Basic Investigations for Switching of RF Signals

Abstract

A major advantage of electromechanical RF relays is their capability to carry and to switch signals from DC up to the GHz range. Up to now the switching capability of miniature RF relays was limited to a few Watts, which was not really satisfactory. Basic investigations were performed to understand the mechanism when high frequency signals are switched, as no data was previously available. When high frequency signals are interrupted, the arc performs like a DC arc due to its thermal characteristics and burns for several periods of the signal. The arc is an adjustable resistor and just changes the amplitude of the output signal. When the contact gap increases, the arc finally extinguishes at current zero in a similar way as an AC arc. At the time the arc extinguishes the signal makes a phase shift as the open contact can be considered to be a capacitance. Practical tests were performed on a new type of high performance low-cost ultra-miniature RF relay with DC loads up to 60 W, low frequency AC loads up to 62.5 VA and RF loads with a maximum power of 37 W. The results obtained confirm the theoretical approach. Major advantages of bridge contacts providing two contact gaps in series were found, yielding excellent RF characteristics as well as outstanding switching performance in all frequency ranges from DC to RF. Even after 1 million operations no relevant changes of the RF characteristics were found, although a load of 37 W was hot switched.