Abstract
In this paper, a novel intrinsically switched tunable bandpass filter based on a dual-mode T-shaped varactor-loaded resonator is presented. The varactors loaded in the T-shaped resonator are capable of efficiently tuning the resonant frequencies of the even and odd modes, as well as the transmission-zero frequency. Without any additional RF switches, the passband of the filter can be intrinsically switched off by adjusting the transmission zero to the resonant frequencies. In the switch-on state, the constant absolute bandwidth (CABW) or constant fractional bandwidth (CFBW) passband can be achieved by controlling the frequency space between the two resonances. For a demonstration, a 0.8–1.1 GHz intrinsically switched tunable bandpass filter with 74 MHz CABW or 8.5% CFBW was fabricated and tested. In the whole operating band with |S11| < 10 dB, the insertion losses for CABW and CFBW are better than 3.3 dB and 3 dB, respectively, and the isolations are better than 20 dB in the switch-off state. The measured results have a good agreement with simulated results, which verifies the design theory.
Highlights
Switched Tunable constant absolute bandwidth (CABW)/constant fractional bandwidth (CFBW)Reconfigurable filters have been extensively applied in the frequency-agile and software-defined radio systems due to their adjustable operating performance [1,2]
In order to reduce the number of external control variables and simplify the control complexity, intrinsically switched tunable bandpass filters are proposed [17]
GHz tunable 74 MHz CABW or 8.5% CFBW filter with intrinsically switchable function is developed and characterized
Summary
Reconfigurable filters have been extensively applied in the frequency-agile and software-defined radio systems due to their adjustable operating performance [1,2]. Through utilizing combinations of pin diodes and varactors, the center-frequency-tunable filters can be switched in on/off state or in high/low passband [15,16]. In order to reduce the number of external control variables and simplify the control complexity, intrinsically switched tunable bandpass filters are proposed [17]. In these structures, the off states can be obtained by the tuning elements which are used to tune the center frequencies, bandwidths or coupling coefficients. The other efficient way is to use the transmission zeros to switch off the passbands constructed by the spacing between transmission zeros [20,21,22] These bandpass filters require more cascaded bandstop filters to realize wide out-band suppression.
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