Helicon isolators for meter and decameter waves

Abstract

Helicon isolators are an analogue of ferrite microwave isolators and can be used for decoupling in range of meter and decameter waves in the radiotechnical hardware of various purposes. Different ferrite devices containing a medium with a permeability tensor m, in helicon isolator semiconductor media, and with an equivalent permettivity tensor e, placed to a static magnetic field are used.

We have investigated the helicon isolator characteristics with several options of attaching a nonreciprocal transformer. The most acceptable characteristics, with the least direct losses for the isolator based on a bandpass filter are obtained. The investigations of utmost dynamic characteristics of isolator in the operating frequency range were made. The best characteristics with the direct losses less than 1 dB, attenuation on backward direction on the average frequency between 20 and 25 dB, and the bandwidth near 40% at the level of return attenuation about 15 dB have been obtained in the frequency range of 20 to 100 MHz. Advancement to the higher frequency range is connected with the necessity of manufacturing of very thin (0.1 to 0.5 mm) helicon resonators, as well as with selection of suitable material. At present the maximum operating frequency of helicon resonator of about 400 to 500 MHz is achieved. Advancement to the lower frequency range is connected with the growth of magnetic system dimensions and increasing of the forward direction loss. The bottom operating frequency 1 MHz is at present achieved at the expense of increasing direct losses to 1.5 dB and decreasing return attenuation to 20 dB. The maximum dissipation power is determined by the temperature of semiconductor. For a used n-InSb sample this temperature value is between 80 to 100 °C.

During investigations there was revealed that the extremespecific dissipation power of isolator in continuous mode in the backward direction is about 5 to 10 W/cm² and is determined by the temperature gradient of the thickness pulse mode revealed so far. In the forward direction the extreme transmitted power depends on the helicon isolator direct losses and achieves 20 to 30 W/cm². Isolator operating efficiency rises essentially if the helicon isolator is cooled.

Such isolators can be used for: decoupling in heterodyne circuits on intermediate frequencies; decoupling of some connected transmitters, operating with the same antenna; protection of transmitters, operating with the variable load; reduction of the intermodulation distortions; decoupling of generator on the measuring ranges.