Photonic nanojet antenna using a single-material dielectric element with …

Description (excerpt)

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U.S. patent application Ser. No. 18/122,055 entitled “Photonic Nanojet Antennas Using a Single-Material Dielectric Sphere or Cylinder” and filed 15 Mar. 2023, which in turn claims priority under 35 U.S.C. § 119 (e) to U.S. Provisional Application Ser. No. 63/319,939 entitled “Photonic Nanojet Antennas Using a Single-Material Dielectric Sphere or Cylinder” and filed 15 Mar. 2022, the contents of which are each incorporated herein by reference in their entireties. RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. FIELD OF THE INVENTION The present invention relates generally to antennas and, more particularly, to dielectric lens antennas. BACKGROUND OF THE INVENTION Non-spherical dielectric lens antennas. FIG. 1 A depicts a prior art collimation action of a dielectric lens antenna (n>1) in a receiving mode. FIG. 1 B depicts a prior art collimation action of a dielectric lens antenna (n>1) in a transmitting mode. Lens antennas are composed of a dielectric lens and a source/receiving (feed) antenna. Electromagnetic waves go through the collimating action by the dielectric lens in the transmitting mode and incoming plane waves converge to a point in the receiving mode as shown in FIGS. 1 A- 1 B . In both cases, the source/receiving (feed) antenna needs to be placed at the focal point for efficient operation. Otherwise, ideal collimation cannot be fully utilized. Properly designed dielectric lens antennas can transform divergent energy into plane waves, and thus they can be used for the purpose of high-gain antenna system. These lens antennas are typically used above 3 GHz for achieving high gain and narrow beam width because the weight and dimensions of the lens become very large at lower frequencies. Also, it should be noted that the focal point of a conventional dielectric lens antenna is usually placed wavelengths away from the surface of the lens antenna. The collimation action of electromagnetic waves by a dielectric lens for the receiving mode shown in FIG. 1 A is achieved by ray bending through velocity retardation/acceleration. On the other hand, spherical wave fronts from the source antenna become converted to plane waves after the waves go through the lens as shown in FIG. 1 B . There are three different types of lenses in terms of their refractive index (n) of the lens material (n>1, n<1 and variable refractive index). Beam steering can be done for parabolic reflector antennas or ordinary lens antennas. However, in these cases, the parabolic reflector antennas need to be moved mechanically, which requires complexity and costs for operation. Additionally, they have high scanning loss in general. Non-spherical lens antennas also have these same issues. Luneburg lens antennas. FIG. 2 depicts a prior art Luneburg lens antenna in the transmitting mode. FIG. 3 depicts a prior art commercial Luneburg lens. The illustrated Luneburg lens antenna is a spherical dielectric lens-type antenna, and the refractive index of the Luneburg lens has variable values inside of the lens region. See R. K. Luneburg, U.S. Pat. No. 2,328,157 issued on Aug. 31, 1943, which is hereby incorporated in its entirety by reference. The refractive index of the Luneburg lens is given by: n ⁡ ( r ) = ε ( r ) = 2 - ( r a ) 2 <