Microstrip patch designs which do not excite surface waves

Two types of microstrip antennas are presented which do not excite the dominant TM/sub 0/ surface wave, and thus have a radiation efficiency of 100%. The first design is a circular path antenna with a 'cored' substrate, in which a circular piece of substrate material is removed from the region directly below the patch, with the resulting hole filled by a material (such as air) which has a lower permittivity. The second design consists of an annular ring patch which is short-circuited to the ground plane at the inner boundary. Both designs are based on the concept that a circular ring of magnetic current of appropriate radius will not launch any TM/sub 0/ surface wave power. Results are shown for the normalized E-plane field measured from a conventional circular patch, and for a cored-substrate patch.<
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