Abstract
Development of local oscillator (LO) sources based on amplifier multiplier chains (AMC) have steadily progressed in recent years, with more power and more bandwidth available at mm and sub-mm wavelengths. Recent radio astronomy receiver projects are, however, aiming at duplicating the RF bandwidth, with fractional bandwidth around 60%, even at frequencies as high as 500 GHz. In particular, National Astronomical Observatory of Japan (NAOJ) is developing wideband SIS mixers for a combined Atacama Large Millimeter/Submillimeter Array (ALMA) band 7 and 8 receiver, extending from 275 to 500 GHz. Currently, LO sources are not available for such a wide frequency band. To solve this problem, we have developed a waveguide diplexer to combine the output power of two different LO sources for ALMA band 7 (275-373 GHz) and band 8 (385-500 GHz). The proposed waveguide diplexer is based on hybrid couplers and waveguide filters. Two units of the designed component have been fabricated and S-parameters have been measured with good agreement with simulations. Initial tests to combine the LO power of band 7 and 8, LO sources at cryogenic temperature to pump a wideband 275-500 GHz SIS mixer have been successful.
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