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A reconfigurable transmitarray with beam steering and polarization manipulation capabilities is presented. The transmitarray element consists of an active side, a 360° reflective phase shifter, and a passive side. The active side is made of a polarization tunable patch structure, which can radiate electromagnetic wave at dual linear polarization. The passive side composed of a two-layer patch structure is unitized as a receiver cell. We adopt 8 \times 8 unit cells to construct the whole transmitarray, and then place it above a horn antenna. The measured results show that the transmitarray-based horn antenna achieves beam steering with the scan range of \pm 60^\circ \times \pm 60^\circ at 5.4 GHz, and this steering capability can be realized in two orthogonal linearly polarized modes. The polarization manipulation capability of this transmitarray is then studied, and it is found that four different output polarization modes, including two circular polarizations [right-handed circular polarization (RHCP) and left-handed circular polarization (LHCP)] and two linear polarizations, can be obtained over an 8.5% fractional bandwidth, with cross-polarization ratio larger than 15 dB. [ABSTRACT FROM PUBLISHER]

This paper presents, for the first time, the linearity study of a varactor-based microwave attenuator. In particular, a novel technique is proposed to linearize the attenuator in terms of both main-tone and intermodulation distortion (IMD) performance. The enhancement circuit is simple to implement and can offer a reduction of the IMD level of over 20 dB. Linearization is achieved by shifting the biasing point of the tuning diodes (under large attenuation operation) away from the highly nonlinear region. For verification, both simulated and measured results of a 1-GHz variable attenuator with and without linearization are given. [ABSTRACT FROM PUBLISHER]

Frequency multipliers are an attractive solution for signal generation in CMOS near and above cutoff frequencies (f\max) of active devices. This work focuses on nonlinear transmission line (NLTL) based frequency multipliers, which can be employed for high output power and broadband operation. The performance of an NLTL-based multiplier is limited by the phase mismatch at frequencies of interest caused by dispersion. We propose an alternate NLTL and engineer dispersion to eliminate phase mismatch between desired harmonics. We build two prototypes. First, a 20-GHz frequency doubler is implemented in a 65-nm CMOS process. Second, to show the feasibility of our approach near f\max, a 100-GHz frequency tripler is demonstrated in a 130-nm CMOS process (f\max < 130 GHz). The achieved conversion loss is 3.5 and 12.2 dB for the doubler and tripler, respectively. The frequency tripler generates maximum power of -\1.5 dBm. The relative bandwidth of the doubler and tripler is about 23% and 12.3%, respectively. To the best of our knowledge, the frequency tripler outperforms any previously reported work implemented in a 130-nm CMOS at or above 100 GHz in terms of output power and bandwidth. [ABSTRACT FROM PUBLISHER]

An analog phase shifter based on distributed MEMS transmission line (DMTL) is designed for Ku band applications. Traditional RF MEMS phase shifter comprising 6 switches has limited phase shift of 37.75° due to instability region. A new concept of stopper is incorporated to achieve high phase shift. In the present paper, optimisation of the analog phase shifter is done to increase its phase shift upto 88.63°. Phase shift is a strong function of capacitance ratio which is increased from 1.75 to 2.95. The maximum operating voltage and mechanical resonant frequency for the phase shifter are 16 V and 8.3 KHz, respectively. The switching time is calculated to 56 μs. The simulated insertion loss of the phase shifter is -1.75 dB with return loss of -20.49 dB at 17 GHz. The simulated results are verified with analytical modelling which are in close match. [ABSTRACT FROM AUTHOR]

With the aim of achieving constant insertion loss, this paper presents the design of a 24 GHz reflective-type phase shifter (RTPS) integrated with a switched Π-attenuator for phased array transmitters. Three RTPS circuits with hybrid coupler and capacitive-type reflective loads are cascaded to obtain required phase-shift. Accumulation-mode MOS (AMOS) varactors are used as reflective loads for phase control. In order to achieve a compact scheme, the hybrid couplers are designed using lumped elements. A switched Π-attenuator is used in front of the RTPS for gain control. Body switching technique is applied in series switch of the Π-attenuator to improve its switching performance. Consuming zero DC power, the proposed circuit demonstrates a maximal relative phase-shift range of 185°, a constant insertion loss of 10.7 dB, and a worst-case input return loss better than 15 dB at 24 GHz. The circuit is implemented in a standard 0.18 μm CMOS technology and the post-layout simulation results are reported. [ABSTRACT FROM AUTHOR]

This paper presents the design and reliability tests of a novel micro-electro mechanical varactor based on a double actuation mechanism allowing for overall capacitive ratio C r of 5.2 and continuous capacitive ratio C r ⁎ of 2.6. The device has been modeled in ANSYS® multiphysics environment and manufactured by using the 8-masks FBK-irst RF MEMS process. The performance was tested on 10 samples showing good mechanical reproducibility and negligible capacitance ratios variation (C r = 5.2 ± 5%, C r ⁎ = 2.6 ± 4%). Self-biasing tests have been performed by applying an equivalent V rms on the RF central conductor, showing an insignificant capacitance ratio variation up to 13.5 V rms . Finally, cycling test was performed on the DUT up to 10 8 cycles, showing negligible variation of the capacitance. [ABSTRACT FROM AUTHOR]

A new methodology for the design of single/multi-band power amplifiers (PAs) with dynamic load modulation (DLM) is presented. First, the topology for the output matching network (OMN) including the control varactor is selected. A comprehensive optimization of the OMN parameters is then developed by which varactor and transistor losses are considered to ensure maximum efficiency enhancement at each frequency. To verify the method, a dual-band PA with DLM is realized. Drain efficiencies of 75% and 60% at 685 MHz and 1.84 GHz, respectively, are measured at peak output power. At 10-dB output power back-off efficiencies of 43.5% and 49.5%, respectively, are obtained. Linearized modulated measurements with a 6.5-dB peak-to-average power ratio WCDMA signal show average drain efficiencies of 56% and 54% at 685 MHz and 1.84 GHz, respectively, at an adjacent channel leakage ratio of -\49 and - \47.5 dBc, respectively. The proposed method shows the effectiveness of applying an optimization process for the design of single- or multi-band DLM PAs. The results demonstrate that near-optimum performance may be obtained in terms of efficiency enhancement for a given transistor and varactor-based OMN, thus making DLM competitive against other load modulation techniques. [ABSTRACT FROM AUTHOR]

Based on advanced industrial fabrication processes and on specialized design strategies, a new class of ferroelectric metal–insulator–metal (MIM) capacitors with high tunability and high quality factor (Q-factor) is here presented. Modeled by means of lumped element equivalent circuits and experimentally validated up to 67 GHz, a maximum tunability of 81% (0–20-V bias), and a Q-factor improvement up to 30% (at 0 V) could be demonstrated at 1 GHz. These varactors have been exploited in the design of reconfigurable filters, with a center frequency at around 1 GHz that can be tuned up to 112%, and a figure of merit (FoM) per applied bias better than \31.5~\dB^-1 /\kV. Owing to their promising features, these materials have been exploited to design small-size capacitors suitable for millimeter-wave frequencies. The results demonstrate tunabilities and FoMs superior to the state-of-the-art. Based on this, two 60-GHz tunable phase shifters are proposed. They represent the first example of such devices based on MIM (\Ba,Sr)\TiO3 (BST) capacitors. In terms of insertion loss, size, FoM, and FoM per bias they show a remarkable improvement with respect to the state-of-the-art of ferroelectric-based devices, thus proving that the BST represents a promising candidate to operate into the millimeter frequency band. [ABSTRACT FROM AUTHOR]

A new electro-thermally driven high Q tunable RF MEMS capacitor is proposed in this paper. The tuning mechanism of the varactor is chosen to obtain tuning; hence the capacitor has linear tuning range. In order to satisfy the low voltage operation of the varactor electro-thermal actuators were chosen as the drive and latching mechanism. However, those actuators consume lots of power, accordingly, in order to suppress that shortcoming a true mechanically latching mechanism is proposed which considerably decreases the total power consumption of the varactor. In order to investigate important operational aspects of the proposed varactor, different FEM simulations are carried out. The results are as follow; the Q-factor is 43.39 at 1 GHz for a 0.46 pF capacitance value. The tuning ratio is 1.17:1 and self-resonant frequency is 16.61 GHz. The propose varactor works by applying an actuation voltage of 3.1 V and consumes a power of 180 mW for about 2.7 ms for each tuning steps. The proposed varavtor of this paper can be a promising choice for low lass and low power RF tunable networks. [ABSTRACT FROM AUTHOR]

A reconfigurable microstrip antenna with a circularly polarized (CP) beam-scanning feature is proposed in this paper. Such feature is attained using a novel methodology that effectively tunes the electrical size of a patch antenna. The proposed antenna is a microstrip Yagi-Uda antenna consisting of two square patches. One patch is driven with two orthogonal feeds for CP operation, whereas the other patch is a parasitic one of tunable electrical size for beam scanning. The parasitic patch is loaded with a narrow square slot and four lumped varactors along with their dc biasing network to effectively tune its electrical size. Because the main beam direction is determined by the electrical size of the parasitic patch, electronic beam scanning is allowed by changing the capacitance value through the applied reverse dc biasing voltage. An antenna prototype has been fabricated for experimental validation. Operating at 2.45 GHz, the antenna performance shows a monotonic CP beam scanning that ranges from –36° to 3° with a 0.48–6.64 pF tuning capacitance. The achieved peak value for the realized gain is 8.1 dBic with 2.4-dB variation along the entire scanning range. [ABSTRACT FROM PUBLISHER]

This paper presents reflection-type phase shifters (RTPSs) with very high figure-of-merit (FoM) and low insertion-loss variation, achieving up to 360^\circ relative phase shifts. Two compact topologies are proposed. They were implemented at the working frequency of 2 GHz on a printed circuit board technology. The reflection loads are based on the use of one transmission line loaded by varactors, forming L- or \pi-type networks. An automatic procedure is given to design the electrical length and the characteristic impedance of the transmission line of the reflection loads as well as the output impedance of the 3-dB branch-line coupler in order to get phase shifters with the highest possible FoM. Measurement results of the first L-type network RTPS showed a relative phase shift of 201^\circ for only 0.54 dB \pm \0.09 dB of insertion loss, leading to a FoM of 319^\circ/dB. A relative phase shift of 385^\circ was achieved for the \pi-type network RTPS with insertion loss of only 0.98 dB \pm \0.58 dB, leading to an FoM of 246^\circ/dB. In both cases, simulation and measurement results fit very well. Moreover, the return loss over a 10% bandwidth is always better than 10.9 dB for the first RTPS and better than 12.3 dB for the second one, respectively. The comparison with previous works shows more compact reflection loads with electrical performance equal to the state-of-the-art. [ABSTRACT FROM PUBLISHER]

Frequency reconfigurable antenna designs often suffer from limited tuning ranges and complex bias networks. This paper describes a dual varactor-tuned miniaturized antenna with a single bias introduced through the RF feed that addresses these challenges. The dual varactors provide a large tuning range (410–990 MHz, 2.1–3.5 GHz; \bfVSWR = \bf2:1), while the single bias voltage applied to both varactors greatly simplifies the bias network. The introduction of the bias through the RF feed eliminates the need for separate bias lines. As a result, when the electrical size of the antenna is decreased through tuning, undesired bias line coupling and radiation effects are nonexistent. The design highlights the radiation efficiency limitations associated with the desirable planar topology for electrically small antennas with very wide tuning range requirements. An overview of the antenna’s geometry and operation is presented along with detailed measurements to characterize its performance. [ABSTRACT FROM PUBLISHER]

This article discusses the development of an electronically tunable filter capable of a wide frequency tuning range. Variation of bias (0-5V) changes the center frequency of the filter within 10% while achieving a 1-dB of typical insertion loss. The concept of tuning a filter's 3-dB bandwidth with voltage is demonstrated and the effect of the bandwidth tuning elements on the tunable filter performance is discussed. The designed filter has a simple structure and the characteristics of wide tuning range of 1800MHz to 2000MHz and low insertion loss of less than -1.20 dB. The tunable bandpass filter can be scaled to the commercial frequencies up to 2.5GHz, offering advantages for most ISM and cellular band applications. [ABSTRACT FROM AUTHOR]

This paper presents a broadband frequency tunable and polarization reconfigurable circularly polarized (CP) antenna, using a novel active electromagnetic band gap (EBG) structure. The EBG surface employs identical metallic rectangular patch arrays on both sides of a thin substrate, but rotated by 90^\circ from each other. The active bias circuits are also orthogonal for each surface, enabling the reflection phases for orthogonal incident waves to be tuned independently in a wide frequency range. By placing a wideband coplanar waveguide (CPW) fed monopole antenna above the EBG surface, and properly tuning the bias voltages across the varactors in each direction, CP waves can be generated at any desired frequency over a broad band. In accordance with simulations, the measured 3 dB axial ratio (AR) bandwidth reaches 40% (1.03–1.54 GHz), with good input matching (S11) and radiation patterns at six presented sampling frequencies. The polarization reconfigurability is verified by simulations and measurements, and shown to be capable of switching between left hand circular polarization (LHCP) and right hand circular polarization (RHCP). [ABSTRACT FROM PUBLISHER]

Performance and characterization of harmonic transponders is investigated both theoretically and experimentally. The harmonic response of a transponder based on a Schottky diode is analytically derived in the case when the excitation power is low. Theoretical calculations prove that at high frequencies, capacitive nonlinearity contributes more to frequency multiplication than resistive nonlinearity. This means that the feasibility of a particular diode for harmonic transponder applications largely depends on its varactor properties. Figures-of-merit (FOM) are derived both for the mixing diode and the transponder antenna. The validity of the proposed theoretical model is investigated experimentally using a harmonic transponder operating at 1 GHz fundamental frequency. [ABSTRACT FROM PUBLISHER]

A broadband Class-J power amplifier (PA) with dynamic load modulation (DLM) is presented. It is theoretically shown that a PA with judicious variation of the load resistance and a purely reactive load modulation can maintain 70% drain efficiency over 73% fractional bandwidth and 8.5 dB dynamic range. The theory is verified by a demonstrator PA based on a gallium nitride (GaN) device and a varactor as the tuneable element. The load modulation shows good results from 1.7 GHz to 2.3 GHz and up to 50% of power added efficiency (PAE) is obtained. It is shown that the average PAE for a modulated signal with 7 dB peak-to-average ratio is improved by 15%. [ABSTRACT FROM PUBLISHER]

A compact tunable bandpass filter (BPF) with a broad stopband is presented. The proposed filter is composed of two modified coupled lines and one varactor-loaded stub. In terms of measurement, the tunable BPF with the transmission zero within the higher passband skirt has a very wide tuning range, from 0.95 to 1.55 GHz (48%). Moreover, with the return loss > 10 dB, there is a controllable constant passband bandwidth 120 MHz. Furthermore, within the tuning range, the insertion loss is from 2.4 to 2.8 dB and the return loss is > 20 dB. [ABSTRACT FROM AUTHOR]

This paper theoretically and experimentally investigates frequency-tuned and impedance-tuned wireless non-radiative power-transfer (WNPT) systems. Closed-form expressions for the efficiencies of both types of systems are presented as functions of frequency and system (circuit) parameters. In the frequency-tuned system, the operating frequency is adjusted to compensate for changes in mutual inductance that occur for variations of transmitter and receiver loop positions. Frequency-tuning is employed for a range of distances over which the loops are strongly coupled. In contrast, the impedance-tuned system employs varactor-based matching networks to compensate for changes in mutual inductance, and to achieve a simultaneous conjugate impedance match over a range of distances. The frequency-tuned system is simpler to implement, while the impedance-tuned system is more complex, but can achieve higher efficiencies. Both of the experimental wireless non-radiative power-transfer systems studied employ resonant shielded loops as transmitting and receiving devices. [ABSTRACT FROM AUTHOR]

In this paper, tunable microstrip bandpass filters with two adjustable transmission poles and compensable coupling are proposed. The fundamental structure is based on a half-wavelength (\lambda/2) resonator with a center-tapped open-stub. Microwave varactors placed at various internal nodes separately adjust the filter's center frequency and bandwidth over a wide tuning range. The constant absolute bandwidth is achieved at different center frequencies by maintaining the distance between the in-band transmission poles. Meanwhile, the coupling strength could be compensable by tuning varactors that are side and embedding loaded in the parallel coupled microstrip lines (PCMLs). As a demonstrator, a second-order filter with seven tuning varactors is implemented and verified. A frequency range of 0.58–0.91 GHz with a 1-dB bandwidth tuning from 115 to 315 MHz (i.e., 12.6%–54.3% fractional bandwidth) is demonstrated. Specifically, the return loss of passbands with different operating center frequencies can be achieved with same level, i.e., about 13.1 and 11.6 dB for narrow and wide passband responses, respectively. To further verify the etch-tolerance characteristics of the proposed prototype fitler, another second-order filter with nine tuning varactors is proposed and fabricated. The measured results exhibit that the tunable fitler with the embedded varactor-loaded PCML has less sensitivity to fabrication tolerances. Meanwhile, the passband return loss can be achieved with same level of 20 dB for narrow and wide passband responses, respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A Q-band pHEMT image-rejection low-noise amplifier (IRLNA) is presented using inter-stage tunable resonators. The inter-stage L-C resonators can maximize an image rejection by functioning as inter-stage matching circuits at an operating frequency (FOP) and short circuits at an image frequency (FIM). In addition, it also brings more wideband image rejection than conventional notch filters. Moreover, tunable varactors in L-C resonators not only compensate for the mismatch of an image frequency induced by the process variation or model error but can also change the image frequency according to a required RF frequency. The implemented pHEMT IR-LNA shows 54.3 dB maximum image rejection ratio (IRR). By changing the varactor bias, the image frequency shifts from 27 GHz to 37 GHz with over 40 dB IRR, a 19.1 dB to 17.6 dB peak gain, and 3.2 dB to 4.3 dB noise figure. To the best of the authors' knowledge, it shows the highest IRR and FIM/FOP of the reported millimeter/quasi-millimeter wave IR-LNAs. [ABSTRACT FROM AUTHOR]

We suggest new planar metastructures 'ferrite plate-varactor-loaded resonant element' that provide voltage tunable nonreciprocity of microwaves transmission in contrast to traditional magnetic control. The effect is observed by tuning varactor capacitance with changing reverse-bias voltages under the ferromagnetic resonance excitation near the varactor-loaded element resonance frequency. Wide tuning range has been obtained with nonreciprocity 19 dB between 5.4 and 5.9 GHz. Presented metastructures are useful for the development of quick-tunable nonreciprocal systems. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The room temperature, dark and photo-dielectric properties of the novel crystals TlGaSeS are investigated in the frequency, intensity and biasing voltage having ranges of ~ 1-120 MHz, 14-40 klux and 0-1 V, respectively. The crystals are observed to exhibit a dark high frequency effective dielectric constant value of ~ 10·65 × 10 with a quality factor of ~ 8·84 × 10 at ~ 120 MHz. The dielectric spectra showed sharp resonance- antiresonance peaks in the frequency range of ~ 25-250 kHz. When photoexcited, pronounced increase in the dielectric constant and in the quality factor values with increasing illumination intensity are observed. Signal amplification up to ~ 33% with improved signal quality up to ~ 29% is attainable via photoexcitation. On the other hand, the illuminated capacitance-voltage characteristics of the crystals reflected a downward shift in the voltage biasing and in the built-in voltage of the device that is associated with increase in the uncompensated carrier density. The increase in the dielectric constant with increasing illumination intensity is ascribed to the decrease in the crystal's resistance as a result of increased free carrier density. The light sensitivity of the crystals, the improved dielectric properties and the lower biasing voltage obtained via photoexcitation and the well-enhanced signal quality factor of the crystals make them promising candidates for optical communication systems. [ABSTRACT FROM AUTHOR]

A wireless vapor sensor based on the quantum capacitance effect in graphene is demonstrated. The sensor consists of a metal-oxide-graphene variable capacitor (varactor) coupled to an inductor, creating a resonant oscillator circuit. The resonant frequency is found to shift in proportion to water vapor concentration for relative humidity (RH) values ranging from 1% to 97% with a linear frequency shift of 5.7 kHz/%RH ± 0.3 kHz/%RH. The capacitance values extracted from the wireless measurements agree with those determined from capacitance-voltage measurements, providing strong evidence that the sensing arises from the variable quantum capacitance in graphene. These results represent a new sensor transduction mechanism and pave the way for graphene quantum capacitance sensors to be studied for a wide range of chemical and biological sensing applications. [ABSTRACT FROM PUBLISHER]

We report on GaN microwave varactors with capacitively coupled isolated electrodes. Metal-insulator-semiconductor (MIS) varactors have 4-5 orders of magni-tude lower leakage currents than similar devices with Schottky contacts. Low leakage capacitively coupled contacts enable microwave switches and power limiters with low loss, high RF power and excellent temperature stability up to at least 200 °C. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this paper, two LC Voltage-Controlled Oscillators (LC-LCVCO1 and LC-VCO2) are designed using TSMC 65 nm LP/MS/ RF CMOS technology. Two arrays, one of which is a 6-bit capacitor array and the other -- an array of MOS varactors, provide a wide LC-VCO frequency tuning range. Post-layout simulation results unveiled that at 1.8 V supply voltage the tuning range of LC-VCO1 spans from 5.17 GHz to 6.76 GHz and for LC-VCO2 the range spans from 6.33 GHz to 8.08 GHz. The phase noise at 1 MHz offset frequency is about -123.1 dBc/Hz for LC-VCO1 and -121.6 dBc/Hz for LC-VCO2. The power dissipation at maximum carrier is 30.47 mW for LC-VCO1 and 30.5 mW for LC-VCO2. The layout area is 285x335 μm and 255x305 μm, respectively for LC-VCO1 and LC-VCO2. [ABSTRACT FROM AUTHOR]

A method of using frequency selective surface (FSS) to dynamically control beamwidth of antenna is proposed. The unit cell is composed of a two-layer periodic H-shape structure loaded with varactors. By tuning the bias voltage applied to the varactors, the unit cell has two different states that are transparent and absorptive to the incident wave at a certain frequency, respectively. We can control the transparent region of the whole FSS through reasonably setting the capacitance of the varactor loaded on each unit cell, and thus the beamwidth of the transmitted wave could be tuned. The above property has been validated by putting the FSS above the horn antenna array as superstrate. Simulation results show that E-plane beamwidth of the antenna can be enlarged from 13.2° to 31.1° at 5.5 GHz, and experimental results agree well with the simulated ones. In addition, it is found that the operation frequency for beamwidth control can be tuned as well. [ABSTRACT FROM AUTHOR]