阅读说明：本技术 一种天线单元、阵列天线及水流测速雷达 (Antenna unit, array antenna and water flow velocity measurement radar ) 是由 曹振新 马境泽 许湘剑 袁红泉 于 2021-07-09 设计创作，主要内容包括：本发明公开了一种天线单元、阵列天线及水流测速雷达,其中天线单元包括介质基板以及设置在介质基板上的匹配巴伦、辐射振子臂、微带馈线和匹配网络；所述微带馈线与匹配网路连接；所述匹配巴伦为一金属层,在所述金属层上开有用于电磁耦合馈电的缝隙；所述匹配巴伦为开槽的金属层；所述辐射振子臂位于所述匹配巴伦上端两侧；在所述辐射振子臂上加载有分布式电阻。与现有技术相比,本发明阵列天线可以实现290MHz-390MHz频段范围内垂直极化稳定的电磁辐射,具有风阻小、重量轻、剖面低、无源及有源驻波频带宽、辐射方向图稳定、水平方向图副瓣电平低、垂直方向图波束宽度窄且灵活可变的特点。(The invention discloses an antenna unit, an array antenna and a water flow speed measuring radar, wherein the antenna unit comprises a dielectric substrate, and a matching balun, a radiation oscillator arm, a micro-strip feeder line and a matching network which are arranged on the dielectric substrate; the microstrip feeder is connected with the matching network; the matching balun is a metal layer, and a gap for electromagnetic coupling feed is formed in the metal layer; the matching balun is a slotted metal layer; the radiation oscillator arms are positioned on two sides of the upper end of the matching balun; and a distributed resistor is loaded on the radiation oscillator arm. Compared with the prior art, the array antenna can realize electromagnetic radiation with stable vertical polarization in the frequency range of 290MHz-390MHz, and has the characteristics of small wind resistance, light weight, low section, wide passive and active standing wave frequency bands, stable radiation pattern, low horizontal pattern side lobe level, narrow vertical pattern beam width and flexibility and variability.)

1. An antenna unit comprises a dielectric substrate, and a matching balun, a radiation oscillator arm, a microstrip feeder line and a matching network which are arranged on the dielectric substrate; the microstrip feeder is connected with the matching network; the matching balun is a metal layer, and a first gap for electromagnetic coupling feed is formed in the metal layer; the radiation oscillator arms are positioned on two sides of the upper end of the matching balun; the distributed resistor is loaded on the radiation oscillator arm.

2. The antenna unit of claim 1, wherein: the radiation oscillator arms are parallelograms inclining downwards, the matching balun is rectangular, the gap is arranged in the middle of the upper end of the rectangle, and the two oscillator arms and the matching balun form an umbrella-shaped structure; at least 1 second gap parallel to the matching balun is formed in each radiation oscillator arm, and the distributed resistors are arranged in the second gaps.

3. The antenna unit of claim 2, wherein: the number of the second gaps on each oscillator arm is N, a row of distributed resistors loaded by a plurality of patches in parallel is arranged in each second gap, and the parallel resistance values of the N rows of distributed resistors are respectively as follows:

wherein i takes a value of 0-N-1; r₀Is the resistance value at the start of loading; r_iIs the loaded resistance value; a is a constant, and 10-20 is selected; l is the single-arm length of the umbrella antenna; y is₀The distance between the initial loading point and the feeding point is set; y is_iIs the distance between the loading point i and the feeding point.

4. The antenna unit of claim 2, wherein: the matching network is composed of a first microstrip line matching section, a second microstrip line matching section and a third open-circuit microstrip line matching section, and the first microstrip line matching section is connected with the microstrip feeder line; the second microstrip line matching section is a bending section, and the third open-circuit microstrip line matching section is parallel to the first microstrip line matching section.

5. An array antenna comprising a reflecting surface, a power divider, a beam former, and an antenna element according to any one of claims 1-4; the antenna unit is fixed on the reflecting surface and connected with the power divider; the power divider is connected with the beam former.

6. The array antenna of claim 5, wherein the reflective surface is a metal mesh reflective surface; the power divider is a horizontal power divider; the beam former is a vertical direction digital beam former.

7. The array antenna of claim 6, wherein a spacer is further disposed on the reflective surface for adjusting mutual coupling between the antenna elements; the isolating strip is positioned near the midpoint of a connecting line of the tail ends of the two printed dipole antenna unit oscillator arms in the horizontal direction, and the isolating strip is perpendicular to the reflecting surface of the metal gridThe vertical surface and the horizontal surface parallel to the metal grid reflecting surface; the height of the vertical surface of the isolating strip is 0.05 lambda₁～0.15λ₁Length of 0.05 lambda₁～0.15λ₁(ii) a The horizontal surface length of the isolating strip is 0.05 lambda₁～0.15λ₁Width of 0.05 lambda₁～0.1λ₁Wherein λ is₁340MHz vacuum wavelength.

8. The array antenna of claim 6, wherein: the spacing gaps of the reflecting surface of the metal grid are square or circular, and the side length of the square is 0.01 lambda₁～0.1λ₁The radius of the circle is 0.01 lambda₁～0.05λ₁Wherein λ is₁340MHz vacuum wavelength.

9. The array antenna of claim 6, wherein: the vertical direction digital beam former comprises a receiving module, a beam former, a self-adaptive beam forming controller and a control module; the receiving module is responsible for carrying out secondary low-noise amplification, intermediate frequency amplification after frequency mixing, quadrature phase detection and low-pass filtering on signals received in the vertical direction of the antenna array; the beam former is responsible for channel calibration and weight storage, and realizes multi-beam generation through multiply-add operation; the adaptive beam forming controller is responsible for generating a weight network by using a self-adaptive algorithm by using a received signal and prior information and sending an amplitude-phase coefficient to the control module; the control module is responsible for transmitting the amplitude-phase coefficient to the digital phase shifter and the beam former in real time and controlling the digital phase shifter and the beam former to carry out corresponding phase shifting and weight coefficient multiplication.

10. A water flow velocity radar comprising an array antenna according to any one of claims 5 to 9; used for transmitting and receiving the vertical polarization space electromagnetic wave of 290MHz to 390 MHz.

Technical Field

The invention relates to the technical field of antennas, in particular to an array antenna applied to a water flow speed measuring radar and the water flow speed measuring radar.

Background

The water flow speed measuring radar mainly utilizes backward Bragg scattering and Doppler effect of water waves on radar electromagnetic waves to obtain radial flow velocity information. The UHF radar has the wavelength of about 880mm, can simultaneously extract the information of water wave capillary waves and gravity waves, is sensitive to the action of the water waves, and can realize the fine measurement of the surface flow velocity of the river.

In a water flow velocity measurement radar system, an antenna plays a role in radiating and receiving electromagnetic waves. The traditional dipole antenna has narrow frequency band and has great limitation on the measurement sensitivity and the detection efficiency of a radio frequency electromagnetic field; the commonly used yagi antenna array has a too high profile, an active standing wave is not easy to adjust, the system is complex, and the wind resistance coefficient is large. The array antenna with excellent performance and applied to the water flow velocity measuring radar has the index requirements of narrow lobe width, low level of side lobes, wide working frequency band, high gain and small return loss. On the premise of meeting the index requirements, the antenna array is required to reduce the section height, reduce the wind resistance coefficient, reduce the weight and the volume of the system and reduce the complexity of the system as much as possible.

Disclosure of Invention

In view of the above-mentioned drawbacks and needs of the prior art, the present invention provides an antenna unit, an array antenna, and a water flow velocity radar.

In order to solve the technical problems, the invention adopts the technical scheme that:

an antenna unit comprises a dielectric substrate, and a matching balun, a radiation oscillator arm, a microstrip feeder line and a matching network which are arranged on the dielectric substrate; the microstrip feeder is connected with the matching network; the matching balun is a metal layer, and a gap for electromagnetic coupling feed is formed in the metal layer; the matching balun is a slotted metal layer; the radiation oscillator arms are positioned on two sides of the upper end of the matching balun; the distributed resistor is loaded on the radiation oscillator arm.

An array antenna, characterized in that, it includes reflecting surface, power divider, beam former and the antenna unit; the antenna unit is fixed on the reflecting surface and connected with the power divider; the power divider is connected with the beam former.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the antenna unit, the design of distributed resistance loading is carried out on the printed dipole antenna, so that the passive standing wave bandwidth of the antenna unit is greatly expanded on the premise of sacrificing small radiation efficiency, and the pulse tailing amplitude is remarkably reduced.

2. According to the antenna unit, the umbrella-shaped oscillator arm is designed, so that the wind resistance coefficient is reduced, the space between the antenna units in the vertical direction of the array is reduced, and the cross section height is greatly reduced compared with the traditional antenna arrays such as a yagi antenna array due to the adoption of the antenna units in the form of printed dipoles.

3. The array antenna realizes the extension of the frequency bandwidth of the active standing wave in the feed network with specific horizontal direction power division ratio and vertical direction amplitude-phase weighting by reasonably adjusting the width of the microstrip line of the matching network and the length of the oscillator arm and matching with the loading of the isolating strip, and the frequency band range of the whole active standing wave less than 2 reaches 290 MHz-390 MHz.

4. The array antenna realizes the reduction of the level of the side lobe of the horizontal directional diagram by designing the unequal power divider weighted by Chebyshev in the horizontal direction, so that SLL is more than 20 dB.

5. The array antenna realizes the reduction of the whole weight of the antenna array through the hollow design of the metal grid reflecting surface.

6. The array antenna of the invention mainly utilizes the vertical direction digital beam former composed of the receiving module, the beam former, the self-adaptive beam forming controller and the control module to realize the function of vertical direction digital beam forming, and can flexibly carry out weighting phase shift according to the field test environment and the received echo, so that the receiving gain is concentrated in one direction, and the spatial resolution is improved.

Drawings

Fig. 1 is a three-dimensional structural diagram of the front surface of an array antenna applied to a water flow velocity measuring radar according to the present invention;

FIG. 2 is a three-dimensional structure diagram of the reverse side of an array antenna applied to a water flow velocity measuring radar according to the present invention;

fig. 3 is a front view of a printed dipole antenna element;

FIG. 4 is a diagram of a reverse side of a printed dipole antenna element;

FIG. 5 is a graph comparing the standing wave curve of the antenna unit without loading the resistor and the standing wave curve of the antenna unit with the resistor;

fig. 6 is a radiation waveform diagram of an antenna unit loaded with distributed resistors and unloaded with distributed resistors;

FIG. 7 is a schematic diagram of a horizontal power divider;

FIG. 8 is an H-plane directional diagram of the array antenna of the present invention at 340 MHz;

FIG. 9 is a block diagram of the basic structure of a vertical digital beamformer;

FIG. 10 is an E-plane directional diagram of the array antenna of the present invention at a frequency point of 340MHz under a specific beamforming condition;

FIG. 11 is a graph of the results of actual measurements of two unit active standing waves in the middle of the array antenna and two unit active standing waves in the middle of the yagi antenna of the present invention;

fig. 12 is a graph showing the measurement result of the standing wave of the array antenna system of the present invention.

Detailed Description

Fig. 1-2 show an array antenna, which can be applied to a water flow velocity radar, and includes a printed dipole antenna unit 1, a metal grid reflecting surface 2, a horizontal power divider 3, a vertical beam former 4, and a spacer 5. The isolation strips are fixed on the fixed baffle of the metal grid reflecting surface through screws, so that the mutual coupling effect among the antenna units is adjusted, and the active standing wave bandwidth is expanded. The horizontal power divider and the vertical digital beam former are arranged on the other side of the metal grid reflecting surface, and the digital beam former can be flexibly arranged in the case of the radar host according to the assembly conditions of an actual test field. The printed dipole antenna unit is connected with the horizontal power divider through a flexible radio frequency cable in the horizontal direction; the horizontal power divider is connected with the vertical digital beam former through a flexible radio frequency cable in the vertical direction. And the horizontal direction power divider is used for reducing the level of the horizontal directional diagram side lobe. A vertical beamformer, for use in particular spatial beamforming, may concentrate vertical electromagnetic energy in a range from normal to downtilt 20, for example, under one use condition.

The antenna array is used for transmitting and receiving vertical polarization space electromagnetic waves from 290MHz to 390 MHz.

The isolation strip is positioned near the midpoint of a connecting line of the tail ends of the two printed dipole antenna unit oscillator arms in the horizontal direction, and the isolation strip is composed of a vertical surface perpendicular to the metal grid reflecting surface and a horizontal surface parallel to the metal grid reflecting surface. The height of the vertical surface of the isolating bar is 0.05 lambda₁～0.15λ₁Length of 0.05 lambda₁～0.15λ₁(ii) a The horizontal surface length of the isolating strip is 0.05 lambda₁～0.15λ₁Width of 0.05 lambda₁～0.1λ₁Wherein λ is₁340MHz vacuum wavelength. It is worth emphasizing that due to actual machining errors and the influence of the test environment, the isolation bars do not need to be loaded completely, and only need to be loaded partially according to the field test result.

In one embodiment, shown in fig. 1, a 4 × 6 area array printed dipole vertically polarized array antenna has 24 antenna elements with a horizontal spacing of 0.3 λ₁～0.7λ₁At a pitch of 0.4 λ in the vertical direction₁～0.8λ₁Wherein λ is₁340MHz vacuum wavelength.

The printed dipole antenna unit 1 is fixed above the metal grid reflecting surface 2 through a metal chassis with plastic slots, the horizontal power divider 3 is fixed below the metal grid reflecting surface 2 through screws, the vertical digital beam former 4 is fixed below the metal grid reflecting surface 2 through screws, the printed dipole antenna unit 1 is connected with the horizontal power divider 3 through a flexible radio frequency cable, and the horizontal power divider 3 is connected with the vertical digital beam former 4 through a flexible radio frequency cable. The spacing strip 5 is fixed on the fixed baffle of the metal grid reflecting surface 2 through screws.

Fig. 3-4 show block diagrams of printed dipole antenna elements. The printed dipole antenna unit 1 includes a dielectric substrate 11, a microstrip feeder 12, a matching network 13, a matching balun 14, and a radiating dipole arm 15.

In one embodiment, the antenna unit further comprises a radome 16. The antenna housing 16 is located outside the dielectric substrate, the matching balun, the radiating dipole arm, the microstrip feeder line and the matching network, and is used for protecting the structure inside the antenna housing from being damaged in the transportation and use processes and playing a waterproof role.

Specifically, the dielectric substrate 11 is a PCB plate having a relative dielectric constant of 2.55 and a thickness of 1mm, and has an umbrella shape. The width of the microstrip feed line 12 is 2.74mm, so that the characteristic impedance is 50 Ω, the length is 50mm, and the feed point position is located at the bottom quarter point of the dielectric substrate 11.

Specifically, the matching network 13 is composed of a first microstrip line matching section 131, a second microstrip line matching section 132, and a third open-circuit microstrip line matching section 133. The first microstrip line matching section 131 is 1.4mm wide and 134.3mm long and is connected with the microstrip feeder line 12; the second microstrip line matching section 132 is 2.4mm wide and 60mm long, and is connected with the first microstrip line matching section 131; the third open-circuit microstrip matching section 133 is 1.4mm wide and 112.3mm long, and is connected to the second microstrip matching section 132.

Specifically, the matching balun 14 is a rectangular copper foil with a slotted gap, is coated on the surface of the dielectric substrate 11, and has a height of 0.2 λ₁～0.4λ₁，λ₁340MHz vacuum wavelength. The width of the slot is 1mm, so that the characteristic impedance of the coplanar waveguide formed by the balun and the dielectric substrate is close to 50 omega, the impedance matching of the next matching section is further facilitated, and the length of the slot is 170 mm.

The radiation vibrator arm 15 has a front view shape of a parallelogram inclined downward, which has a lower wind impedance characteristic and can optimally reduce the overall size of the antenna array in the vertical direction compared to a conventional rectangular radiation vibrator arm.

The radiation oscillator arm can be in an umbrella shape, an oval shape, a triangular shape or the like besides the rectangular shape.

Specifically, at the arm length 3/5 from the tail end of the radiation oscillator arm 15, N slits are opened, where N is greater than or equal to 2. And carrying out distributed resistance loading in the gap. In the invention, a distributed resistor loading design is innovatively carried out on the printed dipole antenna unit, the loading resistors 151, 152 and 153 do not carry out resistance value loading according to a conventional Wu-King distributed resistor loading equation, but a formula (1) based on exponential resistor loading is selected, and on the premise of ensuring the radiation efficiency as much as possible, the obtained results are obtained through multiple times of debugging and sorting.

Wherein i takes a value of 0-2; r₀Is the resistance value at the start of loading; r_iIs the loaded resistance value; a is a constant, and 10-20 is selected; l is the single-arm length of the umbrella antenna; y is₀The distance between the initial loading point and the feeding point is set; y is_iIs the distance between the loading point i and the feeding point.

In one embodiment, there are 3 slots at the end of the dipole arm 15, and the loaded resistors are 151, 152, 153 toward the end of the dipole arm. Two arms of the radiation oscillator arm are respectively divided into three gaps with the width of 1.2mm, and the gaps are symmetrical left and right. 11 loading resistors are arranged in each gap respectively and are in the form of chip resistors; the resistors 151, 152 and 153 are loaded in parallel to the resistance R in the tail end direction of the oscillator arm₀、R₁And R₂3.6 omega and 18 respectively.2Ω、72.7Ω。

Because the distributed resistance loading is only carried out at the position close to the tail end of the oscillator arm, compared with the traditional mode of carrying out the distributed resistance loading on the oscillator arm, the radiation efficiency index is ensured, and the radiation efficiency is only reduced by 20 percent through simulation and test (testing the actual gain in a darkroom), but the passive standing wave bandwidth is greatly improved. Through actual processing tests, compared with a Wu-King loading formula, the passive standing wave bandwidth obtained according to the exponential resistance loading formula is wider and is improved from 302 MHz-378 MHz to 295 MHz-384 MHz, so that the exponential formula is selected to carry out distributed resistance loading on the array antenna unit. Fig. 5 shows a comparison graph of standing wave curves of the antenna unit after resistance loading is not carried out, distributed resistance loading is carried out according to the Wu-King loading formula, and distributed resistance loading is carried out according to the exponential type formula.

Because the duty ratio of the waveform transmitted by the water flow speed measuring radar is very small and is similar to pulse waves, the fidelity of the waveform after the waveform is radiated to the space is very important, the radiation waveform of the conventional printed dipole antenna without the loaded distributed resistor has larger tailing due to the tail end current reflection effect, the pulse tailing can be obviously inhibited after the resistor is loaded, and the resolution ratio of the radar system is improved.

Specifically, the metal grid reflecting surface 2 is in a square or round hole digging shape on a rectangular surface, and the side length of the square is 0.01-0.1 lambda₁The radius of the circle is 0.01-0.05 lambda₁Wherein λ is₁340MHz vacuum wavelength.

Fig. 7 shows a schematic structural diagram of the horizontal power divider 3. The horizontal power divider 3 is composed of a strip line 31, upper and lower dielectric substrates 32, an isolation chip resistor 33, a shielding cavity 34 and an SMA-K connector 35, wherein the strip line 31 is printed on the surface of the lower dielectric substrate and is pressed in the center by the upper and lower dielectric substrates 32 through plastic screws, and the isolation chip resistor 33 is welded at a specific position of the strip line 31 to play a role in isolating a power dividing port. The upper medium substrate 32 and the lower medium substrate 32 are wrapped by the shielding cavity 34 to protect the internal structure and shield electromagnetic interference, and the SMA-K joint 35 is welded at the output port and the output port of the power divider to connect cables. The horizontal power divider 3 is an unequal power divider, the power dividing ratio is 0.4:1:1:0.4, the standing-wave ratio of each port is good, the isolation effect of the output port is excellent, and the function of reducing the level of the side lobe in the horizontal direction is obvious. Under the condition that the digital beam former in the vertical direction does not work (namely, the digital beam former in the vertical direction is excited in phase with equal amplitude), an H-plane directional pattern of the array antenna at a 340MHz frequency point is obtained, and the H-plane directional pattern is shown in FIG. 8. As can be seen from the figure, the half-power beam width of the array antenna is 32.6 degrees, the index requirement of less than 35 degrees is met, the sidelobe level control is very low, the SLL is more than 21dB, and the capability of the array antenna for resisting electromagnetic interference is improved.

Specifically, the vertical direction digital beamformer 4 is composed of a receiving module, a beamformer, an adaptive beamforming controller, and a software control module, and a basic schematic structural block diagram thereof is shown in fig. 9. The adaptive beam forming controller obtains corresponding amplitude and phase coefficients according to an adaptive algorithm based on received signals and priori knowledge, and is also the core of the vertical digital beam former. The rough working principle is based on known parameters such as sampling frequency, sampling bandwidth, transmitting antenna track height, antenna installation angle, carrier central frequency and the like; combining the received delay of each channel relative to the central channel and the received signal intensity of the real-time channel; and generating a real-time amplitude-phase coefficient according to a target beam coverage range and a target beam width preset in a test field. The vertical digital beam former can be fixedly arranged on the lower side of the metal grid reflecting surface and can also be flexibly arranged in a case of the radar host. In a particular case, the amplitude-phase weighting coefficients are determined by an adaptive algorithm based on an optimized neural network, such that the electromagnetic energy is concentrated in the vertical direction in the range from the normal direction to 20 ° down, with amplitude weighting coefficients of 0.6, 1, 0.55, 0.1, 0.2, 0.18, respectively, and phase shift angles of-35 °, 15 °, 25 °, 21 °, 70 °, 30 °, respectively. Under the special condition, an E-plane directional pattern of the array antenna after digital beam forming at a frequency point of 340MHz is obtained, which is shown in fig. 10. As can be seen from the figure, in the range from the normal direction to the depression angle of 90 degrees, the far-field energy of the array antenna is intensively radiated in the range from 0 degree to 25 degrees, the half-power beam width of the antenna is 18.7 degrees, and the target echo can be accurately detected.

Fig. 11 is a graph showing the actual measurement results of the two-unit active standing wave in the middle of the array antenna and the two-unit active standing wave in the middle of the yagi antenna. The test method is mainly obtained by measuring the coupling coefficient between the antennas under the passive condition through the formulas (2) and (3):

wherein, in the array antenna of the invention, n is 24, S_nxThe coupling coefficient between the nth radiation unit and the xth radiation unit; a is_nA complex voltage excited for the nth radiating element under active conditions; a is_xComplex voltage excited under active condition for the x-th radiation unit; tau is_xIs the active reflection coefficient of the x-th radiating element; VSWR_xIs the active standing wave ratio of the x-th radiation unit.

The active standing wave bandwidth of the antenna units in the array can be effectively improved by adjusting the matching network of the antenna units and the height and width of the isolation strip 5. As can be seen from fig. 11, the active standing wave of the array antenna (the two middle units, which are also the largest due to the two radiation units as reference) of the present invention is substantially less than 2 in the frequency band range, and most of the active standing wave of the yagi antenna array is greater than 2 in the frequency band range.

Fig. 12 is a graph showing the measurement result of the standing wave of the array antenna system of the present invention. It can be seen from the figure that the standing wave of the array antenna system of the invention is less than 2 in the frequency band range, and the result reflects the whole standing wave ratio of the antenna feed network when the printed dipole antenna unit, the horizontal power divider and the vertical digital beam former are connected together, and the array antenna of the invention can well meet the performance requirement of the water flow speed measuring radar.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.