| 摘要 |
<p>A quadrifilar helical antenna including four conductive helices having a common central axis, a common direction of turn about said axis, a common pitch, and a common length between opposite ends, the helices being uniformly spaced from each other by 90 degree , and a single dielectric helix concentric with the common axis, lying within and supporting the conductive helices at a nominal diameter. The dielectric helix has opposite ends, a plurality of turns having said common direction of turn, and a second pitch substantially greater than said common pitch. A casing contains the helices and is rotatably fixed to one end of the dielectric helix. A tuning device is fixed to the other end of the dielectric helix and rotatable relative to said casing, so that rotation of the tuning device twists the dielectric helix to alter the common pitch of the conductive helices without substantial variation from said nominal diameter.</p> |
