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Wideband Leaky-Wave Antennas Loaded With Gradient Metasurface for Fixed-Beam Radiations With Customized Tilting Angles

We propose a hybrid dispersion compensation method to design wideband fixed-beam leaky-wave antennas (LWAs), with the tilting angle customizable in both forward and backward quadrants. In a previous work, a triangular dispersive prism constituted by metallic pins was presented to compensate for the dispersion of traditional LWAs and achieve a squint-free radiation in a relative bandwidth of 20%. However, that design suffered from the drawbacks of large geometry and limited angular range. To overcome these limitations, here a broadband gradient metasurface based on geometric phase theory is loaded in front of the prism to customize the radiation angle and reduce the total prism size. In addition, a novel ridged gap waveguide is employed to improve the linearity of LWA dispersion, which is beneficial to maintain the bandwidth of LWA with reduced size. Two examples are presented to demonstrate the excellent performance of the designed antennas. One antenna radiates at an angle of 39.5° in a squint-free bandwidth of 20%, but the prism size is decreased to a quarter of the original one, while the other realizes a broadside radiation with a squint-free bandwidth of 18%. Good agreement is exhibited between simulated and experimental results. The proposed method can be further extended to compensate for the dispersion of antenna arrays and improve the angular stability of the radiation beams in a large frequency band.