A flush-mounted leaky-wave antenna with predictable patterns

This paper describes the design and the measured performance of a large, flat antenna consisting of an inductive grid spaced over a conducting surface. The analysis employs the transverse-resonance method to determine the radiating properties of the structure. This analytical technique is shown to predict very accurately the amplitude and phase of the illumination along the aperture of the antenna. An antenna was built with an 18- by 24-inch aperture and tested over the frequency band from 7-to-13 kmc. The results of these tests confirm the theoretical predictions in every detail. A pencil beam from the antenna scans in the H-plane (perpendicular to the antenna) from to from the normal to the aperture as the frequency changes from 7-to-13 kmc. The H-plane beamwidth remains virtually constant over most of this band. The first H-plane sidelobe or shoulder is at least 29 db below the main lobe from 7-to-10 kmc, and at least 23 db below from 10-to-13 kmc. All H-plane sidelobes beyond three or four beamwidths on either side of the main lobe are at least 40 db below the main lobe everywhere in the 7-to-13 kmc band. At the design frequency the measured pattern agrees with the theoretical pattern within a fraction of a db down to 40 db below the peak of the main lobe, even though the gain of the antenna at this frequency is only 33 db.