Highly-Directive Cross-Polarized Backscatterers Integrated With a Ground Plane

Cross-polarized backscatterers integrated with a ground plane are a key element of different applications, including chipless RFIDs, sensing, ambient backscattering communications, and data storage. The use of a cross-polarized signal removes the difficulties arising from the strong copolar signal reflected by the ground plane. Concurrently, the cross-polarized signal is typically very weak, hindering the effectiveness of crosspolarized backscatterers in noisy and uncontrolled environments. Herein, the generalized optical theorem is used to derive upper bounds on the cross-polarized backscattering cross section of systems integrated with a ground plane and identify viable strategies to design them based on highly directive scattering systems. Popular antenna configurations, including elementary electric and magnetic dipoles and their combinations, such as Huygens sources and endfire arrays, are examined to ascertain which ones can be used to realize highly directive cross-polarized backscattering performance when they are integrated with a ground plane. Realistic single-antenna elements that attain the upper-bound performance are identified. A two-element endfire array based on crossed electric dipole elements also achieves the upper bound performance, further confirming the efficacy of the derived cross-polarized backscattering bounds.