Ka-Band Surface-Mount Cross-Coupled SIW Filter with Multi-Layered Microstrip-to-GCPW Transition

This paper presents the design of a Ka-band cross-coupled substrate-integrated waveguide (SIW) bandpass filter using a newly proposed cross-coupling structure. The benefits of using the new cross-coupling structure and the design approach for it will be discussed in this paper. The filter design adopts TE-{101} resonant mode, and the target center frequency and bandwidth of the filter are 38.8 GHz and 2.3 GHz, respectively. Although the filter can be used as is, it can also be mounted on a motherboard as per end-users' need. For the purpose of mounting the proposed filter on a motherboard, a design methodology for a multi-layered transition from a microstrip line to a grounded coplanar waveguide (GCPW) operating at Ka-band is presented. The transition aims to provide the integration between two different layers using a via hole for the vertical integration. The proposed filter with the GCPWs have been fabricated using a Rogers 4350 substrate with a thickness of 0.508 mm, and the motherboard with microstrip has been fabricated using an Astra MT 77 substrate with the thickness of 0.127 mm. The measured results of the fabricated filter are in good agreement with simulated results, and the measured S-parameters of the fabricated transition exhibits the return loss better than 12 dB over the frequency range of interests.