Abstract
This paper presents a new, compact, dual-frequency design of single-feed circular microstrip antennas with an offset circular slot placed close to the patch boundary. It is found that, when the radius of the offset slot is about 0.38–0.62 times the radius of the circular patch, dual-frequency operation can be achieved using a single probe feed. The two operating frequencies have orthogonal polarization planes, and have a low frequency ratio of about 1.15–1.18. The two frequencies can also be much lower than the fundamental resonant frequency of a corresponding simple circular patch antenna without the offset slot. This behavior makes the proposed antenna have a reduced antenna size as compared to a simple circular patch antenna operated at either one of the two frequencies. Details of the antenna design and experimental results are presented. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 254–256, 1999.
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