Reconfigurable UWB Circularly Polarized Slot Antenna with Three Modes of Operation and Continuous Tuning Rang

In this communication, a tunable circularly polarized (CP) antenna with a reconfigurable integrated feed network is proposed for cognitive radio (CR) applications. The integrated feed network is composed of an ultrawideband (UWB) bandpass filter (BPF), a continuously tunable T-shaped resonator, and an L-shaped microstrip line. The feed network employs three p-i-n diodes to switch between different RF paths, resulting in three modes of operation: An UWB mode (3.5-8.5 GHz), a narrowband bandpass (BP) mode and a narrowband bandstop (BS) mode. The continuous tuning range of the BP/BS narrowband mode is realized by two dc-controlled varactor diodes. The stand-Alone antenna attains a-10 dB impedance bandwidth of 92.3% (3.5-9.5 GHz), while it attains an axial ratio (AR) bandwidth of 88.3% (3.1-8 GHz) in its wideband mode. The overlapped bandwidth (matching and AR) of the reconfigurable antenna is 78.2% (3.5-8 GHz). The communicating state covers 80% of the sensing spectrum while maintaining CP radiation. The measured peak realized gain values for the wideband mode range from 2 to 3.2 dBic while the maximum gain for the narrowband mode ranged from 1.95 to 3.1 dBic. The measured results show that the proposed filtenna is suitable for UWB CR systems.