Circularly-polarized and dual-circularly-polarized conformal omnidirectional antenna

Abstract

The invention discloses a conformal omnidirectional antenna for realizing circular polarization and dual circular polarization, the circular polarization conformal omnidirectional antenna comprises a coaxial line, cylinders, a resonant cavity and two metal rings, the coaxial line is arranged in the center of the resonant cavity as a feed source, and the resonant cavity is connected with the upper and lower cylinders to form a conformal structure. A plurality of rectangular inclined grooves which are uniformly distributed at equal intervals and are consistent in inclination direction are formed in the middle height of the cavity wall, the two metal rings surround the periphery of the cylinder and are located on the upper side and the lower side of the resonant cavity, a circle of arc-shaped grooves are formed in the metal rings, and the grooves are gradually deepened from the outer edges of the rings to the centers of the rings. A main body part of the dual-circularly-polarized conformal omnidirectional antenna is formed by connecting two circularly-polarized conformal omnidirectional antennas, the two parts are separated by a parasitic slot, two resonant cavities are provided with inclined slots in opposite directions, and narrow vertical slots are added to the centers of the inclined slots. The invention has the advantages of flexible left-handed and right-handed circular polarization realization, good conformality and omnidirectivity, light weight and high isolation, and is suitable for the field of missile-borne rockets.

Description

Technical Field

[0001] This invention belongs to the technical field of circularly polarized antennas, specifically relating to a circularly polarized and dual-circularly polarized conformal omnidirectional antenna. Background Technology

[0002] As a research hotspot in modern antenna technology, conformal antennas have broad application prospects in both military and civilian communications, especially on carriers such as aircraft. Conformal antennas can effectively integrate with the carrier without affecting its aerodynamic performance, while also possessing excellent electrical performance. For rotating missile communication systems or satellites, to prevent the receiving antenna from being affected by the aircraft's motion and thus losing signal reception, the mounted antenna must meet omnidirectional radiation requirements. Meanwhile, the complex and ever-changing communication environment in space poses a significant challenge to the antenna's anti-interference capabilities. Therefore, designing a conformal omnidirectional antenna with good anti-interference capabilities is currently a key challenge.

[0003] To address this issue, existing technologies employ microstrip patch antenna elements conformally to the cylindrical surface to achieve omnidirectional radiation. However, microstrip patch antennas still have some drawbacks: narrow bandwidth; multiple patch elements are typically required to achieve good omnidirectional performance, resulting in mutual coupling losses between these elements; different patch elements require consistent amplitude and phase feeding, necessitating complex feeding networks and increasing feeding losses; and there may be significant cross-polarization components in the radiated field. Furthermore, single-polarized conformal omnidirectional patch antennas struggle to adapt to complex and variable environments. In conclusion, the application of conformal omnidirectional antennas in missile-borne rockets or satellites still has considerable potential for development. Summary of the Invention

[0004] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a circularly polarized or dual-circularly polarized conformal omnidirectional antenna that generates circularly polarized waves through a cylindrical resonant cavity, reducing interference from the outside world, and at the same time uses tilted slots to convert linearly polarized waves into circularly polarized waves, thus achieving good circular polarization performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a circularly polarized conformal omnidirectional antenna, comprising a coaxial line, a cylinder, a resonant cavity, and two metal rings. The resonant cavity is disposed inside the cylinder and forms a conformal structure with the cylinder. The coaxial line is used for coaxial feeding of the resonant cavity. Multiple evenly spaced and uniformly distributed inclined slots with the same tilt direction are formed on the cavity wall of the resonant cavity at a mid-height position. The top and bottom ends of the inclined slots are respectively on the same plane. The two metal rings are respectively attached to the planes corresponding to the top and bottom ends of the inclined slots on the cylinder, and the metal rings have an arc-shaped gradient structure. The resonant cavity operates in... TM01 In this mode, the resonant cavity center is excited by a coaxial line to generate a vertically polarized wave. The vertically polarized wave is decomposed into mutually orthogonal horizontally polarized waves and vertically polarized waves through an inclined slot. The horizontally polarized waves and vertically polarized waves generate a 90-degree phase difference through a metal ring.

[0006] As a preferred technical solution, the resonant frequency of the resonant cavity is calculated using the following formula: ; in f 0n0 yes TM 01 The resonant frequency of the mode, c It's the speed of light. m r It is the relative permeability of the medium filling the resonant cavity, ∈ r R is the relative permittivity of the medium filling the resonant cavity, and R is the radius of the cylindrical resonant cavity. x 0n It is the zero of the Bessel function with the nth zero.

[0007] As a preferred technical solution, the resonant cavity in TM 01 In this mode, the center of the resonant cavity is excited by a coaxial line to generate a vertically polarized wave. There is a uniformly distributed ring magnetic field in the horizontal direction on the wall of the resonant cavity, which will generate a vertically induced current on the wall of the resonant cavity. The radius of the resonant cavity is 0.51. l 0, height is 0.53 l 0, where l 0 is the free-space wavelength corresponding to the center frequency.

[0008] As a preferred technical solution, the angle between the inclined slot on the resonant cavity and the positive direction of the horizontal plane is +45 degrees or -45 degrees; when the angle between the inclined slot and the positive direction of the horizontal plane is +45 degrees, a left-hand circularly polarized antenna is formed; when it is -45 degrees, a right-hand circularly polarized antenna is formed; the length of the inclined slot is 0.5. l 0~0.6 l 0, width is 0.1 l 0~0.18 l 0, the spacing between adjacent inclined slots is 0.5. l 0, where l 0 is the free-space wavelength corresponding to the center frequency.

[0009] As a preferred technical solution, the radius of the metal ring is 0.2. l 0~0.3 l 0, height is 0.38 l 0~0.43 l 0, where l 0 is the free space wavelength corresponding to the center frequency. Adjusting the radius and height of the metal ring can adjust the circular polarization performance of the antenna.

[0010] As a preferred technical solution, the arc-shaped gradient structure is formed by开槽 on the side of the metal ring close to the resonant cavity and surrounding the central axis for one week. The gradient structure is开槽 towards the central axis of the antenna, and the depth of the slot gradually increases. Moreover, the greater the increase in depth, the overall shows a "撇" shape. The depth of the arc-shaped gradient structure is 0.05 l 0~0.1 l 0, and the length is 0.15 l 0~0.2 l 0, where l 0 is the free space wavelength corresponding to the center frequency; the arc-shaped gradient structure is used to suppress the high-order modes radiated by the resonant cavity and achieve that the amplitudes of the mutually orthogonal horizontal polarization wave and vertical polarization wave are the same and the phase difference is 90 degrees, thereby reducing the cross polarization of the antenna.

[0011] As a preferred technical solution, the overall depth of the arc-shaped gradient structure is 0.1 l 0, and the length is 0.19 l 0, where l 0 is the free space wavelength corresponding to the center frequency.

[0012] In the second aspect, the present invention provides a dual circular polarization conformal omnidirectional antenna, including two circular polarization conformal omnidirectional antennas; the ends without coaxial cables of the two circular polarization conformal omnidirectional antennas are connected relatively to form an intermediate connection part; the coaxial cables of the two circular polarization conformal omnidirectional antennas are respectively located at the upper and lower ends for coaxial feeding; the inclination directions of the inclined slots of the two circular polarization conformal omnidirectional antennas are opposite, respectively generating left-handed circular polarization waves and right-handed circular polarization waves; a parasitic slot is formed at the intermediate connection part.

[0013] As a preferred technical solution, the inclination angle of the inclined slot of one circular polarization conformal omnidirectional antenna is 50 degrees with respect to the positive direction of the horizontal plane, and the inclination angle of the inclined slot of the other circular polarization conformal omnidirectional antenna is -50 degrees with respect to the positive direction of the horizontal plane; a vertical vertical gap is provided at the center of each inclined slot, and the vertical gap is 0.4 l 0, and the width is 0.03 l 0, which is used to optimize the axial ratio performance of the antenna.

[0014] As a preferred technical solution, the parasitic slot is used to improve the isolation degree of the two circular polarization conformal omnidirectional antennas, and the height of the parasitic slot is 0.1 l 0~0.2 l 0, where l 0 is the free space wavelength corresponding to the center frequency.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Most circularly polarized antennas (such as single-fed microstrip patches, multi-fed arrays, etc.) require feeding two spatially orthogonal linear polarization modes with equal amplitude currents and a 90-degree phase difference. Any amplitude imbalance or phase deviation will directly lead to a deterioration in circular polarization and an increase in cross-polarization levels. The circularly polarized conformal omnidirectional antenna of this invention uses a coaxial line to feed the resonant cavity within a conformal cylinder, exciting it to operate in... TM 01 The mode generates a vertically linearly polarized wave. Eight 45-degree angled slots are evenly spaced along the middle of the resonant cavity wall. Two identical metal rings are attached to the upper and lower sides of the resonant cavity. The metal rings and the sloping slots work together to convert the linearly polarized wave into a left-handed circularly polarized wave, achieving omnidirectional radiation. Simultaneously, the arc-shaped gradient structure on the metal rings effectively reduces the antenna's cross-polarization component. While achieving good omnidirectional circular polarization characteristics, it eliminates the need for complex feed networks and phase shifters, significantly reducing design complexity and manufacturing costs. The antenna has a hollow structure covered with a metal layer, making it lightweight and meeting the requirement of minimizing the mass of the antenna mounted on a missile-borne rocket. By adjusting the resonant cavity size, tilt slot parameters, and metal ring specifications, the antenna impedance bandwidth covers the 14.98-17.20GHz frequency band, and the axial ratio bandwidth covers the 14.21-17.80GHz frequency band. Within the frequency band, the non-circularity of the main polarization gain of the antenna's horizontal plane pattern is less than 2dB, and the gain is greater than 1dB. While achieving conformal characteristics, it also has good circular polarization, omnidirectional radiation performance, and anti-interference characteristics.

[0016] 2. The dual circularly polarized conformal omnidirectional antenna of the present invention inherits the advantages of the circularly polarized conformal omnidirectional antenna. The main body of the antenna is formed by connecting two of the above-mentioned circularly polarized conformal omnidirectional antennas without a feed end. The slotting directions of the upper and lower resonant cavities form angles of 50 degrees and -50 degrees with the positive direction of the horizontal plane, respectively. The generation of left-hand and right-hand circularly polarized waves is controlled by simultaneously or separately exciting the resonant cavities through coaxial feeding at both ends. A vertical gap is set at the center of the inclined slot to optimize the axial ratio performance of the antenna. The upper and lower antennas are separated by a parasitic slot, which effectively improves the antenna's performance. The isolation of the antenna, as well as the depth and length of the arc-shaped gradient structure on the metal ring, are adjusted according to the circular polarization performance of the antenna. Ultimately, the antenna impedance bandwidth covers the 15.08-17.06GHz band, the axial ratio bandwidth covers the 14.74-17.02GHz band, and the antenna isolation reaches more than 40dB. Furthermore, within the frequency band, the non-circularity of the main polarization gain of the antenna's horizontal plane pattern is less than 2dB, and the gain is greater than 1dB. It combines efficient dual circular polarization, omnidirectional coverage, high isolation, and low cross-polarization characteristics, making it suitable for complex electromagnetic environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the overall structure of the circularly polarized conformal omnidirectional antenna in an embodiment of the present invention; Figure 2 This is a schematic diagram of the S-parameters of a circularly polarized conformal omnidirectional antenna in an embodiment of the present invention; Figure 3 This is a orientation diagram of the horizontal plane before the addition of the arc-shaped gradient structure in this embodiment of the invention; Figure 4 This is a orientation diagram of the horizontal plane after adding an arc-shaped gradient structure in an embodiment of the present invention; Figure 5 This is a direction diagram of the vertical plane before the addition of the arc-shaped gradient structure in this embodiment of the invention; Figure 6 This is a direction diagram of the vertical surface after adding the arc-shaped gradient structure in an embodiment of the present invention; Figure 7 This is an axial ratio diagram of the circularly polarized conformal omnidirectional antenna in an embodiment of the present invention; Figure 8 This is a schematic diagram of the overall structure of the dual-circularly polarized conformal omnidirectional antenna in an embodiment of the present invention; Figure 9 This is a schematic diagram of the S-parameters of the dual-circularly polarized conformal omnidirectional antenna in an embodiment of the present invention; Figure 10 This is the radiation pattern of the xoy plane of the dual circularly polarized conformal omnidirectional antenna in this embodiment of the invention; Figure 11 This is an aspect ratio diagram of the dual circularly polarized conformal omnidirectional antenna in an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures: 100-Circularly polarized conformal omnidirectional antenna; 101-Coaxial line; 102-Cylinder; 103-Resonant cavity; 104-Metal ring; 105-Tilted slot; 106-Arc-shaped gradient structure; 200-Dual circularly polarized conformal omnidirectional antenna; 201-Intermediate connection part; 202-Parasitic slot; 203-Vertical gap. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0021] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0022] Example 1 like Figure 1 As shown, this embodiment provides a circularly polarized conformal omnidirectional antenna 100, including a coaxial line 101, a cylinder 102, a resonant cavity 103, and two metal rings 104; the resonant cavity 103 is disposed inside the cylinder 102 and forms a conformal structure with the cylinder; eight evenly spaced and uniformly distributed inclined slots 105 with the same tilt direction are formed on the cavity wall of the resonant cavity 103 at the middle height; the top and bottom ends of the inclined slots 105 are respectively on the same plane (i.e., Figure 1 (A and B surfaces); two metal rings are respectively attached to the plane on the cylinder corresponding to the top of the inclined groove. Figure 1 (A-side in the middle) and the plane where the bottom end is located ( Figure 1 (B-side of the antenna); the metal ring 104 is provided with an arc-shaped gradient structure 106, which is used to suppress higher-order modes and ensure that the amplitudes of the two orthogonal modes that achieve circular polarization are the same and the phase difference is 90 degrees, so as to reduce the cross-polarization component of the antenna.

[0023] Furthermore, the coaxial cable 101 is a 50-ohm coaxial cable, used to coaxially feed the resonant cavity 103 to excite the resonant cavity 103 to operate at... TM 01 In this mode, the resonant cavity center is excited by a coaxial line to generate a vertically polarized wave. The vertically polarized wave is decomposed into mutually orthogonal horizontally polarized waves and vertically polarized waves through an inclined slot. The horizontally polarized waves and vertically polarized waves generate a 90-degree phase difference through a metal ring.

[0024] It is understood that, in this embodiment, a circularly polarized conformal omnidirectional antenna enables the resonant cavity to operate in... TM 01The mode is beneficial for omnidirectional radiation of the antenna. Given a specific resonant mode, the resonant frequency of the resonant cavity 103 is determined by the radius of the cylindrical resonant cavity. Increasing the radius of the resonant cavity leads to a decrease in the resonant frequency, while the thickness of the resonant cavity has little impact on the resonant frequency within a certain range. The resonant cavity is controlled at a suitable resonant frequency by adjusting its radius. It should be noted that creating a tilted slot on the resonant cavity increases the actual resonant frequency; therefore, it is necessary to first design a mode that operates in a lower frequency band and whose main mode is... TM 01 The resonant cavity of the mode. The resonant frequency of the resonant cavity is calculated using the following formula: ; in f 0n0 yes TM 01 The resonant frequency of the mode, c It's the speed of light. m r It is the relative permeability of the medium filling the resonant cavity, ∈ r R is the relative permittivity of the medium filling the resonant cavity, and R is the radius of the cylindrical resonant cavity. x 0n It is the zero of the Bessel function with the nth zero.

[0025] The resonant cavity 103 is in TM 01 In this mode, a vertically polarized wave is generated at the center of the resonant cavity by coaxial line 101. A uniformly distributed annular magnetic field in the horizontal direction exists on the cavity wall of the resonant cavity 103, which induces a vertical current on the cavity wall. For example, the radius of the resonant cavity 103 is 0.51. l 0, height is 0.53 l 0, where l 0 is the free-space wavelength corresponding to the center frequency.

[0026] Furthermore, eight evenly spaced inclined slots 105 are formed at the midpoint of the cavity wall of the resonant cavity 103. The inclined slots 105 all have the same inclination direction, achieving relatively good omnidirectional characteristics. Different inclination directions of the inclined slots 105 determine whether the resulting circular polarization is left-handed or right-handed. A 45-degree angle between the inclined slot and the positive direction of the horizontal plane indicates left-handed circular polarization, while a negative 45-degree angle indicates right-handed circular polarization. The inclined slots 105, together with the metal rings 104 above and below the resonant cavity 103, enable the wave radiated from the resonant cavity to be converted from linear polarization to circular polarization. The length, width, and position of the inclined slots 105 affect the circular polarization performance of the antenna. Specifically, the length of the inclined slot 105 is 0.5... l 0~0.6 l0, with a width of 0.1 l 0 to 0.18 l 0, with a spacing of 0.5 between adjacent inclined slots l 0, where l 0 is the free - space wavelength corresponding to the center frequency.

[0027] It can be understood that there is a metal ring at each of the upper and lower parts of the antenna resonator cavity. The metal ring and the center resonator cavity wall form a center groove. Adjusting the radius and height of the metal ring will also affect the circular polarization performance of the antenna. The principles of the two affecting the circular polarization performance of the antenna are as follows: The slots in the resonator cavity are analogous to an inclined opening at the end of a waveguide. The upper and lower metal rings of the resonator cavity are approximately two rows of metal walls introduced near the open waveguide mouth and their bottoms are connected. At this time, the waveguide and the metal walls form a center groove as a whole. In this case, the electromagnetic wave excited by the waveguide is divided into a horizontally polarized wave and a vertically polarized wave of the orthogonal electric field in the center groove after passing through the opening, and a 90 - degree phase difference is generated after passing through the metal walls, realizing the transformation from linear polarization to circular polarization.

[0028] Furthermore, the radius of the metal ring 104 is 0.2 l 0 to 0.3 l 0, with a height of 0.38 l 0 to 0.43 l 0, where l 0 is the free - space wavelength corresponding to the center frequency. Adjusting the radius and height of the metal ring 104 can adjust the circular polarization performance of the antenna.

[0029] Further, on the entire cylinder conformal to the resonator cavity 103, except for the part covered by the metal ring, there are also parts of the cylinder extending up and down. The radius and height of this part also have an impact on the circular polarization performance. Therefore, it is necessary to comprehensively adjust multiple factors affecting the circular polarization performance of the antenna in order to achieve the best effect.

[0030] Please refer to again Figure 1 , By a method of grooving on the metal ring to form an arc - shaped gradient structure 106 to reduce the cross - polarization of the antenna. The arc - shaped structure suppresses the high - order modes that have a negative impact on the circular polarization performance, and maintains the same amplitude and a 90 - degree phase difference of the two orthogonal modes for realizing circular polarization, reducing the cross - polarization of the antenna. Specifically, the arc - shaped gradient structure 106 is formed by grooving on the side of the metal ring close to the resonator cavity and surrounding the central axis for one week. The gradient structure grooves towards the central axis of the antenna, and the depth of the groove gradually increases. Moreover, the greater the increase in depth, the overall shape presents a "撇" - shaped. The depth of the arc - shaped gradient structure is 0.05 l 0 to 0.1 l 0, with a length of 0.15 l 0 to 0.2 l 0, where l 0 is the free-space wavelength corresponding to the center frequency.

[0031] In this embodiment, the S-parameters of the circularly polarized conformal omnidirectional antenna are as follows: Figure 2 As shown, the antenna's impedance bandwidth covers the 14.98-17.20 GHz frequency band. The horizontal and vertical radiation patterns before and after adding the arc-shaped gradient structure are shown below. Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, the arc-shaped gradient structure can significantly reduce antenna cross-polarization while maintaining omnidirectional performance. This is because, on the one hand, the gradient structure typically only supports the smooth transmission of the fundamental mode, while reflecting or suppressing the generation of higher-order modes that are detrimental to good circular polarization purity. On the other hand, it can adjust the amplitude and phase of the two orthogonally polarized waves that affect the circular polarization performance of the antenna, making them better meet the conditions of equal amplitude and a 90-degree phase difference, thereby reducing antenna cross-polarization.

[0032] In this embodiment, the axis of the circularly polarized conformal omnidirectional antenna is as follows: Figure 7 As shown, the frequency band with an axial ratio bandwidth of 14.21-17.80 GHz covers the antenna's impedance bandwidth, indicating that the antenna has good circular polarization characteristics within the operating frequency band.

[0033] In a more specific embodiment, the circularly polarized conformal omnidirectional antenna consists of a 50-ohm coaxial line, a cylinder, a cylindrical resonant cavity, and two metal rings. The cylinder is made of copper, with a diameter of 20.2 mm and a height of 40 mm. The cylindrical resonant cavity, made of copper, is coaxially disposed inside the conformal cylinder, with a radius of 9.6 mm, a height of 10 mm, and a thickness of 0.5 mm. By adjusting the radius and height, the dominant mode of the resonant cavity is adjusted to... TM 01 The mode, with the resonant frequency controlled at 16GHz.

[0034] At the middle height of the cavity wall of the resonant cavity (i.e., 5 mm from each of the upper and lower ends of the resonant cavity), eight inclined slots are equally spaced circumferentially. The angular interval between adjacent inclined slots is 45 degrees. All the inclined slots have the same inclination direction and are in the shape of a "撇" character, with an inclination angle of 45 degrees. The length of a single inclined slot is 11 mm, the width is 2 mm, and the depth is the same as the wall thickness of the resonant cavity (i.e., 0.5 mm). Both metal rings are copper rings with a radius matching the diameter of the conformal cylinder (i.e., 20.2 mm), a thickness of 4 mm, and a height of 8 mm. They are respectively fixed tightly on the outside of the conformal cylinder directly above and below the corresponding inclined slots, forming radiation slots together with the inclined slots. An arc-shaped gradient structure is provided at the outer edge of the metal ring. The depth of the arc-shaped slot is 1.9 mm, and the arc length is 5 mm. By suppressing high-order modes and ensuring that the amplitudes of the two orthogonal modes for realizing circular polarization are the same and the phase difference is 90 degrees, the cross-polarization component is attenuated.

[0035] The performance of this antenna is tested, and the results show that: the impedance bandwidth of the antenna covers the frequency band of 14.98 - 17.20 GHz, and the impedance matching is good; the axial ratio bandwidth of the antenna covers the frequency band of 14.21 - 17.80 GHz. The non-circularity of the main polarization gain of the antenna horizontal plane pattern within the frequency band is less than 2 dB, the gain is greater than 1 dB, and the circular polarization characteristics are excellent; compared with the antenna without the arc-shaped gradient structure, the cross-polarization component of this antenna is reduced by 5 - 10 dB, meeting the usage requirements of the missile-borne rocket for an omnidirectional circular polarization antenna.

[0036] In this embodiment, the resonant cavity is excited to operate in TM 01 mode through a coaxial feeding method, thereby generating a linearly polarized wave in the vertical direction. To achieve the conversion of the linearly polarized wave to a circularly polarized wave and radiate it outward, eight inclined slots are circumferentially opened at the middle height of the cavity wall of the resonant cavity, and a metal ring is respectively arranged on the upper and lower sides of the resonant cavity. The linearly polarized wave in the resonant cavity is decomposed into two mutually orthogonal polarization components after passing through the inclined slots, and then a 90-degree phase difference is formed through the metal ring to realize circular polarization; at the same time, due to the evenly distributed design of the inclined slots on the cavity wall of the resonant cavity at equal intervals, the antenna achieves good omnidirectionality.

[0037] Embodiment 2 As Figure 8 shown, this embodiment provides a dual circular polarization conformal omnidirectional antenna 200, which includes two circular polarization conformal omnidirectional antennas 100 in the above-mentioned Embodiment 1; the ends without coaxial lines of the two circular polarization conformal omnidirectional antennas are connected relatively to form an intermediate connection part 201; the coaxial lines of the two circular polarization conformal omnidirectional antennas are respectively located at the upper and lower ends for coaxial feeding; the inclination directions of the inclined slots of the two circular polarization conformal omnidirectional antennas are opposite, respectively generating left-handed circularly polarized waves and right-handed circularly polarized waves, that is, the upper half realizes right-handed circular polarization and the lower half realizes left-handed circular polarization; a parasitic slot 202 is formed at the intermediate connection part.

[0038] The dual-circularly polarized conformal omnidirectional antenna is implemented based on the circularly polarized conformal omnidirectional antenna, so the size of the resonant cavity remains unchanged, and the resonant mode remains the same. TM 01 The mode is the dominant mode.

[0039] Furthermore, in the dual-circularly polarized conformal omnidirectional antenna 200, the slots on the upper and lower resonant cavity walls are oriented in opposite directions. Combining this with the principle of converting linearly polarized waves to circularly polarized waves in Embodiment 1, the skewed slots can generate circularly polarized waves. Different tilt angles will cause changes in the horizontally and vertically polarized wave components obtained through the skewed slots, thereby altering the axial ratio of the circular polarization. Unlike the 45-degree skewed slots in Embodiment 1, the dual-circularly polarized section adjusts the tilted slot angle to 50 degrees. One circularly polarized conformal omnidirectional antenna has a 50-degree tilt angle relative to the positive direction of the horizontal plane, while the other circularly polarized conformal omnidirectional antenna has a negative 50-degree tilt angle relative to the positive direction of the horizontal plane. Each skewed slot has a vertical gap 203 at its center, with a length of 0.4 mm. l 0, width 0.03 l 0 is used to optimize the axial ratio performance of the antenna.

[0040] It is understandable that, since the upper and lower conformal cylinders of the dual-circularly polarized conformal omnidirectional antenna 200 in this embodiment are connected, together with the two adjacent metal rings, they form a parasitic slot 202. Its function and principle are as follows: Due to the different phase velocities of the two mutually perpendicular polarized waves in the resonant cavity's radiating slot, a certain phase difference exists on the radiating surface. Therefore, a parasitic slot is introduced in the middle to suppress horizontally polarized waves and guide vertically polarized waves. This guided wave superimposes with the vertically polarized wave at the central slot, thereby improving the circular polarization axis ratio. The height of the radiating slot and the height of the parasitic slot affect the vertical isolation of the antenna. While ensuring circular polarization performance, the antenna isolation can be increased by appropriately increasing the height. Specifically, the height of the parasitic slot 202 is 0.1. l 0~0.2 l 0, where l 0 is the free-space wavelength corresponding to the center frequency.

[0041] In this embodiment, the dual-circularly polarized conformal omnidirectional antenna 200 also utilizes an arc-shaped gradient structure on the metal ring to reduce cross-polarization. However, due to the change in the overall antenna structure, the depth of the arc-shaped structure is 0.05. l 0~0.1 l 0, length is 0.15 l 0~0.2 l 0, all require appropriate adjustment; preferably, the overall depth of the arc-shaped gradient structure is 0.1. l 0, length is 0.19 l0。

[0042] The S parameters and the radiation pattern in the xoy plane of the dual - circular - polarization conformal omnidirectional antenna 200 under single - port excitation in this embodiment are as Figure 9 and Figure 10 shown. Figure 9 In it, the impedance bandwidth of the antenna covers the frequency band of 15.08 - 17.06 GHz, and the isolation of the antenna is above 40 dB, indicating that the interference between the left - hand and right - hand circular polarizations is very small. From the Figure 10 radiation pattern, it can be seen that the cross - polarization gain of the antenna within the frequency band differs from the main polarization by more than 15 dB, and the influence of cross - polarization on the main polarization is small.

[0043] In this embodiment, the axial ratio of the dual - circular - polarization conformal omnidirectional antenna is as Figure 11 shown. It can be seen that the axial - ratio bandwidth of the antenna is in the frequency band of 14.74 - 17.02 GHZ, which basically covers the frequency band of the antenna impedance bandwidth, and has good circular - polarization characteristics.

[0044] In a specific embodiment, this embodiment provides a dual - circular - polarization conformal omnidirectional antenna, whose structure is as Figure 8 shown. Based on the circular - polarization conformal omnidirectional antenna in Embodiment 1, the ends of the two circular - polarization antennas that are not connected to the 50 - ohm coaxial line are oppositely butted, and the butt joint is fixed by welding to form an intermediate connection part. The two 50 - ohm coaxial lines are respectively located at the top and bottom of the overall antenna structure for realizing coaxial feeding at the upper and lower ends.

[0045] Among them, the inclined slots of the upper - half circular - polarization antenna still maintain the "left - slanting" shape for generating left - hand circular - polarization waves; the inclined slots of the lower - half circular - polarization antenna are adjusted to the "right - slanting" shape; the inclination angles are both changed to 50 degrees, and a vertical gap is added to each inclined slot. The length of the vertical gap is 8 mm and the width is 0.5 mm, which is located at the middle position of the inclined slot. At the intermediate connection part, two metal rings (with a spacing of 3.5 mm) and the conformal cylinder together form a parasitic slot, and the height of the parasitic slot is 3.5 mm; at the same time, the arc - shaped gradient structures on the upper and lower metal rings are adjusted, and the depth of the arc - shaped slot is reduced to 1 mm and the arc length is extended to 3.5 mm to adapt to the cross - polarization suppression requirements of the dual - polarization structure.

[0046] Performance tests were conducted on the dual-circular polarization antenna. The results showed that the antenna's impedance bandwidth covered the 15.08-17.06 GHz frequency band, and the isolation between the upper and lower ports reached more than 42 dB, indicating that the mutual coupling interference between the left-hand and right-hand circularly polarized waves was minimal. The antenna's axial ratio bandwidth covered the 14.74-17.02 GHz frequency band, and the non-circularity of the main polarization gain in the horizontal plane pattern of the antenna within the frequency band was less than 2 dB, while the gain was greater than 1 dB, indicating stable circular polarization performance. The antenna maintained good dual-circular polarization characteristics and omnidirectional radiation characteristics in the horizontal plane, which can adapt to the communication needs in complex electromagnetic environments.

[0047] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A circularly polarized conformal omnidirectional antenna, characterized in that, The system includes a coaxial cable, a cylinder, a resonant cavity, and two metal rings. The resonant cavity is disposed inside the cylinder and forms a conformal structure with the cylinder. The coaxial cable is used to coaxially feed the resonant cavity. Multiple evenly spaced and uniformly distributed inclined slots with the same inclination direction are formed on the cavity wall at a mid-height point. The top and bottom ends of the inclined slots are on the same plane. The two metal rings are respectively attached to the planes corresponding to the top and bottom ends of the inclined slots on the cylinder, and the metal rings have an arc-shaped gradient structure. The resonant cavity operates at... TM 01 In this mode, the resonant cavity center is excited by a coaxial line to generate a vertically polarized wave. The vertically polarized wave is decomposed into mutually orthogonal horizontally polarized waves and vertically polarized waves through an inclined slot. The horizontally polarized waves and vertically polarized waves generate a 90-degree phase difference through a metal ring.

2. The circularly polarized conformal omnidirectional antenna according to claim 1, characterized in that, The resonant frequency of the resonant cavity is calculated using the following formula: ； in f 0n0 yes TM 01 The resonant frequency of the mode, c It's the speed of light. μ r It is the relative permeability of the medium filling the resonant cavity, ∈ r R is the relative permittivity of the medium filling the resonant cavity, and R is the radius of the cylindrical resonant cavity. x 0n It is the zero of the Bessel function with the nth zero.

3. A circularly polarized conformal omnidirectional antenna according to claim 1, characterized in that, The resonant cavity is TM 01 In this mode, the center of the resonant cavity is excited by a coaxial line to generate a vertically polarized wave. There is a uniformly distributed ring magnetic field in the horizontal direction on the wall of the resonant cavity, which will generate a vertically induced current on the wall of the resonant cavity. The radius of the resonant cavity is 0.

51. λ 0, height is 0.53 λ 0, where λ 0 is the free-space wavelength corresponding to the center frequency.

4. A circularly polarized conformal omnidirectional antenna according to claim 1, characterized in that, The angle between the inclined slot on the resonant cavity and the positive direction of the horizontal plane is either +45 degrees or -45 degrees; when the angle is +45 degrees, it forms a left-hand circularly polarized antenna, and when it is -45 degrees, it forms a right-hand circularly polarized antenna; the length of the inclined slot is 0.

5. λ 0~0.6 λ 0, width is 0.1 λ 0~0.18 λ 0, the spacing between adjacent inclined slots is 0.

5. λ 0, where λ 0 is the free-space wavelength corresponding to the center frequency.

5. A circularly polarized conformal omnidirectional antenna according to claim 1, characterized in that, The radius of the metal ring is 0.

2. λ 0~0.3 λ 0, height is 0.38 λ 0~0.43 λ 0, where λ 0 is the free space wavelength corresponding to the center frequency. Adjusting the radius and height of the metal ring can adjust the circular polarization performance of the antenna.

6. A circularly polarized conformal omnidirectional antenna according to claim 1, characterized in that, The arc-shaped gradient structure is formed by开槽 on one side of the metal ring close to the resonant cavity and surrounding the central axis for one week. The gradient structure开槽 towards the central axis of the antenna, and the depth of the slot gradually increases. Moreover, the greater the amplitude of the depth increase, the overall shape呈现 a "撇" shape. The depth of the arc-shaped gradient structure is 0.05 λ 0~0.1 λ 0, with a length of 0.15 λ 0~0.2 λ 0, where λ 0 is the free space wavelength corresponding to the center frequency; the arc-shaped gradient structure is used to suppress the high-order modes radiated by the resonant cavity and achieve the same amplitude and a phase difference of 90 degrees for the horizontally polarized wave and the vertically polarized wave that are mutually orthogonal, thereby reducing the cross polarization of the antenna. Note: The "开槽" in the translation is a literal translation of the Chinese term which may need to be replaced with a more accurate technical term depending on the specific context in the patent.

7. A circularly polarized conformal omnidirectional antenna according to claim 6, characterized in that, The overall depth of the arc-shaped gradient structure is 0.

1. λ 0, length is 0.19 λ 0, where λ 0 is the free-space wavelength corresponding to the center frequency.

8. A dual-circularly polarized conformal omnidirectional antenna, characterized in that, It includes two circularly polarized conformal omnidirectional antennas as described in claim 1; the ends of the two circularly polarized conformal omnidirectional antennas without a coaxial line are connected to each other to form an intermediate connection part; the coaxial lines of the two circularly polarized conformal omnidirectional antennas are located at the upper and lower ends respectively for coaxial feeding; the tilting slots of the two circularly polarized conformal omnidirectional antennas have opposite tilting directions, generating left-hand circularly polarized waves and right-hand circularly polarized waves respectively; a parasitic slot is formed at the intermediate connection part.

9. The dual-circularly polarized conformal omnidirectional antenna according to claim 8, characterized in that, One circularly polarized conformal omnidirectional antenna has a slot tilted at an angle of 50 degrees to the positive direction of the horizontal plane, while the other circularly polarized conformal omnidirectional antenna has a slot tilted at an angle of -50 degrees to the positive direction of the horizontal plane. Each slot has a vertical gap at its center, with a length of 0.4 mm. λ 0, width 0.03 λ 0 is used to optimize the axial ratio performance of the antenna.

10. The dual-circularly polarized conformal omnidirectional antenna according to claim 8, characterized in that, The parasitic slot is used to improve the isolation between the two circularly polarized conformal omnidirectional antennas, and the height of the parasitic slot is 0.

1. λ 0~0.2 λ 0, where λ 0 is the free-space wavelength corresponding to the center frequency.

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