Broadband Pattern Reconfigurable Filtering Microstrip Antenna with Quasi-Yagi Structure
In this letter, a compact pattern reconfigurable filtering microstrip antenna is presented with broad bandwidth, good selectivity at the passband edge, and flat gain frequency response. The pattern reconfigurable filtering antenna has four resonant modes which can be adjusted independently, three of them are created by multi-mode resonator (MMR) and the other one is by radiator. The four resonant modes are well distributed in desired band and the resonant mode of radiator is located between the first two resonant modes of MMR. By the incorporation of two PIN diodes and metal strips, the radiation patterns can be reconfigured. When the resonant mode of radiator shifts slightly, the bandwidth and in-band characteristic of filtering antenna is basically unaffected.Finally, a pattern reconfigurable filtering antennaprototype with a fractional bandwidth (FBW) of 25% at 5.2 GHz is designed and manu- factured. The measured results are well followed designed ones.
The design method of filter has been used as a popular technique for compact filtering antenna design, which replaces the last-stage resonator with antenna radiator. However, it is difficult to use conventional filter synthesis approach to design broadband or UWB filtering microstrip antennas. On the other hand, there are seldom reports about pattern reconfigurable filtering antenna. This letter presents a compact quad-mode broadband pattern reconfigurable inverted-L filtering microstrip antenna with good selectivity at the passband edge and flat gain frequency response. The radiation pattern changes from a nearly omnidirectional to two opposite end-fire patterns by using the strip quasi-Yagi structure.