FIG. 1a shows the fuselage of an aircraft fuselage. It is desirable to mount an antenna on the underside of the fuselage behind the landing gear. However, at least portions of the landing gear (particularly its support strut) block the antenna radiation in the forward direction.
There are many other instances where some element protrudes (or could protrude) from the body of a vehicle which protruding element interferes or obstructs (or could interfere or obstruct) RF reception to and/or transmission from an antenna also on the body of the vehicle. If the vehicle is currently being designed, perhaps it will be possible to move either the antenna or the interfering or obstructing element. Other times, that cannot be done and if the vehicle has already been built it can be very inconvenient to do so, if not impossible to do so. This invention relates to techniques which can be used to mitigate the effects of such elements which otherwise can interfere or obstruct RF reception to and/or transmission from an antenna also on the body of the vehicle. An interfering or obstructing element is generically referred to as a blockage herein.
The prior art includes:    D. J. Gregoire and J. S. Colburn, “Artificial impedance surface antenna design and simulation”, 2010 Antenna Applications Symposium, pp. 288-303, the disclosure of which is hereby incorporated herein by reference.    Fong, B. H.; Colburn, J. S.; Ottusch, J. J.; Visher, J. L.; Sievenpiper, D. F., “Scalar and Tensor Holographic Artificial Impedance Surfaces”, IEEE Trans. Antennas Prop., vol. 58, pp. 3212-3221, 2010, the disclosure of which is hereby incorporated herein by reference.    Ottusch, J. J.; Kabakian, A.; Visher, J. L.; Fong, B. H.; Colburn, J. S.; and Sievenpiper, D. F.; “Tensor Impedance Surfaces”, AFOSR Electromagnetics Meeting, Jan. 6, 2009, the disclosure of which is hereby incorporated herein by reference.
Artificial impedance surface antennas (AISA) are formed from modulated artificial impedance surfaces (AIS). The AIS are typically fabricated using a grounded dielectric topped with a grid of metallic patches. The article by Fong presents a detailed description of the methods used for designing and fabricating linearly and circularly polarized AISAs using scalar and tensor impedance maps, respectively.