1. INTRODUCTION TO MICROSTRIP ANTENNAS

A very popular antenna for many applications is the ‘’patch’’ or ‘’panel’’ antenna. A patch

antenna gains its name from the fact that it basically consists of a metal patch suspended over

a ground plane. The assembly is usually contained in a plastic Radom, which protects the

structure from damage (as well as concealing its essential simplicity). Patch antennas are

simple to fabricate and easy to modify and customize. They are closely related to microstrip

antennas, which are just patch antennas constructed on a dielectric substrate, usually

employing the same sort of lithographic patterning used to fabricate printed circuit boards.

A microstrip or patch antenna has a number of advantages over other antennas -- it is

lightweight, inexpensive, and easy to integrate with accompanying electronics. While the

antenna can be 3-D in structure (wrapped around an object, for example), the elements are

usually flat; hence their other name, planar antennas. Note that a planar antenna is not always

a patch antenna.

The following drawing shows a patch antenna in its basic form: a flat plate over a ground

plane (usually a PC board). The center conductor of a coax serves as the feed probe to couple

electromagnetic energy in and/or out of the patch.

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Figure1.1: layout of patch antenna

Despite of many advantages of patch antennas, they do have some considerable drawbacks.

One of main limitation with patch antenna is there inherently narrowband performance due to

its resonant nature. With bandwidth as low as a few percent [2], broadband applications using

conventional patch design are limited. Other characteristics of patch antenna include low

efficiencies, limited power capacity, spurious fed radiation, poor polarization purity, and

manufacturing tolerance

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