Abstract
Filters play an invaluable role in most detection and communication systems, blocking unwanted, harmonic or mirrored waves. In this paper, two 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order quasi-elliptical waveguide bandpass filters working at 400 GHz are developed based on TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> -mode oversized resonators. Transmission zeros are generated through the physical cross-couplings and the mixed modal bypass couplings. H-plane off-axis coupling structures without any fragile irises are adopted to strengthen robustness and simplify manufacturing at such high terahertz frequencies. Effects of processing uncertainties on filters performance are discussed in detail to display error sensitivity. Two computer numerical control (CNC) machined filters exhibit a minimum insertion loss of about 1.5 dB in a 3 dB fractional bandwidth (FBW) with 12% centered at 390 GHz @ Filter-I, and 9% FBW with a center frequency of 394 GHz @ Filter-II, which are all mainly agreement with simulations. The performance is highlighted with the reported terahertz filters, which indicates that both architectural designs are still suited for the delicate CNC-milling restriction in such high WR-2.2 band.
Highlights
Terahertz (THz) domain, loosely defined as 100 GHz ∼ 10 THz, has great potential applications in wireless communications [1], imaging radars [2], astrophysics and planetary science
This computer numerical control (CNC) based waveguide can obtain a comparable performance with some advanced ones in such high WR-2.2 band
Two 3rd-order waveguide bandpass filters working on WR-2.2 band have been designed and evaluated based on oversized mixed-mode resonators and physical off-axis couplings
Summary
Terahertz (THz) domain, loosely defined as 100 GHz ∼ 10 THz, has great potential applications in wireless communications [1], imaging radars [2], astrophysics and planetary science. Band, the metal sealed waveguides can exhibit advantages of low loss (high Q-factor), power handling, easy assembling and interconnection, which are preferred transmission medium to realize components and systems from W-band up to THz band [1]–[11]. Because of waveguide filters working in THz band suffer from fine dimension drawback, various micro-machining technologies with high precision have been employed for fabrications, such as laser sintering [13], silicon based MEMS [14]–[18] and thick SU-8 photoresists [19], [20], especially for the components working from 300 GHz and beyond. Micro-machined waveguide filters are usually difficult to exhibit great insertion loss due to additional fixtures, connection or misalignment problems [21]. Two transmission zeros (TZs) were achieved based on quasi-TM110 mode elliptic cavity and specific angle coupling [17], which are really difficult to be implemented with general processing method
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