A W-Band Bandpass Filter With Dual Behavior Resonators Fabricated by Additive Manufacturing

This letter presents a $W$ -band bandpass filter (BPF) with multiple transmission zeros (TZs) based on additively manufactured rectangular micro-coaxial lines (MCLs). Compared to common simple dual behavior resonators (DBRs), the mixed open-short-circuited DBR used in this work creates a pair of TZs nearer to the passband at both sides of the passband. Hence, the maximum $2N$ TZs can be obtained for such an $N$ th-order filter without any cross-coupling. A new ordering strategy of DBRs is introduced to realize the design within a significantly limited admittance range of the MCL. As an example, a fourth-order filter with a center frequency of 90 GHz and a fractional bandwidth of 10% is designed, fabricated, and measured. Excellent agreement between simulated and measured results is achieved. The measured passband return loss is better than 15 dB, and the minimum insertion loss (IL) is 1.2 dB. Eight TZs can be obtained, resulting in an excellent roll-off rate and out-of-band rejection.