Compact Filter-Rotator of Polarization Plane with Uniform Angular Response

The paper proposes a narrow-band polarization plane filter-rotator in a circular waveguide with minimal longitudinal dimensions (~λ/30) and a 2–3% bandwidth at a return loss level of 20 dB in the center of a double-humped passband. The rotator consists of two closely spaced irises, each with a single centered rectangular slot. In contrast to rotators with rotational symmetry C_n of order n > 2, which rotate an incoming linearly polarized wave by the same angle irrespective of its polarization direction, the proposed device allows us to rotate a wave polarized orthogonally to the wide wall of the rectangular slot of the first iris. The possibility of rotation at any angle slightly less than 90° is demonstrated. The polarization plane’s rotation angle differs from the second iris’s rotation angle by fractions of a degree. Therefore, the design of the device allows us to use an intuitive synthesis algorithm. The mutual influence and permutation of the complex eigenfrequencies of the meta-cell from a pair of single-slot irises explain the double-humped AFC. The device can provide a smooth mechanical adjustment of the polarization plane within ±14° with good matching by rotating the second iris around its axis. We used our implementation of the mode-matching techniques and the method of generalized scattering matrices for the calculations.