A W‐band air‐filled coaxial bandpass filter employing micro metal additive manufacturing technology

Abstract

This article presents a W-band air-filled coaxial bandpass filter with multiple transmission zeros using micro metal additive manufacturing technology. The coaxial structure was fabricated through the electroforming of thick copper layer by layer and inner conductor of coax is supported by SU-8 photo-resist. The internal cross-section size of the coaxial lines is 0.3 mm  0.3 mm, which is very compact. The filter is composed of five paralleled dual-behavior resonators (DBRs), four transformers and a pair of coax-to-CPW (Co-plane waveguide) transitions to facilitate the measurement. The relative bandwidth in a wide range can be realized by manipulating the location of the connection points among the resonators and the transformers instead of changing the characteristic impedance of the transformers. Hence, the extreme width of coaxial line and dimensional discontinuities can be avoided to facilitate the fabrication. To validate the filtering design and the manufacturing technology, a fifth order bandpass filter prototype with center frequency 96 GHz, bandwidth of 8 GHz was designed and fabricated. The complete fabrication process was also given in detail. The measured results are in good agreement with simulation: overall insertion loss (IL) of 2.05 dB, 7.95 GHz bandwidth and return loss better than 15 dB in passband. In addition, the influence of processing technology on IL is also discussed, showing that this technology can achieve excellent surface finish and the impact of non-zero surface roughness filtering IL is insignificant. K E Y W O R D Sair-filled coaxial TL, bandpass filter, micro metal additive manufacturing | INTRODUCTIONMillimeter wave (MMW) devices are now widely used in communication and radar systems. Lightweight, a high level of integration and miniaturization are some of the main requirements of the MMW devices. Traditional MMW devices are usually implemented based on CNC milled waveguides, however, the package used in practice is large. 1 Therefore, the bulky dimensions and weight impede the integration and miniaturization of the whole system. Also, when the frequency increases, the fabrication cost also increases a lot. In recent years, some other Zixian Wu and Guanghua Shi are Co-first authors.

A micromachined ultra‐wide stopband lowpass filter based on stepped impedance resonator loaded T‐shaped structure

“…The 3D model of the SIR-based LPF is shown in Figure 4, which is based on micro-coaxial lines. 22 Extra release holes are added in the structure to make it easier to wash away photoresist during the manufacturing process. The simulation results are demonstrated in Figure 4.…”

“…Besides, many of the mentioned design methods, with respective pros and cons, are exploited for half-open-structure transmission line (TL) like microstrip line. When it comes to millimeter wave and terahertz range, a LPF design method suitable for close-structure TL like micro-coaxial line 22 is highly demanded.…”

Miniaturized W‐band bandpass filter based on rectangular micro‐coaxial structure

“…Rectangular micro-coaxial line is a kind of coaxial lines and can be implemented based on surface micromachining technology. [10][11][12] With the merits of low dielectric loss, wide operating frequency, integration ability, and high-power handing capacity, rectangular micro-coaxial structure is suitable for the design of millimeter wave and terahertz components.…”

“…With the development of micro‐electromechanical system (MEMS), surface micromachining technology continues to be improved, and more complex 3D structures can be realized. Rectangular micro‐coaxial line is a kind of coaxial lines and can be implemented based on surface micromachining technology 10–12 . With the merits of low dielectric loss, wide operating frequency, integration ability, and high‐power handing capacity, rectangular micro‐coaxial structure is suitable for the design of millimeter wave and terahertz components.…”