Abstract: A low profile antenna comprised of a driven element and a parasitic element spaced above a ground plane. The driven element is connected at one end to the feedpoint of the radio device to which it is attached, the opposite end thereof being free. The parasitic element is connected to the ground plane by its end nearest the feedpoint, the opposite end thereof being free. In the preferred embodiment the parasitic element length and the driven element length are both approximately equal to a quarter wavelength at the operating frequency.

Abstract: A low profile antenna comprised of a driven element and a parasitic element spaced above a ground plane. The driven element is connected at one end to the feedpoint of the radio device to which it is attached, the opposite end thereof being free. The parasitic element is connected to the ground plane by its end nearest the feedpoint, the opposite end thereof being free. In the preferred embodiment the parasitic element length and the driven element length are both approximately equal to a quarter wavelength at the operating frequency.

Abstract: An adaptable homotropic antenna system for use with a portable communication transceiver is described. The antenna system can be used for reception or transmission and can be completely enclosed within the portable transceiver housing. The homotropic antenna system evaluates the quality of a received signal and if the signal is below a predetermined threshold level, an alternate antenna will be selected. The antenna system will continue to sample the available antennas until an antenna produces a signal of acceptable quality.

Abstract: A circuit and technique for directing an adaptable antenna system is described. The invention is coupled to the output of an RF receiver configured to provide a data signal output, and evaluates the quality of the receiver data signal. The invention switches antennas when the signal quality deteriorates below a predetermined level.

Abstract: Transmission line filter adapted to respond to a predetermined frequency, having a resonator conducting layer with dielectric material on opposite sides thereof and a ground plane conducting layer on the outside surfaces of the dielectric material. The filter may be of the stripline or microstrip type having a resonator constructed so that it tends to operate at a frequency different from the desired frequency, and which is not accessible for trimming after the filter is constructed. The ground plane layer is accessible so that a portion thereof can be removed after the filter is constructed to change the electrical parameters of the line formed by the resonator and the ground plane layer to change the response frequency of the filter. Alternatively, conducting material can be added to an opening in the ground plane conducting layer to change the response frequency of the filter.