Abstract
This paper reports on a tunable bandstop filter (BSF) with both flexible center frequency and bandwidth. The tunable BSF is based on half-mode substrate integrated waveguide (HMSIW), of which the broadside is coupled with reconfigurable resonators. Using liquid crystal (LC) material as the substrate, a tunable stopband could be obtained by adjusting the bias voltage of the interdigitated microstrip resonator on LC. In order to increase the tunable range of stopband bandwidth, two additional open resonators are implemented at the broadside of HMSIW cavity. For practical validation, the bandstop HMSIW filter using LC is designed and fabricated. Numerical results demonstrate that,by adjusting the voltages of three resonators on LC, either the lower or the higher cutoff frequency could be controlled independently, leading to the flexible and independent tuning ranges of both center frequency from 4.9 to 5.4 GHz and 3-dB bandwidth of stopband from 1.2 to 1.8 GHz (@5.1 GHz).
Highlights
Microwave filters play an important role in RF front-ends for modern remote sensing and wireless communication systems
Tunable bandstop filter (BSF) are performed to eliminate the signals at a controllable frequency band, and can be regarded as one of the essential components in specific practical scenarios
To enable a flexible stop center frequency, various BSFs were developed by adding microstrip resonators loaded with silicon varactor diodes [15]–[17]
Summary
Microwave filters play an important role in RF front-ends for modern remote sensing and wireless communication systems. To enable a flexible stop center frequency, various BSFs were developed by adding microstrip resonators loaded with silicon varactor diodes [15]–[17]. The aforementioned BSFs can only control either the center frequency or the bandwidth of stopband in a limited tunable range. LC-based notch filters with tunable frequencies were reported by [23] and [24] Since it was demonstrated by [25] that LC has the potential for designing microwave devices at high frequency owing to its merits of low dielectric loss and variable permittivity controlled by an electrical or magnetic bias field. Suppose Leff as the effective length of microstrip structure, and recall (3) - (4), the center frequency and the bandwidth of BSF in (1) and (2) can be respectively given by. It is thereby expected that a tunable BSF performance could be obtained by using a specific material of a variable permittivity
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