Short-wave sky wave channel propagation parameter optimization method based on antenna directivity

Abstract

The invention belongs to the technical field of short-wave communication, and particularly relates to a short-wave sky wave channel propagation parameter optimization method based on antenna directivity, which comprises the following steps: acquiring directivity diagrams of a transmitting antenna and a receiving antenna; determining a propagation path of sky wave rays from a transmitting antenna to a receiving antenna by adopting a numerical ray tracing algorithm; according to the propagation path, calculating free space propagation loss, ionosphere loss and ground reflection loss; performing directional gain correction on the signal intensity on the propagation path according to the directional diagrams of the transmitting antenna and the receiving antenna; calculating the total propagation loss according to the free space loss, the ionosphere loss, the ground reflection loss and the antenna directivity correction value; outputting propagation parameters including the total propagation loss, the propagation path, the antenna directivity correction value and the time delay; according to the method, antenna directivity parameters and propagation path loss are dynamically coupled, and the defect that a traditional model ignores the influence of antenna radiation directivity on signal strength is overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of short-wave communication, and particularly relates to a method for optimizing propagation parameters of a short-wave skywave channel based on antenna directivity. Background Art

[0002] Due to its unique ionospheric reflection characteristics, short-wave skywave communication can achieve over-the-horizon and low-cost long-distance communication, and is irreplaceable in the fields of emergency communication, maritime communication, polar scientific research, etc. However, its propagation channel is affected by multiple factors such as the ionosphere, multipath effect, and antenna directivity. On the one hand, the antenna directivity seriously affects the prediction accuracy of short-wave multipath channel parameters. On the other hand, it will also cause significant errors in the prediction of propagation loss, directly affecting the design and performance evaluation of communication systems.

[0003] The traditional propagation calculation methods mainly have the following technical bottlenecks: 1) Lack of antenna directivity modeling: The existing international standard methods are based on the assumption of isotropic antennas, ignoring the asymmetric radiation characteristics of actual short-wave antennas (such as rhombic antennas and log-periodic antennas). Experimental data shows that when the azimuth deviation between the main lobe direction of the antenna and the ionospheric reflection area exceeds 10°, the error of the spatial gain distribution predicted by the traditional model can reach 12 - 15 dB, and the error increases non-linearly with the change of the elevation angle. This directivity mismatch not only causes distortion of the field strength prediction but also leads to a calculation deviation of the multipath delay spread parameter exceeding 30%. 2) Over-simplification of path modeling: The mainstream ray tracing algorithms (such as the two-dimensional parabolic equation method) often ignore the reflected propagation of multi-hop paths between the ionosphere and the ground in order to reduce the calculation complexity, and do not consider the influence of the dynamic changes of the complex ionosphere on the propagation path, resulting in distortion of the loss calculation in multi-mode propagation scenarios. This will also cause distortion of the multipath superposition effect modeling. Especially when the D layer of the ionosphere disappears at night, the traditional model cannot represent the time-delay diversity signals generated by multiple reflections through the E / F layers, resulting in a time-delay estimation error exceeding 50%.

[0004] Although there are individual studies attempting to introduce directivity factor correction at present, it still has a major defect, that is, it does not establish a dynamic mapping mechanism between the directivity pattern and the ray propagation direction, and cannot adapt to the direction-of-arrival offset caused by the dynamic changes of the ionosphere. Summary of the Invention

[0005] To solve the problems existing in the above prior art, the present invention proposes an optimization method for short-wave skywave channel propagation parameters based on antenna directivity. The method includes: obtaining the directivity patterns of the transmitting antenna and the receiving antenna; using the numerical ray tracing algorithm to determine the propagation path of the skywave ray from the transmitting antenna to the receiving antenna; calculating the free-space propagation loss, ionospheric loss, and ground reflection loss respectively according to the propagation path; performing directivity gain correction on the signal intensity on the propagation path according to the directivity patterns of the transmitting antenna and the receiving antenna; calculating the total propagation loss according to the free-space loss, ionospheric loss, ground reflection loss, and antenna directivity correction value; and outputting the propagation parameters including the total propagation loss, propagation path, antenna directivity correction value, and time delay.

[0006] Advantages of the present invention:

[0007] The present invention dynamically couples the antenna directivity parameters with the propagation path loss, overcoming the defect that the traditional model ignores the influence of antenna radiation directivity on the signal intensity. Through the directivity gain correction, the present invention significantly improves the accuracy of the signal intensity calculation during the three-dimensional propagation of short-wave signals; the propagation parameters output by the present invention not only include the total loss, but also provide key information such as the propagation path and time delay, providing a multi-dimensional quantitative basis for engineering practices such as antenna array optimization, frequency selection, and link budget in short-wave communication systems, and having stronger guiding value compared with the traditional single-parameter output model; the present invention establishes a complete closed-loop system from antenna characteristics to propagation environment to loss calculation, realizing the co-simulation of the entire "radiation - propagation - reception" link, breaking through the limitations of the existing segmented modeling method in system-level optimization, and providing a new technical framework for building a high-precision channel simulation platform. Description of the Drawings

[0008] Figure 1 It is the overall flowchart of the propagation calculation method for the short-wave skywave channel based on antenna directivity of the present invention;

[0009] Figure 2 It is the geometric structure of the double-layer log-periodic antenna and G5RV of the present invention;

[0010] Figure 3 It is the directivity gain in the vertical plane of the 5MHz and 15MHz double-layer log-periodic antennas of the present invention;

[0011] Figure 4 It is the three-dimensional direction pattern of the 5MHz and 15MHz G5RV antennas of the present invention;

[0012] Figure 5 It is the electron density profile of the ionospheric background model of the present invention;

[0013] Figure 6This is the time-of-flight diagram of the skywave propagation from Xinjiang to Finland with UTC = 202408280530 for the present invention;

[0014] Figure 7 This is the total loss of the present invention based on the antenna frequency of 15 MHz, UTC = 202408280530, and the skywave propagation from Xinjiang to Finland;

[0015] Figure 8 This is the distribution characteristic of the delay parameter of the present invention based on the antenna frequency of 15 MHz, UTC = 202408280530, and the skywave propagation from Xinjiang to Finland. Detailed implementation manners

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] An optimization method for the propagation parameters of a shortwave skywave channel based on antenna directivity, as Figure 1 shown, the method includes: obtaining the directivity patterns of the transmitting antenna and the receiving antenna; using the numerical ray tracing algorithm to determine the propagation path of the skywave ray from the transmitting antenna to the receiving antenna; calculating the free space propagation loss, ionospheric loss, and ground reflection loss respectively according to the propagation path; performing directivity gain correction on the signal intensity on the propagation path according to the directivity patterns of the transmitting antenna and the receiving antenna; calculating the total propagation loss according to the free space loss, ionospheric loss, ground reflection loss, and the antenna directivity correction value; outputting the propagation parameters including the total propagation loss, propagation path, antenna directivity correction value, and time delay.

[0018] Obtaining the antenna directivity parameters includes: modeling the antenna geometric structure; setting the material parameters of each part of the antenna; setting the far-field electromagnetic parameters of the antenna; applying excitation to the antenna feeder port and applying characteristic impedance to the antenna load port; obtaining the directivity parameters of the antenna radiation.

[0019] The gain calculation is specifically as follows: First, the electric field data in the three-dimensional direction of the shortwave antenna can be obtained through the electromagnetic simulation software COMSOL or actual measurement Then, the radiation intensity is calculated according to the electric field as:

[0020]

[0021] In the formula, Z0 = 377Ω is the free space wave impedance, and r is the observation distance. Finally, the ratio of the radiation intensity to the radiation intensity of the ideal point source antenna at this point is obtained as:

[0022]

[0023] Among them

[0024]

[0025] In the above formula, P in is the antenna input power, and U iso represents the radiation intensity of the point source antenna at this point. To clearly display the antenna directivity parameters, the present invention simulates two short-wave antennas, namely a double-layer log-periodic antenna (transmitting antenna) and a G5RV (receiving antenna). Figure 2 are the geometric structure diagrams of the two antennas Figure 3 and Figure 4 are the directivity gains of the two antennas at frequencies of 5 MHz and 15 MHz respectively

[0026] In this embodiment, the propagation calculation method of the skywave channel includes a numerical ray tracing algorithm and an ionospheric background model

[0027] Ray tracing technology is one of the basic methods for studying radio wave propagation, and there are mainly two types: analytical ray tracing and numerical ray tracing. The former ignores the geomagnetic field and collision effects, and at the same time assumes that the ionosphere is spherically symmetrically distributed. The latter takes into account both the geomagnetic field and collision effects, and by applying the principle of Hamiltonian dynamics and numerically solving the Haselgrove equation, important channel parameters such as group path, time delay, wave vector, ionospheric absorption, etc. of the radio wave ray during propagation can be obtained. Although this method has the problem of large computational amount, numerical ray tracing can obtain relatively accurate channel propagation parameters. Due to the complex and harsh environment of the short-wave channel, the geomagnetic field and collision effects cannot be ignored, so the present invention uses numerical ray tracing for simulation

[0028] The main construction elements of the propagation calculation method of the skywave channel based on numerical ray tracing are mainly in two aspects. One is the solution of the ray equation, and the other is the ionospheric background model. The two are inseparable, and the solution of the ray equation depends on the ionospheric background model. In the spherical coordinate system, any point on the radio wave ray can be expressed as The wave vector of this point is The Hamiltonian 3D ray equation set with the point P' on the radio wave group path as the parameter is

[0029]

[0030] Haselgrove introduced the relationship between the Hamiltonian operator and the wave vector and refractive index, and defined the Hamiltonian operator H as

[0031]

[0032] In the above formulas (4)-(5), \(n = \mu - j\chi\), where \(\mu\) and \(\chi\) are the real and imaginary parts of the refractive index respectively, and the wave vector satisfies where \(k\) ρ , \(k\) θ , are the three components of the wave vector in the spherical coordinate system respectively. The relationships between the three components of the wave vector in the Cartesian coordinate system and the spherical coordinate system are:

[0033]

[0034] In formula (6), \(k\) x , \(k\) y , \(k\) z are the three components of the wave vector in the Cartesian coordinate system respectively. In formula (5), the parameter \(c\) is the speed of light in vacuum, \(\omega\) is the angular frequency of the incident wave, \(n\) 2 is the refractive index of the ionosphere. The refractive index can be determined by the Appleton - Hartree equation (A - H):

[0035]

[0036] In the above formula, the symbols correspond to the extraordinary wave (X - wave) and ordinary wave (O - wave) of short - wave respectively. Among them, \(X\), \(Y\) T , \(Y\) L , \(Z\) are calculated by the following formulas respectively:

[0037]

[0038] In formulas (8)-(10), \(e\) and \(m\) are the electric charge and mass of the electron respectively, \(\varepsilon\) is the dielectric constant in the ionospheric medium, \(v\) is the collision frequency, \(f\) is the radio wave frequency, \(N\) e is the electron density of the ionosphere, \(B\) L , \(B\) T are the components of the geomagnetic intensity in the direction of the wave vector and perpendicular to the wave vector respectively. Analyzing formulas (4)-(10), it can be seen that both the wave vector and the ionospheric refractive index affect the solution of the propagation path trajectory. At the same time, the refractive index affects the wave vector of the radio wave, and the refractive index is jointly affected by the geomagnetic field and the ionospheric electron density. Therefore, the refractive index of the ionosphere is the key factor affecting the solution of ray propagation.

[0039] To solve the ray equation of formula (4), it is also necessary to determine the initial values of the wave vector and the position of the radio wave ray. The initial value of the wave vector is:

[0040]

[0041] In the formula, \(\varphi\) and \(\Theta\) refer to the azimuth angle and elevation angle of the main beam of the transmitting antenna respectively, which is the direction with the maximum gain in the antenna directivity. And the initial value of the ray position is:

[0042]

[0043] In the formula, h0 is the height of the transmitting antenna of the short-wave station, and lat and lon are the latitude and longitude of the transmitting antenna respectively.

[0044] In this embodiment, to solve the ray equation in Equation (4), it can be seen from the calculation of the ionospheric refractive index in Equations (7)-(10) that the electron density is an important factor affecting short-wave propagation. NeQuick is an ionospheric electron density model developed jointly by the Laboratory for Aeronomy and Radio Propagation of the International Center for Theoretical Physics (ICTP) in Italy and the Institute of Geophysics, Astrophysics, and Meteorology (IGAM) of the University of Graz in Austria. The upper specification standard of the electron density of the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) is parameterized by the NeQuick model parameters, and the electron density profile is described by the semi-Epstein layer, which is given by Equation (13):

[0045]

[0046] Where:

[0047]

[0048] In the formula, N e (h) is the electron density function of altitude h, NmF2 is the monthly median of the electron density, hmF2 is the ionospheric peak height, r, g, and H0 are three empirical parameter values, H0 is the scale height at the peak height of the F2 layer, g is the gradient of H, and r characterizes the asymptote of H. Figure 5 is the comparison of the electron density profiles between the Empirical Canadian High Arctic Ionospheric Model and the International Reference Ionosphere (IRI) at the geographical location of 68°N, 24°E when UTC = 202408150800 (i.e., 08:00 on August 15, 2024, Universal Time). To ensure the accuracy of ionospheric data as much as possible during the skywave propagation process, IRI grid is used for the middle and low latitude regions passed by the ray, and E-CHAIM grid is used for the ionosphere with a latitude higher than 50°N.

[0049] Through the initial values of the wave vector and the initial values of the ray position in equations (11)-(12), and then by combining equations (4)-(10) and equations (13)-(14), the points passed by the skywave ray during its propagation in the ionosphere can be solved. Connecting these points can form the path of the skywave ray group. After solving the ray equation in the above manner, given the propagation trajectory of the ray group path, through the line integral along the curve of the group path, the group path length can be calculated as follows:

[0050]

[0051] where α is the angle between the skywave ray direction and the wave vector direction, and μ is the real part of the refractive index. The flight time of the skywave ray in the ionospheric atmosphere can be determined by the following formula:

[0052]

[0053] Assume that the change of the group path with frequency during the propagation of any shortwave ray is very small or even negligible. At this time, the second term can be eliminated, and substituting into equation (15) can simplify equation (16) to:

[0054]

[0055] There is the following relationship between the flight time tof and the time delay:

[0056]

[0057] where min{.} represents taking the minimum value, and R represents the number of skywave rays that can reach the receiving antenna. Figure 6 Shows the flight time of skywave propagation from the Xinjiang transmitting station (41οN, 84οE) to the Finnish receiving station (68οN, 24οE) at UTC = 202408280530 through the above numerical ray tracing and ionospheric background model calculations.

[0058] In this embodiment, the calculation method of the large-scale basic loss of the skywave channel includes free space loss, ionospheric absorption loss, and ground reflection loss. The calculation basis of these large-scale losses is the above numerical ray tracing algorithm and ionospheric background model. Among them, the free space loss is calculated as:

[0059]

[0060] where λ is the wavelength of the skywave, and d is the straight-line distance between the transmitting antenna and the receiving antenna. The absorption loss of the ionosphere is calculated on the premise that the propagation path and ionospheric refraction data have been obtained by numerical ray tracing, specifically as:

[0061]

[0062] Where χ is the imaginary part of the refractive index, f is still the skywave frequency, and α is still the angle between the skywave ray and the wave type. The skywave ray is reflected by both the ionosphere and the ground, so the attenuation of the ray intensity by the ground cannot be ignored. The echo loss of the ray along the ground can be calculated from the reflection coefficient as:

[0063] L g (dB) = -20 log 10 |Γ| (20)

[0064] Among them, the calculation of the reflection coefficient is related to the characteristic impedance of the medium, specifically:

[0065]

[0066] Among them, Γ is the reflection coefficient, Z L , Z0 are the characteristic impedances of the ground and air respectively (the characteristic impedance of air is 377 Ω), and ε, σ, θ are the dielectric constant, conductivity, and permeability of the ground respectively.

[0067] In this embodiment, the calculation of the large-scale total loss of the skywave channel also includes the antenna directivity gain parameter. The formula for the total loss of large-scale propagation of the skywave channel is:

[0068] L total (dB) = G tx (dB) + G rx (dB) + L1(dB) + L2(dB) + L g (dB) (22)

[0069] Among them

[0070]

[0071] Here it is assumed that the dBi gain value of an isotropic antenna is known and is 0. Figure 7 is the calculated value of the large-scale loss of skywave propagation considering two shortwave antennas, namely the double-layer log-periodic antenna and the G5RV antenna, at a frequency of 15 MHz, UTC = 202408280530 from the Xinjiang transmitter to the Finnish receiver.

[0072] In this embodiment, the calculation of the propagation parameters of the skywave channel is not limited to the above-mentioned large-scale attenuation value of intensity, and the delay distribution parameter of the skywave channel can also be calculated. Figure 8 is the delay distribution parameter of skywave propagation considering the antenna directivity parameter, at a frequency of 15 MHz, UTC = 202408280530 from the Xinjiang transmitter to the Finnish receiver.

[0073] In this embodiment, there are certain errors in the proposed propagation calculation method for short-wave skywave channels based on antenna directivity. There are three reasons for this error. Firstly, inaccurate geometric structure modeling of short-wave antennas will deteriorate the antenna directivity parameters. Secondly, the principle of the numerical ray tracing algorithm using geometric optical approximation means will deteriorate parameters such as the skywave propagation path. Thirdly, the deviation between the ionospheric background model data and the actual communication channel environment will also introduce errors.

[0074] Traditional calculation methods for short-wave skywave channel propagation loss usually rely on simplified models and do not fully integrate the influence of antenna directivity on signal propagation, resulting in insufficient prediction accuracy. Short-wave skywave communication relies on ionospheric reflection, and the propagation path is complex (involving free-space propagation, ionospheric reflection, and ground reflection). Existing methods have problems such as missing directivity gain and insufficient modeling of multimode propagation paths.

[0075] To address the above problems, this embodiment elaborates in detail the core steps of this propagation calculation method for short-wave skywave channels based on antenna directivity and numerical ray tracing. Specifically, the present invention realizes high-precision calculation of short-wave skywave channel propagation loss by integrating antenna directivity parameters, numerical ray tracing algorithms, and multi-loss coupling models, significantly enhancing the modeling ability of complex propagation paths and dynamic directivity gain.

[0076] Those of ordinary skill in the art can understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing relevant hardware through a program. This program can be stored in a computer-readable storage medium, and the storage medium can include: ROM, RAM, disk, or optical disc, etc.

[0077] The above-mentioned embodiments further elaborate in detail the purpose, technical solution, and advantages of the present invention. It should be understood that the above-mentioned embodiments are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made to the present invention within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for optimizing shortwave skywave channel propagation parameters based on antenna directivity, characterized in that: include: Obtain the directivity patterns of the transmitting and receiving antennas; A numerical ray tracing algorithm is used to determine the propagation path of skywave rays from the transmitting antenna to the receiving antenna; The free space propagation loss, ionospheric loss and ground reflection loss are calculated according to the propagation path; the directional gain correction of the signal strength on the propagation path is performed according to the directivity diagrams of the transmitting antenna and the receiving antenna; the total propagation loss is calculated based on the free space loss, ionospheric loss, ground reflection loss and antenna directivity correction value; the propagation parameters including the total propagation loss, propagation path, antenna directivity correction value and delay are output.

2. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 1, characterized in that: Obtaining the directivity diagrams of the transmitting antenna and the receiving antenna includes: obtaining material parameters, setting boundary conditions and excitation sources, defining input ports as lumped ports, inputting power values, selecting free tetrahedral meshes, and setting solvers; solving finite element problems and obtaining 3D directivity diagrams through radiation directions, and obtaining the directivity diagrams of the transmitting antenna and the receiving antenna based on the 3D directivity diagrams.

3. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 1, characterized in that: The numerical ray tracing algorithm is used to determine the propagation path of sky wave rays, including: initializing the rays, that is, taking the position of the transmitting antenna as the initial point, initializing multiple rays, each ray representing a propagation direction; tracing the propagation path of each ray according to the reflection and refraction laws of the ionosphere and the ground reflection laws, until the ray reaches the receiving antenna or exceeds the preset range; screening the propagation path to obtain an effective propagation path that can reach the receiving antenna.

4. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 1, characterized in that: The formula for calculating free space propagation loss is: Among them, λ is the wavelength of the transmitted sky wave, and d is the straight-line distance between the transmitting antenna and the receiving antenna.

5. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 1, characterized in that: Calculating ionospheric loss includes: obtaining the refractive index of the ionosphere, the frequency of the transmitted sky wave and the propagation path; and calculating the ionospheric loss using the ionospheric loss formula based on the refractive index of the ionosphere, the frequency of the transmitted sky wave and the propagation path. The expression is: Where χ is the imaginary part of the ionospheric refractive index, α is the angle between the ray direction and the wave vector direction, f is the sky wave frequency, and ray(P') is the ray trajectory reaching the receiving antenna.

6. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 1, characterized in that: The ground reflection loss calculation formula is: L g (dB)=-20log 10 |C| Where Γ is the reflection coefficient of air and ground medium.

7. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 1, characterized in that: Directional gain correction of signal strength on a propagation path includes: determining the propagation direction of the signal at a transmitting antenna and a receiving antenna according to the propagation path; obtaining antenna gains in the transmitting direction and the receiving direction according to directivity diagrams or directivity functions of the transmitting antenna and the receiving antenna, respectively; and combining the directional gains of the transmitting antenna and the receiving antenna to obtain an antenna directivity correction value.

8. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 7, characterized in that: The antenna gain in the transmitting and receiving directions is obtained as follows: the solution area is divided into a finite number of tetrahedrons by the finite element method, and the electric field in each tetrahedron is approximately represented by a basis function; the discretized frequency-domain Maxwell equations are solved to obtain the electric field strength at each point in space; finally, the antenna gain is calculated based on the electric field strength.

9. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 7, characterized in that: The core governing equation when solving the discretized frequency domain Maxwell equations is: in, is the relative magnetic permeability, ε r is the relative dielectric constant, k0 is the free space wave number, f is the radio wave frequency, is the vacuum magnetic permeability, ε0 ​​is the vacuum dielectric constant, is the Nabla operator, and E is the electric field intensity.

10. The method for optimizing shortwave skywave channel propagation parameters based on antenna directivity according to claim 7, characterized in that: The directivity function of the antenna is: Among them, U iso is the radiation intensity of the omnidirectional point source antenna at that point, Z0 is the free space wave impedance, r is the observation distance, dBi is the antenna directional gain, θ is the azimuth angle, is the elevation angle, and E is the electric field strength.

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