Synthesis and Design of Filtering Antenna With Flexible Passband and Radiation Null Based on Parallel Scheme

The synthesis and design methods of a novel filtering antenna with flexible passband and radiation null based on parallel scheme are presented in this letter. The filtering antenna is constructed by parallelly connecting two inverted-fed resonant antenna elements to a common feed point. The two resonant antenna elements can be separately designed and adjusted. A specific filtering performance with a radiation null can be synthesized using the proposed sum-of-transfer-functions method based on resonant frequencies and quality factors of the two elements. Finally, a practical filtering antenna centered at 5.78 GHz with the bandwidth of 190 MHz and a radiation null at 5.6 GHz is fabricated. The gain of 5.0 dBi is reached within the total size of 0.864
λ
₀
 × 0.576
λ
₀
 × 0.020
λ
₀
, where
λ
₀
is the free-space wavelength of the center frequency.