A Highly Compact 530-610 GHz Bandpass Filter Using Patch Resonators to Develop SSB Spectrometer

In double sideband (DSB) receiver systems, both the desired signals and unwanted image frequencies are downconverted, necessitating effective filtering to enhance system selectivity and sensitivity. This manuscript presents a novel submillimeter-wave bandpass filter developed to suppress the unwanted image frequencies in a spectrometer system that is optimized to detect key atmospheric constituents in the passband, including water vapor (H₂¹⁶O – 559.9 GHz), deuterium oxide (HDO – 539.0 GHz), and oxygen (O₃ – 570.1 GHz). The filter design employs compact triangular microstrip patch resonators that achieve sharp roll-off characteristics and wide stopband performance, making it ideal for image rejection applications across submillimeter-wave and THz bands. The filter is fabricated on a 15 μm quartz substrate with 0.5 μm gold metallization, providing a 3 dB bandwidth of approximately 80 GHz with well-defined rejection bands below 530 GHz and above 610 GHz. Signal coupling is accomplished through microstrip waveguide feed probes for input and output. The design methodology offers significant flexibility, allowing straightforward scaling and adjustment of center frequency and bandwidth for implementations ranging from 1 GHz to 2 THz. The versatility of the filter architecture presented has utility in radio astronomy, defense systems, and high-frequency communication network applications.