Showing papers in "IEEE Transactions on Microwave Theory and Techniques in 2004"

Terahertz technology in biology and medicine

Abstract: Terahertz irradiation and sensing is being applied for the first time to a wide range of fields outside the traditional niches of space science, molecular line spectroscopy, and plasma diagnostics. This paper surveys some of the terahertz measurements and applications of interest in the biological and medical sciences.

Space mapping: the state of the art

Abstract: We review the space-mapping (SM) technique and the SM-based surrogate (modeling) concept and their applications in engineering design optimization. For the first time, we present a mathematical motivation and place SM into the context of classical optimization. The aim of SM is to achieve a satisfactory solution with a minimal number of computationally expensive "fine" model evaluations. SM procedures iteratively update and optimize surrogates based on a fast physically based "coarse" model. Proposed approaches to SM-based optimization include the original algorithm, the Broyden-based aggressive SM algorithm, various trust-region approaches, neural SM, and implicit SM. Parameter extraction is an essential SM subproblem. It is used to align the surrogate (enhanced coarse model) with the fine model. Different approaches to enhance uniqueness are suggested, including the recent gradient parameter-extraction approach. Novel physical illustrations are presented, including the cheese-cutting and wedge-cutting problems. Significant practical applications are reviewed.

Design of a multiband OFDM system for realistic UWB channel environments

Abstract: In February 2002, the Federal Communications Commission allocated 7500 MHz of spectrum for unlicensed use of commercial ultra-wideband (UWB) communication devices. This spectral allocation has initiated an extremely productive activity for industry and academia. Wireless communications experts now consider UWB as available spectrum to be utilized with a variety of techniques, and not specifically related to the generation and detection of short RF pulses as in the past. There are many differences between real-world behavior of narrow-band and UWB systems. All wireless systems must be able to deal with the challenges of operating over a multipath propagation channel, where objects in the environment can cause multiple reflections to arrive at the receiver (RX). For narrow-band systems, these reflections will not be resolvable by the RX when the narrow-band system bandwidth is less than the coherence bandwidth of the channel. The large bandwidth of UWB waveforms, instead, significantly increases the ability of the RX to resolve the different reflections in the channel. The UWB channel model developed by the IEEE 802.15.3a standard body is described in this paper. For highly dispersive channels, an orthogonal frequency-division multiplexing (OFDM) RX is more efficient at capturing multipath energy than an equivalent single-carrier system using the same total bandwidth. OFDM systems possess additional desirable properties, such as high spectral efficiency, inherent resilience to narrow-band RF interference, and spectral flexibility, which is important because the regulatory rules for UWB devices have not been finalized throughout the entire world. This paper describes the design of a UWB system optimized for very high bit-rate, low-cost, and low-power wireless networks for personal computing (PC), consumer electronics (CE), and mobile applications. The system combines OFDM modulation technique with a multibanding approach, which divides the spectrum into several sub-bands, whose bandwidth is approximately 500 MHz. The system described in this paper has been selected by several key industry organizations [Mulitband OFDM Alliance, WiMedia, Wireless Universal Serial Bus (USB)] because of its very good technical characteristics for the diverse set of high performance short-range applications that are eagerly anticipated for CE, PC, and mobile applications.

Implanted antennas inside a human body: simulations, designs, and characterizations

Abstract: Antennas implanted in a human body are largely applicable to hyperthermia and biotelemetry. To make practical use of antennas inside a human body, resonance characteristics of the implanted antennas and their radiation signature outside the body must be evaluated through numerical analysis and measurement setup. Most importantly, the antenna must be designed with an in-depth consideration given to its surrounding environment. In this paper, the spherical dyadic Green's function (DGF) expansions and finite-difference time-domain (FDTD) code are applied to analyze the electromagnetic characteristics of dipole antennas and low-profile patch antennas implanted in the human head and body. All studies to characterize and design the implanted antennas are performed at the biomedical frequency band of 402-405 MHz. By comparing the results from two numerical methodologies, the accuracy of the spherical DGF application for a dipole antenna at the center of the head is evaluated. We also consider how much impact a shoulder has on the performance of the dipole inside the head using FDTD. For the ease of the design of implanted low-profile antennas, simplified planar geometries based on a real human body are proposed. Two types of low-profile antennas, i.e., a spiral microstrip antenna and a planar inverted-F antenna, with superstrate dielectric layers are initially designed for medical devices implanted in the chest of the human body using FDTD simulations. The radiation performances of the designed low-profile antennas are estimated in terms of radiation patterns, radiation efficiency, and specific absorption rate. Maximum available power calculated to characterize the performance of a communication link between the designed antennas and an exterior antenna show how sensitive receivers are required to build a reliable telemetry link.

Recent system applications of short-pulse ultra-wideband (UWB) technology

Abstract: Developed in the early 1960s, time-domain electromagnetics, the study of electromagnetic-wave propagation from a time-domain perspective, has given birth to a fascinating new technology, which today is commonly referred to as ultra-wideband (UWB). It has now been slightly more than 25 years since the 1978 seminal paper of Bennett and Ross, which summarized UWB's early applications. It thus seems appropriate, given the tremendous increase in interest in the technology since the Federal Communications Commission modified its Part 15 rules to accommodate UWB transmissions, to take a look at more recent system applications of this unique technology. This paper provides a brief historical perspective of UWB, discusses recent techniques for the generation and reception of short-pulse electromagnetic waveforms, and examines a number of recently developed UWB systems in the communications, radar, and precision-positioning fields. Finally, a brief assessment of future trends for the technology is provided.

Recycling ambient microwave energy with broad-band rectenna arrays

Abstract: This paper presents a study of reception and rectification of broad-band statistically time-varying low-power-density microwave radiation. The applications are in wireless powering of industrial sensors and recycling of ambient RF energy. A 64-element dual-circularly-polarized spiral rectenna array is designed and characterized over a frequency range of 2-18 GHz with single-tone and multitone incident waves. The integrated design of the antenna and rectifier, using a combination of full-wave electromagnetic field analysis and harmonic balance nonlinear circuit analysis, eliminates matching and filtering circuits, allowing for a compact element design. The rectified dc power and efficiency is characterized as a function of dc load and dc circuit topology, RF frequency, polarization, and incidence angle for power densities between 10/sup -5/-10/sup -1/ mW/cm/sup 2/. In addition, the increase in rectenna efficiency for multitone input waves is presented.

Range correlation and I/Q performance benefits in single-chip silicon Doppler radars for noncontact cardiopulmonary monitoring

Abstract: Direct-conversion microwave Doppler-radar transceivers have been fully integrated in 0.25-/spl mu/m silicon CMOS and BiCMOS technologies. These chips, operating at 1.6 and 2.4 GHz, have detected movement due to heartbeat and respiration 50 cm from the subject, which may be useful in infant and adult apnea monitoring. The range-correlation effect on residual phase noise is a critical factor when detecting small phase fluctuations with a high-phase-noise on-chip oscillator. Phase-noise reduction due to range correlation was experimentally evaluated, and the measured residual phase noise was within 5 dB of predicted values on average. In a direct-conversion receiver, the phase relationship between the received signal and the local oscillator has a significant effect on the demodulation sensitivity, and the null points can be avoided with a quadrature (I/Q) receiver. In this paper, measurements that highlight the performance benefits of an I/Q receiver are presented. While the accuracy of the heart rate measured with the single-channel chip ranges from 40% to 100%, depending on positioning, the quadrature chip accuracy is always better than 80%.

Characterization of liquid crystal polymer (LCP) material and transmission lines on LCP substrates from 30 to 110 GHz

Abstract: Liquid crystal polymer (LCP) is a material that has gained attention as a potential high-performance microwave substrate and packaging material. This investigation uses several methods to determine the electrical properties of LCP for millimeter-wave frequencies. Microstrip ring resonators and cavity resonators are measured in order to characterize the dielectric constant (/spl epsi//sub r/) and loss tangent (tan/spl delta/) of LCP above 30 GHz. The measured dielectric constant is shown to be steady near 3.16, and the loss tangent stays below 0.0049. In addition, various transmission lines are fabricated on different LCP substrate thicknesses and the loss characteristics are given in decibels per centimeter from 2 to 110 GHz. Peak transmission-line losses at 110 GHz vary between 0.88-2.55 dB/cm, depending on the line type and geometry. These results show, for the first time, that LCP has excellent dielectric properties for applications extending through millimeter-wave frequencies.

CMOS low-noise amplifier design optimization techniques

Abstract: This paper reviews and analyzes four reported low-noise amplifier (LNA) design techniques applied to the cascode topology based on CMOS technology: classical noise matching, simultaneous noise and input matching (SNIM), power-constrained noise optimization, and power-constrained simultaneous noise and input matching (PCSNIM) techniques. Very simple and insightful sets of noise parameter expressions are newly introduced for the SNIM and PCSNIM techniques. Based on the noise parameter equations, this paper provides clear understanding of the design principles, fundamental limitations, and advantages of the four reported LNA design techniques so that the designers can get the overall LNA design perspective. As a demonstration for the proposed design principle of the PCSNIM technique, a very low-power folded-cascode LNA is implemented based on 0.25-/spl mu/m CMOS technology for 900-MHz Zigbee applications. Measurement results show the noise figure of 1.35 dB, power gain of 12 dB, and input third-order intermodulation product of -4dBm while dissipating 1.6 mA from a 1.25-V supply (0.7 mA for the input NMOS transistor only). The overall behavior of the implemented LNA shows good agreement with theoretical predictions.

A novel composite right-/left-handed coupled-line directional coupler with arbitrary coupling level and broad bandwidth

Abstract: A novel composite right-/left-handed (CRLH) backward-wave coupled-line directional coupler with arbitrary coupling level and broad bandwidth is presented, explained by even/odd-mode analysis, validated by full-wave simulations, and demonstrated by experiments. First, the CRLH-transmission-line (CRLH TL) theory is given, and a microstrip implementation of a CRLH TL is described. A simple circuit model is then proposed both for the understanding and design of the coupler. The coupler exhibits very unusual characteristics, such as zero electrical length, imaginary even/odd-mode characteristic impedances, and coupling dependence on even/odd attenuation length (instead of propagation length). Both a quasi-0and 3-dB coupler are demonstrated experimentally. The 3-dB coupler exhibits amplitude balance of /spl plusmn/2 dB over a huge bandwidth of 50% (3.5-5.8 GHz), phase balance of 90/spl deg//spl plusmn/5/spl deg/ from 3.0 to 4.0 GHz and directivity of 20 dB.

Arbitrary dual-band components using composite right/left-handed transmission lines

Abstract: Arbitrary dual-band microstrip components using composite right/left-handed (CRLH) transmission lines (TLs) are presented. Theory, synthesis procedure, and implementation of the dual-band quarter-wave (/spl lambda//4) CRLH TL are presented. Arbitrary dual-band operation is achieved by the frequency offset and the phase slope of the CRLH TL. The frequency ratio of the two operating frequencies can be a noninteger. The dual-band /spl lambda//4 open/short-circuit stub, dual-band branch-line coupler (BLC), and dual-band rat-race coupler (RRC) are also demonstrated. The performances of these dual-band components are demonstrated by both simulated and measured results. Insertion loss is larger than 23 dB for the shunt /spl lambda//4 CRLH TL open-circuit stub and less than 0.25 dB for the shunt /spl lambda//4 CRLH TL short-circuit stub at each passband. The dual-band BLC exhibits S/sub 21/ and S/sub 31/ larger than -4.034 dB, return losses larger than 17 dB, isolations larger than 13 dB, phase differences 90/spl deg//spl plusmn/1.5/spl deg/, and gain imbalance less than 0.5 dB at each passband. The dual-band RRC exhibits S/sub 21/ and S/sub 31/ larger than -4.126 dB, return losses larger than 12 dB, isolations larger than 30 dB, phase difference 180/spl deg//spl plusmn/4/spl deg/, and gain imbalance less than 0.2 dB at each passband.

Design of implantable microstrip antenna for communication with medical implants

Abstract: The objective of this paper is to design a microstrip patch antenna for communication with medical implants in the 402-405-MHz Medical Implant Communications Services band. Microstrip antenna design parameters are evaluated using the finite-difference time-domain method, and are compared to measured results. The effects of shape, length, size, location of feed point and ground point, substrate and superstrate materials, and their thicknesses are evaluated. An extensive study of the performance of the antennas to changes in these parameters was undertaken. The results of this paper provide guidance in the design of implantable microstrip antennas.

Dual-band bandpass filters using equal-length coupled-serial-shunted lines and Z-transform technique

Abstract: A synthesizing method is presented to design and implement digital dual-band filters in the microwave frequency range. A dual-band filter consists of a bandstop filter and a wide-band bandpass filter in a cascade connection, wherein the transfer functions of both the bandpass filter and bandstop filter are expressed in the Z domain. The bandstop filter is implemented by using a coupled-serial-shunted line structure, while the wide-band bandpass filter is constructed by using a serial-shunted line configuration. In particular, the bandwidth of each passband of the dual-band filter is controllable by adjusting the characteristics of both the bandpass filter and bandstop filter. By neglecting the dispersion effect between microstrip lines of different widths over a wide bandwidth, a dual-band filter is realized in the form of microstrip lines and its frequency responses are measured to validate this method.

Microwave imaging via space-time beamforming: experimental investigation of tumor detection in multilayer breast phantoms

Abstract: Microwave imaging via space-time (MIST) beamforming has been proposed recently for detecting small malignant breast tumors. In this paper, we extend the previously presented two-dimensional space-time beamformer design to three-dimensional (3-D), and demonstrate its efficacy using experimental data obtained with a multilayer breast phantom. The breast phantom consists of a homogeneous normal breast tissue simulant covered by a thin layer of skin simulant. A small synthetic malignant tumor is embedded in the breast phantom. We have developed several tumor simulants that yield the range of dielectric contrasts between normal and malignant tissue that are expected in clinical scenarios. A microwave sensor comprised of a synthetic planar array of compact ultrawide-band (UWB) antennas is immersed in a coupling medium above the breast tissue phantom. At each position in the array, the antenna transmits a synthetically generated pulse (1-11 GHz) into the phantom. The received backscatter signals are processed by a data-adaptive algorithm that removes the artifact caused by antenna reverberation and backscatter from the skin-breast interface, followed by 3-D space-time beamforming to image backscattered energy as a function of location. Our investigation includes a numerical (finite difference time domain) and experimental study of the UWB antenna performance in the immersion medium, as well as a study of the influence of malignant-to-normal breast tissue dielectric contrast on dynamic range requirements and tumor detectability. This paper represents the first experimental demonstration of 3-D MIST beamforming in multilayer breast phantoms with malignant-to-normal dielectric contrasts down to 1.5 : 1 for a 4-mm synthetic tumor.

Planar distributed structures with negative refractive index

Abstract: Planar distributed periodic structures of microstrip-line and stripline types, which support left-handed (LH) waves are presented and their negative refractive index (NRI) properties are shown theoretically, numerically, and experimentally. The supported LH wave is fully characterized based on the composite right/left-handed transmission-line theory and the dispersion characteristics, refractive indexes, and Bloch impedance are derived theoretically. In addition, formulas to extract equivalent-circuit parameters from full-wave simulation are given. Open (microstrip) and closed (stripline) structures with a 5/spl times/5 mm/sup 2/ unit cell operating at approximately 4 GHz are designed and characterized by full-wave finite-element-method simulations. A 20 /spl times/ 6 unit-cell NRI lens structure interfaced with two parallel-plate waveguides is designed. The focusing/refocusing effect of the lens is observed by both circuit theory and full-wave simulations. Focusing in the NRI lens is also observed experimentally in excellent agreement with circuit theory and numerical predictions. This result represents the first experimental demonstration of NRI property using a purely distributed planar structure.

EM-based optimization of microwave circuits using artificial neural networks: the state-of-the-art

Abstract: This paper reviews the current state-of-the-art in electromagnetic (EM)-based design and optimization of microwave circuits using artificial neural networks (ANNs). Measurement-based design of microwave circuits using ANNs is also reviewed. The conventional microwave neural optimization approach is surveyed, along with typical enhancing techniques, such as segmentation, decomposition, hierarchy, design of experiments, and clusterization. Innovative strategies for ANN-based design exploiting microwave knowledge are reviewed, including neural space-mapping methods. The problem of developing synthesis neural networks is treated. EM-based statistical analysis and yield optimization using neural networks is reviewed. The key issues in transient EM-based design using neural networks are summarized. The use of ANNs to speed up "global modeling" for EM-based design of monolithic microwave integrated circuits is briefly described. Future directions in ANN techniques to microwave design are suggested.

Ultra-wideband radar sensors for short-range vehicular applications

Abstract: The recent approval granted by the Federal Communications Commission (FCC) for the use of ultra-wideband signals for vehicular radar applications has provided a gateway for the introduction of these sensors in the commercial arena as early as 2004. However, the rules governing the allowable spectral occupancy create significant constraints on the sensors' operation. This is further complicated by the variety of applications that these sensors are being required to fulfill. A review of the motivation for the development of these sensors is followed by a discussion of the consequent implications for waveform design and limitations on system architecture. Other practical considerations such as available semiconductor technology, packaging, and assembly techniques are reviewed, and results are presented for conventional surface-mount plastic packages illustrating their usefulness in the greater than 20-GHz frequency range. Suitable antenna technology for wide-band transmission is presented that is compliant with the specific restrictions stipulated in the FCC ruling. Finally, all of these considerations are combined with the presentation of a compatible integrated-circuit-based transceiver architecture. Measured results are presented for several critical circuit components including a +12-dBm driver amplifier for the transmitter, an RF pulse generator that can produce sub-1-ns pulses at a carrier frequency of 24 GHz, and a single-chip homodyne in-phase/quadrature down-conversion receiver that has a cascaded noise figure of less than 7 dB. All circuit components are fabricated in SiGe.

Control of bandstop response of Hi-Lo microstrip low-pass filter using slot in ground plane

Abstract: This paper examines the effect of the geometrical shapes of a defected ground-plane structure (DGS) slot on performance of the Hi-Lo microstrip low-pass filter (LPF). A three-pole LPF based on an arrowhead DGS slot has 67% less length as compared to a conventional three-pole LPF. It has insertion loss of 0.5 dB and 15-dB rejection in the stopband up to three times the cutoff frequency.

Guided modes in a waveguide filled with a pair of single-negative (SNG), double-negative (DNG), and/or double-positive (DPS) layers

Abstract: Here we present the results of our theoretical analysis for guided modes in parallel-plate waveguides filled with pairs of parallel layers made of any two of the following materials: (1) a material with negative real permittivity, but positive real permeability (epsilon-negative); (2) a material with negative real permeability, but positive real permittivity (mu-negative); (3) a material with both negative real permittivity and permeability (double-negative); and (4) a conventional material with both positive real permittivity and permeability (double-positive) in a given range of frequency. Salient properties of these guided modes are studied in terms of how these materials and their parameters are chosen to be paired, and are then compared and contrasted with those of the guided modes in conventional waveguides. Special features such as monomodality in thick waveguides and presence of TE modes with no-cutoff thickness in thin parallel-plate waveguides are highlighted and discussed. Physical insights and intuitive justifications for the mathematical findings are also presented.

Theory and experiment of dual-mode microstrip triangular patch resonators and filters

Abstract: In this paper, we report on the results of an investigation into dual-mode operation of microstrip triangular patch resonators and their applications for designing dual-mode bandpass filters. It has been found theoretically that the dual modes can result from the rotation and superposition of a fundamental mode. The characteristics of the dual modes and their mode splitting are described. The applications of this new type of dual-mode microstrip patch resonator in the design of microwave planar filter are presented. A circuit model for operation of this type of filter is proposed. Two- and four-pole filters of this type are demonstrated for the first time. Both theoretical and experimental results are presented.

A novel approach to the design and implementation of dual-band compact planar 90/spl deg/ branch-line coupler

Abstract: This paper presents the design of a novel branch-line coupler that can operate at two arbitrary frequencies. The proposed circuit also features compact size and planar structure. Explicit design formulas of the proposed dual-band coupler are analytically derived. Moreover, practical issues such as the realization of branch-line impedance and optimum choice of circuit topologies are addressed. For verification purposes, both simulated and measured results of a microstrip branch-line coupler operating at 900/2000 MHz are included.

Dynamic behavioral modeling of 3G power amplifiers using real-valued time-delay neural networks

Abstract: In this paper, we propose a novel real-valued time-delay neural network (RVTDNN) suitable for dynamic modeling of the baseband nonlinear behaviors of third-generation (3G) base-station power amplifiers (PA) Parameters (weights and biases) of the proposed model are identified using the back-propagation algorithm, which is applied to the input and output waveforms of the PA recorded under real operation conditions Time- and frequency-domain simulation of a 90-W LDMOS PA output using this novel neural-network model exhibit a good agreement between the RVTDNN behavioral model's predicted results and measured ones along with a good generality Moreover, dynamic AM/AM and AM/PM characteristics obtained using the proposed model demonstrated that the RVTDNN can track and account for the memory effects of the PAs well These characteristics also point out that the small-signal response of the LDMOS PA is more affected by the memory effects than the PAs large-signal response when it is driven by 3G signals This RVTDNN model requires a significantly reduced complexity and shorter processing time in the analysis and training procedures, when driven with complex modulated and highly varying envelope signals such as 3G signals, than previously published neural-network-based PA models

Description of coupling between degenerate modes of a dual-mode microstrip loop resonator using a novel perturbation arrangement and its dual-mode bandpass filter applications

Abstract: A novel dual-mode resonator with square-patch or corner-cut elements located at four corners of a conventional microstrip loop resonator is proposed. One of these patches or corner cuts is called the perturbation element, while the others are called reference elements. In the proposed design method, the transmission zeros are created or eliminated without sacrificing the passband response by changing the perturbation's size depending on the size of the reference elements. A simple transmission-line model is used to calculate the frequencies of the two transmission zeros. It is shown that the nature of the coupling between the degenerate modes determines the type of filter characteristic, whether it is Chebyshev or elliptic. Finally, two dual-mode microstrip bandpass filters are designed and realized using degenerate modes of the novel dual-mode resonator. The filters are evaluated by experiment and simulation with very good agreement.

A compact enhanced-bandwidth hybrid ring using an artificial lumped-element left-handed transmission-line section

Abstract: A new type of compact enhanced-bandwidth hybrid ring using an artificial lumped-element left-handed (LH) transmission-line (TL) section is proposed. The replacement of the 270/spl deg/ branch of the conventional hybrid ring by a -90/spl deg/ LH-TL branch results in both size reduction and bandwidth enhancement. The working principle of the LH TL used in the hybrid ring is explained and the performances of the component are demonstrated by measurement results. The proposed hybrid exhibits 67% size reduction compared to the conventional one, and shows a 58% and 49% bandwidth enhancements at 2 GHz in the 180/spl deg/-out-of-phase and in-phase operations, respectively.

Miniaturized fractal rat-race, branch-line, and coupled-line hybrids

Abstract: In this paper, space-filling curves have been used to realize a family of miniaturized hybrids. The large surface area occupied by a conventional structure has been significantly reduced through the use of space-filling curves having the same electrical characteristics. Several space-filling curves have been studied and implemented in different designs. The second-iteration Moore rat-race coupler occupies only 12.6% of the conventional coupler's area, while the area of the second-iteration Sierpinski branch-line coupler is 24.7% of the conventional case. On the other hand, a nine-section Minkowski coupled-line balun is confined in 60% of the conventional balun's area. However, the effective size reduction depends on the used space-filling curve, compression ratio, and associated coupling between segments. The performance of the proposed space-filling hybrids is as good as that of the corresponding conventional structures, and even better in some cases. The design and simulation of the proposed space-filling hybrids have been performed using a moment-method-based full-wave electromagnetic simulator. Measurements of one fabricated coupler prototype are in good agreement with simulation results.

An RF electronically controlled impedance tuning network design and its application to an antenna input impedance automatic matching system

Abstract: A novel design is proposed for an electronically tunable impedance unit. The prototypes include lumped elements, but no electromechanical control methods. The devices can tune many different complex impedances at minimum manufacture costs. Two antenna input impedance automatic matching systems are also presented, based on the tuning network. One includes a simplified version of the generic tuner, which can achieve good matching levels between the antenna and the power module with low losses. In a more complete version, an application specific integrated circuit control unit is developed including a complex search algorithm. In order to obtain a good matching level, both systems require a control module to select the proper tuner impedance configuration. The measurements and results of both constructed prototypes are presented. The designs were carried on terrestrial trunked radio mobile stations in the 380-400-MHz frequency band and supported high power levels (greater than 40 dBm).

Implicit space mapping optimization exploiting preassigned parameters

Abstract: We introduce the idea of implicit space mapping (ISM) and show how it relates to the well-established (explicit) space mapping between coarse and fine device models. Through comparison, a general space mapping concept is proposed. A simple algorithm based on the novel ISM concept is implemented. It is illustrated on a contrived "cheese-cutting problem" and is applied to electromagnetics-based microwave modeling and design. An auxiliary set of parameters (selected preassigned parameters) is extracted to match the coarse model with the fine model. The calibrated coarse model (the surrogate) is then (re)optimized to predict a better fine model solution. This is an easy space mapping technique to implement since the mapping itself is embedded in the calibrated coarse model and updated automatically in the procedure of parameter extraction. We illustrate our approach through optimization of a high-temperature superconducting filter using Agilent ADS with Momentum and Agilent ADS with Sonnet's em.

An all-solid-state broad-band frequency multiplier chain at 1500 GHz

Abstract: We report the results of a high-performance all-solid-state broad-band frequency multiplier chain at 1500 GHz, which uses four cascaded planar Schottky-barrier varactor doublers. The multipliers are driven by monolithic-microwave integrated-circuit-based high electron-mobility transistor power amplifiers around 95 GHz with 100-150 mW of pump power. The design incorporates balanced doublers utilizing novel substrateless and membrane device fabrication technologies, achieving low-loss broad-band multipliers working in the terahertz range. For a drive power of approximately 100 mW in the 88-99-GHz range, the doublers achieved room-temperature peak efficiencies of approximately 30% at the 190-GHz stage, 20% at 375 GHz, 9% at 750 GHz, and 4% at the 1500-GHz stage. When the chain was cooled to 120 K, approximately 40 /spl mu/W of peak output power was measured for 100 mW of input pump power.

On the linearity and efficiency of outphasing microwave amplifiers

Abstract: A new approach for the analysis of the efficiency and linearity of Chireix-outphasing combiners is presented. The approach takes into account, in an explicit manner, the effect of impedance mismatch between the amplifiers and the lossless combining structure. It is shown that the impedance mismatch leads to new expressions for the output voltages from both branches of the amplifier. These expressions explain the origin of the lack of linearity reported in the literature for the Chireix architecture and lead to a new expression for the instantaneous efficiency of a Chireix combiner. Various simulations using a commercial simulator are performed and their results are compared to those predicted by the derived equations. A quasi-exact agreement between the simulator and derived equations is found for all simulations conducted, including voltage expressions, linearity analysis, and instantaneous and average efficiency calculations for a code-division multiple-access signal. The impact of combiner parameters on its linearity and efficiency is also studied.

Ultrawide-band transitions and new microwave components using double-sided parallel-strip lines

Abstract: 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.