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This paper presents tunable 2- and 4-pole bandpass filters with a wide tuning range based on dual zero-value couplings. The zero-value coupling is achieved using a coupled line with two coupling paths. The proposed filter also has bandwidth tunability. Frequency and bandwidth tunings are achieved using silicon varactor diodes. Three types of tunable filters are designed and built on a substrate with \varepsilon r = 3.55 and h = 25 mil, two filters with two separate frequency bands (2- and 4-pole: Filter A) and one filter with contiguous frequency tuning (4-pole: Filter B). The 2-pole filter results in an insertion loss of 2.9–4.7 dB with a tuning range of 0.75–1.09 and 1.70–2.18 GHz. Filter A with a 4-pole response results in an insertion loss 3.7–7.9 dB and a -\1-dB bandwidth of 68–87 MHz with a tuning ranges of 0.77–1.10 and 1.70–2.10 GHz. Filter B shows an insertion loss of 4.4–6.6 dB and a -\1-dB bandwidth of 39–68 MHz with a tuning range of 0.70–1.44 GHz. The application areas are in wideband tunable filters requiring contiguous and noncontiguous frequency coverage with bandwidth tunability in separate bands. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we present a tri-band bandpass filter (BPF) based on a stub-loaded stepped-impedance resonator (SIR). The proposed resonator has the compact size based on a short-circuited SIR as well as the controllability of three resonant frequencies by adjusting impedance ratios. Bandwidths for the first and second passbands can be independently controlled using two coupling paths between resonators, while the third bandwidth can be designed by adjusting dimensions of an open-stub loaded to the resonator. Two-pole tri-band BPF is designed and tested at center frequencies of 1.575, 2.4, and 3.5 GHz with fractional bandwidths of 10%, 6%, and 4%, respectively. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2907-2910, 2014 [ABSTRACT FROM AUTHOR]

A 0.7–1.0-GHz reconfigurable bandpass-to-bandstop filter with selectable 2- and 4-pole responses is presented. The proposed filter can act as a 2- or 4-pole bandpass or bandstop filter by changing the coupling paths using zero-value coupling coefficients. The 4-pole bandpass filter mode also includes bandwidth control. The filter is built on a Duroid substrate with \varepsilon r=10.2 and h=25 mil. The center frequency tuning, as well as the bandpass-to-bandstop transformation and the selection of the number of poles are achieved using silicon varactor diodes and RF microelectromechanical systems switches. In the 2- and 4-pole bandpass modes, an insertion loss of 4.9–2.9 and 6.1–4.8 dB is measured at 0.71–0.99 and 0.72–1.01 GHz, respectively. The 4-pole bandpass mode also shows a bandwidth tuning of 28–85 MHz at 0.9 GHz. In the 2- and 4-pole bandstop modes, rejection levels of 24–28 and 32–41 dB are measured at 0.64–0.96 and 0.71–0.96 GHz, respectively. The application areas are in reconfigurable filters for wideband radios under high interference environments. [ABSTRACT FROM AUTHOR]

Two- and four-pole 0.7–1.1-GHz tunable bandpass-to-bandstop filters with bandwidth control are presented. The bandpass-to-bandstop transformation and the bandwidth control are achieved by adjusting the coupling coefficients in an asymmetrically loaded microstrip resonator. The source/load and input/output coupling coefficients are controlled using an RF microelectromechanical systems (RF MEMS) switch and a series coupling varactor, respectively. The two- and four-pole filters are built on a Duroid substrate with \varepsilon r=6.15 and h=25\ \mil. The tuning for the center frequency and the bandwidth is done using silicon varactor diodes, and RF MEMS switches are used for the bandpass-to-bandstop transformation. In the bandpass mode of the two-pole filter, a center frequency tuning of 0.78–1.10 GHz is achieved with a tunable 1-dB bandwidth of 68–120 MHz at 0.95 GHz. The rejection level of the two-pole bandstop mode is higher than 30 dB. The bandpass mode in the four-pole filter has a center frequency tuning of 0.76–1.08 GHz and a tunable 1-dB bandwidth of 64–115 MHz at 0.94 GHz. The rejection level of the four-pole bandstop mode is larger than 40 dB. The application areas are in wideband cognitive radios under high interference environments. [ABSTRACT FROM AUTHOR]

This paper presents a tunable bandpass filter with a reconfigurable-pole response. 2-, 3-, and 4-pole states can be obtained based on employing series resonators with RF switches. The synthesis for the proposed filter is established, and the bandwidth for each pole state can be selected based on theory. The filter is built on a Duroid substrate with \varepsilon r=10.2 and h=25\ \mil. The tuning for the center frequency is done using Schottky diodes, and the selection of the filter poles is achieved using RF microelectromechanical systems switches. A tuning of 0.73–1.03 GHz is achieved with a 1-dB fractional bandwidth of 3.9%–5.2%. The rejection levels at 200-MHz offset frequency of 2-, 3-, and 4-pole states are 28, 36, and 45 dB, respectively. This filter topology can find applications in reconfigurable radios with dynamic rejection levels. [ABSTRACT FROM AUTHOR]