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Piezoelectric vibration isolation and energy harvesting applications have been extensively studied in the literature. The studies include linear and nonlinear approaches. Linear methods are simpler but possess inherent limitations. On the other hand, nonlinear ones could perform better over a broader operating frequency range. Nonlinearity can be introduced in the mechanical domain or electrical domain actively or passively. Since electrical components can be on smaller scales compared to mechanical counterparts, inducing nonlinearity on the mechanical system through the electrical domain can be more practical. Moreover, passive structures require no energy supply and controller therefore they are simpler and more reliable than active ones. In this paper, a novel way to attain passive hardening stiffness was suggested by introducing an electrical component in a shunt circuit for passive nonlinear piezoelectric vibration isolation or energy harvesting applications and the induced structural non-linearity is demonstrated experimentally. A passive nonlinear component is suggested to be a hardening capacitor obtained by the P–N junction. An analytic model is derived for parallel connected macro-fiber composite (MFC) piezoelectric material attached bimorph configuration on a cantilever beam and the model is solved numerically. MFC integrated bimorph model, and P–N junction approximate model are presented. The frequency response of the coupled system is obtained by using numerical models and experiments. Both numerical analysis and experiments validated the hardening stiffness effect of the P–N junction. To the best of the authors' knowledge, this study is the first study to demonstrate that nonlinear capacitance of P–N junctions can be used to attain nonlinearity in a mechanical system. [ABSTRACT FROM AUTHOR]

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In this paper, a type of reflective coding metasurface (MS) for reconfigurable multi-beams is proposed. The unit cell of MS is composed of a split I-shaped patch loaded with one varactor. By changing the bias voltage, the reflection phase of the unit cell can be adjusted in the range of 0°–180°. At the same time, vias are introduced between adjacent unit cells to restrain the coupling between unit cells and improve the scattering performance of the MS. The whole coding MS is composed of multiple "0" and "1" supercells. First, the supercell in which all the unit cells have same reflection phases of 0° or 180° is coded as "0" or "1." By dynamically changing the coding sequence, reconfigurable dual beams are realized. Then, the unit cells with different reflection phases are employed to code the "0" or "1" supercell innovatively, and reconfigurable three beams are achieved. The results indicate that the regulated ranges of dual and three beams are θ = 5°–42° and 9°–42°, respectively. [ABSTRACT FROM AUTHOR]

The object of research is a frequency-reconfigurable L-Shape antenna. This paper presents an innovative study focusing on the design and analysis of a frequency-reconfigurable L-Shape antenna with a specific application in Hyperthermia Treatment. The antenna, operating in the frequency range of 2.5 to 8 GHz, utilizes a varactor to achieve agility and simplify design, thereby reducing component count. Constructed with a Roggers RT5880 (lossy) substrate, the L-Shape configuration ensures optimal performance. The incorporation of a single varactor, acting as a junction capacitance, not only enables straightforward tuning but also contributes to enhanced energy efficiency by reducing overall power consumption in the reconfigurable antenna system. The study employed CST Microwave Studio’s 3D Electromagnetic field simulation software for time domain solver-based simulations, with validation conducted using the frequency domain solver. Results from the simulations showcase the antenna’s performance at different frequency states. At the tuning state frequency of 2.7 GHz, the antenna exhibits an impressive gain of 1.905 dB and a directivity of 7.530 dB. Similarly, at the tuning state frequency of 6.89 GHz, the gain is measured at 6.806 dB with a directivity of 7.490 dB. The proposed L-Shape antenna design not only demonstrates significant potential for Hyperthermia Treatment, allowing targeted heating within the 2.5 to 8 GHz frequency range but also aligns with the multidisciplinary focus of medical science. This contribution reflects the commitment to advancing medical science through original research, fostering innovation, and promoting energy-efficient solutions with practical applications in clinical settings. [ABSTRACT FROM AUTHOR]

This article presents the design and optimization of a tunable quadrature differential LC CMOS voltage-controlled oscillator (VCO) with a D flip-flop (DFF) frequency divider. The VCO is designed for the low-power and low-phase-noise applications of 2.4 GHz IoT/BLE receivers and wireless sensor devices. The proposed design comprises the proper stacking of an LC VCO and a DFF frequency divider and is simulated using a TSMC 65 nm CMOS technology, and it has a tuning range of 4.4 to 5.7 GHz. The voltage headroom is preserved using a high-impedance on-chip passive inductor at the tail for filtering and enabling true differential operation. The VCO and frequency divider consume as low as 2.02 mW altogether, with the VCO section consuming only 0.47 mW. The active area of the chip including the pads is only 0.47 mm2. The designed VCO achieved a much better phase noise of −118.36 dBc/Hz at a 1 MHz offset frequency with 1.2 V supply voltages. The design produced a much better FoM of −196.44 dBc/Hz compared to other related research. [ABSTRACT FROM AUTHOR]

This paper presents a new MEMS varactor that uses repulsive actuation to achieve an ultra-linear capacitance-to-voltage response. The approach proposed involves actuating the moveable electrode away from the fixed electrode, instead of the conventional closing-the-gap direction. This increasing-gap movement reduces the capacitance as the actuation voltage increases. The MEMS variable capacitor is fabricated using PolyMUMPs technology and exhibits an excellent linearity factor of 99.7% in capacitance-to-voltage response, and a capacitance tuning ratio of 11× was achieved. The proposed strategy will enable the development of high-performance MEMS-based tunable devices for various applications. [ABSTRACT FROM AUTHOR]

This paper presents a new MEMS varactor that uses repulsive actuation to achieve an ultra-linear capacitance-to-voltage response. The approach proposed involves actuating the moveable electrode away from the fixed electrode, instead of the conventional closing-the-gap direction. This increasing-gap movement reduces the capacitance as the actuation voltage increases. The MEMS variable capacitor is fabricated using PolyMUMPs technology and exhibits an excellent linearity factor of 99.7% in capacitance-to-voltage response, and a capacitance tuning ratio of 11× was achieved. The proposed strategy will enable the development of high-performance MEMS-based tunable devices for various applications.

In this paper, we propose a dual-mode frequency selective rasorber (FSR) with tunable transmission and absorption windows at the X-band, which shows a broad passband in each transmission window. The proposed tunable FSR consists of a lossy absorption layer, a lossless transmission layer, and an air gap between them. The top frequency selective surface (FSS) layer is a cross-shaped meandering line with resistors and varactors for tunable absorption, and the bottom layer is a cross-shaped gap with varactors to achieve tunable bandpass. The equivalent circuit model (ECM) is investigated, and the 3D full wave simulation is performed. The results are based on simulations, and the simulation results show that the passband can be tuned from 12 to 8  G H z  with an insertion loss between 0.5 and 1.4  d B  by sweeping the capacitance of the varactors. The proposed design decreases the chances of detection by adversary devices and assures spectrum-safe communication, thereby creating new avenues for radar stealth and target concealment. [ABSTRACT FROM AUTHOR]

In this study, we designed an MOS varactor for application in the differential voltage-controlled oscillator (VCO). To improve the quality factor of the MOS varactor, we proposed a symmetric layout technique of the MOS varactor with reduced parasitic components. Compared with the typical MOS varactor layout, the metal line for the interconnection of the MOS varactors that is inevitable in the typical MOS varactors for the cross-coupled VCO was minimized to reduce the parasitic resistance. In addition, with the reduced interconnection metal line, the overall size of the proposed MOS varactor was also reduced compared with the typical one. To verify the feasibility of the proposed MOS varactor structure, the typical and proposed MOS varactors were designed using a 180 nm RFCMOS process. Compared to the typical MOS varactor, the measured quality factor of the proposed MOS varactor was improved by approximately 32% at the operating frequency of 5.0 GHz. Additionally, we successfully verified that the parasitic capacitance induced by the lossy silicon substrate was reduced in the proposed MOS varactor structure. [ABSTRACT FROM AUTHOR]

A wideband frequency reconfigurable antenna based on active artificial magnetic conductor (AAMC) surface is proposed with improved gain. The AAMC element consists of a composite polygon‐rectangle‐ring with five patches and a cross‐strip inside. A reverse‐bias varactor is inserted between the ring and ground plane to make the in‐phase reflection frequency bands adjustable. A dipole is placed above the AAMC surface which is composed of 5 × 5 unit cells. The measured results show that the reconfigurable frequency ranges from 1.64 to 4.16 GHz while maintaining the radiation patterns stable. Moreover, the peak gain reaches 10.65 dBi at 3.5 GHz. [ABSTRACT FROM AUTHOR]

The design, fabrication and measurement of a continuously tunable RF MEMS capacitor is described. The capacitor’s dual gap height architecture allows for electrostatic tuning with low resistive loss and a large tuning range. A new dual tuning scheme is introduced for use with two voltage sources. This dual tuning, coupled with a stress-induced bridge, is used to reach further device tuning. Measurements indicate a continuously tunable capacitance range of 6.2:1 with a quality factor over 50 at 30 GHz for 310 fF.

This study proposes a high-temperature superconducting (HTS) bandpass filter with a continuously tunable bandwidth and center frequency. The proposed filter combines several gallium arsenide varactors and a dual-mode resonator (DMR). The even and odd modes of the DMR can be tuned simultaneously using a single bias voltage. The capacitive value of varactors in the circuit is tuned continuously under continuous voltage and frequency tunability. External couplings and the interstage can be realized using an interdigital coupling structure; a fixed capacitor is added to the feeder to improve its coupling strength. A low-insertion loss within the band is obtained using HTS technology. Additionally, the proposed filter is etched on a 0.5 mm-thick MgO substrate and combined with YBCO thin films for demonstration. For the as-fabricated device, the tuning frequency range of 1.22~1.34 GHz was 9.4%; the 3-dB fractional bandwidth was 12.95~17.39%, and the insertion loss was 2.28~3.59 dB. The simulation and experimental measurement results were highly consistent. [ABSTRACT FROM AUTHOR]

To meet the demand for simultaneously supporting the microwave and millimeter-wave technologies in emerging industrial wireless systems, research on dual-band components with a large frequency ratio has been conducted recently. However, it is challenging to implement independent frequency tunability on bandpass filters with both compactness and high performance. This article presents a dual-band bandpass filter with a large frequency ratio, independently tunable frequencies, and an ultrawide stopband. This is achieved by artfully incorporating a harmonic-controllable varactor-loaded microstrip BPF and a wide-stopband dielectric-loaded cavity BPF with the bandgap-embedded aperture coupling mechanism. Extremely compact size can be achieved without additional filtering elements. Two pairs of transmission zeros can be allocated beside two passbands for good selectivity due to the separate path and cross-coupling in the resonators. For validation, a prototype is designed, fabricated and measured. It can provide two independent tunable frequency ranges (3.22–3.52 GHz and 25–27.06 GHz), exhibiting a large frequency ratio up to 8.3. Mid-band suppression better than 20 dB and ultra-wide stopband up to 32.5 GHz with 20 dB suppression level are achieved. Low insertion loss and good selectivity can also be observed. [ABSTRACT FROM AUTHOR]

In this paper, we introduce an electronically tuneable band-stop filter based on a dielectric resonator, along with its design principles and equivalent circuit model aimed at the coexistence of intelligent transport systems (ITS) and cellular vehicle-to-everything (C-V2X) communications operating at 5.9 GHz, with the widely spread vehicular dedicated short range communications (DSRC) at 5.8 GHz. The proposed architecture involves a dielectric resonator coupled via a microstrip transmission line to a planar ring resonator. The resonance is electronically tuned by varying the bias voltage of a varactor diode placed in the ring. This design is analyzed theoretically and experimentally. For validation, a filter operating at 5.8 GHz was designed. The prototype is capable of enhancing coexistence exhibiting to features. First, when inserted into the ITS transmitter chain, it reduces unwanted transmitter emissions in the out-of-band spectrum occupied by the DSRC carriers in the 5.8 GHz frequency band of at least 25 dB, with a minimal insertion loss at 5. 9 GHz of 1.6 dB; secondly, when inserted in the ITS receiver chain, it exhibits high linearity that prevents the generation of intermodulation products falling into the filter pass band. The prototype features more than 21 dBm of third-order input intercept points, and a tuning range of 26 MHz while maintaining a minimal loaded Q factor of 93. The prototype is discussed regarding the detailed equivalent circuit parameter extraction and their dependency upon the control voltage. [ABSTRACT FROM AUTHOR]

In this article, we propose a reconfigurable metasurface emitter (MSE) with beam shaping capability without using any phase shifter or a superstrate. MSEs consist of repeating radiative inclusions (unit cells) distributed on a surface. The type, shape, geometry, and the arrangement of the radiative inclusions provide great flexibility to design high efficiency reconfigurable radiative surfaces with almost any desired property. Here, we propose a new metasurface emitter with parasitic inclusions for enhanced bandwidth and increased beam rotation as a special case of beam shaping. The design procedure of such MSE is explained, and its performance as an emitting surface is investigated through full wave simulations and measurements. In addition, we propose a technique for beam steering by integration of tunable components such as varactors to each inclusion. Using tunable components can provide reconfigurability for the radiated beam of MSE. [ABSTRACT FROM AUTHOR]

Abstract In reconfigurable frequency selective surface, FSS, bias lines can suppress a resonant frequency. This is a disadvantage, as it reduces a FSS potential application. In this paper, a procedure to recover the suppressed resonant frequency is described. A FSS based on four arms star geometry is considered and its reconfigurability is achieved by the use of varactors, for which bias lines suppress the x polarization resonance. So, dipoles are added to the unit cell geometry recovering this resonance. In order to validate the proposed procedure, a reconfigurable FSS using the varactor SMV1231 (0. 466 pF ≤ Cv < 2. 35 pF) was fabricated and characterized. Numerical and measured results shown a good agreement, confirming that the FSS reconfigurability is preserved and the suppressed resonance recovered.

Abstract In this article, we propose a reconfigurable metasurface emitter (MSE) with beam shaping capability without using any phase shifter or a superstrate. MSEs consist of repeating radiative inclusions (unit cells) distributed on a surface. The type, shape, geometry, and the arrangement of the radiative inclusions provide great flexibility to design high efficiency reconfigurable radiative surfaces with almost any desired property. Here, we propose a new metasurface emitter with parasitic inclusions for enhanced bandwidth and increased beam rotation as a special case of beam shaping. The design procedure of such MSE is explained, and its performance as an emitting surface is investigated through full wave simulations and measurements. In addition, we propose a technique for beam steering by integration of tunable components such as varactors to each inclusion. Using tunable components can provide reconfigurability for the radiated beam of MSE.

In this paper, we propose a dual-mode frequency selective rasorber (FSR) with tunable transmission and absorption windows at the X-band, which shows a broad passband in each transmission window. The proposed tunable FSR consists of a lossy absorption layer, a lossless transmission layer, and an air gap between them. The top frequency selective surface (FSS) layer is a cross-shaped meandering line with resistors and varactors for tunable absorption, and the bottom layer is a cross-shaped gap with varactors to achieve tunable bandpass. The equivalent circuit model (ECM) is investigated, and the 3D full wave simulation is performed. The results are based on simulations, and the simulation results show that the passband can be tuned from 12 to 8 GHz with an insertion loss between 0.5 and 1.4 dB by sweeping the capacitance of the varactors. The proposed design decreases the chances of detection by adversary devices and assures spectrum-safe communication, thereby creating new avenues for radar stealth and target concealment.

In this brief, numerical analysis on spatio-temporally modulated (STM) non-reciprocal bandpass filters is methodically demonstrated to corroborate the underlying phenomenon. The concept of a 3D coupling matrix is illustrated for the first time, which provides an analytical insight into the distribution of RF energy among the intermodulation (IM) products generated in time-modulated resonators. Flagship equations based on coupling matrix are proposed that bypass the tedious analysis of spectral admittance and ABCD matrices. These equations can be modified to design any ordered filters and with varying cross-coupling instances. The experimental validation confirms the accuracy of the numerical equations, and the model can be utilized to further the development in this burgeoning yet eccentric research domain. [ABSTRACT FROM AUTHOR]

A miniaturized electrical beam-scanning reflectarray antenna providing a directional beam and wide steering ranges with fixed $\theta $ -polarization is proposed. To accomplish these properties, we devise a new active reflectarray cell that can control both the phase and polarization of incident waves. Accordingly, we can enforce all reflected waves to constructively interfere with each other in all target directions. To feed the proposed reflectarray cells, an omnidirectional monopole antenna is installed at the center of the reflectarray, which illuminates the reflectarray evenly. In addition, because the monopole feeder is directly connected to the reflectarray, we can significantly reduce the overall volume of the antenna down to about $0.5~\lambda ^{3}$ with a small F/D ratio of 0.147. Consequently, the proposed antenna attains a wide scan coverage and directional beam patterns. Moreover, the antenna can also maintain polarization direction stably, which is strongly required for dynamically moving platforms such as drones and unmanned aerial vehicles (UAVs). The experimental results agree well with the predictions, proving the validity of our approach. [ABSTRACT FROM AUTHOR]

In the paper, a compact complex impedance transformer (CIT) composed of the cascading of three varactors loaded coupled lines and two variable shunt susceptances was proposed. Highly flexible tunability functions including only frequency tunable, only impedance tunable, and both frequency and impedance tunable can be achieved by tuning the capacitance of two types of varactors and the value of the susceptance. Design equations were derived using the even–odd mode analysis and examples are given for descripting the design procedures. For validation, a prototype was designed and fabricated. During measurement, three cases were exhibited. When the termination impedance was fixed, the measured center frequency can be tuned in the range of 1.1–2.1 GHz (62.5%). When the frequency was determined, different terminal impedances can be matched by the prototype. The function of frequency tunable at different terminal impedances is also trated by the measured results. After comparison, the potential of the proposed CIT for applications in radio frequency front-end were demonstrated. [ABSTRACT FROM AUTHOR]

The paper presents the design, modelling, fabrication and testing of a new electromechanical structure for a tuneable RF MEMS capacitor based on an in-plane torsion generated by the in-plane forces developing during polarization of a parallel plate capacitor with partially overlapping electrodes. The designs explore the possibility to exploit an in plane rotation to extend the dynamic tuning range of a variable capacitor beyond the limits of conventional parallel plate capacitor and to determine the obtainable dynamic ranges and the limitations. These first prototypes adopt a butterfly structure suspended above the fixed electrodes. A small pivot point underneath the center of the mobile electrode acts as rest point after the pull-in and low friction pivot point for the rotation. Different suspension springs have been explored. A first pull-in followed by a parabolic branch with continuous tuning and a second pull-in characterize the C/V measurements. The measurements show a measured capacitance ratio ranging from 1.1 up to 1.6 with a 0–50V bias voltage. The capacitance values measured range from 286 fF up to 687 fF depending on the device type. Theoretical analysis shows that the capacitance ratio can easily be increased by a factor of 20 simply by reducing the initial overlap of the electrodes. [ABSTRACT FROM AUTHOR]

This paper proposes a tunable dual band-notched ultrawideband monopole antenna for ultrawideband applications. The proposed antenna consists of a circular ring monopole antenna as a main radiator with two unequally sized semi-circular stubs added near the inner edge of the circular ring to achieve dual bandnotching. The band-notching tuning is achieved by connecting the larger stub to the main radiator via a single varactor diode. The proposed antenna exhibits a wide impedance bandwidth from 2.8 to 21.9 GHz (154.6%), which is much wider than that of other published antennas. The center frequencies of the dual band-notched are simultaneously tuned using only one active element from 3.5 GHz to 3.8 GHz and from 6.7 GHz to 7.2 GHz, which can reject the WiMAX and the lower X-band applications. The measured results show good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

In this interdisciplinary work, a low-power varactor-tunable frequency selective surface is presented for use with a multiplexed remote sensor system. Combined with a low power sensor and control system, voltage biasing of the proposed frequency selective surface panel can be used to modulate the center frequency of a reflection peak, which in turn may be detected by remote interrogation through a radar system. The control board and frequency selective surface were found to draw only $200~\mu \text{A}$ of current during typical operation from two 3V CR2032 button batteries, enabling continuous operation for weeks at a time (even longer if operated in wake-up mode) when used in conjunction with a suitably low power sensor. Centered at 3 GHz, the backscatter peak can be modulated across a range of 200 MHz, and the combined system was shown to successfully differentiate between various concentrations of ammonia under test conditions.

A broadband balun with tunable phase-shifting function is presented in this article. The proposed structure is based on a typical tapered balun loaded with several extra varactors. The proposed balun operates similar to a loaded line (LL) phase shifter, in which the varactors are added between the microstrip line and ground plane. It can provide balanced feed for broadband antennas and, at the same time, change the phase of the balanced feed in a cost-efficient way. It is found that range of the tunable phase shift relies on the number and variable capacitance of the varactors. To simplify the design procedure and explore the optimum performance, characteristics of a uniform microstrip line loaded with lumped capacitors are studied. It is found that gap between the capacitors and length of the microstrip line has relatively large effects on the impedance matching characteristics. According to this observation, the proposed balun is designed by applying the LL structure to a tapered balun. Within the frequency range of 0.8–2 GHz, the proposed balun loaded with two varactors achieves a tunable phase shift ranging from 17° to 61°. If the number of varactors increases to four, the range of tunable phase shift is from 41° to 161°. Finally, potential usage of the new structure for low-cost phased array is briefly discussed. [ABSTRACT FROM AUTHOR]

This paper presents a dual-polarized reconfigurable antenna loading electronically steerable parasitic patches. The proposed dual-polarized antenna is surrounded by four parasitic patches each of which is mounted by two varactor diodes on the ground. By tuning the varactors, continuous two-dimensional beamsteering can be achieved for each of the polarization. A prototype of the proposed antenna is fabricated and measured. Excellent agreement between the simulated and measured results is observed. It is observed that the maximum beam-scanning angles in E-plane and H-plane are greater than ±25, which is suitable for 5G base station applications. [ABSTRACT FROM AUTHOR]

A ferroelectric metal insulator metal (MIM) varactor structure incorporating a floating metal and coplanar waveguide (CPW) has been introduced here. The work of the proposed varactor is based on the field-dependent material properties of (Ba, Sr) TiO3 (BST) thin film. A capacitance tunability of 44% has been achieved for the bias voltage of 0–10 V over a frequency range of 1–3 GHz. The proposed varactor structure yields a compact area, high capacitance density, and reduced mask process (two masks). [ABSTRACT FROM AUTHOR]

Abstract A modeling of the resonant behavior of a continuously reconfigurable frequency selective surface, FSS, is described in this paper. The FSS is based on four arms star geometry and its reconfigurability is achieved by the use of varactors. FSS, four arms star geometry and varactor principles are explained. Considering available a set of measured or numerical data, with frequency responses for different varactor capacitance values, the FSS equivalent circuit is stablished. Then, the varactor capacitance effect is included and the resonant behavior can be easily determined. After stablished, the FSS equivalent circuit can be applied even for a different varactor. In order to validate the proposed modeling, the equivalent circuit of a reconfigurable FSS using the varactor SMV1231 (0.466 pF ≤ Cv ≤ 2.35 pF is obtained. The equivalent circuit results are compared to numerical (ANSYS) and measured results, verifying a good agreement. Following, for the same geometry, the equivalent circuit is applied to a reconfigurable FSS using the SMV1234 varactor (1.32 pF ≤ Cv ≤ 9.63 pF) and once more a good agreement between the results is observed, indicating the applicability of the proposed modeling, which is especially attractive for optimization process.

A performance comparison between series and parallel resonant circuits in the Reflection-Type Phase Shifter (RTPS) configuration is presented in this article. Initially, equations are derived to theoretically assess the fundamental limits of both configurations, in terms of the optimum values of the required resonant inductances and, subsequently, the maximum obtainable phase shifts of both configurations, as a function of the reactive parameters of the varactor diode. Then, based on these predictions, two sets of three RTPSs (three series-circuit and three parallel-circuit) operating at a center frequency of 2.3 GHz are designed, simulated, fabricated and their performance was measured and compared with the theoretically predicted results. For each set of the RTPS, the intrinsic parameters of the varactor diode (minimum capacitance and tuning ratio) are altered by the addition of a lumped element. This is done in order to adequately assess the performance of phase shifters for different characteristics of the active element. Then, based on the derived equations, the corresponding RTPS is designed so as to provide maximum phase shift. The theoretical analysis indicates that the parallel resonant configuration is inherently more capable of providing higher values of shift compared to its series resonant circuit counterpart, reaching 360° in the limit case. The measurement results largely confirm these theoretical findings, and the parallel RTPS configuration is shown to outperform the series RTPS configuration under most conditions. Results are discussed in detail.

This study proposes a high-temperature superconducting (HTS) bandpass filter with a continuously tunable bandwidth and center frequency. The proposed filter combines several gallium arsenide varactors and a dual-mode resonator (DMR). The even and odd modes of the DMR can be tuned simultaneously using a single bias voltage. The capacitive value of varactors in the circuit is tuned continuously under continuous voltage and frequency tunability. External couplings and the interstage can be realized using an interdigital coupling structure; a fixed capacitor is added to the feeder to improve its coupling strength. A low-insertion loss within the band is obtained using HTS technology. Additionally, the proposed filter is etched on a 0.5 mm-thick MgO substrate and combined with YBCO thin films for demonstration. For the as-fabricated device, the tuning frequency range of 1.22~1.34 GHz was 9.4%; the 3-dB fractional bandwidth was 12.95~17.39%, and the insertion loss was 2.28~3.59 dB. The simulation and experimental measurement results were highly consistent.

This paper presents a wide tuning range voltage-controlled oscillator (VCO) circuit in 180 nm CMOS technology using an inversion mode MOSFET (IMOS) varactor in delay stages. Frequency variation in the VCO has been achieved by changing the capacitance of the output node with the use of an IMOS varactor comprised of two NMOS transistors connected in parallel. The VCO circuit uses a CMOS inverter and output frequency tuning that has been attained by varying the back-gate voltage (V_sb ) and source/drain voltage (V_ct ) of the IMOS varactor. Supply voltage variations from 1 V to 3 V achieves a tuning range from 0.280 GHz to 1.163 GHz along with power dissipation of 0.003 mW to 3.290 mW. Source/drain voltage (V_ct ) variations from 0.1 V to 1.5 V achieve a tuning range of 0.685 GHz to 0.816 GHz along with power dissipation of 0.465 mW. Furthermore, the frequency varies from 0.810 GHz to 0.843 GHz with back-gate voltage (V_sb ) tuning of the IMOS varactor. The results were obtained with different IMOS varactor widths and various combinations of supply voltages to achieve output frequency, power dissipation as well as phase noise. The VCO shows a phase noise of 102.81 dBc/Hz@1MHz and a figure of merit (FoM) is -162.10 dBc/Hz. The proposed VCO circuit attains reasonable performance results that are appropriate for low power radio frequency applications.

A liquid precursor for 3D printing ultramicroporous carbons (pore width <0.7 nm) to create a novel in-plane capacitive-analog of semiconductor-based diodes (CAPodes) is presented. This proof-of-concept integrates functional EDLCs into microstructured iontronic devices. The working principle is based on selective ion-sieving, controlling the size of the electrolyte ions, and the nanoporous sieving carbon's pore size. By blocking bulky electrolyte ions from entering the sub-nanometer pores, a unidirectional charging characteristic with controllable ion flux is achieved, leading to diodic U-I characteristics with a high rectification ratio. The liquid precursor approach enables successful printing of miniaturized in-plane CAPodes. A combination of inkjet and extrusion printing techniques with suitable inks is explored to fabricate electrode materials with engineered porosity. Deliberate fine-tuning of the ultramicroporous carbon's porosity and surface area is achieved using a customized carbon precursor and CO 2 etching techniques. Electrochemical evaluation of the printed CAPodes demonstrates successful miniaturization compared with macroscopic film assembly. 3D manufacturing and miniaturization allow for the integration of CAPodes into logic gate circuits (OR, AND). For the first time, these switchable devices are used as variable capacitors in a high-pass filter application, adjusting the cut-off frequency of applied alternating voltage analogous to an I-MOS varactor., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

This article presents a dual‐band bandpass (BP) to bandstop (BS) switchable filter with independently tunable center frequency and bandwidth. Two different length half‐wavelength resonators are coupled with two separate coupling lines. Each resonator consists of a varactor‐loaded stub at the center to tune the even mode frequencies, whereas two identical varactors are connected at the ends to tune odd and even mode frequencies simultaneously. The center frequency of the first passband is tuned from 1.03 to 1.4 GHz with constant fractional bandwidth (CFBW) of 3.4%, and second passband from 1.35 to 1.74 GHz with CFBW of 2%. BP to BS switching is achieved by connecting a p‐i‐n diode between input and output feedlines. [ABSTRACT FROM AUTHOR]

Modern era of wireless communication relies on the evolution of adaptive antennas. This influences the new age antenna designs to adapt themselves to the changing RF environment. Reconfigurable antennas are one such design where the operating frequency, radiation pattern, and polarization can be altered according to the user's requirement. Numerous research works have been contributed to the design of reconfigurable antennas. In view of that, this work proposes a detailed survey on reconfigurable antennas. The key motivation behind the survey is to provide an elaborate idea on the existing reconfigurable antenna designs so that the antenna researchers can perform possible analysis to overcome shortcomings or can enhance the performance of the existing designs. The evolution of reconfigurable antennas, the need for different reconfigurations and their design specifications are presented in this survey. Further, a comparative study on different switching mechanisms, deployment of various techniques to enhance antenna performance, diverse applications and existing design challenges are also addressed as a part of this review. Hence, this survey will be useful to the researchers in developing futuristic reconfigurable radiating structures that can be well suited for applications like Cognitive Radio, 5G and Multiple Input Multiple Output systems. [ABSTRACT FROM AUTHOR]

In this article, we present the capacitance–voltage (${C}$ – ${V}$) characteristics of HfxZr1−xO2 metal–ferroelectric–metal (MFM) thin-film capacitors with various Zr doping, thicknesses, and annealing temperatures. The influence of doping, electric field cycling, and annealing temperature on tuning characteristics (tunability) was analyzed and an optimized bias region for the maximum tunability was defined. Additional focus was made on an antiferroelectric-like (AFE) behavior, which occurs for > 50% Zr doping. The presence of both the ferroelectric and the AFE phase manifests itself in specific ${C}$ – ${V}$ behavior, where a reduced bias range is required for tuning, however, at the cost of a smaller tunability. The suitability of this behavior for varactor applications is also discussed. [ABSTRACT FROM AUTHOR]

A compact differential tunable dual-band bandpass filter is achieved by using cascaded capacitor-loaded coupled microstrip lines and voltage-controlled varactors. Six differential-mode (DM) transmission zeros (TZs), four DM transmission poles (TPs), and four common-mode (CM) TZs can be obtained by controlling values and positions of capacitors and the even-odd mode impedances of coupled microstrip lines. What's more, the first three DM TZs, two TPs and three CM TZs will change with the capacitance of varactors. Thus, the proposed filter possesses a tunable lower passband and a fixed upper passband. Compared with the state-of-the-art differential tunable DBBFs, the proposed design has the advantages of wide tuning range, compact size, low number of control voltages, and simple structure. Theoretic analysis, parametric study and design procedure are carried out completely. A prototype with the size of 58.2 × 10.1 mm (1.13 λg × 0.20 λg, λg is the microstrip guided wavelength at the center frequency of the upper passband) is designed for demonstration, which exhibits the center frequency of the lower passband can be tuned from 1.55 to 2.42 GHz. Meanwhile, the center frequency and 3-dB bandwidth of the upper passband keep constant at 3.79 GHz and 8.5%, respectively. [ABSTRACT FROM AUTHOR]

A reconfigurable transmitarray antenna (RTA) with 360° continuous transmission phase controlling capability is designed and experimentally validated in this letter. The proposed RTA element is based on the receiver-transmitter structure. A compact varactor-based analog phase shifter using a coupled-line structure is utilized to provide a 0° to 180° continuous transmission phase. Two PIN diodes integrated on the active transmitter patch are alternatively turned on to generate an additional 180° phase shift using the current reversal mechanism. The element simulations show a magnitude insertion loss varying from 0.95 to 1.35 dB at 5.6 GHz, and a wide 3-dB transmission bandwidth of 16.7%. A prototype composed of ${\rm{16 \times 16}}$ elements is fabricated and measured. The measured broadside gain is 23.7 dBi at the design frequency with a 3-dB gain bandwidth of 15.7%. Good two-dimensional (2-D) beam steering capability within ±60° is also experimentally verified. [ABSTRACT FROM AUTHOR]

This article introduces a multifunctional polarization insensitive frequency selective rasorber (MF-FSR) comprised of periodic metallic patterns printed on two dielectric substrates and separated by an air-spacer. The novelty of the proposed MF-FSR lies in its combined feature of mode switching and frequency tuning characteristics. This uniquely offers a real-time and multifunctional capability to switch from “rasorber mode (FSA-T)” into an “absorber with notch band (FSA-N)” mode where both modes support continuous tunability of their “transmission” or “notch” band. By controlling the reverse bias voltage of the embedded varactor, the transmission band in FSA-T mode can be tuned from 3.76 to 4.26 GHz with a very low insertion loss in the range of 0.62–0.95 dB. In complementary FSA-N mode, the notch band is also tunable from 4.17 to 4.71 GHz. Moreover, the same varactor set can control the tuning of transmission or the notch band depending upon MF-FSR’s basic state of operation which is further independently controllable by the p-i-n diode. Equivalent circuit models are also thoroughly examined. Finally, a prototype is fabricated and experimentally tested, showing a good agreement with the predicted results. [ABSTRACT FROM AUTHOR]

This paper presents a bandwidth and center frequency tunable bandpass filter with wide tuning range. The proposed filter employs two cascade cross‐shaped resonators. The cross‐shaped resonator can generate two independent tunable transmission zeros by introducing two microwave varactors. The center frequency and bandwidth can be tuned by adjusting the DC bias voltages applied to the varactors. For demonstration, a filter example was designed, fabricated and measured. The tuning 3‐dB bandwidth from 20% to 30% is achieved when the center frequency is tuned from 3.5 to 5 GHz. Meanwhile the insertion loss is less than 4 dB with a high selectivity. The size of the filter is 0.32λg × 0.36λg where λg is the guided‐wavelength at the center frequency. [ABSTRACT FROM AUTHOR]

In reconfigurable frequency selective surface, FSS, bias lines can suppress a resonant frequency. This is a disadvantage, as it reduces a FSS potential application. In this paper, a procedure to recover the suppressed resonant frequency is described. A FSS based on four arms star geometry is considered and its reconfigurability is achieved by the use of varactors, for which bias lines suppress the polarization resonance. So, dipoles are added to the unit cell geometry recovering this resonance. In order to validate the proposed procedure, a reconfigurable FSS using the varactor SMV1231was fabricated and characterized. Numerical and measured results shown a good agreement, confirming that the FSS reconfigurability is preserved and the suppressed resonance recovered. [ABSTRACT FROM AUTHOR]

This paper presents the extraction of an equivalent circuit model for PIN diodes and varactors in the millimeter waves. This circuit model is handy for new communication applications involving, for example, electronic beam reconfigurability, where diodes are commonly used. For parameter extraction, the proposed model includes the effects of the device, the pads, and the gap underneath the device. From the measurement at various bias points (varactor) or states (PIN diode), it is possible to extract an equivalent circuit to properly model the behavior of these devices when using them to design reconfigurable elements. The results are validated experimentally, obtaining an excellent agreement between the measurements and the equivalent circuit models in a large frequency band up to 67 GHz. • We propose a broadband parasitic model for PIN diodes and varactors up to 67 GHz. • The results of the analytical circuit show an excellent agreement with measurements. • We demonstrate that parasitic effects must be considered from approximately 40 GHz. • The proposed model can be easily implemented for designing reconfigurable devices. [ABSTRACT FROM AUTHOR]

This paper presents a kind of broadband, low-loss tunable phase shifter based on transmission line metamaterial. An inherent high-pass backward-wave response property of a left-handed metamaterial based on coplanar waveguide (CPW) transmission line was used to realize a microwave phase shifter. The commercial software Ansoft HFSS was used to design and analyze for the transmission line metamaterial phase shifter structure, and the resulting S-parameters were used to characterize its performance. A transmission line metamaterial phase shifter was fabricated on Copper-Clad Board. The designed four unit-cells phase shifter provides a 0-190o continuous phase shift at 7.2 GHz using varactors biased from 0 V to 6 V with relatively low insertion loss.