Suppressing of undesired modes in push-pull active integrated antenna

The paper considers a design of a push-pull oscillator for an active integrated patch antenna. The patch is fed at two points with signals having 180 degrees phase shift in order to excite the desired mode. Since a system of two active elements may operate in odd and even modes on the design frequency and its harmonics, the undesired modes have to be suppressed. This is obtained by controlling the negative resistance at the oscillator outputs and the coupling between the active elements. Further suppression has been obtained by symmetrical design of the active antenna. An active rectangular patch antenna with push-pull oscillator has been manufactured. The theoretical results have been compared with measurement. The antenna showed stable operation and very good radiation properties.