Browse Prior Art Database

Termination for a Spiral Antenna

IP.com Disclosure Number: IPCOM000045621D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Goldstone, LL: AUTHOR

Abstract

A planar, cavity-backed sprial antenna can be resistively terminated, thus eliminating the need for coating the active radiating surface with lossy material. This extends the operating frequency below that other-wise obtained with ]a spiral of given size.

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Termination for a Spiral Antenna

A planar, cavity-backed sprial antenna can be resistively terminated, thus eliminating the need for coating the active radiating surface with lossy material. This extends the operating frequency below that other-wise obtained with ]a spiral of given size.

Referring to the figure, a bifilar, spiral-wound planar antenna has its conductors 1, 2 terminated on opposite corners of the plane by short-circuiting 3 to the preceding winding. Back one-quarter wave-length from the short-circuit connection for each conductor is a resistor 4 connecting the last winding and the preceding winding. Although the implementation is diagrammed for a square spiral, the termination is equally valid for a round spiral.

This termination is effective since the currents in the last and adjacent turns are in phase with no potential difference. The short circuit provides a ring of circulating current without disturbing the current distribution in either of the last two turns. The resistor provides a termination for any out-of-phase or unbalanced currents that may be present. Additional resistors can be added at other distances from the short circuit to fine tune the termination for frequencies above or below the frequency for which the radiation region is located near the last turn. At the higher frequencies, the energy is radiated before reaching the end of the spiral so that the termination need only be tuned to the lower end of the operating band. The in-p...