Multi-frequency antenna

Claim 1

In a multi-frequency antenna which includes: a first rod; a second rod movably supported on said first rod by a phase shifter for extending and contracting movements relative to said first rod; a hollow third rod on which said first rod is movably supported and which is capable of accepting and storing said first and second rods therein; and outer pipe disposed around and immovably supporting said third rod, said outer pipe being supported by a car body so that a predetermined lengthwise portion of said outer pipe is disposed under the car body and is grounded at a predetermined position; a power feeding coaxial cable having a core connected to said third rod and having an outer skin ground connected to said outer pipe; antenna driving means for extending and contracting said second rod relative to said first rod and said first rod relative to said third rod and outer pipe; and impedance matching means which includes said third rod, said coaxial cable and said outer pipe being configured to form a coaxial line arrangement of an open trap type so that an input impedance of the outer pipe is continuous; the improvement comprising wherein said phase shifter is a dielectric element which is approximately λ/4 long electrically, is inserted in a portion of said first rod, and has second rod extending through an opening therein, and means defining between said first rod and said dielectric element an air gap having a selected size which effects a predetermined dielectric constant in the phase shifter, wherein the antenna gain and phase are dependent on said dielectric constant.