UHF Amplifiers Research Articles

A fully integrated broadband, high-gain, high-power and high-efficiency UHF amplifier using GaAs HBT and GaN HEMT

A fully integrated broadband, high-gain, high-power and high-efficiency UHF amplifier using GaAs HBT and GaN HEMT

A compact 10 kW, 476 MHz solid state radio frequency amplifier for pre-buncher cavity of free electron laser injector linear accelerator

A 10 kW, 476 MHz, 0.1% duty cycle solid state RF amplifier system for driving sub-harmonic, pre-buncher cavity of IR-FEL injector LINAC, has been developed at RRCAT. The 10 kW power is achieved by combining output of eight 1400 W amplifier modules using 8-way planar corporate combiner. The solid state amplifier modules have been developed using 50 V RF LDMOS transistors which although meant for push-pull operation are being used in single ended configuration with matching circuit developed on a thin (25 mils), high dielectric constant (9.7), low loss microwave laminate with an aim to have a compact structure. Ease of fabrication, modularity, small size, and low cost are the important features of this design which could be used as a template for low duty cycle medium to high pulsed power UHF amplifier system.

Identification of insulation defects in gas-insulated switchgear by chaotic analysis of partial discharge

The recent increase in the number of failures during the installation and insulation of gas-insulated switchgear (GIS) has led to a need for a reliable risk assessment technique. Accordingly, in this study, a fundamental database of UHF partial discharge (PD) patterns corresponding to different types of defects is presented for risk assessment and for the observation and diagnosis of the state of insulation of GIS at field sites; the patterns have been obtained by modelling a number of defects that have been reported to be the most critical in GIS. For the realisation of a system that can simultaneously detect and analyse UHF PD (it is internationally accepted that the use of such a system is the most effective method to diagnose GIS insulation), a wideband UHF sensor and amplifier are designed and fabricated. The system operation is then investigated. In addition, a chaotic analysis of partial discharge (CAPD) is proposed. This analysis can identify the type of defect by means of PD pattern classification without employing the phase information of the applied voltage signal. The proposed CAPD can replace the conventional phase-resolved partial discharge (PRPD) analysis and can be employed at field sites when the phase information is unavailable. Especially, the PD patterns of free-moving conducting particles, known to be very important in GIS, can be distinguished from those of other defects when using the CAPD method, which is not the case when the PRPD analysis is being performed.

Residual phase noise measurements of VHF, UHF, and microwave components

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Status of solid state amplifier application to plasma heating and Klystrode development.

The radio frequency (RF) systems in fusion plasma heating often use broadcasting transmitter techniques. For example, the RF heating system in JT-60 was built using broadcasting technology. Also, a new, high efficiency UHF power amplifier electron tube, the Klystrode, which was developed in the USA for TV can be used for fusion plasma systems. While Japanese broadcasting engineers had an effort to develop solid state UHF amplifiers with high power, the USA is developing new high power tubes such as the klystrode. In this paper we will discuss the feasibility of applying a solid state amplifier and klystrode for fusion plasma heating.

Intermodulation Performance of Solid-State UHF Class-C Power Amplifiers

In any frequency-division-multiple-access (FDMA) satellite communication system the control of intermodulation noise must be considered if all signals are amplified by a single nonlinear power amplifier in the satellite transponder. The subject of this paper is the use of Fourier-Bessel series expansion models in the prediction of the intermodulation performance of both traveling-wave-tube (TWT) amplifiers and solid-state class-C UHF amplifiers. Both theoretical and experimental results are described and compared. It is shown that in the case of the solid-state amplifiers a dynamic characteristic measurement technique must be used before reliable predictions can be achieved. A simple intermodulation noise reduction scheme is described for use with high-power efficient class-C solidstate amplifiers. It is demonstrated that a carrier-carrier-to-intermodulation noise power ratio improvement of 10 dB can be achieved with a minimal decrease in prime-power efficiency.

Design of a Low Noise Amplifier for UHF Radio Relay System

The design theory of a UHF Amplifier for the front end of a Radio Relay System (380–400 MHz) is presented. Two methods are available for choosing proper source and load terminations for stable operation. The first method, Linvill technique, determines device stability, gain and bandwidth in terms of two port transistor parameters. Though the technique is conventionally graphical, a computer programme has been used here which with given ‘Y’ parameters calculates optimum source and load terminations and maximum power gain at the frequency of operation. Taking the source and load terminations, input and output matching circuit details are worked out. The second method is Stern's method, which is primarily circuit stability oriented and calculates input and output loading for maximum power gain. Two stage amplifiers are constructed based on both the design solutions and their performance discussed. Both lumped element and microstrip circuit realisations are given.

Notes on the Conjugate Matched Two-Port As an UHF Amplifier (Short Papers)

Because of the relative simplicity of measurement of scattering parameters of active two-ports at frequencies up to the lower microwave region, investigations have been made into the application of these parameters to the design of UHF amplifiers. The theory of generalized scattering parameters has been developed by Kurokawa, applied to two-port power-flow analysis by Bodway, and used in the design of a single-stage UHF amplifier by Froehner. In this last paper, the bandwidth limitations imposed by the matching networks were not considered, nor was the capacitive matching arrangement to a purely resistive load fully developed. Both of these topics are the subject of this short paper, in which the relevant design expressions are also given.

Analysis of a bridge circuit for studying phase characteristics of UHF amplifiers

Analysis of a bridge circuit for studying phase characteristics of UHF amplifiers

A new uhf/vhf silicon transistor for the consumer market

Within the past year, transistors have been used in increasing numbers in the oscillator stages of uhf television tuners. This application not only represents the introduction of the first transistors in television receivers; it also indicates that transistors capable of good uhf and vhf performance can be mass-produced at consumer prices. Both germanium and silicon devices which are suitable for use in the oscillator function are now commercially available. The question arises as to the relative merits of amplifier versions of these devices for uhf and vhf amplifier service. Until recently, silicon transistors had not been considered for use in rf amplifier stages in consumer applications because of high noise figures or high cost, the former not being particularly significant in oscillator service. (Although silicon n-p-n uhf low-noise amplifiers have been available for some time, their use in consumer products has been restricted by their high cost.) This paper describes a new n-p-n silicon uhf-vhf transistor, RCA Dev. No. TA2503, having electrical characteristics tailored for consumer amplifier applications at frequencies up to 900 megacycles. Gain and noise through the useful frequency range are discussed, and relative performance is given for various vhf and uhf applications.

Diffused silicon nonlinear capacitors

Diffused silicon nonlinear capacitors have been fabricated by solid-state diffusion. The resulting graded p-n junction is a planar structure which permits low series resistance R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> relative to the minimum capacitance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_{\min}</tex> , which is measured at a reverse voltage slightly less than the breakdown voltage. A cutoff frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f_{c} = (2\piR_{s}C_{\min})^{-1}</tex> is used as a figure of merit; values up to 150 kmc have been obtained. These "varactor" diodes may be used as UHF and microwave amplifiers and as harmonic generators. The noise figures of the UHF amplifiers are better than the best noise figures obtainable by present electron-tube techniques. These diodes are also efficient harmonic generators.

A one kilowatt high level modulated UHFamplifier with low distortion

The Communications Laboratory of RADC has completed the development of a vital communications link in the short range ground-to-air communieations. This link is the 1 KW Amplifier - Modulator Group which operates in the military UHF 100-watt transmitters for line of sight (los), ground-to-air communications. The design, development and fabrication of the 1 KW UHF Amplifier - Modulator is discussed. The equipment described provides an RF output of at least one kilowatt over the range 225 - 400 Mcps, when driven by an 80-watt exciter. The equipment also provides high level amplitude modulation (AM) of this RF. 90% or more AM is obtained over the audio range 200 - 22,OOO cps, and 80% or more AM is obtained over the range 22,000 - 25,OOO cps. With 80% modulation of an 1100-watt carrier, the total RMS harmonic distortion over the audio range 200 - 20,OOOcps is less than 3%. It is noted that the design solutions for this project have been jointly solved by engineers of General Electric Canpany, McIntosh Electronics and Rome Air Development Center.

UHF Tuner Design for the 6BA4

Tuner design concepts for uhf grounded grid amplifiers using the new 6BA4 rocket tube are discussed. The four terminal admittances are used as the basis for these concepts. A brief review of noise and gain considerations of a uhf amplifler tube is included. A number of types of circuit parameters such as lumped constants, and coaxial lines are given consideration as applied to input and output uhf amplifiers. Both boosters and tuners are included in the circuit discussion, and noise figure, gain and bandwidth data on experimental models is compared to theory.

A Disc-Seal Triode as a UHF Amplifier

A disc-seal planar triode and its performance as a UHF amplifier are discussed. The description of mechanical features is followed by calculations of available power gain, and the measured gain is shown to be close to that computed by theory. The noise figure is calculated by conventional means, but the measured value is found to be higher. Reasons for the discrepancy are pointed out. The four pole admittances, y ij , and their influence on practical circuit design, are discussed.

UHF Amplifier Tubes by the Dynamic Negative Resistance (II)

UHF Amplifier Tubes by the Dynamic Negative Resistance (II)

UHF Amplifier Tubes by the Dynamic Negative Resistance. -(I)

UHF Amplifier Tubes by the Dynamic Negative Resistance. -(I)