Wideband and Aperture-Efficient Traveling-Wave Endfire Antenna Designs Using the First Higher-Order Transmission Line Mode

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In this article, we propose a traveling-wave endfire antenna based on the first higher-order transmission line (TL) mode, and it features wide bandwidth, high gain, and large aperture efficiency. We propose two essential conditions for the realization of the proposed wideband endfire antenna. First, the dispersion curve of the first higher-order mode should be made close to that of the air line across a wide frequency band. Second, the fundamental mode should be suppressed to allow single higher-order mode operation across a wide frequency band. Following these principles, we provide a design for an endfire antenna based on a periodically slotted parallel stripline, where the periodic meandered slots suppress the fundamental mode and hence allow single higher-order mode radiation. To verify the proposed approach, a prototype has been designed and fabricated. The antenna can achieve endfire radiation within a 1:2 frequency band (8.5–17.5 GHz), with an average gain of 10.7 dBi, and large aperture efficiency up to 6.38 dBi/λ ²₀.