Reduced mutual coupling for through wall radars using orthogonally polarized antennas

Abstract

There has been a growing interest in building through-the-wall radars (TWR) for law enforcement, security and biomedical applications for tracking humans in urban environments. Designing the antennas for such systems is a challenging task due to constraints such as mutual coupling effects between antenna elements, cross-polarization in dual-polarized operation and adverse wall effects on the elements’ input impedance and gain when the array is operating in close proximity to an exterior wall. The objective of this thesis is to provide a transmitter-receiver antenna configuration with low mutual coupling between the transmitter and receiver antenna elements, wide frequency bands of operation, high gain and wide field-of-view. The quadrifilar helix antennas were chosen because of their high gain, wide bandwidth and compact size. The mutual coupling between the transmitter and receiver was reduced by using oppositely polarized antennas. Multiple helical antennas were configured in a manner to obtain high field-of-view at both the transmitter and receiver. The experiments for this thesis work have been performed over the range of 3-4GHz. The resonant frequency for the quadrifilar helix antenna is chosen to be 3.4GHz. The antennas have been simulated on Computer Simulation tool (CST), then fabricated and mounted. The design of the feeding network of the antenna has been done in the Advanced System Design (ADS) tool. Final measurements of mutual coupling in the system have been done with the help of a vector network analyzer (VNA). The system is tested in line-of-sight conditions with and without a target.