H-Band elevated CPW band-pass filters on GaAs substrate

This paper describes, for the first time, the design, fabrication and measurement of band-pass filters at H-band (220-320 GHz) frequency range. Two filters are considered, each using a different fabrication technology. The first uses conventional CPW and the second utilises a standard MMIC compatible airbridge process to elevate the ground and signal traces (ECPW) 8μm above a GaAs substrate. The ECPW filter achieves a 3 dB bandwidth of 78 GHz with an insertion loss of approximately 3 dB at the centre frequency of 211 GHz. When compared with the CPW filter, the ECPW circuit shows a performance enhancement of approximately 3 dB in insertion loss, a narrower bandwidth and a sharper roll-off characteristic. Simulated and experimental results over the range 0.01-320 GHz are compared and excellent agreement is obtained for both filters. The performance enhancement is thought to be due to the superior performance shown by ECPW short circuit stubs compared with their CPW counterparts. Results for such stubs at H-Band are also included and show a much narrower bandwidth and higher rejection in the ECPW case.