Novel terahertz scanning reflector antenna system

Abstract

This paper presents a number of proposed reflector antennas to realize near-field focusingof high-resolution, THz imaging signals while scanning along a focal line. The proposed reflectors are reasonable-order polynomial shapes, with illumination of different parts of the reflector leading to focusing at different points along a focal line. As such, the design process takes advantage of prolate spheroid (ellipses rotated about the focal axis) geometry, attempting to approximate these spheroids in many areas to produce many focal points. The reflector system uses a directional feed on a rotating arm, that makes an arc around the origin, allowing the illumination of small, but overlapping, areas of the reflector and hence the scanning. The reflectors are then analyzed for phase coherence for each scan point, as well as focal spot width. This is treated as a quasi-optical problem, so much of this analysis uses ray tracing techniques. It is found that the initial development ideas, which include approximating two or three prolate spheroids with a polynomial equation at the edges of the reflector, are not sufficient to maintain coherence and high resolution for all desired scan points. The feed can be focused excellently by the polynomial reflector at the points where the matching to the spheroid is done, but the focusing ability degrades fast as the feed is scanned to adjacent points. It is found that allowing the feed to rotate on its scan arm, that is to illuminate not directly through the origin, allows the system to achieve focal points almost continuously along the focal line, with wide enough feed beamwidth for substantial illumination overlap on the reflector, making this a useful antenna design.--Author's abstract