Compact, low-profile UWB antennas exploiting the concept of closely-coupled dual-mode radiators

In this paper, the concept of closely-coupled, dual-mode radiators is utilized to design a compact, low-profile, ultra-wideband antenna. An antenna that consists of two closely-coupled loops is shown to exhibit two distinct modes of operation, which have complementary frequency bands of operation. By combining the two modes using a feed network that employs a frequency-dependent phase shifter, the antenna is automatically excited in its appropriate mode of operation depending on the input frequency. With the aid of the feed network, the antenna is demonstrated to achieve a larger overall bandwidth compared with what can be obtained using each mode individually. A prototype of the antenna was fabricated and measured and good agreement between measurements and simulations is observed.