1. The value of the directive gain of an antenna in the direction of its maximum value.

2. The ratio of the power measured at the forward-wave sampling terminals of a directional coupler, with only a forward wave present in the transmission line, to the power measured at the same terminals when the direction of the forward wave in the line is reversed; the ratio is usually expressed in decibels.

The ability of a logic circuit to ensure that the input signal is not affected by the output signal.