A single-arm circular spiral antenna with inner/outer feed circuitry for changing polarization and beam characteristics

A single-arm circular spiral antenna has been investigated to get adaptable circular polarization and tilt beam. Circular spiral is printed on a finite size dielectric substrate (/spl epsiv//sub r/=3.27) backed by a finite size-conducting plane. Circular spiral radiates Right Handed Circular Polarization (RHCP) in its inner feed and Left Hand Circular Polarization (LHCP) in its outer feed in one antenna element .Circular spiral has an axial beam (L1=1.64/spl lambda//sub g/) in the z-axis and two-tilted beams (L2=3.25/spl lambda//sub g/, L3=5.55/spl lambda//sub g/) of RHCP in inner feed and LHCP in outer feed at 10GHz, where L is a horizontal arm length. The frequency bandwidth for a 3-dB axial ratio criterion is about 25% in both inner and outer feed at L1=1.64/spl lambda//sub g/.