3D Printed, Self-Temperature Compensated Microwave Cavity Notch Filters

Gregory Peter Le Sage,Ray Stringfellow

doi:10.1109/access.2021.3060637

Abstract

Utilizing 3D printing to create custom microwave filters has promising aspects such as light weight and low cost, most importantly including the fact that complicated structures can be printed quickly and inexpensively. Some SLA resins have very high Coefficient of Thermal Expansion (CTE) compared to metal, so SLA 3D printed microwave filters can have frequency responses that are strongly dependent on temperature—a serious problem for narrow band filters. The presented technique overcomes this limitation, and in fact yields an SLA 3D printed filter with better temperature stability than an uncompensated metal 3D printed or a conventionally machined metal filter. Two 3D printed, temperature compensated microwave cavity notch filters have been fabricated using stereolithography (SLA) resins. Both use two different values of CTE for compensation. The 3D printed plastic parts are electroplated with copper. One filter consists of a resonant cavity with the TE011 mode coupled to a TE10 waveguide. The other is a TE101 resonant cavity coupled to TE10 waveguide. As temperature increases, the side walls of the cavities grow, lowering the resonant frequency. At the same time, for the TE011 cavity, an end-wall tuning plunger made of stereolithography resin with a higher CTE than the cavity walls expands at a faster rate. The end wall expansion increases the resonant frequency. In the case of the TE101 cavity, a metallic plunger expands much more slowly than the cavity and effectively withdraws as temperature increases, which increases the resonant frequency.

Highlights

Fabrication of microwave slot array antennas and bandpass and notch filters using 3D printing and electroplating has significant advantages in terms of speed, cost, and obtained mechanical complexity compared to conventional metal fabrication [1]–[3]
One disadvantage of Stereolithography (SLA) 3D printed, copper plated microwave components is that some SLA resins have a high Coefficient of Thermal Expansion (CTE), quoted in micrometers per meter per degree [4]
To compensate high CTE induced frequency shifts with temperature, resonant cavity notch filters were designed with two different resins that expand with increasing temperature at different rates

Summary

Introduction

Fabrication of microwave slot array antennas and bandpass and notch filters using 3D printing and electroplating has significant advantages in terms of speed, cost, and obtained mechanical complexity compared to conventional metal fabrication [1]–[3]. To compensate high CTE induced frequency shifts with temperature, resonant cavity notch filters were designed with two different resins that expand with increasing temperature at different rates. The resonant frequency of a TE011 cavity as a function of temperature and CTE (without temperature compensation) is shown in Fig. 1 for CTE’s of 20, 50, and 100 10−6 K−1.

Results

Conclusion