Analysis and design of planar metallic surface lenses for controlled wave guidance

Abstract

Surface waves (SWs) on planar substrates are generally considered an adverse effect that can degrade the performance of printed circuits and antenna arrays. However, with appropriate conditions, these SW fields can be employed for controlled propagation along a planar guiding surface. For example, by the addition of a periodic configuration of microstrip lines printed on top of a grounded dielectric slab, an effective phase constant can be achieved, refracting cylindrical SWs transmitted from a slot source etched in the ground plane. A design approach for these surface lenses is presented as well as a specific structure that can generate a bound and guided plane-wave. Applications for these printed metallic lenses include new quasi-optical circuits, novel planar feeds, as well as lowcost leaky-wave antennas for microwave and millimeter-wave frequencies. I. PAPER SUMMARYThe concept of lensing at microwave and millimeter-wave frequencies has sustained much interest in the electromagnetics community [1]-[2]. In general, two different materials can be used to achieve refraction, where the phase velocity of a transmitted wave is altered when passing from one medium to another which can offer the divergence or convergence of freespace waves. This technique for classic field control has also been adopted when designing planar, quasi-optical devices. In particular, one approach to construct a conventional dielectricbased lens for such circuit systems is to embed a new dielectric material (or machine an air-gap) within a host substrate.Similarly, volumetric lens antenna structures for wave control [2] have also been realized by the periodic loading of metallic elements within a host dielectric. In such 3-D lens designs the refractive index, n, or the normalized phase propagation constant,β = β k 0 , can be altered when compared to the surrounding medium. Physically speaking, the propagation of an incident wave can be controlled when a host dielectric medium is periodically loaded with such subwavelength metallic inclusions. This artificial material can be characterized as an effective dielectric constant which can be slightly larger than that of the unloaded medium.In an effort to ease fabrication in such a complex 3-D system, new planar metallic surface wave (SW) lenses are investigated in this work as illustrated in Fig. 1. In particular, by the addition of a periodic configuration of microstrip lines (of width W ) placed on top of a grounded dielectric slab (GDS) which supports planar SWs, a phase constant value can be engineered that is larger than that of the surrounding dielectric medium. The concepts defining artificial dielectrics [2] can Fig. 1. Planar metallic surface lens for control of bound TM SWs. The surface representing the lens region can be modeled as a longitudinal configuration of printed lines having width, W , and subwavelength periodicity, d (<< λ 0 ).also describe the proposed planar metallic SW lens, mainly since, the medium representing the lens can be characterized as a transverse-periodic micro...