Recently, there has been a resurgence in research interest in spherical Luneberg and homogeneous lens antennas for launching multiple pencil beams. With these approaches, all of the generated beams are almost identical because of the inherent symmetry of the structure. The result is very wide scan coverage of up to 180 deg. To specifically target millimeter-wave multi-fan-beam applications, a two dimensional (2D) Luneberg lens was recently proposed by Xidong Wu of Photonic Systems (Billerica, MA) and Jean-Jacques Laurin from the Poly-Grames Research Center at Ecole Polytechnique (Montreal, Canada). This lens is based on a partially-filled parallel plate technique.
A low-cost polymer material was chosen for its ease of matching and low loss tangent. The approach results in the presence of a thick air region at the edge of the parallel plates, which permits the insertion and fine positioning of the feeding element. The feeding element is a tapered slot antenna (TSA), which is oriented to favor the excitation of the TE10 mode between the parallel plates.
The researchers present a detailed design of the 2D Luneberg lens operating at 30 GHz. A combined ray-optics/diffraction method is used to obtain the system's radiation pattern. Results are compared with the predictions of a timedomain numerical solver. For this prototype, 3- dB E- and H-plane beamwidths of 6.6 and 54 deg., respectively, were obtained. The sidelobe level in the E-plane was -17.7 dBc. The measurement results demonstrate broadband characteristics with radiation efficiencies between 43 and 72 percent over the tested frequency band of 26.5 to 37 GHz. See "Fan-Beam Millimeter- Wave antenna Design Based on the Cylindrical Luneberg Lens," IEEE Transactions on Antennas and Propagation, Aug. 2007, p. 2147.
