A wideband bi-semicircular slot antenna

The design of wideband, miniaturized, and efficient radiating elements has become the subject of intense investigation. Ring antennas are considered to be among the narrowband resonant antennas and occupy an area of λ²/4π at their first resonance (Batchelor, J.C. and Langley, R.J., 1996). However, ring antennas do not make efficient use of this area. We present a modified topology for the ring antenna in order to obtain a larger bandwidth without increasing the occupied area. One such topology, based on annular ring slot antennas, is proposed. It is shown that the modified antenna topology has a much gentler input reactance as a function of frequency, which is exploited to achieve much higher bandwidth. This increase in the bandwidth is obtained without putting any constraints on the radiation patterns, antenna efficiency (gain), or adversely affecting the antenna polarization purity. Numerical and experimental results demonstrate that the new topology presents a bandwidth that is by a factor of 7.3 (730%) higher than that of an ordinary annular ring slot antenna. The design procedure and measurement results are presented and discussed.