A cognitive antenna array and method of designing the same

Abstract

The application discloses a kind of perception antenna array and its design method, comprising: nine identical structure embedded antenna unit, eight antenna units are uniformly circularly arranged around central antenna unit to accept signal from any direction, central antenna unit is used as calibration unit. Antenna unit successively utilizes the end-fire radiation mode and dielectric resonance mode of open waveguide antenna from low frequency to high frequency, low frequency band is lowered by loading dielectric rod Its lower limit cutoff frequency, improve directivity at the same time, weaken the influence of surrounding environment on its radiation performance. Due to the height restriction of dielectric rod, the traveling wave end-fire condition of dielectric rod is still not met at high frequency band, and the dielectric rod is designed as a dielectric resonator to work in dielectric resonance mode. The high-order mode inside radiates outward through the top discontinuity.

Description

TECHNICAL FIELD

[0001] The present application relates to a perceptual antenna design method, in particular to a perceptual antenna array and a design method thereof. BACKGROUND

[0002] In order to adapt to the trend of complex and changeable electromagnetic environment in the military battlefield, passive detection technology is widely used in high-speed aircraft direction finding, perception, electromagnetic countermeasure and other fields. Unlike active positioning technology, radio detection directly uses the electromagnetic wave emitted by the outside world to determine the direction of arrival of the measured signal. As the first stage of high-speed aircraft, the antenna plays a crucial role in the performance of the wireless transceiver system. The traditional aircraft antenna has single function and is distributed in a scattered manner. With the increasing demand for communication, the aircraft can perceive more external signals. The radio direction finding technology requires the aircraft antenna to have the performance of wideband and wide beam. If the previous single antenna distribution is adopted, the number of missile-borne antennas needs to be greatly increased, and multiple antenna windows need to be designed correspondingly on the aircraft structure cabin, which brings challenges and risks to the structural strength of the aircraft. The document "Research on electromagnetic properties of thermal insulation materials for hypersonic vehicles" points out that when the high-speed aircraft flies in the near space, its surface temperature can reach 1300℃, and the internal antenna will directly face the severe high-temperature environment, which puts higher requirements on the high-temperature resistance and heat insulation performance of the antenna. Therefore, it is of great significance to design a super wideband high-temperature resistant antenna by integrating various functions.

[0003] In recent years, there are many researches on ultra-wideband antennas, and common ones include log-periodic antenna, spiral antenna, Vivaldi antenna, etc. Considering the working environment of the sensing antenna, the antenna performance is required to have the characteristics of wideband and wide beam coverage, and the structure is required to have the characteristics of miniaturization and low profile. Although the log-periodic antenna and the spiral antenna can maintain good electrical performance in a very wide frequency band, the profile is relatively high, and it is difficult to realize miniaturization of the antenna itself; the Vivaldi antenna is a low-profile antenna, but due to the small radiation window, the surrounding environment will have a great influence on the electromagnetic performance of the antenna. As a traveling wave end-fire antenna, the phase center of the dielectric rod antenna is at the top of the dielectric rod, so the high-temperature-resistant antenna designed by using the structure can reduce the influence from the surrounding environment and has good "inertia". At the same time, the use of low thermal conductivity medium to make the antenna can enhance the heat insulation capacity of the high-temperature-resistant antenna. However, due to the limitation of the installation environment, the antenna array must have the characteristics of low profile, and according to the traditional traveling wave end-fire radiation mechanism of the dielectric rod antenna, the bandwidth is also severely limited. That is, in the narrow installation environment on the aircraft, multiple antenna units in the antenna array must meet the characteristics of low profile, which is a great challenge in the low frequency band. Because the feed waveguide is affected by the cutoff frequency and has a large size in the low frequency band, the dielectric rod is essentially a hybrid TE, TM mode dielectric waveguide, and the influence of the cutoff frequency and the main mode bandwidth must also be considered. Therefore, in order to complete the effective excitation of the rectangular waveguide to the dielectric rod, realize the characteristics of ultra-wideband and wide beam, the dielectric rod antenna needs a certain length of matching section and radiation section, which is contrary to the requirement of the actual narrow installation space. It is found in the design engineering that the dielectric rod cannot meet the condition of traveling wave radiation in the whole frequency band. SUMMARY

[0004] The application aims to solve the above problems, and provides a sensing antenna array and a design method thereof, which can realize the wide beam radiation performance of the low-profile antenna array in the ultra-wideband frequency band in the narrow window on the aircraft. Meanwhile, the antenna units have high isolation characteristics, and have good temperature-resistant and heat-insulating performance in high-temperature environment.

[0005] The technical scheme adopted by the application is a sensing antenna array, which comprises: a plurality of antenna units and a center antenna unit for calibration, the central axes of the antenna units are located on the circumference with the center antenna unit as the center and are arranged at equal distances, and the antenna units are arranged around the center antenna unit.

[0006] Each single antenna unit comprises: a dielectric rod, a dielectric-filled rectangular open waveguide and a coaxial probe, the dielectric-filled rectangular open waveguide comprises a rectangular metal open waveguide and a dielectric filled in the open waveguide, and the inner conductor part of the coaxial probe is vertically inserted into the dielectric filled in the open waveguide.

[0007] The medium-filled rectangular open waveguide serves as an open waveguide antenna at a low frequency and a feed waveguide at a high frequency.

[0008] The medium rod comprises two quadrangular frustums and a cuboid between the two quadrangular frustums.

[0009] The antenna array further comprises a heatproof radome, the heatproof radome comprising a heatproof cover and a heat insulation block, the heat insulation block being filled in the heatproof cover, and the medium rod in the antenna unit being embedded in the heat insulation block.

[0010] The side surface of the medium-filled rectangular open waveguide in the antenna unit is provided with a metal lug for fixing the feed waveguide and the metal flange.

[0011] The heat insulation block is divided into three parts: a circular ring-shaped heat insulation block and two blocks divided along the center symmetry line of the octagonal heat insulation block, eight slots are opened between the circular ring-shaped heat insulation block and the octagonal heat insulation block for mounting the medium rod parts of the eight antenna units, and a slot is opened in the center of the octagonal heat insulation block for mounting the medium rod part of the center antenna unit.

[0012] The present application provides a design method of a perception antenna array, comprising the following steps:

[0013] Step one, constructing a perception antenna array model, including a medium rod antenna unit model and an antenna array model; the medium rod antenna model comprises: a medium rod, a medium-filled rectangular open waveguide and a coaxial probe, the medium-filled rectangular open waveguide comprises a rectangular metal open waveguide and a filling medium in the open waveguide, and the inner conductor part of the coaxial probe is vertically inserted into the filling medium in the open waveguide; the antenna array model comprises: a plurality of antenna units and a center antenna unit for calibration, the central axes of the antenna units are located on the circumference with the center antenna unit as the center and are arranged at equal distances, and each antenna unit is arranged around the center antenna unit;

[0014] Step two, setting the mixed radiation mode condition of the medium rod antenna unit model, comprising:

[0015] The size of the rectangular metal open waveguide is designed according to the following formula:

[0016]

[0017]

[0018] Wherein, W1 and W2 are the wide bottom edge and the narrow bottom edge of the rectangular metal open waveguide, m and n are the mode numbers, and λ is the wavelength corresponding to the working frequency.

[0019] The size of the cuboid part of the medium rod is designed according to the rectangular medium resonator theory, and the calculation formula of the resonant frequency is:

[0020]

[0021] in,

[0022]

[0023]

[0024]

[0025] In the formula, k x k y k z Let ε represent the components of the electromagnetic wave number propagating in the dielectric rod in the x, y, and z directions, respectively. r denoted as dielectric constant, k0 as wave number in vacuum, a and b as the lengths of the long and short sides of the cross-section of the cuboid, d as the height of the cuboid, and m and n as the number of field extrema along the x and y directions, respectively.

[0026] Beneficial Effects: Compared to existing technologies, this invention has the following advantages: The eight antenna elements of the antenna array are uniformly arranged on a circle centered on the central antenna element to receive signals at any angle. The central antenna element serves as a calibration unit to address the effects of antenna structural deformation and material property changes caused by the high temperature and jitter environment of the aircraft. Simultaneously, the radiation mechanism of the waveguide-fed dielectric rod antenna is creatively redesigned, abandoning the traditional traveling wave radiation mode and treating the electromagnetic waves radiated from the aperture of the open waveguide as effective radiation. The antenna elements are designed in conjunction with the dielectric resonant mode. In the X-band, the antenna elements experience two dominant radiation modes from low to high frequency: the open waveguide radiation mode and the dielectric resonant mode. The existence of these two hybrid modes enables the antenna array to achieve excellent end-fire characteristics with ultra-wideband, low profile, and wide beam. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the sensing antenna array described in this invention;

[0028] Figure 2 Here is a cross-sectional view of the heat insulation block of the sensing antenna array described in this invention: (a) is a front view and (b) is a top view;

[0029] Figure 3 The diagram shows the antenna unit of the present invention: (a) is a front view; (b) is a side view.

[0030] Figure 4 The simulation results of the sensing antenna array described in this invention are as follows: (a) and (b) are the S11 curves of the central element of the antenna array of this invention without a dielectric rod and with a dielectric rod, respectively; (c) is the VSWR of the nine ports of the antenna array of this invention; and (d) is the isolation of the antenna array of this invention.

[0031] Figure 5 Three-dimensional radiation pattern of the sensing antenna array of the present application;

[0032] Figure 6 Two-dimensional radiation pattern of the sensing antenna array of the present application;

[0033] Figure 7 Temperature curve of the center antenna unit and the top and feed port position of one of the antenna units of the antenna array of the present application over time. DETAILED DESCRIPTION

[0034] Embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] The overall structure of the sensing antenna array of the present application is shown in Figure 1 which mainly comprises eight antenna units 101 arranged in a circular ring, a center antenna unit for calibration and a heatproof radome. The heatproof radome comprises a heatproof cover 301 and heat insulation blocks. The central axes of the antenna units are located on a circumference with the center antenna unit as the center and are arranged equidistantly, and each antenna unit surrounds the center antenna unit. The heatproof cover 301 and the circular metal flange 209 are fixed to each other by eight screws 208.

[0037] Figure 2 (a) and (b) are respectively the front view and the top view of the heat insulation block. The heat insulation block is filled inside the heatproof cover 301. In order to fix the dielectric rod 101, the heat insulation block is divided into three parts: a circular ring-shaped heat insulation block 302, two blocks 303, 304 divided along the center symmetry line of the octagonal heat insulation block, and a groove 305 is opened at the junction of the circular ring-shaped heat insulation block 302 and the two blocks 303, 304 divided along the center symmetry line of the octagonal heat insulation block for placing the dielectric rod 101. The three heat insulation blocks are equal in height, all being 45 mm, and have a very low cross section.

[0038] A single antenna unit is shown in Figure 3 Figure 3 ​(a) (b) are respectively front view, side view of the antenna unit. Including dielectric rod 101, rectangular metal open waveguide 201, open waveguide filling medium 202, coaxial probe 203, small metal flange 204, screw 205. Wherein the open waveguide filling medium 202 is inside the rectangular metal open waveguide 201; the dielectric rod 101 is inserted into the open waveguide filling medium 202 to help fixation. Small metal flange 204 is fixed on the outer wall of rectangular metal open waveguide 201 by 4 screws 205. Considering the processing and assembly requirements, the heat insulation block is divided into three blocks and grooves are dug to place the dielectric rod, and metal ears 207 are arranged on both sides of the rectangular metal open waveguide 201 and fixed with circular metal flange 208 through screw 206. The dielectric rod includes two upper and lower quadrangular frustums and a cuboid between the two quadrangular frustums, and the height of the cuboid is 1-2 mm.

[0039] In the embodiment, the materials of the antenna heat insulation blocks 302, 303 and 304 are ceramic heat insulation tiles; the heat shield 301 and the dielectric rod 101 adopt quartz reinforced ceramic medium; and the open waveguide filling medium 202 is polytetrafluoroethylene material.

[0040] Embodiment 2

[0041] The design of the antenna array structure in the above embodiment 1 includes two parts of high-temperature-resistant performance design and electrical performance design.

[0042] High-temperature-resistant performance design part:

[0043] The material needs to be selected before the antenna design to meet the high-temperature-resistant characteristics. Generally, there are three ways of heat transfer: heat conduction, heat convection and heat radiation. For the aircraft antenna, the heat source is loaded to the outer surface of the aircraft, passes through the internal heat insulation material, reaches the antenna, and then reaches the feed port position of the radio frequency front end connected with the antenna. The dynamic process of this temperature transfer is basically solid-solid heat transfer, that is, heat conduction. While in the antenna interior, heat convection and heat radiation are almost non-existent. In the field of thermodynamics, generally, the greater the density of an object, the faster the speed of heat transfer, and the density is generally positively correlated with the dielectric constant. Therefore, the dielectric constant 1.3 of the heat insulation tile material is selected to design the dielectric rod antenna in order to obtain good heat-resistant performance.

[0044] Electrical performance design part:

[0045] For the dielectric rod antenna fed by waveguide, the distance from the matching section to the waveguide face needs to be reduced as much as possible, and the feeding probe is close to the bottom of the matching section to reduce the reflected wave back to the feeding position, at this time the probe can be regarded as a quarter wavelength monopole antenna in radiation. In the low frequency band, the antenna can be regarded as the co-radiation of the open waveguide antenna and the quarter monopole antenna. The dielectric rod is equivalent to the dielectric loading of the open waveguide antenna, which improves the directivity of the antenna and reduces the influence of the surrounding environment on the radiation performance. With the increase of frequency, electromagnetic waves gradually enter the dielectric rod, but due to the use of low dielectric constant heat insulation tile material in the dielectric rod, according to the formula:

[0046]

[0047] At this time, the length of the dielectric rod is only 1.6λ g Even in the high frequency band, it cannot meet the condition of traveling wave radiation. Therefore, the mode at this time is designed as a dielectric resonant mode. Electromagnetic waves are transmitted inside the dielectric resonator, and high-order modes are radiated outward through the discontinuity at the top of the radiation section. The existence of the two mixed modes supports the ultra-wideband radiation performance of the antenna. This is completely different from the traveling wave radiation mechanism of the traditional waveguide-fed dielectric rod antenna. It was previously believed that the electromagnetic waves radiated from the open waveguide antenna belonged to leakage and did not belong to effective radiation, resulting in a radiation efficiency of the dielectric rod antenna of only 60-70%. However, through special design, the electromagnetic waves "leaked" by the open waveguide antenna can not affect the end-fire performance of the antenna, and almost no side lobe and back lobe are produced, so the open waveguide can be regarded as one of the main radiation modes of the antenna, and the bandwidth and beam can be expanded by superimposing the dielectric resonant radiation mode.

[0048] The design method of the sensing antenna array disclosed by the application comprises the following steps:

[0049] Step one, constructing a sensing antenna array model, including a dielectric rod antenna unit model and an antenna unit array.

[0050] The dielectric rod antenna model comprises a rectangular metal open waveguide, a dielectric filled in the open waveguide, a coaxial feeding probe and a high dielectric constant ceramic dielectric rod. The matching section of the ceramic dielectric rod is embedded in the filled dielectric; the inner conductor part of the coaxial probe is inserted into the filled dielectric and perpendicular to the transmission surface of the rectangular metal open waveguide, and the matching performance of the overall antenna is improved by adjusting the length and position of the coaxial probe.

[0051] The antenna unit array. In order to detect external signals from 360°, a circular ring array form is adopted, and the array comprises eight antenna units uniformly distributed around and a calibration unit in the middle. Since the high-speed aircraft works in a high-temperature and jitter environment, there is a risk of causing deformation of the antenna structure and change of material properties, and the calibration unit in the center can radiate calibration signals outward and receive reflected signals, and the peripheral units only receive signals.

[0052] Step two, setting the hybrid radiation mode condition of the medium rod antenna model, comprising:

[0053] First, the open waveguide antenna size needs to be designed. For TE mn mode, its size is calculated according to the following formula:

[0054]

[0055]

[0056] Where W1 and W2 are the wide side and narrow side of the rectangular waveguide respectively, m and n are mode numbers, and λ is the wavelength corresponding to the operating frequency. Similarly, the length of the wide side and narrow side of the rectangular waveguide is also set within a certain range for optimization based on the reference values calculated above.

[0057] For the medium rod, the middle cuboid part of the medium rod can be regarded as a rectangular medium resonator, and the following transcendental equation needs to be solved to obtain the resonant frequency:

[0058]

[0059] Where,

[0060]

[0061]

[0062]

[0063] In the formula, k x , k y , and k z are the components of the wave number of the electromagnetic wave propagating in the medium rod in the x, y, and z directions, ε r is the dielectric constant, k0 is the wave number in vacuum, a and b are the length and width of the cross section of the cuboid respectively, d is the height of the cuboid, and m and n are the number of field maxima along the x and y directions respectively.

[0064] Figure 4 The simulation results of the antenna array of the present application are as follows: Figure 4 (a) and (b) are the S11 curves of the center unit of the antenna array of the present application without a medium rod and with a medium rod respectively. Through Figure 4(a), it can be seen that the resonant frequency of the open waveguide is 9.58GHz. After introducing the dielectric rod, the antenna resonates at two frequency points of 9.19GHz and 11.5GHz respectively. It can be seen that the low resonant point is caused by the open waveguide, and the appearance of the high resonant point is because of the dielectric resonant mode of the dielectric rod; in the low frequency band, electromagnetic waves are mainly radiated by the open waveguide antenna mode, and the dielectric rod is equivalent to the dielectric loading of the open waveguide antenna, which enhances the directivity of the antenna. With the gradual increase of frequency (more than 9.19GHz), it is gradually converted into a dielectric resonant mode, and the high-order mode in the dielectric rod is radiated through the top discontinuity. Figure 4 (c) is the standing wave ratio of the antenna array of the application, which realizes the matching performance of VSWR≤2 in the whole X frequency band; Figure 4 (d) is the isolation of the antenna array of the application, which realizes good high isolation performance between the nine ports, and the isolation is greater than 20dB.

[0065] Figure 5 (a), (b), (c), (d) are the three-dimensional radiation patterns of the center unit of the antenna array of the application from 8.5GHz-11.5GHz at an interval of 1GHz, Figure 5 (e), (f), (g), (h) are the three-dimensional radiation patterns of one of the edge antenna units of the antenna array of the application from 8.5GHz-11.5GHz at an interval of 1GHz. It can be seen from the figure that both antenna units realize good end-fire radiation performance.

[0066] Figure 6 (a), (b), (c), (d) are the E-plane and H-plane two-dimensional radiation patterns of the center antenna unit of the antenna array of the application from 8.5GHz-11.5GHz at an interval of 1GHz, Figure 6 (e), (f), (g), (h) are the E-plane and H-plane two-dimensional radiation patterns of one of the edge antenna units of the antenna array of the application from 8.5GHz-11.5GHz at an interval of 1GHz, and the gain pattern is greater than-8dBi within the range of ±60° beam.

[0067] In order to verify the temperature resistance and heat insulation characteristics of the high-temperature resistant antenna array, a commercial software CST Studio Suite is used for thermal simulation. Under the condition of external loading of 1200℃ high temperature, within 2000s, the temperature curves of the center antenna unit and one of the antenna units of the antenna array at the top and feed port position change with time as Figure 7 shown. It can be seen that the high-temperature resistant antenna array works normally at high temperature, and the temperature of the two feed ports is below 150℃ under the high temperature environment of 1200℃ for 2000s.

[0068] In conclusion, the perception antenna of the application adopts a dielectric rod antenna array design, and a series of innovative designs are adopted to realize ultra-wide bandwidth beam high temperature resistance. The dielectric rod adopts low dielectric constant and low thermal conductivity ceramic material, and the high temperature resistant antenna array has all port temperatures below 150 DEG C within 2000s in a high temperature environment of 1200 DEG C, while VSWR is less than or equal to 2 in the entire X wave band, and the gain is greater than -8dBi within the beam ±60 DEG, and the high isolation between units is greater than 20dB.

Claims

1. A cognitive antenna array, characterized by, The application relates to an antenna array and a method for constructing an antenna array model. The antenna array comprises a plurality of antenna units and a central antenna unit for calibration, the central axes of the antenna units are arranged on a circle with the central antenna unit as the center and are equidistantly arranged, and each antenna unit surrounds the central antenna unit. Each antenna unit comprises a dielectric rod, a dielectric-filled rectangular open waveguide and a coaxial probe.

2. The cognitive antenna array of claim 1, wherein: The dielectric-filled rectangular open waveguide comprises a rectangular metal open waveguide and an open waveguide inner filling dielectric, and the inner conductor part of the coaxial probe is vertically inserted into the open waveguide inner filling dielectric.

3. The cognitive antenna array of claim 2, wherein, The dielectric rod comprises two four-prism tables and a cuboid between the two four-prism tables, and the dielectric rod is inserted into the open waveguide inner filling dielectric.

4. The cognitive antenna array of claim 1, wherein, In a low frequency band, the dielectric-filled rectangular open waveguide serves as an open waveguide antenna, the coaxial probe serves as a quarter wavelength monopole antenna, and the antenna unit radiates in an open waveguide radiation mode.

5. A method of designing a cognitive antenna array, characterized by, In a high frequency band, the dielectric-filled rectangular open waveguide serves as a feeding waveguide, the dielectric rod serves as a dielectric rod antenna, and the antenna unit radiates in a dielectric resonance mode. The application further relates to an antenna radome. The radome comprises a heatproof radome and a heat insulation block, the heat insulation block is filled in the heatproof radome, and the dielectric rod in the antenna unit is embedded in the heat insulation block. The heat insulation block is divided into three parts, namely a circular ring-shaped heat insulation block and two blocks divided along the center symmetry line of an octagonal heat insulation block. ， ， wherein, , are the wide and narrow bottom sides of the rectangular metal open waveguide, respectively, , is the mode number, is the wavelength corresponding to the operating frequency; The side surface of the dielectric-filled rectangular open waveguide in the antenna unit is provided with a metal lug for fixing the feeding waveguide and a metal flange. ， The application further relates to a method for constructing an antenna array model. ， ， ， where kx, ky, kzare the components of the wave number of the electromagnetic wave propagating in the dielectric rod in the x, y, z directions, respectively, x , ky, kzare the components of the wave number of the electromagnetic wave propagating in the dielectric rod in the x, y, z directions, respectively, y , ky, kzare the components of the wave number of the electromagnetic wave propagating in the dielectric rod in the x, y, z directions, respectively, z , ky, kzare the components of the wave number of the electromagnetic wave propagating in the dielectric rod in the x, y, z directions, respectively, is the dielectric constant, k0is the wave number in vacuum, a, b are the length of the long side and the width of the rectangular cross section, respectively, d is the height of the rectangular, and m, n are the number of field maxima along the x, y directions, respectively.

6. The method of designing a perceptual antenna array of claim 5, wherein, Step one: constructing an antenna array model for the sensing antenna array in claim 1; 7. The method of designing a perceptual antenna array of claim 6, wherein, Step two: setting a mixed radiation mode condition of the antenna array model, which comprises: The size of the rectangular metal open waveguide is designed according to the following formula: The size of the cuboid part of the dielectric rod is designed according to the rectangular dielectric resonator theory, and the calculation formula of the components of the electromagnetic wave number in the x, y and z directions corresponding to the resonant frequency is as follows: The antenna array model comprises a dielectric rod antenna unit model and an antenna array model. The dielectric rod antenna unit model comprises a dielectric rod, a dielectric-filled rectangular open waveguide and a coaxial probe. The dielectric-filled rectangular open waveguide comprises a rectangular metal open waveguide and an open waveguide inner filling dielectric, and the inner conductor part of the coaxial probe is vertically inserted into the open waveguide inner filling dielectric.

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