Kenneth Nai

This paper significantly improves the previously proposed novel multiband waveguide filter implementation employing cylindrical resonators. The improved model has the advantages of a further reduced footprint using stacking shunt resonators horizontally and vertically and the ability to realise advanced filtering functions, including transmission zeros below and above the passbands. The coupling matrix synthesis with a brief example and a detailed filter design with considerations for additional coupling and in‐line and folded topologies is given. Several filter prototypes, namely third‐order quad‐band and quintuple‐band in‐line filters and a sixth‐order dual‐band folded filter in Ku ‐band, were designed to validate the proposed model. Selective laser melting (SLM), a metal 3‐D printing technique where metal powder is selectively melted with a laser layer by layer, was used to fabricate a dual‐band folded filter prototype in copper to validate the proposed model since the model has a complex inner geometry. Additionally, selective laser melting has the advantage of monolithic near‐net shape fabrication, eliminating assembly, improving reliability, and reducing weight. The measured results show good agreement with the simulations.

The design of a wideband diplexer integrated with a 16‐slot Continuous Transverse Stub (CTS) antenna array is presented. The diplexer‐antenna array module covers the whole WR34 band. The Tx and Rx bands cover 21.7–26 and 27.5–33 GHz ranges, respectively. The diplexer is designed to have a 100 dB attenuation in the stopband and 40 dB isolation between the channels. The antenna array has a high gain, between 26.9 and 31 dBi, at the lowest and highest frequencies. For the preliminary exploration of monolithic metal 3‐D printing of complex geometry integrated RF front ends, two prototypes were manufactured in AlSi10 Mg. One‐piece fabrication eliminates complicated assembly, enhances reliability, and reduces weight, which is more desirable for space applications. Due to several factors, namely, an unpolished inner surface and imperfect printing quality, the diplexer had a poor measured performance. The measured results of the antenna array had a relatively better agreement with simulations. Although, the realised gain was affected by the much lower effective conductivity of the unpolished 3‐D printed material. Hence, the measured realised gain was between 27.8 and 30.9 dBi in the 29–33 GHz range.

This paper proposes a high-Q multiband waveguide filter implementation using spherical resonators and an in-band transmission zeros approach. Three prototype filters in Ku -band, one 3 ^rd order triple-band filter with a fundamental TM ₁₀₁ mode and two 5 ^th order dual-band filters with TM ₁₀₁ and TE ₁₀₁ modes, are designed to validate the model. Compared to the previous multiband waveguide filter model using cylindrical resonators, the presented model can realise all expected N transmission zeros between the bands, where N is the filter order, and has a 112% higher simulated Q _u value. Meanwhile, the designed very narrowband dual-band filter using spherical resonators with TE ₁₀₁ mode has about 287% higher simulated Q _u value than the same filter would have if using rectangular resonator with TE ₁₀₁ mode. For experimental validation, the 3 ^rd order triple-band filter was fabricated using Selective Laser Melting since using traditional milling techniques is not feasible for spherical resonator filters. Monolithic near-net shape fabrication eliminated assembly, improved reliability, and reduced weight. The measured results had a relatively good agreement with the simulations. The measured insertion loss was about 0.54-0.72 dB at the centre frequency of each band, which is a noticeable improvement over the 1.1 dB insertion loss of the previous cylindrical resonator triple-band filter prototype. As there were some deviations between simulated and measured results, the proposed design was inspected in detail, and several improvements for optimising the design for Additive Manufacturing were suggested.

This paper presents a novel multiband waveguide filter model employing cylindrical resonators arranged horizontally and vertically in Olympic and parallel topologies, respectively. The proposed model has the advantages of reduced footprint and the ability to realise more complex filtering functions. 3 ^rd order dual-band, triple-band, quad-band and 5 ^th order dual-band filters in Ku -band were designed to validate the proposed model. Design flexibility in terms of reconfigurability of centre frequencies and bandwidths is demonstrated with dual-band filter examples. The design strategy is presented and validated with a triple-band filter example. For experimental validation of the proposed model, Selective Laser Melting, a metal Additive Manufacturing technique, was used to fabricate triple-band filter prototypes in copper. Since this model has a complex internal structure, 3-D printing allowed us to avoid complicated assembly and manufacture filters in one piece. The measured results of the four prototypes show a good agreement with the simulations and adequate repeatability.

This paper presents metal 3D printed wideband bandpass filters based on a deformed elliptical cavity resonator. The resonator can produce a wide stopband response by realising arbitrary real-frequency transmission zero at prescribed frequencies. The design procedure of canonical filtering functions is detailed. Six design examples of bandpass filters are presented to validate the design methodology. Three of the designed filters were metal 3D printed using Selective Laser Melting in AlSi10Mg and commercially pure copper for experimental verification. Copper filter prototypes were printed in one piece and electro-polished to improve the surface finish. Aluminium filters were printed in three different orientations to the wiper to investigate the influence on RF performance. All measured results have a good agreement with simulations. Furthermore, an in-depth review and discussion of Additive Manufacturing techniques for producing complex microwave components and strategies to mitigate the drawbacks of AM are given.