Varactor Research Articles

A New Varactor-Tuned 5.8 GHz Dielectric Resonator Band-Stop Filter for ITS and C-V2X Coexistence with Vehicular DSRC

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.

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 2D-Programmable and Scalable Reconfigurable Intelligent Surface Remotely Controlled via Digital Infrared Code

Reconfigurable intelligent surfaces (RISs) are promising and relatively low-cost tools for improving signal propagation in wireless communications. A RIS assists a base station (BS) in optimizing the channel and maximizing its capacity by dynamically manipulating the reflected field. Typically, RISs are based on dynamically reconfigurable reflectarrays (RAs), i.e., 2-D arrays of passive patch antennas, individually switchable between two or more reflection phases. The spatial resolution of provided reflected field patterns is governed by the aperture dimensions and the number of patches to meet the requirements of different communication scenarios and environments. Here, we demonstrate a 1 bit RIS for 5 GHz Wi-Fi band made by assembling together multiple independently operating and structurally detached building blocks all powered by the same DC source. Each block contains four separately phase-switchable patch antennas with varactor diodes and a common microcontroller extracting digital control commands from modulated infrared light illuminating the entire RIS. Such distributed light-sensitive controllers grant the possibility of scaling the aperture by adding or removing blocks without redesigning any control circuitry. Moreover, in the proposed RIS a full 2-D phase encoding capability is achieved along with a robust remote infrared control.

Frequency-Reconfigurable Antenna With Wide- and Narrowband Modes for Sub-6 GHz Cognitive Radio

This letter presents a frequency-reconfigurable antenna for cognitive radio application in sub-6 GHz 5G band. The proposed antenna consists of a wideband (WB) monopole integrated with a narrowband microstrip patch in a single-layer substrate. Two PIN diodes are employed to switch between the WB sensing mode and narrowband (NB) communication mode. Three varactor diodes are implemented on the patch to continuously tune the operating frequencies in the NB mode. The proposed antenna produces a wide bandwidth of 54.2% (3.19–5.56 GHz) for the sensing mode and a continuously tunable bandwidth of 44% (3.4–5.32 GHz) for the communication mode. Both modes present good radiation characteristics with peak measured realized gains of 6.02 and 5.37 dB, respectively.

An Enhanced-Sensitivity Tangential Electric Field Probe With Tunable Resonant Frequency

A novel enhanced-sensitivity tangential <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe with tunable resonant frequency is proposed in this paper. This <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe consists of a front-end electric dipole induction part, tunable coupling resonators, a balun transmission section, and a coplanar waveguide transmission part. By introducing an improved electric dipole-induced element and resonant transmission, the detection sensitivity of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe can be significantly improved. Varactor diodes are loaded into the coupling resonators to achieve an adjustable resonant center frequency, thereby minimizing the contradiction between the high sensitivity and test bandwidth of the resonant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field probe. A prototype of this tunable resonant frequency probe was fabricated and measured. When the reverse bias voltage applied to the varactors was tuned from 0 V to 20 V, the probe could obtain enhanced-sensitivity tangential <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field detection within the frequency band of 1.61-2.30 GHz. Moreover, this probe was also adopted to measure the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field components in some areas of the microstrip line and antenna based on FR4. This probe can improve detection efficiency and reduce test costs on the premise of enhanced sensitivity detection. It has broad application prospects for near-field measurement in the future.

Analytical Modeling and Design of 27.12 MHz Single-Switch DC–DC Converter With PCB Transformer

This paper proposes analytical modeling and design of a 27.12 MHz single-switch dc-dc converter with galvanic isolation using a PCB transformer. The ODE-based analytical approach provides a more accurate circuit design by considering the high-order harmonics and non-ideal components such as the diode capacitances. The proposed dimensionless mathematical model simplifies the design of the desired circuit model and requires less tuning procedure. In addition, the effective analytical model offers the design curves to obtain the optimized circuit parameters at any duty ratio. Meanwhile, the multilayer planar PCB transformer is designed to achieve the isolation and high power density for the high-frequency dc-dc converter. Based on Neumann’s formula, the analytical model of the PCB transformer is proposed to calculate the inductances for the spiral structure accurately in the high-frequency conditions. As a result, the computational burden for calculating the coil inductances is alleviated using the proposed method. The simulation and experimental results using a 3W converter prototype verify the effectiveness and feasibility of the analytical modeling and design of the proposed converter.

Compact Dual-polarized Reconfigurable MIMO Antenna Based on a Varactor Diode for 5G Mobile Terminal Applications

Compact Dual-polarized Reconfigurable MIMO Antenna Based on a Varactor Diode for 5G Mobile Terminal Applications

A Low-Cost and Low-Profile Electronically Programmable Bit Array Antenna for Two-Dimensional Wide-Angle Beam Steering

An electronically programmable bit array antenna (PBAA) is designed with a low profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.09\lambda _{0}$ </tex-math></inline-formula> at 11 GHz) and 2-D wide-angle beam steering. The planar PBAA is composed of 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times8$ </tex-math></inline-formula> elements, and each of them can be individually addressed through the meticulously designed dc bias. By controlling two PIN diodes and four varactor diodes embedded, the PBAA element provides a maximum phase shift of 337.5° and 16 (4 bit) phase coding states with a 22.5° regular interval. The design is verified through simulations and measurements. The experimental results of the fabricated sample exhibit a broadside gain of 16 dBi, corresponding to the radiation efficiency of 33.1%, and 3 dB gain bandwidth of 11.8%. The sidelobe and cross-polarization levels of the broadside beam are below −19.6 and −30 dB, respectively. Moreover, the main beam is capable of scanning in the range of ±60° <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$ </tex-math></inline-formula> ±40°, and the gain fluctuations in E- and H-planes are less than 3.6 and 3 dB, respectively. The design provides flexible 2-D beam-scanning capability while being low cost, low profile, low complexity, and low power consumption, which will benefit various applications with sensing and wireless communication through electromagnetic (EM) waves.

Analog Backscatter Video Transmission for Wireless Capsule Endoscope

Wireless capsule endoscopy is a fast-growing technology in healthcare systems. Due to using battery for powering the camera, light source, wireless communication, and other electronics, it has substantial limitations with the image quality, frame rate, and operating time. In this work, we propose a wireless passive video transmission system for capsule endoscopy, in which the power consumption is reduced by using analog camera sensor, and implementing an innovative radar technique for remote reading of the analog video signal using radio frequency backscattering. The power consumption of the capsule communication system tends to zero. The communication electronics system is minimized to a single Varactor diode with appropriate matching circuits and the image sensor power consumption is reduced by eliminating the camera sensor’s analog to digital converter. With these improvements the capsule system can operate for a longer period of time which enables the feasibility of continuous video streaming during the gastric tract screening. The design feasibility is demonstrated in a phantom experiment, and validated in an animal experiment for depths 6–11 cm using a bi-static radar system at 400 MHz, implemented using software defined radio platform.

Slot‐based CubeSat antenna with wide tunning capabilities

AbstractA slot‐based miniaturized antenna design for CubeSat applications that operate in ultra high frequency (UHF) band is presented. The proposed antenna design consists of a frequency reconfigurable (FR) slot‐based antenna integrated on a Rogers RO4350 substrate. The frequency range covered by the FR antenna is 300–450 MHz. A single varactor diode is used to sweep the frequency of the design. The proposed meandered loop‐slot antenna design is small in size and has planar geometry with overall substrate dimensions of 100 × 100 mm2. The proposed downsized antenna with frequency reconfigurability is ideally suited for small satellite applications in the UHF band, especially CubeSats.

Wideband Lorenz Resonance Reconfigurable Metasurface for 5G+ Communications

Reconfigurable intelligent surfaces (RIS) have been considered as a promising solution to enhance the spectrum and energy efficiency of the 5G+ and future 6G wireless communication systems. The performance of RIS will become the key metric of these communication systems. In this paper, we proposed a wideband Lorenz resonance-based metasurface reconfigurable reflectarray (MSRRA) realization scheme with low energy consumption targeted at the center frequency of 28 GHz. A compact voltage bias network for the varactor diodes is carefully designed to reduce losses in RF current and the influence of the bias circuit on the radiating element effectively. An equivalent circuit model for the MSRRA unit cell is also introduced to predict the properties of the MSRRA system, which can be used to optimize the MSRRA design efficiently. In the experimental tests, the proposed MSRRA system can be optimized to cover a dynamic reflection phase range of over 300° with a bandwidth of 3.83 GHz, which is consistent with the simulation results. The measured single-scattering beam bandwidth is 1.85 GHz at the center frequency of 28 GHz, which can fully cover the whole n257 channel of 5G NR. The proposed continuous tunable MSRRA can support 5G+ and 6G indoor, short-range links, and outdoor point-to-point communications.

Comparison of annealing quality after 3e15/cm2 50 keV BF2+ implant between rapid thermal annealing and furnace annealing

Low leakage diodes are necessary in order to manufacture high-quality variable capacitance diodes (varicaps), which are used in voltage-controlled oscillators. Junction leakage current affects the single sideband noise of the oscillator by up-conversion of 1/f and shot noise (Chan et al. in IEEE Trans Electron Devices 54(9):2570–2573, 2007, https://doi.org/10.1109/TED.2007.903201). Several sources show higher leakage current for RTP compared to furnace anneal (Lunnon et al. in J Electrochem Soc 132(10):2473, 1985, https://doi.org/10.1149/1.2113602, Gramenova et al. in J Electrochem Soc 146(1):359, 1999, https://doi.org/10.1149/1.1391613, Mikoshiba et al. in Jpn J Appl Phys, 1986, https://doi.org/10.1143/jjap.25.l631). In our experiments, we found lower leakage currents for RTP compared to furnace annealing. We present results from annealing experiments where we compare three annealing conditions with and without oxidizing annealing conditions.Graphical abstract

A Coupler With Simultaneously Tunable Phase, Frequency and Coupling Coefficient

A novel coupled-line coupler with tunable frequency, coupling coefficient and phase difference is proposed with a reduced number of varactor diodes. The proposed coupler consists of two weakly coupled lines cascaded using varactors and two highly tunable coupled lines loaded with varactors. By varying the cascading capacitances between two weakly coupled lines, the phase difference between the output ports can be tuned with little effect on frequency and amplitude. More importantly, the operating frequency and coupling coefficient can also be independently controlled by choosing the proper combination of the loading capacitances between and on the highly tunable coupled lines. For demonstration, a highly reconfigurable coupler was designed, fabricated and measured. It exhibited a tunable operating frequency ranging from 1.15 GHz to 1.85 GHz with a relative bandwidth larger than 18%. The power division ratio and phase difference between the output ports are also tunable from 0 dB to 7.4 dB and from 65° to 130° respectively.

A miniaturized microstrip antenna with tunable double band-notched characteristics for UWB applications

This paper proposes the step-by-step design procedure for obtaining independent dual band-notch performance, which provides a valuable method for designing tunable dual band-notched UWB antenna. The proposed antenna consists of the semicircle ring-like radiating patch with an elliptical-shaped slot and double split ring resonators on the top surface of the substrate and defected ground structure (DGS) on the bottom surface of the substrate. The operating frequencies ranged from 1.3 to 11.6 GHz (S11 < − 10 dB). By loading varactor diodes at the gap of the resonators structure and changing the varactor diode’s reverse bias voltage(0–30 V), a wider band-notched tuning range from 2.47–4.19 to 4.32–5.96 GHz can be achieved, which covers the whole WiMAX band and WLAN band. The experimental results agree well with the simulated results. The notched gain at notched frequency points is about − 5.3 dBi and − 5 dBi, demonstrating that the narrow-band interference signal could be efficiently suppressed. The security of UWB communication systems can be further enhanced. Meanwhile, the selection of varactor diode and DC bias circuit are fully considered. Hence, the accuracy of the experiment results and antenna operating performance have been improved. Furthermore, the proposed antenna only has an electrical size of 0.26λ*0.19λ at 1.3 GHz. Compared to the related reported antennas, the proposed antenna has achieved a simpler structure, low profile, compact size, tunable dual band-notched characteristics, extensive independent tunable range, and good band-notched performance simultaneously, to the best of our knowledge. The proposed antenna is believed to have a valuable prospect in UWB communication, Wireless Body Area Network, Industry Science Medicine, mobile communication applications, etc.

Reconfigurable matrix multiplier with on-site reinforcement learning.

Matrix multiplication is a fundamental building block for modern information processing and artificial intelligence algorithms. Photonics-based matrix multipliers have recently attracted much attention due to their advantages of low energy and ultrafast speed. Conventionally, achieving matrix multiplication relies on bulky Fourier optical components, and the functionalities are unchangeable once the design is determined. Furthermore, the bottom-up design strategy cannot easily be generalized into concrete and practical guidelines. Here, we introduce a reconfigurable matrix multiplier driven by on-site reinforcement learning. The constituent transmissive metasurfaces incorporating varactor diodes serve as tunable dielectrics based on the effective medium theory. We validate the viability of tunable dielectrics and demonstrate the performance of matrix customization. This work represents a new avenue in realizing reconfigurable photonic matrix multipliers for on-site applications.

Investigation of isolation enhancement and tune‐ability in patch antenna arrays

AbstractThis paper reports the study of a tunable isolator based on a four‐strip resonant structure to reduce the mutual coupling between two patch antennas. Unlike other decoupling structures with a fixed center decoupling frequency, this design provides tunable mutual coupling reduction frequency response and adjustable mutual coupling level by integrating a varactor diode into the strip isolator. This study investigates the effect of the position and capacitance of the varactor diode on mutual coupling. In addition to tune‐ability, the tunable four‐strip resonator reduces the coupling level at all frequencies around 3.5 GHz by at least 6 dB to less than –28 dB without degrading the impedance bandwidth. Compared to the case with the four‐strip resonator structure but without the varactor diode, the isolation is further improved by 2 dB or more. The measured results are consistent with the simulation results.

Reconfigurable Half-Mode SIW Antenna Using Uniaxial Field Programmable Microwave Substrate Structure

This communication presents the design and implementation of a beam steerable leaky wave antenna (LWA) based on integrated electronic devices (varactor diodes). The design uses a half-mode substrate-integrated waveguide (HMSIW) where the short-circuited wall or PEC boundary is realized with field programmable microwave substrate (FPMS)-based unit cells. By virtue of placing integrated varactor diodes in these unit cells, the wavenumber and the phase shift of the propagating signal can be controlled. This allows a beam steering of 25° for a fixed center frequency. Furthermore, control of the varactor bias voltages allows a fixed beam direction over a wide frequency bandwidth. An excellent agreement can be observed between the simulated and measured results, validating the first ever FPMS-based reconfigurable antenna design.

A 1-MHz GaN-Based $LCLC$ Resonant Step-Up Converter With Air-Core Transformer for Satellite Electric Propulsion Application

A gallium nitride (GaN)-based resonant step-up converter is proposed for the application in the satellite electric propulsion (EP) system. This converter consists of a full-bridge inverter, a resonant tank, and a multistage Cockcroft–Walton voltage multiplier to provide a high voltage gain. Additionally, the air-core transformer is introduced due to the megahertz switching frequency allowed by the GaN device. Thus, the limited magnetizing inductance of transformer and the remarkable junction capacitance of diode have to be carefully considered in the resonant tank design, especially after considering that this converter normally operates at the light load in the EP system. In this work, the fourth-order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ LCLC$</tex-math></inline-formula> resonant converter is investigated. The recommended parameter selection for the fourth-order resonant tank is also provided. A 1.2-MHz, 23-V/2.5-kV, and 6-W prototype is demonstrated. It achieves a low harmonics distortion and a low power loss with the zero voltage switching.

60 GHz Electronically Tunable Leaky-Wave Antenna Based on Annular Surface Plasmon Polariton Media for Continuous Azimuth Scanning

This article proposes a single-layered electronically tunable annular surface plasmon polariton (SPP)-based leaky-wave antenna at 60 GHz for continuous azimuthal beam scanning. Initially, the groundless annular SPP transmission line is designed having specialized feeding mechanism which is operational at 60 GHz under SPP mode. Periodic radiating semicircular patches are incorporated into the vicinity of the TL that form an additional momentum caused to convert the slow-wave SP mode to radiating leaky-mode and placement of extra metallic ground makes the radiated beam unidirectional. Furthermore, implementation of the varactor diodes with imposed suitable switching conditions make the geometry electronically tunable to achieve a continuous complete azimuth coverage. The theoretical predictions, numerical simulations and the experimental validations of the proposed structure show good agreement. The proposed antenna show an overall scanning range of 275°, peak gain of 19.9 dBi with average sidelobe level of −10 dB and minimum cross polar level of −20 dB. Availing the benefits from the low-profile compactness and improved performance, the proposed groundless LWA appears as a promising candidate for integration in 60-GHz mm-wave applications.

Tunable Multibeam Holographic Metasurface Antenna

A metasurface beam-steering antenna at microwaves is proposed in this letter, which is designed according to holographic theory and has the ability to create multibeam radiation patterns with independent control of the individual beam direction. The holographic design approach of the modulated impedance surface follows the methodology of linear superposition of individual field patterns for each beam. The unit cell of the proposed antenna is tuned with a low-loss varactor diode, and its dispersion diagram is obtained with a transverse resonance technique. A novel multibeam antenna fed by a single source is designed with independent beam steering of each beam at around 7.2 GHz. The dual-beam antenna exhibits an average of 11.6 dBi of realized gain for each independent beam.