Search

This paper describes a technique for reconstructing one-dimensional stratified permittivity profiles. The proposed technique is based on the inversion of the measured frequency-domain reflection coefficient of the profile into a virtual time domain. The inversion of the reflection coefficient is based on the super-resolution technique root multiple-signal classification. The advantage of using this technique is its ability to remove the sidelobe effect caused by the limited measurement bandwidth. Measurements using different materials have been carried out to validate the quality of the proposed technique. [ABSTRACT FROM AUTHOR]

In this paper, a new methodology for the design of compact planar filters in microstrip technology is proposed. This is based on cascading filter stages consisting of the combination of complementary split-ring resonators (CSRRs), recently proposed by the authors, series capacitive gaps, and grounded stubs. By this means, we achieve the necessary flexibility to simultaneously obtain quite symmetric frequency responses, controllable bandwidths, and compact dimensions. Two prototype device bandpass filters are provided to illustrate the potentiality of the proposed approach. In the first prototype, the structure is periodic (i.e., composed of identical cells) and behaves as a left-handed transmission line with controllable bandwidth. In the second prototype device, periodicity is sacrificed with an eye toward the synthesis of a standard (Chebyshev) approximation. The measured frequency responses point out low insertion losses in the passband, as well as high-frequency selectivity with small dimensions. As compared to conventional parallel coupled line filters, reduction of device length by a factor of 2.4 is demonstrated. This is the first time that planar filters with controllable bandwidth based on CSRRS are achieved. These structures can be of interest in those applications where miniaturization and compatibility with planar circuit technology are key issues. [ABSTRACT FROM AUTHOR]

This paper presents the theory, design procedure, and implementation of a dual-band planar quadrature hybrid with enhanced bandwidth. The topology of the circuit is a three-branch-line (3-BL) quadrature hybrid, which provides much larger flexibility to allocate the desired operating frequencies and necessary bandwidths than other previously published configurations. A performance comparison with other dual-band planar topologies is presented. Finally, a 3-BL quadrature hybrid for dual band (2.4 and 5 GHz) wireless local area network systems was fabricated, aimed to cover the bands corresponding to the standards IEEE802.11a/b. The measurements show a 16% and 18% bandwidth for the lower and upper frequency, respectively, satisfying and exceeding the bandwidth requirements for the above standards. [ABSTRACT FROM AUTHOR]

CMOS broad-band compact high-linearity binary phase-shift keying (BPSK) and IQ modulators are proposed and analyzed in this paper. The modulators are constructed utilizing a modified reflection-type topology with the transmission lines implemented on the thick SiO2 layer to avoid the lossy silicon substrate. The monolithic microwave integrated circuit (MMIC) chips were fabricated using standard bulk 0.13-μm MS/RF CMOS process and demonstrated an ultracompact layout with more than 80% chip size reduction. The broadside couplers and 180° hybrid for the modulators in the CMOS process are broad-band designs with low phase/amplitude errors. The dc offset and imbalance for the proposed topology are investigated and compared with the conventional reflection-type modulators. The measured dc offset was improved by more than 10 dB. Both BPSK and IQ modulators feature a conversion loss of 13 dB, a modulation bandwidth of wider than 1 GHz, and second- and third-order spur suppressions of better than -30 dBc. The IQ modulator shows good sideband suppression with high local-oscillator suppression from 20 to 40 GHz. The modulators are also evaluated with a digital modulation signal and demonstrate excellent modulator quality and adjacent channel power ratio. [ABSTRACT FROM AUTHOR]

This paper proposes a novel frequency channel blocking (FCB) scheme in mesh-topology millimeter-wave broad- hand entrance networks. In the FCB scheme, any frequency channel is determined to be blocked according to not only the network throughput, but also the newly defined fairness index. As the results, the FCB scheme yields better throughput and fairness performances with a little increase in computational complexity compared to the conventional scheme. [ABSTRACT FROM AUTHOR]

A proof-of-concept broad-band 180° phase shifter operating at 220 GHz and based on planar integrated Schottky diodes is presented. The phase shifter is a monolithic implementation incorporating impedance transformers designed to yield broad-band operation and compensate for amplitude imbalance between bias states of the diodes. The circuit described in this paper has yielded a phase shift of 180° ± 15° over a 55-GHz band with average insertion loss of 5.5 dB. Moreover, the phase shifter is demonstrated and tested as a sideband generator where it has exhibited an average carrier-to-single sideband conversion loss of 10 dB. The circuit architecture is scalable to submillimeter frequencies where phase shifters are often employed for sideband generation and parametric upconversion. [ABSTRACT FROM AUTHOR]

This paper presents efficiency optimization of X-band two-stage microwave power amplifiers (PAs) in which the output stage is designed to operate in class-E mode. A hybrid PA which uses the same MESFET devices in both stages achieves 16 dB of saturated gain with an output power of 20 dBm and total power added efficiency (PAE) of 52% at 10 GHz. A broadband monolithic two-stage double heterojunction bipolar transistor PA, fabricated by Northrop Grumman Space Technology, with a class-AB first stage and class-E second stage achieves 24.6 dBm of output power with 24.6-dB gain and total PAE of 52% at 8 GHz. The design is performed starting from class-E theory and using load-pull measurements and/or nonlinear simulations. [ABSTRACT FROM AUTHOR]

In this paper, V-band high-order frequency divider monolithic microwave integrated circuits (MMICs) showing wide bandwidth and low-power dissipation are presented. For high-order (divide-by-four) frequency division, a super-harmonic signal is injected into a self-oscillating subharmonic mixer loop consisting of cascode field-effect transistors (FETs). Cascode FET-based harmonic injection locking allows high-frequency operation, simple circuit configuration, reduced FET count, and thus, low dc power consumption. Bias circuits and quarter-wavelength stubs are used to effectively suppress unwanted harmonic and spurious signals in the oscillation loop. A simple analysis method employing two-tone harmonic-balance simulation and an ideal directional coupler is developed to optimize the performance of the high-order divider. The designed V-band frequency dividers are fabricated with a commercial 0.15-μm GaAs pseudomorphic high electron-mobility transistor foundry. The measurement of a divide-by-four MMIC shows a bandwidth of 2.81 GHz around 64.0 GHz under very small dc power consumption of 7.5 mW. The circuit concept has been extended to a divide-by-five MMIC by adding a frequency doubler in the feedback loop, which shows the bandwidth of 1.02 GHz at V-band. To the best of our knowledge, the frequency dividers of this study show the best performance in terms of division order and dc power consumption among the reported millimeter-wave analog frequency dividers at V-band and above. [ABSTRACT FROM AUTHOR]

In this paper, a new architecture for baseband digital predistortion dedicated to wide-hand transmissions is presented. The proposed predistorter consists of a cascade of a static lookup table-based predistorter and a subband filtering block. The subband filtering technique is used to improve the correction bandwidth limitation of conventional architectures. The cases of four- and eight-subband decomposition were considered and compared to the case where the fullband signal is processed. This revealed that the subband processing results in a better sensitivity and an independent tuning ability of the predistorter at each subband. In addition, it was shown that, in the proposed predistorter, the computational complexity and the required processing speed are reduced proportionally to the number of subbands. Moreover, in an adaptive digital predistortion context, a quicker convergence can be achieved. Experimental validation of the subband-based predistortion concept was successfully carried on a 100-W peak envelop power lateral double diffused metal-oxide semiconductor power amplifier. [ABSTRACT FROM AUTHOR]

This paper presents a state-of-the-art RF micro- electromechanical systems wide-baud miniature tunable filter designed for 6.5-10-GHz frequency range. The differential filter, fabricated on a glass substrate using digital capacitor banks and microstrip lines, results in a tuning range of 44% with very fine resolution, and return loss better than 16 dB for the whole tuning range. The relative bandwidth of the filter is 5.1±0.4% over the tuning range and the size of the filter is 5 mm × 4 mm. The insertion loss is 4.1 and 5.6 dE at 9.8 and 6.5 GHz, respectively, for a 1-kΩ/sq fabricated bias line. The simulations show that, for a bias line with 10- kΩ/sq resistance or more, the insertion loss improves to 3 dB at 9.8 GHz and 4 dB at 6.5 GHz. The measured IIP3 level is > 45 dBm for Δf > 500 kHz, and the filter can handle 250 mW of RF power for hot and cold switching. [ABSTRACT FROM AUTHOR]

A fully integrated very wide-band (WB) digital receiver subsystem has been developed to support the Navy Advanced Multifunction RF Concept test-bed program. Input RF signals in the 6-18-GHz band are processed to provide digital outputs for narrow-band and digital beam outputs for WB applications having instantaneous bandwidths of 22 and 230 MHz, respectively. This paper describes the design and performance of the digital receiver subsystem. [ABSTRACT FROM AUTHOR]

This paper presents integrated antennas, which can fulfil both the functions of an antenna and a power combiner, thus reducing the circuit loss. This will be useful for linear amplification using nonlinear components systems, where the circuit-level power-combiner losses degrade overall efficiency. Two antennas, which use a single-layer structure and a multi- layer structure, respectively, are designed. Both antennas achieve good impedance-matching characteristics under both even- and odd-mode excitations. The single-layer antenna has a narrow bandwidth, and the even-mode radiated power at boresight is 33 and 26 dB lower than that of the odd-mode radiated power at the E- and H-plane, respectively, thus demonstrating the effective suppression of even-mode radiation. The other antenna using multilayer structure achieves a broad-hand bandwidth (S11 < - 10 dB) of 15.5% and 8% under the odd- and even-mode excitation, respectively. Across the bandwidth, broadside radiation patterns with low cross-polar levels (< -21 dB) are achieved under the odd-mode excitation, while the even-mode radiation is also suppressed. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for the design of broad-band waveguide polarizers. It consists of an interactive procedure where the designer places the zeros of the reflection coefficient for one polarization, simultaneously also controlling the frequency response of the other one and vice versa. In this way, the best matching condition for both polarizations can be found. This design tool is based on an automated phase control procedure and on an algorithmic characterization of the relationship between the two frequency responses. The spurious effects of multimodal interactions, frequency dispersion, and losses are taken into account and compensated by characterizing them with suitable transfer functions. Designs of iris-loaded polarizers in square and circular waveguides are described, with operative bandwidths up to 30%. Measurements on a 10% bandwidth K a-band prototype show reflection and cross-polarization levels of approximately -50 dB, with a phase error of approximately 0.4°. [ABSTRACT FROM AUTHOR]

Area-efficient single-ended-to-differential phase-splitter (balun) integration is difficult for frequencies below 6 GHz. Few broad-band solutions are available, and those given in the literature often introduce quite high amplitude and/or phase errors to differential signaling. In this paper, a cascade of differential pairs is shown always to outperform any single-stage solution, and the measurement data for a two-amplifier prototype are supplied to support the theory. The prototype circuit was realized on 0.8-μm SiGe as a 2.5-V RF integrated circuit measuring 1.2 × 1.2 mm² including pads. The measured gain error is better than -1 dB up to 4.6 GHz, while phase difference is between 179.7°-180.9° in 0.6-4.1 GHz. The application of the realized phase splitter in a broad-band quadrature modulator is discussed. [ABSTRACT FROM AUTHOR]

This paper presents the design, numerical analysis, and testing of several symmetric periodic mode converters of two generic types: a uniform ripple-wall converter and a nonuniform ripple-wall converter. All designs operate at a central frequency of 17.136 GHz and convert circular electric modes (TE0n) from one radial mode to the next higher mode. The emphasis of the design study is to maximize the bandwidth of the device without sacrificing mode purity. Mode converters from the TE01 to TE02 mode and from the TE02 to TE03 mode were investigated in depth, and two designs, each with six periods, were constructed and tested. The nonuniform ripple seems to have a significant advantage over the constant ripple design for the higher mode converter, while the designs for the lower mode converter are comparable. Experimental measurements agree well with the theoretical results both in terms of bandwidth and mode content. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive wide-band digitally controlled RF envelope predistortion linearization system for power amplifiers (PAs). A field-programmable gate-array-based lookup table is indexed by a digitized envelope power signal, and instantaneously adjusts the input signal amplitude and phase via an RF vector modulator to compensate for the AM--AM and AM--PM distortion. The advantages of this predistortion architecture over conventional baseband digital approaches are that a 20%-33% wider correction bandwidth is achievable at the same clock speeds, and linearization can be performed without the need for a digital baseband input signal. The timing match between the input RF signal and predistorting signal, which is one of the critical factors for performance, was investigated and adjusted to obtain optimum performance. Using three-carrier cdmaOne and wide-band multitone signals, the linearization performances for a 0.5-W GaAs heterostructure field-effect transistor, a 90-W peak-envelope-power (PEP) silicon LDMOS PA, and a 680-W PEP LDMOS PA were examined. In addition, the predistortion performance variation for different signals was studied in terms of signal envelope statistics, output powers, and PA power capacities. [ABSTRACT FROM AUTHOR]

As the complexity of modem modulation schemes increases, the noise levels inserted in the receive band by the transmitter are also increased. In this paper, a technique to enhance the isolation of a surface acoustic wave duplexer is introduced, which reduces the noise levels in the receive band of the system. Feedforward techniques are used to create an adaptive null in the receive band, which can be targeted at any channel across the band. This null has been shown to give an improved isolation of 20 dB for the duplexer over a 2-MHz bandwidth. This feedforward system is implemented using a barium strontium titanate phase shifter to enable tunability of the enhancement null. Multipath feedforward techniques are also used to create extra nulls in the receive band and, hence, further improve isolation. [ABSTRACT FROM AUTHOR]

This paper reports on a novel lumped balun topology, the second-order lattice balun, with broad-band performance. The design is based on synthetic transmission lines operating as impedance transformers, The characteristic impedance of the synthetic transmission lines may be chosen to obtain inherent impedance transformation. An analytical investigation results in closed formulas for optimum performance over a given band-width. It is shown that it is possible to design for equal ripple in amplitude balance and input reflection coefficient. The phase balance is theoretically perfect over the entire bandwidth. The concept is experimentally validated by a 1-GHz prototype fabricated with surface mounted chip components. It exhibits an amplitude balance better than 0.5 dB and a phase balance better than ±8° over an octave bandwidth. The effective area of the prototype is 7 × 9 mm⊃. [ABSTRACT FROM AUTHOR]

The relatively less exploited terahertz band possesses great potential for a variety of important applications, including communication applications that would benefit from the enormous bandwidth within the terahertz spectrum. This paper, overviews an approach toward terahertz applications based on SiGe heterojunction bipolar transistor (HBT) technology, focusing on broad-band communication applications. The design, characteristics, and reliability of SiGe HBTs exhibiting record fT of 375 GHz and associated fmax of 210 GHz are presented. The impact of device optimization on noise characteristics is described for both low-frequency and broad-band noise. Circuit implementations of SiGe technologies are demonstrated with selected circuit blocks for broad-band communication systems, including a 3.9-ps emitter coupled logic ring oscillator, a 100-GHz frequency divider, 40-GHz voltage-controlled oscillator, and a 70-Gb/s 4:1 multiplexer. With no visible limitation for further enhancement of device speed at hand, the march toward terahertz band with Si-based technology will continue for the foreseeable future. [ABSTRACT FROM AUTHOR]

Double-sided parallel-strip lines have been used as a balanced transmission line to feed double-sided printed antennas or to fabricate microwave components such as balanced mixers. In this paper, ultrawide-band transitions from microstrip line to double-sided parallel-strip line are developed with 1-30-GHz bandwidth. New microwave components using double-sided parallel-strip lines are designed with good measured results. The double-sided parallel-strip line has an advantage of easy realization of low-impedance lines, which are important for many component designs. [ABSTRACT FROM AUTHOR]

Abstract-This paper describes the design of millimeter-wave wide-band monolithic GaAs passive high electron-mobility transistor (HEMT) switches using the traveling-wave concept. This type of switch combined the off-state shunt transistors and series microstrip lines to form an artificial transmission line with 50-Ω characteristic impedance. A 15-80-GHz single-pole double-throw (SPDT) switch in conjunction with quarter-wavelength impedance transformers demonstrates an insertion loss of less than 3.6 dB and an Isolation of better than 25 dB. Another type of wide-band switch was designed by using a series HEMT switch to replace the quarter-wavelength transformer, and the operating band can be extended to dc. With this scheme, dc-80-GHz single-pole single-throw (SPST) and dc.-60-GHz SPDT switches are also developed with compact chip size. From dc to 80 GHz, the insertion loss and isolation of the SPST switch are better than 3 and 24 dB, respectively. The SPDT switch has an insertion loss of better than 3 dB and an isolation of better than 25 dB from dc to 60 GHz. The analysis of circuit characteristics and design procedures are also included. It is concluded that the device periphery can be selected for the desired bandwidth, while the number of transistors is decided to achieve the isolation. [ABSTRACT FROM AUTHOR]

In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constunt within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line makes it difficult to design a tunable bundpass filter with minimum degradation in passband performance. By using step-impedance microstrip lines, couplings between resonators can be controlled so that the constant bandwidth requirement could be satisfied with reasonable design parameter values. Lumped inductors are used for input and output coupling networks. Design equations are derived, and experimental results ale compared with theoretical ones based on these equations. [ABSTRACT FROM AUTHOR]

In this paper, active control schemes are presented to optimize the performance of the distributed amplifier (DA) subject to the process variation. A detailed analysis of the DA with mismatched termination loads has been performed, which reveals that pronounced gain and group-delay ripple arises at the low-frequency end from the reflected waves in the artificial transmission line. To solve this problem, an active variable resistor is proposed as the gate-line termination load. The gain and stability of the cascode DA has also been analyzed, which identifies the most critical component determining the tradeoff between the gain-bandwidth product (GBP) and the stability to be the gate feedback resistor of common-gate field-effect transistor. It is also replaced with the active resistor to maximize GBP, while avoiding oscillations. A nine-section cascode DA with active control features is designed and fabricated using commercial GaAs pseudomorphic high electron-mobility transistor foundry. The measurement shows that the gain and group-delay ripple can be minimized, and GBP can be maximized without oscillations by the active bias controls. Active control schemes allow the monolithic DAs to be fine tuned after the fabrication and, thus, can be a robust DA design methodology against process variation and inaccurate device models. [ABSTRACT FROM AUTHOR]

For personal communication systems, the highest possible integration into monolithic technology of all RF functions are desirable. A frequency band around 60 GHz is assigned for future mobile communication fourth-generation systems (i.e., mobile broad-band systems concept). In this paper, the design and test of two monolithic class-A power amplifiers with 0.15 μm pseudomorphic heterojunction FET (PMHFET) technology is presented. One of the amplifiers is a three-stage cascade 50 Ω amplifier and the second is a balanced amplifier based on the previous one, but matched for integration on a waveguide carrier. A study on the accuracy of the passive elements and discontinuities models at 60 GHz was performed. Models for the microstrip discontinuities were obtained from electromagnetic simulation. In order to choose the best FET bias, a nonlinear model for the PMHFETs devices, based on continuous DC and AC measurements, were derived. For comparison purposes, the FET simulation results with a nonlinear model based on pulsed measurements are also presented. To avoid stability problems, at the device level an RC feedback network was introduced. A 1-dB compression point of 18 dBm was measured on-wafer for both amplifiers at 62 GHz with VDSbias=3.5 V. The three-stage and balanced amplifiers chip sizes are 3 mm×1.5 mm and 3 mm×4 mm, respectively [ABSTRACT FROM PUBLISHER]

This paper investigates the use of amplifier linearization for performance improvement on a power amplifier developed for a wide-band CDMA (W-CDMA) system. A predistortion technique was chosen due to its compact size, which is suitable to implement in handsets. A predistorter (PD) monolithic-microwave integrated-circuit based on a heterojunction FET (HJFET) was designed and fabricated. Depending on the control voltage, the PD achieves both gain expansion and compression characteristics, which is shown to be important for compensating various amplifier nonlinearities. The power performances of an HJFET amplifier with and without a PD are compared. Due to the variation of the amplifier's responses under high and low quiescent current levels, the PD response required for optimum distortion cancellation in each case is examined. The linearized amplifier demonstrates a state-of-the-art power-added efficiency (PAE) of 57.4% under W-CDMA criteria, resulting from a 5-dB reduction in adjacent channel leakage power ratio. In addition, the use of power control in a W-CDMA system requires amplifiers with good efficiency over a wide range of output power. By combining a bias control scheme with predistortion, it is shown that a high PAE of over 40% can also be achieved for a 20 dB output power range. The improvements achieved are attributed to the alleviation of amplifier's nonlinearities after linearization [ABSTRACT FROM PUBLISHER]