Low-Noise Design of Microwave Transistor Amplifiers (Short Papers)

Parameters are derived for circles of constant overall noise figure on the source admittance plane of a preamplifier cascaded with a noisy main amplifier. It is shown that the noise figure and noise measure of an amplifier can be expressed in terms of the scattering parameters of a lossless two-port network connected at the input of the amplifier. Examples are given which demonstrate how this network can be synthesized to meet amplifier noise specifications.     

Scattering Parameter Approach to the Design of Narrow-Band Amplifiers Employing Conditionally Stable Active Elements (Short Papers)

In terms of scattering parameters, the equation transducer power gain is shown to be capable of representation as a family of circles of constant gain from which the design of load and source terminations to achieve a restricted bandwidth can be obtained. This is an extension of an earlier approach which only allowed either load reflection coefficient or source reflection coefficient to be considered in a given design. Through the use of a specification statement of VSWR, it is shown how a marginal stability factor can be derived. From the study of the interaction between the input and output reflection coefficients, a detuning factor is analytically derived to correlate the interaction between the input and output reflection coefficients. Either of these factors can be chosen and used to select optimum input and output reflection coefficients which provide stable operation for an amplifying stage that is to employ a conditionally stable active element. An example using these factors is given.     

A Technique for the Design of Microwave Transistor Oscillators (Short Paper)

A technique for the design of microwave transistor oscillators is presented in which measurements made on an experimentally optimized amplifier are used to calculate six basis oscillator circuits which yield maximum power output. The procedure has been experimentally verified by the construction of a silicon bipolar transistor test oscillator at 1 GHz.     

Equivalent Circuit of the Schottky-Barrier Field-Effect Transistor at Microwave Frequencies (Short Papers)

Johnson's high-frequency representation theory for MOSFET's, experimentally confirmed by Hopkins up to 1 GHz, is extended in this short paper for SBFET's and is found to substantially agree with data for 1-mu m- and 1/2-mu m-gate GaAs SBFET's up to 12 GHz. Regenerative-feedback conductance not accounted for by conventional models is seen to be present in SBFET's at microwave frequencies.     

Power Generation and Efficiency in GaAs Traveling-Wave Amplifiers (Short Papers)

The effect of the dielectric loading in a bidimensional analysis that follows. GaAs traveling-wave amplifier (TWA) is investigated, with respect to the EM power generated by the structure and the efficiency of the dc to RF conversion. The validity of some usual approximations and assumptions is studied and a parameter, i.e., the power gain X efficiency product, is proposed as a useful tool for comparing the possible performances of TWA's.     

微波晶体管放大器的计算机辅助设计

本文系统叙述了按最大平坦增益、最佳噪声及最小M的设计要求,设计低噪声宽频带微波晶体管放大器的拓扑结构、数学模型及计算机辅助设计程序.     

Matching Network Design Studies for Microwave Transistor Amplifiers

Several techniques for design of microwave amplifiers using lumped-element and distributed matching networks are discussed. An extension to the Remez-algorithm design approaches is proposed, whereby gain and ripple quantities may be adjusted using a numerical optimization procedure in order to achieve complete absorption of device model elements and also impedance transformation.     

The Segmentation Method--An Approach to the Analysis of Microwave Planar Circuits (Short Papers)

In many practical planar circuitries, the circuit pattern can be divided into several segments which themselves have simpler shapes such as rectangles. The segmentation method proposed in this short paper is a method in which the characteristics of a planar circuit are computed by combining those of the segmented elements. It features a relatively short computer time required. The principle and computer algorithm are described. Finally, as an example, the application of the proposed method to the trial-and-error optimum design of a ladder-type 3-dB hybrid is described.     

A Multiple-Animal Array for Equal Power Density Microwave Irradiation (Short Papers)

The introduction of multiple subjects into a microwave field invariably results in perturbations and interference patterns which make it difficult to accurately determine power densities at any specified location. To overcome this problem, investigators have restricted the number of subjects, which is inefficient, or used techniques to illuminate large volumes, which still results in large variations in power density due to curvature of the microwave field. An exposure array has been devised that negates these disadvantages and enables simultaneous irradiations of multiple animals at uniform average power density (/spl plusmn/5 percent). The array consists of microwave transparent cages positioned in accordance with the natural characteristics of the microwave field and separated sufficiently to insure minimum interaction between animals due to microwave reflection. The results of testing the array in an anechoic chamber at a freqnency of 2450 MHz using an isotropic field probe are presented.     

Microwave Irradiation Design Using Dielectric Lenses (Short Papers)

Theoretical calculations and electric-field measurements were made to investigate the focusing effects of plane-wave-irradiated dielectric spheres (lenses). Spheres of different diameters and dielectric properties and plane wave sources of different frequencies were used in the calculations. The results indicate the feasibility of using dielectric lenses for selective partial-body irradiation in biological experiments.     

Gain-Bandwidth Limitations of Microwave Transistor Amplifiers

Gain-bandwidth limitations of broad-band single-stage microwave transistor amplifiers are related to a simple transistor circuit model, to constraints on characteristic impedance in a distributed-element equalizer, and to the line lengths of this equalizer. The gain-bandwidth performance of commensurate distributed-element equalizers is compared with the performance of a lumped-element equalizer, and four distributed-element design examples are presented, including two commensurate equalizers and two computer-optimized networks.     

Hysteresis Effects in Microwave Amplifiers and Phase-Locked Oscillators Caused by Amplitude-Dependent Susceptance (Short Papers)

A possible explanation for a type of experimentally observed amplitude instability for amplifiers and locked oscillators is given. The results obtained are in good agreement qualitatively with measurements on IMPATT-diode amplifiers. The theory shows that the susceptsnce of the active element has to be amplitude dependent to create the actual type of instability.     

An Empirical Design Technique for Microwave Oscillators (Short Papers)

A large-signal design technique for series-type microwave oscillators using three-terminal active devices is described. Using this technique, the characteristics of the embedding circuits required for maximum output power are measured directly under actual oscillation conditions. A two-signal technique is used in the measurement to establish the required oscillation conditions and to prevent oscillation at unwanted frequencies. The design technique has been verified by the construction of a 2.7-GHz bipolar transistor oscillator.     

A Microwave Decoupled Electrode for the Electroencephalogram (Short Papers)

The recording of the electroencephalogram (EEG) in an amplitude-modulated microwave field presents two related but distinct problems when conventional electrodes are employed. The electrode and its associated conductors extract power from the incident radiation, resulting in increased local power deposition which confounds dosimetric arguments and imposes local thermalization; the electrode tissue interface is a nonlinear system that demodulates amplitude-modulated signals with the results that the demodulate is additively mixed with the EEG. The problems were studied in a series of bench tests with conventional and thin-film microwave integrated circuit (MIC) electrodes. The latter are decoupled from the magnetic component of the field by virtue of radically reduced dimensions of the thin-loop component of its geometry, and suppression of dipole (i.e., electric field interaction) currents by use of integrated Nichrome series resistance. The result is that the demodulation artifact is undetectable in the ensemble averaged-power spectrum from the in vitro electrode up to an S-band incident-power density of 100 mW/cm/sup 2/. Thermalization was studied in a dielectric brain phantom with high-resistance monofilament leads to the MIC with a result that 0.6/spl deg/C heating is attributable to the electrode with prolonged exposure to a 50-mW/cm/sup 2/ field.     

Optimization of Microwave Networks (Short Papers)

The application of a new algorithm for minimax optimization is investigated. Unlike most of the previously published algorithms the new algorithm uses to its advantage certain obvious properties of the minimax function, namely, that the discontinuities in the first derivatives can be characterized by projections. An N-section transmission-line transformer is used as a test problem.     

Pump Noise Transfer in Parametric Amplifiers (Short Papers)

Pump noise transfer in paramps is related to the sensitivity of amplifier gain to AM and FM pump modulation. Measurements performed on an S-band paramp with an 18.4-GHz pump are described. The significance of the results is made explicit by using them to calculate the increase in amplifier noise temperature associated with an IMPATT oscillator pump.     

Design and Analysis of a Waveguide-Sandwich Microwave Filter (Short Papers)

In 1972 Konishi proposed a unique waveguide filter of sandwich-like construction that was attractive because of its simplicity. This short paper presents an analysis of the sandwich filter that has a conductive sheet with finite thickness sandwiched between waveguide shells. An equivalent circuit is derived, design charts are proposed, and Young's technique is applied to the design of an M-band waveguide filter. The experimental results were found to be in good agreement with the theory and analysis techniques developed herein.     

Bipolar Microwave Linear Power Transistor Design

Design considerations for n-p-n bipolar microwave linear power transistors are discussed. Optimization procedures are presented for determining emitter width for a specfic operation frequency, emitter ballasting resistance, and active area geometry based on calculated temperature distributions. A transistor chip designed for 4-GHz operations using these procedures achieved a linear power output of 27.5 dBm at a 1-dB compressed gain of 7 dB with a power added efficiency of 23 percent. Junction temperature rise was limited to 90/spl deg/C.     

Microwave Four-Mirror Ring Resonator (Short Papers)

Experiments on an X-band four-mirror ring resonator are described. Measured frequency spacing and quality factor values are given. Clockwise and counterclockwise circulating modes are excited with different amplitudes. Fundamental mode patterns are shown across the circulating beam and across a mirror. They indicate that such modes are similar to those of a two-mirror Fabry-Perot (FP) resonator.