Wideband low-profile circularly polarized cross-dipole antenna based on AMC reflector

Abstract

The present application relates to the technical fields of wireless communication antennas, and more particularly to a wideband low-profile circularly polarized cross-dipole antenna based on an AMC reflector plate. Cross-dipole radiating units are printed on the upper and lower surfaces of a radiating dielectric substrate and are composed of two pairs of orthogonally arranged dipole arms. Phase delay structures are connected to the heads and tails of the orthogonally arranged dipole arms, respectively, to provide phase difference excitation for the two pairs of dipole arms to generate circularly polarized radiation. A plurality of parasitic patches are symmetrically arranged at the gaps between the dipole arms. An AMC artificial magnetic conductor reflector plate is horizontally arranged between the cross-dipole radiating units and a metal ground plate. The metal ground plate is arranged below the AMC artificial magnetic conductor reflector plate. An air isolation layer is filled between the AMC artificial magnetic conductor reflector plate and the metal ground plate. A plurality of groups of vertical metal strips are symmetrically arranged along the edges of the metal ground plate. The inner conductor and the outer conductor of the feed interface are connected to the dipole arms on the upper and lower layers of the radiating dielectric substrate, respectively, to access external radio frequency signals.

Description

Technical Field

[0001] This invention relates to the field of wireless communication antenna technology, and more specifically to a broadband low-profile circularly polarized cross dipole antenna based on an AMC reflector. Background Technology

[0002] In modern wireless communication systems, circularly polarized antennas can effectively alleviate polarization mismatch and suppress multipath fading, and are widely used in terminal equipment such as satellite navigation and satellite communication. Currently, with the continuous increase in frequency bands covered by various wireless services, the installation space left for antennas in terminal equipment is constantly shrinking. The industry is simultaneously demanding wide bandwidth, low profile, and high gain in antenna design. Crossed dipole circularly polarized antennas, due to their simple feeding and ease of achieving circular polarization radiation, have become the mainstream research direction in this field.

[0003] Traditional crossed dipole antennas have a single resonant mode and narrow circular polarization bandwidth, limiting their application scenarios. Existing bandwidth-enhancing schemes generally have drawbacks: 1. While adding additional parasitic magnetoelectric dipoles or multilayer parasitic patch structures can extend the axial ratio bandwidth, it increases the antenna profile size, introduces additional losses, and reduces radiation efficiency; 2. Using inclined fences, short-circuit pins, or dual-cavity back-support structures can achieve broadband, but the antenna gain is low or the profile height is too large; 3. Schemes that simply introduce artificial magnetic conductors (AMC) to achieve a low profile have insufficient circular polarization bandwidth and cannot simultaneously achieve broadband characteristics.

[0004] Existing technologies cannot simultaneously achieve the three core indicators of ultra-low profile, wide impedance / axis ratio bandwidth, and high radiation gain. Traditional design schemes have mutually restrictive bandwidth, profile, and gain performance, which cannot meet the usage requirements of miniaturization, multi-band, and high receiving sensitivity of next-generation satellite navigation and satellite communication terminals.

[0005] Therefore, how to provide a broadband low-profile circularly polarized cross dipole antenna based on an AMC reflector is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a broadband low-profile circularly polarized cross dipole antenna based on an AMC reflector, which aims to solve the above-mentioned technical problems.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A broadband low-profile circularly polarized cross dipole antenna based on an AMC reflector includes a radiating dielectric substrate, a cross dipole radiating element, a phase delay structure, several parasitic patches, an AMC artificial magnetic conductor reflector, a metal ground plane, an air isolation layer, multiple sets of vertical metal strips, and a feed interface. The cross-dipole radiating unit is printed on the upper and lower surfaces of the radiating dielectric substrate and consists of two pairs of orthogonally arranged dipole arms. The phase delay structure is connected end-to-end to the orthogonally arranged dipole arms to provide phase difference excitation for the two dipole arms to generate circularly polarized radiation. Several parasitic patches are symmetrically arranged in the gaps between the dipole arms. The AMC artificial magnetic conductor reflector is horizontally arranged between the cross-dipole radiating unit and the metal ground plane. The metal ground plane is located below the AMC artificial magnetic conductor reflector. The air isolation layer is filled between the AMC artificial magnetic conductor reflector and the metal ground plane. Multiple sets of vertical metal strips are symmetrically arranged along the edge of the metal ground plane. The inner and outer conductors of the feed interface are respectively connected to the dipole arms of the upper and lower layers of the radiating dielectric substrate for receiving external radio frequency signals.

[0008] Furthermore, the cross-dipole radiation unit is a pair of orthogonal asymmetric butterfly half-wave cross-dipole radiation units; the phase delay structure is two sets of 90° phase delay rings; the parasitic patch is four quadrilateral parasitic patches symmetrically etched in the gaps of the butterfly dipole arms; the AMC artificial magnetic conductor reflector is a coin-shaped AMC artificial magnetic conductor reflector; the metal ground plane is a bottom square metal ground plane; the vertical metal strips are four pairs of vertical metal strips symmetrically arranged along the edge of the bottom square metal ground plane; and the power supply interface is a 50Ω coaxial power supply interface.

[0009] Furthermore, the radiating medium substrate is FR4 flame-retardant board with a dielectric constant of 4.4, a loss tangent of 0.02, an overall size of 74mm × 74mm, and a thickness of 0.8mm; the substrate of the coin-shaped AMC artificial magnetic conductor reflector is FR4 board with a thickness of 1mm; the air isolation layer height H2 between the coin-shaped AMC artificial magnetic conductor reflector and the bottom square metal ground plane is 15mm; the side length of the bottom square metal ground plane is 145mm; the overall profile height of the antenna is 0.12λ of the free space wavelength corresponding to the lowest operating frequency. L .

[0010] Furthermore, the dipole main arm dimensions of the orthogonal asymmetric butterfly half-wave cross dipole radiation unit are 33mm, 19.5mm, and 11.5mm; the linewidth of the 90° phase delay ring is 0.5mm, and the two phase delay rings provide a 90° phase difference excitation for the radiation unit, generating orthogonal equal amplitude currents to achieve right-hand circular polarization radiation.

[0011] Furthermore, the four quadrilateral parasitic patches are uniformly and symmetrically distributed between the butterfly dipole arms, with patch sizes of 8mm, 12mm, 22.5mm, 21.5mm, and 25.5mm. These parasitic patches induce currents through near-field electromagnetic coupling, expanding the current distribution range on the antenna surface, lengthening the equivalent current path, and simultaneously widening... 10dB impedance bandwidth and 3dB axial ratio bandwidth.

[0012] Furthermore, the unit of the copper coin-shaped AMC artificial magnetic conductor reflector is composed of a circular metal patch with four triangular notches and a central rectangular through hole. The outer radius of the patch is R3=14.5mm and the unit spacing is 0.5mm. Multiple sets of copper coin-shaped AMC units are periodically arranged on the top surface of a 1mm thick FR4 substrate.

[0013] Furthermore, the in-phase reflection phase range of the copper coin-type AMC unit covers 1.36–2.57 GHz, and the relative bandwidth of the in-phase reflection is 62%; the equivalent circuit of the AMC unit consists of the patch gap equivalent capacitance C. a Metal patch body equivalent inductance L a equivalent inductance L of air isolation layer d By constructing an LC parallel resonant circuit, electromagnetic waves are reflected in phase, thus compressing the overall profile height of the antenna.

[0014] Furthermore, the four pairs of vertical metal strips are symmetrically fixed around the square ground plane, with a height of 24mm and a width of 5mm. The vertical metal strips are used to optimize the surface current distribution of the bottom ground plane, suppress the induced current generated by the coupling between the AMC reflector and the cross dipole unit, eliminate the defect of axial ratio deterioration in the mid-frequency band within the passband, and realize stable right-hand circular polarization radiation across the entire operating frequency band.

[0015] Furthermore, all metal radiating structures, quadrilateral parasitic patches, coin-shaped AMC metal units, vertical metal strips at the edges, and the bottom metal ground plane of the antenna are integrally formed using PCB printing copper plating process; the radiating dielectric substrate, AMC reflective substrate, and bottom metal ground plane are supported and fixed by nylon insulating pillars to ensure that the height of the air isolation layer remains constant.

[0016] Furthermore, actual antenna measurements The 10dB impedance bandwidth covers 1.51–2.54GHz, with a relative bandwidth of 50.9%; the 3dB axial ratio bandwidth covers 1.53–2.51GHz, with a relative bandwidth of 48.5%; the impedance bandwidth and axial ratio bandwidth overlap, with an operating bandwidth of 48.5%; the peak right-hand circular polarization gain in the passband is 8.5dBic, and the average gain is 7.05dBic; the gain of the right-hand circular polarization wave in the main radiation direction is more than 15dB higher than that of the left-hand circular polarization wave, indicating high polarization purity.

[0017] Compared to existing technologies, this invention uses a coin-shaped AMC reflector to replace the traditional metal reflector ground, compressing the antenna profile to 0.12λ. L This design achieves an ultra-low profile structure, making it suitable for miniaturized satellite navigation and communication terminal equipment. It widens the current path through an asymmetric butterfly dipole and four-sided parasitic patches, while edge metal strips suppress coupled stray currents, simultaneously achieving ultra-wide impedance bandwidth and axial ratio bandwidth, covering mainstream GPS and satellite communication operating frequency bands. It features stable right-hand circular polarization radiation across the entire frequency band, with a peak gain of 8.5 dBic and an average gain of 7.05 dBic, significantly improving gain performance and receiving sensitivity compared to AMC circular polarization antennas with the same profile. The overall structure is fabricated using a single-layer printed PCB, eliminating the need for multi-layer cavities and complex decoupling networks, resulting in simple processing, low production costs, and high integration. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 The diagram shows the overall three-dimensional model structure of the antenna of the present invention, including (a) a three-dimensional view, (b) a side view, (c) the upper surface of the dipole antenna layer, and (d) the lower surface of the dipole antenna layer. Figure 2 This is a schematic diagram illustrating the evolution of the antenna of the present invention; Figure 3 This is a comparative distribution diagram of surface current at 2GHz with and without parasitic patches in this invention; Figure 4 The diagram shows the simulation results of the antenna evolution process of the present invention. The left diagram shows the reflection coefficient of each model in the evolution process from antenna 1 to antenna 5, and the right diagram shows the corresponding axial ratio. Figure 5 This is a comparison diagram of the surface current distribution of antennas IV and V at 1.6 GHz. Figure 6 The following is a simulation curve of the copper coin-type AMC unit structure, in-phase reflection phase, and reflection coefficient of the present invention; Figure 7 This is a schematic diagram illustrating the evolution process of the AMC unit of the present invention; Figure 8 The simulation results diagram corresponding to the evolution process of the AMC unit of this invention are shown. Figure 9 This is a schematic diagram of the LC equivalent circuit model of the AMC reflector of the present invention. Figure 10This is a simulation curve showing the effect of the AMC unit patch radius R3 and air layer height H2 on the reflection phase in this invention. Figure 11 This is a design drawing of the antenna of the present invention after adding nylon pillars; Figure 12 These are images of the actual prototype of the antenna fabrication process and the experimental environment in the microwave anechoic chamber for this invention. Figure 13 This is a comparison curve of the simulated and measured impedance bandwidth, axial ratio, and gain of the antenna of this invention; Figure 14 The images show the radiation patterns of the xoz and yoz principal planes at frequencies of 1.6 GHz, 2.1 GHz, and 2.4 GHz, respectively. (a) shows the simulated and measured radiation patterns of left and right circular polarization at 1.6 GHz, (b) shows the simulated and measured radiation patterns of left and right circular polarization at 2.1 GHz, and (c) shows the simulated and measured radiation patterns of left and right circular polarization at 2.4 GHz. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, a broadband low-profile circularly polarized cross dipole antenna based on an AMC reflector includes a radiating dielectric substrate 1 with dimensions of 74mm × 74mm and a thickness of 0.8mm; a bottom square metal ground plane 2 with a side length of 74mm; a coin-shaped AMC reflector 3 arranged between the radiating dielectric substrate and the bottom metal ground plane, with a thickness of 1mm; an air isolation layer 4 filled between the AMC reflector and the bottom ground plane, with a height H2 = 15mm; four pairs of vertical metal strips 5 symmetrically arranged along the four sides of the bottom ground plane; orthogonal asymmetric butterfly cross dipole radiating elements 6 printed on the upper and lower surfaces of the radiating dielectric substrate; four quadrilateral parasitic patches 7 etched into the gaps between the butterfly dipole arms; two sets of 90° phase delay rings 8 connected to the butterfly dipole arms; and 50Ω coaxial feed interfaces 9 connected to the upper and lower dipole arms of the radiating substrate respectively; the radiating substrate, AMC plate, and bottom ground plane are supported and fixed by nylon insulating pillars 10. This solution achieves an integrated design of ultra-low profile, wideband circular polarization, and high gain, making it suitable for small satellite communication terminals.

[0022] like Figure 2As shown, the antenna of this invention has a five-layer iterative optimization structure: antenna I is only a basic symmetrical butterfly-shaped cross dipole; antenna II is improved to an asymmetrical butterfly-shaped dipole; antenna III adds a quadrilateral parasitic patch; antenna IV adds a copper coin-shaped AMC reflector; antenna V loads four pairs of vertical metal strips on the edge of the ground plane, which is the structure of the final embodiment of this invention.

[0023] like Figure 3 As shown, without parasitic patches, the surface current is concentrated only in the dipole arm, resulting in a narrow current distribution and an imbalance of orthogonal components. After adding quadrilateral parasitic patches, the parasitic patches couple to generate induced current, which greatly expands the current coverage range and simultaneously optimizes impedance matching and axial ratio performance.

[0024] like Figure 4 As shown, the reflection coefficient and axial ratio of each antenna during the antenna evolution process are illustrated. From Antenna I (impedance bandwidth only 1.39-1.53 ​​GHz, axial ratio above 10dB across the entire frequency band, no effective circular polarization) containing only orthogonal bowtie dipoles and a 90° phase-shifting ring, to Antenna II, which initially achieved circular polarization capability by introducing asymmetric dipole arms, to Antenna III, which added parasitic patches to extend the -10 dB impedance bandwidth to 1.57-2.44 GHz and the 3 dB axial ratio bandwidth covering 1.83-2.29 GHz, to Antenna IV, which added an AMC reflector, further broadened the impedance bandwidth while compressing the profile to 0.12λ_L, but the axial ratio deteriorated near 2 GHz due to the coupling between the AMC and the radiating element, and finally, Antenna V, which added four pairs of vertical metal strips at the edge of the ground plane, effectively suppressed the coupled stray currents and achieved an impedance bandwidth of 1.49-2.56 GHz and an axial ratio bandwidth of 1.50-2.47 GHz, verifying the synergistic effect of each optimized structure.

[0025] like Figure 5 As shown, to address the axial ratio degradation issue of antenna IV, antenna V has four pairs of metal strips symmetrically arranged at the edge of the ground plane. When t = T / 4, the superimposed current of both antennas is along the +y direction; when t = 0, in addition to the main current distribution along the +x direction, antenna IV also experiences a strong induced current along the +y direction on the dipole due to the coupling between the dipole radiator and the AMC, which reduces the antenna's axial ratio performance. Compared to the current distribution on the metal ground plane of antenna IV, the introduction of the metal strips extends the current path of the metal ground plane along the +y axis, effectively suppressing unnecessary y-axis current. Figure 4 It can be seen that after adding the metal strip, The impedance bandwidth is extended to 1.49–2.56 GHz, and the axial ratio bandwidth covers 1.50–2.47 GHz, achieving stable circularly polarized radiation across the entire frequency band while balancing low profile and wide bandwidth performance.

[0026] like Figure 6 As shown, the copper coin-shaped AMC unit consists of a circular metal patch with four hollowed-out triangles and a central rectangular through hole. The units are periodically arranged on the top surface of a 1mm thick FR4 substrate. The AMC unit has an in-phase reflection range of 1.36–2.57GHz and a relative bandwidth of 62%, which can achieve in-phase reflection across the entire operating frequency band of the antenna and reduce the profile height.

[0027] The evolution of AMC is as follows Figure 7 As shown, Figure 8 This corresponds to the in-phase reflection coefficient of each AMC, which gradually evolves from the basic circular AMC unit to the designed coin-shaped AMC unit. As the AMC evolves, its corresponding reflection range gradually coincides with the axial ratio bandwidth of the antenna, matching the target frequency band and the resonance point is highly consistent.

[0028] like Figure 9 As shown, the AMC unit is equivalent to an LC parallel resonant circuit, and the gap between the surface mounts forms an equivalent capacitance C. a The equivalent inductance L of the metal patch body a equivalent inductance L of the air isolation layer d By adjusting the patch size and air layer height, the LC parameters are changed to match the target frequency band resonance.

[0029] like Figure 10 The diagram illustrates the influence of the coin-shaped patch diameter R3 and the air layer height H2 on the reflection phase of the proposed AMC unit. It can be seen that the AMC unit parameter R3, as well as the reflector and the AMC unit air layer height H2, have a significant impact on the in-phase reflection range of the AMC reflector. As R3 increases from 14mm to 15mm, the in-phase reflection frequency band shifts to lower frequencies, while as H2 increases from 14mm to 16mm, the in-phase reflection interval between -90° and +90° also shifts to lower frequencies. Therefore, we can adjust the resonant frequency and the in-phase reflection range bandwidth by changing the values ​​of R3 and H2 to meet the design requirements.

[0030] The dimensional parameters of each core structure in this embodiment are as follows: Butterfly-shaped dipole main arms: 33mm, 11.5mm, 19.5mm; Quadrilateral parasitic patch: The lengths of the four sides are 8mm, 12mm, 22.5mm, and 21.5mm, and the length of the diagonal is 25.5mm; The 90° phase delay loop has a linewidth of 0.5 mm. AMC unit sizes: 10mm, 14.5mm; unit pitch: 0.5mm; Vertical metal strip: 24mm in length and 5mm in width; The height of the AMC relative to the ground air layer is H2 = 15mm, and the overall profile height of the antenna is 0.12λ.L .

[0031] The specific implementation process is as follows: This embodiment employs standard PCB printing and etching processes to fabricate three substrates: a radiating dielectric substrate, an AMC reflector substrate, and a bottom metal ground plane. The top and bottom surfaces of the radiating substrate are etched with orthogonal butterfly dipoles, phase delay loops, and parasitic patch metal patterns. The top surface of the AMC substrate features a periodic array of copper coin-shaped AMC metal units. The bottom substrate is entirely copper-clad to form a square ground plane, with pre-reserved metal strip mounting points along the edges. The three substrates are fixed in layers using nylon insulating pillars, with the air isolation layer height strictly controlled at 15mm. The coaxial feed point is led out using a half-hole process to connect to external RF cables. A detailed antenna assembly diagram is shown below. Figure 11 As shown.

[0032] Figure 12 To create the antenna prototype and test scenario diagram, the antenna simulation optimization was completed using the electromagnetic simulation software HFSS. After the prototype was fabricated, the actual test was completed in a microwave anechoic chamber. The S11 impedance characteristics were tested using a vector network analyzer, and the axial ratio, gain, and radiation pattern were tested in a far-field anechoic chamber.

[0033] like Figure 13 The impedance curve is shown in the simulation. The 10dB impedance bandwidth is 1.49–2.56GHz (relative bandwidth 52.84%), and the measured impedance bandwidth is 1.51–2.54GHz (relative bandwidth 50.9%). The measured frequency band has a slight shift towards higher frequencies, and the error comes from PCB manufacturing tolerances and test environment losses.

[0034] like Figure 13 As shown in the axial ratio and gain curves, the simulated 3dB axial ratio bandwidth is 1.50–2.47GHz (48.87%), while the measured axial ratio bandwidth is 1.53–2.51GHz (48.51%). The peak gain across the entire frequency band is 8.5dBic, and the average gain is 7.05dBic. The simulated and measured gain curves are in high agreement.

[0035] like Figure 14 As shown in the radiation pattern, the measured and simulated radiation patterns of the xoz and yoz main planes at the three characteristic frequency points of 1.6GHz, 2.1GHz, and 2.4GHz are basically coincident. The right-hand circularly polarized wave is significantly dominant in the main radiation direction. The RHCP gain is at least 15dB higher than that of LHCP, the polarization purity is excellent, the radiation pattern beam is stable, and there is no obvious distortion.

[0036] Table 1. Performance comparison of the antenna of this invention with other similar antennas.

[0037] Compared to the antenna in reference [1], this antenna has an advantage in size; in addition, it has a wider circular polarization bandwidth and a higher peak gain than the antennas in references [1], [3], [6] and [7]. Although the circular polarization bandwidth of this antenna is slightly smaller than that of the schemes in references [2], [4] and [5], its cross-sectional dimensions are more advantageous.

[0038] The overall size of the antenna of this invention is 0.73λ. L ×0.73λ L ×0.12λ L Compared with existing cross-dipole circularly polarized antennas of the same type, this antenna has a significantly reduced profile height while maintaining similar bandwidth and high gain. It has a simple structure that is easy to manufacture and can be widely used in GPS receivers, portable satellite communication terminals, UAV navigation and communication equipment and other scenarios.

[0039] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0040] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector, characterized in that, It includes a radiation dielectric substrate, a cross-dipole radiation unit, a phase delay structure, several parasitic patches, an AMC artificial magnetic conductor reflector, a metal ground plane, an air isolation layer, multiple sets of vertical metal strips, and a power supply interface. The cross-dipole radiating unit is printed on the upper and lower surfaces of the radiating dielectric substrate and consists of two pairs of orthogonally arranged dipole arms. The phase delay structure is connected end-to-end to the orthogonally arranged dipole arms to provide phase difference excitation for the two dipole arms to generate circularly polarized radiation. Several parasitic patches are symmetrically arranged in the gaps between the dipole arms. The AMC artificial magnetic conductor reflector is horizontally arranged between the cross-dipole radiating unit and the metal ground plane. The metal ground plane is located below the AMC artificial magnetic conductor reflector. The air isolation layer is filled between the AMC artificial magnetic conductor reflector and the metal ground plane. Multiple sets of vertical metal strips are symmetrically arranged along the edge of the metal ground plane. The inner and outer conductors of the feed interface are respectively connected to the dipole arms of the upper and lower layers of the radiating dielectric substrate for receiving external radio frequency signals.

2. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The cross-dipole radiating unit is a pair of orthogonal asymmetric butterfly half-wave cross-dipole radiating units; the phase delay structure is two sets of 90° phase delay rings; the parasitic patch is four quadrilateral parasitic patches symmetrically etched in the gaps of the butterfly dipole arms; the AMC artificial magnetic conductor reflector is a coin-shaped AMC artificial magnetic conductor reflector; the metal ground plane is a bottom square metal ground plane; the vertical metal strips are four pairs of vertical metal strips symmetrically arranged along the edge of the bottom square metal ground plane; the power supply interface is a 50Ω coaxial power supply interface.

3. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The radiating medium substrate is FR4 flame-retardant board with a dielectric constant of 4.4, a loss tangent of 0.02, overall dimensions of 74mm × 74mm, and a thickness of 0.8mm; the substrate of the coin-shaped AMC artificial magnetic conductor reflector is FR4 board with a thickness of 1mm; the air isolation layer height H2 between the coin-shaped AMC artificial magnetic conductor reflector and the bottom square metal ground plane is 15mm; the side length of the bottom square metal ground plane is 145mm; the overall profile height of the antenna is 0.12λ of the free space wavelength corresponding to the lowest operating frequency. L .

4. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The dipole main arm dimensions of the orthogonal asymmetric butterfly half-wave cross dipole radiation unit are 33mm, 19.5mm, and 11.5mm; the linewidth of the 90° phase delay ring is 0.5mm. The two phase delay rings provide a 90° phase difference excitation for the radiation unit, generating orthogonal equal amplitude currents to achieve right-hand circular polarization radiation.

5. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The four quadrilateral parasitic patches are evenly and symmetrically distributed between the butterfly dipole arms, with patch sizes of 8mm, 12mm, 22.5mm, 21.5mm, and 25.5mm. These parasitic patches induce currents through near-field electromagnetic coupling, expanding the current distribution range on the antenna surface, lengthening the equivalent current path, and simultaneously widening... 10dB impedance bandwidth and 3dB axial ratio bandwidth.

6. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The unit of the copper coin-shaped AMC artificial magnetic conductor reflector is composed of a circular metal patch with four triangular notches and a central rectangular through hole. The outer radius of the patch is R3=14.5mm and the unit spacing is 0.5mm. Multiple sets of copper coin-shaped AMC units are periodically arranged on the top surface of a 1mm thick FR4 substrate.

7. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The in-phase reflection phase range of the copper coin-type AMC unit covers 1.36–2.57 GHz, and the relative bandwidth of the in-phase reflection is 62%; the equivalent circuit of the AMC unit consists of the patch gap equivalent capacitance C. a Metal patch body equivalent inductance L a equivalent inductance L of air isolation layer d By forming an LC parallel resonant circuit, electromagnetic waves are reflected in phase, thus compressing the overall profile height of the antenna.

8. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, The four pairs of vertical metal strips are symmetrically fixed around the square ground plane. The metal strips are 24mm high and 5mm wide. The vertical metal strips are used to optimize the surface current distribution of the bottom ground plane, suppress the induced current generated by the coupling between the AMC reflector and the cross dipole unit, eliminate the defect of axial ratio deterioration in the mid-frequency band within the passband, and realize stable right-hand circular polarization radiation across the entire operating frequency band.

9. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, All metal radiating structures, quadrilateral parasitic patches, coin-shaped AMC metal units, vertical metal strips at the edges, and bottom metal ground plane of the antenna are integrally formed using PCB printing copper-clad process; the radiating dielectric substrate, AMC reflective substrate, and bottom metal ground plane are supported and fixed by nylon insulating pillars to ensure that the height of the air isolation layer remains constant.

10. A broadband low-profile circularly polarized crossed dipole antenna based on an AMC reflector according to claim 1, characterized in that, Antenna Measurement The 10dB impedance bandwidth covers 1.51–2.54GHz, with a relative bandwidth of 50.9%; the 3dB axial ratio bandwidth covers 1.53–2.51GHz, with a relative bandwidth of 48.5%; the impedance bandwidth and axial ratio bandwidth overlap, with an operating bandwidth of 48.5%; the peak right-hand circular polarization gain in the passband is 8.5dBic, and the average gain is 7.05dBic; the gain of the right-hand circular polarization wave in the main radiation direction is more than 15dB higher than that of the left-hand circular polarization wave, indicating high polarization purity.

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