Abstract :
The use of r.f. switching and hybrid ring circuits in radio astronomy arises from the necessity of comparing small r.f. noise powers without introducing lossy switching elements in the receiver input. At frequencies where coaxial techniques are appropriate r.f. switches commonly use crystal diodes. This paper compares the series and stub connections of such switches, showing that the minimum loss is the same but that the practical details usually favour the stub connection. For the half-wave switching function used in interferometer aerial systems, the stub diode switch is shown to be a special case of the hybrid ring. Hybrid rings may be used either as splitter circuits or as bridges for comparing impedances. Reference is made to these applications in radio astronomy.
