Directive Coupled Sectorial Loops Antenna for Ultrawideband Applications

This letter presents a modified coupled sectorial loops antenna (CSLA) architecture with electrically small dimensions capable of unidirectional radiation over a very wide bandwidth. The proposed antenna is composed of two nonplanar sectorial loops in conjunction with a tapered slot fin in front that bisects the angle between the loops, all backed by a metallic reflector. The metallic reflector produces the required front-to-back ratio, and the tapered slot facilitates forward radiation of high-frequency components. The antenna can fit in a box having dimensions $0.43\lambda \times 0.32\lambda\times 0.25\lambda$ , where $\lambda$ is the wavelength at the lowest operating frequency. The antenna shows excellent impedance matching over the frequency band 0.56 GHz and a stable radiation pattern in the band 0.52.25 GHz, with front-to-back ratio better than 10 dB and gain higher than 5 dBi. The antenna was designed, fabricated, and measured. The measured results show good agreement with the simulation results and validate the design accuracy and performance of the antenna. The antenna is proposed for usage in low-frequency, ultrawideband (UWB) radars requiring a compact antenna with relatively high directivity.