An active phased array K-band radar based on collimated vortex waves

This paper investigates a nonconventional planar active phased array (PA) radar. This radar operates by creating and controlling collimated electromagnetic vortex waves (VW). The core idea is built upon Schelkunoff's equivalence principle (SEP). The VW’s are generated by an equivalent flat radiating aperture (RAP). The fields on the RAP are calculated by using a virtual antenna (VA) which generates the desired collimated VW’s. According to SEP, the RAP radiates the same field as the VA, though with some precision differences. By adjusting the angle at which the RAP is tilted relative to the VA, the direction of the VW beam can be controlled. Each tilt angle of the RAP corresponds to a different distribution of the field on it, and this unique distribution for each angle becomes the basis for this nonconventional PA radar. To manage the complexity, the RAP is divided into smaller square sections known as subapertures (SAPs), which are placed close to each other at distances nearly equal to a wavelength. This arrangement reduces the required number of SAPs. The PA employs microstrip elements fed by transmission-reception TR modules to replace these SAPs. Additionally, any unwanted grating and side lobes in the resulting pattern are mitigated using subarrays within the SAPs. The VW-based PA radar is applied to a K-band radar. The VW radar's theory and its signal processing are described highlighting the advantages of electronically adjusting the scanning direction. The numerical results given validate the methods and the designs.