Antenna for portable radio communication apparatus

Claim 1

An antenna mounted on and retractable into a casing of a portable radio communication apparatus, comprising: a first movable axial extending conductor covered with an insulator; a tubular second movable conductor for receiving said first conductor therein; a connection conductor fitted on a lower end of said first conductor for maintaining said first conductor and said second conductor in contact at all times; a cover member covering an upper end portion of said first conductor over a predetermined length and having a greater diameter than said second conductor to thereby prevent retraction of said upper end portion into said casing when said antenna is retracted into said casing; and a metallic grounding part for grounding a lower end of said second conductor only when said antenna is retracted into said casing; a length of said first conductor and a length of said second conductor being chosen so that an impedance of said upper end portion of said first conductor when said antenna is in a retracted position is substantially equal to an impedance of said antenna in an extended position.