t limeter wave junction circulators using asthe-eye.eu/public/books/electronic archive/pg74.pdf ·...

New Self Biased Circulators

High internal (anisotropy) magnetic jields in fem'tes are exploited to design microstrip and waveguide junction circulators near 31 GHz which provide over 20 dB isolation, below 1 dB loss, yet require no external magnets.

Jerald A. Weiss Massachusetts Znstitute of Technology Lincoln Laboratoiy Lexington, Massachusetts and The Department of Physics Worcester PoEytechnic Znstitute Worcester; Massachusetts

Nigel G. Watson Gerald F. Dionne Lincoln Laboratoiy

his paper describes our development of millimeter wave junction circulators using as T the nonreciprocal (gyrotropic) element ma-

terials of the magnetoplumbite (or hexagonal-ferrite, or uniaxial-ferrite) type. Our principal objec- tive has been to explore the feasibility of eliminating altogether the need for an external dc bias magnet. This idea has been appealing and dis- cussed in the literature as long as these distinctive materials themselves have been available for microwave applications, since the 1950's.

Today, system design has been transformed by the introduction of microwave integrated circuits with components on a miniature scale. But success in the miniaturization of nonreciprocal devices has lagged far behind, to the point where the circulators, for example, now tend to appear as hulking monsters beside the intricate but miniature circuits they are intended to serve.

Systems designed today use miniature scale integrated circuits but the miniaturization of nonreciprocal devices has lagged far behind.

74 APPLIED MICROWAVE Fall 1990

To be sure, some inexorable physical laws stand in the way - such as the elementary relation be- tween frequency and wavelength. Plenty of room still exists, however, for design efficiency and inge- nuity within those constraints. Indeed, great progress has been achieved and is continuing in the effort to minimize size and weight, as may be seen in modern products of the ferrite device industry.

Elimination of the external magnet is a significant step toward more compact circulators.

Nonetheless, elimination of the external magnet wves as a very significant step toward more compact device designs. In this paper we describe the principles underlying this idea and the key relations governing the ferrimagnetic resonance effect on which the self biased circulator depends.

We discuss the relevant properties of the materials - specifically, high magnetocrystalline anisotropy and high coercivity, as well as other qualifica- tions which the materials must have for microwave use. Two device configurations have been built, rec- tangular-waveguide and microstrip junction circulators for millimeter wave use.

This work has also demonstrated the unexpected possibility of adopting for millimeter-wave applications certain sintered hexagonal ferrites which are widely marketed today for a variety of commercial purposes, but were not formulated with microwave applications in mind.

This work demonstrated the unexpected possibility of adopting certain fem'tes not formulated with microwave applications in mind.

Historical Background Byway of historical background references [l-161

represent a selection keyed to this paper. There has been much more written about this subject, and we would be happy to share our extended bibliography with interested readers.

Polder's theoretical analysis of resonance in materials having gyromagnetic properties, including definition of the permeability tensor now known by his name, was published in 1949. Rathenau pre-

sented details of the basic magnetic properties of barium ferrite and of derivative magnetoplumbites in 1953. In 1955 his associates Smit and Beljers at the Philips laboratories in Eindhoven, the Nether- lands, published a thorough analysis of the theory of magnetic resonance for partially and fully mag- netized anisotropic materials, together with experimental measurements on barium ferrite. That same year, M.T. Weiss and P.W. Anderson at Bell Tele- phone Laboratories briefly presented resonance re- sults on Ferroxdure (a Philips tradename), together with a similar formulation of the theory.

In 1959, Casimir reviewed ferrite research at Philips in a report that included important data on the temperature dependence of magnetic parameters of the magnetoplumbites. Progress in the areas of materials and device research and development was reviewed at successive stages by Rodri- gue, Pippin and Wallace in 1962, by Wijn in 1970, by Okazaki, Horiguchi and Akaiwa in 1974, by Winckler and Dotsch in 1979, and by Harrison in 1981.

Perhaps the earliest device exploiting oriented hexagonal ferrite, a millimeter wave resonance isolator, was reported by Kravitz and Heller of MIT Lincoln Laboratory in 1959. They used Indox V, one of the commercial materials similar to those on which we are reporting. A dc magnetic field of 8 kiloersteads was required.

A 73.5 GHz waveguide junction circulator without a magnet was presented by Akaiwa and Oka- zaki in 1974. So far as we know, theirs was the first reported successful embodiment of the idea of eliminating the external magnet.

Present Approach Our waveguide circulator, at 31 GHz, is adapted

from a design due to Piotrowski and Raue, 1976, chiefly by replacing the magnetically isotropic element by a hexagonal ferrite. Our microstrip junction layout takes its design style from the type ex- emplified by G.P. Riblet in 1980 and by Xu and Miao in 1988.

The relevant design principles are contained in Appendix A. This gives in conventional notation, a simplified form of the magnetic energy density G (properly, the free enthalpy density) of the specimen, including the anisotropy energy for the uniaxial case (KA is the anisotropy energy constant); magnetic field energy in terms of the applied field Ho and magnetization M; and the demagnetization correction to the magnetic field energy, in terms of M and the three principal demagnetizing factors N.

APPLIED MICROWAVE Fall 1990 75

Hamilton’s equations are applied to derive the equations of motion for small oscillations due to stimulation by a microwave electromagnetic field, and to solve for the condition of ferrimagnetic resonance. Here nu is the resonance frequency (Hertz) and gamma is the electron gyromagnetic ratio, the value of which is shown in Appendix A.

We limit ourselves to the simplest cases which are relevant to the circulators of interest. Here, the orientations of both the easy axis of anisotropy and the resultant magnetization are in the direction of the axis of cylindrical symmetry of the specimen, that is Nx = Ny = Nt (transverse).

Illustrating with a typical example, we find for barium ferrite with no dc field (Ho = 0), for a thin disk the resonance frequency is 36.4 GHz and for an ”equilateral” cylinder it is 47.6 GHz. These resonance frequencies are above the operating frequency of 31 GHz for our devices - a relationship termed ”above resonance operation”.

However the nonreciprocal performance of the devices depends on the parameters mu and kappa of the Polder permeability tensor, whose influence ranges far above and below resonance. We believe that our circulators are operating in the “above resonance” regime; that is, with the effective internal dc field somewhat on the high side of the resonance value for the frequency of operation.

A photograph of our waveguide three port junction circulator is shown assembled (left) and open (halves at right) in Figure 1.. The ferrite elements are two cylinders of a commercial strontium ferrite

made by the D.M. Steward Co., called F-520, with orientation axis aligned with the junction symmetry axis.

The structure, an adaptation of that by Pio- trowski and Raue, is shown in Figure 2. wherein nickel ferrite used by those authors has been re- placed by the magnetoplumbite F-520. There are two ferrite cylinders separated by a metal septum, and an arrangement of dielectric spacers and metal matching transformer. After assembly, the material is brought to the remanent state with use of a laboratory electromagnet, following which the circulator is then removed from the electromagnet and operated with no external magnet of its own.

A somewhat different structure was used by Akaiwa and Okazaki in their barium-ferrite waveguide circulator at 73.5 GHz with no magnet. The combination of parameters suggests that their device operated in the “below resonance” regime, a different mode compared to ours which could have favorable significance with regard to bandwidth and temperature stability for some applications.

A network analyzer plot showing good isolation peaks for the three ports at about 30.7 GHz is shown in Figure 3. Other data we have obtained for nominally the same structure show slightly poorer symmetry but better insertion loss, less than 0.5 dB over about a 1.5 percent bandwidth.

Consider the oriented hexagonal ferrites. In Fig- ure 4 we have an example of a hysteresis loop for a highly oriented barium-strontium ferrite made by the Stackpole Corp., called S-7. This is an admira-

Figure l. Photograph of the assembled (len) and disassembled three port, Self biased, waveguide circulator.


Figure 2. Plan view of the self biased waveguide circulator (after Piotrowski & Raue).

0

29.8 30.4 31.0 31.6 FREOUENCY (QHr)

Figure 3. Measured insertion loss and isolation at 3 ports for the waveguide circulator.

Oe

Figure 4. The hysteresis loop for a highly oriented barium-strontium ferrite, Stackpole 5-7.


bly square loop with high coercive field Hc of about 3700 Oe; the remanent magnetization Mr is3475 G.

Note the part of the loop in the second (upper left) quadrant, which permanent magnet specialists call the “demagnetizing curve”. This is shown in detail in Figure 5. for the Stackpole S-7 material.

The demagnetizing line indicated in Figure 5 has a slope of -1, appropriate for a thin disk; magnetization is about 3150 G and the demagnetizing field is of equal magnitude, 3150 Oe. This material has anisotropy field HA = 21 kOe (Compared to 17 kOe for barium ferrite). Resistivity is at least 1 million ohm-cm, probably substantially higher.

The density is about 90% compared to the nomi- nal X-ray value of 5.14 gramsicubic centimeter for this composition. The degree of orientation must be very high, judging by the squareness of the hysteresis loop. All these properties are favorable for microwave applications and lend themselves particu- larly well to planar circuit designs.

In Figure 6 is shown the demagnetizing curve for the D.M. Steward Co. material called F-520 which was used in the both of the circulators presented in this paper. The intrinsic remanence is high, about 4000 Gauss; the coercivity is 1280 Oe. The intersec- tion of the curve with the diagonal demagnetizing line represents the remanent state of the specimen. The slope is -3, appropriate for an “equilateral” cylinder.

0

Figure 5. Detail view of the “demagnetizing curve’’ (upper left quadrant of the hysteresis loop) for Stackpele s-7 material.

78 APPLIED MICROWAVE Full 1990

Figure 6. Demagnetizing curve for the Steward F-520 material used for the waveguide and microstrip experimental circulators.

This shows a stable state of high magnetization, about 3500 G, with an internal reverse field of 1270 Oe. The waveguide junction design calls for a pair of such cylinders close together on a common axis which, being axially longer, actually confers a somewhat more favorable magnetic state (that is, weaker internal demagnetizing field) than this demagnetizing line would indicate.

Since temperature stability is an important system requirement, we must consider the temperature dependence of the magnetic parameters, illustrated for barium ferrite in Figure 7. The graph, showing saturation magnetization, anisotropy energy parameter, and effective anisotropy field, is from the work of Casimir as cited in the handbook of microwave ferrites by von Aulock. Although 4sMs and K1 are steeply declining functions of temperature, the anisotropy field HA, which is equal to the ratio KI/Ms tends to he relatively temperature stable.

Isolation was better than 20 dB from 0 to 50 degrees C, but at -20 C it was poox

The net influence on the waveguide circulator performance is shown in Figure 8. Over the range from 0 to 50 degrees Centigrade, isolation remains

- 6

2 - - 4 Lo

7 P

- 2

. - 0

0 200 400 600 800 TEMPERATURE (K)

Figure 7. Temperature dependence of the magnetic parameters for the barium ferrite.

greater than 20 dB, but at -20 C it is poor. Insertion loss remains better than 2 dB over the entire temperature range investigated.

The photograph of our microstrip 31 GHz circulator which also operates with no magnet is shown in Figure 9. Actually, the junction overlay pattern is not fully shown here. Figure 10. shows the layout together with a sectional view. Note that, because we were working with the relatively low-coercivity D.M. Steward material, we obtained the benefit of a lower demagnetizing field by making a socket in

301 V 40 I

25x6 30.4 a1.0 31.6 FREOUENCY (GHz)

Figure 8. Insertion loss and isolation measured over temperature for the waveguide circulator.


Figure 9. Photograph of the microstrip 31 Ghz circulator.

the ground plane and inserting one of our equilateral cylinder specimens. The substrate is 10 mils thick; the ferrite is 60 mils in both axial length and diameter.

The merit of this strategy to overcome the limita- tion of low coercive field is thus demonstrated; we also hope to show that substitution of a suitable oriented material of sufficiently high coercivity, at least equal to remanent magnetization 47rMr, would allow the use of a thin disk. The overlay pattern illustrated here is of the type described by G.P. Riblet. We are also working with the type of pattern, of Xu and Mido, shown in Figure II.

In some devices symmetly and insertion loss were problems, but we believe they stem from mechanical defects of the models, not fundamental limitations.

Representative performance for the microstrip circulator is shown in Figure 12. The curves of insertion loss and isolation show best performance at about 31 GHz. In some of our experimental devices, symmetry and insertion loss were problems, but we believe they stem from defects in the mechanical structure of the experimental models and are not fundamental to the approach or materials.

Expectations Self biased circulators such as this one but at

different frequencies could be scaled provided the disc size is appropriately adjusted - inversely pro- portional to frequency together with a correction for any wavelength change due to a different effec-

JUNCTION OVERLAY

STRIP. / K CONNECTORS

GROUND PL ENT

JUNCTION: CONDUCTOR CONFIGURATION

Figure 10. Layout drawings of the overlay pattern and assembly section for the microstrip circulator.

Y Circulator Strlpllne Figure 11. An alternate microstrip center conductor pat- lern being explored.

40 29.0 30.0 31.0 32.0 33.0

FREQUENCY (GHZ)

Figure 12. Insertion loss (upper curve) and isolation (lower curve) for the microstrip circulator.


tive permeability and dielectric constant. Further- more, the effective internal magnetic bias field must be suitably adjusted. This adjustment involves the magnetocrystalline anisotropy field (HA), the saturation magnetization and other properties of the material.

We believe that these prototype devices have only just begun to indicate the possibilities which might be achieved. Adaptation to higher and lower frequencies and improvements in bandwidth, insertion loss, and isolation, combined with more compact and more light-weight designs, are feasible. The promise of materials of the magnetoplumbite class for the future of the microwave art appears to be at least as bright as ever.

This work was sponsored by the U.S. Air Force.

References 1. Polder, D.: On the theoq of ferromagnetic resonance;

Phil. Mag. 40 (1949) p. 99. 2. Rathenau, G.W.: Saturation and magnetization of hexag-

onal iron oxide compounds; Rev. Mod. Phys. 25 (1953) p. 279.

3. Smit, J. & Beljers, H.G.: Ferromagnetic resonance absorp- tion in BaFel2019, a highly anisotropic crystal; Philips Res. Rep. 10 (1955) pp. 113-130.

4. Weiss, M.T. &Anderson, P.W.: Ferromagnetic resonance in Ferroxdure; Phys. Rev. 98 (May 15, 1955) pp. 925-926.

5. Casimir, H.B.G. et al.: Rapport sur quelques recherches dans le domaine du magnetisme aux Laboratoires Philips; J. Phys. Radium 20 (1959) p. 360.

6. Rodrigue G.P., Pippin, J.E. &Wallace, M.E.: Hexagonal ferrites for use at X to V hand frequencies; J. Appl. Phys. 33s (Mar. 1962) pp. 1366-1368.

7. Wijn, H.P.J.: Hexagonal ferrites; Landolt-Boernstein, Group 111, vol. 4h, Sec. 7, p. 547 (1970). [8 ] Okazaki, T., Horiguchi, Y. & Akaiwa, Y.: Characteristics of polycrystal- line hexagonal ferrites for use at millimeter-wave frequencies: Elec. Comm. Japan 57-C (July 1974) pp. 128-136.

9. Winkler, G. & Doetsch, H.: Hexagonal ferrites at millimeter waves; Ninth European Microwave Conf. (1979).

10. Harrison, G.R.: Hexagonal ferrites for millimeter-wave applications; SPIE - Intl. Soc. for Opt. Eng. 317 (Integrated Optics and Millimeter and Microwave Integrated Cir- cuits); Huntsville AL, Nov. 16-19, 1981; pp. 251-261.

11. Kravitz, L.C. & Heller, G.S.: Resonance isolator at 70 KMC; Proc. IRE 47 (1959) p. 331.

12. Akaiwa. Y. & Okazaki. T.: An aoolication of a hexaeonal

13.

14.

ferrite to a millimeter wave Y ‘iirculator; IEEE frans. MAG-I0 (1974) pp. 374-378. Piotrowski, W.S. & Raue, J.E.: Low-loss broad-band EHF circulator; IEEE Trans. MTT-24 (1976) pp. 863-866. Rihlet, G.P.: Techniques for broad-handing above-resonance circulator junctions without the use of external matching networks; IEEE Trans. MTT-28 (1980) pp. 125- 174

15. Y. & Miao. J.: Theorv and desien of stub tuned nonrecioro- cal stripline junctidns and hrculators; Microw.& Opt. Tech. Let. 1 (19881 351-356.

16. von Aulock, W.H.: Handbook of Microwave Ferrite Mate- rials; Academic Press, 1965: Sec. 4.

17. Weiss, Watson & Dionne: This work was described in “New Uniaxial-Ferrite Millimeter-Wave Junction Circula- tors”; IEEE MTT/S Intl. Microwave Symp., Long Beach CA, June 13, 1989.


~ ~~

Jerald A. Wciss received the BS and MS degrees in physics from the Ohio State University in 1949 and the PhD degree inphysics, also form Ohio Stare, in 1953. From 1953 to 1960, he was a member of the technical staffof Bell Telephone Laboratories (now AT&T Bell Labs) at Murray Hill, NJ, where he engaged in microwave com- ponent development with applications of magnetic materials. He joined in the founding of Hylerronics Cop. for design and manufacture of microwave devices and subsystems in 1960. I n 1962 he joined the faculty of the Physics Department at Worcester Potytechnic Institute, and that year he was also appointed as consultant at MIT Lincoln Laboratory in work relating 10 array radar development.

Professor Wei.s.7 has conducted academic research in a number offields and has been active in physics education and educational innovation. He has published on subjects including transmis.sion line theory; instrumentation, measuremenr.s and applications of magneti.sm; and microwave and millimeter wave !he09 measurements and devices.

Nigel Watson joined the MITLin- coln Laboratory in 19870s a member of the Space Radar Technology Group. He has been involrsed in the development of lighnveigtit TIR mod- ule design al Rayrheon Equipment Di- vi.7ion and Spew Coporation. Mr Watson received a BS in physics fmm CIarkson College of Technology in 1979 and an MSEEfrom the Univer- siw of Massachusett.7, Amherst, in 1981. He is a member of the IEEE and the MTT-S.

Gerald F. Dionne received a BSc degee from Concordia University in 1956, a BEngfrom McGill University in 1958, and an MS in physics from Carnegie-Mellon University in 1959. A f m two years of semiconductor device development work with IBMand GTE, he returned to McCiil for doc- toral work in physics, with a thesis in electron paramagnetic resonance. From 1964 lo 1966, he carried out research in electron emission and sur- face ionization for thermionic energy conversion at United Technologies.

Since 1966 he has been a member of the technical staff at MIT Lincoln Laboratory, where he has made nu- merous contributions of basic and applied research in a broad spectrum of filds that include magnetism theory, ferrimagnetic materiak for microwave and millimeter wave applications, secon- dary electron emission for cold cathodes, submillimeter wave spec- troscopy and radiometry, and magneto-optic materials and devices forfiber-optic systems. Most recent& he has been developing theor- ies for high-temperature superconductivity. DK Dionne i.7 a Senior Member of the IEEE and a member of

the American Physical Society and Sigma Xi.

Appendix

The magnetic free energy density G:

ANISOTROPY + APPLIED-FIELD + DEMAGNETIZATION 1 KA sin2 8 - HoM cos2 8 + ,M2(NS sin2 8 cos2 e+N, sin2 8 sin2 d+N, cos2 8 )

Resonance: for If0 applied parallel to the easy axis (z-axis),

[fl = [(HO t H A ) + (Nz - Nz)M] [(HO + R A ) + (Nv - Nz)M] where 7 = 2.80 MHz Oe-' , H A = % For cylindrical symmetry (N, = N, = Nt):

Y - = [(HO + H A ) + (Nt - Nz)M] 7

Example: Let El0 = 0, H A = 17 kOe, 4rM = 4000 G (Ba ferrite):

Thin disk (Nt = O,N, = 4r) v = 36.4 GHz "Equilateral" cylinder (Nt = N, = 9) v = 47.6 GHz

2 .


t limeter wave junction circulators using asthe-eye.eu/public/books/electronic archive/pg74.pdf ·...

Documents