Broadband 100 GHz Substrate-Integrated Waveguide couplers with irregularly shaped Via holes for higher-order mode suppression

This paper introduces a 3 dB and a 23 dB coupler in Substrate-Integrated Waveguide (SIW) technology for future applications in radio astronomy instrumentation. In order to meet the often challenging specifications of such equipment in terms of both operating frequency and bandwidth, via holes of irregular shape are used to suppress higher-order mode excitation commonly observed in waveguide couplers. Prototypes have been manufactured and measured. For the 23 dB SIW coupler, measurements across the 85-115 GHz band show an isolation level higher than 35 dB, an average insertion loss of 3.75 dB, a coupling factor of 27 dB and a reflection coefficient better than -16.7 dB. The phase difference between the direct and coupled ports is 94.3°±2.3°. In the 83-111 GHz band and in the case of the 3 dB coupler, isolation is higher than 20 dB, insertion losses are 4.2 dB±0.6 dB, and the reflection coefficient is better than -16.6 dB. The phase difference between the direct and coupled ports is 94.2°±2.1°.