UNIFORM BEAMWIDTH UWB FEED ANTENNA USING LOSSY TRANSMISSION LINES

Abstract

The ideal ultra-wideband (UWB) antenna feed for lens and reflector systems radiates a uniform and customizable beamwidth vs. frequency. Here, a new antenna concept for radiating frequency-independent Gaussian beams with arbitrary bandwidths and beamwidths is reported. It is analytically shown how to resistively load a transmission line network to maintain a Gaussian amplitude taper across an antenna array aperture. In contrast to many other feed antennas, the radiation properties here can be tailored without time-consuming full wave optimizations. The radiated beamwidth, bandwidth, antenna size, radiation efficiency, and gain can all be quickly estimated using the derived closed-form expressions. An example, 16 × 16 Vivaldi element array is fed with a network of resistively loaded microstrip lines. The simulated array radiates a Gaussian beam with 10 dB full beamwidth of 35◦ ± 5◦ and directivity of 20 dB ± 1.5 dB over 6.5GHz–19GHz (3 : 1 bandwidth ratio). However, the radiation efficiency is inherently low due to the large loss associated with generating the Gaussian amplitude taper at all frequencies. The example array has a simulated radiation efficiency of 1% at the higher operating frequencies. The array was fabricated and measured. The measured beamwidths agree well with simulation to validate the reported theory. This architecture is a particularly attractive option for feed antennas that require customizable directivities, and can tolerate low radiation efficiencies such as test and measurement.