NOVEL ELECTRONIC TUNER USING VARACTORS FOR TUNABLE RF FRONT-ENDS

This paper presents a novel electronic tuner with high power handling capability utilizing varactors based on the asymmetric bilateral coupled microstrip transmission line. Through varying the bias voltage of the varactor at the Ultra High Frequency (UHF) band, the performance of the tuner is demonstrated according to simulated and measured results from several cases with the return loss (S11 ) below -20 dB and the insertion loss (S21 ) within ±0.5 dB. Compared with tuners using p and t network, electronic tuner of this paper shows superior frequency agility as well as wide impendence coverage. Advanced biasing structure has been developed to improve power handling for high power level applications. It is expected that the novel tuner would be part of intelligent Radio Frequency (RF) front-ends system and cognitive wireless system in the future.

Improvements in reverse breakdown characteristics of THz GaAs Schottky barrier varactor based on metal-brim structure

The excellent reverse breakdown characteristics of Schottky barrier varactor(SBV)are crucially required for the application of high power and high efficiency multipliers.The SBV with a novel Schottky structure named metal-brim is fabricated and systemically evaluated.Compared with normal structure,the reverse breakdown voltage of the new type SBV improves from-7.31 V to-8.75 V.The simulation of the Schottky metal-brim SBV is also proposed.Three factors,namely distribution of leakage current,the electric field,and the area of space charge region are mostly concerned to explain the physical mechanism.Schottky metal-brim structure is a promising approach to improve the reverse breakdown voltage and reduce leakage current by eliminating the accumulation of charge at Schottky electrode edge.

A k-band broadband monolithic distributed frequency multiplier based on nonlinear transmission line

A fabrication technology of GaAs planar Schottky varactor diode （PSVD） is successfully developed and used to design and manufacture CaAs-based monolithic frequency multiplication based on 23-section nonlinear transmission lines （NLTLs） consisting of a coplanar waveguide transmission line and periodically distributed PSVDs. The throughout design and optimization procedure of 23-section monolithic NLTLs for frequency multiplication in the k-band range is based on a large signal equivalent model of PSVD extracted from small-signal S-parameter measurements. This paper reports that the distributed SPVD exhibits a capacitance ratio of 5.4, a normalized capacitance of 0.86 fF/μm2 and a breakdown voltage in excess of 22 V. The integrated 23-section NLTLs fed by 20-dBm input power demonstrates a 26-GHz peak second harmonic output power of 14-dBm with 25.3% conversion efficiency in the second harmonic output frequency range of 6 GHz-26 GHz.

Design of a tunable frequency selective surface absorber as a loaded receiving antenna array

An effective approach to designing a tunable electromagnetic absorber is presented and experimentally verified; it is based on an idea that an existing frequency selective surface （FSS） absorber is regarded as a loaded receiving antenna array. The existing absorber is effectively simplified by withdrawing half of the loaded resistors; a more compact one is obtained when lumped capacitors are introduced. Building on this, a varactor-tunable absorber with a proper bias network is proposed. Numerical simulations of one tunable absorber with 1.6 mm in thickness show that a wide tuning range from 3.05 GHz to 1.96 GHz is achieved by changing the capacitance of the loaded varactor from 0.5 pF to 5.0 pF. An experiment is carried out using a rectangular waveguide measurement setup and excellent agreement between the simulated and measured results is demonstrated.

INDEPENDENTLY-TUNED CONCURRENT DUAL-BAND BRANCH-LINE COUPLER USING VARACTOR

This paper presents a concurrent dual-band branch-line coupler with an independently tunable center frequency. In the proposed architecture, the quarter-wavelength lines, which work at two separated bands concurrently and can be tuned in one of them, are key components. Based on the analysis of ABCD-matrix, a novel hybrid structure and a pair of varactors topology are utilized to achieve concurrent dual-band operation and independent tunability, respectively. Using this configuration, it is convenient to tune the center frequency of the upper band, while the responses of the lower band remain unaltered. To verify the proposed idea, a demonstration is implemented and the simulated results are presented.

Superconducting tunable filter with constant bandwidth using coplanar waveguide resonators

In this paper we propose a two-pole varactor-tuned superconducting filter using coplanar waveguide （CPW） spiralin-spiral-out （SISO） resonators. Novel internal and external coupling structures are introduced to meet the requirements for a tunable filter with a constant absolute bandwidth. The fabricated device has a frequency tuning range of 14.4% at frequencies ranging from 274.1 MHz to 317.7 MHz, a 3-dB bandwidth of 5.14±0.06 MHz, and an insertion loss of 0.08 dB-0.70 dB. The simulated and measured results are in excellent agreement with each other.

A GaAs planar Schottky varactor diode for left-handed nonlinear transmission line applications

The left-handed nonlinear transmission line （LH-NLTL） based on monolithic microwave integrated circuit （MMIC） technology possesses significant advantages such as wide frequency band, high operating frequency, high conversion efficiency, and applications in millimeter and submillimeter wave frequency multiplier. The planar Schottky varactor diode （PSVD） is a major limitation to the performance of the LH-NLTL frequency multiplier as a nonlinear component. The design and the fabrication of the diode for such an application are presented. An accurate large-signal model of the diode is proposed. A 16 GHz-39,6 GHz LH NLTL frequency doubler using our large-signal model is reported for the first time. The measured maximum output powers of the 2nd harmonic are up to 8 dBm at 26.4 GHz, and above 0 dBm from 16 GHz to 39.6 GHz when the input power is 20 dBm. The application of the LH-NLTL frequency doubler furthermore validates the accuracy of the large-signal model of the PSVD.

Varactor-tunable frequency selective surface with an embedded bias network

A new technique for designing a varactor-tunable frequency selective surface （FSS） with an embedded bias network is proposed and experimentally verified. The proposed FSS is based on a square-ring slot FSS. The frequency tuning is achieved by inserting varactor diodes between the square mesh and each unattached square patch. The square mesh is divided into two parts for biasing the varactor diodes. Full-wave numerical simulations show that a wide tuning range can be achieved by changing the capacitances of these loaded varactors. Two homo-type samples using fixed lumped capacitors are fabricated and measured using a standard waveguide measurement setup. Excellent agreement between the measured and simulated results is demonstrated.

Optimization of terahertz monolithic integrated frequency multiplier based on trap-assisted physics model of THz Schottky barrier varactor

The optimization of high power terahertz monolithic integrated circuit (TMIC) is systemically studied based on the physical model of the Schottky barrier varactor (SBV) with interface defects and tunneling effect. An ultra-thin dielectric layer is added to describe the extra tunneling effect and the damping of thermionic emission current induced by the interface defects. Power consumption of the dielectric layer results in the decrease of capacitance modulation ration (Cmax/Cmin), and thus leads to poor nonlinear C–V characteristics. The proposed Schottky metal-brim (SMB) terminal structure could improve the capacitance modulation ration by reducing the influence of the interface charge and eliminating the fringing capacitance effect. Finally, a 215 GHz tripler TMIC is fabricated based on the SMB terminal structure. The output power is above 5 mW at 210–218 GHz and the maximum could exceed 10 mW at 216 GHz, which could be widely used in terahertz imaging, radiometers, and so on. This paper also provides theoretical support for the SMB structure to optimize the TMIC performance.

Design of a varactor-tunable metamaterial absorber

In this paper, we design a varactor-tunable metamaterial absorber （MA）. The tunable MA is based on a mushroom-type high impedance surface （HIS）, in which varactors are loaded between adjacent metal patches to adjust the capacitance and tune the resonance frequency, the primary ground plane is etched as the bias network to bias all of the varactors in parallel, and another ultra-thin grounded film is attached to the bottom. Its absorption characteristics are realized for electrically dielectric loss. The simulated values of a sample indicate that a tunable frequency range from 2.85 GHz to 2.22 GHz is achieved by adjusting the varactor capacitance from 0.1 pF to 2.0 pF, and better than 0.97 absorbance is realized; in addition, the tunable frequency range is expanded from 4.12 GHz to 1.70 GHz after optimization.

Analysis and Design of a 3 dB Tunable Lumped-Element Directional Coupler

An analysis of a 3 dB lumped-element directional coupler （LEDC） based on arbitrary terminal impedance is described numerically. To solve the conflicted requirement for broad bandwidth and small size in LEDC, a new structure of coupler is introduced, which can significantly improve bandwidth and whose size is only 3 cm×4 cm on the conditions of the frequency domain of 410 MHz to 490 MHz. The measure results are in good agreement with simulations despite the unexpected resistor loss.

Development and Experimental Measurements of a Tunable Antenna

Modern telecommunication systems need to be equipped with antennas that are precisely tuned to more than one frequency in order to allow operation in several bands. Antenna precise tuning to the desired frequency is very important for system performance. In this paper the operating frequency of a PIFA antenna is adjusted using a varactor. This configuration has the advantage of continuous tuning, thus correcting any frequency deviation due to environmental or other changes. The PIFA antenna’s tuning ranges from 860 MHz to 1025 MHz. Also, the geometry of the antenna is studied through simulations and the effect of the varactor is tested experimentally.

Novel design of a compact tunable dual band wireless power transfer(TDB-WPT)system for multiple WPT applications

In this study we present the design and realization of a tunable dual band wireless power transfer(TDB-WPT)coupled resonator system.The frequency response of the tunable band can be controlled using a surface-mounted varactor.The transmitter(Tx)and the receiver(Rx)circuits are symmetric.The top layer contains a feed line with an impedance of 50Ω.Two identical half rings defected ground structures(HR-DGSs)are loaded on the bottom using a varactor diode.We propose a solution for restricted WPT systems working at a single band application according to the operating frequency.The effects of geometry,orientation,relative distance,and misalignments on the coupling coefficients were studied.To validate the simulation results,the proposed TDB-WPT system was fabricated and tested.The system occupied a space of 40 mm×40 mm.It can deliver power to the receiver with an average coupling efficiency of 98%at the tuned band from 817 to 1018 MHz and an efficiency of 95%at a fixed band of 1.6 GHz at a significant transmission distance of 22 mm.The results of the measurements accorded well with those of an equivalent model and the simulation.

A 4.2-5GHz,low phase noise LC-VCO with constant bandwidth and small tuning gain

As the tuning frequency of an integrated LC-voltage controlled oscillator （LC-VCO） increases, it is difficult to co-design the active negative resistance core and the varactor to achieve wideband frequency range, low phase noise, constant bandwidth and small tuning gain together. The presented VCO solves the problem by designing a set of changeable varactor units. The whole VCO was implemented in a 0.18μm CMOS process. The measured result shows -120 dBc/Hz phase noise at 1 MHz offset. The measured tuning range is from 4.2 to 5 GHz and the tuning gain is 8-10 MHz/V. The VCO draws 4 mA from a 1.5 V supply voltage.

IC design of low power, wide tuning range VCO in 90 nm CMOS technology

A low power VCO with a wide tuning range and low phase noise has been designed and realized in a standard 90 nm CMOS technology. A newly proposed current-reuse cross-connected pair is utilized as a negative conductance generator to compensate the energy loss of the resonator. The supply current is reduced by half compared to that of the conventional LC-VCO. An improved inversion-mode MOSFET（IMOS） varactor is introduced to extend the capacitance tuning range from 32.8% to 66%. A detailed analysis of the proposed varactor is provided. The VCO achieves a tuning range of 27–32.5 GHz, exhibiting a frequency tuning range（FTR） of 18.4%and a phase noise of –101.38 dBc/Hz at 1 MHz offset from a 30 GHz carrier, and shows an excellent FOM of –185dBc/Hz. With the voltage supply of 1.5 V, the core circuit of VCO draws only 2.1 m A DC current.

A 2.4 GHz high-linearity low-phase-noise CMOS LC-VCO based on capacitance compensation

A 2.4 GHz high-linearity low-phase-noise cross-coupled CMOS LC voltage-controlled oscillator（VCO） is implemented in standard 0.18-μm CMOS technology.An equalization structure for tuning sensitivity base on the three-stage distributed biased switched-varactor bank and the differential switched-capacitor bank is adopted to reduce the variations of the VCO gain,achieve high linearity,and optimize the phase-noise performance.Compared to the conventional VCO,the proposed VCO has more constant gain over the entire tuning range.The tuning range is about 18.7%from 2.23 to 2.69 GHz,and the phase noise is-95 dBc/Hz at 100-kHz offset and-117 dBc/Hz at 1-MHz offset from the carrier frequency of 2.42 GHz.The power dissipation is 2.1 mW from a 1.8 V power supply.The active area of this VCO is 500×810μm^2.

Fully integrated low phase noise multi-band LC-tank voltage controlled oscillator with switched-capacitor resonator

This paper presents the design and implementation of a fully integrated low noise multi-band LC-tank voltage-controlled-oscillator （VCO）. Multi-band operation is achieved by using switched-capacitor resonator. Additional three-bit binary weighted capacitor array is also used to extend frequency tuning range in each band. To lower phase noise, two noise filters are added and a linear varactor is adopted. Implemented in a 0.18 ~tm complementary-metal- oxide-semiconductor （CMOS） process, the VCO achieves a frequency tuning range covering 2.26-2.48 GHz, 2.48- 2.78 GHz, 2.94-3.38 GHz, and 3.45-4.23 GHz while occupies a chip area of 0.52 mm2. With a 1.8 V power supply, it draws a current of 10.9 mA, 10.6 mA, 8.8 mA, and 6.2 mA from the lowest band to the highest band respectively. The measured phase noise is - 109-- 120 dBc/Hz and - 121-- 131 dBc/Hz at a 1 MHz and 2.5 MHz offset from the carrier, respectively.

A 20–25.5 GHz VCO using a new variable inductor for K band application

A novel transformer-type variable inductor is proposed to achieve a wide tuning range at frequencies as high as K band. The variable inductor is designed, and an intuitive model is built to analyze its performance by HFSS. A lot of mathematical analysis is done in detail. A VCO using the proposed variable inductor is designed with TSMC 0.13 μm CMOS technology for verification. The frequency tuning range of the VCO depends on the proposed variable inductor. The phase noise of the VCO depends on the quality of the LC tank （including the proposed variable inductor and varactors）. So a specific AMOS varactor is implemented to improve its quality factor. The VCO is simulated at three typical TSMC fabrication comers （TT, FF, SS） to predict its measure results. The post simulation results shows that the VCO achieves a 20-25.5 GHz continuous tuning range. Its phase noise results at 1 MHz offset are -108.4 dBc/Hz and -100.5 dBc/Hz respectively at the tuning frequencies of 19.6 GHz and 25.5 GHz. The VCO draws only 3 to 6 mA from a 1.2 V power supply.

A fully integrated CMOS VCXO-IC with low phase noise, wide tuning range and high tuning linearity

This paper describes a low phase noise, wide tuning range and high tuning linearity CMOS voltage controlled crystal oscillator IC （VCXO-IC） with LVCMOS and LVPECL output. A differential coupled frequency doubling Colpitts oscillator is adopted to obtain low noise 2x frequency output. Wide tuning range and high lin- earity are simultaneously achieved by using MOS varactor arrays. The measurement results show that the designed VCXO-IC achieves -134 dBc/Hz phase noise at 1 kHz offset frequency and 4-135 ppm output frequency tuning range within 3% linearity by using 40 MHz fundamental AT-cut crystal. The VCXO-IC is fabricated in the chartered 0.35/zm standard CMOS process and occupies a total silicon area of 2.4 mm2.

Planar Schottky varactor diode and corresponding large signal model for millimeterwave applications

A GaAs-based planar Schottky varactor diode （PSVD） is successfully developed to meet the demand of millimeter-wave harmonic generation. Based on the measured S-parameter, I-V and C-V characteristics, an accurate and reliable extraction method of the millimeter-wave large signal equivalent circuit model of the PSVD is proposed and used to extract the model parameters of two PSVDs with Schottky contact areas of 160 μm2 and 49 μm2, respectively. The simulated S-parameter, I-V and C-V performances of the proposed physics-based model are in good agreement with the measured one over the frequency range from 0.1 to 40 GHz for wide operation bias range from -10 to 0.6 V for these two PSVDs. The proposed equivalent large signal circuit model of this PSVD has been proven to be reliable and can potentially be used to design microwave circuits.