A Low-Profile Frequency-reconfigurable Filtering Patch Antenna

A low-profile (
$0.035\lambda _{0}$
) frequency-reconfigurable filtering patch antenna with a single-layered substrate is proposed in this communication. Parasitic strips and stubs are utilized to realize the filtering characteristics while using a simple probe feed. Frequency agility is implemented by adding three sets of varactor diodes on different parts of the radiating structure. These sets of varactors control the lower radiation null, the resonance frequency, and the upper radiation null, respectively. By optimizing the tuning characteristics of each set, only two biasing voltages are required, which simplifies the biasing circuit. The proposed antenna exhibits a tuning range of 21.9% with approximately 10 dB gain suppression level in its stopband, which is validated by experimental characterization.