Analysis of resistive-vee dipole antennas for producing polarization diversity
Sustman, James William
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This thesis presents a new dual circularly polarized antenna for ground penetrating radar applications. The new antenna design uses four crossed Resistive-Vee Dipoles (RVD) operating in bistatic mode to measure multiple polarizations. The antenna system is able to distinguish radially symmetric and linear targets with its ability to transmit right-hand circularly polarized (RHCP) fields and receive both left-hand circularly polarized (LHCP) and RHCP scattered fields. The type of target can be identified by comparing the relative amplitudes of the received LHCP fields and RHCP fields. For example, linear targets such as wires may be identified by equal amounts of scattered LHCP and RHCP fields. Numerical modeling was used to optimize the arrangement of the four RVDs in the RVD-based CP antenna to have low coupling and good circular polarization at close range. The resulting antenna design is shown to be very effective at finding buried wire targets without being costly. Additional modeling was performed to improve the circular polarization by changing the arm shape and resistive profile of the RVDs. Three methods are developed for estimating the spatial orientation angle of a detected wire target. The first method involves synthesizing transmission and reception of linear polarization at many angles to find the angle that matches the angle of the wire target. The second and third methods involve directly computing the angle of the wire target from the phase difference in the co-polarization and cross-polarization responses. All three methods provide accurate estimates. The RVD-based CP antenna enables strong detection of subsurface targets along with geometry-based classification of targets. The RVD-based CP antenna is well suited for finding buried wires and rejecting miscellaneous clutter that may be present in the ground.