Showing papers in "IEEE Transactions on Microwave Theory and Techniques in 1989"

Modeling of noise parameters of MESFETs and MODFETs and their frequency and temperature dependence

Abstract: A simple noise model of a microwave MESFET (MODFET, HEMT, etc.) is described and verified at room and cryogenic temperatures. Closed-form expressions for the minimum noise temperature, the optimum generator impedance, the noise conductance, and the generator-impedance-minimizing noise measure are given in terms of the frequency, the elements of a FET equivalent circuit, and the equivalent temperatures of intrinsic gate resistance and drain conductance to be determined from noise measurements. These equivalent temperatures are demonstrated in the case of a Fujitsu FHR01FH MODFET to be independent of frequency in the frequency range in which 1/f noise is negligible. Thus, the model allows prediction of noise parameters for a broad frequency range from a single frequency noise parameter measurement. The relationships between this approach and other relevant studies are established. >

The tapered slot antenna-a new integrated element for millimeter-wave applications

Abstract: Tapered slot antennas (TSAs) with a number of potential applications as single elements and focal plane arrays are discussed. TSAs are fabricated with photolithographic techniques and integrated in either hybrid or MMIC circuits with receiver or transmitter components. They offer considerably narrower beams than other integrated antenna elements and have high aperture efficiency and packing density as array elements. Both the circuit and radiation properties of TSAs are reviewed. Topics covered include: antenna beamwidth, directivity, and gain of single-element TSAs; their beam shape and the effect of different taper shapes; and the input impedance and the effects of using thick dielectrics. These characteristics are also given for TSA arrays as are the circuit properties of the array elements. Different array structures and their applications are also described. >

Measurement and simulation of memory effects in predistortion linearizers

Abstract: Detrimental effects of memories in linearizers are described, and two efficient techniques are presented to measure them. These techniques allow a real-time adjustment and correction of the linearizer and/or amplifier circuits and an overall improvement of the intermodulation performance over a wide envelope frequency band. This is especially important for broadband applications, where high efficiency and linearity are required, and where memory effects, if not detected and properly corrected, may significantly degrade the system's performance. Experimental results for a 20-W linearized L-band power amplifier are presented to illustrate the effects of memory. The two techniques-a dynamic AM/AM and AM/PM measurement system and a pulse power measurement system-are described. A simulation approach that can be used to predict the influence of memory effects in practical systems is illustrated for nonlinear amplifiers. Adaptive linearization techniques are discussed. >

Miniaturized hairpin resonator filters and their application to receiver front-end MICs

Abstract: The authors describe the fundamental characteristics of miniaturized hairpin resonators having parallel coupled lines and show their applications to bandpass filters and receiver front-end microwave integrated circuits (MICs). A method for calculating filter coupling parameters using a general-purpose microwave circuit simulator is presented. The bandpass filters have a suitable structure for MICs, and their size is one-half that of conventional hairpin resonators without increasing insertion losses. Trial receiver front-end MICs using these filters have been developed and have shown good characteristics such as low noise and a high image suppression ratio. They are applicable to a frequency range above the L-band. >

The generalized method of characteristics for waveform relaxation analysis of lossy coupled transmission lines

Abstract: The transient response of lossy coupled transmission lines is simulated by iterative waveform relaxation analyses of equivalent disjoint networks constructed with congruence transformers, fast Fourier transform (FFT) waveform generators, and characteristic impedances synthesized by the Pade approximation. A two order reduction of CPU time and one order savings in computer memory are achieved. A lossy directional coupler is simulated for illustration. >

Accuracy improvements in microwave noise parameter measurements

Abstract: Factors contributing to the accuracy of microwave noise parameter measurements are examined theoretically and experimentally. It is shown that for good accuracy the test source impedances need not be grouped around the impedance that produces the minimum noise figure. System calibration and device under test (DUT) S-parameter accuracy are important to the derived noise parameter accuracy, and the use of a vector network analyzer is advantageous. An algorithm is implemented which avoids errors caused by different noise-source 'on' and 'off' impedances. >

GaAs heterojunction bipolar transistor device and IC technology for high-performance analog and microwave applications

Abstract: GaAs-AlGaAs n-p-n heterojunction bipolar transistor (GaAs HBT) technology and its application to analog and microwave functions for high-performance military and commercial systems are discussed. In many applications the GaAs HBT offers key advantages over the alternative advanced silicon bipolar and III-V compound field-effect-transistor (FET) approaches. TRW's GaAs HBT device and IC fabrication process, basic HBT DC and RF performance, examples of applications, and technology qualification work are presented and serve as a basis for addressing general capability issues. A related 3- mu m emitter-up, self-aligned HBT IC process provides excellent DC and RF performance, with simultaneous gain-bandwidth product, f/sub T/, and maximum frequency of oscillation, f/sub max/, of approximately 20-40 GHz and DC current gain beta approximately=50-100 at useful collector current densities approximately=3-10 kA/cm/sup 2/, early voltage approximately=500-1000 V, and MSI-LSI integration levels. These capabilities facilitate versatile DC-20-GHz analog/microwave as well as 3-6 Gb/s digital applications, 2-3 G sample/s A/D conversion, and single-chip multifunctions with producibility. >

Lossless broad-band monolithic microwave active inductors

Abstract: Lossless broadband microwave active inductors for general-purpose use in microwave circuits are proposed, and their characteristics are discussed. These active inductors are composed of a common-source cascode FET and a feedback FET, and operate in a wide frequency range with very low series resistance. Their low-loss characteristics are demonstrated by simulation and experimental results. A maximum Q factor of 65 is obtained. Theoretically, it can reach infinity. The inductance value can be controlled by an external voltage control. >

Determination of the correlation spectrum of oscillators with low noise

Abstract: A general expression for the correlation spectrum of an oscillator, described by a set of nonlinear ordinary differential equations with intrinsic noise sources, is derived by a first-order perturbation theory. The analytical derivations are well suited to the numerical determination of the correlation spectrum by Poincare mapping methods. The theory is applied to a lumped circuit model of Colpitts oscillator. It is concluded that the noise behavior of complex oscillator circuits used in microwave engineering can be simulated by the derived method. >

On the application of complex resistive boundary conditions to model transmission lines consisting of very thin superconductors

Abstract: A resistive boundary condition for the case where the resistivity is assumed to be a complex quantity is shown to be an accurate model for a superconducting film which is thin compared to the super-conducting penetration depth. The imaginary part of the conductivity is the dominant terms and is a measure of the inductive energy stored in the superconductor. Numerical solutions of superconducting microstrip are obtained and compared to experimental results and to analytic solutions for superconducting parallel-plate waveguides. Excellent agreement is found between experimental, analytical, and numerical results. >

Microwave radiometry: its importance to the detection of cancer

Abstract: The author discusses developments in the medical uses of microwave radiometry, particularly in relation to the early detection of cancer, as well as the significance of and progress in related antenna technology. In the treatment of cancer, microwave hyperthermia is accepted as an adjunct to radiation therapy in the treatment of superficial lesions. Although not as widely reported, the use of microwave radiometry as a noninvasive, passive technique for the early detection of cancer appears promising. Wider acceptance of these methods, however, awaits fundamental improvements in the ability to focus energy at depth in human tissue, an important and nontrivial antenna problem. Antenna development is described, and the improvements required if microwave technology is to provide a practical solution to the detection and treatment of cancer are indicated. >

Determination of the resonant frequencies in a complex cavity using the scattering matrix formulation

Abstract: A method for computing the resonant frequency in a complex cavity consisting of a series of waveguide sections is derived. The analysis is restricted to transitions in which one waveguide is wholly contained in the other. An eigenvalue problem is formed by cascading the scattering matrix from a given section outwards to the ends of the complex cavity, with appropriate boundary conditions at the ends. The eigenvalue equation is solved numerically by searching for a complex frequency, the cavity Q being determined by half of the ratio of the real to the imaginary part of the frequency. The technique is easily implemented numerically and shows good agreement with experiment. This method is suitable for modeling both abrupt changes in radius and smoothly varying tapers. >

Recent European developments in active microwave imaging for industrial, scientific, and medical applications

Abstract: The authors present some representative results which have been obtained during the last decade and discuss the general trends concerning their continuation and extension in the next few years. The research effort has been conducted within the framework of national or European cooperative programs at three levels: basic research in reconstruction algorithms, development of imaging equipment, and feasibility studies and evaluation of prototypes. Special emphasis is given to equipment, which the authors believe provides the real measure of the impact of the technologies. They discuss biomedical applications, buried object detection, vision and robotics applications, and applications to nondestructive testing and quality control of materials. >

Phenomenological loss equivalence method for planar quasi-TEM transmission lines with a thin normal conductor or superconductor

Abstract: The incremental inductance rule for conductor loss calculations is not valid if conductor thickness decreases and becomes comparable to the penetration depth A simple approach, referred to as the phenomenological loss equivalence method is proposed for characterizing a planar quasi-TEM transmission line with a thin normal conductor or superconductor over a wide range of field penetrations For microstrip lines with a thin copper or high-T/sub c/ superconductor, the conductor losses calculated by this method agree very well with the published data calculated by the finite-element method and the Monte Carlo method, respectively Because of the simplicity of the calculation, the method should be very useful for the computer-aided design of monolithic microwave circuits >

Full-wave, finite element analysis of irregular microstrip discontinuities

Abstract: Finite-element expansion currents are used to formulate a full-wave analysis of microstrip discontinuities With this approach, a rigorous analysis of fairly irregular structures is possible, including radiation and surface wave effects as well as coupling between closely spaced junctions The step, stub, and bent-stub discontinuities are analyzed using this technique Measurements are made of three stub structures Measured resonant frequencies agree with full-wave calculations to within 2% when the nominal measured dielectric constant and structure dimensions are used as input Using the absolute worst case dielectric constants and dimensions as input gives an error of 3% for the low-frequency stub and less than that for the other stubs >

Monolithic FET structures for high-power control component applications

Abstract: A monolithic FET switch is described that can be integrated with other monolithic functions or used as a discrete component in a microwave integrated circuit structure. This device increases the power-handling capability of the conventional single FET switch by an order of magnitude. It does this by overcoming the breakdown voltage limitation of the FET device. The design, fabrication and performance of two high-power control components using these circuits are described as examples of the implementation of this technology. They are an L-band terminated single-pole, single-throw (SPST) switch and an L-band limiter. >

Spectral-domain analysis of E-plane waveguide to microstrip transitions

Abstract: The spectral-domain technique and a residue calculus theorem are used to compute the input impedance of a microstrip transition to a rectangular waveguide. The transition consists of a printed circuit board inserted into a waveguide housing along the E-plane. The effects of the dielectric layer are considered in the present analysis. The behavior of the input impedance of the transition is studied with respect to the critical dimensions of the probe length and backshort location. Calculated results by the new formulation agree well with those computed using an integral equation and those measured at Ka-band frequencies. >

Full-wave analysis of coplanar waveguide and slotline using the time-domain finite-difference method

Abstract: The authors present a detailed full-wave analysis of a coplanar waveguide (CPW) and a slotline by the time-domain finite-difference (TD-FD) method. The transient waveforms propagating along the coplanar waveguide and slotline, which are excited by retarded Gaussian pulses, are found in the time domain. After the time-domain field distributions are obtained, frequency-domain parameters such as the effective dielectric constant and the complex characteristic impedance are calculated using Fourier transformations. The results agree well with available theoretical and experimental data over a wide frequency range. The validity of the quasi-TEM assumptions for CPW and slotline analyses is also checked by evaluating the ratios of the longitudinal and transverse field components directly. >

Measurement of magnitude and phase of harmonics generated in nonlinear microwave two-ports

Abstract: A method for simultaneously measuring the magnitude and phase of the harmonics generated by a microwave two-port is reported. The two-port under test is driven with a sinusoidal microwave signal strong enough to force it into nonlinear operation. Its output harmonics are measured in the frequency domain with a setup that includes a vector network analyzer. For phase calibration at the harmonic frequencies, a millimeter-wave Schottky diode is used as a reference device. The system allows the measurement of harmonics with a phase accuracy of about +or-10 degrees at 20 GHz (referred to f/sub 1/=5 GHz). It can be built for any frequency ( >

Double-sided MICs and their applications

Abstract: The basic concept and features are presented of double-sided microwave integrated circuits (double-sided MICs), which effectively utilize various kinds of transmission lines on both sides of a substrate. The fundamental circuits such as 180 degrees hybrids (magic Ts) and many application circuits described here are very useful in developing microwave and millimeter-wave band equipment. The concept of the double-sided MIC technique is also suitable for application to monolithic MICs. >

Analysis of transients in nonuniform and uniform multiconductor transmission lines

Abstract: The author presents an effective method for computation of the transient response of multiple nonuniform transmission lines. This time-domain analysis technique can predict reflections and crosstalk. The proposed spectral technique is used to transform partial differential equations describing a system of transmission lines into a set of linear ordinary differential equations, which can be solved with one of the many well-developed integration techniques. Numerical experiments performed with the prototype program showed that the method can solve specific problems (lossless, uniform lines) just as fast as less general methods based on modal analysis exploiting the particular properties of lines. >

Experiments on injection locking of active antenna elements for active phased arrays and spatial power combiners

Abstract: Two types of active antenna elements have been studied experimentally. One type uses a microstrip antenna with an active device mounted directly on the antenna. The other uses an active device coupled to a microstrip patch antenna through an aperture. Microstrip active antenna elements and two-element arrays have been demonstrated for both types of circuits. Injection locking of the antenna elements has been achieved through space and mutual coupling. The circuit Q factor was calculated based on the locking gain and the locking bandwidth. The power output from two elements has been successfully combined in free space with a combining efficiency of over 90%. For a single active antenna with a Gunn diode mounted directly on the patch, an electronic tuning range exceeding 9% has been achieved by varying the DC bias. The results should have many applications in low-cost active arrays, active transmitters, and spatial power combiners. >

Computer-aided noise analysis of MESFET and HEMT mixers

Abstract: A numerical approach to the noise analysis of MESFET and HEMT mixers of arbitrary topology is discussed. A qualitative picture of the complex physical mechanisms responsible for the generation of the intermediate frequency (IF) noise is outlined, and the corresponding computational algorithms are presented. The derivation of a noisy nonlinear model for the microwave FET is addressed, and it is shown that a satisfactory solution to this problem can be obtained by combining a conventional time-domain model with standard noise information. The method has been implemented in a computer program designed to work in conjunction with an existing general-purpose harmonic-balance simulator. An application is described in detail to demonstrate the excellent performance of this software tool. >

Mode conversion at discontinuities in finite-width conductor-backed coplanar waveguide

Abstract: The effect of overmoding in a conductor-backed coplanar waveguide is discussed, with special emphasis on mode conversion of discontinuities. The coplanar waveguide gap end and shorted end are studied by means of a fully electromagnetic application of the moment-method technique. Significant conversion occurs at the gap end. The results of a simple experiment which partially verify the analysis are described. >

Analysis of a centered-inclined waveguide slot coupler

Abstract: Integral equations are developed for a centered-inclined coupling slot (including the effect of finite wall-thickness of the common broad-wall) and the slot-aperture electric intensity field is found using the method of moments. Numerical results for resonant length, backscattered wave amplitude, and phase variation off-resonance are presented over a range of values of the waveguide b dimension, wall thickness, slot width, and frequency. It is shown that the resonant length is relatively insensitive to slot tilt, theta , for a standard-height X-band waveguide, whereas its dependence on theta is significant for reduced-height waveguides. The phase variation of scattered TE/sub 10/ waves in both waveguides off-resonance is less for wider slots and smaller b dimensions. Shunt-series coupling slots exhibit greater phase variation off resonance when compared to a centred-inclined coupling slot. Also, the former has a longer resonant length for a smaller b dimension and for a wider slot. Thus the centred-inclined slot coupler possesses superior characteristics. The higher-order mode coupling between a centred-inclined slot coupler and a pair of straddling radiating slots in the branch waveguide is significant. >

Synthesis, design, and construction of ultra-wide-band nonuniform quadrature directional couplers in inhomogeneous media

Abstract: A computer-aided synthesis design procedure is given for nonuniform quadrature directional couplers in inhomogeneous media A wiggly geometry is used which effectively slows the odd-mode phase velocity to match the even-mode phase velocity The wiggly geometry results in improved isolation and increased effective dielectric constant This technique provides a shorter coupler length due to increased effective dielectric constant Cubic splines of strip width, strip spacing, and wiggle depth as functions of coupling coefficient are computed using static capacitances of uniform coupled lines These functions are then used as synthesis functions to evaluate the continuous physical parameters of nonuniform coupled lines by using the continuously varying coupling coefficient A nonuniform interdigitated coupler is introduced to realize the tight coupling values >

Pulse distortion on multilayer coupled microstrip lines

Abstract: The distortion of pulses due to dispersion and coupling on generalized planar microstrip is investigated. A simple, general form for the Green's function is obtained by solving the boundary value problem separately for the TE and TM modes. The mechanism of even/odd-mode distortion is discussed and numerical results are presented illustrating its effect. The design of structures with low even/odd-mode distortion is considered. Results for pulse distortion on this type of microstrip are also included. >

Characterization of microstrip discontinuities on multilayer dielectric substrates including radiation losses

Abstract: A two-dimensional space-domain method-of-moments treatment of open microstrip discontinuities on multi-dielectric-layer substrates is presented. The full-wave analysis accounts for electromagnetic coupling, radiation, and all substrate effects. The technique is utilized to characterize commonly used discontinuities on one and two dielectric layers, and numerical results for step, corner, and T-junction discontinuities are included. On the microstrip conductors, both current components are expanded by rooftop basis functions. Once the current distribution is evaluated, transmission line theory is used to determine the network parameters. Numerical results from this technique demonstrate excellent agreement with measurement and the spectral-domain technique in the case of single dielectric layers. >

Multimode network description of a planar periodic metal-strip grating at a dielectric interface. I. Rigorous network formulations

Abstract: The problem of a plane wave incident at an arbitrary angle on a metal strip grating of arbitrary period located at an air-dielectric interface is formulated rigorously in terms of a pair of static integral equations, from which equivalent multimode network descriptions are derived. Both aperture and obstacle approaches are treated, and both TE and TM polarizations are considered explicitly. >

Spectral-domain computation of characteristic impedances and multiport parameters of multiple coupled microstrip lines

Abstract: A numerical procedure based on the spectral-domain techniques is formulated to compute all the frequency-dependent normal-mode parameters of general multiple coupled line structures in an inhomogeneous medium. In addition to the phase and attenuation constants for all the normal modes, these parameters include the line-mode and decoupled line modal impedances and the current and equivalent voltage eigenvector matrices of the coupled system. The multiport admittance (and impedance) matrices and coupled line equivalent-circuit model parameters are evaluated in terms of these normal-mode parameters. Numerical results for these normal-mode parameters for typical asymmetric two-, three-, and four-line microstrip structures are included to demonstrate the procedure and the frequency dependence of these parameters. >