Capacitance Of Varactor Diode Research Articles

Pattern-reconfigurable integrated array antenna based on a coding metasurface.

An electrically tunable pattern-reconfigurable integrated array antenna based on a 1-bit digital coding metasurface is proposed in this paper. The array antenna consists of 8 × 8 unit cells which is divided into the radiation antenna and the phase control metasurface. The rectangular microstrip patch antenna is used as the radiation source. The phase control metasurface includes three stacked layers of square slot units loaded with varactor diodes and a biasing circuit layer. The metasurface regulates the transmission phase of the quasi-plane wave generated by the radiation antenna. The pattern reconfigurability is achieved by switching coding sequences of the metasurface which can be regulated by the capacitance of varactor diodes. The measured results show the design has the capability of pencil-beam radiation, beam deflection, and multi-beam radiation at 5 GHz. The proposed array antenna preserves the coding metasurface without requiring the additional horn antenna. This highly integrated design is more concise and reduces the profile height. This article offers what we believe is a new method for the design of high integration, multi-unit, and electrically tunable reconfigurable array antenna.

A design of impedance transformer with tunable center frequencies using filter synthesis approach

Microwave impedance transformer (IT) with center frequency tunable capability is one of great research issue for better utilization of frequency spectrum resources and system miniaturization of next generation wireless communication systems. This article presents a filter synthesis approach for designing IT with center frequency tunable capability using single dc-bias controlled tunable resonators. The proposed IT provides bandpass filtering response and is designed by properly coupling quarter-wave tunable resonators with alternate J- and K-inverters. The J-inverters are realized using a parallel-coupled line, whereas K-inverter is implemented with T-type short-circuited TL. Using filter theory, analytical design equations are derived to calculate the circuit parameters. The center frequency of the proposed IT is tuned over a wide frequency tuning range (FTR) by changing the varactor diode capacitance of quarter-wave resonators. For experimental demonstration, a prototype of 25-to-50 Ω IT is designed, simulated, and measured. The measured results confirmed that the center frequency of the proposed IT is tuned from 2.05 to 2.91 GHz (860 MHz or 34.68% FTR) with an insertion loss variation of 2.57 to 1.76 dB.

Frequency tunable circularly polarized antenna with branch line coupler feed network for wireless applications

In this article, frequency tuning and circularly polarized concentric circular microstrip antenna is investigated. The proposed antenna consist of varactor diode for frequency tuning and branch line coupler (BLC) feed network to achieve the circular polarization (RHCP/LHCP). By changing the varactor diode capacitance between 12.33 pF (0 V) to 1.30 pF (15 V) attain the frequency tuning (2.34-2.68 GHz). The right hand circular polarization (RHCP) and left hand circular polarizations (LHCP) are realized in the antenna through BLC feed network output ports. The impedance bandwidth (2.05-3.13 GHz) of BLC feed network is well-matched with the circular microstrip antenna frequency tunable bandwidth. The proposed antenna is fabricated, and simulated results are verified using the mathematical modeling and experimental verification.

In‐band phase deviation minimization method for wideband tunable phase shifter

AbstractThis article provides a novel approach to analyze and design wideband tunable reflection‐type phase shifter (RTPS) with low in‐band phase deviation (IBPD) error. The proposed RTPS consists of coupled lines where through and coupled ports are terminated with varactor diodes. The coupled lines can minimize the parasitic elements of varactor diode to achieve high phase shift range (PSR). In addition, the measured frequency‐dependent capacitance of varactor diode was used in the analytical analysis to obtain minimum IBPD error and high PSR. For experimental demonstration, phase shifter was fabricated at the center frequency of 2.5 GHz. The measured results show that the fabricated circuit achieved 126.85° PSR with ±6.48° IBPD error for 500 MHz bandwidth (BW). In addition, the measured maximum insertion loss variation and input/output return losses are within ±0.34 dB and higher than 16.85 dB within 500 MHz BW, respectively.

Electronically switchable compact quad-band microstrip bandpass filter using varactor perturbed dual-mode resonators

In this paper, an electronically switchable quad-band microstrip bandpass filter is designed using varactor perturbed dual-mode resonators. For this purpose, four meandered dual-mode square loop resonators (DMSLRs) having reference patches are nested and varactor diodes are used to serve as perturbation elements. The designed resonator is analyzed by deriving even/odd mode resonance conditions. S-parameters are also calculated according to the even and odd mode input impedances. Stub loaded feedlines are used to couple the DMSLRs to Input/Output (I/O) ports. According to the capacitances of varactor diodes, each passband can be independently turned on and off. Coupling scheme and coupling matrix of the designed filter are introduced to realize the coupling descriptions. Switching operations are also investigated over the frequency responses obtained from coupling matrix. Passbands of the filter are adjusted to 1.4, 1.7, 2.25, and 2.7 GHz. The designed filter was also fabricated and measured results show a good agreement with the simulated and theoretical results.

Dual‐mode dual‐band microstrip bandstop filter design with independently tunable center frequencies

AbstractIn this article, a novel dual‐mode dual‐band bandstop filter design with independently tunable center frequencies is presented by using dual‐mode square loop resonators. Tuning operation can be achieved with a constant fractional bandwidth. Varactor diodes are used instead of perturbation and reference elements. Two dual‐mode square loop resonators in different electrical lengths are coupled to a transmission line connecting input and output ports. Center frequencies of both stopbands can be independently tuned by changing the capacitances of varactor diodes of both perturbation and reference elements. While the perturbation and reference varactors tune even mode resonance frequency together, odd mode resonance frequency can only be tuned by reference varactors. The designed filter was also fabricated for the experimental studies and it exhibits acceptable tunability operations in measurements. Center frequencies of the first and second stopbands can be tuned between 2.2 and 2.54 GHz and between 3 and 3.38 GHz, respectively. Rejection levels for both stopbands were obtained as better than −13 dB in the whole tuning range.

Reconfigurable-focus flat lens based on gradient index metamaterials

We propose a reconfigurable-focus flat lens based on a gradient index metamaterial, which is composed of metal hole arrays incorporated with varactor diodes and is able to transform a plane wave into a cylindrical wave. The transmission phase of each metal hole array is modified by changing the width of the rectangular holes. With the gradient transmission phase along the lateral direction of a flat lens, a plane wave can be transformed into a cylindrical wave. By delicately designing the capacitance of varactor diodes, the focus length of a flat lens can be reconfigured by 1.3 cm. Furthermore, the focusing performance of a flat lens is still preserved for oblique incidence.

곡면 재구성 주파수 선택막의 투과특성

In this paper, the flexible and reconfigurable frequency selective surface for C-band was designed using patch array and grid structure for radome and other curved surface applications. Frequency reconfigurability was obtained by varying the capacitance of varactor diode and flexibility is implemented by using flexible PCB. For the validity of the proposed structure, we fabricated the flexible and reconfigurable frequency selective structure and measured the frequency reconfigurability for different bias voltages and different curvature surfaces from the optimized design parameters. From the measurement results, we know that the proposed structure has the wideband reconfigurable frequency bandwidth of 6.05-7.08GHz. We can apply this proposed structure to the curved surface like as radome of aircraft or warship.

Wide-Range Varactor-Tuned Terahertz Oscillator Using Resonant Tunneling Diode

We propose a wide-range varactor-tuned terahertz oscillator using a resonant tunneling diode (RTD) and estimate the tuning range. In a slot antenna, a varactor diode is placed in parallel with an RTD and can be operated with different bias voltages. Frequency tuning is possible by changing the varactor-diode capacitance with the bias voltage. A wide frequency tuning range >200 GHz (500 to 740 GHz) is obtained with an oscillator with a 20-μm-long antenna, 1.3-μm2 RTD mesa, and 16-μm2 varactor-diode mesa by electromagnetic-field analysis including a varactor-diode model.

Compact UWB Antenna With Tunable Band-Notched Characteristic Based on Microstrip Open-Loop Resonator

A compact ultrawideband (UWB) antenna with an electronically tunable notched band is proposed for UWB communication applications. The proposed antenna utilized a C-shaped ground to realize miniaturization and a pair of open-loop resonators (OLRs) to create notched band. The center frequency of the notched band can be electronically tuned by changing the effective electrical length of the OLRs, which is achieved by employing varactor diodes. A prototype with an overall size of 24 × 28 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was constructed, and good agreement has been obtained between simulation and measurement. The experimental results show that, for a varactor diode capacitance approximately ranging from 0.63-2.67 pF, a continuous tuning notched band range from 5.1 to 5.9 GHz is achieved.

A Compact Frequency-Reconfigurable Metamaterial-Inspired Antenna

Adding frequency reconfigurability to a compact metamaterial-inspired antenna is investigated. The antenna is a printed monopole with an incorporated slot and is fed by a coplanar waveguide (CPW) line. This antenna was originally inspired from the concept of negative-refractive-index metamaterial transmission lines and exhibits a dual-band behavior. By using a varactor diode, the lower band (narrowband) of the antenna, which is due to radiation from the incorporated slot, can be tuned over a broad frequency range, while the higher band (broadband) remains effectively constant. A detailed equivalent circuit model is developed that predicts the frequency-tuning behavior for the lower band of the antenna. The circuit model shows the involvement of both CPW even and odd modes in the operation of the antenna. Experimental results show that, for a varactor diode capacitance approximately ranging from 0.1-0.7 pF, a tuning range of 1.6-2.23 GHz is achieved. The size of the antenna at the maximum frequency is 0.056 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.047 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and the antenna is placed over a 0.237 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.111 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> CPW ground plane (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> being the wavelength in vacuum).

ASK modulator for 900‐MHz RFID system with defected ground structure

AbstractIn this article, an amplitude shift keying (ASK) modulator with defected ground structure (DGS) is proposed for UHF radio frequency identification (RFID) system. Proposed variable DGS resonator with a varactor diode will be able to adjust the resonance frequency to achieve the ASK modulation. The variable resonance characteristics can be obtained by controlling capacitance of varactor diode, placed on the defected ground. To clarify corresponding method, we manufactured RFID system board using variable DGS resonator and measured the corresponding performance. As almost 93% of extracted data from modulation index characteristic is satisfied with both EPC class‐1 Gen2 Type‐B and Type‐C standard protocols, we obtained stable tag response of RFID system. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2513–2516, 2007; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.22760

Analysis of symmetric varactor frequency multipliers

We investigate efficiency limitations of frequency multipliers with the use of a simple model for symmetric varactors. Our calculations show that the conversion efficiency is improved for a C(V) shape with large nonlinearity at zero volt bias. For quintuplers, the optimal embedding impedance at the third harmonic is an inductance in resonance with the varactor diode capacitance. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 26–29, 1997.

Accurate Determination of Varactor Resistance at UHF and Its Relation to Parametric Amplifier Noise Temperature

A thorough investigation is made on the frequency-dependent properties of a varactor diode loss resistance at UHF. The variation of the losses with frequency in a varactor diode mounted cavity has been theoretically investigated, and it is shown that the previously reported inverse-squared frequency dependence of the varactor loss resistance can be attributed to the distributed cavity losses transformed across the varactor diode. A new measurement technique is introduced in which the circuit losses are first matched to the input line instead of the varactor loss resistance as an application of the relative impedance method. Measurements carried out with this technique for five different varactor diodes showed that the loss resistances of these diodes are not frequency dependent. It is also shown that the choice of the varactor diode capacitance plays an important role on the parametric amplifier noise temperature at UHF. In an experimental parametric amplifier the effect of varactor diode capacitance on the noise temperature has been demonstrated. It has been theoretically and experimentally shown that, generally, varactor diodes having higher capacitances result in better noise temperature at UHF.

Relation between amplification and bandwidth of parametric travelling-wave amplifiers using varactor diodes

The paper discusses parametric travelling-wave amplifiers whose wave-guide has the character of a band-pass filter. For two band-pass structures of practical importance which contain as lumped capacitances merely the basic capacitances of varactor diodes, the maximum product is estimated of the gain per diode at the mid-band frequency by the relative bandwidth that can be attained with parametric travelling-wave amplification. It is assumed that the mid-band frequency of the amplifying action equals half the pump frequency, that it is at the centre of the pass-band of the band-pass guide, and that the bandwidth of the amplifying action agrees with the bandwidth of the band-pass guide. It is further assumed that the amplitude of the controlled diode capacitance variation is 50% of the basic diode capacitance. A maximum of about 2 dB per diode results for the aforementioned product which we term “effectiveness”. Unlike the bandwidth-gain product of conventional amplifiers, it is thus for the here discussed parametric travelling-wave amplifiers no longer the absolute, but the relative bandwidth which is representative. Effectiveness values of about 0·5 to 1·4 dB per diode can be gathered from existing experimental results of the author and others.