A Compact Mass-producible E-band Bandpass Filter Based on Multi-layer Waveguide Technology

This paper presents the design, implementation and experimental validation of a bandpass filter for high-data rate point-to-point link applications at E-band. The proposed design is developed in multilayer waveguide (MLW) technology, where an air-filled waveguide transmission line is formed by stacking several unconnected thin metal plates. Our MLW bandpass filter is designed by combining low-pass and high-pass filtering structures, and consists of 19 separate metal layers. An array of glide-symmetric holes, which act as an electromagnetic band gap (EBG) structure, are used to prevent any possible field leakage due to the air gaps between the layers. The fabricated filter provides a bandpass from 71.5 to 76 GHz with measured return loss better than 15 dB, and insertion loss better than 1.3 dB. The investigation of the potential for mass-production, as well as an evaluation of the MLW filter response for temperature variations from $- 30 ^{\circ }\mathrm {C}$ to $+ 70 ^{\circ }\mathrm {C}$ are discussed in this paper. The measured results show that the MLW filter has a center frequency thermal stability parameter of 9.3 ppm$/ ^{\circ }\mathrm {C}$, and center frequency drift of less than 0.12% over the whole temperature range. These results confirm the advantages of MLW technology for implementing ultra-compact bandpass filters showing low loss and potential for being mass-produced at millimeter-wave frequencies.