Microstrip antennas offer the advantages of thin profile,light weight, low cost, and conformability to a shaped surface and compatibility with integrated circuitry. In addition to military applications, they have become attractive candidates in a variety
of commercial applications such as mobile satellite communications, the direct broadcast (DBS) system, global positioning system (GPS), remote sensing and hyperthermia. This is due in large measure to the extensive research aimed at improving the impedance bandwidth of microstrip antennas in the last several years. The basic form of the microstrip antenna, consisting of a conducting patch printed on a grounded substrate, has an impedance bandwidth of 1-2%. One way of improving the bandwidth to
IO-20% is to use parasitic patches, either in another layer [I] (stacked geometry) or in the same layer [2, 31 (coplanar geometry). However, the stacked geometry has the disadvantage of increasing the thickness of the antenna while the coplanar geometry has the disadvantage of increasing the lateral size of the antenna. It would therefore be of considerable interest if a single-layer single-patch wide band microstrip antenna could be developed. Such an antenna would better preserve the thin profile characteristics and would not introduce grating lobe problems when used in an array
environment. In this article, we report the experimental results of a rectangular patch with a U-shaped slot which appears to have wide bandwidth characteristics.