A planar orthogonal antenna array, a radiometer therefor, and a detection method therefor

Abstract

The present invention relates to the field of microwave radiometers, and in particular to a planar orthogonal antenna array, a radiometer thereof, and a detection method thereof. The radiometer comprises: a planar orthogonal antenna array, a common noise source, a first and a second calibration switch, a correlation system receiver, and a complex correlator; wherein the planar orthogonal antenna array comprises: a first planar subarray and a second planar subarray arranged orthogonally in space, wherein the first planar subarray and the second planar subarray comprise: an independent feeding system, and have the same phase center and the same beam pointing, for simultaneously observing the radiation signal of the same target, and outputting independent observation signals respectively. The planar orthogonal antenna array, the radiometer thereof, and the detection method thereof provided by the present invention realize a spatial narrow beam by correlating two planar orthogonal antenna arrays, simplify the calibration scheme, solve the noise interference introduced by the feed line loss and antenna loss before the calibration switch, and reduce the system complexity and implementation cost.

Description

Technical Field

[0001] The invention relates to the field of microwave radiometers, and in particular to a planar orthogonal antenna array, a radiometer thereof and a detection method thereof. Background Art

[0002] Passive microwave remote sensing radiometer is one of the important means to realize earth remote sensing observation. It receives the radiation signal of the observed target to obtain the brightness and temperature distribution of the target area, so as to further analyze the various physical characteristics of the target. In microwave radiometer observation, the size of the antenna array determines the spatial resolution of the observation, and the performance of the receiver affects the stability and sensitivity of the system. Both are important components of the radiometer system. At present, the radiation measurement technology mainly includes a single-channel traditional receiver architecture measurement system and a multi-channel correlation receiver architecture measurement system. Compared with the single-channel traditional architecture radiometer, the correlation architecture radiation measurement system contains two independent receivers and a complex correlator. While completing the basic measurement, the relevant information of the observed target signal can be obtained through the correlator to achieve the measurement of more signals. Most of the current new system and new concept radiometers are based on the design architecture of the correlation system.

[0003] The radiation measurement technology based on the correlation system has been developed from radio astronomy, such as interferometric measurement technology, and has been applied to earth remote sensing, namely interferometric synthetic aperture microwave radiometer technology (reference [1]: CSRuf, CTSwift, ABTanner and DMLe Vine, "Interferometric synthetic aperture microwave radiometry for the remote sensing of the earth", IEEE Trans. GRS, Vol. 26, No. 5, pp. 597-611, Sep. 1988). Interferometric synthetic aperture technology disperses a large aperture antenna into several small aperture antennas, measures the signals of these small aperture antennas separately and correlates them, and realizes the spatial frequency domain measurement of the brightness temperature of the observed scene. Then, the actual scene brightness temperature distribution is obtained through Fourier transform to complete the target remote sensing. The interferometric synthetic aperture microwave radiometer combines a sparse array of small aperture antennas with a correlation system receiver, which greatly improves the spatial resolution of remote sensing observations and solves the problems of mechanical scanning and the difficulty of designing large aperture antennas.

[0004] In addition to the interferometric aperture microwave radiometer based on the multi-channel array correlation architecture, the correlation receiver architecture is also widely used in other new radiometer systems, realizing a system for observing targets with the advantages of polarization measurement, spectrum measurement and stability improvement. In the full polarization radiation measurement, the direct correlation full polarization radiometer (reference [2]: N. Skou, B. Laursen and S. Sobjaerg, "Polarimetric radiometer configurations: potential accuracy and sensitivity," in IEEE Transactions on Geoscience and Remote Sensing, vol. 37, no. 5, pp. 2165-2171, Sept. 1999, doi: 10.1109 / 36.789613.) measurement technology can be used to obtain all Stokes parameters through the correlation results of the horizontally polarized and vertically polarized signals received by the two polarization channel receivers, thus completing the full polarization measurement. Compared with the combined full-polarization radiometer, the direct correlation full-polarization radiometer has a simpler structure and has obvious advantages in power consumption, size, weight, system complexity and cost. In addition, the correlation system has also been applied to the single-channel receiver architecture to realize the microwave spectrum radiometer design in the form of an autocorrelation spectrometer. In the application of measuring the thickness of lake ice pack or snow, wideband autocorrelation radiometry (WiBAR) (reference [3]: S. Mousavi, RD De Roo, K. Sarabandi, AWEngland, SYE Wong and H. Nejati, "Lake ice pack and dry snow pack thickness measurement using wideband autocorrelation radiometry", IEEE Trans. Geosci. Remote Sens., vol. 56, no. 3, pp. 1637-1651, Mar. 2018.) provides a new method for measuring ice and snow thickness and has developed rapidly in recent years. This technology measures the microwave propagation time τ delay of multipath microwave emission from the low-loss layered surface of dry snow piles or freshwater lake ice packs, thereby obtaining the thickness parameters of lake ice packs or snow. Compared with active remote sensing, broadband autocorrelation radiation measurement has the advantages of all-weather, low power consumption and low cost.In addition to the above-mentioned radiometer systems with related reception and architecture, a pseudo-correlation radiometer design scheme is proposed with reference to the relevant system to improve the performance of the radiometer. By continuously comparing and differentiating the two input signals, the overall stability of the system is improved (Reference [4]: ​​Andrews, M., et al. "The Ultra-Wideband Software Defined Microwave Radiometer (UWBRAD) for Ice sheet subsurface temperature sensing: Calibration and campaign results." IGARSS 2017-2017 IEEE International Geoscience and Remote Sensing Symposium IEEE, 2017.).

[0005] In addition, for the antenna array design of correlation system radiation measurement, the interferometric aperture radiometer adopts a one-dimensional or two-dimensional sparse array, while other correlation system radiometers, such as full polarization radiometers and autocorrelation radiometers, generally adopt a real aperture array design. In addition to the above antenna arrays, Mills et al. proposed a special antenna design form of a "cross" array composed of two long antennas (reference [5]: Mills, BY, and AG Little. "A High-resolution Aerial System of a New Type." Australian Journal of Physics 6.3 (1953)), and used it in conjunction with a correlation system receiver. Through the correlation of the spatial orthogonal fan-shaped beam patterns of the two linear array antennas, a two-dimensional narrow beam observation is formed, which greatly reduces the difficulty and cost of antenna design. Based on the Mills cross array, David Le Vien et al. proposed to further realize two-dimensional spatial beam electronic scanning by transforming two linear arrays into a phased system (Reference [6]: DM Le Vine, The sensitivity of synthetic aperture radiometers for remote sensing applications from space, Radio Sci., vol. 25, no. 4, pp. 441–453, 1990.).

[0006] Interferometric synthetic aperture radiometers based on multi-channel array correlation architecture achieve high-resolution and large-field-of-view imaging through interferometric measurement, but this will increase the design complexity and calibration difficulty of the system. Other correlation system radiometers, such as full polarization radiometers and autocorrelation radiometers, generally adopt real aperture array design, which has the problem of high difficulty in designing large antennas and difficulty in correcting the brightness temperature introduced by the feeder's own losses during calibration. The Mills cross antenna array can eliminate the non-correlated signals introduced by the antenna end through the correlation signals, but the antenna array is only composed of two crossed linear arrays. The correlation pattern obtained by multiplying the array factors has large side lobes and low main beam efficiency, which has a great impact on the observation sensitivity of the system. Summary of the invention

[0007] The purpose of the present invention is to solve the problem of large side lobes and low main beam efficiency of the Mills cross antenna array, and at the same time solve the problem that the brightness temperature introduced by the antenna and its feeder losses before the calibration switch is difficult to correct, thereby proposing a planar orthogonal antenna array, a radiometer and a detection method thereof. The present invention provides a planar orthogonal antenna array, a radiometer and a detection method thereof, which realize a spatial narrow beam through the correlation of two planar orthogonal antenna arrays, simplify the calibration scheme, and reduce the system complexity and implementation cost.

[0008] To achieve the above-mentioned purpose of the invention, a planar orthogonal antenna array of the present invention is characterized in that the array includes: a first planar sub-array and a second planar sub-array arranged orthogonally in space, wherein the first planar sub-array and the second planar sub-array include: an independent feeding system, and have the same phase center and the same beam pointing, for simultaneously observing the radiation signal of the same target, and outputting independent observation signals respectively.

[0009] As an improvement of the above device, in the planar orthogonal antenna array, the first planar subarray is an expanded first one-dimensional subarray T x , the second plane subarray is the expanded second one-dimensional subarray T y ;in,

[0010] The phase centers of the first one-dimensional subarray and the second one-dimensional subarray coincide with each other and are arranged orthogonally in space to form a cross orthogonal array;

[0011] Based on the required information of the relevant radiometer and the carrying platform, the first one-dimensional subarray T x It includes 2M antenna elements, and the unit spacing is d x ; The second one-dimensional subarray T y ; The second one-dimensional subarray T y It includes 2N antenna elements, and the unit spacing is d y ;in,

[0012] The first one-dimensional subarray T x and the second one-dimensional subarray T y In the embodiment, each of the antenna units is numbered based on the distance from the phase center; wherein the numbers from near to far are: x ±1 ,x ±3 ,…,x ±(2M-1) and ±1 ,y ±3 ,…,y ±(2N-1) , where '±' means on both sides of the phase center;

[0013] Each antenna element x of the first one-dimensional subarray i As the base point, the first one-dimensional subarray T x In the vertical direction, the antennas are spaced d apart. y The distance between antenna units x i Add m on both sides of i The antenna units form the expanded first one-dimensional subarray as the first planar subarray; wherein x i is the ith antenna element of the first one-dimensional subarray, m i The antenna unit x i As the base point, the number of antenna units added on one side, i = ±1, ±3, ... ±(2M-1);

[0014] Each unit antenna y of the second one-dimensional subarray j As the base point, the second one-dimensional sub-line array T y In the vertical direction, the antennas are spaced d apart. x The distance between antenna unit y j Add n on both sides of j antenna units to form an extended second one-dimensional subarray as the second plane subarray; wherein y j is the jth antenna element of the second one-dimensional subarray, n j The unit antenna y j As the base point, the number of antenna units added on one side is j = ±1, ±3, ... ±(2N-1).

[0015] As an improvement of the above device, the first and second one-dimensional sub-arrays include: an even number of antenna units that are evenly distributed; and the cross orthogonal array has a central symmetric characteristic.

[0016] As an improvement of the above device, the total number of antenna units added is 2m, taking the i-th and j-th antenna units as base points respectively. i and 2n jis an even number and is symmetrically distributed on both sides of the i-th and j-th antenna units; the m i and n j The following relations are satisfied:

[0017] m ±(2M-1) ≤m ±(2M-3) ≤…≤m ±1 ≤N

[0018] n ±(2N-1) ≤n ±(2N-3) ≤…≤n ±1 ≤M

[0019] Among them, i=±1,±3,…±(2M-1), N is half of the total number of antennas in the first one-dimensional subarray Tx in the horizontal direction, and M is half of the total number of antennas in the second one-dimensional subarray Ty in the horizontal direction.

[0020] As an improvement to the above device, the shape of the planar orthogonal antenna array includes: a polygon.

[0021] As an improvement of the above device, the directional patterns of the first and second planar sub-arrays arranged orthogonally in space are multiplied to obtain the directional pattern of the planar orthogonal antenna array: the specific process includes:

[0022] Based on the first and second planar sub-arrays, the directional patterns f1(ξ,η) and f2(ξ,η) of the two planar sub-arrays are obtained:

[0023]

[0024] in, is the radiation pattern of a single antenna unit; N0 and M0 are the antenna units of two planar subarrays; (u l ,v l )=(D xl ,D yl ) / λ、(u k ,v k )=(D xk ,D yk ) / λ, where λ is the operating wavelength of the planar orthogonal antenna array, (D xl ,D yl )、(D xk ,D yk ) is the distance between the antenna unit and the phase center; (ξ,η)=(sin(θ)cos(φ),sin(θ)sin(φ)) represents the direction cosine, where θ and φ are the elevation angle and azimuth angle of the observation direction of the antenna unit, and the superscript 1j is an imaginary number symbol. By multiplying the directional patterns of the two planar subarrays, the product directional pattern of the orthogonal correlation array is obtained:

[0025] F(ξ,η)=f1(ξ,η)·f2(ξ,η)

[0026] Wherein, f1(ξ,η) and f2(ξ,η) are the directional patterns of the first and second planar sub-arrays respectively.

[0027] The product radiation pattern of the two sub-arrays forms a pencil beam in space, with narrow beam widths in different directions, which improves the spatial resolution of the antenna. At the same time, compared with the Mill's cross array, the orthogonal array improves the main beam efficiency and reduces the sidelobe level, greatly improving the array performance.

[0028] To achieve another object of the present invention, the present invention provides a planar orthogonal array correlation radiometer, which is implemented based on the above-mentioned planar orthogonal antenna array. The radiometer includes: a planar orthogonal antenna array, a common noise source, a first calibration switch, a second calibration switch, a correlation system receiver and a complex correlator; wherein,

[0029] The public calibration source is used to output a noise signal S0 during calibration observation; the noise signal S0 is divided by the power divider to form a first division signal S 01 and the second division signal S 02 , and transmitted to the first and second calibration switches respectively;

[0030] The planar orthogonal antenna array comprises: a first planar sub-array and a second planar sub-array arranged orthogonally in space; when detecting a target, the planar orthogonal antenna array is used to simultaneously observe and receive radiation signals s1 and s2 of the same target, and output independent first and second observation signals a1 and a2 respectively;

[0031] The first and second calibration switches periodically switch between the planar orthogonal antenna array and the common noise source; during calibration observation, they are used to respectively receive the first division signal S 01 and the second division signal S 02 , and output the first and second calibration switch signals c1 and c2, where The first and second calibration switches are used to receive the first and second observation signals b1 and b2 after feeder loss when detecting a target, and output the first and second calibration switch signals c1 and c2; the correlation system receiver includes: two independent receiving channels, used to receive the first and second calibration switch signals c1 and c2 respectively, perform amplification and filtering processing, form two receiving signals d1 and d2, and input them into the complex correlator;

[0032] The complex correlator is used to perform correlation operation based on the two received signals d1 and d2, and output correlation results of the two paths of the observation signals.

[0033] To achieve another purpose of the present invention, the present invention provides a detection method of a planar orthogonal array correlation radiometer, which is implemented based on the planar orthogonal array correlation radiometer. The planar orthogonal correlation radiometer provided by the present invention receives radiation signals from two orthogonal and in-phase planar sub-arrays of the planar orthogonal correlation array, transmits them to a two-channel receiver, and finally outputs the correlation results of the two signals. Therefore, the radiometer observation scheme of this system can solve the problem that the brightness temperature introduced by the loss of the antenna and its feeder before the calibration switch is difficult to correct and simplify the calibration difficulty, and includes the following steps:

[0034] Step 1) simultaneously observing and receiving radiation signals s1 and s2 of the same target through the first planar subarray and the second planar subarray of the planar orthogonal antenna array, and outputting independent first and second observation signals a1 and a2 respectively;

[0035] Step 2) receiving the first and second observation signals b1 and b2 of the loss at the corresponding calibration planes through the first and second calibration switches, and outputting the first and second calibration switch signals c1 and c2;

[0036] Step 3) The correlation system receiver receives the first and second calibration switch signals c1 and c2 through two independent receiving channels, performs amplification and filtering, forms the first and second output signals d1 and d2, and inputs them into the complex correlator;

[0037] Step 4) The complex correlator performs a correlation operation based on the two output signals d1 and d2, and outputs a correlation result C of the two observation signals. a .

[0038] As an improvement of the above method, the detection method further includes: the first and second calibration switches are periodically switched to a common noise source for calibration observation; wherein the common noise source is used to output a noise signal S0; the noise signal S0 is divided by a power divider to form a first division signal S 01 and the second division signal S 02 , and are transmitted to the first and second calibration switches for calibration respectively. The planar orthogonal correlation radiometer system realizes target observation and system calibration observation through two calibration switches, and the front side of the calibration switch is used as the calibration plane. The system signal transfer equation is obtained by analyzing the calibration plane.

[0039] As an improvement of the above method, the step 1) specifically includes: the first plane subarray and the second plane subarray of the planar orthogonal antenna array simultaneously observe the same target source, receive target radiation signals s1 and s2 respectively, and output two observation signals a1 and a2 respectively:

[0040]

[0041]

[0042] Among them, η1 and η2 are the antenna radiation efficiencies, n a1 and n a2 are the self-radiated noises of the two planar sub-arrays.

[0043] As an improvement of the above method, the first and second observation signals b1 and b2 lost in step 2) are respectively:

[0044]

[0045]

[0046] Wherein, β1 and β2 are the losses of the feeder before the first and second calibration switches, respectively, and n1 and n2 are the radiation noise of the feeder before the first and second calibration switches, respectively.

[0047] Because n a1 、n a2 , n1, n2 are the noises introduced before the calibration switch, so they cannot be calibrated through the common noise source calibration process. However, the planar orthogonal correlation radiometer system achieves target observation by correlating the two observation signals of the two planar orthogonal subarrays. The two orthogonal subarrays are observed separately, so the noise signal n introduced before the calibration plane a1 、n a2 , n1, and n2 are unrelated to each other, that is, This eliminates the noise interference introduced by antenna loss and feed line loss before the calibration switch, and improves measurement accuracy.

[0048] For signals b1 and b2, the related results are:

[0049]

[0050] In , <·> indicates correlation operation, and '*' indicates conjugation.

[0051] As an improvement of the above method, the first and second calibration switch output signals c1 and c2 are respectively:

[0052]

[0053]

[0054] Where l1 and l2 are the losses of the first and second calibration switches, respectively, and n l1 and n l2 are the noise signals of the first and second calibration switches respectively.

[0055] As an improvement of the above method, the first and second output signals d1 and d2 are respectively:

[0056]

[0057]

[0058] Among them, g r1 and g r2 are the voltage gains of the two receiving channels of the receiver of the relevant system respectively; n r1 and n r2 are the equivalent noise signals of the two receiving channels of the receiver of the correlation system respectively; and They are respectively the phase shifts produced by the two receiving channels of the correlation system receiver, where the superscript 1j is an imaginary number symbol.

[0059] As an improvement of the above method, the step 4) specifically includes:

[0060] Step 4-1) When acquiring the observed target, the complex correlation output C of the correlation system receiver output signals d1 and d2 a :

[0061]

[0062] Among them, n r1 、n r2 、n l1 、n l2 are uncorrelated with each other and are uncorrelated with b1 and b2; then the complex correlation output of the correlation system receiver output signal d1 and d2 is

[0063] in, T a is the apparent temperature of the antenna after calibration, k is the Boltzmann constant, is the phase difference between the two channels of the receiver of the correlation system, where the superscript 1j is an imaginary number symbol, Represents the power gain of the receiver of the relevant system.

[0064] As an improvement of the above method, the radiometer can realize the calibration of the receiver system through only one common noise source. When the two calibration switches are connected to the common noise source, the receiver related output result C during calibration observation can be obtained. o for:

[0065]

[0066] Among them, T o is the common noise source temperature, the coefficient It is generated by the common noise source signal input to the two receiving channels through the power divider. According to the above analysis, the planar orthogonal correlation radiometer system only needs to pass a common noise source T o The real-time calibration of parameters G and Δφ can be achieved:

[0067]

[0068] Δφ=angle(C o )

[0069] Among them, |·| means taking the absolute value, and angle(·) means taking the phase.

[0070] The apparent temperature of the antenna after calibration is Among them, T o is the common noise source temperature, C o is the output correlation result of the correlation system receiver during calibration observation, wherein,

[0071] The present invention is characterized in that:

[0072] 1. The planar orthogonal correlation radiometer provided by the present invention has a simple structure, is easy to implement, and reduces costs;

[0073] 2. The planar orthogonal antenna array can obtain a narrow pencil beam by multiplying the orthogonal beams of two orthogonal sub-arrays. Compared with the orthogonal cross array, it has better sidelobe level and main beam efficiency;

[0074] 3. The system eliminates the influence of the receiving link noise inside the radiometer on the observed signal through signal correlation, especially the influence of the noise signal of the antenna and feeder before the calibration switch;

[0075] 4. The radiometer system only needs one common noise source to achieve real-time internal calibration, which simplifies the calibration scheme and reduces the receiver sensitivity loss caused by calibration observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 It is a schematic diagram of the planar orthogonal correlation radiometer system framework of the present invention;

[0077] Figure 2 A flow chart of a method for designing a planar correlation antenna array of a microwave radiometer of the present invention;

[0078] Figure 3 The orthogonal cross antenna array of the present invention;

[0079] Figure 4 This is a real-time calibration timing diagram of the planar orthogonal correlation radiometer of the present invention;

[0080] Figure 5The quadrilateral correlation antenna array obtained by expanding the cross orthogonal array when 2M=2N=6 according to the present invention;

[0081] Figure 6 The curve of the beam efficiency of the quadrilateral correlation antenna array correlation direction function obtained by N=M expansion with N and M

[0082] Figure 7 It is a hexagonal correlated antenna array obtained by expanding a cross orthogonal array when 2M=4 and 2N=6. DETAILED DESCRIPTION

[0083] The technical solution provided by the present invention is further described below in conjunction with embodiments.

[0084] The present invention will now be further described with reference to the accompanying drawings.

[0085] Embodiment 1:

[0086] The planar orthogonal correlation radiometer provided by the present invention is a radiometer system based on a correlation receiver architecture, comprising a planar orthogonal antenna array and a correlation receiver. Figure 1 The example is a planar orthogonal correlation radiometer system framework diagram using a direct amplification receiver. In addition, a superheterodyne receiver structure can also be used to achieve correlation reception. The method is as follows:

[0087] (I) Planar orthogonal antenna array is a beamforming correlation antenna array suitable for correlation receiver system. The design process is as follows Figure 2 As shown, the method includes:

[0088] Obtain system and platform requirements, determine array size, and calculate antenna element spacing

[0089] Based on the acquired array information, two uniformly distributed one-dimensional subarrays with an even number of antenna elements are designed. The array length and antenna element spacing are D and x d x and D y d y , the number of antenna units is 2N, 2M. Let the phase centers of the two one-dimensional arrays coincide and be arranged orthogonally in space to form a cross orthogonal array.

[0090] Figure 3 The orthogonal cross array obtained by the above method has a phase center that coincides with the array center, and array units are evenly and symmetrically distributed on both sides of the phase center. With the phase center as the origin, an orthogonal coordinate system is established with the two linear arrays as the x and y axes. The unit distance on the coordinate axis corresponds to or The antenna units are numbered according to their distance from the origin of the coordinate system. From near to far, they can be numbered as follows:

[0091] x ±1 ,x ±3 ,…,x ±(2M-1) ,y ±1 ,y ±3 ,…,y ±(2N-1)

[0092] Then the antenna unit x i or j The distance from the phase center can be expressed as or The subscript indicates the coordinate of the antenna element on the x-axis or y-axis.

[0093] Add antenna units with each antenna unit as the base point. Specifically, for the antenna unit on the x-axis, select the antenna at coordinate 1 as the base point, and add antenna units every d in the vertical direction of the x-axis. y Add antenna units on both sides with a distance of m1; repeat the above process, taking other antenna units on the x-axis as base points, and add m i antenna units, i is the coordinate of the base point antenna on the x-axis.

[0094] Referring to the expansion method of the antenna units on the x-axis, take the 2N antennas on the y-axis as the base points and expand them every d in the vertical direction. x Add n to the distance on both sides j Antenna unit, j is the y-axis coordinate of the base point antenna.

[0095] In the cross array expansion, the antenna units added at each base point antenna should be symmetrically distributed on both sides of the antenna.

[0096] For two base point antennas symmetrical about the origin on the same coordinate axis, we have:

[0097] m i =m -i 、n j =n -j

[0098] Standardize the number of antenna elements added to the base antenna at different locations:

[0099] m 2M-1 ≤m 2M-3 ≤…≤m1≤N

[0100] n 2N-1 ≤n 2N-3 ≤…≤n1≤M

[0101] The obtained new planar correlation array is judged. If the antenna performance does not meet the design requirements, a unit antenna is added at the base point antenna again until an antenna array that meets the design requirements is obtained.

[0102] Based on the obtained planar orthogonal antenna array, its two planar sub-arrays synthesize two beam signals:

[0103]

[0104]

[0105] The narrow composite beam obtained by multiplying the two composite beam signals is:

[0106]

[0107] (II) Reference Figure 1 The block diagram of the planar orthogonal correlation radiometer model is shown, and the signal transmission model and calibration scheme of the radiometer are analyzed. The method is as follows:

[0108] When realizing target observation, the first plane subarray and the second plane subarray of the planar orthogonal antenna array simultaneously observe the same target source, and the received target radiation signals are s1 and s2, and then two observation signals a1 and a2 are output:

[0109]

[0110]

[0111] Among them, η1 and η2 are the antenna radiation efficiencies, n a1 、n a2 are the self-radiated noises of the two planar sub-arrays.

[0112] Considering the feeder loss, the signals b1 and b2 at the calibration plane B are:

[0113]

[0114]

[0115] Among them, β1 and β2 are the losses of the feeder before the calibration switch; n1 and n2 are the radiation noise of the feeder itself before the calibration switch. The planar orthogonal correlation radiometer system realizes target observation and system calibration observation through two calibration switches. The calibration plane is taken as the calibration plane, and the system signal transfer equation is obtained by analyzing the calibration plane. Signals b1 and b2 are received at the calibration plane. When the calibration switch is used, the observed signal can obtain the signal at plane C through the calibration switch when the calibration switch loss is considered. The output signals c1 and c2 are:

[0116]

[0117] Where l1 and l2 are the calibration switch and calibration switch loss; n l1 、n l2is the noise signal of the calibration switch. The signals c1 and c2 output by the calibration switch are transmitted to the two channels of the relevant receiver for amplification and filtering, and output d1 and d2:

[0118]

[0119]

[0120] In the formula, g r1 , g r2 is the voltage gain of the receiver; n r1 、n r2 represents the noise signal of the receiver; The phase shift generated by the receiver channel. The signals d1 and d2 received by the receiver are sampled and correlated to obtain the relevant output of the radiometer system:

[0121]

[0122] In the formula, 〈·〉 represents a correlation operation, and '*' represents conjugation.

[0123] Compared with the traditional radiometer system, the two received signals of the planar orthogonal correlation radiometer are received by two sub-arrays with orthogonal and co-phase centers and transmitted through two channels. Therefore, the noise signals introduced by the calibration switch, feeder loss, receiver, etc. during the signal reception process are uncorrelated. When the two receptions are complex correlated, the correlation between the uncorrelated signals introduced by the radiometer system is 0, thereby eliminating the influence of the receiver system noise, and establishing the relationship between the correlation output of the radiometer system and the calibration switch input signal.

[0124] Specifically, the radiation signal of the observed target is collected by two orthogonal sub-arrays of the planar orthogonal antenna array and received through two receiver channels. Therefore, the antenna loss, feeder loss and noise signal introduced by the receiver are uncorrelated. Therefore, the relevant output result when observing the target can be obtained as follows:

[0125]

[0126] in, T a is the apparent temperature of the antenna, k is the Boltzmann constant, is the phase difference produced by the receiver channel, 1j is the imaginary number symbol, Represents the receiver system power gain.

[0127] like Figure 4 The figure shows the timing diagram of the real-time calibration of the radiometer. The calibration switch periodically switches between the antenna and the common noise source to calibrate the system in real time. When the radiometer is calibrated, the relevant output of the radiometer during calibration is:

[0128]

[0129] T o is the brightness temperature of the common noise source, the coefficient It is generated by the common noise source signal input to the two receiving channels through the power divider. According to the above analysis, it can be known that the radiometer system can be calibrated through a common noise source, and its calibration parameters are:

[0130]

[0131]

[0132] Among them, |·| means taking the absolute value, and angle(·) means taking the phase.

[0133] The antenna apparent temperature after calibration is T a for:

[0134]

[0135] The final correlation operation output of the radiometer is only related to the brightness temperature of the overlapping part of the field of view covered by the two sub-array radiation patterns; the two sub-array antenna losses, feeder losses and receiver noise are all uncorrelated noises and do not contribute to the correlation measurement results. During the calibration process, the receiver input-output relationship calibration can be completed by only one common noise source. Therefore, the planar orthogonal correlation radiometer solves the problem of difficulty in correcting the brightness temperature introduced by the antenna and its feeder losses before the calibration switch, and at the same time simplifies the calibration scheme of the receiver, reduces the system calibration observation time, and reduces the sensitivity loss caused by calibration.

[0136] Embodiment 2:

[0137] In this simulation example, the antenna unit is an isotropic antenna with an antenna spacing of d. x =d y =0.5λ, design two uniformly distributed arrays with 2N=2M=2N0 units and form an orthogonal cross array with the same phase center. In the orthogonal cross array, the two arms of the array are T x 、T y .like Figure 2 , for T x 、T y The antenna units are numbered, x ±1 ,x ±3 ,…,x ±(2M-1) ,y ±1 ,y ±3 ,…,y ±(2N-1) .

[0138] Based on the above antenna unit numbering, select the antenna unit numbered x1 as the base point, and x Every d in the vertical direction y Add antenna units on both sides at a distance of m1; repeat the above process in turn with linear array T x The other antenna units on the top are taken as base points, and m is added i Antenna elements:

[0139] x i :m i =2N0-|i|-1 i=±1,±3,…,±(2N0-1)

[0140] Reference Line Array T x The expansion method is to use the line array T y Antenna unit y on j As the base point, the line array T y Every d in the vertical direction x Add antenna units on both sides, the number is n j :

[0141] y j :n j =2N0-|j|-1 j=±1,±3,…,±(2N0-1)

[0142] Through the above process, the expansion of the mills cross array antenna is completed to obtain a quadrilateral correlation antenna array. When 2N = 2M = 6, the expanded quadrilateral correlation array is as follows Figure 5 shown.

[0143] Further analysis of the obtained quadrilateral correlation antenna array, the correlation pattern is obtained through the voltage pattern of the two plane sub-arrays, and the calculated beam efficiency changes with N and M are shown as follows: Figure 6 As shown, calculate the 3dB beamwidth θ 3dB for:

[0144]

[0145] Among them, d i Take d x or y ;

[0146] Embodiment 3:

[0147] In this simulation example, the antenna unit is an isotropic antenna, and the antenna spacing is d x =d y =0.5λ, design two uniformly distributed arrays with 2M<2N units and form an orthogonal cross array with the same phase center. In the orthogonal cross array, the two arms of the array are Tx 、T y .like Figure 3 , for T x 、T y The antenna units are numbered, x ±1 ,x ±3 ,…,x ±(2M-1) ,y ±1 ,y ±3 ,…,y ±(2N-1) .

[0148] Based on the above antenna unit numbering, T x Antenna unit x i As the base point, the line array T x Every d in the vertical direction y Add antenna units on both sides with a distance of m i :

[0149] x i :m i =2N-|i|-1 i=±1,±3,…,±(2M-1)

[0150] Reference Line Array T x The expansion method is to use the line array T y Antenna unit y on j As the base point, the line array T y Every d in the vertical direction x Add antenna units on both sides, the number is n j , if its y-axis coordinate j≤2N-2M+1, add the following to the corresponding antenna unit:

[0151] y j :n j =M-2 j=±1,±3,…,±(2N-2M+1)

[0152] If the y-axis coordinate of the base point antenna satisfies 2N-2M+3≤|j|≤2N-1, the number of antenna units added is:

[0153] y j :n j =2N-|j|-1 |j|=2N-2M+3,…,2N-1

[0154] Through the above process, the expansion of the mills cross array antenna is completed to obtain a hexagonal correlation antenna array. When N = 4 and M = 6, the expanded hexagonal correlation array is as follows: Figure 7 shown.

[0155] From the above specific description of the present invention, it can be seen that the planar orthogonal correlation radiometer provided by the present invention has a simple structure, is easy to implement and reduces costs; the planar orthogonal antenna array can obtain a narrow pencil beam by multiplying the orthogonal beams of two orthogonal sub-arrays, and has good sidelobe levels and main beam efficiency compared to the orthogonal cross array; the planar orthogonal array correlation radiometer system eliminates the influence of the internal receiving link noise of the radiometer on the observation signal through signal correlation, especially eliminates the influence of noise signals such as antennas and feeders before the calibration switch; the radiometer system only needs one common noise source to realize real-time internal calibration, simplifies the calibration scheme, and reduces the receiver sensitivity loss caused by calibration observation.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A planar orthogonal array correlation radiometer, implemented based on a planar orthogonal antenna array, the array comprising: A first planar sub-array and a second planar sub-array arranged orthogonally in space, wherein the first planar sub-array and the second planar sub-array include: an independent feeding system, and have the same phase center and the same beam pointing, for simultaneously observing the radiation signal of the same target, and outputting independent observation signals respectively; characterized in that, The radiometer comprises: a planar orthogonal antenna array, a common noise source, a first calibration switch, a second calibration switch, a correlation system receiver and a complex correlator; wherein, The common noise source is used to output a noise signal S0 during calibration observation; the noise signal S0 is divided by the power divider to form a first power division signal S 01 and the second power division signal S 02 , and transmitted to the first and second calibration switches respectively; The planar orthogonal antenna array comprises: a first planar sub-array and a second planar sub-array arranged orthogonally in space; when detecting a target, the planar orthogonal antenna array is used to simultaneously observe and receive radiation signals s1 and s2 of the same target, and output independent first and second observation signals a1 and a2 respectively; The first and second calibration switches periodically switch between the planar orthogonal antenna array and the common noise source; during calibration observation, they are used to respectively receive the first power division signal S 01 and the second power division signal S 02 , and output the first and second calibration switch signals c1 and c2; the first and second calibration switches, when detecting a target, are used to receive the first and second observation signals b1 and b2 after feeder loss, and output the first and second calibration switch signals c1 and c2; The correlation system receiver comprises: two independent receiving channels, respectively used to receive the first and second calibration switch signals c1 and c2, perform amplification and filtering processing, form two output signals d1 and d2, and input them into the complex correlator; The complex correlator is used to perform correlation operation based on the two output signals d1 and d2, and output correlation results of the two observation signals.

2. The planar orthogonal array correlation radiometer according to claim 1, characterized in that: The first plane subarray is the expanded first one-dimensional subarray T x , the second plane subarray is the expanded second one-dimensional subarray T y ;in, The phase centers of the first one-dimensional subarray and the second one-dimensional subarray coincide with each other and are arranged orthogonally in space to form a cross orthogonal array; Based on the required information of the relevant radiometer and the carrying platform, the first one-dimensional subarray T x It includes 2M antenna elements, and the unit spacing is d x ; The second one-dimensional subarray T y It consists of 2N antenna elements with a unit spacing of d y ;in, The first one-dimensional subarray T x and the second one-dimensional subarray T y In the embodiment, each of the antenna units is numbered based on the distance from the phase center; wherein the numbers from near to far are: x ±1 ,x ±3 ,…,x ±(2M-1) and ±1 ,y ±3 ,…,y ±(2N-1) , where '±' means on both sides of the phase center; Each antenna element x of the first one-dimensional subarray i As the base point, the first one-dimensional subarray T x In the vertical direction, the antennas are spaced d apart. y The distance between antenna units x i Add m on both sides of i The antenna units form the expanded first one-dimensional subarray as the first planar subarray; wherein x i is the first one-dimensional subarray T of the i-th x Antenna unit, i = ±1, ±3, ... ±(2M-1); Each unit antenna y of the second one-dimensional subarray j As the base point, the second one-dimensional sub-line array T y In the vertical direction, the antennas are spaced d apart. x The distance between antenna unit y j Add n on both sides of j antenna units to form an extended second one-dimensional subarray as the second plane subarray; wherein y j is the jth second one-dimensional subarray T y Antenna unit, j = ±1, ±3, … ±(2N-1).

3. The planar orthogonal array correlation radiometer according to claim 2, characterized in that: Taking the i-th and j-th antenna units as the base points, the total number of added antenna units is 2m i and 2n j is an even number and is symmetrically distributed on both sides of the i-th and j-th antenna units; the m i and n j The following relations are satisfied: m ±(2M-1) ≤m ±(2M-3) ≤…≤m ±1 ≤N n ±(2N-1) ≤n ±(2N-3) ≤…≤n ±1 ≤M Wherein, i = ±1, ±3, ... ±(2M-1), N is the second one-dimensional subarray T y Half of the total number of antennas, M is the first one-dimensional subarray T x Half of the total number of antennas.

4. The planar orthogonal array correlation radiometer according to claim 1, characterized in that: The shape of the planar orthogonal antenna array includes: a polygon.

5. The planar orthogonal array correlation radiometer according to claim 1, characterized in that: The directional patterns of the first and second planar sub-arrays arranged orthogonally in the space are multiplied to obtain the directional pattern of the planar orthogonal antenna array. The specific process includes: Based on the first and second plane sub-arrays, the directional pattern f1(ξ,η) of the first plane sub-array and the directional pattern f2(ξ,η) of the second plane sub-array are obtained: Among them, f a (ξ,η) is the radiation pattern of a single antenna unit; {N0} and {M0} are the antenna unit sets of two planar subarrays, respectively. l ,v l )=(D xl ,D yl ) / λ,(u k ,v k )=(D xk ,D yk ) / λ, where λ is the operating wavelength of the planar orthogonal antenna array, (D xl ,D yl ) and (D xk ,D yk ) are the distances between the antenna unit and the phase center, (ξ,η) represent direction cosines, and (ξ,η)=(sin(θ)cos(φ),sin(θ)sin(φ)), where θ and φ are the elevation and azimuth angles observed by the antenna, respectively, and the superscript 1j is an imaginary number symbol; By multiplying the directional patterns f1 and f2 of the two planar sub-arrays, the product directional pattern of the orthogonal correlation array is obtained: F(ξ,η)=f1(ξ,η)·f2(ξ,η).

6. A detection method of a planar orthogonal array correlation radiometer, implemented based on the planar orthogonal array correlation radiometer of claim 1, comprising the following steps: Step 1) simultaneously observing and receiving radiation signals s1 and s2 of the same target through the first planar subarray and the second planar subarray of the planar orthogonal antenna array, and outputting independent first and second observation signals a1 and a2 respectively; Step 2) receiving the first and second observation signals b1 and b2 of the loss at the corresponding calibration planes through the first and second calibration switches, and outputting the first and second calibration switch signals c1 and c2; Step 3) The correlation system receiver receives the first and second calibration switch signals c1 and c2 through two independent receiving channels, performs amplification and filtering, forms the first and second output signals d1 and d2, and inputs them into the complex correlator; Step 4) The complex correlator performs a correlation operation based on the two output signals d1 and d2, and outputs a correlation result C of the two observation signals. a .

7. The detection method of a planar orthogonal array correlation radiometer according to claim 6, characterized in that: The detection method further includes: the first and second calibration switches are periodically switched to a common noise source for calibration observation; wherein the common noise source is used to output a noise signal S0; the noise signal S0 is divided by a power divider to form a first power division signal S 01 and the second power division signal S 02 , and are transmitted to the first and second calibration switches for calibration respectively.

8. The detection method of the planar orthogonal array correlation radiometer according to claim 6, characterized in that: The step 1) specifically includes: the first plane subarray and the second plane subarray of the planar orthogonal antenna array simultaneously observe the same target source, receive target radiation signals s1 and s2 respectively, and output two observation signals a1 and a2 respectively: Among them, η1 and η2 are the antenna radiation efficiencies, n a1 and n a2 are the self-radiated noises of the two planar sub-arrays.

9. The detection method of the planar orthogonal array correlation radiometer according to claim 8, characterized in that: The first and second observation signals b1 and b2 lost in step 2) are respectively: Wherein, β1 and β2 are the losses of the feeder before the first and second calibration switches, respectively, and n1 and n2 are the radiation noise of the feeder before the first and second calibration switches, respectively.

10. The detection method of the planar orthogonal array correlation radiometer according to claim 9, characterized in that: The first and second calibration switch signals c1 and c2 are respectively: Where l1 and l2 are the losses of the first and second calibration switches, respectively, and n l1 and n l2 are the noise signals of the first and second calibration switches respectively.

11. The detection method of the planar orthogonal array correlation radiometer according to claim 10, characterized in that: The first and second output signals d1 and d2 are respectively: Among them, g r1 and g r2 are the voltage gains of the two receiving channels of the receiver of the relevant system respectively; n r1 and n r2 are the equivalent noise signals of the two receiving channels of the receiver of the correlation system respectively; and They are the phase shifts produced by the two receiving channels of the receiver of the correlation system; the superscript 1j is an imaginary number symbol.

12. The detection method of the planar orthogonal array correlation radiometer according to claim 11, characterized in that: The step 4) specifically includes: Step 4-1) When acquiring the observed target, the complex correlation output C of the correlation system receiver output signals d1 and d2 a : Among them, n r1 、n r2 、n l1 、n l2 are uncorrelated with each other and are uncorrelated with b1 and b2; the complex correlation output of the correlation system receiver output signals d1 and d2 in, T a is the apparent temperature of the antenna after calibration, k is the Boltzmann constant, is the phase difference between the two channels of the receiver of the correlation system, the superscript 1j is the imaginary number symbol, Represents the power gain of the receiver of the relevant system.

13. The detection method of a planar orthogonal array correlation radiometer according to claim 12, characterized in that: The antenna apparent temperature after calibration is Among them, T o is the common noise source temperature, C o is the output correlation result of the correlation system receiver during calibration observation, wherein,

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