Full resolution (JPEG) - On this page / på denna sida - 1958, H. 7 - Microwave Load Isolators and Related Components, by Per Erik Ljung
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Fig. 12. Recommended isolator design principles for
different operating conditions. Abbreviations denote:
FR Faraday rotation
RA Resonance absorption
FD Field displacement
PS Phase-shift circulator
NR None recommended
culator utilizes the gyrator effect obtained in a
transversely magnetized, asymmetrically
ferrite-loaded rectangular waveguide. Such a device can be
built in many ways, one of which is illustrated in
fig. 11.
The arrangement consists of two magic tees,
connected as shown. In one of the connecting branches
a gyrator is located, giving the wave travelling from
left to right an additional phase shift of jt radians.
Obviously, the order of circulation will be that
indicated by the figures.
In this arrangement any two consecutive ports may
be terminated and the remaining two used as isolator
input and output respectively. The backward loss
may be of the order of 20 to 30 db and the forward
loss about 0.5 db. VSWR:s are highly dependent on
the reflections of the hybrid junctions, which is
likewise true for the bandwidth of these units.
The power handling capability is about the same
as that of absorption isolators. This is due to the
fact that nonlinear effects can be minimized by
proper shaping of the ferrite elements of the
gyrator, and that these can be mounted in contact with
the waveguide wall. Geometries similar to that of
fig. 6 b or ferrite slabs extending from top to bottom
of the guide placed in thermal contact with the side
walls may be used. It can also be noted that only
one half of the total power is transmitted through
the gyrator section.
Phase-shift isolators require less static magnetic
field strength than the absorption type. Their greater
mechanical complexity, however, is a definite
disadvantage. It should be kept in mind, though, that a
circulator can be used for a variety of purposes such
as duplexing, which makes it a very useful
instrument in system engineering.
Conclusion
A number of other isolator designs have been
described in the litterature. None of these has,
however, come into wide use, and some have not
been sufficiently investigated to permit a
description of their properties. It is strongly felt, that the
types described above present quite a satisfactory
set of models for the constructor of microwave
equipment.
In fig. 12 an attempt has been made to summarize
the properties of different isolators to simplify the
choice of the proper isolator design for given
operating conditions. Average power level, wavelength
region, bandwidth and reverse to forward loss ratio
have been considered.
Resonance absorption and Faraday rotation devices
are seen to dominate. The former can be used
everywhere as long as the low loss ratio can be tolerated.
Rotation devices perform better in this respect but
are more complex at power levels where forced
cooling becomes a necessity. As a laboratory instrument
the phase-shift circulator seems to be a logical choice
as it can be used for a number of other applications
apart from the isolator function.
Acknowledgement
The majority of isolator performance data given
in this paper have been obtained in conjunction with
a research program on microwave ferrites and ferrite
components carried out at the Research Institute of
National Defence, Stockholm, Sweden. The
permission to publish this material is thankfully
acknowledged.
References
1. Chait H N: Non-reciprocal Microwave Components. IRE Conv.
Rec. 1954, pt 8, pp. 82—87.
2. Fox A G, Miller S E, Weiss M T: Behaviour and Applications
of Ferrites in the Microwave Region. Bell Syst. Techn. J., Jan. 1955,
pp. 5—103.
3. Högan C L: The Ferromagnetic Faraday Effect at Microwave
Frequencies and its Applications — The Microwave Gyrator. Bell
Syst. Techn. J., Jan. 1952, pp. 1—31.
4. Lax B, Button K J, Roth L M: Ferrite Phase Shifters in
Rectangular Wave Guide. J. of Appl. Phys., Nov. 1954, pp. 1413—1421.
5. Loss M R: Broadband Characteristics of Ferrites. IRE Conv.
Rec. 1955, pt 8, pp. 109—112.
6. Ohm E A: A Broad-Band Microwave Circulator. Bell Lab. Bee.,
Aug. 1957, pp. 293—297.
7. Reggia F, Spencer E G: A New Technique in Ferrite Phase
Shifting for Beam Scanning of Microwave Antennas. FIRE, Nov.
1957, pp. 1510—1517.
8. Rizzi P A: High-Power Ferrite Circulators. TIRE, MTT, Oct.
1957, pp. 230—236.
9. Sakiotis N G, Chait H N: Properties of Ferrites in
Waveguides. TIRE, MTT, Nov. 1953, pp. 11—16.
10. Schäfer J P: Ferrite Isolators at 11 000 Megacycles. Bell Lai).
Rec., Oct. 1955, pp. 385—389.
11. Stewart C: Some Applications and Characteristics of Ferrite
at Wavelengths of 0.87 cms and 1.9 cms. IRE Conv. Rec., MTT 3,
pt 8 1955, pp. 100—104.
12. Thompson G II R: Ferrites in Waveguides. J. of the Brit. Inst,
of Badio Engrs, June 1956, pp. 311—328.
13. Vinding J P: Microwave Devices using Ferrite and Transverse
Magnetic Field. IBE Conv. Bee. 1955, pt 8, pp. 105—108.
14. Weisbaum S, Seidel H: The Field Displacement Isolator. Bell
Syst. Techn. J., July 1956, pp. 877—898.
15. Weisbaum S, Boyet H: A Double-Slab Ferrite Field
Displacement Isolator at 11 kmc. PIBE, April 1956, pp. 554—555.
16. Weisbaum S, Boyet H: Broad-Band Non-reciprocal Phase Shifts
— Analysis of Two Ferrite Slabs in Rectangular Guide. J. of Appl.
Phys., May 1956, pp. 519—524.
A number of papers concerning these subjects also appear in the
Proceedings of the IBE Vol. 44, No. 10, October 1956 and
Supplements 5 and 6 of the Proceedings of the IEE, Pt B, Vol. 104, 1957,
which deal exclusively with microwave ferrites and their
applications.
1 108 ELTEKN I K 1958
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