阅读说明：本技术 基于口径电流法的相控阵天线方向图预测方法及系统 (Phased array antenna directional pattern prediction method and system based on aperture current method ) 是由 周建华 毛小莲 栗曦 李吉龙 张捷俊 任振 葛鲁宁 于 2020-09-02 设计创作，主要内容包括：本申请公开了一种基于口径电流法的相控阵天线方向图预测方法。步骤S10：通过测量得到相控阵天线端口的有源散射参数矩阵；所述相控阵天线端口的有源散射参数矩阵是指相控阵天线所有天线单元同时进行激励、在波束扫描状态下得到的散射参数矩阵,此时考虑了阵中单元间的耦合影响。步骤S20：计算得到相控阵天线工作状态下的真实口径电流分布；所述相控阵天线工作状态下的真实口径电流分布是指相控阵天线所有天线单元同时进行激励、在波束扫描状态下的真实口径电流分布,此时考虑了阵中单元间的耦合影响。步骤S30：预估相控阵天线的全阵方向图。本申请可以提高相控阵天线的方向图的预估精度和效率。(The application discloses a phased array antenna directional diagram prediction method based on an aperture current method. Step S10: obtaining an active scattering parameter matrix of a phased array antenna port through measurement; the active scattering parameter matrix of the phased array antenna port refers to a scattering parameter matrix obtained in a beam scanning state by simultaneously exciting all antenna units of the phased array antenna, and the coupling influence among the units in the array is considered at the moment. Step S20: calculating to obtain the real aperture current distribution of the phased array antenna in the working state; the real aperture current distribution of the phased array antenna in the working state refers to the real aperture current distribution of the phased array antenna in the beam scanning state when all antenna units are excited simultaneously, and the coupling influence among the array units is considered at the moment. Step S30: and estimating a full-array directional diagram of the phased-array antenna. The method and the device can improve the pre-estimation precision and efficiency of the directional diagram of the phased array antenna.)

1. A phased array antenna directional pattern prediction method based on an aperture current method is characterized by comprising the following steps;

step S10: obtaining an active scattering parameter matrix of a phased array antenna port through measurement; assuming that the phased array antenna has N antenna elements, namely N channels, the measurement method is to control the signal source to generate the excitation signals A with different amplitudes and phases required by the N channels₁，A₂，……A_NAll the antenna units are simultaneously and respectively connected into the excitation signals, the coupling influence among the antenna units is considered at the moment, and a complete scattering parameter matrix SNAP of all the antenna units is directly obtained through one-time measurement and is called as an active scattering parameter matrix;

each element S therein_ijThe scattering parameters of the phased array antenna are represented, and the value ranges of i and j are both 1 to N;

step S20: calculating to obtain the real aperture current distribution I of the phased array antenna in the working state₁，I₂，……I_N；

；

Wherein the active scattering parameter matrix SNAP is obtained in step S10 in consideration of the coupling effect between the antenna elements;

step S30: and estimating a full-array directional diagram of the phased-array antenna according to the superposition principle of the array antenna.

2. The method of claim 1, wherein the phased array antenna directional pattern prediction method based on the aperture current method is characterized in that, assuming that the phased array antenna has M wave position states, the step S10 of obtaining the active scattering parameter matrix of the phased array antenna port by measurement further comprises the following steps:

step S110: calibrating a hardware measurement channel, wherein a calibrated reference surface is an input port surface of the phased array antenna;

step S112: setting the phased array antenna to work in a certain wave position state, wherein the phased array antenna corresponds to a wave beam scanning angle of the phased array antenna; the control signal source generates excitation signals with different amplitudes and phases required by the N channels;

step S114: acquiring reflection levels and incidence levels of N channels through a multi-channel receiver, wherein the scattering parameter of each channel is equal to the ratio of the reflection level to the incidence level, and obtaining an active scattering parameter matrix of the phased array antenna through one-time measurement; at the moment, all the antenna units work simultaneously, signals radiated to the air by each antenna unit are received by other antenna units, mixed into port reflection levels to synthesize a signal, and collected by a receiver together, so that the obtained active scattering parameter matrix takes the coupling influence among the antenna units into consideration;

step S116: repeating the steps S112 to S114, and switching the wave position state of the phased array antenna in the step S112; and measuring the active scattering parameter matrix corresponding to each wave position state until the traversal of the M wave position states is completed.

3. The aperture current method based phased array antenna pattern prediction method of claim 1, wherein assuming that the phased array antenna has M wave position states, said step S30 further comprises the steps of;

step S310: measuring to obtain an array unit directional diagram of the phased array antenna unit;

step S312: under a certain wave position state, estimating a full array directional diagram of the phased array antenna according to the superposition principle of the array antenna;

step S314: and switching the wave position state, and repeating the step S312 until the traversal of the M wave position states is completed, and predicting the directional diagram corresponding to the scanning directions of the M wave beams.

4. The aperture current method based phased array antenna pattern prediction method of claim 1, wherein the superposition principle of the array antenna is the pattern product theorem.

5. A phased array antenna pattern prediction system based on aperture current method for implementing the method of any one of claims 1 to 4; the device is characterized by comprising an active scattering parameter acquisition unit, an aperture current calculation unit and a directional diagram estimation unit;

the active scattering parameter acquisition unit is used for obtaining an active scattering parameter matrix of the phased array antenna port through measurement; assuming that the phased array antenna has N antenna units, namely N channels, the active scattering parameter acquisition unit controls the signal source to generate excitation signals A with different amplitudes and phases required by the N channels₁，A₂，……A_NAll the antenna units are simultaneously and respectively connected into the excitation signals, the coupling influence among the antenna units is considered at the moment, and a complete scattering parameter matrix SNAP of all the antenna units is directly obtained through one-time measurement and is called as an active scattering parameter matrix;

each element S therein_ijThe scattering parameters of the phased array antenna are represented, and the value ranges of i and j are both 1 to N;

the aperture current calculation unit is used for obtaining the real aperture current distribution I of the phased array antenna in the working state through calculation₁，I₂，……I_N；

；

The active scattering parameter matrix SNAP is obtained by the active scattering parameter obtaining unit under the consideration of the coupling influence among the antenna units;

the directional diagram prediction unit is used for predicting a full-array directional diagram of the phased-array antenna according to the superposition principle of the array antenna.

6. The system of claim 5, wherein the active scattering parameter acquisition unit further comprises a multi-channel signal source, a beam former, and a multi-channel receiver;

the multi-channel signal source is used for providing original excitation signals of N channels of the phased array antenna;

the beam former is used for adjusting the amplitude and the phase of the original excitation signal and providing the excitation signals A with different amplitudes and phases required by beam scanning for N channels of the phased array antenna₁，A₂，……A_N(ii) a The beam former is also used for setting wave position states;

the multi-channel receiver is used for simultaneously receiving and collecting reflection levels and incidence levels of N channels of the phased array antenna so as to calculate scattering parameters of each antenna unit port.

7. The system of claim 6, wherein the beamformer further comprises attenuators, phase shifters, switches, and matching loads.

Technical Field

The application relates to a microwave measurement (microwave measurement) technology, in particular to an aperture current method-based prediction method for a directional diagram (antenna pattern, also called radiation pattern or far-field directional diagram far-field pattern) of a phased array antenna (phased array antenna).

Background

Currently, calibration algorithms for phased array antennas are under study.

The russian scientist proposed a phase-shift measurement method (phase-shift measurement method) for phased array antennas in the middle and late 1980 s, and applied the method to the measurement and diagnosis of phased array antennas. Hampson, in 1999, implemented fast calibration of active phased array antennas using commutation measurements in conjunction with FFT (fast Fourier transform). In 2010, a commutation measurement method is theoretically and in detail studied in doctor's academic paper "fast phased array antenna measurement and calibration technology research" of the professor of the level of the Shang army of the university of the Western-An electronic technology, and the commutation measurement method is applied to fast calibration of the phased array antenna. It is known that israel scientists have measured and diagnosed phased array antenna characteristics in a similar manner, but have not reported any literature data.

In the 80's of the 20 th century, various national scholars began research on phased array antenna calibration techniques. In 1982, Kojima N and Shiramatsu K first proposed that rotating-electric-vector method (REV method) measure the amplitude-phase excitation of the unit and apply it to the calibration of phased-array antennas. Nobuyasu et al, a scholars of japan, in 2001, proposed a rotating electrical vector method considering phase error of a phase shifter (phase shifter), the basic idea of which is that a receiving probe is placed in front of the measured antenna array surface, the measured antenna elements are sequentially phase-shifted, and the phases of the other antenna elements are not changed; the amplitude-phase characteristics of the antenna unit to be detected can be determined and faults can be detected through the ratio of the maximum value and the minimum value of the received signal energy of the receiving probe and the state of the phase shifter where the maximum value of the signal energy is located.

American scholars Aumann M and Fenn J et al proposed a method for rapidly calibrating a phased array antenna using mutual coupling (mutual coupling) between phased array units in 1989, and chinese scholars high-speed railway et al applied the mutual coupling calibration method to a large active phased array antenna. U.S. scholars Silverstein D proposed in 1996 a method of measuring and calibrating a phased array antenna on a communication satellite using a switching matrix (switchmatrix) encoding method.

However, the estimation of the directional pattern of the phased array antenna is mainly based on the pattern multiplication theorem (array factor) to theoretically calculate the array factor (array factor), and the directional pattern in the actual measurement array is taken as the element factor, but the estimation effect is poor.

Disclosure of Invention

The technical problem to be solved in the application is to provide a phased array antenna directional diagram prediction method based on a caliber current method, wherein the actual caliber current distribution (adaptive current distribution) of each antenna unit (antenna element) of an array antenna (array antenna) is obtained by establishing an active scattering parameter matrix solution, and then a far field directional diagram of the phased array antenna is predicted through field superposition.

In order to solve the technical problem, the application provides a phased array antenna directional pattern prediction method based on an aperture current method, which comprises the following steps. Step S10: obtaining an active scattering parameter matrix of a phased array antenna port through measurement; assuming that the phased array antenna has N antenna elements, namely N channels, the measurement method is to control the signal source to generate the excitation signals A with different amplitudes and phases required by the N channels₁，A₂，……A_NAll the antenna units are simultaneously and respectively connected into the excitation signal, the coupling influence among the antenna units is considered at the moment, and a complete scattering parameter matrix SNAP of all the antenna units is directly obtained through one-time measurement, as shown in a formula I, the scattering parameter matrix SNAP is called as an active scattering parameter matrix. Each element S in formula one_ijAnd (3) representing scattering parameters of the phased array antenna, wherein the value ranges of i and j are both 1 to N. Step S20: calculating to obtain the real aperture current distribution I of the phased array antenna in the working state₁，I₂，……I_NAs shown in equation two. The active scattering parameter matrix SNAP in the formula two is obtained by considering the antenna unit in step S10Obtained under the influence of coupling between the elements. Step S30: and estimating a full-array directional diagram of the phased-array antenna according to the superposition principle of the array antenna.

(formula one).

(formula two).

The method and the device are used for pre-estimating the directional diagram of the phased array antenna. The phased array antenna is an array antenna in a special form, consists of a plurality of antenna units, and can realize the rapid scanning of antenna beams by changing the phase and amplitude of a transmission signal of each antenna unit channel and changing the aperture irradiation function of the phased array antenna. Therefore, the directional diagram characteristic of the phased array antenna in the wave beam scanning under the real working state is estimated, and the method is important for quickly evaluating the performance of the phased array antenna array surface. The prediction needs to simulate the working state of beam scanning of the phased array antenna, simultaneously excites all antenna units of the phased array antenna under the condition of given amplitude and phase, obtains active scattering parameters, calculates the real aperture current distribution, predicts the directional diagram of the phased array antenna according to the active scattering parameters, can effectively improve the precision and quickens the research and development production efficiency of the phased array antenna.

Further, assuming that the phased array antenna has M wave position states, the step S10 of obtaining the active scattering parameter matrix of the phased array antenna port by using the measurement method includes the following steps. Step S110: and calibrating a hardware measurement channel, wherein the calibrated reference surface is the input port surface of the phased array antenna. Step S112: setting the phased array antenna to work in a certain wave position state, wherein the phased array antenna corresponds to a wave beam scanning angle of the phased array antenna; the control signal source generates the excitation signals of different amplitudes and phases required by the N channels. Step S114: acquiring reflection levels and incidence levels of N channels through a multi-channel receiver, wherein the scattering parameter of each channel is equal to the ratio of the reflection level to the incidence level, and obtaining an active scattering parameter matrix of the phased array antenna through one-time measurement; at this time, all the antenna units work simultaneously, signals radiated to the air by each antenna unit are received by other antenna units, mixed into port reflection levels to synthesize a signal, and collected by a receiver, so that the obtained active scattering parameter matrix considers the coupling influence among the antenna units. Step S116: repeating the steps S112 to S114, and switching the wave position state of the phased array antenna in the step S112; and measuring the active scattering parameter matrix corresponding to each wave position state until the traversal of the M wave position states is completed. One specific implementation of step S10 is presented herein.

Further, the step S30 further includes the following steps; step S310: and measuring to obtain an array unit directional diagram of the phased array antenna unit. Step S312: and under a certain wave position state, estimating a full array directional diagram of the phased array antenna according to the superposition principle of the array antenna. Step S314: and switching the wave position state, and repeating the step S312 until the traversal of the M wave position states is completed, and predicting the directional diagram corresponding to the scanning directions of the M wave beams. This is a detailed description of step S30.

Preferably, the superposition principle of the array antenna is referred to as a pattern product theorem. This is a preferred example.

The application also provides a phased array antenna directional pattern prediction system based on the aperture current method, which corresponds to the method; the device comprises an active scattering parameter acquisition unit, an aperture current calculation unit and a directional diagram estimation unit. The active scattering parameter acquisition unit is used for obtaining an active scattering parameter matrix of the phased array antenna port through measurement; assuming that the phased array antenna has N antenna units, namely N channels, the active scattering parameter acquisition unit controls the signal source to generate excitation signals A with different amplitudes and phases required by the N channels₁，A₂，……A_NAll the antenna units are simultaneously and respectively connected into the excitation signal, the coupling influence among the antenna units is considered at the moment, and a complete scattering parameter matrix SNAP of all the antenna units is directly obtained through one-time measurement, as shown in a formula I, the scattering parameter matrix SNAP is called as an active scattering parameter matrix. Each element S in formula one_ijThe scattering parameters of the phased array antenna are represented, and the value ranges of i and j are both 1 to N;the aperture current calculation unit is used for obtaining the real aperture current distribution I of the phased array antenna in the working state through calculation₁，I₂，……I_N(ii) a As shown in equation two. The active scattering parameter matrix SNAP in the formula two is obtained by the active scattering parameter obtaining unit under the consideration of the coupling influence between the antenna units. The directional diagram prediction unit is used for predicting a full-array directional diagram of the phased-array antenna according to the superposition principle of the array antenna. The working state of beam scanning of phased array antenna is simulated, all antenna elements of phased array antenna are excited simultaneously under the condition of given amplitude and phase, active scattering parameters are obtained, real aperture current distribution is calculated, the directional diagram of phased array antenna is estimated accordingly, the precision can be effectively improved, and the research and development production efficiency of phased array antenna is accelerated.

Further, the active scattering parameter acquisition unit further comprises a multi-channel signal source, a beam former and a multi-channel receiver. The multi-channel signal source is used for providing original excitation signals of N channels of the phased array antenna. The beam former is used for adjusting the amplitude and the phase of the original excitation signal and providing the excitation signals A with different amplitudes and phases required by beam scanning for N channels of the phased array antenna₁，A₂，……A_N(ii) a The beamformer is also used to set the wave bit states. The multi-channel receiver is used for simultaneously receiving and collecting reflection levels and incidence levels of N channels of the phased array antenna so as to calculate scattering parameters of each antenna unit port. This is a specific implementation of the active scattering parameter acquisition unit.

Preferably, the beamformer further comprises attenuators, phase shifters, switches, matching loads. This is a detailed description of the beamformer.

The traditional directional diagram product theorem takes the input of the phased array antenna port as the actual aperture field of the array antenna, which is inaccurate, and the method can obtain the actual aperture field of the array, so the method can improve the prediction precision of the directional diagram of the phased array antenna.

Drawings

Fig. 1 is a schematic diagram of the input and aperture currents of a phased array antenna having N antenna elements.

Fig. 2 is a flowchart of a phased array antenna pattern prediction method based on an aperture current method according to the present application.

Fig. 3 is a detailed flowchart of one implementation of step S10 in fig. 2.

Fig. 4 is a detailed flowchart of one implementation of step S30 in fig. 2.

Fig. 5 is a schematic structural diagram of a phased array antenna pattern prediction system based on an aperture current method according to the present application.

Fig. 6 is a specific structural diagram of an implementation manner of the active scattering parameter acquisition unit in fig. 5.

The reference numbers in the figures illustrate: 10 is an active scattering parameter acquisition unit; 110 is a multi-channel signal source; 120 is a beam former; 130 is a multi-channel receiver; 20 is a caliber current calculating unit; 30 is a pattern estimation unit.

Detailed Description

Referring to fig. 1, assume that the phased array antenna has N antenna elements, and the input is a₁，A₂，……A_NThe aperture current (also called aperture current) of each antenna unit is I₁，I₂，……I_N。A₁，A₂，……A_NBy physical meaning is meant the excitation coefficient of each antenna element.

Referring to fig. 2, the method for predicting a directional pattern of a phased array antenna based on an aperture current method includes the following steps.

Step S10: obtaining an active scattering parameter matrix of a phased array antenna port through measurement; the active scattering parameter matrix of the phased array antenna port refers to a scattering parameter matrix obtained in a beam scanning state by simultaneously exciting all antenna units of the phased array antenna, and the coupling influence among the units in the array is considered at the moment.

Assuming a phased array antenna having N antenna elements, i.e., N channels, the measurement is made by controlling the generation of a signal sourceExcitation signals A of different amplitudes and phases required by the N channels₁，A₂，……A_NThe antenna elements of the phased array antenna simultaneously have excitation signals A₁，A₂，……A_NAnd inputting, namely taking the coupling influence among the antenna units into consideration at the moment, and directly obtaining a complete active scattering parameter matrix SNAP of all antenna unit ports of the phased array antenna by one-time measurement, as shown in a formula I. The active scattering parameter matrix SNAP is a scattering matrix (scattering matrix) of an array antenna, in which each element S is present_ijThe scattering parameter (also called S-parameter) of the array antenna is shown, and the values of i and j are in the range of 1 to N. The array antenna with N antenna units has N²A scattering parameter.

Step S20: calculating to obtain the real aperture current distribution I of the phased array antenna in the working state₁，I₂，……I_NAs shown in equation two. The active scattering parameter matrix SNAP is obtained in step S10, taking into account the coupling effect between the antenna elements.

Step S30: a full-array directional diagram of the phased-array antenna is estimated through a superposition principle (superposition principle) of the array antenna. For example, the superposition principle of the array antenna is referred to as a pattern product theorem.

Referring to fig. 3, assuming that the phased array antenna has M wave position states, the step S10 of obtaining the active scattering parameter matrix of the phased array antenna port by using the measurement method further includes the following steps.

Step S110: and calibrating a hardware measurement channel, wherein the calibrated reference surface is the input port surface of the phased array antenna to be measured. The calibration is to measure the channel error of the active scattering parameter acquisition unit, correct the measured data through a compensation calibration algorithm, and remove the error caused by the hardware system. The calibrated reference plane is used to define a calibrated channel range, as shown in fig. 6, the channel range of the active scattering parameter obtaining unit 10 is from the multi-channel signal source 110 to the input port of the to-be-tested phased array antenna, and is terminated at the cable output port of the multi-channel receiver 130 connected to the to-be-tested phased array antenna. The input port surface of the phased array antenna refers to an excitation signal input port of the phased array antenna to be tested, such as a dotted line position in fig. 6.

Step S112: and setting the phased array antenna to work in a certain wave position state, wherein the wave position state corresponds to a wave beam scanning angle of the phased array antenna. The setting of the wave bit states is performed, for example, by the beamformer 120 in fig. 6, which controls the multi-channel signal source 110 to generate excitation signals of different amplitudes and phases required for the N channels.

Step S114: the reflection level and the incidence level of N channels are collected through a multi-channel receiver, the scattering parameter of each channel is equal to the reflection level to the incidence level, and an active scattering parameter matrix of the phased array antenna is obtained through one-time measurement. At the moment, all the antenna units work simultaneously, signals radiated to the air by each antenna unit are received by other antenna units, mixed into port reflection levels to synthesize a signal, and collected by a receiver, so that the obtained active scattering parameter matrix considers the coupling influence among the antenna units, and the active scattering parameter matrix of the phased array antenna is obtained through measurement.

In the general measurement of the scattering parameter matrix, only one antenna unit is connected into excitation, other units are connected into matched load (namely in a non-working state), the scattering parameter matrixes of all groups of ports are sequentially tested in a rotation mode, and the scattering parameter matrixes of the whole array are obtained through superposition. Different from a general scattering parameter matrix measuring principle, all antenna units are simultaneously connected into excitation when active scattering parameter matrix measurement is carried out, and the scattering parameter matrix of all the units of the reverse full array is obtained through one-time test. The key for distinguishing the two scattering parameter matrixes is that whether the units in all the matrixes are simultaneously connected with excitation is judged, the state is the real state of the phased array antenna during working, the coupling influence generated among the units in the matrixes is different, the obtained scattering parameter matrixes are also different, the directional diagram of the array is estimated according to the result obtained by measurement, and the prediction precision can be improved.

The consideration of coupling when a scattering matrix is obtained through simulation is a conventional technical means of technicians in the field, but in the engineering implementation, due to the limitation of hardware resources, a general vector network analyzer is two-port or four-port, and cannot realize that all ports are accessed with excitation signals, so that the measurement of multi-port active scattering parameters cannot be realized. The method is suitable for testing and debugging the array surface of the phased array antenna, the real working state of the phased array antenna can be simulated, the units in all the arrays are excited simultaneously, the active scattering parameter matrix is obtained, the directional diagram is estimated in the state, the precision can be improved, and the measurement efficiency can be obviously improved.

Step S116: repeating the steps S112 to S114, and switching the wave position state of the phased array antenna in the step S112; and measuring the active scattering parameter matrix corresponding to each group of wave bit states until the traversal of the M wave bit states is completed.

Referring to fig. 4, assuming that the phased array antenna has M wave bit states, the step S30 further includes the following steps.

Step S310: and measuring to obtain an array unit directional diagram of the phased array antenna unit.

Step S312: and under a certain wave position state, estimating a full array directional diagram of the array antenna according to the superposition principle of the array antenna.

Step S314: and switching the wave position state, and repeating the step S312 until the traversal of the M wave position states is completed, and predicting the directional diagram corresponding to the scanning directions of the M wave beams.

Corresponding to fig. 2, please refer to fig. 5, the phased array antenna directional pattern prediction system based on the aperture current method according to the present application includes an active scattering parameter obtaining unit 10, an aperture current calculating unit 20, and a directional pattern prediction unit 30.

The active scattering parameter obtaining unit 10 is configured to obtain an active scattering parameter matrix of the phased array antenna port through measurement. Assuming that the phased array antenna has N antenna elements, i.e. N channels, the active scattering parameter obtaining unit 10 controls the signal source to generate the excitation signals a with different amplitudes and phases required by the N channels₁，A₂，……A_NAll the antenna units are simultaneously and respectively connected into the excitation signal, the coupling influence among the antenna units is considered, and the complete active scattering parameters of all the antenna units are directly obtained through one-time measurementThe matrix SNAP is shown in equation one. Each element S therein_ijAnd (3) representing scattering parameters of the phased array antenna, wherein the value ranges of i and j are both 1 to N.

The aperture current calculating unit 20 is used for obtaining the real aperture current distribution I of the phased array antenna in the working state through calculation₁，I₂，……I_NAs shown in equation two. The active scattering parameter matrix SNAP is obtained by the active scattering parameter obtaining unit 10 under consideration of the coupling effect between the antenna elements.

The directional pattern estimation unit 30 is used for estimating a full-array directional pattern of the phased array antenna according to the superposition principle of the array antenna.

Referring to fig. 6, the active scattering parameter acquiring unit 10 further includes a multi-channel signal source 110, a beam former 120 and a multi-channel receiver 130.

The multi-channel signal source 110 is used to provide the original excitation signals of the N channels of the phased array antenna.

The beamformer 120 is used to amplitude and phase adjust the original excitation signal to provide different amplitude and phase excitation signals A for the N channels of the phased array antenna as required for beam scanning₁，A₂，……A_N. The beamformer 120 is also used to set the wave bit states. For example, the beamformer further includes attenuators, phase shifters, switches, matched loads, and the like.

The multi-channel receiver 130 is used to simultaneously receive and collect the reflection levels and incidence levels of the N channels of the phased array antenna to calculate the scattering parameters for each antenna element port.

The above are merely preferred embodiments of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.