Microwave and Millimeter Wave Technologies A New X-Band Mobile Direction Finder

Abstract

Nowadays, the radio direction finding (DF) has numerous applications in a variety of fields such as radio monitoring, navigation, disaster response, wildlife tracking, electronic warfare [Poisel, 2005], and personal locating service [Xiaobo & Zhenghe, 2002]. DF also forms an important branch of electronic intelligence. With the aim to get high resolution, a large baseline is usually used. In this case the most common DF approach uses phase interferometry method in which the phase delay across the array length (baseline) is measured. Many of DF techniques such as interferometer, correlative interferometer and multiple signal classification [Jnkins, 1991; Schmidt, 1986; Jun-Ho Choi et al., 2008] use the phase information to estimate the angle of arrival. It is well-known that increasing the element spacing increases the resolution, but also proportionally increases the phase ambiguities that must be resolved. These ambiguities occur when the spacing between antenna elements is greater than half of the signal wavelength. As a result of this, multiple baselines are commonly used to resolve ambiguities in DF systems [Pace, 2001; Kwai et al., 2008]. However, there is a need to take into account that the presence of unknown mutual coupling between array elements degrades significantly the performance of most highresolution DF algorithms. Therefore, many array calibration methods have treated mutual coupling calibration as a parameter estimation problem [Friedlander & Weiss, 1991; See & Poh, 1999; Bu-hong et al., 2008]. It is appropriate mention here that fairly often the DF systems use very small individual radiators with degraded gain when the overall dimensions are important in contrast to the DF antennas in telecommunications systems, where gain or directivity is a prime requirement [Peyrot-Solis et al., 2005; Schantz, 2004; Chevalier et al., 2007]. As regards the wireless communications, during last decade the radio systems operating at frequencies higher 1GHz are widely used. Among them we can point 12