Method and Apparatus for Quadrifilar Antenna with Open Circuit Element Terminations

A QHA antenna comprising:

• a plurality of helical arms, each comprising a conductor extending a length in a helical winding direction about a longitudinal axis, each having a first distal end and a second distal end;
• and
• a differential termination phase shift feed network, having an input port, a first phase shift output port coupled to the first helical conducting arm, a second phase shift output port coupled to the second helical conducting arm, a third phase shift output port coupled to the third helical conducting arm, a fourth phase shift output port coupled to the fourth helical conducting arm, a first isolation port, a second isolation port, and a differential impedance element connected between the first isolation port and the second isolation port,
• wherein the differential termination phase shift feed network is constructed and arranged to provide a first directional transmission path, having a first phase shift, from the input port to the first phase shift output port, a second directional transmission path, having a second phase shift, from the input port to the second phase shift output port, a third directional transmission path, having a third phase shift, from the input port to the third phase shift output port, and a fourth directional transmission path, having a fourth phase shift, from the input port to the fourth phase shift output port, and
• wherein the differential termination phase shift feed network is constructed and arranged to provide a first reverse directional path from the first phase shift output port to the first isolation port, a second reverse directional path from the second phase shift output port to the first isolation port, a third reverse directional path from the third phase shift output port to the second isolation port, and a fourth reverse directional path from the fourth phase shift output port to the second isolation port.

A method for inspecting a QHA antenna, comprising:

• providing a QHA having a plurality of helical arms;
• providing a plurality of concurrently extant directional phase shifted transmission paths, each extending from a given antenna feed input port to a corresponding one of the plurality of helical arms;
• providing a plurality of first directional reflection paths, extant concurrent with the plurality of directional phase shifted transmission paths, each extending from a different one among a first plurality of the helical arms to a first isolation port;
• providing a plurality of second directional reflection paths, extant concurrent with the plurality of directional phase shifted transmission paths and the plurality of first directional reflection paths, each extending from a different one among a second plurality of the helical arms to a second isolation port;
• feeding an externally generated feed signal to the antenna feed input port;
• measuring a magnitude of a signal on the first isolation port and a magnitude of a signal on the second isolation port;
• measuring a phase difference between a signal on the first isolation port and a signal on the second isolation port;
• determining, based on the measuring of a magnitude and the measuring a phase difference, a tuning value of the QHA.