Reconfigurable Bandpass Filter Research Articles

A reconfigurable narrow-band bandpass filter using electrically-coupled open-loop resonators based on liquid crystals

Abstract This paper introduces an electrically reconfigurable narrowband bandpass filter that exploits liquid-crystal technology. The filter uses two electrically-coupled open-loop resonators to produce two transmission zeros, resulting in a more compact structure than a single open-loop resonator. The spacing between resonators contributes to easy manipulation of the fractional bandwidth (FBW) and return loss. Theoretical calculations of the electrical length using multilayer microstrip line equations are presented. Experimental results demonstrate that the center frequency can be tuned from 9.70 GHz to 10.86 GHz with a maximum bias voltage of 30 V, achieving a tuning range of 11.34%. With applied bias, the maximum FBW reaches 8.10% and the maximum return loss attains 15.97 dB in each biased state.

Dual-port circularly polarized dielectric resonator–based antenna with reconfigurable integrated multifunctional filter for 5G cognitive radio applications

Abstract In this paper, the design of a circularly polarized (CP) multiple-input–multiple-output (MIMO) antenna system is presented, utilizing a dielectric resonator (DR). This presented antenna system is subsequently integrated with a multifunctional filter, all meticulously structured on a single substrate. The multifunctional filter operates in three modes: reconfigurable band-pass and band-reject filter as well as all-pass filter. The overall structure works as a tunable filtenna. The designed filtenna is expanded into a two-port MIMO system on a unified substrate, providing strong port isolation below −28.5 dB. The overall dimension of proposed radiator is 180 × 180 × 1.6 mm3. The value of peak gain is 5.19 dBic. By switching the states of PIN diodes, the designed filtenna operates as a sensing and communicating antenna for interweave and underlay cognitive radios (CRs). The proposed antenna supports the CP waves within the working band, i.e., 3.6–4.5 GHz. The simulated results are validated by comparing them with the measured results showing less variation among them. MIMO parameters, including the envelope correlation coefficient and diversity gain, have been calculated for the proposed filtenna, representing its suitability for 5G-CR applications.

A simple and modular quasi stepped impedance resonator based reconfigurable bandpass filter for 5G applications

A small-sized quasi-stepped impedance resonator (SIR) based single-band to dual-band reconfigurable bandpass filter is presented in this work. The proposed quasi-SIR filter is modular in nature and can be easily scaled to higher- or lower-frequency bands. To this end, a single- to dual-band reconfigurable modified SIR is designed. The designed reconfigurable resonator was then used to develop a single-band to dual-band reconfigurable filter. The proposed filter structure comprises two resonators loaded with PIN diodes to provide the switching. The filter allows switching between single and dual-band frequencies. In the OFF state, PIN diodes provide single-band resonance with a resonant frequency of 3.8 GHz. While the ON state of PIN diodes provides dual-band resonance of 3.35 GHz and 4.3 GHz. The structure of the filter is modular and is designed, analysed, and fabricated on a low-cost FR4 dielectric substrate with a 4.3 dielectric constant and 0.78 mm thickness. The measured results are in good agreement with the simulation results. The filter is designed to operate in the sub-6 GHz band, a designated band for 5G communication, and is thus suitable for incorporation in 5G devices with reconfigurability applications.

Reconfigurable bandpass filter with flexible tuning of both center frequency and bandwidth

This paper proposes a novel reconfigurable filter that can flexibly tune both the center frequency and bandwidth simultaneously. This reconfigurable filter consists of a filter network with Chebyshev properties and a parallel resonator. These two structures are symmetrical and can be analyzed using the odd-even mode analysis method for the filtering network. With the addition of a tuning factor, the Chebyshev filter network provides a shift in passband and coupling coefficients that can be adjusted to maintain a stable bandwidth; the parallel resonators will produce adjustable transmission zeros on either side of the passband, providing good out-of-band rejection when adjusting the bandwidth and center frequency. By using the transformation of the resonant frequency of two filtering networks, filters of different orders can also be achieved. This reconfigurable filter can achieve continuous bandwidth and center frequency adjustment and can maintain a constant absolute bandwidth during the center frequency adjustment process, with flexible tuning methods. Through simulation and experiments, it has been proven that this reconfigurable filter has a tunable frequency coverage range of 0.4GHz to 2GHz, with a large tunable range.

Design and development frequency reconfigurable microwave filter for wireless application

This paper presents a novel reconfigurable bandpass filter with three reconfigurable states used for C band wireless applications. The frequency reconfigurable is achieved using the combination of a different microstrip coupled resonator structure and switching device as PIN diodes. The open-loop filter structure provides three narrow band states at 5.1, 5.2, and 5.8 GHz. The frequency reconfiguration is obtained without compromising performances. The compact size of the proposed designed along with the targeted frequency bands at lower wireless local area network (WLAN) (5.1, 5.2 GHz), and worldwide interoperability for microwave access (WiMAX) (5.8 GHz) applications. The prototype is constructed on an RT duroid 5880 substrate and tested for validation in vector network analyzer (VNA). The designed filter provides excellent selectivity and good rejection at desired resonant frequencies.

Reconfigurable bandpass filter using Ce-doped YIG ferrites for wideband applications

Integration of compact, tunable, low-cost monolithic microwave integrated circuit-based bandpass filters on a semiconductor substrate has been a persistent requirement in the communication industry. In the present investigation, a compact reconfigurable bandpass filter is fabricated using a double T-transducer based on the phenomena of magnetostatic surface spin waves (MSSWs). The Ce-doped Bi0.1YIG 500 μm thick disks with cerium concentration in the range of 0.2–1.0 provide the path for the propagation of MSSWs. The operating frequency for this device extends from S to X band Rogers RT/duroid® substrate, which is used for planar microstrip filter design, fabrication, and testing for practical applications. The effect of the coupling gap between the two transducers was optimized using appropriate choice of lumped components to improve the performance of the filter. The best coupling was observed for 1.2 mm coupling gap. The simulated and experimental results confirm the lowest insertion loss of −1.24 dB. The operating frequency shows a large tunability of 132.3% with a relatively small bias field of 0.3–2.1 kOe. The promising characteristics of bandpass filters such as low passband insertion loss, narrow bandwidth, high bandpass reflection coefficient, and high band-stop rejection were achieved by varying the Ce concentration in YIG samples.

Microwave band-pass filter in frequency reconfiguration with super substrate on cross-coupled line structure for LTE 2500, WiMAX and 5G based internet of things applications

In this paper, the conceptualization of frequency reconfigurable microwave band-pass filter with a super substrate in odd-even method, for Internet of Things (IoT) applications is explained. The prototype consists of band pass filter in cross-coupled line structure with a symmetric structure on dielectric substrate and rectangular slot joining the cross coupled lines. A two different types of super substrate are placed in the rectangular slot one after the other. In parallel to the process, another two different types of dielectric substrate (FR4 epoxy, Rogers RT/duroid 6010 LM (tm)) are placed one after the other above the proposed system producing a total of 6 combinations, each capitulate unique impedance parameters in the transmission poles and transmission zeros. The dimensional framework of the developed design structure have FR4 epoxy (εr = 4.4 and tan δ = 0.02) substrate with 1.6 mm thickness. In the first case, FR4 epoxy substrate is used to place in the rectangular slot in addition the same substrate is placed on top of the prototype. In the second case, slot is covered with Rogers RT/duroid 6010 LM (tm) (εr = 2.2 and tan δ = 0.0009) substrate and the same substrate is placed on the top. When the higher dielectric constant material is used as the addition of substrate the output range of the bandwidths are increased. In all the two cases, the proposed system demonstrates the ability to reconfigure the operating frequencies and bandwidth shifts from LTE 2500 (2496-2690 MHz), WiMAX (2500-2700 MHz, 3400-3600 MHz) to 5 G (3200- 3670 MHz).

Filtenna with Frequency Reconfigurable Operation for Cognitive Radio and Wireless Applications.

A reconfigurable wideband monopole antenna is introduced in this paper for cognitive radio and wireless applications. The reconfigurability was achieved by four varactor diodes embedded in the band pass filter (BPF) structure which was integrated with the suggested antenna through its feed line. The simulated impedance characteristics coped with the measured ones after fabricating the suggested model with/without the reconfigurable BPF. Furthermore, the model achieved the desired radiation characteristics in terms of radiation pattern with acceptable gain values at the selected frequencies within the achieved frequency range (1.3-3 GHz).

A 2.2–3.6 GHz CMOS Reconfigurable Fourth-Order Bandpass Filter With Compact Size and High Selectivity Using Transformer-Type Resonators

A compact reconfigurable CMOS bandpass filter (BPF) with high selectivity is proposed using transformer-type resonators in this article. The transformer-type resonator is constructed by a transformer loaded with parallel varactors for frequency tuning, and two varactors are then added across primary wind and secondary wind for coupling tuning. With the transformer-type structure, one resonator is formed inside another resonator, thus fully utilizing the chip area and resulting in a miniaturized structure. Magnetic and electrical couplings are formed within the transformer-type resonator and facilitate the bandwidth (BW) tuning. The quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) of each resonator is improved by cross-coupled negative resistance structure. Meanwhile, two pairs of transformer-type resonators are placed side-by-side and naturally form a quadruplet structure; as a result, two transmission zeros (TZs) are introduced at each side of the passband thus significantly improving the selectivity and stopband rejection of the BPF. The proposed tunable on-chip BPF is manufactured by a commercial 55 nm bulk CMOS technology with a core area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.48 \times 0.54$ </tex-math></inline-formula> mm2. The filter center frequency (CF) can be tuned from 2.2 to 3.6 GHz, while the 3 dB fractional BW (FBW) can be tuned from 14% to 33%. The shape factor of the proposed filter is 1.4–1.9.

Wide tunable range bandpass filter with three transmission zeros

This paper proposes a reconfigurable bandpass filter with a wide tunable range, which is achieved by connecting two tunable passbands with switching diodes. A pair of transmission zeros (TZs) are introduced through the cross-coupling structure to improve the passband selectivity of the filter, and one more transmission zero is added by the interdigital coupling line to enhance the out-of-band suppression and broaden the upper stopband. The simulation and experimental results show that the designed filter with an absolute bandwidth of 100 MHz realizes a tunable frequency band covering 1.5–3 GHz, corresponding to a fractional tunable range of 66.7%. The dimension of the fabricated filter is 0.32 λg × 0.34 λg.

An Analysis and Design Method for Wide Range Reconfigurable Filter Bank Using Parallel Inductive Switch Network

In this brief, an analysis and design method for wide range reconfigurable filter bank using parallel inductive switch network (PISN) is proposed. The proposed lumped element filter bank consists of three standalone reconfigurable filters which are directly connected together to the common input/output ports without using series single-pole triple-throw (SP3T) RF switches. Instead, inductive PIN diodes are placed parallel to resonators for switching between three frequency bands. An equivalent and iterative method are proposed to analyze and eliminate impedance loading effects between multiple filter channels for the first time. To verify the proposed design and analysis, a reconfigurable bandpass filter bank was designed and fabricated. The measurement shows that a wide frequency tuning range (FTR) of 94–417 MHz (more than 2 octaves) with less than 5 dB insertion loss and more than 40 dB of suppression in adjacent bands is achieved. Detailed theory and measurement are given with good agreement.

Tunable and Reconfigurable Microwave Photonic Bandpass Filter Based on Cascaded Silicon Microring Resonators

A tunable and reconfigurable bandpass microwave photonic filter (MPF) is demanded in scenarios where different center frequencies and bandwidths are required. Here, we propose and demonstrate a silicon-on-insulator (SOI)-based microwave photonic bandpass filter, whose center frequency and bandwidth can be adjusted. The MPF is implemented by using four cascaded microring resonators (MRRs) that fabricated based on SOI wafer. Each MRR combines the design of multi-mode waveguides and tunable coupling regions, thereby exhibiting simultaneous high frequency selectivity and excellent reconfigurability. The center frequency can be tuned by adjusting the resonant wavelengths of the MRRs, and the bandwidth can be reconfigured by adjusting the coupling coefficients as well as the resonant wavelengths of the MRRs. The operation state of each MRR can be monitored and thus the MPF can be adjusted precisely. In the experiment, the bandwidth and center frequency of the MPF are adjusted from 0.7 to 2 GHz and from 5.2 to 35.8 GHz, respectively. During the adjustment, the rejection ratio of the MPF remains above 40 dB. The link performance, including the link gain, noise figure and spurious-free dynamic range, are also charactered. The achieved MPF can be potentially applied to radar, sensor networks, and wireless communications.

Novel Hybrid Electric/Magnetic Bias Concept for Tunable Liquid Crystal Based Filter

This paper presents a novel hybrid bias concept for liquid crystal (LC) filter by using simultaneously electric and magnetic bias fields. It enables continuous tuning with a simplified electrode design, decreased number of electrodes and reduced bias voltage. Furthermore, the tuning efficiency is increased, since the homogeneous bias fields enable a full exploitation of the LC's anisotropy. To demonstrate this concept, a novel reconfigurable gap waveguide two-pole bandpass filter with tunable center frequency and coupling elements is designed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$30 \,\mathrm{GHz}$</tex-math></inline-formula> . Liquid crystal technology is applied as tunable material, whereby tunability of the center frequency and coupling elements is obtained by controlling the LC's effective permittivity. The presented filter's center frequency can be tuned from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$28.88 \,\mathrm{GHz}\,\mathrm{to}\, 29.88 \,\mathrm{GHz}$</tex-math></inline-formula> with a maximum bias voltage of 100 V, with a return loss of 20 dB and low insertion loss of only 1.65 to 1.95 dB.

Low Profile Dielectric Rod Tuned Reconfigurable Band Pass Filters

A novel low profile mechanical tuning technique is introduced in this paper to change the center frequency of substrate integrated waveguide (SIW) based reconfigurable bandpass filters (BPF), by loading dielectric rods of different permittivity in resonant cavities and coupling apertures. The technique is simple, cost-effective (rods are machined from conventional substrates), and the same physical structure provides a wide frequency tuning. First, the tunability of center frequency of the SIW cavity resonator is theoretically explained and then estimated with the help of full-wave 3D EM simulator and electrical equivalent circuit. This concept is extended to the tuning of coupled resonator BPF loaded with dielectric rods followed by the analysis of maintaining constant bandwidth. Following the analysis technique, the tunability concept is studied for different arrangements of dielectric rods inside the SIW BPFs. The characteristics of the fabricated filters are experimentally validated. It is shown that center frequency tunability can be achieved by simply varying the permittivity of all the dielectric rods simultaneously. The proposed technique is further extended for obtaining wider tunability and constant bandwidth by using dielectric rods of dissimilar permittivities from a look up table. These designs demonstrate a simple and cost-effective passive tuning technique achieving high Q-factors in the range of 102–210.5, lowest insertion loss <2dB above 10 GHz, and wide tuning bandwidth in X-band. The reconfigurable filters are developed for advanced high-speed, long-distance, and fixed wireless connectivity in a rural area at a low cost. The technique can also be used for temperature compensation and overcoming fabrication uncertainty.

Compact reconfigurable bandpass filter using quarter wavelength stubs for ultra-wideband applications

In this article, the design of a compact reconfigurable bandpass filter using quarter-wavelength open/short-ended stubs for Ultra-Wideband applications is presented. The filter has been designed using three quarter wavelength stubs. Stubs are designed for specific frequencies. At the designed frequency, the quarter-wavelength stub exhibits either bandpass or bandstop characteristics according to its short or open-circuited configuration, respectively. The proposed filter generates five passbands and twelve transmission zeros through four reconfigurable states. The direct and higher-order responses of each stub are effectively utilized to achieve five passbands, which are at 3.8 GHz – 7.8 GHz (notch band from 5.9 GHz to 6.4 GHz), 2.8 GHz − 5.9 GHz, 5.2 GHz − 8.0 GHz, 5.2 GHz – 5.88 GHz, and 1.7 GHz to 4.1 GHz. The filter is designed on FR-4 substrate and simulated in High Frequency Structure Simulator. To analytically validate the results, an equivalent transmission line circuit is extracted, and ABCD parameters have been derived. The S-parameters are derived from the ABCD parameters and plotted through MATLAB software. The designed filter is fabricated and tested. There is a good agreement between simulated and measured responses. The overall size of the filter is 24 × 15 × 0.8 mm3.

A dual‐band filtering structure for highly selective reconfigurable bandpass filter and filtering balun

This article proposes a filtering structure consisting of two half-wavelength resonators and two open-stub loaded resonators, which generates two third-order passbands. Multiple transmission zeros are introduced by the newly developed coupling scheme, resulting in extremely sharp roll-off desirable for highly selective filters. The proposed structure is applied to design a PIN-diodes switch-controlled reconfigurable dual-band bandpass filter (BPF) with four-state filtering responses: both passbands ON, both passbands OFF, high-frequency passband ON, and low-frequency passband ON. Stepped-impedance open stubs and one-end-grounded coupled lines are studied and employed in the design to suppress unwanted responses. In addition, two filtering structures are placed symmetrically to design a dual-band balun BPF. Double-sided parallel-strip lines are added in the input port of the filter, and their inherent out-of-phase feature enables the balun filter to convert unbalanced signal to balanced signal at desired frequencies. The measured results of both fabricated devices agree well with the simulated results. The switchable BPF and balun BPF have two passbands (2.8 and 4.8 GHz) with high selectivity with the minimum roll-offs from −3 to −15 dB are 1.70 × 103 and 2.71 × 103 dB/decade, respectively. The insertion loss of the switchable BPF is 2.3/2.0 dB and the minimum signal suppressions level OFF state is measured as −18.2 dB. The insertion loss of the balun BPF is 1.8/1.4 dB, and the phase and magnitude imbalances are less than 0.3 dB and 5°, respectively. The excellent performances of the implemented filter and filtering balun successfully demonstrate the advantages and design efficacy of the proposed filtering structure for different applications.

Compact Low-Cost Reconfigurable Microwave Bandpass Filter Using Stub-Loaded Multiple Mode Resonator for WiMAX, 5G and WLAN Applications

This paper presents a compact, low-cost reconfigurable bandpass filter (BPF) for WiMax, 5G, and WLAN applications. The BPF consists of a half-wavelength resonator folded as C-shaped by a pair of symmetrical PIN diodes and a central quarter-wavelength resonator to form an E-shaped stub-loaded multiple-mode resonator (SL-MMR). The feed line is made of two subsections separated by a gap which acts as a fixed capacitance and allows the filter to have bandpass behavior. The proposed filter is modeled using the even and odd mode analysis to predict the locations of the resonant frequencies. The simulation results show that the filter covers the frequency range (3.38-3.95) GHz with a center frequency of 3.52 GHz at the ON state of a pair of PIN diodes. On the other hand, the BPF covers the frequency range (4.7-5.93) GHz with a center frequency of 5.2 GHz, at the OFF state of the diodes. The results also show a small insertion loss at the filter passband with two sharp transmission zeros at the stopband.

A 0.015mW quasi-passive reconfigurable complex band-pass filter for analog baseband

A 0.015mW quasi-passive reconfigurable complex band-pass filter for analog baseband

Constant Absolute Bandwidth Tunable Symmetric and Asymmetric Bandpass Responses Based on Reconfigurable Transmission Zeros and Bandwidth

A two-pole reconfigurable and tunable bandpass filter (BPF) with constant absolute bandwidth (CABW) and tunable transmission zeros (TZs) is presented in this paper. The BPF consists of asymmetrical spiral resonators having open ends on one side and capacitor loaded on the other side. The varactor loaded coupled-feed scheme is used at input and output. The two coupling feed-lines are also coupled to each other. It is shown that the control over TZs using the coupling-capacitor loaded between the two resonators leads to two different symmetric frequency responses – first with one TZ on each side of the passband, second with no TZ on either side of the passband. Further, asymmetrical frequency responses having single TZ either on lower or upper side of the passband are achieved by varying the capacitors loaded to the end of coupling-line. CABW while tuning as well as tunable bandwidth (BW) are achieved in all type of responses by using the coupling-capacitor. While tuning, quality factor is maintained by varying the capacitor loaded at the end of the coupled-feed. For the demonstration of the concept, a two-pole tunable BPF is designed and fabricated. The fabricated BPF having size of 13.1 mm × 9.4 mm, shows four different responses based on the position of TZs. All four CABW responses of the BPF have a tuning range of 300 MHz. Also, a tunable bandwidth is achieved in every response of the BPF.

Fully reconfigurable microstrip bandpass filter with tunable equivalent impedance and six transmission zeros

In this paper, a reconfigurable filter is designed by adjusting the microstrip line impedance for the first time, which breaks the single situation that the resonator can only adjust the electrical length in the previous microstrip reconfigurable circuits. This fully reconfigurable filter loads varactors between three parallel coupling lines to realize the reconfiguration of equivalent impedance. Changing the equivalent impedance of the resonator can use harmonics to introduce transmission poles (TPs) and transmission zeros (TZs), which not only effectively improves the selectivity of the filter but also greatly improves the stopband suppression. Finally, this fully reconfigurable filter can not only tune the center frequency but also the bandwidth. A total of six TZs are introduced, three can be generated by the resonator itself, and the other three are introduced by loading adjustable stubs. The final size of this filter is 0.34 λ g × 0.25 λ g . The measured results are in good agreement with the simulation results.