Tunable Bandpass-to-Bandstop Quasi-Yagi-Uda Antenna With Sum and Difference Radiation Patterns

A design of the double-element E-plane quasi-Yagi-Uda antenna is proposed offering two different radiation patterns and reconfigurable bandpass-to-bandstop frequency-tunable responses. The double-element antenna covers a wide frequency range that is exploited for the realization of the tunable operation modes. This is achieved by the integration of a pair of bandpass-to-bandstop filters, each of which can be reconfigured using two varactor diodes and one p-i-n diode. The p-i-n diode serves the function of switching between bandpass and bandstop states, and the varactors facilitate the frequency tunability for both states of operation. The bandpass filter provides a continuous frequency tuning function with a minimum rolloff rate of 57 dB/GHz and out-of-band transmission coefficient