A method for improving the measurement accuracy of the RCS of an active antenna target

Abstract

The present invention relates to a method for improving the measurement accuracy of the RCS of an active antenna target, belonging to the field of antennas, and includes studying the electromagnetic scattering principle of the active antenna target and analyzing the scattering characteristics of a single-port active antenna; analyzing the antenna mode term and studying its influence on the scattering of the overall structure term; the present invention has the advantages of proposing a method for improving the measurement accuracy of the RCS of an active antenna target, obtaining more accurate scattering measurement data by analyzing the errors of the traditional RCS data test method for the active antenna target and removing the influence of the mode term on the scattering of the structure term.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, and particularly to a method for improving the measurement accuracy of the RCS of an active antenna target. Background Art

[0002] The test methods for the electromagnetic scattering characteristics of antenna targets are single, and it is impossible to accurately obtain the electromagnetic scattering characteristics under the working state of the antenna. As a special scatterer, the electromagnetic scattering characteristics of the antenna are related to factors such as the basic radiation performance of the antenna and the load state connected to the antenna. Generally, the electromagnetic scattering field of the antenna can be divided into two parts: the structural term and the mode term. At present, for the measurement of the electromagnetic scattering characteristics of antenna targets, the measurement methods for the electromagnetic scattering characteristics of traditional targets are adopted, that is, when the antenna load is artificially set to be matched, the antenna target is used as an ordinary target for electromagnetic scattering characteristics measurement. The data obtained by this traditional method is not accurate. Although the mode term scattering is much smaller than the structural term scattering when the antenna and the feeding network are well matched, in today's increasingly fierce electronic countermeasures, the accurate measurement and reduction of the antenna mode term scattering have attracted more and more attention. Therefore, for this special scatterer of the antenna, the measurement method for its electromagnetic scattering characteristics under the actual working state needs to be studied urgently.

[0003] In view of the above deficiencies, a method for improving the measurement accuracy of the RCS of an active antenna target is required. Summary of the Invention

[0004] (I) Technical Problems to be Solved

[0005] The technical problem to be solved by the present invention is that there is an urgent need to study the measurement method for the electromagnetic scattering characteristics under the actual working state.

[0006] (II) Technical Solutions

[0007] To solve the above technical problems, the present invention provides a method for improving the measurement accuracy of the RCS of an active antenna target, including the following steps.

[0008] Ⅰ. Analysis of the scattering characteristics of a single-port active antenna, specifically:

[0009] Arbitrarily take a cross-section S1 at the feeding port of the antenna, and select a closed curve as the antenna-enclosing S2 at a distance r = r0 from the antenna. Through analysis, the total scattering field E S (Z i ) is:

[0010] E S (Z i ) = E S (Z c ) + E a (Z i)

[0011] Among them, E S (Z c ) is the scattered field of the structural item, representing the scattered field when the antenna is perfectly matched with the load;

[0012] E a (Z i ) is the scattered field of the antenna pattern, representing the scattered field generated when a part of the incident wave is absorbed and another part is reflected when the receiver is terminated with an arbitrary load, and then re-radiated back into free space through the antenna;

[0013] II. Extraction of the scattered field of the structural item of the active antenna, obtaining:

[0014]

[0015] Among them, Z in is the input impedance of the antenna, and Z c is the characteristic impedance of the transmission line;

[0016] T1 is the terminal reflection coefficient.

[0017] As a further description of the present invention, preferably, the terminal reflection coefficient T1 is specifically:

[0018]

[0019] Z1 is the terminal load impedance of the antenna.

[0020] As a further description of the present invention, preferably, the scattered field E S (Z c ) is defined as:

[0021]

[0022] is the basis function of the outgoing wave;

[0023] is the scattering amplitude when the antenna is load-matched.

[0024] As a further description of the present invention, preferably, the scattering amplitude when the antenna is load-matched is defined as:

[0025]

[0026] The value after the equal sign is the scattering field amplitude value generated by the incident wave a i in the far field.

[0027] As a further illustration of the present invention, preferably, when analyzing the scattering characteristics of the single-port active antenna, first expand the radiation field and scattering field of the antenna with vector spherical wave functions in the region outside the plane S2, and obtain:

[0028]

[0029] where a i and b i represent the complex amplitudes of the ith incident wave and outgoing wave;

[0030] and represent the basis functions of the incident wave and outgoing wave respectively.

[0031] As a further illustration of the present invention, preferably, the reflection / reception amplitude b0 of the antenna is expressed as:

[0032]

[0033] The first term on the right side of the equal sign represents the amplitude value of the reflected field generated by the incident wave a0 at the plane S1;

[0034] The second term on the right side of the equal sign represents the amplitude value of the scattered field generated by the incident wave a i in the far field at the plane S1.

[0035] As a further illustration of the present invention, preferably, when the load is mismatched with the port, the reflection / reception amplitude b0 of the antenna is expressed as:

[0036]

[0037] Γ l is the reflection coefficient of the receiver load;

[0038] Γ a is the antenna reflection coefficient;

[0039] is the matched reception amplitude.

[0040] As a further illustration of the present invention, preferably, the reflection coefficient Γ l of the receiver load is expressed as:

[0041]

[0042] When in the ideal state, that is, when the load is matched with the port, Z l = Z c , then Γ l = 0.

[0043] As a further illustration of the present invention, preferably, to separate the structural term scattered field and the mode term scattered field from the scattered field, first short-circuit the load, then we have:

[0044]

[0045] where Z c is the characteristic impedance of the transmission line;

[0046] T a is the antenna reflection coefficient;

[0047] is the received amplitude in the matched state;

[0048] is the radiated electric field in the case of unit amplitude excitation.

[0049] As a further illustration of the present invention, preferably, secondly, open-circuit the load to obtain the open-circuit scattered field:

[0050]

[0051] Obtain the antenna structure scattered field and the antenna mode term scattered field from the scattered field of the short-circuited load and the scattered field of the open-circuited load, and finally substitute them into the basic theoretical formula of antenna scattering to obtain the scattered field under any load condition.

[0052] (III) Advantageous Effects

[0053] The above technical solution of the present invention has the following advantages:

[0054] The present invention proposes a method for improving the measurement accuracy of the target RCS of an active antenna. By analyzing the errors of the traditional method for testing the RCS data of an active antenna target, the influence of the mode term on the structural term scattering is removed, and more accurate scattered measurement data are obtained. Description of the Drawings

[0055] Figure 1 is the flowchart of the present invention;

[0056] Figure 2 is the schematic diagram of antenna scattering of the present invention. Detailed Embodiments

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. 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.

[0058] A method for improving the measurement accuracy of the RCS of an active antenna target. First, an analysis method is given to analyze the electromagnetic scattering characteristics of a single-port active antenna, and the principle of the superposition and separation of the scattering of the target structure term and the mode term of the active antenna is obtained; the separation method of the scattering characteristics of the mode term and the structure term is analyzed, and the influence of the mode term scattering is removed; finally, according to the obtained influence relationship between the structure term and the mode term, the simulation results of a typical active patch antenna target are carried out to obtain higher-precision target RCS scattering data.

[0059] The method specifically includes:

[0060] S1. Analysis of the electromagnetic scattering principle of a single-port active antenna

[0061] The schematic diagram of antenna scattering is as Figure 2 shown. The antenna has special scattering characteristics, and its scattering characteristics are not only related to the geometric structure of the antenna itself, but also related to the transmitting and receiving characteristics of the antenna. Compared with ordinary targets, its scattering mechanism is more complex. As Figure 2 shown, S1 is an arbitrary cross-section taken at the feeding port of the antenna as a reference plane; S2 is a closed surface surrounding the antenna at a distance r = r0 from the antenna; (a0, b0) are the amplitudes of the incident wave and the outgoing wave at the surface S1. In the region outside the surface S2, the radiation field and the scattering field of the antenna are expanded using vector spherical wave functions, and the following can be obtained:

[0062]

[0063] where a i and b i represent the complex amplitudes of the th incident wave and the outgoing wave;

[0064] and respectively represent the basis functions of the incident wave and the outgoing wave.

[0065] Then the scattering characteristics of the antenna can be expressed as:

[0066]

[0067] Expanding it, we get:

[0068] b0 = S 00 a0 + [S 0j [a j

[0069] [b0] = [S i0 a0 + [S ij [a j

[0070] Expanding, the reflection / reception amplitude of the antenna can be obtained as:​​

[0071]

[0072] The first term on the right side of the equal sign represents the amplitude value of the reflected field generated by the incident wave a0 at the surface S1;

[0073] The second term on the right side of the equal sign represents the amplitude value of the received field generated by the incident spherical wave a i at the surface S1.

[0074] From this, it can be seen that the meaning of the above formula is: at the antenna feed surface, the energy transmitted to the receiver is the sum of the port reflection energy and the antenna received energy.

[0075] Expanding from the above formula, it can be seen that the amplitude of the radiation / scattering in the far field of the antenna is:

[0076]

[0077] The first term on the right side of the equal sign represents the amplitude value of the reflected field generated by the incident wave a0 at the surface S1;

[0078] The second term on the right side of the equal sign represents the incident wave a i at the surface S1 and the amplitude value of the scattered field generated in the far field.

[0079] When the antenna is in the radiation state, a i = 0 (i≠0), then the above two expressions can be expressed as:

[0080] b0 = S 00 a0 (reflection amplitude)

[0081] b i = S i0 a0 (radiation amplitude)

[0082] Among them,

[0083] (antenna reflection coefficient)

[0084] Therefore, represents the radiation characteristics of the antenna.

[0085] When the antenna is in the receiving and scattering states, the incident wave b0 is transmitted to the receiver through the antenna feeder line. Due to the incomplete matching between the antenna and the receiver load, the outgoing wave is a0, and the two satisfy the relationship a0 = Γ l b0, where Γ l is the reflection coefficient of the receiver load.

[0086]

[0087] When in the ideal state, that is, when the load is matched with the port, Z l = Zc , Γ l = 0, a0 = 0, then can be changed to:

[0088]

[0089] represents the matched receiving amplitude. If the load does not match the port, then can be transformed to:

[0090]

[0091] it can be obtained that:

[0092]

[0093] The above formula indicates the relationship between the receiving amplitude and the matched receiving amplitude when the antenna is terminated with a general load. Among them, Γ l is the reflection coefficient of the receiver load; Γ a is the antenna reflection coefficient; is the matched receiving amplitude.

[0094] From and a0 = Γ l b0, it can be obtained that:

[0095]

[0096] Similarly, define as the scattering amplitude when the antenna load is matched:

[0097]

[0098] Combining the above formula, can be written as:

[0099]

[0100] where b i represents the antenna scattering amplitude. Multiply each term in the above formula by the outgoing spherical wave basis function to obtain the scattering field of the i-th port. By summing the external scattering field vectors of the antenna, the total scattering field of the antenna can be obtained as:

[0101]

[0102] Define:

[0103]

[0104]

[0105] Where Z l and Z c are the load impedance and the matching load of the antenna, respectively.

[0106] Substituting the two defined equations into the total scattering field equation of the antenna, the total scattering of the antenna can be expressed as:

[0107] E S (Z l ) = E S (Z c ) + E a (Z l )

[0108] The first term E S (Z c ) of this equation is defined as the structural term scattering field, which represents the scattering field when the antenna is perfectly matched with the load. At this time, due to the perfect match of the antenna, Γ l = 0, the incident electromagnetic wave is completely absorbed, and the scattering field only comes from the scattering of the antenna's own geometric structure; the second term E a (Z l ) is defined as the antenna mode term scattering field, which represents the scattering field generated when a part of the incident wave is absorbed and another part is reflected when the receiver is terminated with an arbitrary load, and then re-radiated back into free space through the antenna.

[0109] Dividing the radar cross section σ Total of the antenna into the structural term RCS (σ S ) and the mode term RCS (σ a ), and the phase difference between the two is Ф. After superposition, we can get:

[0110]

[0111] S2. Method for Extracting the Structural Term Scattering Field of an Active Antenna

[0112] The basic theoretical formula for antenna scattering is:

[0113]

[0114] In the formula, is the terminal reflection coefficient, that is, the reflection coefficient looking from the transmission line to the load; is the antenna reflection coefficient; Z1 is the terminal load impedance of the antenna; Z in is the input impedance of the antenna; Z c is the characteristic impedance of the transmission line. is the received amplitude in the matching state, is the radiated electric field in the case of unit amplitude excitation.

[0115] To separate the structural term scattering field and the mode term scattering field from the scattered field, first short-circuit the load, Z1 = 0; T1 = 0, then the above equation becomes:

[0116]

[0117] Secondly, open-circuit the load, Z1 = ∞; T1 = 1, to obtain the scattered field of its open circuit:

[0118]

[0119] Solving from the above two equations gives:

[0120]

[0121]

[0122] E S (Z c ) is the scattering field of the antenna structural term, is the scattering field of the antenna mode term. By substituting Equation E S (Z c ) and Equation into the basic theoretical formula of antenna scattering, the scattered field under any load condition can be obtained:

[0123]

[0124] This method can calculate the structural term scattering, mode term scattering of the antenna and the total scattering under any load condition based on the scattered fields of the open-circuit and short-circuit models, as well as the port characteristics of the antenna, and has strong operability.

[0125] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the measurement accuracy of the RCS of an active antenna, characterized in that: Including the following steps, Ⅰ. Analysis of the scattering characteristics of a single-port active antenna, specifically: Arbitrarily take a cross-section S1 at the feeding port of the antenna, and select a closed curve as the antenna-enclosing S2 at a distance r = r0 from the antenna. The total scattered field E of the antenna is obtained through analysis. S (Z i ) is as follows: E S (Z i ) = E S (Z c ) + E a (Z i ) Among which E S (Z c ) is the scattered field of the structural item, representing the scattered field when the antenna is perfectly matched with the load; E a (Z i ) is the scattered field of the antenna pattern, which represents the scattered field generated when a part of the incident wave is absorbed and the other part is reflected when the receiver is terminated with an arbitrary load, and then re-radiated back into free space through the antenna; Ⅱ. Extraction of the scattered field of the structural term of the active antenna, obtaining: Among them, Z in is the input impedance of the antenna, and Z c is the characteristic impedance of the transmission line; T1 is the terminal reflection coefficient.

2. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 1, characterized in that: The terminal reflection coefficient T1 is specifically: Z1 is the terminal load impedance of the antenna.

3. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 1, characterized in that: Structural item scattered field E S (Z c ) is defined as: is the basis function of the outgoing wave; is the scattering amplitude when the antenna load is matched.

4. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 3, characterized in that: Scattering amplitude during antenna load matching It is defined as: The value after the equal sign is equal to the incident wave a i The amplitude value of the scattered field generated in the far field.

5. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 1, characterized in that: When analyzing the scattering characteristics of a single-port active antenna, first expand the radiation field and scattered field of the antenna with vector spherical wave functions in the region outside the surface S2, obtaining: where a i and b i represent the complex amplitudes of the \(i\)-th incident and outgoing waves; and respectively represent the basis functions of the incident wave and the outgoing wave.

6. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 5, characterized in that: The reflection / reception amplitude b0 of the antenna is expressed as: The first term on the right side of the equal sign represents the amplitude value of the reflected field generated by the incident wave a0 at the surface S1; The second term on the right side of the equal sign represents the amplitude value of the scattered field generated in the far field by the incident wave a at the surface S1. i ​ 7. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 6, characterized in that: When the load is mismatched with the port, the reflection / reception amplitude b0 of the antenna is expressed as: Γ l is the reflection coefficient of the receiver load; Γ a is the antenna reflection coefficient; To match the received amplitude.

8. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 7, characterized in that: Reflection coefficient Γ of the receiver load l It is expressed as: When in an ideal state, that is, when the load matches the port, Z l = Z c , then Γ l = 0.

9. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 1, characterized in that: To separate the structural term scattered field and the mode term scattered field from the scattered field, first short-circuit the load, then: Among them, Z c is the characteristic impedance of the transmission line; T a is the antenna reflection coefficient; The received amplitude in the matching state; Radiation electric field for the case of unit amplitude excitation.

10. A method for improving the measurement accuracy of the target RCS of an active antenna according to claim 9, characterized in that: Secondly, open-circuit the load to obtain the open-circuit scattered field: Obtain the antenna structure scattered field and the antenna mode term scattered field from the scattered field of the short-circuited load and the scattered field of the open-circuited load, and finally substitute them into the basic theoretical formula of antenna scattering to obtain the scattered field under any load condition.

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