Fully adaptable band‐stop filter using varactor diodes

Abstract

In this article a reconfigurable band-stop filter able to reconfigure center frequency, bandwidth, and selectivity for fine tuning applications is demonstrated, device topology discussion and implementation details are given, and followed by discussion on simulations and measurements. The reconfigurable filter topology has four poles and a quasi-elliptic band-stop filter response. The device is tuned by varactor diodes placed at different locations on the filter; varactors are voltage controlled in pairs due to filter symmetry for center frequency and bandwidth control. An additional varactor is placed on a crossing line to move a pair of transmission zeros, closer or farther to the filter center frequency, which tunes filter selectivity. Simulations show a tuneable center frequency range from 1.42 to 1.48 GHz, a tuneable fractional bandwidth range from 9.46 to 12.96%, and a tuneable selectivity range from 0.53 to 0.65 dB/MHz. Measurements show a tuneable center frequency range from 1.37 to 1.43 GHz, a tuneable fractional bandwidth range from 11.31 to 15.93%, and a selectivity tuning range from 0.37 to 0.40 dB/MHz. Simulations and measurements are in good agreement.

Design and application of quasi-elliptic bandstop filters

“…The proposed resonators are coupled to the main transmission line using an interdigital capacitor. The normalized reactance-slope parameter related to the degree of coupling between the resonators and the main transmission line is given by (9) [17]. Where, Z 0 is the characteristic impedance of the main transmission line and ǻFBW is the 3dB fractional bandwidth of the filter.…”

“…However, for applications such as mobile communications and radio astronomy receivers, high performance band-stop filters have been proposed to decrease interference with the addition of transmission zeros and therefore, increasing selectivity [7][8][9][10]. In this paper a detailed design procedure is provided for 4 th order filters with extra transmission zeroes made on microwave laminates.…”

Developing One-Dimensional Electronically Tunable Microwave and Millimeter-Wave Components and Devices Towards Two-Dimensional Electromagnetically Reconfigurable Platform

“…In [6] and [7], a continuously frequency and bandwidth tunable bandpass filter using compact hairpin resonators and a combline structure was described. In [8], a fully adaptable bandstop filter, which is able to reconfigure its center frequency, bandwidth, and selectivity, was demonstrated. The bandwidth tuning is achieved by varactor diodes that are used in coupling resonators to transmission line while the center frequency is controlled by varactor diodes connected at the end of transmission line resonators.…”

Interferometer Instantaneous Frequency Identifier

“…16 operate in a similar way to the ones exposed in section IV. The RFM can also include reconfigurable bandstop filters [16] instead of the phase shifter to produce a branch that can produce more than one bit as an alternative design.…”