Design of an S-Band Diplexer for Telemetry and Telecommand Subsystems in LEO Satellites

This study investigates the design requirements for telemetry and telecommand subsystems in satellites operating in low Earth orbit (LEO) and outlines the specifications for a diplexer suited for the S-band frequency range. The analysis emphasizes the critical impact of transmitter signal leakage and noise floor levels on diplexer performance. The proposed diplexer incorporates two bandpass filters operating at distinct frequency bands, enabling simultaneous transmission and reception through a single antenna in two-way communication systems. One of the primary design challenges stems from satellites' limited power generation capabilities, necessitating a strong focus on minimizing power consumption across all subsystems. In this context, reducing power loss in the telemetry and telecommand subsystem is crucial, as the diplexer directly influences transmitter power consumption and receiver sensitivity. Therefore, achieving minimal transmission loss is a critical design objective, which requires employing high-quality factor (Q-factor) technologies in the design of the filters. While waveguides provide superior Q-factors, their large dimensions and high mass render them unsuitable for S-band applications in satellite systems. Similarly, due to sublayer losses, ceramic substrate technologies, such as microstrip and stripline, fall short of the required Q-factor. To overcome these limitations, this study introduces a diplexer designed using coaxial technology, which offers an optimal balance of high Q-factor, compact dimensions, and low mass. The designed diplexer achieves a return loss greater than 20 dB, a transmission loss of less than 0.5 dB, and an isolation exceeding 50 dB, meeting the stringent requirements of LEO satellite subsystems.