Antenna Structures for Resolving Ambiguities in the Dual-Antenna Approach and Measuring Phase Differences

A few years ago, we proposed a system based on two-antenna transmitters (called a “Grin-Loc”). The latter emit two locally synchronized signals from two antennas which are less than one wavelength apart, making the phase difference measurement between the two signals unambiguous. In the case of GNSS signals, we have shown that a standard receiver is already able to process them and to provide a position. The dual-antenna positioning system is made of several such dual antenna transmitters and delivers high performance (decimeter accuracy in indoor environments), while eliminating the need to synchronize the different transmitters. This unique feature makes deployment particularly easy. Nevertheless, the narrow spacing between the two antennas of a Grin-Loc is problem when one wants to increase the positioning accuracy. In fact, the greater the spacing, the smaller is the error in determining the angle of arrival of the signals of a Grin-Loc on the receiver. In L-band radio signals (1 to 3 GHz), the wavelength remains small (from 1 to 3 dm). Here, we propose an approach that can significantly increase this spacing and thus improve the accuracy of the measurements. The theoretical aspects are described, following a description of a practical realization of the initial system. A few simulation results are then given regarding the expected performance of the proposed approach.