Helicon isolator transient studies
Journal Title: Вісник НТУУ КПІ. Серія Радіотехніка, Радіоапаратобудування - Year 2013, Vol 0, Issue 53
Abstract
Introduction. Design of modern powerful transistor generators with external exitation in meter and decameter wave ranges requires maximum utilisation of the transistor power capabilities. Transistors have no margins on the maximum permissible parameters and even minor derivations from normal mode can cause it fail. Known protection devices for band power amplifiers have a time constant greater than 20-30us permissible overhead of transistor and can not protect the amplifier from short-circuit load or its failure. Helicon isolator at the output of transmitters for meter and decameter waves protects the transistor from the load mismatch and also decreases the intermodulation distortions level. The goal of this work is to study the on-turn transient of helicon isolator during the antenna break or short-circuit. Formulation of the problem. The maximum power dissipation in the helicon isolator de-pends on the maximum allowable temperature of the semiconductor resonator plate. In this work the transient processes in the helicon isolator after the sudden load mismatch are studied in order to reduce its sizes and weight for the given power level. Simulation. Temperature changes of the main part of helicon isolator – helicon resonator with sizes 10x10x10 mm3 of indium antimonide dopped with tellurium with concentration 2.1 1023 m-3 are simulated in the approximation of one-dimensional model. The termal time constant was calculated. The resonator temperature variations are calculated with the different backward power levels. It is shown, that the time to reach the critical temperature 600С for the isolator with 10W dissipation power level is more than 0.1s and much more then required timeout for even simple emergency shutdown system of the band power amplifier for transmitters. Experimental results. Experimental study of the helicon isolator transient shows that the reverse attenuation decreases from -23dB to -20db in 0.6s and to -15dB in 1.1s. This timeout is enough to protect the transistor amplifier of the transmitter in emergency mode up to the power supply shutdown. Conclusion. Helicon isolators are efficient protection of transistor transmitters from load mismatch in meter and decameter wave ranges. The reflected power is adsorbed in the isolator at antenna break or short-circuits. The thermal time constant of the isolator is enough for even the very simple emergency power shutdown system to switch.
Authors and Affiliations
Yu. Vountesmery
Keywords
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- EP ID EP309067
- DOI 10.20535/RADAP.2013.53.60-67
- Views 68
- Downloads 0
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