Abstract: A directional antenna suitable for use with the transmission and reception of information related to the traffic alert and collision avoidance systems (TCAS) of a monitoring aircraft is disclosed. The directional antenna includes four monopole antennas positioned and electrically coupled in a manner to produce a radiation pattern having unique directional characteristics. The disclosed antenna can transmit radiation in a directional pattern. The antenna can also receive radiation from a transponder equipped intruder aircraft (i.e., an aircraft within a predetermined range of the monitoring aircraft). By comparing the amplitudes of the signals induced in the plurality of antenna elements by the received radiation, the bearing (direction) of the intruder aircraft relative to the monitoring aircraft can be determined. The antenna is fabricated to provide a reduced cross-sectional profile, for example by providing a folded monopole antenna structure, thereby reducing the antenna profile in aircraft applications.

Abstract: The microwave frequency characteristics of a cavity having a center conducting element and conducting cavity are modified by changing the length of the center conducting element. The resonating structure is comprised of a coaxial member providing the principal resonating surfaces. One end of the coaxial member is coupled to a wall of the cavity surrounding the center conducting member with provision for access to the interior of the center conducting member from a position exterior to the cavity. The second end of the center conducting element is free. In addition, the second end of the resonating element has threads fabricated on an interior surface and a self-locking insert positioned in the threaded portion. A threaded rod is inserted through the self-locking insert and extends beyond the center conducting element into the cavity.