Acknowledgements

This chapter was supported in part by the Ministry of Science and Technology of Taiwan and in part by China Steel Company/HIMAG Magnetic Corporation, Taiwan. The author is grateful to the Taiwan Branch of ANSYS Inc. for technical assistance and to Dr. Hsein-Wen Chao and Mr. Wei-Chien Kao for their assistance in the full-wave simulation. Dr. Hsin-Yu Yao and Mr. Shih-Chieh Su are appreciated for the discussion of the ferrites' characterization.

In addition to the stripline circulator, there are other types such as the microstrip circulator and the waveguide circulator. The microstrip circulator is similar to the stripline circulator in many ways. Here we show a waveguide circulator which is

(a) Schematic diagrams of the operation of a waveguide circulator. A full-wave solver, HFSS, is used with the saturation magnetization (4πMs) is 1600 G, the dielectric constantε<sup>0</sup> is 13.0, and the resonance linewidth ΔH is 10 Oe. The radius and thickness of the ferrite disks in rust red are R = 21.0 mm and t = 5 mm, respectively.

(b) Simulation results of the waveguide circulator like the one in Part (a). The solid red curve is the transmission or insertion loss; the blue curve represents the reflection loss, and the black is the isolation.

. The electric field pattern is displayed in color.

The waveguide is a standard WR 340 with 86.36 � 43.18 mm<sup>2</sup>

Electromagnetic Materials and Devices

The isolator is one of the useful microwave ferrite components. As shown in Figure 9, the isolator is generally a two-port device having unidirectional transmission characteristics (nonreciprocity). From Port 1 to Port 2 (S21), the forward transmission is high (i.e., low insertion loss in Figure 9(a)). However, from Port 2 to Port 1 (S12), the reverse transmission is low (i.e., high isolation in Figure 9(b)). Besides, the reflection (S11 and S22) should be as low as possible. The simulation parameters in Figure 9 are the same as Ex. 9.2 of Pozar's textbook [5]. The simula-

tion parameters and the sample's geometry are described in the caption.

capable of high-power operation. Figure 8(a) shows the structure of the nonreciprocal device and the simulated electric field strength. The simulation parameters are described in the caption. The circulator is, in general, a three-port device. If the incident wave is injected from Port 1, then the wave will ideally go to Port 2, while Port 3 will be isolated as shown in Figure 8(b). On the other hand, if the wave is injected from Port 2, it will go to Port 3 and be isolated from Port 1 as

The simulated field strength for a two-port isolator using the full-wave solver. (a) The high forward transmission (S21) and (b) the low reverse transmission (S12). The saturation magnetization (4πMs) is 1700 G, the dielectric constant ε<sup>0</sup> is 13.0, and the resonance linewidth ΔH is 200 Oe. The length and thickness

shown in Figure 8(b).

of the ferrite are L = 24.0 mm and t = 0.5 mm.

4.3 Isolator

146

Figure 8.

Figure 9.

Electromagnetic Materials and Devices

References

[1] Okamoto A. The invention of ferrites

DOI: http://dx.doi.org/10.5772/intechopen.84623

field method. The Review of Scientific

[11] Chao HW, Chang TH. Wide-range permittivity measurement with a parametric-dependent cavity. IEEE Transactions on Microwave Theory and

[12] Skyworks. Test for Line Width and Gyromagnetic Ratio [Internet]. 1999.

skyworksinc.com/uploads/documents/ Test\_for\_Line\_Width\_Gyromagnetic\_

[13] Fuller AJB. Ferrites at Microwave Frequencies. London: Peter Peregrinus;

[14] Pardavi-Horvath M. Microwave applications of soft ferrites. Journal of Magnetism and Magnetic Materials.

[15] Schloemann E. Advances in ferrite microwave materials and devices. Journal of Magnetism and Magnetic

[16] Harris VG, Geiler A, Chen Y, Yoon SD, Wu M, Yang A, et al. Recent advances in processing and applications of microwave ferrites. Journal of Magnetism and Magnetic Materials.

[17] Helszajn J. The Stripline Circulators: Theory and Practice. Hoboken, New Jersey: John Wiley & Sons; 2008

[19] Linkhart DK. Microwave Circulator Design. 2nd ed. Norwood, MA: Artech House Microwave Library; 2014

[18] Chao HW, Wu SY, Chang TH. Bandwidth broadening for stripline circulator. The Review of Scientific Instruments. 2017;88:024706

Instruments. 2015;86:114701

Techniques. 2018;66:4641-4648

Available from: http://www.

Ratio\_202837B.pdf [Accessed:

2018-12-20]

2000;215:171-183

Materials. 2000;209:15-20

2009;321:2035-2047

1987

Globecom Workshops. 2009:1-42. DOI: 10.1109/GLOCOMW.2009.5360693.

[2] Néel L. Magnetic Properties of Ferrites: Ferrimagnetism and Antiferromagnetism. Annales de

and their contribution to the miniaturization of radios. IEEE

Ferrite Materials and Applications

ISBN 978-1-4244-5626-0

Physique. 1948;3:137-198

9780444601193

[3] Chen CW. Magnetism and

tism/ [Accessed: 2018-12-20]

Metallurgy of Soft Magnetic Materials. Elsevier; 1977. 15–60 p. DOI: 10.1016/ B978-0-7204-0706-8.X5001-1. ISBN:

[4] McGrayne SB, Suckling EE, Kashy E, Robinson FNH, Bleaney B. Magnetism Physics; 2018. Available from: https:// www.britannica.com/science/magne

[5] Pozar DM. Chap. 9. In: Microwave Engineering. 4th ed. Hoboken, New Jersey: John Wiley & Sons, Inc.; 2011

[6] Collin RE. Chap. 6. In: Foundations for Microwave Engineering. 2nd ed. New York: McGraw Hill; 1992

[7] Chang TH. Gyromagnetically-induced transparency for ferrites. American Journal of Physics. 2016;84:279-283

[9] Chen LF, Ong CK, Neo CP, Varadan

Electronics: Measurement and Materials Characterization. Hoboken, New Jersey:

[10] Chao HW, Wong WS, Chang TH. Characterizing the complex permittivity of high-κ dielectrics using enhanced

VV, Varadan VK. Microwave

John Wiley & Sons Inc.; 2004

[8] Cohn SB, Kelly KC. Microwave measurement of high-dielectricconstant materials. IEEE Transactions on Microwave Theory and Techniques.

1966;14:406-410

149
