Page 364 - Maxwell House

344 Chapter 6

(right or left) of H-field. Clearly, each of these waves has the propagation coefficient =
±
0� meaning that the phase variations are defined by the factor �− ± � . The simplest
±
nonreciprocal WR phase shifter based on this effect schematically shown in Figure 6.8.3a.

Figure 6.8.3 WR phase shifter: a) Schematic drawing, b) RF H-field in WR (view from the
top), c) Two-stub design, d) Latching design, e) Twin-toroid design
The G-shape electromagnet (shown in green with red coil) exerts static magnetic field that can
be varied by changing up and down the current from power supply (not shown). The force

lines of bias field H0 are depicted in green. The thin longitudinal ferrite stub is located in the
WR cross section where H-field (blue dot-line with arrows) of TE10-mode has CP, i.e. ()
+
in Figure 6.8.3b, for example. Previously in Section 6.6.4 of this chapter, we learned that it
−1
⁄
happens when = ( )sin (/2). If so, the forward wave gets the phase shift =
0
+
� while the backward CP wave in the same WR cross section being polarized ()
0 + −
, i.e. ≠ . Here is the ferrite stub length
gets the different phase shift = � − + −
−
0
and as well as are some equivalent constants of ferrite medium filling WR only
±
partially. The best way to estimate the real phase shift and maximize its value is a numerical
simulation because the presents of ferrite stub itself alters more or less TE10-mode field structure
making it really complicated and obstructs the finding the optimal cross section with CP.
Note that the phase shift is almost doubled if we put two ferrite stubs symmetrically and
magnetize them in opposite directions by two electromagnets as Figure 6.8.3c demonstrates. It
turns out that two heavy and bulky magnets might be replaced with a single magnetizing
conductor (see Figure 6.8.3d) passing through and carrying relatively large DC-current. To
diminish the current magnitude, the two-plate stub should be replaced with single- or twin-
toroid assembly thereby creating the closed magnetic path and minimizing the bias field
scattering. The dielectric spacer regulates the EM energy density in ferrites and optimizes the
phase shifter performance. Even more, the toroids produced from ferrite with magnetic memory
are able to keep or “remember” their state of magnetization in the absence of external source.
As such, they should be magnetized and re-magnetized by current pulses of different polarity
or magnitude. Just note that WR and coaxial ferrite phase shifters are superior in average and
pulse power handling than similar semiconductor ones, but they certainly lose the competition
in weight and switching time. The nonreciprocal phase shifters are integral parts of so-called