X-Band Near-Field GPR Based on Collimated and Focused Vortex Waves Using Ellipsoidal Reflector

Electromagnetic vortex waves (VW) with orbital angular momentum (OAM), generated by a uniform circular array (UCA), are collimated and focused in the ground by an elliptical reflector in the near field (NF). This antenna system is used in a conceptual design of an X-band $(9.3 \mathrm{GHz})$ high-resolution ground penetrating radar (GPR) for the localization of multiple buried targets. Physical optics and ray tracing are used to calculate the underground NF. The relevant NF radar equation is developed using the Lorenz reciprocity theorem. The formulations of field in the ground are given. The algorithms used for the simultaneous localization of multiple targets are based on the orthogonality of OAM modes. The radar uses wide-band $(8.6 \%)$ FMCW waveform with coherent and noncoherent integration. The signal-to-noise ratio and the detection probability of small targets are calculated. We applied the method to a $\sim \mathbf{1 \%}$ moist sandy loam soil up to a depth of 1 m.