Frequency selective improvement of the directivity of a return loss bridge

Abstract

A frequency selective improved directivity of a return loss bridge is achieved by generating a counteractive reflected energy vector to cancel a reflected energy vector caused by imperfections, such as parasitic effects and an unbalanced balun, in the return loss bridge. The counteractive reflected energy vector of equal magnitude, but opposite in phase, to the undesired reflected energy vector may be induced into a transmission path between a test port and a coupled port. In one embodiment an open circuit stub in the transmission path between the test port and a coupling resistor coupled to the coupled port may be inserted to generate the counteractive reflected energy vector of the desired magnitude with a transmission line between the open circuit stub and the coupling resistor providing the desired phase. Alternatively the counteractive reflected energy vector may be coupled from the return loss path between the coupling resistor and the test port to the coupling port, the magnitude of the counteractive reflected energy vector being determined by a coupling coefficient and the phase being determined by a length of transmission line. To provide tunability PIN diodes may be used with the transmission line to control both the magnitude and phase of the energy at the coupled port, the coupling coefficient being greater than that needed for counteracting the magnitude of the reflected energy vector.

Dependencies are inferred from the claim text.