Abstract
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.
Highlights
Microwave resonators are the building blocks of passive microwave devices such as filters and multiplexers
The spherical resonator suffered from spurious modes spectrally close to the fundamental mode
We focus on improving the spurious-free region of the spherical resonator bandpass filter (BPF)
Summary
Microwave resonators are the building blocks of passive microwave devices such as filters and multiplexers. The spherical resonator suffered from spurious modes spectrally close to the fundamental mode This degraded the stopband performance of the filter. F. Zhang et al.: 3-D Printed Slotted Spherical Resonator BPFs With Spurious Suppression excellent filtering performance. We focus on improving the spurious-free region of the spherical resonator BPFs. A new approach aiming to maximize the spurious suppression through slotting the cavities is presented. The spurious TM211 and TE101 modes of the spherical resonator are effectively suppressed without compromising the high Qu of the fundamental TM101 mode. The proposed method of slotting in this work significantly enhances the spurious-free region. All the simulations were performed using Computer Simulation Technology (CST) Studio Suite [19]
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