Microwave Near-Field Focusing Properties of Width-Tapered Microstrip Leaky-Wave Antenna

The possibility of microwave near-field focusing using a simple width-tapered microstrip leaky-wave antenna is theoretically and experimentally proven in this paper. The design procedure to obtain the modulation of the microstrip width along the antenna length is described, illustrating the conditions and limitations for optimum focusing at a certain focal point and using a given substrate. A 7.5 lambda(0)-long microstrip lens is designed to operate at 15 GHz, and its focusing properties are studied. An array of two in-phase microstrip lenses located front-to-front is proposed to obtain a symmetric focusing pattern with higher spatial resolution. Theoretical and experimental results demonstrate the optimum synthesis of a focusing region with focal length of 3 lambda(0), presenting focal width of only 0.33 lambda(0), and focal depth of 1.25 lambda(0). Finally, it is reported the frequency focus-scanning performance in the range 14-17 GHz. All these features make the proposed microstrip lens a simpler alternative solution to focused planar phased-arrays.