Design of Ku-band Transmit Reject Filter Based on Suspended Substrate Stripline

In this paper, a quasi-elliptic low-pass filter with steep cut-off characteristics using suspended substrate stripline is designed to meet the application requirements of transmit reject filter (TRF) in radio frequency system of Ku-band very small aperture terminal satellite communication. The filter is composed of multiple cascaded T-junctions and provided with excellent cut-off characteristics, which is obtained by optimizing the connection parameters of T-junctions. In order to simplify the requirements of simulation and design, the suspended stripline T-junction structure is analyzed in detail and the equivalent circuit model is given. Based on it, the lumped parameter model of the low-pass filter is proposed. Then, the initial parameters of the distributed circuit structure can be obtained, which effectively improves the optimization design efficiency. In order to validate the performance of the proposed filter, two low-pass filters for Ku-band TRF application are designed. Measurement result shows that insertion loss of the designed filters is less than 0. 3 dB and 0. 4 dB respectively, the out of band rejection is better than 33 dB and 38 dB, and the attenuation slope of the transition band can reach 120 dB/ GHz.