Abstract: A tunable microwave cavity permits adjustment of the penetration of a power coupling probe into the main cavity by adjusting a grounded element of the cavity. A pair of conductive tubes are in telescoping relationship and have mutually engaging threads so that a rotation of one tube causes one tube to pass over the other. A first one of the tubes is mounted to the main cavity and around an aperture in the cavity wall. A power coupling connector is mounted with the second tube, and a rotating electrical contactor is disposed between the outer conductor of the connector and the second tube so that the connector does not rotate with the second tube. A power coupling probe affixed to the end of the inner conductor of the connector assumes various penetration depths within the main cavity in response to a rotation of the second tube. The cavity may be used in a light source including a high frequency power source and an electrodeless lamp disposed in the main cavity.

Abstract: In a light source in which an electrodeless lamp is excited by high frequency power coupled into a lamp termination fixture having an inner and outer conductor, the fixture has a dynamically variable characteristic impedance, thereby facilitating dynamic matching of the variable impedance of the lamp during the lamp-off to lamp-run conditions to the output impedance of the power source. This feature is possible because the position of the inner conductor with respect to the outer conductor is controlled as a function of the heat generated within the fixture. The inner conductor is made of a conductive material having a non-uniform coefficient of thermal expansion. When the fixture is cold, the lamp and the lamp-coupled end of the inner conductor are substantially concentric to the outer conductor thereby creating a high characteristic impedance to match the high starting lamp impedance to the source impedance.