Single Varactor Diode Research Articles

Varactor-Based Tunable Sensor for Dielectric Measurements of Solid and Liquid Materials

In this article, a tunable RF sensor is presented for the measurement of dielectric materials (liquids and solids) based on a metamaterial resonator. The proposed novel configuration sensor has a microstrip line-loaded metamaterial resonator with tunable characteristics by utilizing a single varactor diode in the series of the resonator. CST Microwave studio is employed for 3D simulations of the tunable sensor, and the desired performance is attained by optimizing various structural parameters to enhance the transmission coefficient (S21 magnitude) notch depth performance. The proposed RF sensor can be tuned in L and S-bands using the varactor diode biasing voltage range of 0–20 V. To validate the performance of the sensor, the proposed design has been simulated, fabricated, and tested for the dielectric characterization of different solid and liquid materials. Material testing is performed in the bandwidth of 1354 MHz by incorporating a single metamaterial resonator-based sensor. Agilent’s Network Analyzer is used for measuring the S-parameters of the proposed sensor topology under loaded and unloaded conditions. Simulated and measured S-parameter results correspond substantially in the 1.79 to 3.15 GHz frequency band during the testing of the fabricated sensor. This novel tunable resonator design has various applications in modulators, phase shifters, and filters as well as in biosensors for liquid materials.

Dual-Layer Beamscanning Reflectarray Antenna Operating at Ku-Band

This paper presents a beam scanning electronically reconfigurable reflectarray configuration for Ku-band applications using a single varactor diode. A 15×15 center-fed reconfigurable reflectarray antenna is designed consisting of 225 octagonal shaped unit cells. The proposed tunable element has a unit cell size of 9.8 mm, developed on a 1.575 mm thick Taconic TLY-5 substrate. A single varactor diode is integrated with the tunable element to produce a reflection phase variation of 340° at 14.1 GHz. In this work, both the varactor and biasing circuit are placed beneath the substrate to avoid unexpected reflections, which leads to achieving a pencil beam of 8.1° beamwidth. The simulation results of the reconfigurable reflectarray antenna (RRA) shows good beam-scanning radiation performance of scanning range ±30° and a peak gain of 27.6 dBi. This structure provides a convenient solution for Ku-band distinctive applications like uplink operation in the direct broadcast satellite system, digital video broadcasting, earth exploration satellites, space research satellites, and defense systems.

Ultra‐miniaturized tunable slot‐based antenna design for 5G IoT applications

AbstractThis paper demonstrates a compact‐size folded slot‐based antenna suitable for internet‐of‐things (IoT) applications. The antenna is composed of a folded structure meandered slot loaded with varactor diode. The novel combination of the slot and varactor diode, reactively loading the slot, lead to highly miniaturized antenna. The presented antenna operates in dual frequency bands: from 730 to 965 MHz and 1250 to 1940 MHz. Continuous frequency sweep over the two bands is achieved by the use of a single varactor diode. Due to antenna compact size, it is highly suitable for 5G IoT applications. The total board dimensions of the proposed design are 27 mm × 27 mm.

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.

Reconfigurable fractal microstrip antenna with varactor diode

In this article, a rhombus shaped fractal microstrip frequency reconfiguration patch antenna is presented. The proposed antenna depending upon the capacitance value of varactor diode resonates at ten distinct frequencies as follows: 1.375GHz, 1.525GHz, 1.725GHz, 2.45GHz, 3.45GHz, 4GHz, 5.3GHz, 5.45GHz, 5.5GHz and 5.825GHz. Design and optimization of microstrip antenna with analysis for different capacitance values of varactor diode is carried out using IE3D simulation tool. The proposed design is realized using FR4 (Dielectric constant εr = 4.4) substrate with dimension (41 × 41 × 1.6) mm3. A single varactor diode inserted upon the slot is used to switch the operating frequency. The proposed design of antenna, both simulated and fabricated is seen to have close agreement, and is appropriate to be used in L, S and C band applications.

A Nonlinear Transmission Line Technique for Generating Efficient and Low-Ringing Picosecond Pulses for Ultrabroadband and Ultrafast Systems

This paper presents a nonlinear transmission line (NLTL)-based scheme to develop an efficient and low-ringing picosecond pulse generator for ultrabroadband and ultrafast system applications. The proposed NLTL scheme stems from a unique combination of single varactor diode and stacked varactor diode per NLTL cell, which is designed to exploit a significant effect of non-linearity in connection with the varactor diode. This technique generates a higher compression factor in both rise and fall time of NLTL circuits in comparison to single varactor diodes per NLTL section. This scheme is validated to work well in a triple-stacked NLTL topology by maximizing the compression factor. Two pulse generators are then developed based on the proposed concept, where a mixed SRD topology is used for gaussian pulse generation and integrated with a triple-stacked NLTL. This achieves shorter pulse durations and a higher compression capability. The use of NLTLs with triple-stacked varactor diodes in a cell is also explored theoretically and is shown to maximize the compression capability by effectively increasing the punch through, turn-on, and break down voltages. Theoretical development and simulation of two triple-stacked NLTLs based on the rise and fall time-compression are provided, and final experimental prototypes for pulse generators are fabricated and measured. It is found from measurements that the full-width half maximum (FWHM) of the rise time-compression-based pulse generator is almost 15.78ps with a ringing level of -11.29dB, while the FWHM of the fall time-compression-based pulse generator is almost 17ps with a ringing level of -8.43dB. Finally, these pulse generators are compared with the current states of the art in terms of the implemented scheme, pulse duration, FWHM, pulse shapes, and detailed ringing level. The reconfigurable capability of the pulse generators is also briefly explored, and it is shown that the proposed pulse generators can easily be reconfigured between gaussian and monocycle pulse shapes. The power spectrum of the proposed pulse generators is also presented. It is found that they are well suitable for ultra-broadband and ultrafast systems, such as Impulse Radar Ultrawideband (IR-UWB) applications, due to higher pulse compression capability, ease of integration, flexible pulse tunability, and modification to higher order gaussian waveforms.

Compact single‐varactor diode frequency‐reconfigurable microstrip patch antenna

A single-varactor frequency-reconfigurable microstrip patch antenna is presented. The antenna comprises a symmetrical arrangement of four metallised patches coupled and interconnected via slots and metallic bars, respectively. The antenna structure is excited through a single feed probe connected to one of the patches. To achieve a compact size of 22 × 21 × 1.57 mm, a shorting pin is placed close to the feed point to pull down the antenna's resonant frequency. By adding a varactor diode at the centre of the patch, frequency reconfigurability is introduced. Variation in the varactor's DC reverse bias voltage from 0 to 7.5 V results in a corresponding resonant frequency shift from 1000 to 1150 MHz, thus providing a tuning range of 15%. The proposed design is compact and achieves frequency reconfiguration with a single-varactor diode and a low bias voltage requirement compared with the design characteristics reported in existing works. The antenna can find application in various existing and emerging communication systems.

Reconfigurable SIW-Based Leaky-Wave Antenna Composed of Longitudinal Cells

A novel fixed frequency beam-steering leaky-wave antenna (LWA) is presented in this manuscript. Radiation occurs through thin offset longitudinal slots etched on a substrate integrated waveguide (SIW). The beam-steering is achieved by implementing GaAs varactor diodes on the backside of the antenna. Sweeping the bias voltage from 1V to 15V causes the phase constant variation, leading to the 25° beam-steering at 28.5 GHz. The key novelties of the proposed reconfigurable antenna are the low-profile and electronic beam-steering capability using a single varactor diode per cell located on the antenna's backside. Moreover, placing the components on the backside reduces the unwanted blockage effects on the radiation. The antenna's thickness, length, and width are 0.32 mm, 95 mm, 24 mm, respectively. The measured peak realized gain of the proposed antenna at 28.5 GHz is 9 ± 0.8 dBi. Low-profile, small gain variation, ease of fabrication, and electronic beam-steering capability make the proposed LWA suitable for the 5G beam-steering applications. A detailed sensitivity analysis along with the experimental validations were performed to prove the validity of the proposed novel design.

TUNABLE TRIPLE BAND-NOTCHED UWB ANTENNA USING SINGLE EBG AND VARACTOR DIODE

TUNABLE TRIPLE BAND-NOTCHED UWB ANTENNA USING SINGLE EBG AND VARACTOR DIODE

Delay-Sum Group Delay Controller With Low-Loss and Low-Phase Variation

This article presents a group delay controller (GDC) circuit based on the delay-sum method. The proposed circuit can potentially be employed in a self-interference cancellation circuit in full-duplex radio systems. The proposed GDC splits the input signal into two signals with different magnitudes and then combines them in-phase at the output port. Variable group delay can be achieved by changing the power ratio of the two signals. The power dividing ratio (PDR) is changed by employing a variable power divider/combiner (VPD/VPC). The resonant reflective loads substitute for a single varactor diode such that the limited PDR of the VPD/VPC does not degrade the group delay variation range of the GDC. The resonant load can provide infinite PDR by covering open to short susceptance. In addition, asymmetrically connecting the VPD and VPC provides a flatter group delay response. As a result, the delay-sum method enables the proposed GDC to provide low and constant insertion loss while providing low insertion phase variation. The proposed delay sum GDC is demonstrated at 2.5 GHz. The measured insertion loss is only 2.18± 0.28 dB with a continuously controlled relative group delay of 430 ps. Furthermore, the insertion phase variation is only 7.3° at 2.5 GHz, and input/output matchings are maintained for all delay settings.

Design of a continuously tunable reflectarray element for 5G metrology in the k-band

Abstract. We introduce a new tunable reflectarray element for an operation frequency of 26 GHz in the k-band. It is shown that a 340∘ continuous tunning range of the reflected wave can be accomplished by using an aperture-coupled patch antenna with only one single varactor diode. The simplified design and the small needed space make it usable for k-band reflectarrays with many elements. The functionality of the reflectarray element is explained and the crucial parts are analyzed. The approach to get a full phase shift is discussed in detail. A bias-T is developed to provide the control voltage to the varactor diode without interfering with the high frequency path. The high frequency path and the DC-path are decoupled by 39 dB using a bias-T. A commercial off-the-shelf varactor diode is selected and its functionality at 26 GHz is verified. Therefore, a test printed circuit board with through, reflect, line standards is developed to de-embed the varactor diode and to evaluate it with a vector network analyzer. The reflectarray is simulated in a unit cell with plane wave excitation and periodic boundary condition using the simulation software package CST Microwave Studio™.

Dual Band Filter-Antenna with Fixed Low Band and Frequency-Agile High Band for Wireless Communications

This work proposes a design of compact filter-antenna with fixed and frequency-agile bands for wireless communications and cognitive radio (CR) systems. The filter-antenna is realized by attaching a bandpass filter with an independent fixed band and a tunable band to a UWB antenna. The dual bandpass filter consists of a folded open loop resonator loaded with single varactor diode at a suitable location to achieve reconfigurability operations for the high band while the low band remains fixed at 4.5 GHz. A reconfigurable broadband frequency range of 3.2 GHz from 7.8 to 4.6 GHz is achieved for the high band by changing the capacitance of the varactor from 0.16 to 2.25 pF, respectively. A prototype of the filter-antenna is fabricated and measured at a selected capacitance of 0.6 pF to verify the simulation results. Good agreements between simulated and measured results are obtained.

Split‐ring‐resonator‐loaded multiband frequency agile slot‐based MIMO antenna system

In this work, a compact quad-element multiple-input-multiple-output (MIMO) antenna system is proposed. The design consists of four annular slot-line based MIMO elements, printed on a commercially available RO4350 substrate with a total size of 60 × 120 × 0.76 m m 3 . Each annular slot has a rectangular slot inside it to increase its electrical length to further bring down the resonance frequency. Furthermore, a T-shaped defected ground structure is utilised to increase the isolation between the closely spaced antenna elements. Each element is loaded with a unique split ring resonator (SRR), which results in size reduction as well as multi-band operation covering 1.7–2.28, 2.35–2.85 and 2.9–3.1 GHz. Moreover, by using only a single varactor diode per element, fine frequency tuning over these bands is achieved. A wide frequency sweep over multi-band and a peak gain of 2.95 dBi with 82% maximum radiation efficiency is achieved. Low envelope correlation coefficient values are observed throughout the operating band, thus offering good MIMO performance. The overall planar antenna design is compact, low-profile and can easily be integrated with radio frequency front ends in second generation cognitive radios among many other applications.

Electronically Tunable Reflection Type Phase Shifters

This brief presents a low loss reflection-type phase shifter (RTPS) using a single varactor diode as the load. A parallel combination of an open-circuited stub and a varactor loaded stub are used at the load terminal. This arrangement greatly improves the response of the phase shifter. A transmission line based analysis shows real part of the load plays an important role on both phase variation and insertion loss. Based on the analysis, design guidelines are provided for controlling maximum insertion loss of the phase shifter. A prototype phase shifter is fabricated at 10 GHz. Measurement results of the RTPS show a relative phase variation of 190° with a maximum insertion loss of 2 dB when varactor capacitance is varied over 0.1 pF–0.2 pF. Moreover, the return loss is always better than 20 dB over the entire tuning range of the RTPS.

Compact Reconfigurable Band Notched UWB Cylindrical Dielectric Resonator Antenna Using Single Varactor Diode

This paper presents compact UWB cylindrical dielectric resonator antenna with reconfigurable band notch capability using single varactor diode. Theoretical results are achieved for the design with the range of frequencies 4-10.6 GHz. Using single varactor diode, different notch frequencies can be obtained using different capacitance values. The effect of changing the varactor position is also examined. A Wide range of notch frequencies can be achieved using this simple configuration, which covers most of coexisted narrow band systems. The notch frequency can be lower by increasing the capacitance value. Finite Element Method (FEM) and Finite Integration Technique (FIT) are hired to simulate the proposed antenna structure using HFSS and CST MWS respectively. The notch frequency covers the WLAN band when C=0.9 pF and covers the WiMAX band when the capacitance is changed to 0.8 pF for the same antenna configuration and varactor position. The antenna with DRA has a directive radiation pattern in E-plane and omnidirectional pattern in H-plane. Also, the gain is suppressed in the notched frequency. The group delay is nearly stable in the UWB frequency range, except at the notch frequencies.

Design of compact frequency agile filter-antenna using reconfigurable ring resonator bandpass filter for future cognitive radios

AbstractIn this paper, a new miniaturized frequency agile filter-antenna with a wide reconfigurable frequency band is proposed for interweave cognitive radios (CRs). A tunable bandpass filter (BPF) composed of a symmetrical ring resonator is cascaded to the feed line of an ultra-wideband planar antenna. The structure of the proposed ring resonator BPF is simple and compact so that the total size of the proposed filter-antenna is smaller than that of a conventional system made of a separate antenna and BPF. The reconfigurability of the proposed filter-antenna is achieved by changing the operating frequency of the BPF by loading the ring resonator with a single varactor diode at its center. The fabricated prototype has successfully achieved a wide operational bandwidth of 1.43 GHz which covers continuous narrow bands from 4.65 to 6.08 GHz. Moreover, the operating tunable narrow bands have stable radiation characteristics. Good agreement between measurement and simulation results is demonstrated.

Independently Tunable Concurrent Dual-Band VCO Using Square Open-Loop Resonator

A concurrent dual-band voltage-controlled oscillator (VCO) with independently tunable dual oscillation frequencies is proposed. A shared square open-loop dual-mode resonator and two varactor diodes are the basic units offering flexible tuning for the dual-band operation. A back-to-back varactor diode between the split of the resonator controls the odd-mode resonant frequency, and a single varactor diode is placed at the center of the resonator to adjust the even-mode resonant frequency. By combining the other four resonators with the shared dual-mode resonator, two distinct three-pole tunable bandpass filters (BPF) are designed as two frequency selective elements. Based on the two elements, a parallel-feedback concurrent dual-band VCO is fabricated with independently-tuned dual oscillation frequencies. Moreover, the mathematical deductions are analyzed to optimize the tuning ranges of the dual-oscillation frequencies and the circuit sizes. The measured results show that the two oscillation frequencies cover a tuning range of 5.114–5.28 GHz and 7.61–7.97 GHz, respectively.

Dual-Layer Single-Varactor Driven Reflectarray Cell for Broad-Band Beam-Steering and Frequency Tunable Applications

A dual-layer active reflectarray configuration is proposed for broad-band beam-steering and/or frequency-tunable applications. A unit cell composed by two stacked fixed-size rectangular patches, properly loaded with a single varactor diode, is designed to realize the dynamic phase tuning mechanism. The proposed approach offers wider bandwidths, with respect to the existing varactor-based reflectarray cells, and quite good frequency reconfigurability features, as demanded by several radar or satellite communication applications. An X-band reflectarray cell is fabricated and tested, to prove the effectiveness of the proposed approach, achieving a 318° phase agility within a measured frequency range of about 14.6% with respect to the central design frequency (i.e., 11 GHz). Wideband beam-steering reflectarray designs are demonstrated, showing 1-dB gain bandwidths equal to 9–10%.

Compact Planar Ultrawideband Antennas With Continuously Tunable, Independent Band-Notched Filters

A compact planar ultrawideband antenna with continuously tunable, independent band notches for cognitive radio applications is presented. The antenna is fabricated using a copper-cladded substrate. A radiating patch with an inverted rectangular T-slot is etched on the top side of the substrate. A straight rectangular strip with a complete gap is embedded into the T-slot. By placing a single varactor diode across this gap, a frequency-agile band-notch function below 5 GHz is realized. On the bottom side of the substrate, a U-shaped parasitic element having an interdigitated-structure is placed beneath the radiating patch. The second narrow band notch is created by inserting a second varactor diode into the gap on one leg of the parasitic element. It has a frequency-agile performance above 5 GHz. The presence of the interdigitated structure suppresses higher order resonant modes and enhances the tunability of the notched bandwidth. Because these antenna structures naturally block dc, a very small number of lumped elements are required. The experimental results, which are in good agreement with their simulated values, demonstrate that both band notches can be independently controlled and the entire frequency-agile fractional bandwidth is as high as 74.5%, demonstrating a very wide notched frequency-agile coverage.