The broadband composite structure spiral antenna with a ladder-shaped backed-cavity

A particular backed-cavity with a hybrid structure is proposed for a broadband composite structure spiral antenna. And the antenna is feed by an ultra wideband balun. This cavity makes the spiral antenna work operate from 400MHz to 4GHz and without the loss introduced by absorbing materials that are used conventionally to broadband spirals. Additionally, the cavity also contribute to the unidirectional radiation of microwave. Based on the reflex and superposition characteristic of microwave, a ladder liked metallic body is placed in the internal space of backed-cavity to improve the gain at the most part of the frequency range. According to the simulated results, the antenna performances are effectively improved by using this backed-cavity.