Development of the Impulse Slot Antenna

We describe the development of the Impulse Slot Antenna (ISA), which is a conformal ultra-wideband (UWB) tapered slot antenna, suitable for printing onto a nonconducting aircraft wing [1]. This antenna is designed to look out over the tip of a wing approximately 0.6 m wide by 1.5 m long. It is likely be useful in UWB radar applications having only limited space for an antenna. We describe the design, fabrication, and testing of the ISA; and compare its performance to that of a commercially available TEM horn. The frequency range of interest for the ISA is from 250 MHz to 2 GHz, and we built 1/8-scale antenna models operating in the 2–16 GHz range. We constrained these models to make maximum use of the assumed 2:5 wing aspect ratio, initially investigating tapered slot designs having 50 input impedance. However, none of these antennas exhibited satisfactory performance. This experience led us to develop the ISA, a hybrid antenna consisting of 200flattened biconical coplanar plates near the feed and a spline-tapered slot of gradually increasing impedance toward the aperture. The antenna is fed through a 200twin-line by a 50-to-200splitter-balun. The ISA out-performed its 50predecessor designs and performed nearly as well as the Farr Research Model TEM-1-50 sensor, which has a radiating element with nearly five times the area of the radiating elements of the scale model ISA. Moreover, the conformal ISA completely avoids the aerodynamic drag of a TEM horn, making it practical for use on an aircraft wing. We describe the 1/8-scale ISA, and we compare its performance in terms of return loss, boresight gain, and antenna pattern to the Farr Research TEM sensor. Finally, we note some design improvements that should lead to improved performance in the next generation ISA.