29 July 2003 Phase-correcting zone plate antennas at terahertz frequencies
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Abstract
At terahertz frequencies the attenuation of conventional lenses can be very high. In addition, the fabrication tolerances for standard curved lenses (e.g., hyperboloid in shape) make construction difficult and costly. In contrast, zone plate lenses are thin (typically on the order of a wavelength) and therefore have low loss. In addition, zone plates are planar, and the flat surfaces are easy to fabricate. They are also much lower in weight than a true lens. These considerations have led to the development of several designs at frequencies to 600 GHz. All typical lens materials show an increase in loss tangent at frequencies above 100 GHz, and for some the loss increases at an undesirable rate. For example, polystyrene has much greater loss than Teflon at 600 GHz. Thus, material choices are a consideration, and dielectric constant is also a part of this consideration. At 300 GHz the wavelength is 1 millimeter. A zone plate with this thickness poses support problems, but by the use of material with a dielectric constant of 1.05, the structure becomes about 10 times thicker and therefore more structurally feasible. These options are described, and design cases will be given. Various examples have already been designed, built, and tested at frequencies near 100, 140, 210, 235 and 280 GHz, and their characteristics will be summarized. The result is a compilation of recommendations for usable designs, with information on losses, beamwidths, feed arrangements, and construction considerations, as well as comparisons to conventional lenses.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James C. Wiltse, James C. Wiltse, } "Phase-correcting zone plate antennas at terahertz frequencies", Proc. SPIE 5070, Terahertz for Military and Security Applications, (29 July 2003); doi: 10.1117/12.500321; https://doi.org/10.1117/12.500321
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