A new design of two-dimensional cylindrical Luneberg lens is introduced based on TE10 mode propagation between parallel plates, with special focus on ease of manufacturing. The parallel plates are partially filled with low cost polymer material (Rexolite epsivr = 2.54) to match Luneberg's law. A planar linear tapered slot antenna (LTSA) is inserted into the air region between the parallel plates at the edge of the Luneberg lens as a feed antenna, with fine positioning to the focal point of the Luneberg lens to optimize the antenna system performance. A combined ray-optics/diffraction method is used to obtain the radiation pattern of the system and results are compared with predictions of a time domain numerical solver. Measurements done on a 10-cm Luneberg lens designed for operation at 30 GHz agree very well with predictions. For this prototype, 3-dB E- and if-plane beamwidths of 6.6deg and 54deg respectively were obtained, and the sidelobe level in the E-plane was -17.7-dB. Although the parallel plate configuration should lead to a narrow band design due to the dispersion characteristics of the TE10 mode, the measurement results demonstrate broadband characteristics with radiation efficiencies varying between 43% and 72% over the tested frequency band of 26.5-37 GHz. The designed cylindrical Luneberg lens can be used to launch multiple beams by implementing an arc array of planar LTSA elements at the periphery of the lens, and can be easily extended to higher mm-wave frequencies.

Fan-Beam Millimeter-Wave Antenna Design Based on the Cylindrical Luneberg Lens

Summary-A two-dimensional microwave model of the Luneberg lens has been designed employing the TE 10 mode. It consists of two 36-inch diameter, almost-parallel, conducting plates with the space between plates filled with polystyrene. Its thickness varies with the normalized radius, T, to give the desired index of refraction n = \sqrt{2-r_2} Due to symmetrp about the center, this lens maintains constant gain and beam shape as a feed is scanned over its circumference, while the side lobe level remains at least 18 db below peak power. Experimental patterns show good agreement with computed patterns in the two principal planes.

A two-dimensional microwave luneberg lens

This paper presents an all-metal parallel plate waveguide (PPW) Luneburg lens designed using an array of subwavelength Fakir bed of nails unit-cells Variation of the metal post height and PPW-spacing modulates the effective refractive index The lens operates in the Ku-band of frequencies, with more than 40% bandwidth, in a quasi-TEM mode Broadband and low loss, with high directivity and wide field-of-view, this antenna could be an excellent candidate as a lens-like beamformer for multiple beams satellite communication applications

All-metal Ku-band Luneburg lens antenna based on variable parallel plate spacing Fakir bed of nails

In this letter, a 2-D Luneburg lens sandwiched by two parallel metallic plates is proposed. To support both the vertical and the horizontal polarizations, parallel plate waveguide (PPW) theory is applied to analyze the proposed lens. The results shown that the height of the lens and the consistence of the gains for each polarization has a tradeoff relation. The optimized height of the lens is approximate one operating wavelength. To verify our idea, a cylindrical Luneburg lens is fabricated using 3-D printing technique with a radius of 4.65 λ 0. Using effective medium theory, the relative permittivity in each region of the lens can be obtained by adjusting the air-to-space ratio of the meta-atoms in that region. A dual-polarized patch antenna working around 15 GHz is used to feed the lens. The measured results agree well with the simulated ones, which prove that the gains of the two polarizations can be designed as equality by setting a suitable height of the lens. The measured gain is 15.1 dBi for vertical polarization and 14.7 dBi for horizontal polarization at 15 GHz. The lens-antenna system launches beams which points at −60°, −20°, 20°, 60° in the measurement for verification. The proposed Luneburg lens is suitable for base station which has the requirement of dual-polarized multibeam antennas.

3-D Printed Cylindrical Luneburg Lens for Dual Polarization

Free-space transmission of terahertz waves opens great opportunities for wireless applications including communications and radar, enabling higher information capacity, higher spatial resolution, and yet smaller apertures than using microwaves. Nevertheless, due to the shorter wavelengths, it involves a severe path loss. To compensate for the path loss, point-to-point transmission by beam steering is indispensable. However, the implementation of broadband and low-loss beam steering is still challenging in the terahertz range due mainly to the lack of practical phase shifters. To circumvent this issue, here we demonstrate a novel approach of terahertz beam steering based on trajectory deflection in a dielectric-free Luneburg lens. It converts a point excitation into a deflected beam in the fundamental transverse electric mode inside parallel conducting plates based on graded effective refractive index, which is then launched into free-space. The absence of dielectric medium contributes to reduce the insertion loss and also enables external control of the effective refractive index. Importantly, this approach is assisted by angular leverage; a very little change of the plate tilt results in very large deflection of the beam trajectory. We demonstrate beam steering from –25° to +25° by changing the plate tilt from –25′ to +25′ (–0.42° to +0.42°), which is transferred to the 60 times larger angles. Such a small tilt can easily be generated, for example, by using piezo or MEMS actuators. Since the excitation point can be fixed, the proposed device can easily be coupled to a wide range of chip sources and detectors, offering waveguide integration. As an application example, we implement high-resolution radar that identifies both the direction and range toward an object.

Terahertz Beam Steering Based on Trajectory Deflection in Dielectric-Free Luneburg Lens

For many years it has been known that, in principle, optical lenses could have been made from non-homogeneous glass. For example, if a glass sphere of unit radius were made with refractive index varying according to the relation. ? = ?(2?r2) where ? = refractive index and r = radial distance from centre, it would act as a lens with the focus on the surface of the sphere. Such non-homogeneous glass cannot be produced in practice; however, a microwave analogue has been constructed using spaced conducting sheets to produce a region of refractive index varying in accordance with the above relation. This lens, being circularly symmetrical, is free from aberrations as the feed is moved around the circumference, and is therefore suitable for wide-angle scanning. It will operate only when the direction of polarization is such that the magnetic vector is normal to the conducting sheets.

S.S.D. Jones

Papers

A wide-angle microwave radiator