Microwave propagation in ferrites 23
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This document discusses microwave propagation in ferrites and their use in microwave components. Ferrites have high resistivity and magnetic properties due to electron spin, making them suitable for microwave applications. The document focuses on isolators and circulators, which are nonreciprocal devices that use ferrite material's Faraday rotation property. Circulators allow transmission from port 1 to port 2 to port 3 etc in a circular path but not in reverse. Isolators transmit power in one direction with low loss but absorb power traveling in the opposite direction, providing isolation. Faraday-rotation isolators work by rotating the polarization of the microwave by 45 degrees using a ferrite rod, allowing transmission in one direction but absorbing waves traveling in the reverse direction.
Microwave propagation in ferrites 23
- 1. Microwave propagation in ferrites MR. HIMANSHU DIWAKAR Assistant Professor JETGI MR. HIMANSHU DIWAKAR JETGI 1
- 2. Microwave propagation in ferrites • Ferrites are non metallic materials with resistivity 𝜌 nearly 1014 times greater then metals and with dielectric constant 𝜖 𝑟 around 10-15 and relative permabilities of 1000 order. • These are oxide based compounds having general composition of the form MeO. 𝐹𝑒2 𝑂3 ie mixture of metallic ferrites and ferric oxides. • Ferrites have atoms with large no. of spinning electrons resulting in strong magnetic properties. These magnetic properties are due magnetic dipole moment associated with the electron spin. MR. HIMANSHU DIWAKAR JETGI 2
- 3. Cont’d • These are the raw materials used for making the microwave components. • Irreversible property:- • Whatever you have the property in forward direction it will not be in the reverse direction. • Now we are going towards different microwave components where we are using these ferrite materials. MR. HIMANSHU DIWAKAR JETGI 3
- 4. Cont’d • Gyrator • Isolator • Circulator • We will discuss here only isolators and circulators. MR. HIMANSHU DIWAKAR JETGI 4
- 5. CIRCULATORS AND ISOLATORS • Both microwave circulators and microwave isolators are nonreciprocal transmission devices that use the property of Faraday rotation in the ferrite material. • To understand the operating principles of circulators and isolators, let us describe the behavior of ferrites in the nonreciprocal phase shifter. MR. HIMANSHU DIWAKAR JETGI 5
- 6. Microwave Circulators • A microwave circulator is a multiport waveguide junction in which the wave can flow only from the nth port to the (n + 1)th port in one direction as in figure Although there is no restriction on the number of ports, the four-port microwave circulator is the most common. MR. HIMANSHU DIWAKAR JETGI 6
- 7. Cont’d • One type of four-port microwave circulator is a combination of two 3-dB side-hole directional couplers and a rectangular waveguide with two nonreciprocal phase shifters as shown in Fig. MR. HIMANSHU DIWAKAR JETGI 7
- 8. Cont’d • Each of the two 3-dB couplers in the circulator introduces a phase shift of 90°and each of the two phase shifters produces a certain amount of phase change in a certain direction as indicated. • Since the two waves reaching port 4 are out of phase by 180°, the power transmission from port 1 to port 4 is zero. • In general, the differential propagation constants in the two directions • where m and n are any integers, including zeros. MR. HIMANSHU DIWAKAR JETGI 8
- 9. Cont’d • Many types of microwave circulators are in use today. However, their principles of operation remain the same. • A perfectly matched, lossless, and nonreciprocal four-port circulator has an S matrix of the form MR. HIMANSHU DIWAKAR JETGI 9
- 10. Cont’d • Using the properties of S parameters as described previously, the S matrix in Eq. MR. HIMANSHU DIWAKAR JETGI 10
- 11. Microwave Isolators • An isolator is a nonreciprocal transmission device that is used to isolate one component from reflections of other components in the transmission line. • An ideal isolator completely absorbs the power for propagation in one direction and provides lossless transmission in the opposite direction. • Thus the isolator is usually called uniline. MR. HIMANSHU DIWAKAR JETGI 11
- 12. Cont’d • Isolators are generally used to improve the frequency stability of microwave generators, such as klystrons and magnetrons, in which the reflection from the load affects the generating frequency. • In such cases, the isolator placed between the generator and load prevents the reflected power from the unmatched load from returning to the generator. • As a result, the isolator maintains the frequency stability of the generator. MR. HIMANSHU DIWAKAR JETGI 12
- 13. Faraday-rotation isolator MR. HIMANSHU DIWAKAR JETGI 13
- 14. Cont’d • Isolators can be made by inserting a ferrite rod along the axis of a rectangular waveguide as shown in above Figure. • The input resistive card is in the y-z plane, and the output resistive card is displaced 45° with respect to the input card. The dc magnetic field, which is applied longitudinally to the ferrite rod, rotates the wave plane of polarization by 45°. • The degrees of rotation depend on the length and diameter of the rod and on the applied dc magnetic field. • An input TE10 dominant mode is incident to the left end of the isolator. Since the TE10 mode wave is perpendicular to the input resistive card, the wave passes through the ferrite rod without attenuation. MR. HIMANSHU DIWAKAR JETGI 14
- 15. Cont’d • The wave in the ferrite rod section is rotated clockwise by 45° and is normal to the output resistive card. As a result of rotation, the wave arrives at the output end without attenuation at all. • On the contrary, a reflected wave from the output end is similarly rotated clockwise 45° by the ferrite rod. • However, since the reflected wave is parallel to the input resistive card, the wave is thereby absorbed by the input card. • The typical performance of these isolators is about 1-dB insertion loss in forward transmission and about 20- to 30-dB isolation in reverse attenuation. MR. HIMANSHU DIWAKAR JETGI 15
- 16. Thank you MR. HIMANSHU DIWAKAR JETGI 16