A high-isolation radio altimeter microstrip antenna

Abstract

This invention discloses a high-isolation radio altimeter microstrip antenna, mainly addressing the problem of low isolation in existing antennas. From top to bottom, it includes a radiator (1), an adjustment structure (2), and a ground plane (3). The adjustment structure (2) includes a frame (21), metal stubs (22), shorting pins (23), and a dielectric (24). The metal stubs consist of three parts, with the first part located at the antenna's central axis AA, and the second and third parts symmetrical about the antenna's central axis AA. The shorting pins consist of three groups, with the first group located at the antenna's central axis AA, and the second and third groups symmetrical about the central axis AA. The frame and metal stubs are located on the upper surface of the dielectric, while the shorting pins are located inside the dielectric. This invention uses a split design to form a transmitting antenna and a receiving antenna, which can be flexibly installed in different positions on the device, effectively improving the isolation between the transmitting and receiving antennas. It can be used in radio altimeters or ranging / altitude radars.

Description

Technical Field

[0001] This utility model belongs to the field of radar equipment technology, specifically relating to a radio altimeter microstrip antenna that can be used in altimeter radar. Background Technology

[0002] As a type of altimeter radar, the basic principle of a radio altimeter is to utilize the rectilinear propagation of electromagnetic waves. It measures the round-trip time of the electromagnetic wave—from its emission from the transmitting antenna to its reception by the receiving antenna and back across the Earth's surface—to calculate the corresponding distance to the aircraft, thus completing the altitude measurement function. Radio altimeters employ a dual-antenna operating mode (transmitting and receiving). If the coupling between the transmitting and receiving antennas is too strong and the isolation is insufficient to meet the sensitivity requirements of the radio altimeter, it will be unable to measure altitude correctly. Therefore, isolation is crucial.

[0003] Radio altimeter antennas come in two forms: cavity antennas and microstrip antennas. While cavity antennas offer high isolation, their narrow bandwidth, large size, and heavy weight limit their use. Microstrip antennas, on the other hand, are increasingly popular due to their small size, light weight, low profile, and conformal design to aircraft.

[0004] Patent document CN 112821066 A discloses an EBG structure for improving antenna isolation, which adds an EBG structure between the transmit and receive microstrip antennas, such as... Figure 6 As shown, the EBG structure includes a high-frequency dielectric substrate, a ground plane, and several metal patch units. The high-frequency dielectric substrate is placed on the ground plane, and the metal patch units are placed on the high-frequency dielectric substrate. Each metal patch unit has a through-hole penetrating both the metal patch unit itself and the high-frequency dielectric substrate. This structure requires an integrated design of the transmitting and receiving antennas, necessitating the addition of the EBG structure in the middle. The overall structure is relatively large. While it improves isolation between the transmitting and receiving antennas when they are close together, it becomes even larger when the antennas are far apart. Furthermore, with the development of wireless communication technology and the expansion of aircraft functional requirements, more and more external devices need to be installed on the aircraft surface. This type of antenna installation will conflict with the installation space on the aircraft surface, affecting the improvement of isolation and failing to meet the requirements for radio altimeter use. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a high-isolation radio altimeter microstrip antenna, which designs a transmitting antenna and a receiving antenna to meet antenna performance requirements, thereby improving the isolation between the transmitting and receiving antennas.

[0006] To achieve the above objectives, the high-isolation radio altimeter microstrip antenna of this invention comprises: a radiator and a ground plane, characterized in that:

[0007] An adjustment structure is provided between the radiator and the ground plane, which includes a frame, metal branches, shorting pins, and a dielectric layer, for adjusting the isolation of the antenna;

[0008] The metal stub consists of three sections, with the first section located at the antenna's central axis AA, and the second and third sections being symmetrical with respect to the antenna's central axis AA.

[0009] The shorting pins consist of three groups, each group containing a positive integer number of pins not less than 1. The first group of shorting pins is located at the central axis AA of the antenna, and the second and third groups of shorting pins are symmetrical about the central axis AA.

[0010] The border and metal stub are both located on the upper surface of the dielectric layer, while the short-circuit pin is located inside the dielectric layer.

[0011] Preferably, the frame is a rectangular metal ring with opposite sides having the same width; the dielectric is a microwave laminate with low dielectric constant and low loss tangent, and has three sets of through holes.

[0012] Preferably, the first branch is connected to the ground plane via a first shorting pin group; the second branch is connected to the ground plane via a second shorting pin group; and the third branch is connected to the ground plane via a third shorting pin group.

[0013] Preferably, the radiator includes radiating elements, a feed network, and slots. Each radiating element radiates electromagnetic waves and is connected to the feed network by opening a single-layer rectangular microstrip patch.

[0014] Preferably, the outer dimensions of the dielectric layer are consistent with the outer dimensions of the frame, and the diameters of its three sets of through holes are consistent with the diameters of the three sets of shorting pins.

[0015] Preferably, the adjustment parameters of the antenna include: the length L1 and width W1 of the slot, the length L2 and width W2 of the first stub, the length L3 and width W3 of the second stub, the diameter φ1 of each shorting pin group, the distance L5 between the first shorting pin group and the first stub, and the distance L4 between the second shorting pin group and the second stub.

[0016] Compared with the prior art, this utility model has the following advantages:

[0017] Firstly, this utility model adds an adjustment structure to the existing antenna and sets multiple adjustment parameters. By adjusting these antenna structure parameters, the gain of the antenna coupling angle can be reduced and the antenna isolation can be improved.

[0018] Secondly, because the present invention adopts a separate design for the transmitting and receiving antennas, it can be more flexibly installed on the surface of the device, thereby improving the isolation between the transmitting and receiving antennas at both close and long distances. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the model of this utility model;

[0020] Figure 2 This is an exploded view of the structure of this utility model;

[0021] Figure 3 This is a schematic diagram of the structure of this utility model;

[0022] Figure 4 This is a schematic diagram of the antenna parameters of this utility model;

[0023] Figure 5 This is a model diagram of a split-mounted transceiver antenna according to an embodiment of this utility model;

[0024] Figure 6 This is a schematic diagram of an existing antenna structure;

[0025] Figure 7 The figure shows the simulation results of the standing wave coefficient of the present invention and existing antennas;

[0026] Figure 8 This is a simulation result diagram of the radiation pattern of the plane where the coupling angle of the present invention is located compared with that of an existing antenna;

[0027] Figure 9 This is a simulation result diagram of the isolation degree of an embodiment of this utility model;

[0028] Figure 10 The simulation results for the isolation of the existing antenna are shown in the figure.

[0029] Figure 11 This is a graph showing the difference in isolation between the present invention and existing antennas. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions and effects of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort should all fall within the protection scope of the present invention.

[0031] I. Design Principles

[0032] Antenna isolation is an important parameter for measuring the degree of coupling between transmitting and receiving antennas, defined as the ratio of the signal received by the receiving antenna to the signal received by the transmitting antenna. Coupling between transmitting and receiving antennas includes the direct incoming signal in the antenna coupling direction and the diffracted and reflected signals from the carrier. The magnitude of the direct incoming signal in the antenna coupling direction is related to the antenna gain in that direction and the distance between the transmitting and receiving antennas. The isolation evaluation formula is as follows:

[0033]

[0034] Where A is the isolation between the transmitting and receiving antennas; Pr is the power received by the receiving antenna; Pt is the output power of the transmitting antenna; Gt(θ1) is the gain of the transmitting antenna in the coupling direction; Gr(θ2) is the gain of the receiving antenna in the coupling direction; r is the distance between the transmitting and receiving antennas; λ is the operating wavelength of the antenna; B is the polarization matching coefficient of the transmitting and receiving antennas; and C is the influence of the surrounding environment of the antenna.

[0035] As shown in the above formula, when the polarization matching coefficient of the transmitting and receiving antennas, the installation environment around the antennas, the operating wavelength, and the distance between the transmitting and receiving antennas are all the same, the main factor affecting the isolation is the gain of the transmitting and receiving antennas in the coupling direction. Therefore, under the premise of ensuring performance indicators, it is only necessary to reduce the gain of the transmitting and receiving antennas of the radio altimeter in the coupling direction and make reasonable arrangements to improve the isolation between the antennas.

[0036] II. Antenna Structure

[0037] Reference Figure 1 , Figure 2 and Figure 3 The antenna in this embodiment includes a three-layer structure: a radiator 1, an adjustment structure 2, and a ground plane 3, wherein:

[0038] The radiator 1 comprises four radiating elements 11, a feed network 12, and four slots 13. The four radiating elements are arranged in a 2×2 array. Each radiating element radiates electromagnetic waves through a single-layer rectangular microstrip patch with slots and is connected to the feed network to form the radiator. Considering edge effects, the initial values ​​of the width W and length L of the rectangular microstrip antenna patch are calculated using the following formulas:

[0039]

[0040] in, This indicates the stretch length caused by the edge effect.

[0041] This represents the equivalent relative permittivity of the dielectric substrate.

[0042] c is the speed of light in free space, ε r It is the relative permittivity of the dielectric substrate.

[0043] f is the operating center frequency of the microstrip antenna, and h is the thickness of the dielectric substrate.

[0044] The adjustment structure 2 is located between the radiator 1 and the ground plane 3. It includes a frame 21, a metal branch 22, a short-circuit pin 23, and a medium 24. The frame 21 and the metal branch 22 are both located on the upper surface of the medium 24, and the short-circuit pin 23 is located inside the medium 24.

[0045] The frame 21 is preferably, but not limited to, a rectangular metal ring, wherein opposite sides of the metal ring have the same width;

[0046] The metal stub 22 comprises three metal stubs 221, 222, and 223, wherein the first stub 221 is located at the antenna central axis AA, and the second stub 222 and the third stub 223 are symmetrical with respect to the central axis AA.

[0047] The shorting pin 23 comprises three sets of shorting pins: 231, 232, and 233. Each set contains one shorting pin, all made of copper pillars. The diameter of each shorting pin is set to φ1, and φ1 must not exceed the width W2 of the first branch 221, nor exceed the length L3 of the second and third branches 222 and 223, respectively.

[0048] The first shorting pin group 231 is located at the antenna's central axis AA. The second shorting pin group 232 and the third shorting pin group 233 are symmetrical with respect to the central axis AA. The first shorting pin group is used to connect the first stub 221 to the ground plane 3. The second shorting pin group 232 is used to connect the second stub 222 to the ground plane 3. The third shorting pin group 233 is used to connect the third stub 223 to the ground plane 3. That is, the first stub 221 is connected to the ground plane 3 through the first shorting pin group 231; the second stub 222 is connected to the ground plane through the second shorting pin group 232; and the third stub 223 is connected to the ground plane 3 through the third shorting pin group 233.

[0049] The dielectric 24 is a microwave laminate with low dielectric constant and low loss tangent. Its outer dimensions are the same as those of the frame 21. It has three sets of through holes 241, 242, and 243. These three sets of through holes are cylindrical structures, and their inner diameters are the same as the outer diameters of the shorting pins 231, 232, and 233.

[0050] In this embodiment, the dielectric 24 is selected from materials with, but not limited to, dielectric constant ε. r A microwave laminate with a dielectric thickness of 2.55 mm, a dielectric thickness of h = 2.36 mm, and a loss tangent of tanδ = 0.0019.

[0051] The ground plane 3 is a rectangular metal plate with a circular through hole 31 in the middle. The diameter φ2 of the through hole 31 is larger than the inner conductor diameter φ3 of the feed connector at the rear end of the antenna and smaller than the outer conductor diameter φ4 of the feed connector. The ground plane 3 is connected to the outer conductor of the feed connector at the rear end of the antenna. The inner conductor of the feed connector passes through the through hole 31 and the dielectric plate 24 in sequence and is connected to the radiator 1, so that there is an open circuit between the outer conductor and the inner conductor of the feed connector, ensuring that the feed connector works normally.

[0052] Reference Figure 4 The adjustable parameters of the antenna in this example include: slot length L1, slot width W1, length L2 and width W2 of the first stub 221, length L3 and width W3 of the second stub 222, diameter φ1 of the three shorting pin groups, distance L5 between the first shorting pin group 231 and the first stub 221, and distance L4 between the second shorting pin group 232 and the second stub 222. The adjustable ranges of these parameters are set as follows:

[0053] L1 is 0.2λ g ~0.3λ g W1 is 0.02λ g ~0.03λ g ;

[0054] L2 is 0.32λ g ~0.42λ g W2 is 0.95Z 100 ~1.05Z 100 ;

[0055] L3 is 0.95Z 100 ~1.05Z 100 W3 is 0.1λ g ~0.6λ g ;

[0056] φ1 is not greater than the minimum value of W2 and L3;

[0057] Both L5 and L4 are not less than the value of φ1;

[0058] By adjusting these parameters, the large-angle gain of the antenna coupling surface is reduced, thereby meeting the requirement of high antenna isolation. Specifically, the antenna model is constructed in HFSS electromagnetic simulation software, and its standing wave ratio and coupling angle gain pattern are simulated. The adjusted parameter values ​​that achieve the optimal standing wave ratio and coupling angle gain pattern characteristics are taken as the final microstrip antenna parameter values. Among them, the parameter values ​​that achieve the optimal standing wave ratio and receiving coupling angle θ1 gain pattern characteristics are taken as the transmitting antenna, and the parameter values ​​that achieve the optimal standing wave ratio and transmitting coupling angle θ2 gain pattern characteristics are taken as the receiving antenna.

[0059] In this example, we assume, but are not limited to, that the receiving coupling angle θ1 and the transmitting coupling angle θ2 are +90° and -90°, respectively. Through simulation optimization, the final parameters of the transmit / receive microstrip antenna are as follows:

[0060] The transmit microstrip antenna has a slot length L1 of 13mm and a slot width W1 of 1.35mm. The first stub 221 has a length L2 of 19.55mm and a width W2 of 1.78mm. The second stub 222 has a length L3 of 1.78mm and a width W3 of 6.2mm. The diameter φ1 of the three shorting pin groups is 0.6mm. The distance L5 between the first shorting pin group 231 and the first stub 221 is 8mm. The distance L4 between the second shorting pin group 232 and the second stub 222 is 1.09mm.

[0061] The slot length L1 of the receiving microstrip antenna is 13mm, the slot width W1 is 1.35mm, the length L2 of the first stub 221 is 19.55mm, the width W2 is 1.78mm, the length L3 of the second stub 222 is 1.78mm, the width W3 is 6.2mm, the diameter φ1 of the three shorting pin groups is 0.6mm, the distance L5 between the first shorting pin group 231 and the first stub 221 is 8mm, and the distance L4 between the second shorting pin group 232 and the second stub 222 is 1.09mm.

[0062] Through simulation optimization, the structural parameters of the transmitting antenna and the receiving antenna in this embodiment are the same.

[0063] This invention uses a separate transmitting and receiving antenna as the transmitting and receiving antennas for a radio altimeter, and allows for flexible selection of the installation positions of the transmitting and receiving microstrip antennas on the surface of the device.

[0064] like Figure 5 As shown, in this embodiment, the transmitting and receiving antennas of the radio altimeter are mounted on a metal plate with a spacing of 400mm, with the transmitting antenna on the left and the receiving antenna on the right, and the coupling surfaces are in a straight line. By reducing the gain of the transmitting antenna at +90° and the receiving antenna at -90°, the isolation between the transmitting and receiving antennas can be improved at both short and long distances. Since the transmitting and receiving antennas in this embodiment have the same structural parameters, a single high-isolation radio altimeter microstrip antenna can be used for design, and the isolation between the transmitting and receiving antennas can be met by reducing the ±90° gain requirement.

[0065] The effectiveness of this invention can be further illustrated by the following simulation results.

[0066] I. Simulation Conditions

[0067] Condition 1: Using HFSS electromagnetic simulation software, establish electromagnetic simulation model A for the embodiment of this utility model, such as... Figure 5 As shown.

[0068] Condition 2: Using HFSS electromagnetic simulation software, establish an electromagnetic simulation model B for an existing antenna embodiment, such as... Figure 6 As shown.

[0069] II. Simulation Content

[0070] Simulation 1: Under the above conditions, the standing wave ratios of antenna simulation models A and B are simulated, and the results are as follows. Figure 7 As shown.

[0071] from Figure 7 As can be seen, the standing wave ratio curve of the antenna of this utility model is basically consistent with that of the existing antenna, both being no greater than 2.5, and the bandwidth is 4.65%.

[0072] Simulation 2: Under the above conditions, the plane radiation pattern of the coupling angle between antenna simulation model A and simulation model B is simulated, and the results are as follows. Figure 8 As shown.

[0073] from Figure 8 As can be seen, the antenna of this invention maintains the same radiation pattern curve within the main lobe as the existing antenna, with a gain of 11.67dB and a beamwidth of approximately 47°. At -90°, the gain of the antenna of this invention is 12.52dB lower than that of the existing antenna, and at +90°, the gain of the antenna of this invention is 12dB lower than that of the existing antenna.

[0074] Simulation 3: Under the above conditions, the isolation of the antenna simulation model A of this utility model is simulated, and the results are as follows. Figure 9 As shown.

[0075] from Figure 9 As can be seen, the isolation of this utility model is in the range of -91.3633dB to -89.6428dB in the 4.2GHz to 4.4GHz frequency band, with the worst being -89.6428dB, corresponding to a frequency of 4.28GHz.

[0076] Simulation 4: Under the above conditions, the isolation of the existing antenna simulation model B is simulated, and the results are as follows. Figure 10 As shown.

[0077] from Figure 10 It can be seen that the isolation of the existing antenna in the 4.2GHz to 4.4GHz frequency band is in the range of -83.8927dB to -80.0487dB, with the worst being -80.0487dB, corresponding to the frequency of 4.2GHz.

[0078] Simulation 5: A difference simulation was performed on the isolation simulation values ​​of the antenna simulation model A of this invention and the existing simulation model B. The results are as follows: Figure 11 As shown.

[0079] from Figure 11 As can be seen, the isolation of the antenna of this utility model is improved by 7.471dB to 10.23dB in the 4.2GHz to 4.4GHz frequency band, with the highest improvement at 4.2GHz, corresponding to an isolation of 10.2dB.

[0080] Simulation results show that, while maintaining essentially the same performance as existing antennas, the antenna of this invention can improve the isolation between transmitting and receiving antennas by reducing the antenna gain in the coupling angle direction.

[0081] The antenna of this invention improves isolation by reducing its own coupling angle gain, thus it can be installed at both long and short distances with improved isolation.

Claims

1. A high-isolation radio altimeter microstrip antenna, comprising a radiator (1) and a ground plane (3), characterized in that: An adjustment structure (2) is provided between the radiator (1) and the ground plane (3), which includes a frame (21), a metal branch (22), a shorting pin (23), and a dielectric layer (24) for adjusting the isolation of the antenna; The metal stub (22) comprises three sections, with the first section (221) located at the antenna's central axis AA, and the second section (222) and the third section (223) being symmetrical with respect to the antenna's central axis AA. The shorting pin (23) includes three groups, and the number of shorting pins in each group is a positive integer not less than 1. The first shorting pin group (231) is located at the antenna central axis AA, and the second shorting pin group (232) and the third shorting pin group (233) are symmetrical with respect to the central axis AA. The border (21) and metal stub (22) are both located on the upper surface of the dielectric layer (24), and the short-circuit pin (23) is located inside the dielectric layer (24).

2. The antenna according to claim 1, characterized in that: The frame (21) is a rectangular metal ring with opposite sides having the same width; The dielectric layer (24) is a microwave laminate with low dielectric constant and low loss tangent, and has three sets of through holes (241, 242, 243).

3. The antenna according to claim 1, characterized in that: The first branch (221) is connected to the ground plane (3) through the first shorting pin group (231); The second branch (222) is connected to the ground plane (3) via the second short-circuit pin group (232); The third branch (223) is connected to the ground plane (3) via the third short-circuit pin group (233).

4. The antenna of claim 3, wherein: The radiator (1) includes a radiating element (11), a feed network (12), and a slot (13). Each radiating element radiates electromagnetic waves and is connected to the feed network by opening a single-layer rectangular microstrip patch.

5. The antenna of claim 4, wherein: The outer dimensions of the dielectric layer (24) are consistent with the outer dimensions of the frame (21), and the diameters of its three sets of through holes (241, 242, 243) are consistent with the diameters of its three sets of shorting pins (231, 232, 233).

6. The antenna according to claim 5, characterized in that: The length L1 of the gap (13) is (0.2-0.3) , and the width W1 is (0.02-0.03) ; The length L2 of the first branch (221) is (0.32~0.42). The width W2 is (0.95~1.05). ; The length L3 of the second branch (222) is (0.95~1.05). The width W3 is (0.1~0.6). ; The diameter φ1 of the three sets of shorting pins (231, 232, 233) is not greater than the minimum value of W2 and L3; The distance L5 between the first short-circuit pin group (231) and the first branch (221) is not less than the value of φ1; The distance L4 between the second short-circuit pin group (232) and the second branch (222) is not less than the value of φ1; By adjusting these adjustable parameters of the antenna structure, the gain of the antenna coupling angle can be reduced, thereby improving antenna isolation.

7. The antenna according to claim 1, characterized in that, The ground plane (3) is a rectangular metal plate with a circular through hole (31) in the middle. It is connected to the outer conductor of the feed connector at the rear end of the antenna. The inner conductor of the feed connector passes through the through hole (31) and the dielectric layer (24) in sequence and is connected to the radiator (1) so that the outer conductor and the inner conductor of the feed connector are open-circuited, ensuring that the feed connector works normally.

8. The antenna according to claim 7, characterized in that, The diameter φ2 of the through hole (31) is greater than the inner conductor diameter φ3 of the antenna rear feed connector, but smaller than the outer conductor diameter φ4 of the feed connector.

9. The antenna according to claim 6, characterized in that, Adjusting the parameters of the antenna structure involves constructing the antenna model in HFSS electromagnetic simulation software and simulating the standing wave ratio and receiving coupling angle of the antenna model. Gain pattern, transmit coupling angle Gain pattern analysis will enable the acquisition of optimal VSWR and receiver coupling angle. Adjustable parameters of the gain pattern characteristics are used as structural parameters of the transmitting antenna; this will enable the achievement of optimal standing wave ratio and transmission coupling angle. Adjustable parameters of the gain pattern characteristics are used as structural parameters of the receiving antenna.

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