A Concise Periodic Undulate Sine Rectangular Waveguide Bandpass Filter for Millimeter Wave Region

Abstract

A novel sine rectangular waveguide (SRW) structure with either broad or narrow side periodic undulation is firstly proposed for designing bandpass filter (BPF) at millimeter wave frequency range. The bandpass characteristics of the SRW and two BPFs with a concise transition operated at millimeter wave atmospheric window frequency are studied. The SRW has the advantages of remarkable simplicity and completely closed environment without energy leaking. Besides, energy transmission mode in SRW is a quasi TE₁₀ mode which is similar to that in rectangular waveguide, which means that a SRW can easily get transition to a rectangular waveguide. So, compared to the traditional waveguide cavity BPF using metal diaphragm, printed circuit substrate or complex cross section, the SRW can be directly connected to a standard waveguide without additional metal diaphragm or substrate. To verify the bandpass characteristics of SRW, Ka band SRW BPF was designed and fabricated. Experimental results show low insertion loss (< 0.2 dB) in the whole Ka passband and sharp, wide rejection in the stopband (below-20 dB), with good agreement with simulated results. Therefore, the SRW will have wide potential applications in millimeter wave frequency range.