A Printed Circuit Balun for Use with Spiral Antennas

A novel printed circuit balun is described which is particularly well suited to applications where space is at a premium. The design utilizes unshielded strip transmission line, but is readily adaptable to all of the common printed circuit transmission line techniques. When the balun is housed within the cavity of a spiral antenna, boresight error is virtually eliminated, ellipticity ratios of less than 2 db are maintained over an azimuth angle greater than ± 60°, and the input standing-wave ratio is less than 2:1 over an octave frequency range. Experimental results are given and additional applications are described.