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FEED LINE BASICS 347

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6.8.6b, respectively. Figure 6.8.6c illustrates the power flow while power goes from port 1 to
port 2 of WR Y-circulator.

Figure 6.8.6 Y-circulator: a) Coaxial, b) WR, c) Power flow, d) Triangle ferrite element
It demonstrates the displacement phenomenon described in the previous section when the
maximum of EM field shifts to the left in the direction of port 2 as if “gluing” to the left side of
the ferrite rod. Follow such left rule the TE10-mode in port 2 proceeds to port 3 and only from
port 3 comes back to port 1. Such interpretation of the Y-circulator action let's suggest that the
shape of the ferrite element does not necessarily have to be cylindrical. The triangle element
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works as well (see Figure 6.8.6d ) providing the necessary displacement effect.
The functioning principle of coaxial Y-circulator can be explained by the same displacement
effect in stripline loaded by the magnetized ferrite (see Figure 6.8.5). Typically, the ferrite disks
in Figure 6.8.7a are surrounded by the dielectric sleeve (not shown). The demand for such
sleeve has explained the fact that the ferrites have a quite high dielectric constant. As a result,
the wave going out of the air in dielectric suffers noticeable reflections. The dielectric sleeve
plays the role of matching element like the quarter wavelength transformer we will consider
later in Chapter 7 (see Figure 7.1.10d and the last column in Table 7.1). Note that in recent
years new self-biased magnetic ferrite materials were synthesized (see Section 6.8.4 above and
[18]). It lets successfully design [14] Y-circulators without the permanent external magnet.
Such approach promises a significant reduction in size and weight.
From the above discussion, we know that Y-circulator is a passive nonreciprocal device. The
schematic symbol is shown in Figure 6.8.7a where the solid arrow indicates the path for RF
power from port to port while the dotted arrow is the reverse path for opposite bias direction.

Figure 6.8.7 Y-circulator: a) Circuit symbol, b) Radar application, c) Amplifier protection, d)
Y-circulator as isolator, e) Diplexer

To illustrate the results above consider some typical applications of Y-circulators:

25 Public Domain Image, source: https://www.cst.com/Applications/Article/135
26 Public Domain Image, source: https://www.comsol.com/model/parameterized-circulator-geometry-
10302