A novel microstrip antenna with low radar cross section

Abstract

The present invention discloses a novel microstrip antenna with a low radar cross section. This antenna is formed by etching periodic metal patterns with different structures on the microstrip feeder layer and the intermediate metal layer of the original microstrip coupled-fed antenna. Through partial overlap of the periodic metal patterns with different structures, while having the wave-transmitting characteristic outside the operating band of the antenna, it also has a broadband phase cancellation effect, realizing the reduction of the antenna RCS in the broadband range outside the band. Compared with the traditional low-RCS microstrip antenna based on a single wave-transmitting periodic structure, this antenna greatly improves the reduction effect of the radar cross section.

Description

Technical Field

[0001] The present invention relates to the technical field of microstrip antennas, and particularly to a novel antenna with a low Radar Cross Section (RCS). Background Art

[0002] As an active radiation source and a strong scatterer, the stealth performance of an antenna is a bottleneck restricting the improvement of the overall stealth performance of combat platforms such as fighter jets. By means of changing the shape and using radar absorbing materials, etc., the radar cross section (RCS) of the antenna can be effectively reduced, but the radiation performance of the antenna will be affected.

[0003] The scattering of the antenna mode term is closely related to the radiation performance of the antenna. Therefore, in order to ensure the normal radiation of the antenna, the reduction of its RCS is more considered from the perspective of reducing the structural mode term.

[0004] Due to the structural characteristics of the microstrip antenna, the backward radar cross section outside the band can be defined as: σ = 4πS 2 / λ, where S is the area of the microstrip antenna and λ is the wavelength of the incident electromagnetic wave. It can be seen that the backward RCS of the antenna increases with the increase of frequency.

[0005] For wideband radar detection, the strong scattering in the high-frequency band makes a major contribution to the arithmetic mean value of the antenna in the entire broadband range. Therefore, reducing the RCS peak value in the high-frequency band will help to reduce the overall RCS mean value.

[0006] Adopting a periodic structure with band-stop and band-pass characteristics is a common method for reducing the RCS of an antenna. Applying a band-stop type periodic structure to the antenna can reduce the out-of-band RCS of the antenna. However, the transmission performance of the band-stop type periodic structure outside the working frequency band determines its reduction effect on the out-of-band RCS. Summary of the Invention

[0007] The purpose of the present invention is to provide a novel microstrip antenna with a low radar cross section to achieve the reduction of the antenna RCS in the out-of-band broadband range.

[0008] To this end, the present invention provides a novel microstrip antenna with a low radar cross section. The antenna is a microstrip coupled-fed antenna, which is composed of an upper layer with a radiation patch, an intermediate metal layer with a strip-shaped slot, and a lower layer with a microstrip feeder layer. Among them, the microstrip line of the microstrip feeder layer feeds the antenna through the strip-shaped slot on the intermediate metal layer. Among them, the microstrip feeder layer and the intermediate metal layer are etched with periodic metal patterns with different structures. The periodic metal patterns with different structures partially overlap, having a wave-transmitting characteristic outside the working band of the antenna and simultaneously having a broadband phase cancellation effect, realizing the reduction of the antenna RCS in the out-of-band broadband range.

[0009] Further, the periodic metal pattern etched on the above-mentioned intermediate metal layer is a Minkovski fractal metal ring, and the periodic metal pattern etched on the microstrip feeder layer is a square metal sheet. The parameter sizes of each Minkovski fractal metal ring are the same, and the parameter sizes of each square metal sheet are the same.

[0010] Further, in the above-mentioned novel microstrip antenna with a low radar cross-section, the intermediate metal layer is divided into 9*9 square regions. The metal layer of the 3*3 square regions in the center and the 1*3 rectangular regions that reach the edge of the intermediate metal layer and are centered are reserved, and a Minkovski fractal metal ring is etched in each of the remaining square regions. The microstrip feeder layer is divided into 9*9 square regions. In the 3*3 square regions centered on the three sides other than the side where the microstrip line is located, a square metal sheet is etched in the center of each square region, and in the rectangular regions composed of 1*3 squares extending along the length on the left and right sides of the microstrip line, a square metal sheet is etched in the center of each square region.

[0011] Among them, each square metal sheet is correspondingly arranged in the center position of each Minkovski fractal metal ring.

[0012] Further, in the above-mentioned novel microstrip antenna with a low radar cross-section, the parameter size of the upper layer is: a square with a side length of 57.6 mm; the parameter size of the radiation patch is 13.8 mm * 10 mm, the parameter size of the strip-shaped gap of the intermediate metal layer is 8 mm * 0.7 mm, and the parameter size of the microstrip line of the lower layer is 0.94 mm * 32 mm. The parameter size of the Minkovski fractal metal ring is: the side length l1 = 6.2 mm, the line width w = 0.2 mm, the length a1 of each concave structure is 1.4 mm, the edge distance a2 of each concave structure is 1.0 mm, and the parameter sizes of each square metal sheet are the same: the side length l2 = 4 mm.

[0013] Further, the above-mentioned antenna uses a dielectric plate with a dielectric constant of 4.5 and a loss tangent of 0.02. The thickness of the entire antenna dielectric plate is 3.5 mm. Among them, the thickness of the intermediate metal layer and the lower-layer microstrip feeder layer is 0.5 mm.

[0014] Further, the resonance center frequency of the above-mentioned antenna is at 5.21 GHz, and the working frequency band range is 5.08 - 5.46 GHz.

[0015] This antenna is formed by etching periodic metal patterns with different structures on the microstrip feeder layer and the intermediate metal layer of the original microstrip-coupled feed antenna. Through partial overlap of the periodic metal patterns with different structures, while having the wave-transmitting characteristic outside the antenna operating band, they also have a broadband phase cancellation effect, achieving the reduction of the antenna RCS in the wideband range outside the band. Compared with the traditional low-RCS microstrip antenna based on a single wave-transmitting periodic structure, this antenna greatly improves the reduction effect of the radar cross section.

[0016] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the drawings. Brief Description of the Drawings

[0017] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0018] Figure 1a and Figure 1b show two designed metal structures and their parameter dimensions;

[0019] Figure 2a is a schematic diagram of the original microstrip antenna operating at 5.25 GHz;

[0020] Figure 2b is a schematic diagram of the antenna after loading two structures;

[0021] Figure 3 shows the reflection coefficients of the microstrip antenna before and after loading the periodic structure;

[0022] Figure 4a and Figure 4b are the radiation patterns of the microstrip antenna before and after loading the periodic structure at the resonant frequency point in the xoz and yoz planes;

[0023] Figure 5a shows the curves of the backscattering of the original antenna, the antenna loaded with structure 1, and the antenna loaded with two structures varying with frequency under the condition of vertical incidence;

[0024] Figure 5b gives the bistatic RCS scanning angle curve of the antenna at 13.8 GHz under the condition of vertical incidence; and

[0025] Figure 6 shows the layered structure of the microstrip-coupled feed antenna. Detailed Description of the Embodiments

[0026] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0027] In the present invention, periodic metal patterns with different structures are etched on the microstrip feeder layer and the intermediate metal layer of the original microstrip-coupled feed antenna. The periodic metal patterns with different structures partially overlap, having the wave-transmitting property outside the antenna operating band and simultaneously having the broadband phase cancellation effect, realizing the reduction of the antenna RCS in the wideband range outside the band. This antenna greatly improves the reduction effect of the radar cross section compared with the traditional low-RCS microstrip antenna based on the periodic structure with a single wave-transmitting property.

[0028] Figure 1a and Figure 1b Two designed metal structures and their parameter sizes are given. Structure 1 is a Minkovski fractal metal ring, and structure 2 is a square metal sheet. The specific parameter sizes are: l 1 = 6.2 mm, l 2 = 4 mm, a 1 = 1.4 mm, a 2 = 1.0 mm, w = 0.2 mm.

[0029] An original microstrip antenna operating at 5.25 GHz is designed, as shown in Figure 2a and Figure 6 This antenna is a microstrip-coupled feed antenna, adopting the aperture-coupled feed method, including an upper layer 10 with a radiation patch 11, an intermediate metal layer 20 with a strip slot, and a lower layer 30 with a microstrip feeder layer 31. The microstrip line is used to feed the antenna through the strip slot on the intermediate metal layer.

[0030] The parameter sizes of the upper layer are: a square with a side length of 57.6 mm; the parameter sizes of the radiation patch are 13.8 mm * 10 mm, the parameter sizes of the strip slot on the intermediate metal layer are 8 mm * 0.7 mm, and the parameter sizes of the microstrip line on the lower layer are 0.94 mm * 32 mm.

[0031] The antenna uses a dielectric plate with a dielectric constant of 4.5 and a loss tangent of 0.02. The thickness of the entire antenna dielectric plate is 3.5 mm, and the thickness of the intermediate strip slot layer and the lower microstrip feeder layer is 0.5 mm.

[0032] To achieve better reduction of the antenna RCS, structure 1 is etched on the intermediate strip slot layer of the antenna, and structure 2 is etched on the lower microstrip feeder layer.

[0033] The electric fields below the radiation patch and above the feed line of a traditional aperture-coupled microstrip antenna are perpendicular to the metal ground plane. Therefore, to ensure the radiation performance of the antenna, after etching Structure 1 in the middle strip slot layer of the antenna, a part of the metal area is still reserved below the radiation patch and above the feed line of the antenna to better ensure the normal propagation of the quasi-TEM mode. The schematic diagram of the integrated design scheme of the specific periodic structure and the antenna is as Figure 2b shown. The specific dimensions of the above antenna are as Figure 2a and Figure 2b shown. The parameter dimensions of Structure 1 and Structure 2 are consistent with those in Figure 1a and Figure 1b .

[0034] The method of etching the Minkovski fractal metal ring on the middle metal layer is as follows: divide the middle metal layer into 9*9 square regions, reserve the metal layers of the 3*3 square regions in the center and the 1*3 rectangular regions that reach the edge of the middle metal layer and are centered, and etch the Minkovski fractal metal ring in each of the remaining square regions.

[0035] The method of etching the square metal sheet on the microstrip feed line layer is as follows: divide the microstrip feed line layer into 9*9 square regions. In the 3*3 square regions centered on the three sides except the side where the microstrip line is located, etch a square metal sheet in the center of each square region, and in the rectangular regions composed of 1*3 squares extending along the length on the left and right sides of the microstrip line, etch a square metal sheet in the center of each square region.

[0036] In this way, each square metal sheet is correspondingly arranged in the center position of each Minkovski fractal metal ring.

[0037] Figure 3 shows the reflection coefficients of the microstrip antenna before and after loading the periodic structure obtained by Ansoft HFSS14.0 simulation. It can be seen from the figure that the resonant center frequency of the antenna before loading is 5.25 GHz, and the working frequency band range is 5.1 - 5.45 GHz. After loading the two structures, the reflection coefficient of the antenna basically remains unchanged, the resonant center frequency is at 5.21 GHz, shifted 40 MHz to the lower frequency, and the working frequency band range is 5.08 - 5.46 GHz, indicating that loading the two structures has little impact on the resonant performance of the antenna.

[0038] Figure 4a and Figure 4bThe radiation patterns of the microstrip antenna before and after loading the periodic structure at the resonant frequency point in the xoz and yoz planes are given. It can be seen from the figure that the radiation patterns of the microstrip antenna in the xoz plane and yoz plane basically do not change after loading the periodic structure. The gain of the original antenna is 5.21 dBi, and the gain of the antenna after loading the periodic structure is 5.55 dBi. The above results show that the reasonable loading of the two periodic structures increases the radiation gain of the original antenna by 0.34 dB.

[0039] Figure 5a The curves of the backscattering of the original antenna, the antenna loaded with structure 1, and the antenna loaded with two structures varying with frequency under the condition of vertical incidence are given. It can be seen from the figure that the RCS reduction effect of the antenna loaded with structure 1 is not as obvious as that of the antenna loaded with two structures. After loading the two structures, the RCS reduction reaches 10 dB in the frequency ranges of 2.2 - 2.6 GHz and 7.1 - 16 GHz, and the relative bandwidths of the RCS reduction of 10 dB are 16.7% and 77.1% respectively.

[0040] Figure 5b The bistatic RCS scanning angle curve of the antenna at 13.8 GHz under the condition of vertical incidence is given. It can be seen from the figure that due to the combined action of the wave - transmitting and phase - cancellation characteristics, the strong specular scattering of the antenna is significantly suppressed, and the maximum RCS reduction reaches 32.2 dB. In addition, usually, phase cancellation will disperse the scattering energy to other non - threatening regions, thereby increasing the RCS values at other angles. However, due to the wave - transmitting characteristics of structure 1, the RCS in other directions of this antenna is not increased.

[0041] From the above comparison, it can be seen that in the present invention, the two periodic structures are integrally designed with the microstrip antenna. In the working frequency band of the antenna, the periodic structure ensures the radiation performance of the antenna due to its band - stop characteristics, and outside the working frequency band, broadband antenna RCS reduction is achieved due to the wave - transmitting and phase - cancellation effects.

[0042] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A novel microstrip antenna with a low radar cross section, characterized in that, the antenna is a microstrip coupled-fed antenna, adopting an aperture-coupled feeding method, and is composed of an upper layer with a radiation patch, an intermediate metal layer with a strip slot, and a lower layer with a microstrip feeder layer. Among them, the microstrip line of the microstrip feeder layer feeds the antenna through the strip slot on the intermediate metal layer; wherein, the microstrip feeder layer and the intermediate metal layer are etched with periodic metal patterns of different structures. The periodic metal patterns of different structures partially overlap, having the wave-transmitting characteristic outside the antenna working band and simultaneously having a broadband phase cancellation effect, realizing the reduction of the antenna RCS in the broadband range outside the band; the periodic metal pattern etched on the intermediate metal layer is a Minkovski fractal metal ring, and the periodic metal pattern etched on the microstrip feeder layer is a square metal sheet. The parameter sizes of each Minkovski fractal metal ring are the same, and the parameter sizes of each square metal sheet are the same; the method of etching the Minkovski fractal metal ring on the intermediate metal layer includes: dividing the intermediate metal layer into 9*9 square regions, retaining the metal layer of the 3*3 square regions in the center and the 1*3 rectangular regions that reach the edge of the intermediate metal layer and are centered, and etching the Minkovski fractal metal ring in each of the remaining square regions; the method of etching the square metal sheet on the microstrip feeder layer includes: dividing the microstrip feeder layer into 9*9 square regions. In the 3*3 square regions centered on the three sides except the side where the microstrip line is located, a square metal sheet is etched in the center of each square region, and in the rectangular region composed of 1*3 squares extending along the length of the microstrip line on the left and right sides of the microstrip line, a square metal sheet is etched in the center of each square region. Among them, each square metal sheet is correspondingly arranged at the center position of each Minkovski fractal metal ring; the antenna uses a dielectric plate with a dielectric constant of 4.5, and the working frequency band range of the antenna is 5.08 - 5.46 GHz.

2. The novel microstrip antenna with a low radar cross section according to claim 1, characterized in that, the parameter sizes of the upper layer are: a square with a side length of 57.6 mm; the parameter sizes of the radiation patch are 13.8 mm * 10 mm, the parameter sizes of the strip slot of the intermediate metal layer are 8 mm * 0.7 mm, and the parameter sizes of the microstrip line of the lower layer are 0.94 mm * 32 mm.

3. The novel microstrip antenna with a low radar cross section according to claim 2, characterized in that, The parameter dimensions of the Minkovski fractal metal ring are: side length l 1 =6.2 mm , line width w =0.2 mm , the length of each concave structure a 1 =1.4 mm, The margin of each concave structure a 2 =1.0 mm , the parameter dimensions of each square metal sheet are the same: side length l 2 =4 mm .

4. The novel microstrip antenna with a low radar cross section according to claim 2, characterized in that, the antenna uses a dielectric plate with a loss tangent of 0.

02.

5. The novel microstrip antenna with a low radar cross section according to claim 4, characterized in that, The thickness of the entire antenna dielectric plate is 3.5 mm .

6. The novel microstrip antenna with a low radar cross section according to claim 4, characterized in that, The thicknesses of both the intermediate metal layer and the lower microstrip feeder layer are 0.5 mm .

7. The novel microstrip antenna with a low radar cross section according to claim 2, characterized in that, The resonant center frequency of the antenna is at 5.21 GHz.

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