An extended Malus’ Law for the well-known Polarizer-Analyzer Mounting (PAM) is analytically obtained and investigated. The PAM is composed of two perfectly parallel Metallic Linear Polarizers (MLP), with subwavelength periodic pattern composed of rectangular holes. Our analytical theory especially highlights the influence of multiple reflections between the two MLPs which leads to an extended and tunable Malus Law. We demonstrate that the classical Malus Law (obtained for dichroic polarizers) is modulated by a factor which also depends on the angular difference between both MLP axes. In our analysis, the Malus’ law is studied at the resonance wavelengths. Due to the interactions between the two MLP, the modulation factor is tuned by the optical distance between them which makes substantial variations of the Malus Law. We mention that, for each reflections, the light is re-polarized according to the orientation of the MLP. This tunable Malus’ Law provides an original tool for ultrasensitive detection in the terahertz or microwave regime. For example, one can use an ultra-narrow angle Malus’ Law as a hyper-sensitive device to analyze with a high accuracy the electro-optical response of a material sandwiched between polarizer and analyzer. We theoretically propose one PAM designed to detect a refractive index variation as small as 10−5. Finally, we extend the theory, which takes the form of an extended Jones formalism, to a large number of stacked MLP. It is applied to achieve many polarization manipulation processes as total polarization conversion with tunable spectral bandwidth, for instance.