Retractable antenna assembly with retraction short circuiting

摘要

An antenna assembly comprises an elongate radiating antenna (11) movable between a retracted position and an extended position. A pair of concentric conductors (9,10) provide coaxial feed to the antenna (11). In the retracted position the antenna 11 in conjunction with the coaxial feed (9,10) constitute a quarter wavelength transmission line which is short-circuited by a conductive flange (15) on the antenna. A short-circuited quarter wavelength transmission line electrically appears as an open circuit at the feed point. The antenna is thus automatically decoupled when it is moved to the retracted position without the need for additional switching or screening elements.