(Polarizer) Circular polarizer usually consist of two internal probes set at right angles to each other to detect the incoming signal. The output of one is delayed 1/4 wavelength relative to the other so the signals are added to detect one sense of polarization (LHCP or RHCP); reversing the delay detects the other polarity sense. A pin diode switch controlled by a small dc voltage can be used to select polarity. Such devices can be easily built into the throat of an LNB. Polarizers that combine this method with the mechanically rotated probe can switch at will between both linear and both circular formats.
A scalar feed can be modified to receive circularly polarized signals, albeit with a 2 to 3 dB performance penalty. This is accomplished by inserting a dielectric slab, typically a small rectangular piece of teflon or similar material, into the circular waveguide at a 45° angle from the position of the probe. It acts by "delaying" the circularly polarized signal thus translating it into a linearly polarized signal. Standard scalar feed cannot distinguish between LHCP and RHCP transmissions but this simple retrofit permits detection and discrimination of both circular polarity senses.