[ Home ] [ Cooled Amplifiers ] [ Cooled Systems ] [ Antenna Testing & Design ] [ QuinStar Homepage ] BERKSHIRE TECHNOLOGIES INC. is a small innovative company specializing in the manufacture of ultra low noise microwave amplifiers and systems. Our engineering staff has many years of experience in designing GaAsFET and HEMT* amplifiers tailored for ultra low noise at spot frequencies. We specialize in cryogenic units and amplifiers with special features not supplied by the large manufacturers. We supply a standard line of cooled, low noise amplifiers (LNAs) that cover the most popularly used frequencies in the 1 to 18 GHz range. We also custom design and build special-purpose amplifiers to customer specifications. APPLICATIONS COOLING HEMTs
THE BERKSHIRE LINE OF AMPLIFIERS An amplifier cooled to 20K physical produces the lowest noise temperature, which can be estimated by the relation 1.0K per 1 GHz of operating frequency plus 1K. That is, an amplifier operating at 8.5 GHz can be expected to have a typical noise temperature of 10K (1.0K * 8.5 + 1K). BERKSHIRE SYSTEMS Not shown in the photograph is the compressor, which requires approximately 1.5 KW of power. Cooldown time for such a system is several hours; the exact time depends upon the size of the refrigerator. A 20K cryogenic system of the type described provides nearly the ultimate in noise performance for only moderate complexity and cost. Such systems can be custom built by Berkshire. To exceed its performance, one would have to go to a liquid He system, or employ a refrigerator capable of maintaining the amplifiers at temperatures of 4K. Refrigerator-cooled HEMT systems have been found to be very reliable in field use on antennas. The MTBF for a 20K refrigerator is much greater than one year; amplifier life is indefinitely long based on the performance of hundreds of units operating in the field. BERKSHIRE POWER SUPPLIES BERKSHIRE AUTOMATED NOISE
FIGURE TEST SYSTEMS The system performs noise figure measurements by switching the input of the LNA between a terminated load at ambient temperature, and one at 77K (or other temperature). The Automated Test Bench consists of two units. The RF unit contains a precision test receiver; the D/A unit contains the analog-to-digital converter, relay drivers, and digital-to-analog converters. The Test Bench is controlled by an IBM-PC or compatible computer through the IEEE488 bus. The operating program is written in C and can be customized to allow user-specified details of the measurements. The Test Bench is a custom designed unit, hence a wide variety of options can be arranged to meet user requirements. MANUFACTURING PRACTICES
AND PROCEDURES Noise temperature and gain of our cooled HEMT amplifiers are measured on an automated test system by a special technique developed at Berkshire Technologies. .A specially designed 50 ohm termination is attached to the amplifier under test. The temperature of this termination is varied; the measurement of output power of the amplifier at a series of termination temperatures yields the noise temperature with high precision. The inherent accuracy of a noise determination by this technique is a few tenths of a degree Kelvin. With each amplifier shipped, we provide test data showing frequency range of the amplifier, noise figure, small signal gain, and optimum operating biases. Additional test data over operating temperature and frequency ranges may be available at additional cost. We use best commercial practice in the fabrication of all Berkshire Technologies products.
*HEMT is an acronym for High Electron Mobiliy Transistor. These are Aluminum Gallium Arsenide FET structures in the channel of which a 2 dimensional electron gas forms at the interface between the AlGaAs and the pure GaAs. BERKSHIRE TECHNOLOGIES Inc. |
