An Omnidirectional Planar Filtenna with Simple Structure and Excellent Selectivity

This paper presents a simple omnidirectional planar filtenna (filtering antenna), which is primarily composed of a driven circular patch, a stacked short-circuited circular loop, and an embedded substrate integrated waveguide (SIW) cavity. The circular patch and circular loop can be combined to produce two in-band resonance poles and a higher-band radiation null. The SIW cavity, partially constructed by the short-circuited via array of the circular loop, produces omnidirectional radiation through four rotationally symmetric arc slots. By simultaneously exciting the driven patch and the SIW cavity through a common central probe, an additional resonance pole and an extra radiation null can be generated at the lower band. The embedded SIW cavity design contributes to performance improvement while avoiding an increase in antenna size and complexity. The proposed method for achieving bandpass filtering response eliminates the need for external filtering circuits. The simulated results indicate that the proposed filtenna has a $-10-\text{dB}$ impedance bandwidth of 25.4%, a peak gain of 6.2 dBi, an out-of-roundness of less than 1.3 dB, an out-of-band suppression level of 16 dB, and sharp band-edge rolloff rates. Overall, the proposed planar filtenna is characterized by outstanding advantages in both structure and performance.