A Monolithically 3-D Printed Waveguide Filter Based on Elliptic Cylindrical Resonators With Enhanced Polarization Rotation Flexibility

This paper reports on a new class of waveguide filter with enhanced flexibility in the realization of polarization rotation functionality. The filter is based on elliptic cylindrical resonators (ECRs) that are configured with an in-line coupling topology using cylindrical coupling cavities. The polarization rotation functionality of the filter is enabled by rotating the ECRs along the axis of symmetry with appropriate angle intervals. Any polarization rotation angle between 0°–90° can be readily achieved without any distortion of the filter geometry. An X-band fourth-order filter prototype with a polarization rotation angle of 90° and a Chebyshev bandpass transfer function is designed and implemented. The filter is manufactured monolithically by incorporating Polyjet 3-D printing and electroless copper plating techniques. The 3-D printed filter demonstrates excellent RF performance with passband return loss and insertion loss of over 20 dB and averagely 0.4 dB, respectively.