Image Number 2 for United States Patent #6052089.
A retractable whip antenna incorporating a matching base loading helix for use in mobile communications devices is disclosed. The antenna functions without the use of a matching circuit since selection of the radiating elements provides a constant input impedance to the transceiver circuitry. The resulting antenna provides excellent gain over the PCS frequency band, low SAR values, circuit design flexibility and low cost. In a preferred embodiment, the retractable whip is comprised of a radiating element with an electrical length of 1/2 wavelength and having a first end attached to a conductive spring contact. The base loading helix comprises a radiating helical element with an electrical length of 1/4 wavelength and having a first end connected to a mobile transceiver circuit and a second end comprising a conductive capturing coil. The radiating whip element is constrained within the coil of the helical element and is freely moveable to an extended or a retracted position. When the whip element is in the retracted position, the whip element is disconnected from the radiating circuit. When the whip element is in an extended position, an electrical connection is formed via contact between the conductive spring contact and the conductive capturing coil, wherein the helical element effectively base loads the whip element so that the two radiating elements have a combined electrical length of 3/4 wavelength.