A 3-D printed fourth-order cavity bandpass filter (BPF) centered at 10 GHz and with a 3% fractional bandwidth is presented in this letter. The BPF was designed using two high-Q spherical dual-mode cavity resonators, and was fabricated using a stereolithography-based 3-D printing technique. Compared to dual-mode filters constructed by square or cylindrical resonators, the use of spherical resonator gives a wider spurious-free region. In order to fully exhibit the light weight advantage of additive manufacturing, the redundant material outside of the filter was removed. In addition, rectangular apertures were added through the cavities and waveguide walls without interrupting the surface current distributions, which further yields reduced filter weight as well as easier electroplating. Measured results of the BPF exhibit an excellent agreement with simulations.

This article reports on a new class of broadband and fully 3-D printed E-plane coax-to-waveguide transition and a monolithically 3-D printed waveguide magic-T based on the transition. The transition is constructed by a section of air-filled rectangular coaxial transmission line (TL) that is placed between two broadband coax-to-waveguide probe transitions. It is used to interconnect the magic-T's sum port and the waveguide T-junction. The incorporation of the transition reorients all the waveguide arms of the magic-T into the E-plane. Some X-band prototypes of the proposed transition and the magic-T are designed and implemented. Polymer-based additive manufacturing and copper electroplating techniques are employed to monolithically fabricate each prototype. The transition and the magic-T exhibit broadband and low-loss characteristics from 8.2 to 12.4 GHz with the measured performance well matched with the simulations. In addition, the power handling capability (PHC), including the peak PHC (PPHC) and the average PHC (APHC), of the magic-T is evaluated by simulations, showing that the proposed magic-T could handle 100 W of APHC.

This article presents a comprehensive active N + 4 coupling matrix approach for the design of integrated filter-amplifier. The feedback between gate and drain, which is neglected in a previous work, is considered, which improves the accuracy of the coupling matrix model for transistors. More importantly, the relationship between the coupling matrix and the noise figure is also established, which extends the coupling matrix method to tackle noise-related circuit functions. Substrate integrated waveguide (SIW) filters are used to implement an integrated X-band filter-amplifier design and to validate the design approach in terms of return loss, gain, and noise. Compared with rectangular waveguide, SIW is utilized for its appealing advantages, such as lower production cost, easier fabrication, and most importantly easier integration with active components. A second-order filtering circuit is applied to simultaneously match the input and output of the transistor. The integration reduces the losses from the intermediate networks in conventional designs, which is particularly important when the frequencies go higher. The measurements agree very well with the simulations in terms of S-parameters, gains, and noise figures.

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.

A novel waveguide step‐twist integrated with a bandpass filter is presented in this Letter. The twist is composed of four equally rotated cavities to achieve polarisation rotation and filtering functionalities simultaneously. Such step‐twist can achieve a significant reduction in size and weight. The design is demonstrated at Ka‐band using waveguide technology and is fabricated using a stereolithography apparatus 3D printing together with metal plating. The device is designed to have a centre frequency of 32 GHz and a bandwidth of 1 GHz. The measured result shows good agreement with simulations, with a measured average insertion loss of 0.84 dB and a return loss better than 15 dB across the passband.

This article presents a Ka-band fourth-order slotted spherical resonator waveguide bandpass filter (BPF) with a wide spurious suppression stopband. It uses the first higher-order TM211 mode rather than the fundamental TM101 mode of the spherical resonator in order to obtain a higher unload quality factor (Q _u ) for smaller in-band insertion loss, as well as a larger filter volume that gives better tolerance to fabrication errors in high frequency applications. By introducing slots that interrupt surface currents, the fundamental TM101 and two higher spurious modes (TE101 and TM311) can be suppressed without compromising the unloaded quality factor of the TM211 mode. In addition, the filter topology is optimized to further enhance the suppression level of the spurious passbands. AZ-shaped topology has been found effective in decreasing the coupling strength of the spurious TM311 mode. An analysis is performed to demonstrate the better tolerance of the Z-shaped filter over the conventional TM101-mode spherical resonator filter. For verification, a fourth-order slotted spherical resonator waveguide BPF with a center frequency of 31 GHz and bandwidth of 880 MHz is designed and manufactured using a selective laser melting (SLM) 3-D printing process. The measured results show an average in-band insertion loss of 1.53 dB, and a passband return loss better than 13.6 dB. The stopband of the filter is extended up to 40.9 GHz with a rejection level greater than 20 dB.