Modeling and design of circularly-polarized cylindrical wraparound microstrip antennas

Wraparound microstrip antennas are generating great interest in both the military and commercial sectors. Conformal microstrip antennas which can be wrapped around a missile or a lamp post are particularly useful in providing an inexpensive means of data transmission in applications ranging from telemetry to cellular base stations. Most existing wraparound antennas are linearly-polarized. The design of these wraparound antennas often entails using planar models to generate an initial design, then relying on cut-and-try to compensate for the curvature. When the radius of the mounting cylinder is large (greater than one guided wavelength), the effect of the curvature is negligible; therefore, planar models can be used. However, when the radius of the mounting cylinder becomes small, planar models with the cut-and-try approach are inadequate. This is particularly true for circularly-polarized wraparound arrays where the polarization purity of the array can be affected by the curvature much more than the input impedance. This paper discusses the design and modeling of an omnidirectional circularly-polarized wraparound microstrip array for cylinders with small radii. As shown, the inclusion of the cylindrical curvature effect in the modeling process is crucial in attaining an optimal design.