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Directional couplers in Ultra-Wideband (UWB) High-Voltage (HV) radar systems allow the possibility of using a single antenna for both transmission and reception. In this paper, we continue the development of HV UWB coupled-line directional couplers reported earlier in [1], and first suggested by Baum in [2]. We investigate smoothing the impedance profile, increasing the isolation, and reducing the transmission loss, while maintaining high voltage standoff and high mechanical reliability. Note that a more detailed version of this paper appears in [3] [ABSTRACT FROM AUTHOR]

We describe here a high-voltage cable-fed Impulse Radiating Antenna (IRA) that was developed as part of an Ultra-Wideband (UWB) radar system using a single antenna and a directional coupler [1]. In this configuration, it is not possible to use a sharpening switch at the apex to handle high voltages, so we investigated using higher voltages on a standard IRA with splitter balun. The resulting antenna, referred to as the IRA-6, was built and tested at three different voltage levels. Note that a more complete version of this paper appeared in [2] This antenna is intended to be operated with a pulser with 30 kV peak voltage, 150 ps risetime, 3 ns pulse duration (at 1/e of peak), and 1 kHz maximum pulse repetition frequency (PRF) (manufacturer's specs.). To prevent flashover at this voltage level, we incorporated a number of compromises into the antenna design at the splitter and feed point (focus), which led to somewhat larger reflections in the TDR than we are accustomed to seeing. These compromises also led to reduced realized gain, especially at higher frequencies. Nevertheless, the IRA-6 performed quite well as high as 4 GHz, which met the requirements for the radar system under study. [ABSTRACT FROM AUTHOR]

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 1/8th-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 Ω input impedance. However, none of these antennas exhibited satisfactory performance. This experience led us to develop the ISA, a hybrid antenna consisting of 200-Ωflattened biconical coplanar plates near the feed and a spline-tapered slot of gradually increasing impedance toward the aperture. The antenna is fed through a 200-Ωtwin-line by a 50-to-200-Ω splitter-balun. The ISA out-performed its 50-Ω predecessor 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 1/8th -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 [ABSTRACT FROM AUTHOR]