Design of A Multilayer Millimeter Wave Ultra-Wideband Bandpass Filter

In this paper, a multilayer ultra-wideband bandpass filter with operation band of 20-35GHz is designed. It consists of a three-layer seven-section cascaded coupling structures, each section utilizes a curved T-shaped microstrip patch at the top and bottom layers, forming a broadside coupled structure with a mid-layer coupling slot. In-band performances of this filter can be improved by changing the distance between the curved T-shaped structures, or adjusting the coupling slot size. By adding microstrip stubs at the input and output feed lines, better out-of-band suppression can be achieved. Computer simulations were conducted through HFSS, and the simulation results show that the in-band insertion loss is less than 1.7 dB and the return loss is more than 17 dB with the fractional bandwidth of 55%, indicating good performance.