Bandstop Mode Research Articles

Reconfigurable UWB Circularly Polarized Slot Antenna With Three Modes of Operation and Continuous Tuning Rang

In this communication, a tunable circularly polarized (CP) antenna with a reconfigurable integrated feed network is proposed for cognitive radio (CR) applications. The integrated feed network is composed of an ultrawideband (UWB) bandpass filter (BPF), a continuously tunable T-shaped resonator, and an L-shaped microstrip line. The feed network employs three p-i-n diodes to switch between different RF paths, resulting in three modes of operation: an UWB mode (3.5–8.5 GHz), a narrowband bandpass (BP) mode and a narrowband bandstop (BS) mode. The continuous tuning range of the BP/BS narrowband mode is realized by two dc-controlled varactor diodes. The stand-alone antenna attains a −10 dB impedance bandwidth of 92.3% (3.5–9.5 GHz), while it attains an axial ratio (AR) bandwidth of 88.3% (3.1–8 GHz) in its wideband mode. The overlapped bandwidth (matching and AR) of the reconfigurable antenna is 78.2% (3.5–8 GHz). The communicating state covers 80% of the sensing spectrum while maintaining CP radiation. The measured peak realized gain values for the wideband mode range from 2 to 3.2 dBic while the maximum gain for the narrowband mode ranged from 1.95 to 3.1 dBic. The measured results show that the proposed filtenna is suitable for UWB CR systems.

Reconfigurable All-Pass-to-Bandstop Acoustic-Wave-Lumped-Element Resonator Filters

Acoustic-wave lumped-element resonator (AWLR)based filters with reconfigurable all-pass-to-bandstop transfer function are reported. They are based on in-series cascaded resonant stages that comprise two parallel RF signal paths, namely: 1) a thru-line and 2) an AWLR-based resonant section. Reconfigurability is achieved by altering the phase of the thruline through varactors. In this manner, the filter response can be reconfigured from an all-pass to an enhanced fractional bandwidth (FBW)-i.e., wider than the electromechanical coupling coefficient k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -bandstop one. For practical validation, two prototypes were designed and tested. They include 1) a single-stage prototype with insertion loss (IL) <; 0.38 dB in the all-pass mode and a bandstop mode with a center frequency of 917.5 MHz, an FBW of 0.29% (2.4 k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and a stopband isolation of 21.2 dB and 2) a two-stage prototype that exhibits an all-pass mode with IL <; 0.67 dB and a bandstop mode centered at 916.9 MHz, with an FBW of 0.47% (3.8 k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and a tunable isolation between 20 and 43 dB.

Frequency-Selective Limiters Using Triple-Mode Filters

This paper presents the first frequency-selective limiter (FSL) with both power-activation and user-prompted override that also features a reconfigurable threshold power and frequency tuning with closed-loop feedback. The FSL is based on a tunable absorptive bandstop-to-all-pass filter with integrated electronics. Three distinct modes are available: user-defined bandstop, power-activated bandstop, and all-pass mode. In the user-defined bandstop mode, the FSL presents a measured notch of 45-55 dB at an user-defined center frequency within 1.5-2 GHz tuning range. The out-of-band insertion loss is less 0.8 dB. In the power-activated mode, the FSL switches intrinsically between its bandstop and all-pass responses based on the incident power level at any user-defined power threshold and frequency within the 1.5-2 GHz range. In the all-pass mode, the measured loss is less than 3.1 dB at the user-defined center frequency and less 0.8 dB elsewhere. The measurements are conducted including the two SMA connectors and the associated connector-to-microstrip transitions. The threshold power level is tunable in the -45 to +8 dBm range. The filter is designed and fabricated with high-quality substrate-integrated cavities with an extracted resonator unloaded quality factor (Qu) of 300. The unique features and the measured RF performance of the presented FSL are state-of-the-art results.

Reconfigurable Filter for Bandpass-to-Absorptive Bandstop Responses

A frequency tunable filter with a bandpass-to-absorptive bandstop reconfigurable characteristic is studied, designed and validated theoretically and experimentally. To control the filter bandwidth and impedance matching performance, variable capacitors are used in each external and internal coupling structure, and, by using equivalent circuits, the required frequency responses of two different modes are obtained. Two single-pole double-throw switches embedded in the transmission lines running from the source to the load accommodate external coupling structures to control the operational mode of the proposed filter. All commercially available electronics such as switches and varactor diodes are placed on the microstrip line layer, and the frequency-tunable substrate integrated waveguide (SIW) resonators are coupled to the transmission line through coupling slots. In the absorptive bandstop mode, the stopband is tuned from 1.83 GHz to 2.49 GHz, while the passband can be tuned from 1.86 GHz to 3.3 GHz in the bandpass mode. In both modes, more than 10 dB in return loss over the frequency tuning range of interest has been achieved. Theoretical, simulated, and measured results are in good agreement, which validate the proposed filter structure.

Multiband Acoustic-Wave-Lumped-Element Resonator-Based Bandpass-to-Bandstop Filters

A new class of multiband acoustic-wave resonator-based RF filters with reconfigurable bandpass-to-bandstop (BP-to-BS) transfer function characteristics is reported. They are based on a hybrid integration scheme in which multiresonant acoustic-wave-lumped-element-resonators (AWLRs) are combined with five static and one switched impedance inverters. Each multiresonant AWLR controls the number of bands and their center frequencies. Switching between the bandpass and bandstop modes of operation is achieved by changing the coupling path between its input/output ports through an RF-switched impedance inverter. For practical validation purposes, two prototypes were designed, manufactured, and tested. They include a single-band BP-to-BS filter at 418 MHz and a dual-band BP-to-BS filter with bands centered at 418 and 433.9 MHz.

Compact Bandpass-to-Bandstop Reconfigurable Filter With Wide Tuning Range

A compact reconfigurable bandpass-to-bandstop filter with wide tuning range is presented. The bandpass-to-bandstop transformation is achieved by a p-i-n diode. In the bandstop mode, the two-pole bandstop response is obtained by introducing the inductive coupling between the two resonators of the notch filter. In the bandpass mode, the center frequency and an external quality factor are controlled by two pairs of varactors. A pair of transmission zeros is generated by two transmission paths, which improves the selectivity. The fabricated filter demonstrates a wide frequency tuning range with a miniaturized circuit size of $0.16\lambda _{\mathbf {g}}\times 0.11\lambda _{\mathbf {g}}$ . The simulated and experimental results are presented with good agreement.

Compact Wide-Frequency Tunable Filter With Switchable Bandpass and Bandstop Frequency Response

In this paper, a novel compact wide-frequency tunable filter with switchable bandpass and bandstop frequency response is presented. By employing two PIN diodes between the source and load port, the bandpass and bandstop filtering response can be switched, respectively. Three varactor diodes have been used to tuning the operating frequency of the tunable filter at bandpass and bandstop frequency response. The even- and odd-mode method is applied to analyze the presented tunable filter. When PIN diode is forward-biased, the filter has the bandstop response, and the filter has bandpass response while it is reversed. To verify the proposed tunable filter circuits, the tunable bandpass filter and bandstop filter are designed, fabricated, and measured. It is demonstrated that the center frequency of the fabricated tunable filter is tuned from 0.95 to 1.35 GHz. The measured insertion loss in the band is greater than 13 and 11 dB for bandstop mode and bandpass mode, respectively. Moreover, the fabricated tunable filter has a compact size of 0.24λ g × 0.24λ g (λ g is the wavelength of the center frequency during the tunable frequency range).

Compact Frequency and Bandwidth Tunable Bandpass–Bandstop Microstrip Filter

This letter presents the design and implementation of a compact microstrip filter with frequency and bandwidth (BW) reconfiguration. The proposed filter consists of a transmission line coupled with a U-shaped microstrip line resonator. Varactor diodes are deployed at specific locations and are tuned to achieve BW and frequency reconfiguration from 0.8 to 1.5 GHz. The transition from the bandpass mode to the bandstop mode is achieved by reconfiguring the transmission zeros simultaneously. The filter percentage lower passband edge tuning and 17.33% higher passband edge tuning. The proposed filter has simple geometry, low profile, and offers a higher level of operational flexibility in the designed frequency range. The filter is tuned with the help of simple actuators requiring simple bias circuitry. The prototype filter is fabricated, and the simulation results are validated using the experimental measurements.

A Tunable Dual-Band Bandpass-to-Bandstop Filter Using p-i-n Diodes and Varactors

In this paper, a tunable dual-band bandpass-to-bandstop filter and its analysis are proposed. The bandpass-to-bandstop transformation could be obtained by changing the state of the p-i-n diode. Using two sets of half-wavelength resonators loaded with varactors, the center frequency of each band can be tuned independently by adjusting the varactors. In order to achieve the controlling of the external quality factors ( ${Q} _{e}$ ) for the bandpass mode, the feeding lines are loaded with two varactors and wide tuning range of ${Q} _{e}$ can be obtained. In the bandpass mode, the lower passband tuning range is from 1.7 to 2.2 GHz (25.6% tuning range) with return loss better than 10.5 dB, and the tuning range of higher passband is from 2.2 to 2.7 GHz (20.4% tuning range) with return loss better than 12.9 dB. For the bandstop mode, the lower stopband tuning range is from 1.7 to 2.3 GHz (30% tuning range) and the higher stopband tuning range is from 2.3 to 2.9 GHz (23.1% tuning range), while the rejection level is higher than 16.4 dB in the stopband.

Bandpass-to-Bandstop Reconfigurable Tunable Filters with Frequency and Bandwidth Controls

A novel method is proposed for designing bandpass-to-bandstop reconfigurable tunable filters. The proposed method employs standard bandpass and bandstop design theory which does not require complex coupling synthesizing process, and can be applied for arbitrary-order bandpass-to-bandstop reconfigurable filters with both frequency and bandwidth control. Second-order and third-order bandpass-to-bandstop reconfigurable filters from 2 to 2.7 GHz were built to demonstrate the proposed method. The filters offer wide frequency and bandwidth tuning flexibility in both bandpass and bandstop modes, and occupy an area smaller than 20 mm $\times20$ mm on a substrate with relative dielectric constant $\varepsilon _{r}= 10.8$ substrate. Theory and measured results are presented with good agreement.

A novel broadband bi-mode active frequency selective surface

A novel broadband bi-mode active frequency selective surface (AFSS) is presented in this paper. The proposed structure is composed of a periodic array of convoluted square patches and Jerusalem Crosses. According to simulation results, the frequency response of AFSS definitely exhibits a mode switch feature between band-pass and band-stop modes when the diodes stay in ON and OFF states. In order to apply a uniform bias to each PIN diode, an ingenious biasing network based on the extension of Wheatstone bridge is adopted in prototype AFSS. The test results are in good agreement with the simulation results. A further physical mechanism of the bi-mode AFSS is shown by contrasting the distribution of electric field on the AFSS patterns for the two working states.

A tunable bandpass‐to‐bandstop filter with controllable bandwidth and high rejection level

ABSTRACTA tunable bandpass‐to‐bandstop filter with controllable bandwidth is proposed in this article. The bandpass‐to‐bandstop transformation can be achieved by adjusting the PIN diode, and bandwidth of the bandpass filter can be controlled by adjusting the voltage of varactors, as the coupling coefficients and the external quality factors (Qe) can be tuned by changing the ratios of the loaded capacitances. In the bandpass mode, a tuning range of 805–1032 MHz (24.7%) with return loss better than 11.5 dB can be achieved. In the bandstop mode, a tuning range of 760–1228 MHz (47.1%) can be obtained. The rejection level of the bandstop mode is higher than 40 dB. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:110–113, 2017

0.7–1.0-GHz Reconfigurable Bandpass-to-Bandstop Filter With Selectable 2- and 4-Pole Responses

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 ε 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.

Two- and Four-Pole Tunable 0.7–1.1-GHz Bandpass-to-Bandstop Filters With Bandwidth Control

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 ε 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.

Single-Multi-Single Mode Structure Based Band Pass/Stop Fiber Optic Filter With Tunable Bandwidth

We present a simple, efficient and easy to fabricate single-multi-single mode (SMS) fiber-based tunable bandwidth optical bandpass/bandstop filter. The device exploits the transmission characteristics of an SMS structure near its critical wavelength. Using both temperature and strain tuning, we show that the device can be switched between band pass to band stop modes and that the filter bandwidth in each mode can be dynamically tuned. We present a theoretical analysis of the observed behavior and obtain excellent agreement with the experimental observations.

A Tunable Bandpass-to-Bandstop Reconfigurable Filter With Independent Bandwidths and Tunable Response Shape

The theory of bandpass-to-bandstop reconfigurable filters is developed in this work, and example filters are demonstrated. Designs are developed that allow for reconfigurable response shape and independent bandwidths in the bandpass and bandstop modes of the filter. These capabilities could potentially be useful in dynamic, open spectrums, concurrent transmit-receive systems, and multimode antenna array applications. The demonstrated filters were fabricated using substrate integrated evanescent-mode cavity resonators. The resonators are tuned using deformation of a copper membrane induced by a piezoelectric actuator. In measurement, a 1.06% 3-dB bandwidth bandpass filter with 2.6-dB passband insertion loss was switched to a 0.82% 3-dB S11 bandwidth bandstop filter with 45 dB of isolation.