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FEED LINE BASICS 341

the alternation of linear polarization vector of EM wave as it propagates in such material. For
example, the vertically polarized wave may be converted into horizontally one or CP and vice
versa.

The physics behind this effect is evident. In Chapter 2, we demonstrated that the permeability
of magnetized ferrite depends on what kind of polarization the EM wave magnetic vector has.
Suppose that this vector is polarized vertically (red vector V) as Figure 6.8.1a demonstrates.

Figure 6.8.1 Faraday rotation illustration: a) LP as a superposition of two CP, b) Polarization
rotation

From the discussion surrounding equations (5.4) - (5.6) in Chapter 5, we concluded that any
linearly polarized harmonic (for example, cos ) wave might be represented as a superposition
of two circularly polarized waves () (check the expression (2.92) in Chapter 2). They have
±
equal magnitude depicted as green and blue vectors and rotate in opposite directions. Figure
6.8.1a illustrates this fact in time domain. Both vectors of 0.5 magnitude are in phase at the
moment = 0 and make up the red LP vector V of unite length. Next moment, CP green
vector is rotated clockwise by the angle ( = 4) while CP blue vector is rotated in opposite
⁄
direction by the angle ( = − 4). If so, their sum keeps its vertical orientation but of reduced
⁄
⁄
magnitude that is equals to 0.5( + − ) = cos = 1 √2, as necessary, and so on.
Due to the phenomenon that the ferrite () permeability depends on the rotation direction,
±
(see (2.97) in Chapter 2) the propagation coefficients = 0� should be different. Here
±
±
is the dielectric constant of ferrite typically between 10 and 16. As such, each of waves with

circular polarization acquires its own phase shift = − where is the path traveled
±
±
by both waves. For instance, the phase shift between them is ∆ = − = ( − )
+
−
−
+
while their superposition is the LP wave over again but its polarization vector V is turned
through angle ∆/2 as Figure 6.8.1b demonstrates. Evidently, we may regulate the rotation
angle just adjusting the bias strength. Probably, one of the most curious applications based on
this alternative polarization controlling is the LP modulator for mm-wavelength used in
polarimetry [12, 13] and shown in Figure 6.8.1b. Authors of patent [13] proposed to use this