Detection of polarisation of microwave signals using infrared thermography is described in this paper. A metal grating consisting of parallel, equally spaced metallic strips is placed in between a microwave source (antenna) and a microwave absorption screen for permitting the determination of direction of electric field vector (polarisation). Very low frequency modulation of the microwave source is added to permit lock-in thermography which enhances thermal resolution.In case of linear polarisation when the metallic strips of the grating are parallel to the direction of electric field vector, the temperature rise on the screen as observed by an infrared camera, is minimum. On the other hand if the metallic strips are perpendicular to the electric field vector the temperature rise observed on the screen is maximum. The orientation of the grid is changed by rotating the grid about a central axis perpendicular to its plane. With each different orientation of the grid a change in temperature rise is observed on the screen.In case of circular polarisation the temperature rise on the absorption screen is almost independent of the grid orientation i.e. there is negligible change in temperature rise with each different orientation of the grid, as the electric field strength perpendicular to grid strips is almost constant for all grid orientations, corresponding to an axial ratio of unity. While in case of elliptical polarisation the temperature change is appreciable depending on the axial ratio.The proposed method is validated on linearly, circularly and elliptically polarised patch antennas radiating at 8 GHz. Simulation is carried out in CST MICROWAVE STUDIO (CST MWS2013) and a good agreement between simulated and experimental (thermographic) results is observed. © 2016 IETE.