Background
Wireless communication technology is continuously developing, antennas are an essential part of communication systems, and since the increase of many antenna indexes complicates the design of antennas, it has been a challenging problem to optimally design antennas with satisfactory radiation performance. Antenna optimization often relies on scanning structural parameters, and antenna structures are complex and require a large amount of computing resources and time for optimization. Therefore, a reactive loading array based on port eigenmode theory is introduced.
The reactance loading control array means that only one array element in one array is connected with a feed port, other array elements or parasitic elements are connected with reactance loads as coupling units, and the reactance loading is generally realized by a variable capacitance diode. It has many unique advantages in wireless communications, including simple port feed structure, high reliability, low power consumption and low cost. The reactance control array can save the calculation resource of antenna optimization and realize the functions of multi-frequency, wave beam control, bandwidth enhancement, directional diagram reconstruction and the like.
The current reactance loading control array mainly uses a weight coefficient as an optimization variable and can only be optimized aiming at a single frequency point. The optimized weight coefficient is convenient for calculation of the objective function, but the reactance value actually used for loading is deduced from the weight coefficient, so that the time and calculation resource requirements of the algorithm are high, and the performance requirement of the algorithm is high.
Disclosure of Invention
The invention aims to provide a reactive loading array construction method based on a port characteristic model theory, which is simple and convenient in design and capable of reducing the consumption of memory and time resources, and is suitable for the optimal design of various antenna arrays.
The technical solution for realizing the purpose of the invention is as follows: a reactive loading array construction method based on a port characteristic model theory comprises the following steps:
step 1, obtaining an array port impedance matrix of an antenna structure by utilizing full-wave simulation, establishing a characteristic value equation by the impedance matrix, and solving to obtain characteristic current and a characteristic value so as to obtain a characteristic electric field;
step 2, the port current and the total electric field directional diagram are represented by linear superposition of characteristic current and characteristic electric field, and a plurality of objective functions are set for the port current and the total electric field directional diagram;
step 3, optimizing the reactance value by using a differential evolution algorithm: and each iteration adopts the reactance value to reversely deduce the weight coefficient required by the linear superposition of the characteristic current and the characteristic electric field, thereby judging whether the current reactance value meets the requirement of the objective function or not and obtaining the optimal reactance value for port loading after the termination condition is reached.
Compared with the prior art, the invention has the following remarkable advantages: (1) the optimization design of the reactance loading antenna is simpler and more convenient, and the consumption of a large amount of computing resources and time caused by the original antenna optimization is saved; (2) the reactance value is used as an optimization variable, so that the optimization efficiency is greatly improved; (3) more complex and diversified target functions are designed aiming at the single frequency point to adapt to more design requirements, array parameter optimization of a broadband is supported, and the method has great application value.
Detailed Description
With reference to fig. 1, the invention provides a reactance loading array construction method based on a port characteristic model theory, which includes the following steps:
step 1, obtaining an array port impedance matrix of an antenna structure by utilizing full-wave simulation, establishing a characteristic value equation by the impedance matrix, and solving to obtain characteristic current and a characteristic value so as to obtain a characteristic electric field;
step 2, the port current and the total electric field directional diagram are represented by linear superposition of characteristic current and characteristic electric field, and a plurality of objective functions are set for the port current and the total electric field directional diagram;
step 3, optimizing the reactance value by using a differential evolution algorithm: and each iteration adopts the reactance value to reversely deduce the weight coefficient required by the linear superposition of the characteristic current and the characteristic electric field, thereby judging whether the current reactance value meets the requirement of the objective function or not and obtaining the optimal reactance value for port loading after the termination condition is reached.
Further, in step 1, a specific process of solving the characteristic electric field by the characteristic current is as follows: [ Z ]]N×NSolving a characteristic current matrix [ J ] for an array port impedance matrix of the antenna structureN]Substitution matrix equation [ Z]N×N[JN]N×N=[VN]N×NObtaining a mode voltage matrix [ V ] corresponding to each modeN]N×NAnd setting voltage source parameters of each port of the original antenna array according to the voltage matrix to obtain N characteristic electric fields EiI is 1,2, …, and N is the number of modes and also the number of ports.
Further, the objective function in step 2 is set according to the radiation direction of the total electric field, the maximum radiation direction gain, the side lobe level, the half-power lobe width, and the reflection coefficient, and the specific form is as follows:
F=w1f1+w2f2+w3f3+w4f4+w5f5 (1)
f2=-max(Gain) (3)
wherein F is the total objective function value, w
1~w
5Is a target weight coefficient, f
1~f
5Is an objective function; objective function f
1In (1),
in order to be the direction of maximum radiation,
is a target angle; objective function f
2In the middle, max represents the maximum value, and Gain is the antenna Gain; objective function f
3SLL is the maximum sidelobe level, SLL
dIs a target level; objective function f
4Medium, half power lobe width, HPBW
dFor lobe width, objective function f
5In, S
11Is the reflection coefficient.
Further, in step 3, the reactance value is used to reversely estimate the weight coefficient required by the linear superposition of the characteristic current and the characteristic electric field, and the specific steps are as follows:
(3.1) establishing a relation between a new impedance matrix of the antenna after the load is added and a port current matrix according to the Thevenin equivalent circuit, and obtaining the port current matrix according to the loaded reactance value;
and (3.2) obtaining a weight coefficient by the port current matrix.
Further, in the step (3.1), the relationship between the new impedance matrix of the antenna after the load is added and the port current matrix is as follows:
[ZA+ZL]N×N[Jport]N×1=[Vport]N×1 (7)
wherein N is the total number of ports, Z
AIs an impedance matrix, V
portIs the voltage at the port, and is,
reactance value for port loading, J
portIs the port current.
Further, in the step (3.2), the weight coefficient is obtained from the port current matrix, and the specific form is as follows:
[Jport]N×1=[JN]N×N[α]N×1 (8)
wherein J is the characteristic current obtained by solving, and alpha is the weight coefficient to be solved.
Further, in step 3, the reactance value inversely deduces a weight coefficient required by the linear superposition of the characteristic current and the characteristic electric field, and the specific formula is as follows:
further, in step 3, the reactance value is optimized by using a differential evolution algorithm, and a specific flow of each iteration is as follows:
first generating a random population N of reactance values
POP (k)Setting an initial iteration algebra k to be 0, and setting [ Z ] for each individual of the population for each iteration
L]
(k)All give corresponding individual fitness F
(k)Selecting the individual with the most suitable fitness function value
Then for each individual [ Z
L]
(k)All undergo mutation and cross operation to obtain new variant cross individuals
And obtaining a new population N through selection operation
POP (k+1)To obtain the optimal individual in the new population
And corresponding adaptation function values
If the objective function is set, the objective function f
2Corresponding
weight coefficient w 20, according to whether the convergence condition is satisfied
And whether the iteration algebra k reaches the set maximum iteration algebra k
maxTo decide whether to continue the iteration; if w
2If not, then k is determined according to the maximum iteration algebra
maxTo decide whether to continue the iteration;
and outputting the optimal individual, namely the finally optimized reactance value after the iteration is finished.
The invention is described in further detail below with reference to the figures and specific embodiments.
Examples
The method for constructing the reactance loading array based on the port characteristic mode theory specifically comprises the following steps:
firstly, carrying out characteristic analysis on the array antenna by using a port characteristic model theory, and comprising the following steps:
(1) reading geometric information and control parameters such as frequency, port number and the like;
(2) extracting a port impedance matrix;
(3) establishing a generalized eigenvalue equation by the impedance matrix, and solving the generalized eigenvalue equation;
(4) calculating a characteristic current and a characteristic field;
thirdly, in order to constrain the radiation performance of the antenna array in a certain direction, the objective function may be set as follows:
F=w1f1+w2f2+w3f3+w4f4+w5f5 (1)
f2=-max(Gain) (3)
wherein F is the total objective function value, w
1~w
5Is a target weight coefficient, f
1~f
5Is an objective function. Objective function f
1In (1),
in order to be the direction of maximum radiation,
for the target angle, the objective function f
2In the equation, max represents the maximum value, Gain is the antenna Gain, and the objective function f
3SLL is the maximum sidelobe level, SLL
dFor the target level, the objective function f
4Medium, half power lobe width, HPBW
dFor lobe width, objective function f
5In, S
11Is the reflection coefficient.
And fourthly, optimizing the optimal reactance value by using a differential evolution algorithm (DE) algorithm. Each iteration reversely deduces a weight coefficient required by the linear superposition of the characteristic current and the characteristic electric field by using the reactance value, thereby judging whether the current reactance value meets the requirement of the objective function. According to the multi-port Thevenin equivalent circuit, a new impedance matrix after the antenna is externally connected with a load meets the following requirements:
[ZA+ZL]N×N[Iport]N×1=[Vport]N×1 (7)
wherein N is the total number of ports, Z
AIs an impedance matrix, V
portIs the voltage at the port, and is,
reactance value for port loading, J
portPort current obtained by linear superposition of characteristic currents:
[Jport]N×1=[J]N×N[α]N×1 (8)
wherein J is the characteristic current obtained by solving, and alpha is a weight coefficient.
Substituting equation (8) into equation (7) yields:
and obtaining the weight coefficient, and obtaining the port current and the total electric field through linear superposition so as to obtain an individual adaptive function value F corresponding to the current reactance value. And obtaining a new population through variation crossing and selection, judging whether to continue iteration according to the adaptive function value of the optimal individual in the new population, and stopping iteration to output the optimal reactance value after multiple iterations finally meet the termination condition or reach the maximum iteration step number.
And fifthly, substituting the optimal reactance value optimized by a Differential Evolution (DE) algorithm into a loading port of the full-wave simulation platform for simulation to obtain a reflection coefficient and a gain directional diagram.
To verify the feasibility of the method, an example of a design method for a reactive loading array based on port eigenmode theory is given below, and the feasibility of the method can be seen in the general flow chart of fig. 1. The ten-element yagi antenna loading reactance simulation result in fig. 2: the gain is 13.83dBi and the side lobe level is-15.40 dB. According to the result, the radiation pattern calculated by the method meets the target design requirement, and the correctness of the method is verified.