  Since the start of full science operations from 2004, the Submillimeter Array
has been implementing plans to expand IF bandwidths and upgrade receivers and
cryostats. Metal mesh low-pass filters were designed to block infrared (IR)
radiation to reduce the thermal load on the cryostats. Filters were fabricated
on a quartz wafer through photolithography and coated with anti-reflection (AR)
material. The filters were tested from 200 to 400 GHz to verify their passband
performances. The measurement results were found to be in good agreement with
EM simulation results. They were tested in the far-infrared (FIR) frequency
range to verify out-of-band rejection. The IR reflectivity was found to be
approximately 70%, which corresponded to the percentage of the area blocked by
metal.
