A novel E-plane filtering six-port junction (SPJ) based on waveguide is presented. Different from the traditional designs, the proposed SPJ is formed by two identical filtering 180° couplers and two waveguide couplers with 180° and 90° phase shifts. A coupling-matrix (CM) technique, combining both resonant and non-resonant structures, has been developed to represent the entire SPJ. This has been used to predict the theoretical response as well as to investigate the effect of the couplers on the performance of the SPJ. A demonstrator has been designed to work at 10 GHz with a bandwidth of 0.4 GHz. Stub-loaded waveguide resonators have been used to keep a consistent profile and ease the layout of the complicated waveguide network. A good agreement between the CM-based theoretical responses, simulations and measurement has been achieved. The measured average insertion loss is 0.4 dB and the maximum in-band phase error is 10°. The measured in-band isolation between two input ports is higher than 26 dB.
This paper presents a D-band E-plane 90° filtering coupler and a D-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 twenty 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 non-resonant nodes, based on the coupling topology, was constructed to predict the theoretical responses. Guided by this coupling matrix, the coupler and the SPJ were designed and modelled. 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 bandwidth is 4 GHz. Simulation shows 0.5 to 0.7 dB insertion loss at 150 GHz and maximum 3° phase error in the working band. The measurement gives the same center frequency and bandwidth. The response shows 0.7 to 2.0 dB insertion loss at 150 GHz and maximum 15° phase error in the working band.
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