Analysis and design of helical and spiral antennas

The study presented in this thesis is directed towards the analysisof helical antennas. Helical antennas analysis and more recent numericalmodeling of such antennas with the method of moments are wellestablished fields of study. Helical antennas have widely been used assimple and practical radiation elements of linear and circularpolarization. Because of its circular polarization, high directivity, andrelative simplicity, the helical antenna found a natural home in satellite communications.Archirnedean planar spiral antennas are numerically analyzed inthe presence of a conducting plane reflector to get the radiationcharacteristics and compared with the isolated spiral antennas without theplane reflector. The calculated results are compared with the availablepublished measurements to validate the analysis.The Spiro-helical antenna (SHA) is considered to reduce the heightof the helix and keeping approximately the same radiation characteristicsof the long helix. The SHA is a spiral wire wrapped into a lager helix fedat its end from a coaxial line of which the inner conductor is connected tothe end of the helix and the outer conductor to the ground plane. Theunique advantage of the spiro-helical antenna is its much smaller SIzecompared with the conventional helical antenna used in the CUITenttechnology. Having nearly the same radiation characteristics, includinggain, bandwidth, side lobe level and polarization, the SHA occupiessmaller volume than the conventional helix. With this size reduction,SHA becomes very appealing to many communications and aerospace