A compact, low profile, transmission line antenna--Tunable over greater than octave bandwidth

Techniques for extending the frequency tuning range of low profile top loaded antennas to greater than one octave are described. The compact antenna is a directly driven resonant radiator (DDRR) which consists of a vertical post radiator, the height of which is less than at the highest operating frequency, and which is top loaded by a loosely spiraled unbalanced transmission line which employs a multiple-capacitor tuning scheme to achieve a wide-band, tunable resonant antenna. The measured antenna circuit is of the order of 100 or greater and the radiation efficiency, over a large ground plane, is greater than 50 percent that of a quarter-wave monopole over the full operating range.