In this paper, a novel compact quasi-elliptic waveguide low-pass transmit reject filter (TRF) by using T-shape units is proposed for Ku-band very small aperture terminal (VSAT) transceivers. The equivalent circuit model of the T-shape unit is investigated and shows a topology similar to that of the elliptic low-pass filter. In order to reduce the difficulty in physical realization, which is commonly encountered with a standard elliptic low-pass filter, an approximate elliptic low-pass filter prototype is presented. Accordingly, a synthesis approach is developed to obtain the initial dimensions of the filter. To optimize the performance of the filter, full-wave electromagnetic simulation is used to fine-tune the dimensions of the filter. An eleven-order Ku-band low-pass TRF is designed and fabricated using a WR-75 waveguide. Measured results show it has a low insertion loss of less than 0.3\,dB in the pass band and a high attenuation slope of 78 dB/GHz. Moreover, the miniaturized size of the filter is only 38 mm × 38 mm × 42 mm (WR-75 flange size is 38 mm × 38 mm).
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