In physics, the polarization of electromagnetic radiation is a characteristic of the electromagnetic waves and indicates the oscillation direction of the electric field vector during the wave propagation in space – time (the magnetic field will be polarized along the direction orthogonal to that of the electric field and to the direction of propagation).
Polarization of a Microwaves Beam
An example of a polarized electromagnetic wave is the microwave beam emitted by a gunnplexer (device described in the Post Gunnplexer & Microwave).
The Gunnplexer is a polarized microwave transmitter and receiver. This is because the transmitted electric field wave oscillates in the same direction of the Gunn diode, ie vertically. Thus the output beam from the transceiver is vertically polarized, also the receiver is sensitive only to the electric field polarized in the same direction of the mixer diode, which is also positioned vertically. Turning the receiver around its own axis the intensity read by the receiver passes from a maximum when the transceiver and receiver have the same orientation to a near-zero minimum when they are orthogonal. A microwave polarizing filter can easily build using a simple stripboard PCB, the copper lines absorb the electric field component having the same direction while the orthogonal can pass.
Rotating the polarizing filter around its axis and measuring with the multimeter the wave intensity received by the receiver, one can obtain the data in the table below and shown in the graph.
You can build the appropriate optical filters to obtain linearly polarized light. Polarizing filters are composed of slats spaced between them of the order of the wavelength of the incident light. The slats prevent or dampen the oscillation of the electric field along the direction perpendicular to them, doing so selecting the polarization direction parallel to them.
In the images below we see two filters in place, respectively :
- rotated by 45 °
- rotated by 90 °