Research Non-Reciprocity And Non-Linear In Ferrite Devices

Non-reciprocity and Non-linearity problems of the microwave ferrite are two kinds of basic key technical one. In this thesis, start from procession equation, the gyro-magnetic property of ferrite material,i.e. tensor permeability characteristic and ferromagnetic resonance property are discussed in detail, and electro-magnetic wave propagate in gyro-magnetic medium, in which it produce non-reciprocal transmission effect. In the other hand, in process of magnetic moment procession, due to spin magnetic moment interacting, it deduce high-power non-linearity loss in ferrite material. Some others, magnetic moment procession will be perturbed by vibration, shake and others infect in which appear doubling frequency, mixing frequency, and 3-order inter modulation et al. non-linearity.The main work in this paper is to set up non-reciprocal and non-linear equation about the microwave propagation in gyro-magnetic medium, and to apply high-frequency structure simulation (HFSS) soft-ware as design platform, and to combine practical examples for various design of microwave ferrite devices,and to research their properties quantitatively or qualitatively.The non-reciprocal problem of microwave ferrite is discussed in chapter 3.and 4. The non-reciprocity of microwave ferrite devices are divided into two types of parameter, the amplitude and phase. The non-reciprocity of amplitude means differ loss between the forward propagation and reverse one. The relative devices have various microwave-structure Y-j unction circulator, such as waveguide Y-circulator, strip-line and micro-strip-line Y-circulator, and lumped parameter circulator, and so on. Passing by a series of simulation for above devices,it can be proven that the non-reciprocal equation is exact by numerical resolution for non-reciprocity integration equation,that the principle of non-reciprocity can be used to guide ferrite device's design.Another kind non-reciprocity is phase one, which express with differ phase in differ transmit direction or magnetized direction, and it can be designed as phase-shifter or differential phase circulator.In besides of above, The mechanism problem of non-reciprocity on the microwave ferrite is also very importance which will be discussed, It well known that the tensor permeability property of ferrite related to non-reciprocal transmission characteristics, In order to deepen comprehension of non-reciprocity basic concept. It be quoted non-reciprocity equation which is field integral equation, including magnetic field and tensor permeability. Passing by the high frequency structure simulation (HFSS) and numeral integration, the resolution of non-reciprocity equation can be obtained. At last, the non-reciprocity of some microwave ferrite devices are discussed and calculated one by one through a number of project example, such Y-junction strip-line and micro-strip-line circulator, wave-guide junction circulator and ferrite switch,. For these devices, it is researched in detail, combining with non-reciprocity theory, HFSS-simulation and numerical integration. It should point out that all the non-reciprocity integration equations in the text must adopt normalized form, so as to calculate numeric integral value coincide to simulated resultants.About nonlinear problem of ferrite devices are researched in chapter 5.There are also two classes nonlinearity:The first class is so-called high-power nonlinearity, when microwave power grater then critical power,the ferrite device characteristics become very poor and insert loss increased more and more. Its source to coupling between the uniform procession and spin wave in ferrite, and in order to overcome nonlinear loss it is necessary to adopted higher spin-wave line-widen△Hk of ferrite material as used. Through simulating design and high field strength observed, and the critical power can be estimated which may be resolve high-power device design problem.The second class nonlinearity effect happens in circulator/isolator. As the ferrite material is used in the field of communication, it will appear the second class nonlinear effect, because here exist two adjacent and different frequency signal f1,f2 simultaneously, so that not only there are double-frequency effect(DFE)2f1,2f2,but also mixture-frequency effect(MFE), of which complex effect will induce 3-order inter-modulation(3-IMD) signal 2f1-f2 and 2f2-f1. These signals are the kinds of interference signals to f1 f2, it harm to communication quality. Therefore, it is important to study 3-IMD problem for ferrite applied and how to decrease 3-IMD level. First of all, we shall initiate discussion from magnetization vector procession equation, and in the condition of two greater signal f1, f2, nonlinear effect (NLE) will appear in ferrite material, and to obtain basic formula of the 3-IMD, and then to research IMD mechanism and to overcome it's method. To decrease the 3-IMD,it must be calculate its magnetic spectrum cures of 3-IMD,and through two examples:at the band 869-960MHz and 1805-1880MHz, it point out when operating magnetic field is greater then the ferromagnetic resonance one and harmonic one, minimum 3-IMD level can be obtained. Secondly, the circulator'3-IMD can be calculated by high frequency structure simulation (HFSS) and in combination with numerical integral method. Calculating results point out that the circulator is relative to ferrite material parameter, inner conductor shape/size, and bias magnetic field strength, and two kinds of inner conductor structure with lower 3-IMD operated above two band. At last, the statistical results of two kinds of products with lower 3-IMD are listed and the measure circuit of 3-IMD-measuring is set up.