Hybrid Network Based Broadband Diplexer Technology for Terahertz Space Exploration Systems

Terahertz space exploration systems are undergoing rapid advancement, with clear trends toward multi-channel operation, multi-spectral capabilities, and ultra-wideband performance. To address the requirements of such evolving systems, this paper introduces a novel waveguide hybrid network-based diplexer covering the entire WR-4 band. This device is specifically engineered for local oscillator signal combining and feeding in dual-band solid-state architectures. The design capitalizes on the inherent advantages of hybrid networks, including their excellent anti-reflection properties and high isolation between ports, while incorporating cascaded high-order low-pass filter to achieve precise frequency separation. This configuration results in a mechanically robust assembly that is readily manufacturable using computer numerical control (CNC) techniques and easily integrated into larger systems. The development process encompassed several critical phases: initial conceptual and operational design of the hybrid-network diplexer for full WR-4 band coverage; detailed circuit design of individual components such as hybrid couplers and filters; followed by comprehensive circuit synthesis, optimization, and eventual physical realization through E-plane split-block CNC milling fabrication. Experimental verification confirms the diplexer's outstanding performance in dividing the complete WR-4 spectrum into two well-defined channels spanning 170～210 GHz and 210～260 GHz, respectively. The measured insertion loss remains remarkably low at –1.5 dB for the lower band and –1 dB for the upper band. Impressively, one channel demonstrates isolation characteristics reaching 50 dB, effectively minimizing inter-channel interference. All measured parameters show strong correlation with simulation results, validating both the design methodology and implementation approach. Beyond its core electrical performance, this solid-state diplexer circuit offers numerous practical benefits including simplified mechanical fabrication, straightforward system integration, effortless channel expansion, and straightforward frequency scaling. These attributes make the proposed design particularly suitable for next-generation terahertz systems requiring efficient signal separation and management, while providing a versatile platform for future system enhancements and architectural evolution. The combination of electrical performance, manufacturing practicality, and design flexibility positions this diplexer as an attractive solution for advanced terahertz applications.