Circuit Modeling of 3-D Cells to Design Versatile Full-Metal Polarizers

An original mechanism is here proposed to achieve polarization conversion from linear to circular with the use of full-metal polarizing screens. Such screens are self-supported and conceived from the periodic arrangement of 3-D unit cells. They are built from sections of rectangular waveguides operating below the cutoff frequency and loaded with slotted discontinuities. The polarizer operates in transmission mode; the discontinuities are responsible for both its high return losses and the conversion of the impinging linear polarization to circular. Two types of 3-D cells are presented, and both of them are analyzed and designed through equivalent circuit models (CMs). These models have been thoroughly built in order to capture all the phenomena underlying the discontinuities' behavior. The characterization of the first cell is fully done analytically, whereas the second cell needs reduced help from a full-wave solver. Furthermore, the CMs allow simple design guidelines to be identified for this type of polarizer. Two designs are performed operating in Ka-band, proving that an extension of the operation bandwidth (axial ratio and S11) to 11% is possible by employing the second cell.