Miniaturized Quartz Waveguide Filter using Double-Folded Structure

A miniaturized 28 GHz quartz waveguide bandpass filter using a double-folded structure has been developed. The double-folded structure is used for a footprint reduction less than half of a current single-folded quartz waveguide filter. Some analyses using EM simulation were carried out for studying an electromagnetic coupling between the waveguide resonators. For the double-folded structure, an inductive coupling is appropriate for a main coupling in the vertical direction. The fabricated filter, an 8-pole Chebyshev BPF, has a size of 6.9 × 7.2 × 3.1 mm
³
and measured insertion loss was very low such as 0.74 dB which is same as the current single-folded type. Besides, an 8-pole quasi-elliptic BPF was simulated and its attenuation performance was remarkably improved.