CN107402383B - A kind of bi-phase modulated plate and method for implementing radar frequency spectrum shift - Google Patents

Abstract

The present invention relates to the field of wireless communication, in particular to a two-phase modulation board and a method for implementing radar spectrum shifting. The two-phase modulation board is composed of a frequency selective surface FSS, a dielectric spacer layer and a metal grounding layer; by setting three layers based on the FSS An adjustable frequency reflection modulation board is used to construct a two-phase modulation board; the FSS is constructed as an adjustable resistance, capacitance and inductance; a mathematical model is established by using a dynamic transmission line equivalent circuit; the spectrum shift of a two-phase modulation surface is studied according to the mathematical model; When the two-phase modulation surface is in the state of high impedance and low impedance, the average reflection coefficient in the cycle time is 0, and the energy of the radar reflected echo is moved to the sideband; in other cases, there will be multiple reflections in the modulation board, The frequency response characteristic of the system will be changed; the two-phase modulating board designed in the present invention can transfer the energy of the reflected echo to the sideband, reduce the reflection coefficient at the same time, and have good wave-absorbing ability.

Description

A two-phase modulation board and method for implementing radar spectrum shifting

technical field

The invention relates to the field of radar stealth, in particular to a two-phase modulation board and a method for implementing radar spectrum shifting.

Background technique

With the development of radar technology, the frequency range of radar has been extended from 8-12GHz (X frequency band) and 12-18GHz (Ku frequency band) to 2-18GHz. Therefore, it is necessary to propose materials that can work in low frequency bands and high bandwidth to design radar absorbers. oscilloscope. UHF (300MHz～3000MHz) radar uses modulated electric waves and directional antennas to emit a beam of electromagnetic energy. Using its relatively long wave wavelength, it can detect the speed, angle and other characteristics of ultra-long-distance moving targets, and is widely used in strategic early warning. In various land, sea and air detection systems. The radar signal transmitted in this frequency band has the characteristics of flexible incoming wave direction, large bandwidth (>20%), it is very likely to use multiple frequency points or frequency modulation, and the waveform adopts Linear Frequency Modulation (LFM). The main threat of the UHF frequency band comes from the long-range radar system. Their working methods are flexible and the bandwidth is large (>20%). Meet the right method between the right, and the dielectric constant and magnetic conduct rate are fixed, related parameters are positive, and have a positive refractive index, so they cannot flexibly change the electromagnetic characteristics of the system. It is referred to as RCS) Materials.

In recent years, various artificial composite materials have been used to manufacture ultra-thin broadband radar absorbers. Among them, electromagnetic metamaterials have become a research hotspot in industry and academia. It is a kind of dielectric constant and magnetic permeability that can be controlled artificially. A new type of artificial composite electromagnetic material that can be positive and negative can be used to design radar absorbing materials (Radar absorbing materials, referred to as RAM), and spectrum shifting based on electromagnetic metamaterials is a key technology to realize the structural design of radar absorbers. Utilizing the controllability of the electromagnetic properties of the electromagnetic metamaterial, a spectral reflection modulation plate can be designed to change the electromagnetic properties of the electromagnetic waves irradiated on the plate.

Frequency selecting the surface (FSS) is a two -dimensional cycle array structure, which can be regarded as a space filter. factors. The literature proposes a variety of FSS -based radar suction structures, such as single -layer resistance reflex suctionapses, multi -layer metal super material suction vesters, non -magnetic broadband radar sucks, etc. These structures each have their own advantages and disadvantages, and they show different romance capabilities, which are suitable for specific operating frequency and working bandwidth. FSS -based reflex structures can be classified as damaged FSSS and metal FSSS. The former uses resistance and electronics to minimize scattering energy, and the latter is used to improve the working bandwidth. Once the FSS -based radar -absorbing surface is designed and manufactured, its electromagnetic characteristics will remain fixed, so it cannot be used for complex and variable environments, and it cannot be shifted to the complex bandwidth, multi -directional, and different polarized complex radar signals. In order to perform full reflection or transmission of incident electromagnetic waves at the resonance frequency, a two -phase modulation of radar incident wave waves needs to be used with simple equivalent circuits, and then dynamic changes between high and low impedance dynamic dynamic dynamic changes.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to overcome the deficiencies in the prior art, proposes a kind of two-phase modulation board and method that implements radar spectrum shifting, including:

A two-phase modulation board for implementing radar spectrum shifting includes a two-phase modulation board, and the two-phase modulation board includes a frequency selective surface FSS, a dielectric spacer layer and a metal ground layer.

Further, the FSS is the active impedance layer, the medium partition layer is a medium layer with a thickness of D, and the metal ground layer is a metal backplate. transition between states. Ideally, the controllable active layer is converted between two states: completely transparent (R = ∞) and complete reflection (R = 0).

Further, when d=λ/4, the phase difference of the reflected signals in these two states is 180°, and the composite signal is equivalent to a binary phase modulation signal, also called a binary phase modulation board.

Further, the active impedance layer with adjustable impedance includes a reflective oscillator array of an adjustable semiconductor, wherein the reflective oscillator array of an adjustable semiconductor is a periodic structure, then the transient characteristic impedance of the FSS is based on the equivalent resistance, Capacitance and inductance are derived.

Furthermore, the two-phase modulation board is constructed as an equivalent circuit of the FSS dynamic transmission line, and the adjustable FSS impedance and/or FSS admittance are designed to obtain the impedance relationship of the two-phase modulation surface.

Further, the FSS dynamic transmission line equivalent circuit also includes the transmission line equivalent circuit of the phase-modulated surface absorbing material, including a terminal short-circuit transmission line with length d, characteristic admittance Y, and propagation constant β.

The present invention proposes a method for moving radar spectrum by using a two-phase modulation board, including:

Based on FSS, a three-layer adjustable frequency reflection modulation board is set to construct a two-phase modulation board;

constructing the FSS as a resistor capacitor and an inductor;

Establish a mathematical model using the equivalent circuit of a dynamic transmission line;

The spectral shift of the biphasic modulation plane is studied according to the mathematical model.

Further, the frequency reflection modulation board is equivalent to resistance, capacitance and inductance, including: the two-phase modulation board is composed of a reflective oscillator array loaded with adjustable semiconductors, which is a periodic structure, and the two-phase modulation board The transient characteristic impedance of can be represented by a set of effective resistance, capacitance and inductance;

Further, the establishment of a mathematical model using the dynamic transmission line equivalent circuit includes: the transmission line equivalent circuit of the phase-modulated surface absorbing material includes a terminal short-circuit transmission line with a length of d, a characteristic admittance of Y, a propagation constant of β, and a variable conductance at the input Na Y(t):

Among them, τ is the duration of the variable admittance Y(t) in the state Y ₁ within a period, that is, Y(t) transfers from the state Y ₁ to the state Y ₂ at the time t; T is used to control Y(t ) The signal cycle of the state;

The effective impedance of the equivalent circuit of the transmission line is:

in, is the FSS surface characteristic impedance, j represents the imaginary number unit, ω is the angular frequency; R _s is the FSS surface equivalent resistance, L _s is the FSS surface equivalent inductance, C _s is the FSS surface equivalent capacitance, Z ₀ represents the free space impedance; The medium whose propagation constant is β is free space, β=2π/λ, and λ is the wavelength corresponding to the main frequency of the incoming signal;

Taking the reciprocal of the effective impedance of said equivalent circuit, the input admittance of the state _Y1 and state _Y2 phase modulation surfaces is obtained, expressed as:

Y _in1 = y ₁ -jy ₀ cotβd

Y _in2 = y ₂ -jy ₀ cotβd

Among them, Y ₀ is the admittance of free space, and the reflection coefficients of the incident end in state Y ₁ and state Y ₂ are respectively:

ρ ₁ and ρ ₂ are complex numbers. When the two-phase modulation surface exhibits spectrum shift performance at a specific frequency point, the average reflection coefficient in the period time is 0, namely:

Among them, ρ(t) is the reflection coefficient. If the modulation signal is an ideal square wave, the average reflection coefficient can be expressed as:

Therefore there is When τ = 0.5T, there are:

Let d=0.25λ, λ is the wavelength corresponding to the main frequency of the incoming wave signal, at this time, βd=0.5π, cotβd=0, it can be further obtained:

Divide the impedance of FSS into Z ₁ =1/Y ₁ , Z ₂ =1/Y ₂ , and the corresponding impedance relationship is:

Further, the mathematical model to study the spectrum shift of the two-phase modulation surface includes: according to the two states of high and low impedance obtained by the dynamic transmission line equivalent circuit, two-phase constant-mode modulation is performed on the incident wave to realize the spectrum shift of the reflected wave .

The two-phase modulation plate designed by the invention can transfer the energy of the reflected echo to the sideband, reduce the reflection coefficient at the same time, and has good wave-absorbing ability.

Description of drawings

Fig. 1 is the schematic diagram of FSS three-layer reflective modulation plate of the present invention;

Fig. 2 is a schematic diagram of the state of the reflective phase modulation plate of the present invention;

Fig. 3 is the flow chart of the method for moving the radar spectrum using a two-phase modulation board in the present invention;

Fig. 4 is the equivalent circuit of the transmission line of the two-phase modulation board of the present invention;

Fig. 5 shows the reflection phase and reflection coefficient of the ideal two-phase modulation plate of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages 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. Obviously, the described embodiments are only a part of the embodiments of the present invention, and Not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Below in conjunction with accompanying drawing and specific embodiment the present invention will be further described:

The present invention proposes a two-phase modulation board and method for implementing radar spectrum shifting, including:

A device for shifting the radar spectrum of a two-phase modulation board includes a two-phase modulation board, and the two-phase modulation board includes an FSS, a dielectric spacer layer and a metal ground layer, as shown in FIG. 1 .

Furthermore, the FSS is the active impedance layer, the dielectric spacer layer is a dielectric layer with a thickness of d, and the metal ground layer is a metal backplane. As shown in Figure 2, the impedance of the active impedance layer can vary with the external control signal. switch between impedance states. Ideally, the controllable active layer switches between fully transparent (R=∞) and fully reflective (R=0) states.

Further, when d=λ/4, the phase difference of the reflected signals in these two states is 180°, and the composite signal is equivalent to a binary phase modulation signal, also called a binary phase modulation board.

Furthermore, when the unit intensity plane wave with the center frequency f _c irradiates the surface vertically, the reflected signals can be expressed as cos(2πf _c t) and cos(2πf _c t+βd), where β=2π/λ is the electromagnetic wave The transmission constant in the medium layer.

Further, the active impedance layer with adjustable impedance includes a reflective oscillator array of an adjustable semiconductor, wherein the reflective oscillator array of an adjustable semiconductor is a periodic structure, then the transient characteristic impedance of the FSS is based on the equivalent resistance, Capacitance and inductance are derived.

Furthermore, the two-phase modulation board is constructed as an equivalent circuit of the FSS dynamic transmission line, and the adjustable FSS impedance and/or FSS admittance are designed to obtain the impedance relationship of the two-phase modulation surface.

A method for moving radar spectrum using a two-phase modulation board, as shown in Figure 3, comprising:

Based on FSS, a three-layer adjustable frequency reflection modulation board is set to construct a two-phase modulation board;

The FSS is equivalent to a resistance capacitance and an inductance;

Establish a mathematical model using the equivalent circuit of a dynamic transmission line;

The spectral shift of the biphasic modulation plane is studied according to the mathematical model.

Further, the equivalent of the frequency reflection modulation board as a resistance capacitance and an inductance includes: the two-phase modulation board is composed of a reflective oscillator array loaded with an adjustable semiconductor, which is a periodic structure, and the transient state of the two-phase modulation board is The characteristic impedance of can be represented by a set of effective resistance, capacitance and inductance;

Further, the establishment of a mathematical model using the dynamic transmission line equivalent circuit includes: the transmission line equivalent circuit of the phase-modulated surface absorbing material includes a terminal short-circuit transmission line with a length of d, a characteristic admittance of Y, a propagation constant of β, and a variable conductance at the input Nano Y(t), the medium with the propagation constant β provides a phase difference between the FSS and the ideal electrical conductor PEC, where the PEC can be a metal backplane, as shown in Figure 4:

Among them, 一 is a duration of the variable guidance of Na Y (T) in the period of the state, that is, the time Y (T) is transferred from the state y ₁ to the state y ₂ ; T is used to control Y (T T ₎ ) The signal cycle of the state;

The effective impedance of the equivalent circuit of the transmission line is:

in, is the FSS surface characteristic impedance, j represents the imaginary number unit, ω is the angular frequency; R _s is the FSS surface equivalent resistance, L _s is the FSS surface equivalent inductance, C _s is the FSS surface equivalent capacitance, Z ₀ represents the free space impedance; The medium whose propagation constant is β is free space, β=2π/λ, and λ is the wavelength corresponding to the main frequency of the incoming signal;

Further, calculate the reciprocal of the effective impedance of the equivalent circuit to obtain the input admittance of the state _Y1 and state _Y2 phase modulation surfaces, expressed as:

Y _in1 = y ₁ -jy ₀ cotβd

Y _in2 = y ₂ -jy ₀ cotβd

Among them, Y ₀ is the admittance of free space, and the reflection coefficients of the incident end in state Y ₁ and state Y ₂ are respectively:

Among them, the magnitudes of reflection coefficients at the incident end in state Y ₁ and state Y ₂ are:

ρ ₁ and ρ ₂ are complex numbers. When the two-phase modulation surface exhibits spectrum shift performance at a specific frequency point, the average reflection coefficient in the period time is 0, namely:

Among them, ρ(t) is the reflection coefficient. If the modulation signal is an ideal square wave, the average reflection coefficient can be expressed as:

According to the above formula, it can be obtained

Further, when τ=0.5T, then:

According to the above formula, it can be obtained At this point, βd=0.5π, cotβd=0, it can be further obtained:

Let d=0.25λ, then:

Divide the impedance of FSS into Z ₁ =1/Y ₁ , Z ₂ =1/Y ₂ , and the corresponding impedance relationship is:

Further, in practical applications, the active impedance layer of the two -phase adjustment surface is usually formed by the electrical FSS controlled by the PIN diode.

Based on the designed two-phase modulation board, the reflection characteristics under different equivalent circuit lengths are shown in Table 1.

Table 1 Reflection characteristics under different equivalent circuit lengths

d=0.25λ_c d≠0.25λ_c average reflection coefficient 0 Proportional to cos(βd) reflective properties Front section and metal backplane reflection multiple internal reflections

Further, the mathematical model to study the spectrum shift of the two-phase modulation surface includes: according to the two states of high and low impedance obtained by the dynamic transmission line equivalent circuit, two-phase constant-mode modulation is performed on the incident wave to realize the spectrum shift of the reflected wave .

The two-phase modulation plate designed by the invention can transfer the energy of the reflected echo to the sideband, reduce the reflection coefficient at the same time, and has good wave-absorbing ability.

As a supplementary method, the general single -layer modulation surface has only one layer of active impedance layer and a metal backboard. In some special applications, such as the tail of the missile, this structure is very thin, and the incident electromagnetic waves from two directions need to be shielded. At this time, it will be more effective to replace the metal backplate with another layer of active impedance layer. At work, the impedance of the two -layer active impedance layer can change. If it is controlled for a period of time, repeat this process can achieve good suction performance in two directions.

Further, ideally, the reflection phase and reflection coefficient of the modulation board are shown in Figure 5. Ideally, when the impedance Z ₁ ≈0 ohm of the modulation board, ρ ₁ →-1, the phase is opposite; Z ₂ ≈ When ρ Om, → ₁ →+1, the phase of the phase is the same. At this time, the radar incident wave is only reflected at the front end of the frequency modulation surface and the metal back plate, and multiple reflections will not occur inside. Therefore, within the cycle time T, the average reflection coefficient ρ _average = 0, and the ability of the radar to reflect echoes It was moved to the side petals of the signal. When d≠0.25λ, ρ _average is proportional to cos(βd), and part of the incident wave at the front end will enter the inside of the modulation plate, causing multiple reflections and changing the frequency response characteristics of the system.

Furthermore, the traditional reflective modulation board has only one layer of FSS, and the FSS single-layer reflective structure is a periodic array composed of a large number of passive resonant units, whose impedance is fixed and cannot dynamically change the impedance state with external control signals. Although the traditional one-layer FSS can totally reflect or fully transmit the incident electromagnetic wave at the resonant frequency, it cannot be realized by a simple equivalent circuit, nor can it dynamically change the reflection state.

The frequency reflection modulation plate of the present invention is designed as a three-layer structure, which is composed of a reflective oscillator array loaded with adjustable semiconductors. It is a periodic structure, and its transient characteristic impedance can be determined by a set of effective resistance, capacitance and inductance. Said; no matter what the radar incident signal presents a polarization method, it is equivalent to applying voltage incentives to the modulation board, which will generate resonance current. This current is controlled by the adjustable semiconductor on the reflection modulation board; Form the two states of high and low impedance, and then modify the two -phase constant mode of incident waves; the two -phase adjustment board designed by the present invention can move the energy of the reflection echo to the side. At the same time, the reflection coefficient can be reduced. Absorbing ability.

It should be understood that the above are all different implementation modes of the present invention, and for parts not described in the device embodiments, reference may be made to the descriptions of corresponding parts in the method embodiments, and vice versa.

The above embodiments of the present invention have further described the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above-mentioned embodiments or examples are only preferred embodiments of the present invention, and are not intended to limit the present invention. , any modification, equivalent replacement, improvement, 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 (4)

1. A method for carrying out radar spectrum shifting by adopting a two-phase modulation plate is characterized by comprising the following steps:

setting three layers of adjustable frequency reflection modulation plates based on the frequency selective surface FSS to construct a two-phase modulation plate;

constructing the FSS as a resistor, a capacitor and an inductor;

establishing a mathematical model by using a dynamic transmission line equivalent circuit;

carrying out frequency spectrum shifting of the two-phase modulation surface according to the mathematical model;

the method for establishing the mathematical model by using the dynamic transmission line equivalent circuit comprises the following steps that the transmission line equivalent circuit of the phase modulation surface wave-absorbing material comprises a terminal short-circuit transmission line with the length of d, the characteristic admittance of Y and the propagation constant of β, and the variable admittance of an input end Y (t):

wherein τ is the variable admittance Y (t) in state Y within one period₁I.e. from state Y (t) at time Y (t)₁Transition to State Y₂(ii) a T is the signal period used to control the state of Y (T);

the effective impedance of the transmission line equivalent circuit is as follows:

wherein,is the FSS surface characteristic impedance, j represents the imaginary unit, ω is the angular frequency, R_sIs FSS surface equivalent resistance, L_sIs FSS surface equivalent inductance, C_sIs FSS surface equivalent capacitance, Z₀The medium with the propagation constant of β is free space, β is 2 pi/lambda, and lambda is the wavelength corresponding to the main frequency of the incoming signal;

the effective impedance of the equivalent circuit is inverted to obtain a state Y₁And state Y₂Input admittance to the phase modulation surface, denoted as:

Y_in1＝Y₁-jY₀cotβd

Y_in2＝Y₂-jY₀cotβd

wherein, Y₀Is admittance of free space, state Y₁And state Y₂The following reflection coefficients at the incident end were:

ρ₁and rho₂Complex, mean reflection coefficient rho over a period time when the bi-phase modulation surface exhibits spectral shifting behavior at a particular frequency point_averageIs 0, namely:

where ρ (t) is the reflection coefficient, and if the modulation signal is an ideal square wave, the average reflection coefficient ρ is_averageCan be expressed as:

when τ is 0.5T, then:

when d is 0.25 λ, there are:

dividing the impedance of FSS into Z₁＝1/Y₁，Z₂＝1/Y₂The corresponding impedance relationship is as follows:

2. the method for radar spectrum shifting by using the two-phase modulation board according to claim 1, wherein the setting of the three-layer adjustable frequency reflection modulation board based on the FSS to construct the two-phase modulation board comprises: the two-phase modulation board is constructed into a three-layer structure of an adjustable FSS, a medium spacing layer and a metal grounding layer.

3. The method of claim 1, wherein the equivalent of the FSS as a resistor, a capacitor, and an inductor comprises: the frequency selective surface FSS is a periodic structure whose transient characteristic impedance is represented by a set of effective resistance, capacitance and inductance.

4. The method of claim 1, wherein the performing the spectrum shifting of the two-phase modulation plane according to the mathematical model comprises: and according to the high and low impedance states obtained by the dynamic transmission line equivalent circuit, performing two-phase constant mode modulation on the incident wave of the radar to realize the frequency spectrum shifting of the reflected wave.