W-band layered waveguide filters based on CNC-milling technology

The development of multi-pixel receivers on the millimetre-wave and terahertz bands demands on the integration of key waveguide devices. In this paper, two waveguide bandpass filters operating at the W-band are developed based on the layered integration architecture. First, the traditional fourth-order waveguide filter is perpendicularly folded to realise dual-layered arrangement, meanwhile a cross-coupling between layers is introduced to obtain the standard quasi-elliptical response. Then, two layered approaches including 5-layer and 3-layer are proposed to fabricate filter prototypes integrating with 90 degrees curved waveguides based on the computer numerical control (CNC) technology. Finally, the measurement exhibits that both filters have achieved the 3 dB fractional bandwidth of 14.8% from 85 to 98.5 GHz, low insertion loss of 0.6 dB (5-layer) and 0.4 dB (3-layer), the return loss with better than 20 dB, as well as two obvious transmission zeros in the out-of-band. Besides, the layering error analysis and performance comparison of both filters are discussed, which verify the feasibility of the layered integration for CNC-machined W-band waveguide filters.