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To meet the demand for simultaneously supporting the microwave and millimeter-wave technologies in emerging industrial wireless systems, research on dual-band components with a large frequency ratio has been conducted recently. However, it is challenging to implement independent frequency tunability on bandpass filters with both compactness and high performance. This article presents a dual-band bandpass filter with a large frequency ratio, independently tunable frequencies, and an ultrawide stopband. This is achieved by artfully incorporating a harmonic-controllable varactor-loaded microstrip BPF and a wide-stopband dielectric-loaded cavity BPF with the bandgap-embedded aperture coupling mechanism. Extremely compact size can be achieved without additional filtering elements. Two pairs of transmission zeros can be allocated beside two passbands for good selectivity due to the separate path and cross-coupling in the resonators. For validation, a prototype is designed, fabricated and measured. It can provide two independent tunable frequency ranges (3.22–3.52 GHz and 25–27.06 GHz), exhibiting a large frequency ratio up to 8.3. Mid-band suppression better than 20 dB and ultra-wide stopband up to 32.5 GHz with 20 dB suppression level are achieved. Low insertion loss and good selectivity can also be observed. [ABSTRACT FROM AUTHOR]

A compact differential tunable dual-band bandpass filter is achieved by using cascaded capacitor-loaded coupled microstrip lines and voltage-controlled varactors. Six differential-mode (DM) transmission zeros (TZs), four DM transmission poles (TPs), and four common-mode (CM) TZs can be obtained by controlling values and positions of capacitors and the even-odd mode impedances of coupled microstrip lines. What's more, the first three DM TZs, two TPs and three CM TZs will change with the capacitance of varactors. Thus, the proposed filter possesses a tunable lower passband and a fixed upper passband. Compared with the state-of-the-art differential tunable DBBFs, the proposed design has the advantages of wide tuning range, compact size, low number of control voltages, and simple structure. Theoretic analysis, parametric study and design procedure are carried out completely. A prototype with the size of 58.2 × 10.1 mm (1.13 λg × 0.20 λg, λg is the microstrip guided wavelength at the center frequency of the upper passband) is designed for demonstration, which exhibits the center frequency of the lower passband can be tuned from 1.55 to 2.42 GHz. Meanwhile, the center frequency and 3-dB bandwidth of the upper passband keep constant at 3.79 GHz and 8.5%, respectively. [ABSTRACT FROM AUTHOR]

A reconfigurable transmitarray antenna (RTA) with 360° continuous transmission phase controlling capability is designed and experimentally validated in this letter. The proposed RTA element is based on the receiver-transmitter structure. A compact varactor-based analog phase shifter using a coupled-line structure is utilized to provide a 0° to 180° continuous transmission phase. Two PIN diodes integrated on the active transmitter patch are alternatively turned on to generate an additional 180° phase shift using the current reversal mechanism. The element simulations show a magnitude insertion loss varying from 0.95 to 1.35 dB at 5.6 GHz, and a wide 3-dB transmission bandwidth of 16.7%. A prototype composed of ${\rm{16 \times 16}}$ elements is fabricated and measured. The measured broadside gain is 23.7 dBi at the design frequency with a 3-dB gain bandwidth of 15.7%. Good two-dimensional (2-D) beam steering capability within ±60° is also experimentally verified. [ABSTRACT FROM AUTHOR]

This article introduces a multifunctional polarization insensitive frequency selective rasorber (MF-FSR) comprised of periodic metallic patterns printed on two dielectric substrates and separated by an air-spacer. The novelty of the proposed MF-FSR lies in its combined feature of mode switching and frequency tuning characteristics. This uniquely offers a real-time and multifunctional capability to switch from “rasorber mode (FSA-T)” into an “absorber with notch band (FSA-N)” mode where both modes support continuous tunability of their “transmission” or “notch” band. By controlling the reverse bias voltage of the embedded varactor, the transmission band in FSA-T mode can be tuned from 3.76 to 4.26 GHz with a very low insertion loss in the range of 0.62–0.95 dB. In complementary FSA-N mode, the notch band is also tunable from 4.17 to 4.71 GHz. Moreover, the same varactor set can control the tuning of transmission or the notch band depending upon MF-FSR’s basic state of operation which is further independently controllable by the p-i-n diode. Equivalent circuit models are also thoroughly examined. Finally, a prototype is fabricated and experimentally tested, showing a good agreement with the predicted results. [ABSTRACT FROM AUTHOR]

To satisfy the stringent requirements of the emerging wireless communication system, the dual-band operation and reconfigurability are both desired for the front end. However, few works can realize them simultaneously. In addition, the flexibility of the implemented reconfigurability is limited. In this article, a reconfigurable dual-band quadrature coupler with independently tunable characteristics at the lower band is proposed. Based on the investigation of an ideal model, the design requirements to achieve the previous reconfigurability can be obtained. Thus, the coupled line loaded with varactor is proposed on a patch coupler to implement the desired functionality. By varying the voltages applied on the varactors, the frequency and coupling coefficient at the lower band of the proposed coupler can be tuned independently with the characteristics at the upper band fixed. For validation, a prototype was designed, fabricated, and measured. Measured results show that the frequency of the coupler at the lower band can be tuned from 2.9 to 3.2 GHz. Meanwhile, the corresponding coupling coefficient can be tuned from 3 to 10 dB. During the lower band tuning, 3 dB coupling coefficient and quadrature phase difference can be always maintained for upper band, which is fixed at 4.7 GHz. [ABSTRACT FROM AUTHOR]

A wideband LC-VCO IC with an Inversion-MOS (IMOS)-based novel varactor is proposed in this article. The novel varactor that consists of an IMOS and a fixed metal–insulator–metal (MIM) capacitor is able to provide a continuous tuning range with a single analog control voltage. The proposed VCO IC is designed, fabricated, and fully evaluated on the wafer in 40-nm CMOS SOI. The proposed wideband VCO IC has exhibited a tuning range of 40.3% from 4.14 to 6.23 GHz and a measured FoMT of −197.3 dBc/Hz under a supply voltage of only 0.34 V. [ABSTRACT FROM AUTHOR]

Tunable transmission lines have a high demand in the 5G wireless communication applications. In this brief, a novel transmission line is presented to control both electrical length and characteristic impedance individually, creating flexible functions. For the first function, the proposed transmission line can perform as a tunable phase shifter with 90° phase tuning range and a low insertion loss variation. For the second function, the proposed transmission line can tune the characteristic impedance from 23 Ω to 145 Ω with a fixed phase delay. The ABCD-matrix method is applied to derive the design equations. For the practical implementation, the varactor equivalent parasitic resistances are considered, and the even-odd mode is applied to re-optimize the proposed two tuning functions. To verify the design theory, an experimental prototype is simulated, fabricated, and measured. Both simulation and measurement results match well with the design theory. [ABSTRACT FROM AUTHOR]

Varactors, with its capacitance tunable by the applied voltage, are enabling components for reconfigurable RF systems. The performance of a varactor could be characterized by its ${Q}$ -factor and the capacitance tuning ratio. In this article, we seek to develop a new varactor with very high ${Q}$ -factor and large tuning ratio, enabling reconfigurable RF systems with large bandwidth. There were two main innovations in varactor diode design. One was the use of the fin structure, in which the electrodes were placed on two opposite sidewalls of the mesa structure instead of one on top and the other at the bottom or next to the mesa. This design eliminates the extrinsic series resistance in the conventional varactor diode designs, leading to substantially increased ${Q}$ -factor. The other was the use of a multichannel structure. The structure was composed of multiple AlGaN/GaN heterojunctions with high-mobility 2-D electron gas. The high-mobility electron gas helped lowering the intrinsic series resistance, thereby further improving the ${Q}$ -factor. [ABSTRACT FROM AUTHOR]

This paper demonstrates a tunable synthetic fourth-order bandpass filter (BPF) at microwave frequencies. Two parallel second-order Q-enhanced LC BPFs responses are added with the out of phase to synthesize a fourth-order BPF response. The filter is implemented in a 130-nm SiGe BiCMOS technology with a core die area of $0.53 \times 0.7$ mm2. The filter center frequency can be tuned from 4 to 8 GHz (C-band). The filter also achieves a wide 3-dB fractional bandwidth (BW) tuning range of 2%–25%, with a passband ripple of less than 0.5 dB. The corresponding normalized dynamic range (DR) is 151–166 $\text {dB}\cdot \text {Hz}$ owing to a switched varactor control scheme to realize a large effective tuning range with high linearity. Using the parallel synthesis approach, the filter can maintain the DR of a second-order BPF while achieving a fourth-order frequency selectivity, which is favorable compared to cascading resonators. On the lower side of the band, the filter achieves more than 65 dB of ultimate rejection. On the upper side, the rejection is more than 52 dB. The filter also employs a variable transconductor for noise-linearity tradeoff flexibility. The power consumption of the filter is 112–125 mW over the above fractional BW tuning range at the target C-band. [ABSTRACT FROM AUTHOR]

This paper proposes a varactor-based coupler structure that allows for reconfigurable operating frequency, power-dividing ratio, and coupler to/from crossover responses. Particularly, this coupler can theoretically realize perfect impedance matching and port isolation at all tuning states. The coupler analysis, design equations, and design graphs were conducted, given, and discussed in detail. For demonstration purposes, two prototypes were experimentally developed and characterized. The first quadrature coupler demonstrates a frequency-tuning range from 0.632 to 1.5 GHz with a constant power-dividing ratio of −3 dB, <2.3° phase imbalance, >20-dB isolation, and >14-dB return loss. In the second prototype, for the phase error <6.7°, isolation and return loss >19 dB, the power-dividing ratio was tuned from −6.4 to 20.5 dB at 1 GHz, yielding a 26.9-dB tuning range and crossover characteristics at low bias voltages. Measured and simulated results are in good agreement. [ABSTRACT FROM PUBLISHER]

Varactors are key devices in the design of voltage-controlled oscillators (VCOs), as their quality factor ( Q -factor) at the millimeter-wave frequency range limits the overall LC tank Q -factor. This brief presents a new circuit-level structure, called Q -enhanced varactor (QEV), that is composed of two metal-insulator-metal capacitors (MIMCAPs) and a varactor. Depending on Q -factors and the values of the MIMCAPs, the Q -factor in QEV can be improved more than two times. The QEV parameters are analyzed and a design procedure for QEV is proposed. Also, a QEV with two times Q -factor improvement is employed in the design of a 40-GHz LC-VCO, illustrating more than 6-dB enhancement in the oscillator figure of merit. [ABSTRACT FROM PUBLISHER]

In this paper, a novel tunable coupling mechanism with bandwidth-tunable capability is presented. Metallic via has been utilized to construct the coupling structure, namely via-coupling. Studies show that the via-coupling mechanism provides more flexibility and owns better tolerance to fabrication errors than the traditional gap-coupling. By employing varactor in parallel with the metallic via, the coupling coefficient between each resonator pairs can be effectively tuned. It is worth noting that only one varactor is required for each resonator pair. The lumped-circuit model of the tunable coupling mechanism is investigated and extracted by classical theory derivation and simple programming. For verification, a fourth-order quasi-elliptic bandpass filter (BPF) and a bandwidth-tunable one are designed, fabricated, and measured. For the bandwidth-tunable BPF, the factional bandwidth varies from 2.52% to 5.04%, meaning a double tuning range. The in-band insertion loss varies from 2.8 to 4.8 dB, and the return loss is better than 17 dB. If needed, BPFs with $N$ th-order ( $N > 4$ ) could be designed based on the proposed tunable coupling mechanism and only ( $N + 1$ ) varactors are required. [ABSTRACT FROM AUTHOR]

An extremely compact architecture for a passive 6-bit digital phase shifter is presented. The phase shifter has a range of 360° with 5.6° resolution at 2.4 GHz. The architecture is composed of an ambidextrous quadrant selector in series with a digital fine-tuned phase shifter that makes use of high-ratio symmetrical digitally variable capacitors loading a lumped element transmission line. The phase shifter achieves a 50 $\Omega$ match in all 64 states. The circuit occupies approximately 0.47 mm2 on die, and the entire test chip measured 0.84 mm2, including bond pads and ESD structures. The 1-dB compression point was +23 dBm. The chip was fabricated in a commercial 0.13- \mu\text{m} silicon-on-insulator CMOS process. [ABSTRACT FROM AUTHOR]

This paper presents a second-order Chebyshev constant fractional bandwidth (CFBW) tunable bandpass filter with compact size and frequency invariant-passband characteristics using tunable external quality factors. The filter is designed using a stub loaded dual-mode resonator and two sets of varactors for tuning the center frequency and the return loss level. The design is featured with the net-type filter of a short grounded-stub so that the CFBW property can be assured. In addition to the conventional design, a pair of varactors is included at the ends of feeding transmission lines to keep the external quality factors constant while tuning. Within the tunable range of the varactors, the proposed filter is tunable from 1.7 to 2.1 GHz with a 5% CFBW. The measurement results show a 20-dB return loss and insertion loss below 2.9 dB over the entire tuning range. [ABSTRACT FROM PUBLISHER]

A varactor-tunable second-order bandpass frequency-selective surface (FSS) for microwave frequencies is presented in this article. The FSS is composed of three stacked metallic layers. The wire grid in each layer in combination with metallic vias provides the bias for the varactors. This configuration eliminates the need for a dedicated bias network for the varactors, and thus avoids undesirable responses associated with the added bias grid. An equivalent circuit model together with an analytical design method is provided to simplify the design procedure of the FSS. The performance of the proposed structure is experimentally validated in a parallel-plate waveguide setup. Measurements show that by changing the varactor capacitance from 0.12 to 0.38 pF, the center frequency of the filter is tuned from 5.2 to 3.7 GHz with a consistent fractional bandwidth of 9% and with an insertion loss between 3 and 6 dB. [ABSTRACT FROM PUBLISHER]

This paper presents a LC Voltage-Controlled Oscillator (LC-VCO) with an incorporated Automatic Gain Control (AGC) unit. The LC oscillator is based on the BJT cross-coupled pair topology with tuning varactors and a dual supply source so that the tuning range is maximized. The trade-off between the quality factor, tuning range and number of varactors in parallel is analyzed. In addition, the stability of the AGC system is proven by the estimation of the gain and phase margin. Finally, the phase noise (PN) LC-VCO is estimated using the Leeson model. The oscillator shows a tuning range from 4.3MHz to 6MHz (about 330,000 ppm) and an estimated phase noise of -117.2dB /Hz@ 1kHz. The system shows an improvement of 6dB compared to the same VCO without gain control. The system consumes 47mW of power from a 3V supply. [ABSTRACT FROM PUBLISHER]

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 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 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]

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 two-pole dual-band tunable bandpass filter (BPF) with independently controllable dual passbands based on a novel tunable dual-mode resonator. This resonator principally comprises a \lambda/2 resonator and two varactor diodes. One varactor is placed at the center of the resonator to determine the dominant even-mode resonant frequency; the other is installed between two ends of the resonator to control the dominant odd-mode resonant frequency. These two distinct odd- and even-mode resonances can be independently generated, and they are used to realize the two separated passbands as desired. Detailed discussion is carried on to provide a set of closed-form design equations for determination of all of the elements involved in this tunable filter, inclusive of capacitively loaded quarter-wavelength or \lambda/2 resonators, external quality factor, and coupling coefficient. Finally, a prototype tunable dual-band filter is fabricated and measured. Measured and simulated results are found in good agreement with each other. The results show that the first passband can be tuned in a frequency range from 0.77 to 1.00 GHz with the 3-dB fractional-bandwidth of 20.3%–24.7%, whereas the second passband varies from 1.57 to 2.00 GHz with the 3-dB absolute-bandwidth of 120 \pm 8 MHz. [ABSTRACT FROM PUBLISHER]

This paper presents a compact highly linear tunable second-order quasi-elliptic filter with constant 3-dB bandwidth. The proposed filter is thoroughly analyzed to clearly describe the filter equivalent circuit and the tuning mechanism involved. In addition, the tunable resonator configuration employed is shown to improve filter linearity, especially for low bias voltages where distortion is normally stronger. A quasi-elliptic tunable filter was designed, built, and tested for illustration and verification. With a 3-dB bandwidth variation of only 4.6%, the filter had a frequency coverage from 1.45 to 1.96 GHz, an insertion loss better than 2.5 dB, and measured IIP3 > 43 dBm throughout. The experimental results are in excellent agreement to theory and simulations. [ABSTRACT FROM PUBLISHER]

This paper analyzes various aspects of the performance of LC VCOs over temperature with emphasis on the temperature dependence of Kvco. A novel frequency-tuning scheme is proposed which allows wide temperature range operation while keeping the average Kvco low. [ABSTRACT FROM PUBLISHER]

A varactor and FMR-tuned wideband band-pass filter (BPF) module with versatile frequency tunablity has been devised and realized on RT/Duroid substrate. By connecting four variable capacitance diodes (varactors) to the four open-circuited stubs of an X-band passive composite-BPF and adjusting the reverse bias voltage from 2 to 22 V, the 3 dB passband of the passive composite-BPF was continuously tuned from 7.7–12.4 GHz to 11.4–17.5 GHz. The corresponding bandwidth (BW) was enlarged from 4.7 to 6.1 GHz and the upper frequency of the passband was extended from 12.4 to 17.5 GHz, namely, a total frequency span of 9.8 GHz. The BW of the passive composite-BPF was further FMR-tuned using a pair of Band-Stop Filter (BSF). By setting the reverse bias voltage at 22 V together with the bias magnetic fields at 3250 and 4200 Oe, respectively, to the two BSFs, the 6.1 GHz BW and 9.8 GHz frequency span were compressed to 1.4 GHz toward the high-end frequency. The 4.7 GHz BW and 9.8 GHz frequency span were also compressed to 1.0 GHz toward the low-end frequency with 2650 and 3500 Oe bias magnetic fields and 2 V reverse bias voltage. Thus, the combination of the varactor and FMR-tuning has facilitated versatile passband and its BW tuning covering the X-and Ku-bands with both large frequency tunability and greatly improved frequency selectivity. [ABSTRACT FROM AUTHOR]

In this paper, an X-band low phase-noise voltage-controlled oscillator (VCO) using a novel electronically tunable substrate integrated waveguide (SIW) resonator is proposed and developed for RF/microwave applications on the basis of the substrate integrated circuits concept. In this case, the resonant frequency of the SIW cavity resonator is tuned by different dc-biasing voltages applied over a varactor coupled to the cavity. Measured results show that the tuning range of the resonator is about 630 MHz with an unloaded Q U of 138. Subsequently, a novel reflection-type low phase noise VCO is developed by taking advantage of the proposed tunable resonator. Measured results demonstrate a frequency tuning range of 460 MHz and a phase noise of 88 dBc/Hz at a 100-kHz offset over all oscillation frequencies. The VCO is also able to deliver an output power from 6.5 to 10 dBm. This type of VCO is very suitable for low-cost microwave and millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A reconfigurable planar inverted-F antenna using a switchable PIN-diode and a fine-tuning varactor is presented for mobile communication applications. Selection of operating modes is achieved by switching the PIN-diode between radiators and tuning the varactor on an antenna's shorting line. Mode I, with the PIN-diode off and tuning the varactor, operates for USPCS (1.85-1.99 GHz), WCDMA (1.92-2.18 GHz), and WLAN (5.15-5.825 GHz). As a result, the varactor used to achieve frequency fine-tuning does not need a DC bias circuit and can expand the bandwidth without increasing the physical size. Mode II, with the PIN diode on and the fixed 0-V varactor, operates for USPCS and m-WiMAX (3.4-3.6 GHz). To optimize the antenna structure, a parametric analysis is performed by sweeping the length and width of the radiators. Furthermore, equivalent models of a PIN diode and a varactor are presented for accurate prediction of antenna performances which are also analyzed by varying diode parameters. All simulated results are confirmed with measured data. The peak gains show 2.84, 2.81, 1.25, and 1.49 dBi at USPCS, WCDMA, m-WiMAX, and WLAN, respectively. [ABSTRACT FROM AUTHOR]

A compact notch filter with a wide tunable frequency range is developed. This tunable filter is composed of two varactor-tuned resonators, shunted at input/output ports separately, and one quarter-wavelength transmission line connecting two varactor-tuned resonators. By enlarging impedance of the quarter-wavelength transmission line, the proposed tunable filter can obtain a wide and constant absolute bandwidth within the whole tunable frequency band. The measured results show that there is a wide tuning range, 124.3%. In addition, with insertion loss greater than 20 dB, a wide constant absolute bandwidth can be achieved at 450 MHz. [ABSTRACT FROM PUBLISHER]

We fabricated a wide-range varactor-tuned terahertz oscillator using a resonant tunneling diode (RTD). An AlAs/InGaAs double-barrier RTD and a varactor-diode mesa were integrated into a 20- $\mu $ m-long slot antenna. A wide tuning range of $\sim 11$ % (70 GHz) of the center frequency of 655 GHz was achieved by changing the depletion-layer capacitance of the varactor diode with a dc sweep from −4 to 0.5 V. The dependence of the output power on the varactor-diode bias was also measured. These experimental results agreed well with theory. [ABSTRACT FROM AUTHOR]

A microstrip bandpass filter (BPF) with high center-frequency tunability, bandwidth reconfigurability, and a one-side band edge transmission zero (TZ) is presented. The reconfigurable BPF is developed with a simple T-shaped dual-mode resonator, which is externally coupled and perturbed with varactor diodes. Also, the design of adjustable admittance inverters for tunable resonators external coupling is proposed to mitigate the in-band performance degradation that hurdles the ones with a fixed coupling. It is demonstrated that the 1 dB bandwidth is able to be varied from 55 to 175 MHz for center frequency ranging from 750 to 1240 MHz with a low insertion loss (<2.9 dB). [ABSTRACT FROM PUBLISHER]

This letter presents a superconducting continuously tunable bandpass filter with dual-mode resonator and Gallium arsenide (GaAs) varactors. The even- and odd-modes of the dual-mode resonator can be tuned simultaneously using a single bias voltage. The interstage and external couplings are realized with interdigital coupling structure to enhance the coupling strength. A four-pole dual-mode superconducting filter at L-band with a fractional bandwidth of approximately 20% is successfully designed. Two transmission zeors are generated in the upper stopband to increase the stopband rejection. The tuning range of the filter is 16% from 784.92 to 918.23 MHz. The insertion loss at 918.23 MHz is 0.69 dB with a reverse bias voltage of 9 V. The measurements of the filter match well with the simulated ones. [ABSTRACT FROM PUBLISHER]

A tunable bandpass filter with a wide tuning range is presented in this letter. The proposed filter is composed of two modified parallel-coupled lines and one varactor-loaded stub. Particularly, the modified parallel-coupled line is realized by a varactor connected to one end of the coupled line with asymmetric feeding and an open stub added to the coupled line's other end. Moreover, the varactor-loaded stub is introduced to control the transmission zero around the lower/higher passband skirt. The measured results show that a broad tuning range of 41.7%, from 0.95 to 1.45 GHz, was achieved. Within the tuning range, the insertion loss is from 2.4 to 2.9 dB and the return loss is greater than 15 dB. [ABSTRACT FROM PUBLISHER]

A reconfigurable bandpass filter (BPF) with separately relocatable passband edges is demonstrated. The proposed design approach exploits simple stub-based structures and varactor-tuned microwave resonators for the BPF realization. The filter bandwidth reconfigurability is obtained via a separate relocation of each passband edge, and the harmonics inherited in the varactor-tuned microwave resonators are easily suppressed with the stub-based structures. The fabricated filter has a low passband insertion loss (< 2.0 dB), a 21.8 % higher band edge tuning range, a 18.2 % lower band edge tuning range, as well as wideband suppression (> 15 dB at the frequencies up to 5.5 GHz). [ABSTRACT FROM PUBLISHER]

A high-Q digitally tunable capacitor is demonstrated with 3 and 4 b resolutions for 0.8–3 GHz applications. The device shows a tuning range of 1.0–3.75 pF in the 3 b configuration and 1.25–3.80 pF in the 4 b configuration (\sim1–4 pF simulated). In addition to digital tuning, 30–530 fF of analog tuning is achieved and allows for precision tuning. The measured Q of the digitally tunable capacitor is >100 at 1 GHz and >60 at 2 GHz for all tuning states. A novel circular geometry maintains a high-Q as the capacitance is increased. The device is 2\,\times\,1.8 mm which is ideal for tunable filters, matching networks and antennas. [ABSTRACT FROM PUBLISHER]

This letter presents a reconfigurable active bandpass filter based on a controllable slope parameter. The proposed filter has reconfigurable bandwidths and center frequencies, and both can be continuously changed using varactor diodes as the tuning elements. The wide tuning range of the bandwidth is achieved by adjusting the slope parameter of the resonators. This letter describes the design and testing of a two-pole reconfigurable filter with tuning ranges in the center frequency of 2.0–2.6 GHz and 3 dB bandwidth of 127–598 MHz at the center frequency of 2.15 GHz. [ABSTRACT FROM PUBLISHER]

An intrinsic-tuned, 68 GHz voltage controlled oscillator (VCO) without an extra on-chip accumulation-mode metal oxide semiconductor (MOS)-varactor is demonstrated in a standard, 0.13 mum CMOS technology. This VCO exhibits phase noises of -98.4 dBc/Hz and -115.2 dBc/Hz at 1 and 10 MHz offset, respectively, along with a tuning range of 4.5 % even under a small power consumption of 4.32 mW. Besides, the highest figure-of-merit (taking frequency tuning range into account) of -182 dBc/Hz under the 1 MHz offset condition is achieved among all previously reported >60 GHz CMOS-based VCOs, which is attributed to the proposed intrinsic tuning mechanism. [ABSTRACT FROM PUBLISHER]