Page 363 - House of Maxell

FEED LINE BASICS 343

6. Meanwhile, the reflected wave moves toward the forward wave, i.e. its propagation
coefficient is negative with respect to forwarding one. Besides, the reflected wave
movement and bias are matched now. That brings the second sign minus defining the
rotation direction of a propagating wave in ferrite. Since the product of two minuses is one
plus the polarization vector of reflected wave turns extra 45 degrees counterclockwise
(second long blue dot vector in Figure 6.8.2).
7. Finally, because the blue vector is parallel to R-card surface, the return wave decays rapidly
but not entirely. The long R-card might increase the isolator length and weight,
consequently.
8. The remaining portion of return wave proceeds to the input WR with linear polarization
perpendicular to its broad wall that correspondents to nonpropagating high TE01-mode in
standard WR. If so, the return wave reflects back completely to the R-card keeping its
polarization, decays for the second time, now almost entirely. Check that the something
left comes back to the second R-card to be aligned and absorbed again.

In spite of their complexity, the family of Faraday isolators has critical advantages working
quite well at any frequencies between ~100 MHz (see restrictions in Figure 2.7.4 in Chapter 2)
to at last ~1 THz (wavelength 300 nm belongs to UV optical spectrum) and at high or very high
level of peak and average power.

6.8.4 Phase Shifter
There is a wide variety of ferrite phase shifters in almost any type of feed lines. They could be
reciprocal or non-reciprocal, fixed or electronically variable, digital or analog, with memory or
without. The reciprocal ones are based on the phenomenon that the permeability in magnetized
ferrite depends on the external bias typically created by the solenoid. They are developed such
way that the forward and backward waves acquit the same phase shift.
The non-reciprocal ones are constructed in the fashion that the wave moving forward through
a ferrite sample has, for example, CP polarization of () at frequencies faraway from
+
ferromagnetic resonance to avoid high loss. Meanwhile, the wave moving in opposite direction
through the same sample has CP polarization (). We demonstrated this effect above on WR
−
example in Section 6.6.4 of this chapter. Due to differences in ferrite permeability , each
±
wave gets its own individual phase shift.
The term “with memory” means that ferrite as any magnetic material with hysteresis has the
ability to sustain a particular magnetization level without the need for a continuously holding
bias field (look at Figure 2.6.3 in Chapter 2). This property significantly reduces the power
consumption for bias source since the required for magnetization electric power spends just for
switching from one magnetic state to another but not during the state itself. So-called self-bias
ferrites remain magnetized in the absence of external bias field. To get this effect, the
microscopic ferrite grains of a size of the single magnetic domain are oriented in external
magnetic field, pressed, and fused together under heat. After that, the ferrite compound remains
magnetized in the absence of an external field. As a result, the “magnet-less” microwave
components do not comprise heavy and bulky bias magnet and are regularly tenfold smaller
and lighter than traditional ones [18].

As we demonstrated above describing Faraday rotation, the magnetized ferrite exhibits itself as
the medium with the permeability () (see (2.97) in Chapter 2) depending on CP orientation
±