The Hashemite University

Faculty of Engineering

Department of Electrical Engineering

Report about

Patch AntennaPatch AntennaPatch AntennaPatch Antenna

Prepared by:

Mahmoud Kh. Al-Shattel (631543)

Course Title : Antenna And Wave Propagation (404463)

Supervisor : Dr. Omar Al-Sarayra.

Abstract

Antennas are key components of any wireless communication system. They are

the devices that allow for the transfer of a signal (in a wired system) to waves

that, in turn, propagate through space and can be received by another antenna.

The receiving antenna is responsible for the reciprocal process, i.e., that of

turning an electromagnetic wave into a signal or voltage at its terminals that can

subsequently be processed by the receiver.

The fast growing in communication systems leads by the revolution in Antenna

Engineering, which creates various geometries of antennas like dipoles, Yagi-

Uda, horns and Patch & Microstrip Patch Antenna. Patch Antenna is our concern

in this report.

1.0 INTRODUCTION

Patch Antenna are widely used in microwave frequency region because of there

computability with Printed Circuit Board (PCB) technology and its simplicity in

manufacture. The simplest form of the patch antenna consists of a metal patch (usually

rectangular or circular) over a grounded substrate, as shown in Figure 1.1. (1)

Fig. 1.1: (a) Rectangular Patch Antenna and (b) Circular Patch Antenna

Many methods are used to feed the patch; the most common method is using coaxial

probe feed as depicted in Figure 1.2.

Fig. 1.2: Feeding by coaxial probe

1.1 Main Properties of Patch Antenna

Patch Antennas offer effective low-profile designs for a wide range of wireless

applications. They are inexpensive to fabricate, light in weight, and can be made

conformable with planar and non-planar surfaces. The patch antennas are compact and

compatible with microwave integrated circuits (MICs) for high-frequency applications.

Unfortunately, they have some shortcomings, including relatively low gain, narrow

bandwidth, and sensitivity to fabrication errors. Despite that; and because of rising

demands for multiple frequencies in wireless designs, patch antennas support multiple-

function circuits that will force us to use it as it until we overcome on its disadvantages.

It’s good to mention that The Microstrip Antenna is a paper of The Patch Antenna Tree,

Microstrip is minimized Patch Antenna, widely used in MICs in the form of array.

1.2 Radiation Efficiency and Bandwidth

The radiation depends mainly on the constitutive parameters (ε, σ, µ) of the substrate and

its thickness. Bandwidth increases with the substrate thickness and inversely with its

permittivity (ε), assume a typical Teflon substrate (εr = 2.2) and copper ground plane (σ =

3.0 × 107 S/m). Note that the substrate thickness is limited by the inductance of the

feeding coaxial probe; assume it 50-Ω coaxial feed cable, the probe reactance will

become sufficiently large when the substrate thickness is about 0.018λ0 to render the

antenna non-resonant unless a matching element is used.

2.0 PRINCIPLES OF OPERATION

2.1 Radiation Mechanism

At first glance it might seem that patch antenna can operate very well at all, since it

consists of a horizontal electric surface current (corresponding to the patch current)

suspended (via the substrate) a short distance above a ground plane. Basic image theory

predicts that such a current will not radiate very well the. However, patch and the ground

plane together form a resonant cavity (filled with the substrate material). The cavity is

lossy, due not only to the material (conductor and dielectric) loss, but also to the

(desirable) radiation into space. For a thin substrate, neglecting material loss, the quality

factor Q of the antenna is inversely proportional to the substrate thickness h.

In actuality, the Q is limited by the material losses, so for sufficiently thin substrates it

becomes difficult to obtain a good impedance match (in this region the radiation

efficiency will also be poor). However, even for substrates as thin as 0.005lλ0 a good

match may be obtained with a reasonable efficiency of around 65 percent for a typical

Teflon substrate and copper conductors.

2.2 Modes of Operation

For the rectangular patch, the TMmn mode has a normalized electric field that is given by:

(2-1)

(2-2)

The usual mode of operation for a broadside pattern is the TM10 mode, which has no y

variation and has a length L that is approximately one-half wavelength in the dielectric.

In this mode the patch essentially acts as a wide microstrip line of width W that forms a

Transmission-line resonator of length L. The width W is usually larger than the length L

in order to increase the bandwidth, according to equation (2-2) where Qsp is The Quality Factor for the (desired) radiation into space inversely proportional to Bandwidth (see

equation 2-3). A ratio W/L = 1.5 is typical for rectangular patch antenna.

(2-3)

3.0 RADIATION PATTERNS

The radiation patterns of a patch may be calculated using either an electric-current model

or a magnetic-current model. These models are usually derived assuming that either the

electric current on the patch or the electric field at the boundary of the patch corresponds

to that of the dominant patch mode for a patch with ideal (magnetic-wall) boundaries.

The patterns may be calculated directly for In the second case the ground plane is infinite,

while the substrate is truncated at the edges of the patch The radiation patterns are given

next for the rectangular and circular patches, using the magnetic-current model. (2)

3.1 Rectangular Patch

For the rectangular patch shown in Figure

1-1, the dominant TM10 mode has an

electric field of the form

(3-1)

The far-field pattern may be calculated

assuming that the substrate is infinite or

truncated at the edges of the patch. For

thin substrates the truncation of the

substrate does not have a significant effect

on the pattern except near the horizon (q

approaching 90ο) in the E-plane. For an

infinite substrate the pattern will tuck in

and go to zero at the horizon, while for a

truncated substrate the pattern will remain

nonzero down to the horizon in the E-plane.

Fig. 3.1: The Pattern of Patch

>>>Antenna in Azimuth Plane

Fig. 3.2: Far-field patterns of a rectangular patch

on an infinite ground plane and substrate.

Note that in figure 3.2 The E-

plane is shown with a solid line

and the H-plane is shown with a

dashed line.

3.2 Circular Polarization

A large number of applications, including satellite communication, have trouble with

linear polarization because the orientation of the antennas is variable or unknown.

Luckily, there is another kind of polarization -- circular polarization. In a circular

polarized antenna, the electric field varies in two orthogonal planes (x and y direction)

with the same magnitude and a 90° phase difference. The result is the simultaneous

excitation of two modes, i.e. the TM10 mode (mode in the x direction) and the TM01

(mode in the y direction). One of the modes is excited with a 90° phase delay with

respect to the other mode. A circular polarized antenna can either be right-hand circular

polarized (RHCP) or left-hand circular polarized (LHCP). The antenna is RHCP when

the phases are 0° and -90° for the antenna in the figure below when it radiates towards the

reader, and it is LHCP when the phases are 0° and 90°.

It is possible to fabricate patch antennas that radiate circularly-polarized waves. One

approach is to excite a single square patch using two feeds, with one feed delayed by 90°

with respect to the other. In this fashion, when (say) the vertical current flow is

maximized, the horizontal current flow will be zero, so the radiated electric field will be

vertical; one quarter-cycle later, the situation will have reversed and the field will be

horizontal. The radiated field will thus rotate in time, producing a circularly-polarized

wave. An alternative is to use a single feed but introduce some sort of asymmetric slot or

other feature on the patch, causing the current distribution to be displaced. Note that,

while circular patches can be used for these techniques, a circular patch does not

necessarily radiate circularly-polarized waves! A symmetric circular patch with a single

feed point will create linearly-polarized radiation. Finally, a nearly-square patch can be

driven at the corner; if the length is just a bit less than resonant and the height a bit more

(or vice versa) a circularly-polarized wave will result. (2)

Fig. 3.2: Model of microstrip patch antenna; edge-fed

with quarter wavelength transformer section to 50 Ω

transmission line.

Fig. 5.1: Model of microstrip patch antenna; edge-fed with quarter wavelength

transformer section to 145 Ω transmission line.

4.0 APPLICATIONS

Patch antenna is widely used in many communication systems like GPS satellites which

operate at frequency of 1575 MHz, wireless Local Area Network (LAN) -2.4 GHz and

5.2 GHz -,Broadband Stacked Patch Antenna for Bluetooth Applications and in Cellular

Networks.

Fig. 4.1: Applications on Patch Antenna.

5.0 DESIGN AND SIMULATION The patch antenna model used for the numerical simulation in Ansoft HFSS is shown in

Fig. 1. The patch antenna is designed for 1.0 GHz operation on a substrate with 2.2

permittivity and 2 mm thickness. To determine the width (W), the microstrip patch

antenna calculator (4)

was used to provide an initial starting point. The length (L) was

chosen to be the same as W to obtain a symmetric radiation pattern. The patch without

the feeding network was simulated in Ansoft HFSS to adjust W for resonance at 1.0 GHz.

Next, the input impedance of the patch at the edge was determined by placing a length of

145 Ω transmission line at the edge. (3)

The final dimensions of the entire microstrip patch antenna are

• W: 118.58mm

• L: 100.25 mm

Design and Radiation Pattern Using MATLAB:

6.0 CONCLUSION

This report covered basic antenna definition and explained terms frequently encountered

in examining antenna patterns. Also, the basic properties of linear polarized and circular

polarized patch antennas have been covered. We defined a basic set of specifications that

allow the user to understand and write a set of requirements for a specific application.

The Besides the ones covered here,

7.0 REFERENCES

1) McGraw-Hill - Antenna Engineering Handbook, 4th Edition

Dr. John L. Volakis

2) The Basics of Patch Antennas

Dr. Orban and G.J.K. Moernaut

3) Design and Calculations

http://www.emtalk.com/mpacalc.php?er=2.2&h=2&h_units_list=hmm&fr=1&Operation

=Synthesize&La=99.9973025115&L_units_list=Lmm&Wa=118.288232684&W_units_l

ist=Wmm&Rin=144

4) Microstrip Patch Antenna Calculator

http://www.emtalk.com/mpacalc.php