Broadband antenna device based on multi-band gradient high impedance surface

Abstract

The present invention relates to the technical field of broadband antenna manufacturing, and more specifically, to a broadband antenna device based on a multi-band gradient high-impedance surface suitable for passive guidance radars, passive direction-finding systems, and electronic countermeasure systems. The device is characterized by comprising a broadband butt-to-butt Vivaldi antenna radiator, a metal reflective floor, a multi-sized gradient high-impedance surface, and a microwave absorbing material disposed between the high-impedance surface and the antenna radiator. The multi-sized gradient high-impedance surface is provided with a grounded high-impedance surface electromagnetic bandgap structure having square shapes of decreasing size in order of frequency from low to high, and a groove is etched in the metal region of the broadband butt-to-butt Vivaldi antenna radiator.

Description

Technical field:

[0001] The present invention relates to the technical field of broadband antenna manufacturing, in particular to a broadband antenna device based on a multi-band gradient high-impedance surface suitable for passive guidance radar, passive direction-finding system and electronic countermeasure system. Background technology:

[0002] In broadband passive radar systems on aircraft platforms, a broadband miniaturized antenna sensor is a key component. Due to space constraints on the platform, broadband passive antennas are typically installed within the forward radome of the aircraft, or conformally arranged on the surface of the antenna carrier. Therefore, passive radar antennas require miniaturization and a low profile. Passive radar antennas must detect and track radiation sources within a given spatial region over a wide frequency band. Therefore, the broadband antenna's beam pointing and coverage must be designed and controlled. This is particularly challenging when the aircraft's surface is metallic and the antenna beam is oriented axially. In actual operation, the antenna's radar cross section (RCS) must be controlled to achieve radar stealth. Consequently, many systems also propose technical requirements for antenna stealth, which has become a research hotspot and holds significant engineering significance.

[0003] The tapered slot antenna is a non-periodic continuously gradient traveling wave antenna with the main features of ultra-wide operating frequency band, medium gain end-fire beam, symmetrical E and H plane radiation pattern, low profile structure, etc. It has been widely used in phased array radar, communication and direction finding systems.

[0004] Due to its structure and radiation characteristics, the Vivaldi antenna is easy to load with artificial electromagnetic materials, and a wealth of research results have emerged. Antennas are a significant scattering source for low-observable platforms. Reducing the antenna's RCS is crucial for achieving stealth in electronic warfare. In addition to structural mode scattering caused by the antenna's structure, antenna mode scattering due to load mismatch is also present. Furthermore, the antenna's structure and loading are closely related to its radiation performance. Therefore, reducing the antenna's RCS must first ensure that its radiation is not affected. Antenna system RCS reduction methods are based on numerous constraints. Time-domain stealth for antenna systems aims to achieve stealth during specific time periods. When a radar antenna is powered off, it generates no radar cross section, effectively rendering it invisible. However, when powered on, it contributes a significant radar cross section. Airspace stealth for antenna systems aims to achieve stealth at specific locations in space. Typically, by modifying the aircraft's external structure or antenna configuration, the structural scattering field in the threat zone can be shifted to the remaining non-threat zone. Modal scattering caused by mismatched antenna loads can be reduced through impedance matching, but this also affects antenna radiation. Out-of-band stealth can be achieved using a FSS. FSSs are categorized as either bandpass or bandstop. A bandpass FSS operates in the passband, meaning its transmission efficiency is nearly 1. Conversely, a bandstop FSS operates in the stopband, meaning its transmission efficiency is zero. Typically, a bandpass FSS is combined with a radome, covering the antenna. The FSS's operating frequency band is set within the antenna's operating frequency band. When the antenna is operating, the FSS's all-pass characteristics do not affect normal antenna radiation. Out-of-band, the FSS behaves like a perfect electric conductor (PEC). Combined with the low-scattering radome, it scatters incident waves into non-threat angular regions, achieving out-of-band stealth. For the band-stop FSS, it is generally used directly as the antenna floor. Within the working frequency band of the antenna, the FSS is equivalent to the PEC and does not affect the normal radiation of the antenna. Outside the working frequency band, the external incident electromagnetic waves can pass directly through the antenna floor, thereby reducing the backscattering of the antenna and realizing the reduction of the single-station radar cross-section outside the band. Summary of the invention:

[0005] In view of the shortcomings and deficiencies in the prior art, the present invention proposes a broadband antenna device based on a multi-band gradient high-impedance surface suitable for passive guidance radar, passive direction finding system and electronic countermeasure system.

[0006] The present invention is achieved by the following measures:

[0007] A broadband antenna device based on a multi-band gradient high-impedance surface is characterized by comprising a broadband butt-to-butt Vivaldi antenna radiator, a metal reflective floor, a multi-sized gradient high-impedance surface, and a microwave absorbing material disposed between the high-impedance surface and the antenna radiator. The multi-sized gradient high-impedance surface is provided with grounded high-impedance surface electromagnetic bandgap structures of square sizes from large to small in order of frequency from low to high. a is the patch side length, g is the unit spacing, h is the thickness of the dielectric layer, and d is the diameter of the metallized via. The bandgap center frequency and 3dB bandwidth of the high-impedance surface structure are respectively calculated by the following formulas:

[0008]

[0009]

[0010] Where: f0 is the center frequency of the bandgap; Δf is the bandgap width; η = 120π, which is the wave impedance of free space; the capacitance and inductance of the LC resonant model are:

[0011]

[0012] L=L1=μ0μ r h

[0013] Where: ε1 and ε2 are the dielectric constants of the media above and below the metal patch, respectively. In the single-layer case, the area above the patch is air, ε1 = ε0; μr is the relative permeability of the medium between the patch and the metal floor.

[0014] The broadband heel-to-heel Vivaldi antenna radiator of the present invention has grooves etched in the metal area, and the two curve equations constraining the Vivaldi antenna radiator are:

[0015] y=aexp(r1x)-(w f / 2+a) (1)

[0016] y=aexp(r2x)+(w f / 2-a) (2)

[0017] Where a, r1 and r2 are constants, w f is the width of the starting end of the metal arm of the Vivaldi oscillator.

[0018] The input end of the Vivaldi antenna radiator of the present invention is a microstrip line with a characteristic impedance of 50 ohms to connect to the coaxial line. A gradient line structure is used between the Vivaldi dipole metal arm and the microstrip line to achieve broadband impedance transformation.

[0019] The present invention integrates a modified Vivaldi antenna, microwave absorbing materials, and a gradient high-impedance surface. The antenna's radiation beam direction is regulated based on the electromagnetic boundary conditions of a carrier platform composed of metal conductors. A hybrid layered local loading scheme using the gradient high-impedance surface and microwave absorbing materials is adopted, and the hybrid boundary conditions are utilized to achieve control of the broadband antenna beam direction. Antenna shaping and hybrid layered local loading using the gradient high-impedance surface and microwave absorbing materials are utilized to reduce the antenna's radar cross-section and improve the antenna's stealth performance.

[0020] The broadband antenna based on a multi-band gradient high-impedance surface proposed in this invention is primarily implemented using printed circuits and features a simple structure, flexible design, and excellent mechanical properties, facilitating engineering implementation. The broadband antenna device based on a multi-band gradient high-impedance surface proposed in this invention is suitable for use in passive guidance radars, passive direction-finding systems, and electronic countermeasures systems, demonstrating significant application value and adaptability across multiple platforms. Description of the drawings:

[0021] Figure 1 is a schematic diagram of the structure of the present invention, wherein Figure 1(a) is a schematic diagram of the overall structure, Figure 1(b) is a schematic diagram of the partial structure after removing the antenna circuit board, Figure 1(c) is a schematic diagram of the gradient high-impedance surface, Figure 1(d) is a side schematic diagram, and Figure 1(e) is a side schematic diagram of the present invention from another angle.

[0022] Attachment Figure 2 is a schematic diagram of the structure of the Vivaldi antenna radiator in the present invention, wherein Figure 2 (a) is the structural diagram from the first perspective. Figure 2 (b) is a schematic diagram of the structure in another direction.

[0023] Attachment Figure 3 is a schematic structural diagram of the gradient high impedance surface in the present invention, Figure 3 (a) is the front view, Figure 3 (b) is the back view.

[0024] Attachment Figure 4 is a topological diagram of the high impedance surface bandgap structure in the present invention, Figure 4 (a) is the top view, Figure 4 (b) is a side view.

[0025] Attachment Figure 5 This is the equivalent model diagram of the high impedance surface structure.

[0026] Attachment Figure 6 4 is a simulation diagram of the return loss of the antenna port in an embodiment of the present invention.

[0027] Attachment Figure 7 is the simulation result of the antenna radiation characteristics when the frequency is 1 GHz in the embodiment of the present invention, wherein Figure 7 (a) is the gain pattern on the xoz plane, Figure 7 (b) is the axial ratio direction diagram on the xoz plane, Figure 7 (c) is the gain pattern on the yoz plane, Figure 7 (d) is the axial ratio direction diagram on the yoz plane, Figure 7 (e) is the three-dimensional gain pattern, Figure 7 (f) is the three-dimensional axial ratio direction diagram.

[0028] Attachment Figure 8 is the simulation result of the antenna radiation characteristics when the frequency is 2 GHz in the embodiment of the present invention, wherein Figure 8 (a) is the gain pattern on the xoz plane, Figure 8 (b) is the axial ratio direction diagram on the xoz plane, Figure 8 (c) is the gain pattern on the yoz plane, Figure 8 (d) is the axial ratio direction diagram on the yoz plane, Figure 8 (e) is the three-dimensional gain pattern, Figure 8 (f) is the three-dimensional axial ratio direction diagram.

[0029] Attachment Figure 9 is the simulation result of the antenna radiation characteristics when the frequency is 3 GHz in the embodiment of the present invention, Figure 9 (a) is the gain pattern on the xoz plane, Figure 9 (b) is the axial ratio direction diagram on the xoz plane, Figure 9 (c) is the gain pattern on the yoz plane, Figure 9 (d) is the axial ratio direction diagram on the yoz plane, Figure 9 (e) is the three-dimensional gain pattern, Figure 9 (f) is the three-dimensional axial ratio direction diagram.

[0030] Attachment Figure 10 is the simulation result of scattering characteristics at a frequency of 1 GHz, where Figure 10 (a) Three-dimensional RCS pattern for polarization direction x, Figure 10 (b) Three-dimensional scattering axis ratio pattern for polarization direction x, Figure 10 (c) 3D RCS pattern for polarization direction y, Figure 10 (d) Three-dimensional scattering axis ratio pattern for polarization direction y.

[0031] Attachment Figure 11 is the simulation result of scattering characteristics at a frequency of 2 GHz, where Figure 11 (a) Three-dimensional RCS pattern for polarization direction x, Figure 11 (b) Three-dimensional scattering axis ratio pattern for polarization direction x, Figure 11 (c) 3D RCS pattern for polarization direction y, Figure 11(d) Three-dimensional scattering axis ratio pattern for polarization direction y.

[0032] Attachment Figure 12 is the simulation result of scattering characteristics at a frequency of 3 GHz, where Figure 12 (a) is the three-dimensional RCS pattern in polarization direction x, Figure 12 (b) is the three-dimensional scattering axis ratio pattern in the polarization direction x, Figure 12 (c) is the three-dimensional RCS pattern in polarization direction y, Figure 12 (d) is the three-dimensional scattering axis ratio pattern for polarization direction y.

[0033] Figure 1: 1 is a modified Vivaldi antenna radiator, 2 is a dielectric substrate, 3 is a gradient high impedance surface, 4 is a microwave absorbing material, 5 is a groove, 6 is an impedance gradient line, 7 is a Vivaldi oscillator radiator, 8 is a metal via, 9 is a resistor, and 10 is a metal copper foil floor. Specific implementation method:

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] To address the technical needs of broadband antenna sensors mounted on aircraft platforms, this paper proposes a broadband, opposed-heel Vivaldi antenna structure that incorporates a tapered, multi-sized high-impedance surface and microwave absorbing materials. This solves the beam steering and low-profile design challenges of broadband antennas mounted on metal surfaces, thereby reducing the antenna's radar cross section (RCS). A model of the broadband antenna structure based on the tapered high-impedance surface designed in this paper is shown in Figure 1. Figure 2 This is the structural diagram of the modified Vivaldi antenna. Figure 3 The figure is a schematic diagram of the structure of a gradient high-impedance surface. Normally, the surface of an aircraft carrier is a metal structure, which can be approximated as an electric wall. According to the equivalence principle and the mirror principle, a conventional antenna will produce a mirror effect when installed close to the aircraft surface. Under broadband working conditions, it is difficult to make the antenna have a low profile. Due to the limitation of the installation space on the aircraft, the antenna is usually required to have an extremely low profile size. Therefore, the low-profile design of broadband antennas is an important task. The antenna structure designed in the present invention includes a broadband butt-to-heel Vivaldi antenna radiator, a metal reflective floor, a multi-sized gradient high-impedance surface and a microwave absorbing material between the high-impedance surface and the antenna radiator; in Figure 1, 1 is a modified Vivaldi antenna radiator, 2 is a dielectric substrate, 3 is a gradient high-impedance surface, and 4 is a microwave absorbing material.

[0036] The Vivaldi antenna is an end-fire traveling wave antenna. The electromagnetic wave is transmitted along the exponential slot line and coupled to the free space. The maximum opening width of the Vivaldi antenna corresponds to the minimum operating frequency. Usually, the maximum slot size of the antenna is λ.max / 2, the minimum slot line width corresponds to the highest operating frequency. When the slot line width is much smaller than the wavelength λ of the electromagnetic wave in free space, the energy of the electromagnetic wave will be confined between the metal arms. As the distance between the two radiating arms expands exponentially, the energy of the electromagnetic wave will gradually be coupled and radiated into the free space. At the same time, the energy transmitted along the slot line will gradually weaken. For different frequency points, the effective radiation area of ​​the Vivaldi antenna is variable. Only the area close to the wavelength can form effective radiation. The size of the effective radiation area of ​​the antenna is proportional to the corresponding working wavelength. The electrical size of the antenna can be roughly considered to be unchanged. In order to reduce the radar scattering interface of the antenna, the present invention adopts a modified Vivaldi radiator, etches a groove in the metal area of ​​the Vivaldi antenna, and optimizes the design parameters to reduce the area of ​​the metal part of the antenna radiator. The two curve equations that constrain the Vivaldi antenna radiator are:

[0037] y=aexp(r1x)-(w f / 2+a) (1)

[0038] y=aexp(r2x)+(w f / 2-a) (2)

[0039] Where a, r1 and r2 are constants, w f is the width of the starting end of the metal arm of the Vivaldi oscillator.

[0040] The input end of the Vivaldi antenna radiator is a microstrip line with a characteristic impedance of 50 ohms to connect to the coaxial line. In the Vivaldi antenna designed by the present invention, a gradient line structure is used between the Vivaldi dipole metal arm and the microstrip line to achieve broadband impedance transformation.

[0041] In the low-profile design of broadband antennas, mainly for low-frequency band low-profile design, the present invention adopts a solution of locally changing boundary conditions; for broadband requirements, a multi-size gradient high-impedance surface loading is proposed, and the principle structure of the designed high-impedance surface is as follows Figure 3 As shown. According to the radiation mechanism of the Vivaldi antenna, the high-impedance surface structure is designed in order from large to small in frequency, corresponding to the effect of in-phase reflection at a certain frequency. The present invention adopts a high-impedance surface electromagnetic bandgap structure with a square grounding structure. Figure 4 The structural topology of a square high-impedance surface is shown in Figure 2. a is the patch side length, g is the cell pitch, h is the dielectric thickness, and d is the metallized via diameter. These structural parameters, along with the dielectric constant of the dielectric layer, determine the bandgap frequency of the high-impedance surface. Figure 5An equivalent model for a high-impedance surface structure is given, where C is the gap capacitance between metal patches, and L1 is the inductance caused by the dielectric layer. The bandgap center frequency and 3dB bandwidth of the high-impedance surface structure can be calculated using the following approximate formulas:

[0042]

[0043]

[0044] Where: f0 is the center frequency of the bandgap; Δf is the bandgap width; η = 120π, which is the wave impedance of free space. The capacitance and inductance of the LC resonant model are:

[0045]

[0046] L=L1=μ0μ r h

[0047] Where: ε1 and ε2 are the dielectric constants of the media above and below the metal patch, respectively. In the general single-layer case, the air above the patch is ε1 = ε0; μr is the relative magnetic permeability of the medium between the patch and the metal floor.

[0048] Example:

[0049] This example designs a broadband, low-profile antenna device based on a tapered high-impedance surface. Full-wave electromagnetic simulation technology was used to design an antenna example. Simulation results validate the performance of the proposed broadband, low-profile antenna based on a tapered high-impedance surface. The antenna utilizes high-impedance surfaces constructed in four different sizes, corresponding to four frequency points. This antenna primarily regulates the low-frequency beam and reduces the radar cross-section. The microwave absorbing material is locally loaded, with a loss tangent of 0.5. The antenna width is 60 mm, the distance from the antenna to the metal floor is 10 mm, and the length of the absorbing material is 35 mm.

[0050] The return loss characteristics of the broadband low-profile antenna based on the gradient high-impedance surface designed in this example are as follows: Figure 6 As shown in the figure, it can be seen that in the operating frequency range of 2GHz to 6GHz, the average return loss of the antenna port is approximately less than -10dB, and the return loss at 1GHz is also less than -10dB.

[0051] Figure 7 、 Figure 8 and Figure 9The antenna's radiation patterns at 1 GHz, 2 GHz, and 3 GHz are shown. At each frequency point, the xoz plane, yoz plane, three-dimensional gain, and three-dimensional axial ratio patterns are shown. It can be seen that the introduction of the hybrid boundary shifts the main beam toward endfire, thus achieving beam steering. Figure 10 、 Figure 11 and Figure 12 The scattering characteristics of the antenna at frequencies of 1 GHz, 2 GHz and 3 GHz are given respectively. The results show that the radar cross section of the antenna is reduced due to the combined measures of absorbing materials, high impedance surface and antenna modification.

Claims

1. A broadband antenna device based on a multi-band gradient high impedance surface, characterized in that: It is equipped with a broadband Vivaldi antenna radiator, a metal reflective floor, a multi-sized gradient high-impedance surface and a microwave absorbing material arranged between the high-impedance surface and the antenna radiator. The multi-size gradient high-impedance surface is provided with a grounded high-impedance surface electromagnetic bandgap structure with square sizes ranging from large to small in order of frequency from low to high. a is the side length of the patch, g is the unit spacing, h is the thickness of the dielectric layer, and d is the diameter of the metallized via. The bandgap center frequency and 3 dB bandwidth of the high-impedance surface structure are respectively calculated by the following formulas: （3）， （4）， Where: is the band gap center frequency; ∆f is the band gap width; , which is the wave impedance of free space; the capacitance and inductance of the LC resonance model are: ， ， Where: and They are the dielectric constants of the upper and lower dielectrics of the metal patch, respectively. In the case of a single layer, the dielectric constant above the patch is air. ; µr is the relative magnetic permeability of the medium between the patch and the metal floor; According to the radiation mechanism of the Vivaldi antenna, high-impedance surface structures are designed in descending order of frequency, corresponding to the in-phase reflection effect of a certain frequency.

2. The broadband antenna device based on a multi-band gradient high impedance surface according to claim 1, characterized in that: The metal area of ​​the broadband heel-to-heel Vivaldi antenna radiator is etched with grooves, and the two curve equations constraining the Vivaldi antenna radiator are: （1）， （2）， Where, 、 and is a constant, is the width of the starting end of the metal arm of the Vivaldi oscillator.

3. The broadband antenna device based on a multi-band gradient high impedance surface according to claim 1, characterized in that: The input end of the Vivaldi antenna radiator is a microstrip line with a characteristic impedance of 50 ohms to connect to the coaxial line. A gradient line structure is used between the Vivaldi vibrator metal arm and the microstrip line to achieve broadband impedance transformation.

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