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340 Chapter 6

model to run. Advice is simple: google the internet and specialized literature to find something
close to your vision, then design and run a computer model. Then tune up your model based on
simulation results.

The microwave and antenna science reached the level when practically everything was
developed and tested. As such, the real engineering task now is to be able to navigate the
enormous mass of available information. Finally, you found something acceptable but for
different frequency band or not so broadband. If so, the next and most challenging task is the
frequency scaling. Sometimes, but unfortunately quite seldom, the simple changing the
geometrical sizes of device element proportional to frequency shift could guide you to a
workable model. If not, trust your intuition and carefully analyze simulation results.

6.8 PROPAGATION EM WAVES IN FERRITE LOADED LINES

6.8.1 Introduction

Let us come back to the issue of EM wave propagating in line loaded with magnetized ferrite.
A broad variety of passive and active, linear and nonlinear devices with unique characteristics
have been developed since the 1950s when the first nonreciprocal microwave device based on
the Faraday rotation effect was built and tested. The succeeding efforts have been mainly
directed at improving the properties of existing ferrite and design of a new class of materials
such as rare-earth iron garnets. The latter possess extremely narrow (< 10 A/m) absorption
linewidth (see Figure 2.7.4 of Chapter 2) that ensures a low magnetic loss. Note that the
magnetic loss in modern ferrites typically exceeds their dielectric loss. Another important
feature of ferrites that keeps them in business is their ability to handle substantial average and
peak power, much higher than competing semiconductor elements. Part of this may be
explained by their high density of ceramic style structure and, as a consequence, decent thermal
conductivity. The main disadvantages are relatively high material and production cost as well
the weight of ferrite device due to the presence of bias magnets. Particular attention is required
to the thermal stability of ferrite devices. Remind those ferrites as a ferro-material gradually
loses their magnetic properties as the temperature approaches the Curie point shown in Figure
2.6.1 of Chapter 2. If so, the ferrite devices sometimes require thermostabilization and intensive
water-cooling as well some system to support them. Some concern at high power may be
nonlinearity of spin processing in ferrites mentioned in Chapter 2 and the possible generation
of the second harmonic of not an acceptable level. It can be an issue for high-power radars
operating in the environment saturated by many other radio systems.

We included in the following review the just short description of the most important physical
phenomenon of EM wave interaction with processing spins and some simplest ferrite devices
as exemplary. We hope that it will allow the reader to move on him/her own with the minimum
amount of efforts finding more information in specialized literature [17].

6.8.2 Faraday Rotation
This effect discovered by Michal Faraday in 1845 is the result of the interaction of EM waves
with located in static magnetic or E-field materials like ionospheric plasma in Earth’s magnetic
field, magnetized ferrites, ferromagnetic semiconductor, etc. Essentially, Faraday rotation is