Preliminary experimental study on the influence of

Preliminary experimental study on the influence of magnetic core stress on the phase-shifting characteristics of phase shifter

[Abstract] a preliminary experimental study was carried out on the influence of magnetic core stress caused by external pressure on the phase-shifting characteristics of ferrite phase shifter. The experimental results show that as long as there is residual stress sensitivity in the magnetic core, the adverse effects will gradually appear when the magnetic core is stressed to a certain extent. Therefore, our work should first make the magnetostrictive coefficient of the magnetic core λ S tends to zero as much as possible. Secondly, when determining the tolerance fit between the magnetic core and the shell and assembling the phase shifter, the possible residual stress sensitivity in the magnetic core should still be considered

1 preface

the literature on ferrite phase shifters almost invariably mentions the need to reduce the sensitivity of ferrite cores to stress in order to eliminate the adverse effects of stress on the stability and consistency of phase shifting characteristics. The measures often taken in engineering are adding an appropriate amount of manganese to the material formula and heat treatment annealing. In the phase shifter, the stress that the magnetic core may be subjected to includes the pressure in the vertical and horizontal directions, the pressure or tension in the longitudinal direction, and the torsion caused by the deformation of the shell (Fig. 1)

in order to describe the characteristics of the phase shifter in the light-weight period of the mobile vehicle, we often call the relationship between the differential phase shift and the pulse excitation current as the phase-shift characteristic, and the curve formed from this is called the phase-shift characteristic curve. The stability is relative to a single phase shifter, and the consistency is relative to multiple phase shifters used in the same antenna array

there are few reports about the test of the effect of stress on the characteristics of phase shifter in China. We have made a tentative preliminary experiment in this regard. The experiment is to vertically pressurize the narrow side of the rectangular tubular magnetic core to generate stress in order to simulate the situation that the magnetic core has similar stress, and then test the phase-shifting characteristics of the phase shifter under different pressures. Explore the change law of phase-shifting characteristics when the magnetic core is under different pressures, increase perceptual knowledge, guide practical work, and finally improve the stability and consistency of the performance of Engineering ferrite phase shifter

before the experiment, we made full preparations: in order to obtain accurate and reliable experimental results, if the experimental machine itself does not have high strength, use high-end vector network analyzer to measure the differential phase shift, use computer control to automatically collect experimental data, store and draw the phase shift characteristic curve, and carry out fine machining, fine assembly and fine matching of the experimental phase shifter (magnetic core and shell)

2 source of magnetic core stress

the source of magnetic core stress of ferrite phase shifter mainly includes the following aspects:

2.1 stress from assembly and installation

if the tolerance between the magnetic core and the shell is not matched properly, the size of the magnetic core in the vertical or horizontal direction is too large, during assembly, the magnetic core may be subjected to the pressure from the vertical or horizontal direction of the shell as shown in Figure 1 and Figure 2, causing stress; If the installation position of the phase shifter on the transmission line is not completely consistent, it may cause torsional stress

2.2 stress caused by thermal expansion and cold contraction

when the operating temperature of the phase shifter changes greatly, the thermal expansion coefficient of the metal shell and the magnetic core is inconsistent, which may cause the magnetic core to be under pressure in the vertical and horizontal directions, and under pressure or tension in the longitudinal direction

when the microwave passes through the magnetic core, it is heated due to energy loss. The temperature at the place where the magnetic core contacts the waveguide is lower than its internal temperature, resulting in different degrees of internal and external expansion and stress

2.3 residual stress after grinding

ferrite core must be ground on six sides before phase shifter assembly, and meet the required dimensional and geometric tolerances. After grinding, there is shrinkage stress on the surface of the magnetic core caused by processing. This stress will gradually decrease with time and other factors, thus affecting the stability of phase-shifting characteristics. In order to eliminate this kind of stress in engineering, annealing treatment is generally used

3 test system and experimental phase shifter

test system are shown in Figure 3, which are mainly composed of vector network analyzer, computer, phase shifter exciter, experimental phase shifter, etc. During the test, the phase shifter is first reset excited, and then the computer controls the exciter to automatically send 255 set pulse excitation electricity to the phase shifter from small to large, evenly and incrementally. Hainan will build a port logistics cooperation mechanism flow with the Pan Pearl River Delta and even the ASEAN region. At the same time, the computer also controls the vector network analyzer to automatically measure the corresponding 255 differential phase shifts in turn, and automatically collect the test results. In order to facilitate observation and comparison, the computer is also used to draw the results of each experiment into the corresponding phase-shifting characteristic curve

the experimental phase shifter is an X-band phase shifter that can exert pressure in the vertical direction, as shown in Figure 4. Its shell is made of brass through precision machining, and its main parts adopt precision wire cutting technology. Its rigidity and precision can well meet the requirements of the experiment

4 experimental method

according to the existing experimental conditions, the experimental phase shifter is pressurized quantitatively and non quantitatively in the vertical direction of the magnetic core