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Journal articles on the topic 'Varactors'

Author: Grafiati

Published: 4 June 2021

Last updated: 6 September 2023

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1

Agrawal, Prannoy, Daniel Kienemund, Dominik Walk, Stipo Matic, Nicole Bohn, Kevin Häuser, Thomas Fink, et al. "Suppression of Acoustic Resonances in BST-Based Bulk-Ceramic Varactors by Addition of Magnesium Borate." Crystals 11, no. 7 (July 6, 2021): 786. http://dx.doi.org/10.3390/cryst11070786.

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This work presents a method for reducing acoustic resonances in ferroelectric barium strontium titanate (BST)-based bulk ceramic varactors, which are capable of operation in high-power matching circuits. Two versions of parallel-plate varactors are manufactured here: one with pure BST and one with 10 vol-% magnesium borate, Mg3B2O6 (MBO). Each varactor includes a 0.85-mm-thick ferroelectric layer. Acoustic resonances that are present in the pure BST varactor are strongly suppressed in the BST-MBO varactor and, hence, the Q-factor is increased over a wide frequency range by the addition of small amounts of a low-dielectric-constant (LDK) MBO. Although the tunability is reduced due to the presence of non-tunable MBO, the increased Q-factor extends the varactor’s availability for low-loss and high-power applications.

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2

Lee, Milim, Jaeyong Lee, and Changkun Park. "Layout of MOS Varactor with Improved Quality Factor for Cross-Coupled Differential Voltage-Controlled Oscillator Applications." Electronics 12, no. 6 (March 14, 2023): 1385. http://dx.doi.org/10.3390/electronics12061385.

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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.

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3

Li, Ming, Rony E. Amaya, Robert G. Harrison, and N. Garry Tarr. "Investigation of CMOS Varactors for High-GHz-Range Applications." Research Letters in Electronics 2009 (2009): 1–4. http://dx.doi.org/10.1155/2009/535809.

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This paper explores a variety of different CMOS varactor structures for RF and MMICs. A typical 0.18 μm CMOS foundry process was used as the study platform. The varactors' capacitance-voltage characteristics and cutoff frequencies have been examined up to 55 GHz. The primary aim of this work is to design varactors that can improve nonlinear-transmission-line (NLTL) pulse-compression circuits. The results should also be valuable for other applications up to millimeter wavelengths.

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4

Hsieh, Yu-Li, Liann-Be Chang, Ming-Jer Jeng, Chung-Yi Li, Chien-Fu Shih, Hung-Tsung Wang, Zi-Xin Ding, Chia-Ning Chang, Hao-Zong Lo, and Yuan-Po Chiang. "Annealing-Dependent Breakdown Voltage and Capacitance of Gallium Oxide-Based Gallium Nitride MOSOM Varactors." Materials 13, no. 21 (November 4, 2020): 4956. http://dx.doi.org/10.3390/ma13214956.

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Our laboratory has previously revealed the use of metal-semiconductor-metal (MSM) varactors against malicious pulses, as well as completed the related verification and measurements of such a circuit. To improve the reliability of this protection module further, in this study, we deposited a gallium oxide (Ga2O3) thin film in between the Schottky contact electrode to manufacture a metal-oxide-semiconductor-oxide-metal (MOSOM) varactor. However, the thin-film quality and heterojunction interfaces will affect these fabricated varactors in various ways, such as the asymmetry threshold voltage to the variable capacitance characteristics. This study aims to address the issues associated with the inserted oxide thin film, as well as to determine how improvements could be obtained by using an oxygen furnace annealing process. As a result, the breakdown voltage of the MOSOM varactor was further promoted and a more robust anti-surge module was thus realized.

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5

Song, Jing-Pan, Xin-Yi Wang, Feng Wei, and Xiao-Wei Shi. "Electronically Reconfigurable Varactor-Loaded HMSIW Bandpass Filter." Frequenz 72, no. 5-6 (April 25, 2018): 227–30. http://dx.doi.org/10.1515/freq-2016-0345.

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AbstractA varactor-loaded half-mode substrate integrated waveguide (HMSIW) reconfigurable bandpass filter (BPF) is proposed in this paper. The proposed BPF is composed of complementary split-ring resonators (CSRRs) and varactors. Meanwhile, a nonmetalized via is employed in the center of the CSRR. It is noted that the varactor is embedded into the nonmetalized via, which can significantly reduce the tunable filter size. By changing the reverse bias voltage of the varactor, the resonant frequency of the proposed filter can be adjusted. Moreover, low insert loss (IL) and wide tuning range can be achieved. In order to validate its practicability, a BPF with the frequency ranging from 1.9 GHz to 2.5 GHz is fabricated and good agreement between the simulated and measured results is observed.

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6

Abdulazhanov, Sukhrob, Quang Huy Le, Dang Khoa Huynh, Defu Wang, Maximilian Lederer, Ricardo Olivo, Konstantin Mertens, Jennifer Emara, Thomas Kämpfe, and Gerald Gerlach. "RF-Characterization of HZO Thin Film Varactors." Crystals 11, no. 8 (August 18, 2021): 980. http://dx.doi.org/10.3390/cryst11080980.

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A microwave characterization at UHF band of a ferroelectric hafnium zirconium oxide metal-ferroelectric-metal (MFM) capacitors for varactor applications has been performed. By using an impedance reflectivity method, a complex dielectric permittivity was obtained at frequencies up to 500 MHz. Ferroelectric Hf0.5Zr0.5O2 of 10 nm thickness has demonstrated a stable permittivity switching in the whole frequency range. A constant increase of the calculated dielectric loss is observed, which is shown to be an effect of electric field distribution on highly resistive titanium nitride (TiN) thin film electrodes. The C-V characteristics of a “butterfly” shape was also extracted, where the varactors exhibited a reduction of capacitance tunability from 18.6% at 10 MHz to 15.4% at 500 MHz.

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7

Kienemund, Daniel, Nicole Bohn, Thomas Fink, Mike Abrecht, Walter Bigler, Joachim R. Binder, Rolf Jakoby, and Holger Maune. "Design and demonstration of acoustically optimized, fully-printed, BST MIM varactors for high power matching circuits." International Journal of Microwave and Wireless Technologies 10, no. 5-6 (April 17, 2018): 620–26. http://dx.doi.org/10.1017/s1759078718000387.

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AbstractThis work addresses the piezoelectric induced reduction of quality factor in fully-printed metal-insulator-metal (MIM) barium strontium titanate (BST) thick film varactors designed for high power operation. An acoustically optimized varactor design is presented and compared to a non-optimized high-power varactor. The design is utilized to present a narrowband acoustic suppression technique based on defined weights. The acoustically optimized varactor consists of 162 varactor cells in a capacitive matrix. The cells in the matrix are interconnectable allowing for a variable unbiased capacitance and power rating. Due to this setup, surface acoustic waves are interrupted, and the reduced size of the cells allows for a reduced BST layer thickness, shifting the acoustic resonance away from the operational frequency. Therefore, an inverted behavior in comparison to the high-power varactor is observed with an increasing quality factor with biasing voltage. Compared to the high-power varactor, the acoustically optimized varactor design shows a 40% increased quality factor in biased state. By applying the narrowband acoustic suppression technique, an increase in quality factor of 145% is achieved compared to the unsuppressed design. In comparison to the high-power varactor, the acoustical suppressed design shows an increase in quality factor of 480% at the first acoustic resonance frequency.

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8

Vikulin, I. M., V. N. Litvinenko, S. V. Shutov, A. I. Maronchuk, A. N. Demenskiy, and V. I. Glukhova. "Enhancing parameters of silicon varactors using laser gettering." Технология и конструирование в электронной аппаратуре, no. 2 (2018): 29–32. http://dx.doi.org/10.15222/tkea2018.2.29.

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The authors investigate how and why defects influence the inverse characteristics of varactors. The paper presents experimental results on the effect laser gettering has on the electrical parameters of varactors. The mechanisms of the laser gettering effect on the parameters of varactors are analyzed.

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9

Малеев, Н. А., М. А. Бобров, А. Г. Кузьменков, А. П. Васильев, М. М. Кулагина, С. Н. Малеев, С. А. Блохин, В. Н. Неведомский, and В. М. Устинов. "Эпитаксиальные структуры InGaAs/InAlAs/AlAs для гетеробарьерных варакторов с низким током утечки." Письма в журнал технической физики 44, no. 19 (2018): 16. http://dx.doi.org/10.21883/pjtf.2018.19.46678.17413.

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AbstractThe quality of heteroboundaries and optimal conditions for epitaxial growth are critical parameters for obtaining low leakage currents of heterobarrier varactors in the InGaAs/InAlAs/AlAs material system. Grown by molecular-beam epitaxy, three-barrier heterobarrier varactor structures adjacent to InAlAs/AlAs/InAlAs barrier layers by additional mismatched InGaAs layers subjected to compressive stress show, under optimal epitaxy conditions, extremely low levels of leakage current density (not more than 0.06 A/cm^2 at a voltage of 5 V and 85°C) with relatively thin AlAs inserts (with a thickness of 2 nm).

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10

Shih, Chien-Fu, Yu-Li Hsieh, Liann-Be Chang, Ming-Jer Jeng, Zi-Xin Ding, and Shao-An Huang. "Capacitance Characteristics and Breakdown Mechanism of AlGaN/GaN Metal–Semiconductor–Metal Varactors and their Anti-Surge Application." Crystals 10, no. 4 (April 10, 2020): 292. http://dx.doi.org/10.3390/cryst10040292.

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The AlGaN/GaN materials with a wide band gap, high electron mobility, and high breakdown voltage are suitable for manufacturing high-power and high-frequency electronic devices. In this study, metal Schottky contact electrodes of different dimensions are prepared on AlGaN/GaN wafers to fabricate metal–semiconductor–metal (MSM) varactors. Voltage-dependent capacitance and breakdown voltages of the varactors are measured and studied. The corresponding breakdown mechanisms of varactors with different electrode gaps are proposed. Furthermore, an anti-surge application using GaN-based MSM varactors in a signal transmission module is demonstrated, and its surge suppression capability is shown. We believe that our study will be beneficial in developing surge protection circuits for RF applications.

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11

Kienemund, Daniel, Nicole Bohn, Thomas Fink, Mike Abrecht, Walter Bigler, Joachim R. Binder, Rolf Jakoby, and Holger Maune. "Low loss, fully-printed, ferroelectric varactors for high-power impedance matching at low ISM band frequency." International Journal of Microwave and Wireless Technologies 11, no. 7 (May 23, 2019): 658–65. http://dx.doi.org/10.1017/s1759078719000643.

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AbstractLow loss, ferroelectric, fully-printed varactors for high-power matching applications are presented. Piezoelectric-induced acoustic resonances reduce the power handling capabilities of these varactors by lowering the Q-factor at the operational frequency of 13.56 MHz. Here, a quality factor of maximum 142 is achieved with an interference-based acoustic suppression approach utilizing double metal–insulator–metal structures. The varactors show a tunability of maximum 34% at 300 W of input power. At a power level of 1 kW, the acoustic suppression technique greatly reduces the dissipated power by 62% from 37 W of a previous design to 14.2 W. At this power level, the varactors remain tunable with maximum 18.2% and 200 V of biasing voltage.

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12

Crunteanu, Aurelian, Vincent Muzzupapa, Areski Ghalem, Laure Huitema, Damien Passerieux, Caroline Borderon, Raphael Renoud, and Hartmut W. Gundel. "Characterization and Performance Analysis of BST-Based Ferroelectric Varactors in the Millimeter-Wave Domain." Crystals 11, no. 3 (March 11, 2021): 277. http://dx.doi.org/10.3390/cryst11030277.

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We present the realization and analysis of the microwave performances of interdigited varactors integrating thin ferroelectric layers of barium and strontium titanate (BaxSr1−xTiO3). Devices based on ferroelectric films of different compositions (x = 0.8 and x = 0.5) have been characterized in the millimeter-wave domain, from 200 MHz to 110 GHz. By applying different bias voltages, the tunability of the capacitance can reach up to 40% for the Ba0.8Sr0.2TiO3 composition, under relatively low applied electric fields of about 167 kV/cm. These promising characteristics allow the integration of the varactor devices in tunable antennas for a large frequency domain, from the microwaves to the millimeter waves range.

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13

WANG, CHENLUAN, SHENGXI DIAO, NAN CHEN, FEI JIA, and FUJIANG LIN. "A 7.8 mW 5.2% FSK ERROR TWO-POINT MODULATOR WITHOUT CALIBRATION." Journal of Circuits, Systems and Computers 23, no. 09 (August 25, 2014): 1450125. http://dx.doi.org/10.1142/s0218126614501254.

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A low power phase locked loop (PLL)-based modulator for wireless sensor application is presented in this paper. The modulator adopts two-point modulation architecture in high-pass and low-pass paths of PLL; it modulates the divide ratio through sigma-delta modulator and VCO frequency tuning port simultaneously. An interleave-biased varactor pair is used to linearize the frequency tuning curve of the VCO. Besides, to achieve the desired frequency deviation of 500 kHz, we use a structure with parallel and serial capacitances in combination with tuning varactors. This topology does not need the minimum size varactor, which is sensitive to process variation and mismatch. Implemented in standard 0.18-μm CMOS process, the modulator achieves a 5.2% FSK error for 2 Mbps data rate without using any auto-calibration circuit, consuming 7.8-mW power. Loop filter and crystal are the only off-chip components.

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14

Frerking, M. A., and J. R. East. "Novel heterojunction varactors." Proceedings of the IEEE 80, no. 11 (1992): 1853–60. http://dx.doi.org/10.1109/5.175260.

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15

Nikfalazar, Mohammad, Alex Wiens, Morten Mikolajek, Andreas Friederich, Christian Kohler, Mojtaba Sohrabi, Yuliang Zheng, et al. "Tunable Phase Shifter Based on Inkjet-Printed Ferroelectric MIM Varactors." Frequenz 69, no. 1-2 (December 20, 2014): 39–46. http://dx.doi.org/10.1515/freq-2014-0120.

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Abstract This paper presents a new method for the fabrication of tunable multilayer ferroelectric components based on inkjet printing. Inkjet printing is a low-cost technology for selective film fabrication and has high potential for the preparation of tunable dielectric layers for radio frequency and microwave applications. With this technology, tunable metal-insulator-metal (MIM) capacitor is fabricated, that is composed of inkjet-printed Barium-Strontium-Titanate striplines and photo-lithographically structured gold electrodes. Compared to coplanar capacitors, such MIM varactors require significantly lower DC-voltage for tuning. By applying 20 V across a 1 μm-thick BST film, a tunability of 33% is achieved at 8 GHz and tunability of 60% by applying 50 V. To demonstrate the field of application of this MIM varactor, a tunable phase shifter is designed and fabricated at 8 GHz. A phase shift of 143° and a figure of merit (FoM) of 28°/dB are achieved by applying maximum 50 V tuning voltage.

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16

Venneri, F., S. Costanzo, and G. Di Massa. "Tunable Reflectarray Cell for Wide Angle Beam-Steering Radar Applications." Journal of Electrical and Computer Engineering 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/325746.

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An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46λ-reflectarray cell is designed at the frequency of 11.5 GHz, obtaining a phase agility of about 330°. The cell is successfully adopted for the design of a21 × 21reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated within a wide angular range.

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17

Buisman, Koen, Cong Huang, Peter J. Zampardi, and Leo C. N. de Vreede. "RF Power Insensitive Varactors." IEEE Microwave and Wireless Components Letters 22, no. 8 (August 2012): 418–20. http://dx.doi.org/10.1109/lmwc.2012.2206209.

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18

KIM, JANG-YONG, and ALEXANDER M. GRISHIN. "Na0.5K0.5NbO3 Film Microwave Varactors." Integrated Ferroelectrics 66, no. 1 (January 2004): 291–300. http://dx.doi.org/10.1080/10584580490895752.

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19

Ullah, Farman, Yu Liu, Zhiqiang Li, Xiaosong Wang, Muhammad Sarfraz, and Haiying Zhang. "A Bandwidth-Enhanced Differential LC-Voltage Controlled Oscillator (LC-VCO) and Superharmonic Coupled Quadrature VCO for K-Band Applications." Electronics 7, no. 8 (July 25, 2018): 127. http://dx.doi.org/10.3390/electronics7080127.

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A novel varactor circuit exhibiting a wider tuning range and a new technique for quadrature coupling of LC-Voltage Controlled Oscillator (LC-VCO) is presented and validated on a 25 GHz oscillator. The proposed varactor circuit employs distribute-biased parallel varactors with a series inductor connected at both ends of the varactor bank to extend the tuning range of the oscillator. Similarly, the quadrature coupling is accomplished by employing the 2nd harmonic, explicitly generated in the stand-alone free-running differential oscillator using frequency doubler. As an example, the Differential VCO (DVCO) is tunable between 20 GHz and 31 GHz and exhibits the best Phase Noise (PN) of −100 dBc/Hz at 1 MHz offset frequency. Similarly, the Quadrature VCO (QVCO) covers 42% tuning bandwidth around 25 GHz oscillation frequency, which is significantly wider than other state-of-the-art VCOs at comparable frequencies. In addition, all the oscillators are designed in class-C to further improve their performances both in term of low power and low phase noise. The presented oscillators are designed using high-performance SiGe HBTs of the GlobalFoundries (GFs) 130 nm SiGe BiCMOS 8HP process. The presented DVCO and QVCO draw currents of approximately 10 mA and 21 mA, respectively from a 1.2 V supply.

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20

Amy, SW, and MI Large. "A Simple Microstrip Phase Shifter." Australian Journal of Physics 45, no. 1 (1992): 105. http://dx.doi.org/10.1071/ph920105.

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A novel, inexpensive, series-connected loaded-line (SCOLL) phase shifter has been developed for the Molonglo Observatory Synthesis Telescope. The phase shifter, which operates at 0�843 GHz, consists of a ",3>'/8 length of microstrip with series connected varactors at each end. Although designed as a binary phase shifter, the insertion phase varies almost linearly with varactor reactance, with very little gain variation for phase ranges up to 90�. Thus, driven by a digital-to-analogue (D/ A) converter, a SCOLL becomes a programmable phase shifter of any desired resolution. The same technique would be suitable for narrow-band low power applications in the frequency range 0�1 to 10 GHz. This paper gives the basic theory of SCOLL phase shifters, a design chart, construction details and performance data.

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21

Peikert, T., J. K. Bremer, and W. Mathis. "Modellierungskonzept für MOS Varaktoren zur Minimierung der AM-FM Konversion in VCOs." Advances in Radio Science 8 (October 1, 2010): 143–49. http://dx.doi.org/10.5194/ars-8-143-2010.

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Abstract. In dieser Arbeit wird ein analytisches Simulationsmodell für MOS Varaktoren zur Entwurfsunterstützung von integrierten CMOS LC-Tank VCO-Schaltungen präsentiert. Das analytische Simulationsmodell wurde auf Basis des EKV-Transistormodells implementiert und beinhaltet ausschließlich Design- und Prozessparameter für die Berechnung der Varaktorkapazität. Dieses Simulationsmodell ermöglicht es, die verwendeten Varaktoren im Vorfeld des VCO-Entwurfs zu dimensionieren, die effektive Großsignalkapazität in Abhängigkeit des Ausgangssignals zu berechnen und einzelne Eigenschaften der Varaktoren, wie z.B. das AM-FM Konversionsverhalten zu optimieren. Die Gültigkeit des vorgestellten analytischen Simulationsmodells zur Beschreibung der Varaktorkapazität in CMOS LC-Tank VCOs, wird anhand von Spectre (Cadence) Simulationen auf Basis eines 0.25 μm CMOS Prozesses der Firma IHP (SGB25) und eines 0.35 μm CMOS Prozesses der Firma AMS (C35) verifiziert. In this work an analytical simulation model for MOS varactors, that can be used in a systematically VCO design flow, is presented. The simulation model is based on the EKV transistor model and includes only design and process parameters of the used CMOS technology. The proposed simulation model allows calculating the required design parameters and the effective large signal capacitance of the varactors incorporated into the VCO as a function of the output signal of the VCO. Based on the expression for the effective large signal capacitance it is possible to optimize the AM-FM conversion behavior of the used varactors. The validity and accuracy of the simulation model is verified by Spectre simulations which are based on a 0.25 μm CMOS process (SGB25) from the company IHP and a 0.35 μm CMOS process (C35) from the company AMS. The simulation results show a good accordance in all transistor operating regions for NMOS varactors as well as PMOS varactors.

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22

Shi, Shengnan, Zizhao Chai, Shan Zhang, Yanpeng Shi, and Yifei Zhang. "A Tunable Frequency Selective Rasorber with Broad Passband and Low Transmission Loss at X-Band." Materials 16, no. 17 (August 24, 2023): 5787. http://dx.doi.org/10.3390/ma16175787.

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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.

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23

Guo, Ying Jiang, Xiao Hong Tang, and Kai Da Xu. "Electronically Reconfigurable Notch Filter for Cognitive Radios Application." Journal of Computational and Theoretical Nanoscience 13, no. 10 (October 1, 2016): 6901–5. http://dx.doi.org/10.1166/jctn.2016.5645.

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An electronically reconfigurable notch filter for cognitive radios application is presented. By loading the stub-loaded resonator along the transmission line, two notched bands are created. Central frequency tuning of one notched band is realized by using the silicon varactor diodes, while the other notched band remains almost unchanged during tuning. Bias Ts and the resistors having high resistance value are adopted to function as DC paths for the varactors. A tuning range of 1.92–2.92 GHz for the one notched band with average insertion loss 2.4 dB across the passband (0.1–5 GHz) is achieved, and the other notched band is used to suppress the WiMAX signal (3.3– 3.8 GHz). The highest rejection level of the tunable notched band is 21.5 dB, while the static notched band shows rejection of more than 30 dB at 3.66 GHz.

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24

Jaafar Qassim Kadhim and Adheed H. Sallomi. "Design and Implementation Unit Cell for 6G Reconfigurable Intelligent Surface Application." International Journal of Online and Biomedical Engineering (iJOE) 19, no. 05 (April 27, 2023): 163–71. http://dx.doi.org/10.3991/ijoe.v19i05.37585.

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This article presents a model through which the reflection coefficient amplitude as well as phase of reflective intelligent surfaces can be estimated accurately. The reconfigurability of the surface was achieved by incorporating the varactor diodes into the surface of the cell unit. The manipulation of the phase of the reflection coefficient can be achieved by making adjustments to the biasing state of the varactors. The model, which makes use of a physics-based methodology and is based on a transmission-line circuit description of the Reconfigurable Intelligent surfaces (RIS) unit cells, considers every pertinent electrical and geometrical characteristics of the proposed surface. With the method proposed in this paper, fast and accurate RIS-based communication lines can be created. The recommended accuracy of the proposed method was confirmed through the use of a CST microwave studio full-wave simulations.

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25

Fang, Shaojun, Xiaojian Guo, Hongmei Liu, and Zhongbao Wang. "A Tunable Planar Balun with an Isolation Circuit Using Varactors Loaded Coupled Lines." Electronics 9, no. 3 (February 28, 2020): 401. http://dx.doi.org/10.3390/electronics9030401.

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In this paper, a frequency tunable planar balun composed of varactors loaded coupled lines (VL-CLs) is presented. By tuning the capacitances of the varactors, a wide frequency tuning range is obtained. Moreover, good impedance match, balanced output ports amplitude, and consistent output ports phase difference (PD) are maintained during the tuning. A detailed theoretical analysis using the signal flow diagram and the even-odd mode method is presented to clarify the characteristics of the proposed balun. To achieve ideal output matching and isolation for the proposed balun, a novel frequency tuned isolation circuit (IsC) is designed and connected to the balun. In theory, a frequency tuning range of 200% can be realized. In practice, due to the limited capacitances of the varactors, a prototype with a tunable frequency of 1.0 GHz ~ 2.0 GHz (66.7%) is designed, fabricated, and measured. The measured results show that more than21 dB of return loss (RL), 180° ± 1.8° of phase difference, 0.43 dB of amplitude imbalance (AP), and 22 dB of isolation are obtained at all tuning center frequencies, agreeing well with the simulated results.

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26

Ghavanini, Farzan A., Peter Enoksson, Stefan Bengtsson, and Per Lundgren. "Vertically aligned carbon based varactors." Journal of Applied Physics 110, no. 2 (July 15, 2011): 021101. http://dx.doi.org/10.1063/1.3583536.

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27

Pu, Suan Hui, Andrew S. Holmes, Eric M. Yeatman, Christos Papavassiliou, and Stepan Lucyszyn. "Stable zipping RF MEMS varactors." Journal of Micromechanics and Microengineering 20, no. 3 (March 1, 2010): 035030. http://dx.doi.org/10.1088/0960-1317/20/3/035030.

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28

Chicherin, Dmitry, Mikael Sterner, Dmitri Lioubtchenko, Joachim Oberhammer, and Antti V. Räisänen. "Analog-type millimeter-wave phase shifters based on MEMS tunable high-impedance surface and dielectric rod waveguide." International Journal of Microwave and Wireless Technologies 3, no. 5 (October 2011): 533–38. http://dx.doi.org/10.1017/s1759078711000821.

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Millimeter-wave phase shifters are important components for a wide scope of applications. An analog-type phase shifter for W-band has been designed, analyzed, fabricated, and measured. The phase shifter consists of a reconfigurable high-impedance surface (HIS) controlled by micro-electromechanical system (MEMS) varactors and placed adjacent to a silicon dielectric rod waveguide. The analog-type phase shift in the range of 0–32° is observed at 75 GHz whereas applying bias voltage from 0 to 40 V to the MEMS varactors. The insertion loss of the MEMS tunable HIS is between 1.7 and 5 dB, depending on the frequency.

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Sudheendran, K., and K. C. James Raju. "Realization of Tunable Varactors Using Bi_1.5Zn_1.0Nb_1.5O₇ Thin Films." Key Engineering Materials 421-422 (December 2009): 153–56. http://dx.doi.org/10.4028/www.scientific.net/kem.421-422.153.

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Cubic pyrochlore bismuth zinc niobate thin films are known to exhibit voltage dependent dielectric properties. In this paper, we are demonstrating the fabrication and characterization of interdigital (IDC) and circular patch (CPC) capacitors using the pulsed laser deposited Bi1.5Zn1.0Nb1.5O7 (BZN) thin films on sapphire and platinised silicon substrates respectively. The IDCs fabricated are having 12 fingers of width 12 m each and separated by a gap of 8 m. The CPC are having circular patches with inner radius of 100 m and concentric ground plane with a radius of 300m. The electrical properties of these capacitors were characterized both at low frequencies and at microwave frequencies. The CPC varactors were having a tunability of 25% at 15 Volts. The calculated capacitance of the IDC varactor at 5.3 GHz with 0 V dc bias was 1.1 pF, which has got changed to 0.99 pF by the application of 30 Volts exhibiting a tunability of 10%.

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30

Wu, Wei, Yun-Bo Li, Rui-Yuan Wu, Chuan-Bo Shi, and Tie-Jun Cui. "Band-Notched UWB Antenna with Switchable and Tunable Performance." International Journal of Antennas and Propagation 2016 (2016): 1–6. http://dx.doi.org/10.1155/2016/9612987.

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A band-notched UWB antenna is presented, which can switch between two notch bands and tune the central frequency simultaneously. It is the first time that the switchable and tunable behaviours are combined together in band-notched UWB antennas. In the band-notched structure, PIN diodes are used to switch the lower and upper frequency bands, while varactors could vary the central frequency of each notch band continuously. Measurement results show that the notch bands could switch between 4.2 GHz and 5.8 GHz when the state of varactors is fixed, and the ranges of tuning are 4.2–4.8 GHz and 5.8–6.5 GHz when the state of PIN diodes is ON and OFF, respectively.

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31

MA, XUEPO, WEI ZHANG, and YANG LIU. "A FULLY INTEGRATED MULTI-BAND LCVCO BASED ON CMOS TECHNOLOGY." Journal of Circuits, Systems and Computers 19, no. 06 (October 2010): 1299–305. http://dx.doi.org/10.1142/s0218126610006694.

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In this paper, a cross-coupled complementary inductance–capacitance voltage controlled oscillator (LCVCO) with low phase noise and wide tuning range is presented. It has a multi-band topology and was fabricated with RF CMOS technology. For the purpose of lowering the K VCO and reducing the nonlinearities of varactors, the sizes of the varactors are set small. Also noise filtering technique is adopted to minimize up-conversion of the low frequency noise as well as down-conversion of the high frequency noise, thus the phase noise performance of the VCO is greatly improved. Simulation and experimental results indicate that the LCVCO displays a phase noise of -126.1 dBc at 900 kHz offset in worst case with a tuning range from 1.76 to 1.96 GHz.

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32

Kolberg, E. L., T. J. Tolmunen, M. A. Frerking, and J. R. East. "Current saturation in submillimeter-wave varactors." IEEE Transactions on Microwave Theory and Techniques 40, no. 5 (May 1992): 831–38. http://dx.doi.org/10.1109/22.137387.

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33

Qasrawi, A. F., Khalil O. Abu Muis, Osama H. Abu Al Rob, and A. Mergen. "Electrical characterization of Bi1.50-xYxZn0.92Nb1.5O6.92 varactors." Functional Materials Letters 07, no. 04 (August 2014): 1450044. http://dx.doi.org/10.1142/s1793604714500441.

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The electrical properties of yttrium doped bismuth zinc niobium oxide (BZN) pyrochlore ceramics are explored by means of temperature dependent electrical conductivity dielectric constant and capacitance spectra in the frequency range of 0–3 GHz. It is observed that the doped BZN exhibit a conductivity type conversion from intrinsic to extrinsic as the doping content increased from 0.04 to 0.06. The thermal energy bandgap of the intrinsic type is 3.45 eV. The pyrochlore is observed to exhibit a dielectric breakdown at 395 K. In addition, a negative capacitance (NC) spectrum with main resonance peak position of 23.2 MHz is detected. The NC effect is ascribed to the increased polarization and the availability of more free carriers in the device. When the NC signal amplitude is attenuated in the range of 0–20 dBm at 50 MHz and 150 MHz, wide tunability is monitored. Such characteristics of the Y-doped BZN are attractive for using them to cancel the positive parasitic capacitance of electronic circuits. The canceling of parasitic capacitance improves the high frequency performance of filter inductors and reduces the common mode noise of the resonance signal.

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34

Ingvarson, M., B. Alderman, A. O. Olsen, J. Vukusic, and J. Stake. "Thermal Constraints for Heterostructure Barrier Varactors." IEEE Electron Device Letters 25, no. 11 (November 2004): 713–15. http://dx.doi.org/10.1109/led.2004.836804.

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35

Li, Shuai, and Tao Zhang. "Simulation and Realization of MOS Varactors." Procedia Engineering 29 (2012): 1645–50. http://dx.doi.org/10.1016/j.proeng.2012.01.188.

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36

Kim, Jang-Yong, and Alexander M. Grishin. "Niobate-tantalate thin films microwave varactors." Thin Solid Films 515, no. 2 (October 2006): 619–22. http://dx.doi.org/10.1016/j.tsf.2005.12.212.

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37

Chen, H. C., and H. W. Chiu. "VCO with Miller theorem-based varactors." Electronics Letters 46, no. 14 (2010): 990. http://dx.doi.org/10.1049/el.2010.1014.

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38

Dillner, L., J. Stake, and E. L. Kollberg. "Heterostructure barrier varactors on copper substrate." Electronics Letters 35, no. 4 (1999): 339. http://dx.doi.org/10.1049/el:19990255.

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39

Dalay, �., and S. Akpinar. "Excess capacitance of ZnO-Au varactors." Applied Physics A Solids and Surfaces 42, no. 3 (March 1987): 249–55. http://dx.doi.org/10.1007/bf00620609.

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40

Gaevski, Mikhail, Jianyu Deng, Remis Gaska, Michael Shur, and Grigory Simin. "GaN microwave varactors with insulated electrodes." physica status solidi (c) 11, no. 3-4 (February 2014): 853–56. http://dx.doi.org/10.1002/pssc.201300667.

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41

Du, Tiejun, Boran Guan, Pengquan Zhang, Yue Gu, and Dujuan Wei. "An Intrinsically Switched Tunable CABW/CFBW Bandpass Filter." Electronics 10, no. 11 (May 31, 2021): 1318. http://dx.doi.org/10.3390/electronics10111318.

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In this paper, a novel intrinsically switched tunable bandpass filter based on a dual-mode T-shaped varactor-loaded resonator is presented. The varactors loaded in the T-shaped resonator are capable of efficiently tuning the resonant frequencies of the even and odd modes, as well as the transmission-zero frequency. Without any additional RF switches, the passband of the filter can be intrinsically switched off by adjusting the transmission zero to the resonant frequencies. In the switch-on state, the constant absolute bandwidth (CABW) or constant fractional bandwidth (CFBW) passband can be achieved by controlling the frequency space between the two resonances. For a demonstration, a 0.8–1.1 GHz intrinsically switched tunable bandpass filter with 74 MHz CABW or 8.5% CFBW was fabricated and tested. In the whole operating band with |S11| < 10 dB, the insertion losses for CABW and CFBW are better than 3.3 dB and 3 dB, respectively, and the isolations are better than 20 dB in the switch-off state. The measured results have a good agreement with simulated results, which verifies the design theory.

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42

Feng, Kui-Sheng, Na Li, and Tong Li. "Ultra-thin ultra-wideband tunable radar absorber based on hybrid incorporation of active devices." Acta Physica Sinica 71, no. 3 (2022): 034101. http://dx.doi.org/10.7498/aps.71.20211254.

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Structural radar absorber has important application in stealth field for its ability to effectively absorb incoming radar wave and to bear the load at the same time. Metasurface absorbers can achieve nearly-perfect absorption of radar wave, and have characteristics of light weight and thin structure, but their bandwidth are usually narrow. To solve this problem, a new method of broadening the bandwidth of metasurface absorber is proposed in this work. With varactor and PIN diode integrated in a hybrid manner, the continuous tunning and discrete switching are combined together to broaden the effective absorption bandwidth of the absorber. Using this method, an ultra-wideband tunable metasurface absorber is designed and the absorbing mechanism is analyzed in depth. By changing the bias voltages of PIN diodes and varactors, the absorbing frequency can be continuously tuned within a wide band from 4.57 GHz to 8.51 GHz. Measured results verify the low radar cross section characteristics of the absorber and the effectiveness of the design method. The proposed method is simple and feasible, and can be extended to other broadband structure design.

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43

Xie, Shaoyi, Jiawei Li, Guangjian Deng, Jiaxin Feng, and Shaoqiu Xiao. "A Wide-Angle Scanning Leaky-Wave Antenna Based on a Composite Right/Left-Handed Transmission Line." Applied Sciences 10, no. 6 (March 11, 2020): 1927. http://dx.doi.org/10.3390/app10061927.

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This paper presents a frequency-independent, wide-angle scanning leaky-wave antenna (LWA), based on the composite right/left-handed transmission line (CRLH TL). The proposed LWA consists of a coplanar waveguide-grounded (CPWG) structure loaded by varactors. Loaded varactors are used to control the phase constant of the fundamental mode of the LWA by adjusting the applied DC voltage. The LWA has an excellent wide-angle scanning capability, a simple structure, and low cost. Results show that the main beam of an LWA with 20unit cells can scan from −66° to 62° at the operation frequency of3.0 GHz, with a peak gain of 9.9 dBi, and a gain fluctuation of less than 4.9 dB. The operation bandwidth and radiation efficiency are about 13% and over 50%, respectively. A 10-unit cascaded LWA prototype was designed, fabricated, and measured to verify the design concept.

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44

Wang, Bo, Le Zhao, Xiuhuai Jia, Pan Yang, and Shihui Yu. "Enhanced Tunability Achieving at Low Permittivity and Electric Field in (Ba0.91Ca0.09)(SnxZr0.2−xTi0.8)O3-2 mol% CuO-1 mol% Li2CO3 Ceramics." Materials 16, no. 15 (July 25, 2023): 5226. http://dx.doi.org/10.3390/ma16155226.

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Ferroelectric varactors should have high tunability at low permittivity and a working electric field to obtain better impedance matching and stable tunability. In this work, (Ba0.91Ca0.09)(SnxZr0.2−xTi0.8)O3-2 mol% CuO-1 mol% Li2CO3 (abbreviated as BCSZT100x, x = 0.05, 0.10, 0.15 and 0.20, respectively) are prepared to achieve high tunability at low permittivity and a working electric field. The tunable mechanisms are investigated based on crystal structure, micro-morphology and the permittivity-temperature spectrum. The results show that the shrink of oxygen octahedron and weaker interaction force between Sn4+ and O2− make BCSZT5 ceramic have a higher tunability value of 26.55% at low permittivity (1913) and a working electric field (7.3 kV/cm). The tunability value of BCSZT5 ceramic increases by 58%, while its permittivity decreases by 25%, compared with x = 0. Those advantages make BCSZT5 ceramic have substantial application prospects in varactors.

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45

Huang, Cong, Lawrence E. Larson, Lis K. Nanver, Leo C. N. de Vreede, Francesco Sarubbi, Milos Popadic, Koen Buisman, et al. "Enabling Low-Distortion Varactors for Adaptive Transmitters." IEEE Transactions on Microwave Theory and Techniques 56, no. 5 (May 2008): 1149–63. http://dx.doi.org/10.1109/tmtt.2008.921679.

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46

Kozyrev, A., V. Keis, O. Buslov, A. Ivanov, O. Soldatenkov, V. Loginov, A. Taricin, and J. Graul. "Microwave properties of ferroelectric film planar varactors." Integrated Ferroelectrics 34, no. 1-4 (February 2001): 271–78. http://dx.doi.org/10.1080/10584580108012897.

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47

JAMIL, ASAD, T. S. KALKUR, and N. CRAMER. "VOLTAGE-CONTROLLED OSCILLATOR DESIGN USING FERROELECTRIC VARACTORS." Integrated Ferroelectrics 81, no. 1 (August 17, 2006): 157–63. http://dx.doi.org/10.1080/10584580600660348.

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48

Kozyrev, A., A. Ivanov, A. Prudan, O. Soldatenkov, E. Hollmann, V. Loginov, D. Ginley, and T. Rivkin. "Microwave phase shifter employing srtio3 ferroelectric varactors." Integrated Ferroelectrics 24, no. 1-4 (August 1999): 287–95. http://dx.doi.org/10.1080/10584589908215598.

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49

Maleev, N. A., M. A. Bobrov, A. G. Kuzmenkov, A. P. Vasil’ev, M. M. Kulagina, Yu A. Guseva, S. A. Blokhin, and V. M. Ustinov. "Heterobarrier Varactors with Nonuniformly Doped Modulation Layers." Technical Physics Letters 45, no. 10 (October 2019): 1063–66. http://dx.doi.org/10.1134/s1063785019100250.

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50

Sun, J. P., R. K. Mains, W. L. Chen, J. R. East, and G. I. Haddad. "C‐VandI‐Vcharacteristics of quantum well varactors." Journal of Applied Physics 72, no. 6 (September 15, 1992): 2340–46. http://dx.doi.org/10.1063/1.352322.

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