MM wave transmission polarizer

Anisotropic dielectric transmission polarizers composed of alternate layers of foam and dielectric (See Figure 1) are used at microwave frequencies for producing circular polarization. This type of polarizer, however, is rarely used at millimeter wavelengths because the layers must be thinner than 1/3 wavelength; therefore they become quite thin. A design centered at 94 GHz for example, is limited to a maximum material thickness of 0.030 in. for a polystyrene polarizer with polyfoam spacers. The machining, handling, and assembling of these layers is time consuming, and the parts as well as the resulting assembly are quite fragile and expensive. A design has been developed for an anisotropic dielectric polarizer that overcomes the fabrication difficulties encountered with this type of polarizer design at millimeter wavelengths. Two unique features of this design are: a) a half wavelength electrically invisible center supporting section that permits the polarizer to be fabricated from one piece of dielectric, and b) a quarter wavelength isotropic impedance matching section at each end of the polarizer that provides a relatively reflection free transition into and out of the polarizer for the electromagnetic wave.