ALMA MEMO #468

Designs of Wideband 3dB Branch-line Couplers for ALMA Bands 3 to 10

Hiroya Andoh (Toyota National College of Technology),
Tetsuhiro Minamidani, Norikazu Mizuno, Akira Mizuno, Yasuo Fukui (Nagoya University),
Shin'ichiro Asayama, Yoshinori Yonekura, Hideo Ogawa (Osaka Prefecture University)

2003-07-07

A guiding principle of design of wideband waveguide 3-dB 5-branch-line couplers for ALMA bands 3 to 10 in suitable for use in SSB heterodyne receivers, their designs and their performances are reported. The couplers have good performances, which maintain an amplitude balance to within 1dB and a phase difference of 89-91 degrees over the frequency range of each ALMA band. The couplers for the ALMA band 3, 4, 5, 6, 7, 8, 9 and 10 include WR-10, WR-6, WR-5, WR-3, WR-2.8, WR-2.2, WR-1.5 and WR-1.2 waveguides, respectively. The couplers are designed by a numerical analytical method by using matrices based on the circuit theory and they are optimized with 3D EM simulator (HFSS). The numerical analytical method for seeking S-matrices mentioned in this memo enables quick calculations for performances of 3-dB branch-line couplers in the case of optimization and possesses advantages over electromagnetic simulation software in common use.