Abstract
This paper presents a digitally tunable SIW (substrate integrated waveguide) filter designed for X-band, based on RF-MEMS (radio frequency micro-electrical-mechanical systems) technology. Four commercial off-the-shelf RF-MEMS single-pole single-throw (SPST) switches were directly mounted on the upper surface of the filter, with metallic tuning posts specifically located within each cavity to define the potential achievable frequency range. Fabricated on standard alumina substrate, the design of the filter and the biasing network enabled fine digital frequency control of up to four functional states by the inclusion of wire bondings between each switch and the substrate. A relative tuning range of 2.3% was achieved between the lower and upper discrete states of 2.76% and 2.89% in the 3 dB fractional bandwidths.
Highlights
Tunable filters have been attracting attention over recent years as they are one of the key building blocks for reconfigurable radio front ends, multiband and subsystems
A choice was made to design a solution based on electrically-controlled microelectronic devices (diodes, transistors, radio frequency micro-electrical-mechanical systems (RF-MEMS), etc.) implemented on the top of an substrate integrated waveguide (SIW) structure
We highlighted the possibility of achieving four-state digital tuning of SIW filters with the finely tune thethe frequencies
Summary
Tunable filters have been attracting attention over recent years as they are one of the key building blocks for reconfigurable radio front ends, multiband and subsystems. Recent scientific literature has described several technological options to achieve the tuning of SIW filters [3]. In order to make an SIW filter tunable, the authors of [6] proposed a new concept using vertical metallic posts inserted into the cavity. In [7], the digital tunability of cavities using packaged RF-MEMS switches from the Omron Corporation resulted in a filter with a 28% tuning range, from 1.2 to 1.6 GHz. The relative bandwidth was between 3.2% and 4.2% over the tuning range, and the use of bias and MEMS switches was demonstrated to tightly prescribe the tuning frequency range. To satisfy high-frequency applications, another tunability technique was applied on evanescent-mode cavities, as described in [9] It was performed by using open-ended microstrip stubs, whose lengths can be adjusted by RF-MEMS switches. The proposed filter and biasing network were built on the same alumina substrate plate
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