 S21 Parameter

a. Antenna Gain

Gain of antenna is product of efficiency and directivity when efficiency is 100% then gain is equal to directivity. When direction is not stated power gain is normally taken in direction of maximum radiation. [22]

1. Theoretical Calculation

The free space path loss is proportional to the square of the distance between the transmitter and receiver, and also proportional to the square of the frequency of the radio signal. The free space path loss is given as [37].

2 4 FSPL = πd λ ⎛ ⎜ ⎝ ⎠ ⎞ ⎟ 2 4 = df c π ⎛ ⎜ ⎝ ⎠ ⎞ ⎟

where is the wave length (in meter), f is the signal frequency (in Hertz), d is the distance from the transmitter (in meter) and c is the speed of light in a vacuum,

(in meter per second) λ

2.99792458×108

The free space path loss in term of dB is given as

( )

2 10 4 FSPL dB = 10log df c π ⎛_{⎛ ⎞} ⎞ ⎜⎜ ⎟ ⎜⎝ ⎠ ⎝ ⎠⎟⎟ = 20log₁₀ 4 df c π ⎛ ⎜ ⎝ ⎠ ⎞ ⎟

= 20log ( )+20log₁₀ d ₁₀

( )

f +20log₁₀ 4 c π ⎛ ⎜ ⎝ ⎠ ⎞ ⎟ = 20log ( )+20log₁₀ d ₁₀

( )

f −147.56

For typical radio applications, it is common to find f measured in units of MHz and d in km, the FSPL equation becomes

The distance between the two antennas is d =1m, a theoretical path loss between two antennas in free space with no obstacles is given as

FSPL dB = 20log (0.001)+20log

( )

_{10 10}

(

3050 +32.5

)

= 9.65+32.5 = 42.15

2. Experimental Calculation

In order to measure antenna gain and path loss we used two antennas (Antenna 1, Antenna 2) of same specification connected to port 1 and 2 of network Analyzer. The Fig 4.5 represents a loss in power.

Fig: 4.5 Graph shows Gain of Antenna

Since the theoretical path loss is found to be 42.15dB and the experimental path loss is found to be 28.454dB. The difference between theoretical and experimental value is 13.696dB leads to a 6.8dB gain per antenna with respect to isotropic as a reference antenna.

b. Antenna Beam width