High frequency attenuator using liquid metal micro switches

Resonance within an attenuator relay caused by stray coupling capacitances to, and stray reactance within the switched conductor that replaces the attenuator section, is mitigated by reducing the stray coupling capacitances to as low a value as possible, and by using a conductor that is a section of controlled impedance transmission line that matches the system into which the attenuator relay has been placed. A substrate having SPDT LIMMS switches on either side of a switched transmission line segment and its associated attenuator, all of which are fabricated on the substrate, will have significantly lower stray coupling capacitance across the open parts of the switches when the attenuator segment is in use. This will increase the frequency for the onset of the resonance driven by the RF voltage drop across the attenuator. A reduction in the amplitude of the resonance can be obtained by including on the substrate an additional pair of LIMMS damping switches at each end of the transmission line segment. These damping switches each connect a terminating resistor to the ends of the transmission line segment when the attenuator section is in use. This loads the resonator and reduces the amplitude of the resonance. Still further improvement can be obtained by locating one of the damping switches and its termination resistor near (but preferably not exactly at) the middle of the transmission line segment.