Showing papers in "IEEE Transactions on Microwave Theory and Techniques in 2011"

Chipless RFID Tag Using Hybrid Coding Technique

Abstract: Increasing the coding capacity of chipless RFID tags is a key factor while considering the development of miniaturized tags. A novel hybrid coding technique by combining phase deviation and frequency position encoding is proposed here. A coding capacity of 22.9 bits is obtained simply with five resonators within a reduced dimension of 2 cm × 4 cm. The proposed tag is based on 5 `C' like metallic strip resonators having resonance frequency within the band of 2.5 GHz to 7.5 GHz. The tag is potentially low-cost since only one conductive layer is needed for the fabrication. Different tag configurations are designed and validated with measurement results in bi-static configuration. A good agreement between measurement and simulation validates the theoretical predictions.

2-D Digital Predistortion (2-D-DPD) Architecture for Concurrent Dual-Band Transmitters

Abstract: This paper presents a novel 2-D digital-predistortion (2-D-DPD) technique that is applicable for linearization of concurrent dual-band transmitters. This technique uses a unique way for distortion compensation and linearization of dual-band transmitters by selecting, characterizing, and applying predistortion in each band separately. Compared to conventional linearization techniques, this 2-D-DPD method requires a lower sampling rate for digital-to-analog and analog-to-digital converters. The performance of the 2-D-DPD topology is evaluated using two modulated signals, Worldwide Interoperability for Microwave Access and wideband code-division multiple-access, separated in frequency by 100 MHz. The measurement results show an adjacent channel power ratio of less than -50 dBc and a normalized mean square error of less than -40 dB.

A Novel Fully Electronic Active Real-Time Imager Based on a Planar Multistatic Sparse Array

Abstract: The interest in active millimeter-wave and microwave imaging systems is increasing due to their utilization in security, medical, and industrial applications. Imaging systems using monostatic arrays suffer from the high number of antenna positions, making a fully electronic solution very costly and impractical. Multistatic arrays, however, offer the chance for high reduction factors in the number of antennas, and then allow for fully electronic solutions. Here, a new array architecture is presented, which is suitable for real-time operation and is capable of delivering high image quality in means of resolution and dynamic range. Various technological solutions were developed for the imaging purpose, which are introduced in detail. An example array for operation from 72 to 80 GHz is demonstrated. The imaging system hardware is introduced, along with several imaging results of humans with concealed objects.

Design of Highly Efficient Broadband Class-E Power Amplifier Using Synthesized Low-Pass Matching Networks

Abstract: A new methodology for designing and implementing high-efficiency broadband Class-E power amplifiers (PAs) using high-order low-pass filter-prototype is proposed in this paper. A GaN transistor is used in this work, which is carefully modeled and characterized to prescribe the optimal output impedance for the broadband Class-E operation. A sixth-order low-pass filter-matching network is designed and implemented for the output matching, which provides optimized fundamental and harmonic impedances within an octave bandwidth (L-band). Simulation and experimental results show that an optimal Class-E PA is realized from 1.2 to 2 GHz (50%) with a measured efficiency of 80%-89%, which is the highest reported today for such a bandwidth. An overall PA bandwidth of 0.9-2.2 GHz (84%) is measured with 10-20-W output power, 10-13-dB gain, and 63%-89% efficiency throughout the band. Furthermore, the Class-E PA is characterized through measurements using constant-envelop global system for mobile communications signals, indicating a favorable adjacent channel power ratio from -40 to -50 dBc within the entire bandwidth.

Broadband Electromagnetic Absorbers Using Carbon Nanostructure-Based Composites

Abstract: In this paper, we present the design of nanostructured multilayer absorbers, carried out with the aid of a genetic algorithm (GA). Waveguide measurements are performed to recover the dielectric properties of micrographite single-walled carbon nanotube, micrographite walled carbon nanotube, carbon nanofiber, and fullerene-based composite materials. Conductive fillers are uniformly dispersed in an epoxy resin at different weight percentages (1, 3, 5 wt.%). The electromagnetic (EM) analysis is performed embedding the forward/backward propagation matrix formalism in an in-house GA, thus able to carry out optimization upon oblique incidence over a finite angular range. Developed code minimizes both the reflection and the transmission coefficients under the thickness minimization constraint. Comparison between micrographite and nanopowders absorbers is presented and discussed, when a broadband quasi-perfect absorber is achieved among the X-band combining the two filler families, i.e., exhibiting a loss factor greater than 90% in most of the band, for a thickness of about 1 cm. It is demonstrated that the nanofillers with higher aspect ratio mainly contribute to the EM absorption. Findings are of interest in both radar-absorbing material and shielding structures.

An Analytical Approach for a Novel Coupled-Line Dual-Band Wilkinson Power Divider

Abstract: A novel generalized coupled-line circuit structure for a dual-band Wilkinson power divider is proposed. The proposed power divider is composed of two coupled lines with different even- and odd-mode characteristic impedances and two lumped resistors. Using rigorous even- and odd-mode analysis, the analytical design equations for this proposed power divider are obtained and the ideal closed-form scattering parameters are constructed. Since the traditional transmission line is a special case of coupled line (coupled coefficient is zero), it is found that traditional noncoupled-line dual-band (including single band) Wilkinson power dividers and previous dual-band coupled-line power dividers are special cases of this generalized power divider. As a typical example, which could only be designed by using this given design equations, a compact microstrip 3-dB power divider operating at both 1.1 and 2.2 GHz is designed, fabricated, and measured. There is good agreement between calculated and measured results.

Frequency Response Analysis and Bandwidth Extension of the Doherty Amplifier

Abstract: A complete frequency response analysis of the Doherty amplifier is presented with the conventional output combining network consisting of two quarter-wavelength (λ/4) transmission lines at a center frequency f0 . Expressions for output power and efficiency were derived over the whole dynamic range and at any frequency f. The analysis shows that the amount of efficiency enhancement, as well as the maximum output power, reduce as the deviation from f0 increases. For instance, the derived expressions show that a conventional Doherty amplifier has a drain efficiency of η ≥ 52.7%, which represents at least 13.4% efficiency enhancement over a class B amplifier, and up to 33.3% fractional bandwidth. A modified output combining network, using λ/4 lines with reduced impedance transformation ratio, is also analyzed, which results in a bandwidth extension of the Doherty amplifier when compared to the conventional design. To verify the derived analyses, three unsymmetrical GaN Doherty power amplifiers (DPAs) were designed and characterized; the first DPA was based on the conventional output combining network, while the second DPA was based on the proposed network. Measurements showed that the first DPA had, at 5-6-dB back-off, a drain efficiency of η ≥ 44% and over 28% fractional bandwidth (1.7-2.25 GHz), while the DPA with the proposed output combining network had a better wideband performance than the third reference conventional DPA, with a back-off drain efficiency of η ≥ 41%, and over 42% fractional bandwidth (1.7-2.6 GHz). To the best of authors' knowledge, the designed DPAs have the highest bandwidths reported thus far.

Modified Compact Antipodal Vivaldi Antenna for 4–50-GHz UWB Application

Abstract: A novel way capable of improving low-frequency performance of Vivaldi antennas is presented in this paper. Traditional Vivaldi antennas are modified via introducing the loading structure, i.e., circular-shape-load or slot-load, to match the termination. This modified antenna has been demonstrated to have the impedance bandwidth of over 25:1. It also exhibits symmetric radiation patterns in both the E- and H-plane in addition to the gain varying from 3 to 12 dBi in the measurement bandwidth of 4-50 GHz.

Single-Fed Broadband Circularly Polarized Stacked Patch Antenna With Horizontally Meandered Strip for Universal UHF RFID Applications

Abstract: In this paper, a horizontally meandered strip (HMS) feed technique is proposed to achieve good impedance matching and symmetrical broadside radiation patterns for a single-fed broadband circularly polarized stacked patch antenna, which is suitable for universal ultrahigh frequency (UHF) RF identification (RFID) applications. The antenna is composed of two corner truncated patches and an HMS, all of which are printed on the upper side of the FR4 substrates. One end of the HMS is connected to the main patch by a probe, while the other end is connected to an SMA connector. Simulation results are compared with the measurements, and a good agreement is obtained. The measurements show that the antenna has an impedance bandwidth (VSWR <; 1.5) of about 25.8% (758-983 MHz), a 3-dB axial ratio (AR) bandwidth of about 13.5% (838-959 MHz), and a gain level of about 8.6 dBic or larger within the 3-dB AR bandwidth. Therefore, the proposed antenna can be a good candidate for universal UHF RFID readers operating at the UHF band of 840-955 MHz. In addition, a parametric study and a design guideline of the proposed antenna are presented to provide the engineers with information for designing, modifying, and optimizing such an antenna. At last, the proposed antenna is validated in RFID system applications.

UWB Band-Notched Monopole Antenna Design Using Electromagnetic-Bandgap Structures

Abstract: A new approach is proposed to reject certain bands within the passband of an ultra-wideband planar monopole antenna. The proposed approach that utilizes a mushroom-type electromagnetic-bandgap (EBG) structure is proven to be an effective way for band-notched designs. The approach has many advantages, such as notch-frequency tunability, notch-band width controllable capacity, efficient dual-notch design, and stable radiation patterns. Several design examples using conventional mushroom-type EBG and edge-located vias mushroom-type EBG are presented. The examples exhibit good bandstop characteristics to reject the wireless local-area network interference bands (5.2- and 5.8-GHz bands). Besides, the causes that lead to the discrepancies between the simulations and measurements are discussed.

A 1.2–1.6-GHz Substrate-Integrated-Waveguide RF MEMS Tunable Filter

Abstract: This paper presents a high-performance substrate-integrated-waveguide RF microelectromechanical systems (MEMS) tunable filter for 1.2-1.6-GHz frequency range. The proposed filter is developed using packaged RF MEMS switches and utilizes a two-layer structure that effectively isolates the cavity filter from the RF MEMS switch circuitry. The two-pole filter implemented on RT/Duroid 6010LM exhibits an insertion loss of 2.2-4.1 dB and a return loss better than 15 dB for all tuning states. The relative bandwidth of the filter is 3.7 ± 0.5% over the tuning range. The measured Qu of the filter is 93-132 over the tuning range, which is the best reported Q in filters using off-the-shelf RF MEMS switches on conventional printed circuit board substrates. In addition, an upper stopband rejection better than 28 dB is obtained up to 4.0 GHz by employing low-pass filters at the bandpass filter terminals at the cost of 0.7-1.0-dB increase in the insertion loss.

Physically Inspired Neural Network Model for RF Power Amplifier Behavioral Modeling and Digital Predistortion

Abstract: In this paper, a novel two hidden layers artificial neural network (2HLANN) model is proposed to predict the dynamic nonlinear behavior of wideband RF power amplifiers (PAs). Starting with a generic low-pass equivalent circuit of the PA, several circuit transformations are applied in order to build an appropriate artificial neural network structure and improve the modeling accuracy. This approach culminates in the development of a real-valued and feed-forward 2HLANN-based model. The parameters (number of neurons, memory depth, etc.) of the proposed model and the back propagation learning algorithm (learning rate, momentum term, etc.) used for its training were carefully studied and thoughtfully chosen to ensure the generality of the constructed model. The validation of the proposed models in mimicking the behavior of a 250-W Doherty amplifier driven with a 20-MHz bandwidth signal is carried out in terms of its accuracy in predicting its output spectrum, dynamic AM/AM and AM/PM characteristics, and in minimizing the normalized mean square error. In addition, the linearization of the Doherty PA using the 2HLANN enabled attaining an output power of up to 46.5 dBm and an average efficiency of up to 40% coupled with an adjacent channel power ratio higher than 50 dBc.

On the Extension of the Continuous Class-F Mode Power Amplifier

Abstract: The extended continuous class-F mode RF power amplifier (PA) is presented for the first time. The introduction and experimental validation of this novel PA mode demonstrates a new design space over a wide band of frequencies. This paper will show that high output power and drain efficiency, equivalent to the class-F mode, can be maintained by varying the reactive components of fundamental and second harmonic impedances in accordance with the new formulation of the voltage waveform. Additionally it will be shown that, by varying both phase and magnitude of the fundamental and second harmonic impedances, a yet wider design space can be achieved, where the efficiency is maintained at a level greater than a certain target value. For the validation of this new theory, an experimental investigation was carried out on GaAs pseudomorphic HEMT devices and demonstrates that high output power and drain efficiency between 75%-83% can be achieved over a wide range of fundamental and second harmonic loads.

Design and Linearization of Concurrent Dual-Band Doherty Power Amplifier With Frequency-Dependent Power Ranges

Abstract: A design methodology for a concurrent dual-band Doherty power amplifier (PA) with frequency-dependent backoff power ranges is presented in this paper. Based on a dual-band T-shaped network and a coupled line network, different dual-band components needed in Doherty PA topology, including a 3-dB branch-line coupler, an offset line, and a quarter-wavelength transformer, are developed. Two prototypes with balanced and imbalanced backoff power range modes are implemented to verify the feasibility. Continuous wave signal test results show that the proposed dual-band PA successfully achieves a power-added efficiency of 33% and 30% at the 6-dB backoff point from the saturated output power at 880 and 1960 MHz, respectively. To meet linearity requirements, the PA nonlinear behavior is characterized by using digital multitone signals, which categorize the distortions of a concurrent dual-band PA into intermodulation and cross-modulation. Finally, a 2-D digital predistortion technique is used to compensate for the nonlinearity of PA in dual bands. Two two-tone signals are applied to the dual bands for linearization, and the experimental results show that this technique achieves improvements of better than 19.1 and 24.6 dB for the intermodulation and cross-modulation in the dual bands, respectively.

Active 220- and 325-GHz Frequency Multiplier Chains in an SiGe HBT Technology

Abstract: A 325-GHz ×18 frequency multiplier chain implemented in a fτ/fmax = 250 GHz/380 GHz evaluation SiGe heterojunction bipolar transistor technology is presented. The chain achieves a peak output power of -3 dBm and consists of a balanced doubler driven by two cascaded tripler stages. It operates from 317 to 328 GHz with a 0-dBm 18-GHz input signal and a 1.5-W power consumption. Additionally, 220- and 325-GHz doubler breakout circuits with integrated driver amplifiers are presented. The doublers reach an output power of -1 dBm at 220 GHz and -3 dBm at 325 GHz with a power dissipation of 630 and 420 mW, respectively.

Single-Antenna Doppler Radars Using Self and Mutual Injection Locking for Vital Sign Detection With Random Body Movement Cancellation

Abstract: This work presents a single-antenna self-injection-locked (SIL) radar to reduce the hardware complexity of continuous-wave (CW) Doppler systems. The theory provides a basis for determining the signal-to-noise spectral density ratio (SNDR) with the effects of clutter. Experimental results agree closely with the theoretical predictions, showing that the clutter does not affect the optimal SNR performance in an SIL radar. A single-antenna SIL radar array is designed to detect vital signs with random body movement cancellation. To this end, a subject is placed between two single-antenna SIL radars to measure the rates of respiration and heartbeat using Doppler shift, and the effects of random movement of the subject are cancelled by wireless mutual injection locking (MIL) of the two radars. In an experiment, a prototype of such a two-radar array with a spacing of 2 m was implemented at 2.4 GHz, providing accurate and reliable cardiopulmonary monitoring of a subject who jogged on a treadmill with random body motion of many centimeters.

Compact Low-Loss Integration of High- $Q$ 3-D Filters With Highly Efficient Antennas

Abstract: A novel synthesis technique to integrate high-Q 3-D filters with highly efficient slot antennas is presented in this paper. This technique allows for compact integration of 3-D filters and antennas with very high antenna efficiency and significantly reduced form factor of integrated RF front ends. Prototype four-pole Chebyshev cavity filters integrated with slot antennas are demonstrated at X-band using both coaxial and coplanar waveguide feeding. The center frequency and fractional bandwidth of the filter/antenna system with coaxial feeding are 9.96 GHz and 6.0%, respectively. Due to the high-Q factor (~850) of the cavity resonator, the efficiency of this filter/antenna system is measured to be 89%, compared with the measured S21 of -0.5 dB (89%) for an identical filter. This means a near 100% efficient slot antenna is achieved within this integrated filter/antenna system. The measured impedance matching, efficiency, gain, and radiation pattern closely agree with simulation results. Equivalent-circuit models of the integrated filter/antenna system are developed and verified with full-wave simulations. This technique can be applied for filter/antenna integration in all microwave, millimeter-wave, and submillimeter-wave frequency regions.

A Filtering Microstrip Antenna Array

Abstract: A new filtering microstrip antenna array is presented. The antenna elements, together with the very compact feeding network, function as a third-order bandpass filter. The feeding network, which consists of one power divider and two baluns, provides the first two stages, and the microstrip antenna elements provide the last stage in the filter design. The equivalent lumped circuit model is analyzed, and the detail synthesis procedure is presented. A third-order filtering 2 × 2 microstrip antenna array is designed at a center frequency of 5 GHz with 3% fractional bandwidth and Chebyshev 0.3-dB equal-ripple broadside antenna gain response. The results from circuit model, full-wave simulation, and measurements agree well. Compared to the conventional patch antenna array, the proposed filtering microstrip antenna array successfully suppresses the unwanted signals in out-of-band, preserves good selectivity at band edges, and retains the flatness of the passband broadside antenna gain response.

Power Efficiency and Linearity Enhancement Using Optimized Asymmetrical Doherty Power Amplifiers

Abstract: This paper investigates the virtues of the asymmetrical Doherty power amplifier (PA) for improving the average power efficiency, linearity, and peak envelope power. It commences with an in-depth study of the effects of increasing the size of the peaking amplifier's transistor and its conduction angle on the Doherty PA's RF performance. In particular, the impact of the extended current profile of the peaking amplifier and reduced turn-on effects on the soft-turn characteristic are thoroughly analyzed, and their impacts on the average efficiency and peak power are deduced. Furthermore, the aggravation of the memory effects that accompany the gm3-based nonlinear distortion cancellation is experimentally demonstrated. Two asymmetrical Doherty PAs prototypes are fabricated using 80 W and 150 W laterally diffused metal oxide semiconductor field-effect transistors to individually improve average efficiency and linearity. When driven with a four carrier wideband code division multiple access (4C-WCDMA) signal, the asymmetrical Doherty PA allowed for excellent drain efficiency of approximately 50%, along with high linearity of approximately -50 dBc , using a memory polynomial digital predistorter at an average output power of 50 W. To the best of the authors' knowledge, this achieved efficiency is the highest reported in the literature for a high-power Doherty PA implemented in LDMOS technology.

Theoretical and Experimental Study of a New Class of Reflectionless Filter

Abstract: A design methodology and equations are described for lumped-element filter prototypes having low-pass, high-pass, bandpass, or bandstop characteristics with theoretically perfect input- and output-match at all frequencies. Such filters are a useful building block in a wide variety of systems in which the highly reactive out-of-band termination presented by a conventional filter is undesirable. The filter topology is first derived from basic principles. The relative merits of several implementations and tunings are then compared via simulation. Finally, measured data on low-pass and bandpass filter examples are presented, which illustrate the practical advantages, as well as showing excellent agreement between measurement and theory.

Compact Dual-Mode Triple-Band Bandpass Filters Using Three Pairs of Degenerate Modes in a Ring Resonator

Abstract: In this paper, a class of triple-band bandpass filters with two transmission poles in each passband is proposed using three pairs of degenerate modes in a ring resonator. In order to provide a physical insight into the resonance movements, the equivalent lumped circuits are firstly developed, where two transmission poles in the first and third passbands can be distinctly tracked as a function of port separation angle. Under the choice of 135° and 45° port separations along a ring, four open-circuited stubs are attached symmetrically along the ring and they are treated as perturbation elements to split the two second-order degenerate modes, resulting in a two-pole second passband. To verify the proposed design concept, two filter prototypes on a single microstrip ring resonator are finally designed, fabricated, and measured. The three pairs of transmission poles are achieved in all three passbands, as demonstrated and verified in simulated and measured results.

Optimization for Envelope Shaped Operation of Envelope Tracking Power Amplifier

Abstract: This paper describes the analysis of an optimized envelope shaping function for the envelope tracking power amplifier (ET PA) and its implementation. The proposed shaping function, which is sweet spot tracking with crest factor reduction, improves the efficiency and output power of the power amplifier (PA), as well as its linearity. For an accurate simulation of the supply modulator, an equivalent model of the PA under the envelope shaping is suggested. To achieve high efficiency and wide bandwidth, the CMOS supply modulator has a hybrid structure of a switching amplifier and a linear amplifier. The fabricated ET PA delivers higher efficiency and better linearity than standalone PA for the wideband code division multiple access and long-term evolution signals.

A New Power Management IC Architecture for Envelope Tracking Power Amplifier

Abstract: A new supply modulator architecture for robust performance against the battery voltage variation is presented. The resulting modulator is an optimized power management integrated circuit (PMIC) for an envelope tracking (ET) power amplifier (PA). The basic topology of the PMIC is based on a hybrid switching amplifier combining a wideband class-AB buffered linear amplifier and a highly efficient switching-mode buck converter in a master-slave configuration. The additional boost converter regulates the supply voltage of the linear amplifier, while the supply of the buck converter is directly coupled to the battery. The proposed supply modulator achieves max/min efficiencies of 76.8/69.3% over the entire battery voltage range. The ET PA is operated at 4.5 V, providing higher output power, efficiency, and gain than at nominal 3.5-V design. The robust performance of the proposed PMIC is demonstrated.

A Dual-Input Digitally Driven Doherty Amplifier Architecture for Performance Enhancement of Doherty Transmitters

Abstract: In this paper, the novel architecture of a dual-input and digitally driven Doherty amplifier is proposed with the aim of improving the performance of gallium-nitride (GaN) Doherty transmitters. In this work, the power efficiency is enhanced by using digital adaptive phase alignment to compensate for performance degradation due to bias and power-dependant phase misalignment between the carrier and peaking branches. For experimental validation, the proposed dual-input digital Doherty power amplifier (PA) was implemented using a 10-W GaN transistor. Measurement results demonstrate that the dual-input Doherty prototype exhibited a power-added efficiency (PAE) higher than 50% over an 8-dB output power back-off (OPBO) range. In comparison with the conventional fully analog Doherty PA, this represents a 10% improvement in PAE over the same OPBO range. Using a one-carrier Worldwide Interoperability for Microwave Access signal with a 7-dB peak-to-average power ratio, the dual-input Doherty PA, with digital adaptive phase alignment applied at the input of its peaking path, achieved a PAE of 57% at an average output power of 37.8 dBm, along with a - 22-dBc adjacent channel power ratio (ACPR). This corresponds to an improvement of 7% in PAE and 1 dB in average output power for the same ACPR level in comparison with a conventional fully analog Doherty PA.

Design and Performance of a 600–720-GHz Sideband-Separating Receiver Using ${\hbox{AlO}}_{x}$ and AlN SIS Junctions

Abstract: We present the design, modeling, construction, and characterization of a sideband separating heterodyne receiver that covers the frequency range from 600 to 720 GHz. The receiver has been constructed using waveguide technology in the split-block technique. The core of the mixer consists of a quadrature hybrid, two directional couplers to inject the local oscillator signal, two superconductor-insulator-superconductor (SIS) junctions, three signal-termination loads, and two planar IF/bandpass-filter/dc-bias circuits. The instrument that we have constructed presents excellent performance as demonstrated by two important figures of merit: receiver noise temperature and sideband ratio. Across the entire band, the uncorrected single-sideband noise temperature is below 500 K and reaches 190 K at the best operating point. The sideband ratio is greater than 10 dB over most of the frequency operating range. Superconducting junctions containing AlO∞ - and AlN-tunnel barriers were tested.

Compact Quarter-Wave Resonator and Its Applications to Miniaturized Diplexer and Triplexer

Abstract: Novel and compact composite right/left-handed (CRLH) quarter-wave type resonators are proposed in this paper. The resonator can resonate at the frequency where the electrical length is phase-leading or negative, which results in a smaller size as compared to the conventional phase-delayed microstrip-line resonator. Furthermore, it is only half the size of the CRLH half-wave resonator resonating at the same frequency. In addition, the proposed resonator is capable of engineering the multiresonances very close to each other, which makes it suitable to implement the miniaturized multiband microwave components such as diplexers and triplexers. A very compact diplexer and a very compact triplexer are proposed based on the proposed CRLH quarter-wave resonators in this paper and both of them have demonstrated very good performance. Specifically, compared to the referenced works based on the conventional microstrip resonators, the proposed diplexer and triplexer are 50% and 76% smaller than their microstrip counterparts, respectively.

A Tunable Three-Pole 1.5–2.2-GHz Bandpass Filter With Bandwidth and Transmission Zero Control

Abstract: This paper presents a three-pole tunable combline bandpass filter with center frequency, bandwidth, and zero control. The filter is designed on a Duroid substrate with er=10.2 and h=25 mil . A frequency range of 1.5-2.2 GHz with a 1-dB bandwidth tuning from 50 to 170 MHz (2.2%-11.2% fractional bandwidth) is achieved. The transmission zero can also be controlled, and a zero location of 1.37-1.64 GHz is demonstrated at center frequency fo of 2.05 GHz. The measured third-order intermodulation intercept point and 1-dB power compression point at midband (1.85 GHz) and a bandwidth of 110 MHz are >;15 and 8 dBm, respectively. To our knowledge, this is the first three-pole combline tunable bandpass filter with center frequency, bandwidth, and transmission zero control.

Ultimate RF Performance Potential of Carbon Electronics

Abstract: Carbon electronics based on carbon nanotube array field-effect transistors (AFETs) and 2-D graphene field-effect transistors (GFETs) have recently attracted significant attention for potential RF applications. Here, we explore the ultimate RF performance potential for these two unique devices using semiclassical ballistic transport simulations. It is shown that the intrinsic current-gain and power-gain cutoff frequencies (fT and fMAX ) above 1 THz should be possible in both AFETs and GFETs. Thus, both devices could deliver higher cutoff frequencies than traditional semiconductors such as Si and III-V's. In the case of AFETs, we show that their RF operation is not sensitive to the diameter variation of semiconducting tubes and the presence of metallic tubes in the channel. The ultimate fT and fMAX values in AFETs are observed to be higher than that in GFETs. The optimum device biasing conditions for AFETs require smaller biasing currents, and thus, lower power dissipation compared to GFETs. The degradation in high-frequency performance in the presence of external parasitics is also seen to be lower in AFETs compared to GFETs.

New Ultra-Wide Stopband Low-Pass Filter Using Transformed Radial Stubs

Abstract: A new type of low-pass filter (LPF) with ultra-wide band rejection and compact size by using a proposed transformed radial stubs (TRSs) is introduced and investigated. The operating mechanism of the filter is investigated based on proposed equivalent-circuit model. The implemented LPF with 1-dB cutoff frequency fc of 3 GHz demonstrates stopband rejection up to 8 fc i.e., 24 GHz. The skirt selectivity is achieved up to -144 dB per octave through multiple-zero generation using TRSs. The measured passband insertion loss is less than 1.5 dB. I/O loading cells are used to further extend the deep stopband to more than 13 fc i.e., above 40 GHz. The size of the four-cell LPF is only 0.31 λg × 0.24 λg, (λg is the guide wavelength at center cutoff frequency) without using any lumped elements.

Design of Bandwidth-Enhanced Doherty Power Amplifiers for Handset Applications

Abstract: A quarter-wavelength impedance transformer as well as a number of other factors limit the bandwidth (BW) of Doherty power amplifiers (PAs). We utilize the lower Q of a quarter-wave length transformer and propose a phase compensation circuit and an additional offset line to be incorporated into the matching net works for an enhanced BW of the Doherty PA. The quarter-wave length transformer and the final output circuit have the same Q. Input dividing networks are also analyzed for operation of broad BW. The Doherty PA for long term evolution (LTE) applications is integrated into a 1.4 × 1.4 mm2 die using an InGaP/GaAs hetero junction bipolar transistor (HBT) process. For an LTE signal with a 7.5-dB peak-to-average power ratio (PAPR) and a 10-MHz BW, the PA with a supply voltage of 4.5 V delivers a power-added ef ficiency (PAE) of 36.3% and an adjacent channel leakage ratio (ACLR) of -32 dBc with an average output power of 27.5 dBm at a frequency of 1.85 GHz. Across frequencies from 1.6-2.1 GHz, the PA performs with a PAE of more than 30%, a gain of more than 28 dB and an ACLR of less than -31 dBc at an average output power of 27.5 dBm while satisfying the standard spectrum mask. These figures verify that the proposed bandwidth enhancement techniques are effective for handset Doherty PAs.