Antenna Effects in Depolarization Measurements

Blanchard, A.J.; Jean, Buford Randall, "Antenna Effects in Depolarization Measurements," IEEE Transactions on Geoscience and Remote Sensing, vol.GE-21, no.1, pp.113,117, Jan. 1983, doi: 10.1109/TGRS.1983.350537

Abstract: The depolarization of electromagnetic energy scattered from natural terrain has been of interest to experimenters and theoreticians for many years. However, the reported measurements have not agreed with theoreticaly predicted results. Boresight axial ratio has commonly been used as a figure of merit to describe the polarization isolation properties of the measurement system antennas. Since depolarization measurements from terrain involve extended targets which fill the full antenna beam, boresight axial ratio is often an inadequate measure of antenna polarization purity. This paper describes antenna isolation characteristics which impact the quality of the depolarized measurements. Representative calculations demonstrate the effects of nonideal antenna systems on the observed measurements. A criterion for antenna specification is given which will provide high-quality cross-polarized measurements.

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Holographic Research to Enhance Aircraft Antennas

The US Air Force has funded researchers at HRL Laboratories in Malibu, California to work on innovative new holographic techniques to create antennas that do not detract from an aircrafts aerodynamics.

The team are working on holographic impedance surfaces that will make antennas completely flush with the surface of the aircraft while still maintaining or even enhancing current protruding antenna capabilities.

The team are building the surfaces out of metallic materials on a substrate.

Programme manager at the Air Force Office of Scientific Research, Dr Arje Nachman said that the technology offers several benefits.

"One attractive benefit offered by these interesting surfaces is that if the tail of an aircraft obstructs the beam of an antenna then the tail can be covered by a suitably crafted impedance surface in such a way that the antenna beam flows around the tail as if the tail weren't there," Nachman said.

The HRL team is now trying to extend the capabilities of the electromagnetic impedance and experiment with practical implementations of it.

The researchers plan to create new kinds of unit cells and are also seeking new mapping techniques that allow those cells to be positioned over complex objects.

By Daniel Garrun.