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Evaluation of antenna with periodically variable directivity

In this study, we design and fabricate an antenna whose directivity or antenna pattern can periodically change for a receive diversity scheme. The antenna consists of an active element and a parasitic element which is terminated by a VR (variable reactance) element. To perform time-variable antenna pattern dc and sinusoidal voltages are applied to the VR element. From simulation and experimental results, we confirm that the VR element can periodically work as both director and reflector and make parts of received signals frequency-shift to construct diversity branches. When OFDM signals are received by the antenna, we have obtained that the power of frequency-shifted components can be improved to 4.7 dB less than that of not frequency-shifted component.