Low profile spiral antennas over AMC ground planes

A spiral antenna has a broadside circularly polarized radiation pattern with a wide beamwidth at its fundamental mode. These properties are highly demanded in wireless communication systems such as spread spectrum, multifunction radio frequency systems, and airborne direction finding. Advancements in these applications have increased the demand for low-profile antennas. In recent decades, the development of artificial magnetic conductors (AMC) has opened a new window in low-profile applications, since these surfaces can be used as a ground plane at reduced distances to a planar antenna without sacrificing the antenna radiation performance.In this thesis, low profile circular curl and dual-arm Archimedean spiral antennas are studied using a finite artificial magnetic conducting ground plane. These antennas generate circularly polarized waves with an excellent circular polarization performance. The distance between each antenna and the artificial ground plane is reduced to 0.02lambdao at the operating frequency of 4.5GHz. The overall gain and axial ratio of the designed low profile antenna are comparable with those of the same antenna over a conventional perfect electric conductor (PEC) ground plane at a distance of 0.25lambda o. The artificial ground plane consists of periodic square patches backed by a grounded dielectric slab. Ground planes as small as 4x4 square patches are used without shorting vias. The planar size of the artificial ground plane is about 0.837lambdaox0.837lambdao. To have a physically robust structure, each antenna is printed on a dielectric slab, which is placed over the artificial ground plane. Comprehensive design parametric studies are completed to understand their effects on the overall performance of the antenna.