Guangdong Provincial Mobile Terminal Microwave and Millimeter-Wave Antenna Engineering Research Center, College of Electronics and Information Engineering, Shenzhen University, Shenzhen, China
Yang Yu
Department of Electronic, Electrical, and Systems Engineering, University of Birmingham, Birmingham, U.K.
Cheng Guo
Department of Electronic, Electrical, and Systems Engineering, University of Birmingham, Birmingham, U.K.
Sheng Li
School of Metallurgy and Materials, University of Birmingham, Birmingham, U.K.
Moataz Attallah
School of Metallurgy and Materials, University of Birmingham, Birmingham, U.K.
Xiaobang Shang
National Physical Laboratory, Teddington, U.K.
Yi Wang
Department of Electronic, Electrical, and Systems Engineering, University of Birmingham, Birmingham, U.K.
Michael J. Lancaster
Department of Electronic, Electrical, and Systems Engineering, University of Birmingham, Birmingham, U.K.
Jun Xu
School of Physics, University of Electronic Science and Technology of China, Chengdu, China
In this paper, a third-order waveguide bandpass filter (BPF) based on slotted spherical resonators with a wide spurious-free stopband is presented. The resonator consists of a spherical cavity with slots opened at the top and bottom. Compared with a non-slotted spherical resonator, the slotted resonator suppresses the two spurious modes (TM211 and TE101) whilst maintaining the fundamental TM101 mode. The unloaded quality factor of the TM101 mode is not significantly degraded. This is achieved by interrupting surface current and radiating the unwanted spurious modes with the slots. The BPF is designed at a center frequency of 10 GHz with a fractional bandwidth of 1%. Two filter prototypes are fabricated, one using metal-based selective laser melting (SLM) and the other by polymer-based stereolithography apparatus (SLA) techniques. The slots also facilitate the copper electroplating process for the SLA-printed filter. The measured results show that the average passband insertion losses of the SLM- and SLA-printed filters are 0.33 and 0.2 dB, respectively. The corresponding passband return losses are better than 22 and 20 dB. The filters demonstrate excellent passband performance and wide spurious-free stopbands up to 16 GHz with stopband rejections of over 20 dB.
