New techniques for extremely broadband planar slot spiral antennas

To this point, the frequency dependence of the slot arm termination and of the reflecting cavity have limited the achievable bandwidth of slot spiral antennas. To enable operational bandwidths that approach 100:1, we present two techniques that minimize these limitations. A new termination approach based on the application of lumped element matched attenuators is used to remove the low frequency difficulties resulting from reflections at the end of the antenna. Also, dielectric loading of the reflecting cavity is used to minimize the diameter of the antenna and to increase its usable bandwidth. We first provide a detailed discussion of these techniques, and then present and discuss their extremely broadband performance.