Shape Variable Impulse Radiating Antennas Using Fluid Materials

Abstract

The Impulse Radiating Antenna (IRA) is an ultra-wideband (UWB) antenna which can radiate a sharp waveform with low dispersion and high gain. For this reason, IRAs are useful in a number of applications where broadband is needed such as data communication, radar, and electronic warfare. It could be used more effectively by changing the shape or characteristic of the antenna according to the applications. In this dissertation, shape variable impulse radiating antennas are proposed using fluid materials which are liquid or gas phases. First, using air, inflatable IRA (inf-IRA) was proposed. The inf-IRA is covered by thin films as a main material so that it can be inflated as the air is injected and be packaged small size as the air is deflated. The reflector of inf-IRA, whose diameter and focal length are 0.3 m and 0.15 m, respectively, is made of reflective Mylar film. The parabolic curve is formed by joining planar discs. The structure is supported by attaching internal stays. Two feed arms are printed on a thin Kapton substrate. The arms are designed with an asymptotic conical dipole profile for low input impedance. The reflection coefficients and gain patterns of fabricated inf-IRA are measured and compared to those of simulation and rigid-IRA. Second, a beamwidth controllable IRA using liquid metal was proposed. The typical solid reflector of the IRA was replaced with a wired reflector corresponding to the current flow on the surface of the solid reflector. A strip wired reflector IRA (WIRA) with a diameter of 300 mm was implemented using conductive fabric. The performance of the WIRA was shown to be essentially the same as that of the conventional IRA through simulation and measurement. Then, liquid metal was used to replace the solid wires, and a beamwidth controllable WIRA was implemented. The electrical size of the reflector could be expanded up to approximately 400 mm in the H-plane. The beamwidth control capability was validated through simulation and measurement. It was shown that the beamwidth could be varied in the H-plane up to 44 % while other parameters, such as the input impedance and E-plane beamwidth, remained almost constant.