Subterahertz Filtering Six-Port Junction

Abstract

This article presents a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}$ </tex-math></inline-formula> -band <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> -plane 90° filtering coupler and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}$ </tex-math></inline-formula> -band six-port junction (SPJ), both working at 150 GHz. The coupler is formed by ten resonators, having a fourth-order Chebyshev response. Two of the couplers were combined with a 90° 3-dB branch-line coupler to build the filtering SPJ with 20 resonators in total. Inheriting from the filtering coupler, the SPJ also has a fourth-order Chebyshev response. A coupling matrix (CM) consisting of both resonant and nonresonant nodes, based on the coupling topology, was constructed to predict the theoretical responses. Guided by this CM, the coupler and the SPJ were designed and modeled. In addition, two silicon-based absorber chips were designed and implemented as two matched loads in the filtering SPJ. The SPJ was optimized, fabricated, and tested. The center frequency of the SPJ is 150 GHz and the bandwidthis 4 GHz. Simulation shows 0.5–0.7-dB insertion loss at 150 GHz and a maximum 3° phase error in the working band. The measurement gives the same center frequency andbandwidth. The response shows 0.7–2.0-dB insertion loss at 150 GHz and a maximum 15° phase error in the working band.