Many vehicles (including, but not limited to, missiles, space craft, aircraft, trucks, and automobiles) require an antenna with forward-directed gain, that is, gain that is maximum in the direction of travel. In such vehicles the nose of the vehicle would be the most desirable location for the antenna. However, the nose of the vehicle may be occupied by other equipment, or may be covered by materials that are not transparent to electromagnetic (EM) radiation. Such materials may be required to resist heat caused by high-speed motion, or to protect the vehicle in the event of a collision. In such vehicles, it may not be possible to locate the antenna in the nose, where the antenna could achieve maximum forward directed gain.
Even where the antenna gain is directed in a direction other than the direction of travel, the portion of the vehicle facing in the desired direction of propagation may not be available or suitable for locating an antenna.
As shown in the graph depicted in FIG. 1, aerodynamic friction can cause the skin temperature of high-velocity vehicles to reach ultra-high temperatures (>500° C.). An antenna is often covered by a structure called a radome, to protect the antenna from materials in the surrounding atmosphere. Radomes are preferably fabricated from non-conductive, low-loss materials, to provide for effective propagation of EM radiation.
Where a radome is located on or in the skin of a vehicle, the material of the radome will be subjected to the high temperatures discussed above. Many materials that are suitable for antenna radomes cannot withstand the high temperatures seen during hypersonic flight.
In addition, in some vehicles it is desirable for antenna and radome to be conformal to a surface of the vehicle's wings or fuselage without protruding into the air stream, and to be able to radiate in directions other than normal to that surface.
Technical aspects of surface wave antennas and radomes are described in the following references, which are incorporated in this disclosure by reference as if fully set forth herein:                1) F. Chen, Q. Shen, and L. Zhang, “Electromagnetic Optimal Design And Preparation Of Broadband Ceramic Radome Material With Graded Porous Structure”, Progress In Electromagnetics Research, Vol. 105, 445-461, 2010.        2) F. J. Zucker, “Surface Wave Antennas,” Antenna Engineering Handbook, McGraw-Hill Companies, 2007.        3) J. Langfield, J. T. Mehr, D. J. Carlson, “Conformal Wide Band Surface Wave Radiating Element”, U.S. Pat. No. 8,736,502.        4) R. F. Harrington, Time-Harmonic Electromagnetic Fields, John Wiley & sons, 2001.        