Assessment of antenna performance for ultra-wideband systems

In ultra-wideband (UWB) system development, antennas have to be assessed with respect to their impedance matching and radiation performance. Impedance matching is easily expressed as return loss but the quantification of radiation performance is not so obvious. Nevertheless it is crucial to ensure that the antenna has a sufficiently stable pattern in the directions of interest, over the operating bandwidth, or in other words the antenna transfer function does not vary significantly over the range of operating directions. It has been proposed that this assessment can be conducted with the help of the Pattern Stability Factor (PSF), PSF enables one to compare two or more antennas for pattern stability, define pattern-stable bandwidth of an antenna as well as overall bandwidth of an antenna, and assess the effect of antenna device integration on radiation performance. Calculation of PSF can be done easily with either the impulse response in the time domain or directional transfer functions in the frequency domain. Transfer functions are acquired through time domain electromagnetic simulation followed by Fourier transform or wide-band sweeps in a frequency-domain simulation. Experimental determination of PSF can be done with conventional antenna range measurements or with two port scattering parameter measurements using a vector network analyzer. In this paper we will present preliminary results of the former.