This letter presents a six‐channel bandpass filter bank created on substrate integrated waveguide (SIW) with improved bandwidth and frequency selectivity on the lower band. Through SIW square cavities and slant slots, a two‐dimensional multichannel bandpass filter bank with a transmission zero constructed with the SIW orthogonal resonant modes is produced. The substrate integrated square cavity approach is used to achieve the propagation of the two orthogonal‐oriented transverse electric modes, TE102 and TE201, which resonate on the same frequency and bandwidth, depending on the location of the feed ports. The bandwidth could be altered by the coupling matrix synthesis and coupling windows. Better transmission and bandpass responses are produced in each channel when the feed ports and coupling gaps are positioned and appropriately adjusted. However, a pair of slot lines are imprinted along each cavity's designated diagonal to guarantee better isolation while attaining an increased fractional bandwidth. A 3 × 3 array of six bandpass filters with a center frequency of 8.65 GHz has been built, simulated, and measured to establish the suggested technique. Low insertion loss, high return loss, high isolation, an improved fractional bandwidth, and a compact device were the proposal's advantages.

A novel transition between rectangular waveguide (RWG) and balanced transmission line with magnetic closed loops has been developed. A conventional RWG directly mounts on a printed circuit board that actualizes energy transition. Using a pair of centrosymmetric magnetic closed loop, the TE10 mode converts to TEM mode, and balanced ports are obtained. Based on the structural characteristics investigation, the transition is fabricated and measured. The center frequency of the operation is 32.5 GHz, and the bandwidth is wider than 27% for insertion loss no more than 0.6 dB and return loss more than 15 dB. Between the two balanced ports, the magnitude imbalance is less than 0.4 dB, and the phase difference is less than 3°. Integration within the balanced ports makes the transition a promising candidate for miniaturized system in antenna.

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