Miniaturized Folded Ridged Quarter-Mode Substrate Integrated Waveguide RF MEMS Tunable Bandpass Filter

Thomas R Jones,Mojgan Daneshmand

doi:10.1109/access.2020.3004116

Abstract

This paper presents a miniaturized RF MEMS tunable bandpass filter design developed by application of folded ridged quarter-mode substrate integrated waveguide cavity. Using packaged RF MEMS SP4T chips, a switchable reactive loading is applied to the folded ridged quarter-mode substrate integrated waveguide cavity, tuning the resonance frequency. Overall miniaturizations of 70.3% and 78.8% are achieved for inductively- and capacitively-loaded filters compared to an RF MEMS tunable filter using half-mode substrate integrated waveguide. Here, an analysis of inductive or capacitive loading along with their advantages and disadvantages are discussed. Two different two-pole folded ridged quarter-mode substrate integrated RF MEMS tunable bandpass filters are designed and measured. The first prototype employing inductive loading achieves 4.4% tuning range at a center frequency of 1.713 GHz, insertion loss of 3.10-3.92 dB, and return loss greater than 15 dB for all tuning modes. The second prototype employing capacitive loading is measured with a 35.2% tuning range at a center frequency of 865 MHz, insertion loss of 1.6-4.3 dB, and return loss greater than 10 dB for all tuning modes. The reported performance and extreme miniaturization of folded ridged quarter-mode substrate integrated waveguide cavities shows great promise for their application in tunable filter design.

Highlights

Reconfigurable filters will play a critical role in future mobile communication systems, in which RF microelectromechanical systems (MEMS) based tunable elements offer superior performance in terms of insertion loss, power handling, and linearity [1], [2]
A quarter-mode substrate integrated waveguide (SIW) cavity can be formed from a standard SIW cavity by cutting the waveguide into quarters along planes of symmetry of the fundamental TE1,0,1 resonance, where due to the large width to height ratio of SIW, the open sides can be approximated as perfect magnetic conductor (PMC) walls [6]
The authors presented a similar procedure for the miniaturization of folded ridged SIW (FRSIW) in [12], where a FRSIW cavity is cut into quarters along the planes of symmetry of the fundamental TE1,0,1 resonance mode, forming a folded ridged quarter-mode SIW (FRQMSIW) cavity, reducing the footprint by 98% compared to standard rectangular SIW cavity

Summary

INTRODUCTION

Reconfigurable filters will play a critical role in future mobile communication systems, in which RF microelectromechanical systems (MEMS) based tunable elements offer superior performance in terms of insertion loss, power handling, and linearity [1], [2]. The authors have applied the folded ridged technique to quarter-mode SIW cavity design, with 98% miniaturization compared to standard SIW cavity [12]. The benefits of SIW cavities and packaged RF MEMS switches have previously been combined in [13], where a two-pole SIW bandpass filter achieved a 28% tuning range from 1.2−1.6 GHz with an unloaded quality factor (Qu) from 93 − 132, and insertion losses from 2.2 − 4.1 dB. In [14], a miniaturized two-pole half-mode SIW (HMSIW) bandpass filter was designed using packaged RF MEMS to switch between different inductive loadings along the open side of the waveguide. The potential of the folded ridged quarter-mode substrate integrated waveguide (FRQMSIW) is applied to RF MEMS tunable filter design to reduce the size even further, where miniaturized prototypes utilizing cavity resonators with transverse widths as small as λ/16 are demonstrated. Compared to the miniaturized HMSIW RF MEMS tunable bandpass filter reported in [13], the inductively- and capacitively-tuned filters using FRQMSIW cavity achieve additional miniaturization of 70.3% and 78.8%, respectively, highlighting the extreme amount of miniaturization possible with the proposed designs

PRINCIPLE OF OPERATION

INDUCTIVELY-LOADED FRQMSIW RF MEMS TUNABLE BANDPASS FILTER

Findings

FINAL DISCUSSION

CONCLUSION