A novel interdigital capacitance (IDC) frequency selective surface (FSS) based linear-cross reflective polarizer for K- and Ka-band applications is demonstrated in this work. The suggested device includes an IDC-loaded dipole printed on a thin FR-4 grounded dielectric substrate. From 17.02 to 37.30 GHz, it shows linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) of 20.28 GHz bandwidth (74.7% fractional bandwidth [FBW]) for a y/x polarized incident electromagnetic (EM) wave. Along with linear-cross conversion, this polarizer also performs linear-circular conversions with axial ratio ≤ 3 dB in two frequency bands (Ku band-right circular, 15.13–16.15 GHz; Ka-band-left circular, 38.52–39.78 GHz) with 6.52%, and 3.14% FBW, respectively. The design performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) modes. The polarizer unitcell has structural dimensions 0.177 × 0.177 × 0.061 (Formula presented.) where λL corresponds to the free-space wavelength of the lowest working frequency. The polariser's transmission line equivalent circuit model is extracted, and a good match is observed with the EM solver response. The broadband behavior of FSS and the ground plane is better understood by looking at surface current patterns at resonant frequencies. The proposed design's radar cross-section (RCS) analysis is compared to perfect electric conductor for the bistatic condition. The design novelty lies in its compact architectural volume of the unitcell 1.911 (Formula presented.)), low-profile, broadband PCR response with superior angle stability, dual-polarization conversion with circular rotation switching makes it a good option for real-time applications. © 2022 Wiley Periodicals LLC.