On the Synthesis of Null-Scanning Leaky-Wave Antennas (NSLWAs) for Millimeter-Wave Direction-Finding Applications

The inborn spectral-spatial decomposition property of leaky-wave antennas (LWAs) makes them well-suitable for low-cost direction-finding (DF) applications. Conventional LWAs are characterized by a frequency-scanned directive beam, upon which the DF can be performed by searching the spectral peak of echo signals. In contrast, we study in this work a class of LWAs exhibiting frequency-scanned radiation null, i.e., null-scanning LWAs (NSLWAs), which can be exploited for DF via searching the relevant spectral null. This NSLWA consists of a pair of specially engineered LWA elements that work collaboratively to synthesize a radiation null along the scanning plane. The synthesis theories regarding how to model these LWA elements conforming to certain specifications and how to determine their excitation phases are systematically discussed. Also, a generalized design flow is summarized to facilitate practical developments of this emerging antenna class. A simple NSLWA example based on two typical microstrip combline LWA elements is constructed, simulated, and measured for case studies. Simulated and measured results are in good agreement, and both exhibit the desired characteristic of frequency-scanned radiation null. While the radiation/spectral null essentially has a larger steepness than the relevant peak, the NSLWAs may find greater potential than conventional LWAs in high-performance DF applications.