Log-periodic dipole element-loaded tightly coupled dipole antenna array

Abstract

Disclosed in the present invention is a log-periodic dipole element-loaded tightly coupled dipole antenna array, comprising four metal layers and dielectric substrates interposed between adjacent metal layers. A first metal layer and a second metal layer are each provided with tightly coupled dipole radiation patches; each tightly coupled dipole radiation patch is connected to an auxiliary log-periodic dipole arm; the radiation patches on the two metal layers are arranged rotationally symmetric about the centerlines of antenna array elements, and the dipole arms on the two metal layers are arranged rotationally symmetric about the centerlines of the antenna array elements; the radiation patches of adjacent antenna array elements overlap each other; and an equivalent capacitance is introduced by means of coupling. A third metal layer and a fourth metal layer are located between the first metal layer and the second metal layer, and are each provided with balanced-feed baluns, the balanced-feed baluns employing a microstrip line-to-parallel-strip line transition with a tapered ground plane to realize impedance transformation and feed direction reversal. In the present invention, by means of the cooperation of the tightly coupled dipole radiation patches and the auxiliary log-periodic dipole arms, the desired ultra-wideband radiation characteristics are achieved, thereby avoiding the use of an additional structure such as a wide-angle matching layer or a frequency selection surface, and thus reducing the design costs and the implementation costs.

Description

A tightly coupled dipole antenna array loaded with log-periodic dipoles TECHNICAL FIELD

[0001] The present invention belongs to the field of radar and communication technology, and specifically relates to a tightly coupled antenna array. BACKGROUND

[0002] Based on the need for electromagnetic spectrum sensing and control, effective sensing and analysis of microwave signals are required to achieve effective reduction, control, and countermeasures, encompassing signal detection, sensing, analysis, identification, and control. The microwave frequency band below 18 GHz is widely used in wireless communication, satellite communication, radar, detection, and imaging applications, resulting in complex spectrum utilization. To achieve full-band microwave signal detection below 18 GHz, the antenna front-end must provide the widest possible bandwidth coverage. Typically, the frequency band below 18 GHz is divided into two bands: 0.2-2 GHz and 2-18 GHz, with corresponding octaves usually exceeding 9. This band division allows for efficient system integration but places extremely high demands on the design of related components. To achieve the required ultra-wideband design, commonly used antenna solutions include biconical antennas, helical antennas, and log-periodic antennas designed based on non-frequency-varying antenna theory; Vivaldi antennas designed based on gradient theory; multimode antennas designed based on multimode theory; and tightly coupled antennas designed based on tightly coupled theory, among others. Antennas designed based on non-frequency-varying antenna theory exhibit electrical performance (such as impedance, radiation pattern, and gain) that remains almost unchanged with frequency. They have corresponding antenna modules capable of radiation at each frequency point, and their radiation patterns are relatively stable within the operating frequency range. However, these antennas are typically designed to be the smallest possible size for the lowest frequency, making it difficult to form arrays with small element spacing, thus limiting their practical applications. Vivaldi antennas, on the other hand, are designed based on tapered slot lines, where the width of the radiating arm gradually increases along the antenna length. This tapered structure allows electromagnetic waves to gradually release energy during transmission, achieving efficient radiation and broadband impedance matching characteristics. However, like antennas designed based on non-frequency-varying antenna theory, Vivaldi antennas suffer from the same problem: limited size. The large size of Vivaldi antennas makes it difficult to form arrays with small element spacing, and the required length of their tapered slot lines results in a typically high profile. Furthermore, the structural characteristics of Vivaldi antennas limit the design of dual-polarized antennas, thus limiting their practical applications. Multimode antennas, designed based on multimode theory, can support multiple radiation modes within a single structure, enabling multi-band, multi-polarization, or multi-functional operation. However, achieving multimode operation generally involves high design and manufacturing complexity, and the operating frequencies of multiple modes do not necessarily overlap. They are often used in dual-band or multi-band antenna designs, and the radiation patterns of the multiple modes are usually not identical, limiting their application in ultra-wideband fields. Tight-coupled antennas, with their compact array form, relatively simple antenna design, and wideband impedance matching characteristics, have gained widespread attention in the field of ultra-wideband antennas.

[0003] Tightly coupled antenna arrays are an antenna technology that achieves broadband matching and efficient radiation by closely arranging multiple antenna elements and utilizing the electromagnetic coupling between these elements, resulting in extremely high impedance bandwidth characteristics. This design originates from Huygens' continuous patch array theory. By introducing an additional mutual coupling between antenna elements, the parasitic capacitance generated counteracts the input inductive reactance introduced by the array, allowing the impedance of each element in the array to remain stable over a very wide frequency and angle range. Compared to traditional microstrip patch antennas, its smaller element spacing enables the formation of a continuous current distribution. Compared to traditional antenna arrays, the compact design of tightly coupled antenna arrays significantly reduces size and manufacturing costs. By optimizing the coupling characteristics between antenna elements, interference can also be effectively suppressed, improving communication quality.

[0004] The design and implementation of tightly coupled antenna arrays present numerous design challenges, such as: 1. The core design principle of tightly coupled antenna arrays is to utilize the strong coupling effect between antenna elements to extend the bandwidth. However, the small element spacing leads to strong mutual coupling, affecting the impedance characteristics of the antenna elements and making impedance matching difficult. 2. Broadband antennas need to maintain stable radiation characteristics at different frequencies, while the radiation pattern of tightly coupled antennas may change significantly at high and low frequencies, resulting in a decrease in beam scanning performance. 3. To optimize impedance characteristics, tightly coupled antenna arrays typically use frequency-selective surfaces or wide-angle matching layers as antenna coverage to achieve ultra-wideband impedance matching with free space. However, using these antenna coverage structures can complicate the antenna structure, increase implementation costs, and the non-integrated manufacturing process can significantly increase potential installation errors, affecting the overall performance of the antenna. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator, overcoming the impedance bandwidth problem of existing ultra-wideband phased array antenna arrays and the structural complexity and increased cost caused by the dependence on frequency selective surfaces or wide-angle matching layers.

[0006] Technical Solution: To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A tightly coupled dipole antenna array loaded with a log-periodic dipole, comprising four metal layers and a dielectric substrate between the metal layers. The first and second metal layers are provided with one-dimensionally equally spaced tightly coupled dipole radiating patches of the same geometric size. Each tightly coupled dipole radiating patch is connected to an auxiliary log-periodic dipole arm. The arrangement of the radiating patches and dipole arms on the first and second metal layers is rotationally symmetrical about the center line of the antenna array elements, and the radiating patches of adjacent antenna array elements overlap on the first and second metal layers, introducing equivalent capacitance through coupling. The third and fourth metal layers are located between the first and second metal layers and are provided with a balanced feed balun. A microstrip line to dielectric dual-line with a gradient ground is used to achieve impedance transformation and reversal of the feed direction.

[0007] Furthermore, the auxiliary log-periodic dipole arm is located at the upper end of the tightly coupled dipole radiating patch, and the lower end of the auxiliary log-periodic dipole arm is the tightly coupled dipole corner; the radiating patches on the first metal layer and the second metal layer are segmented, the first segment is the transition segment from the feed line to the rectangular radiating patch, and the second segment is the extension of the rectangular radiating patch; the overlap of the radiating patches on the first metal layer and the second metal layer is located at the end of the rectangular radiating patch.

[0008] Furthermore, the length of the transition section from the first feed line to the rectangular radiating patch does not exceed that of the rectangular radiating patch, and the length of the tightly coupled dipole radiating patch is not less than the length of the longest set of oscillator arms in the auxiliary log-periodic dipole oscillator arms.

[0009] Furthermore, the radiating patch on the first metal layer constitutes the right radiating arm of the tightly coupled dipole, and the radiating patch on the second metal layer constitutes the left radiating arm of the tightly coupled dipole; the first-stage oscillator arm on the first metal layer constitutes the left oscillator arm of the dipole structure, then the first-stage oscillator arm on the second metal layer constitutes the right oscillator arm of the dipole structure, the second-stage oscillator arm on the first metal layer constitutes the right oscillator arm of the dipole structure, then the second-stage oscillator arm on the second metal layer constitutes the left oscillator arm of the dipole structure.

[0010] Furthermore, the auxiliary log-periodic dipole arms include five groups. The left arm of the first, third, and fifth groups of dipole arms is located in the first metal layer, and the right arm is located in the second metal layer. The left arm of the second and fourth groups of dipole arms is located in the second metal layer, and the right arm is located in the first metal layer. The length, width, and spacing of the multiple groups of dipole arms gradually increase from the radiation direction to the feeding direction.

[0011] Furthermore, the balanced feed balun backplane adopts an exponential gradient line structure to achieve impedance matching. By adjusting the slope of the gradient line, the coverage frequency band of the balanced feed balun is extended.

[0012] Furthermore, the balanced feed balun includes a coaxial connector metal strip, a trapezoidal impedance transformation section, a feed line section, a coaxial connector metal backplate, and an exponential impedance transformation section; the feed line section and the exponential impedance transformation section form a dielectric bi-wire structure; the top of the feed line section is connected to the auxiliary logarithmic periodic dipole arm via a probe, and the bottom is connected to the trapezoidal impedance transformation section; the trapezoidal impedance transformation section is fed by connecting to the coaxial feed line via the coaxial connector metal strip; the coaxial connector metal strip adopts a ground-cut microstrip line structure.

[0013] Furthermore, the tightly coupled dipole radiating patch and the auxiliary log-periodic dipole arm are fed in the opposite direction by a balanced feeding balun and a probe. The feeding line first passes through the auxiliary log-periodic dipole arm and then feeds to the tightly coupled dipole radiating patch, forming forward unidirectional radiation.

[0014] Furthermore, the feed probes are located in the dielectric substrate between the first and third metal layers, and in the dielectric substrate between the fourth and second metal layers. The feed probes transmit the current in reverse to the first and second metal layers, thus forming the radiation conditions of the tightly coupled dipole antenna.

[0015] Furthermore, the tightly coupled dipole antenna array is a one-dimensional linear array, fabricated in units of sub-arrays. One end of the sub-array has an outwardly extending protrusion that matches the tightly coupled dipole radiating patch, and the other end has a recess that matches the protrusion.

[0016] Beneficial effects: The present invention provides a tightly coupled dipole antenna array loaded with log-periodic dipoles. The balanced feed balun uses a microstrip line to dielectric biwire with a gradient ground to achieve ultra-wideband impedance transformation and reverse the feed direction. By adjusting the length of the radiating arm and the coupling area between the radiating arms, the parasitic inductance and coupling capacitance characteristics of the antenna can be adjusted to achieve a bandwidth exceeding the limit of the radiating arm length. In the auxiliary log-periodic dipole arm, the free space impedance matching of the tightly coupled dipole antenna array without a wide-angle matching layer is achieved by adjusting the length change of the log-periodic dipole, the dipole spacing and the length of the longest and shortest dipole arm, and the bandwidth is extended to higher frequencies. Compared with the prior art, the present invention has the following advantages: (1) The present invention proposes a scheme for a tightly coupled antenna with a log-periodic structure. Combining the characteristics of the tightly coupled antenna and the log-periodic dipole array, the balanced feed balun is used to reverse the feed direction, achieve the ultra-wideband performance of the antenna, and avoid the use of additional structures such as a wide-angle matching layer or a frequency selective surface, thereby reducing the design cost and implementation cost.

[0017] (2) The present invention uses the dipole antenna arm with a log-periodic structure as the upper cover of the tightly coupled dipole antenna, replacing the use of the frequency selective surface, to achieve integrated processing. At the same time, the bandwidth can be extended to higher frequencies by utilizing the log-periodic dipole radiating arm, while maintaining the stability of the radiation pattern and increasing the application range of the antenna.

[0018] (3) The tightly coupled antenna array provided by the present invention has a compact and simple structure; it is easy to process and manufacture, and can be assembled by screwing together, resulting in low production and maintenance costs; it is detachable and has a wide range of applications; the array has good stability, and the impedance of each unit in the array can remain stable over a very wide frequency band and angle range, thus realizing the wide bandwidth and angle characteristics of the array. Attached Figure Description

[0019] Figure 1 is a schematic diagram of the overall structure stacking of an embodiment of the present invention.

[0020] Figure 2 is a top-view perspective diagram of an embodiment of the present invention.

[0021] Figure 3 is a cross-sectional diagram with an oblique view of an embodiment of the present invention.

[0022] Figure 4 is an enlarged schematic diagram of the tightly coupled dipole radiating patch in an embodiment of the present invention.

[0023] Figure 5 is an enlarged schematic diagram of the auxiliary log-periodic dipole arm in an embodiment of the present invention.

[0024] Figure 6 is a schematic diagram of the layering of the auxiliary log-periodic dipole oscillator arms in an embodiment of the present invention; wherein (a) is a schematic diagram of the oscillator arm distribution on the second metal layer; and (b) is a schematic diagram of the oscillator arm distribution on the first metal layer.

[0025] Figure 7 is a schematic diagram of the balanced feed balun in an embodiment of the present invention; where (a) is a schematic diagram of the back plate; and (b) is a schematic diagram of the front plate.

[0026] Figure 8 is a schematic diagram of the structure of each metal layer in the one-dimensional subarray example of the present invention; wherein (a) is a schematic diagram of the structure of the first metal layer of the one-dimensional subarray; (b) is a schematic diagram of the structure of the third metal layer of the one-dimensional subarray; (c) is a schematic diagram of the structure of the fourth metal layer of the one-dimensional subarray; and (d) is a schematic diagram of the structure of the second metal layer of the one-dimensional subarray.

[0027] Figure 9 is a comparison of the simulated and measured standing wave curves of an embodiment of the present invention.

[0028] Figure 10 shows the gain curves in the 0° direction of the E-plane, comparing the simulation and actual measurements of a tightly coupled dipole antenna array with 22 antenna elements.

[0029] Figure 11 shows the gain curves in the 30° direction of the E plane, comparing the simulation and actual measurements of a tightly coupled dipole antenna array with 22 antenna elements.

[0030] Figure 12 shows the gain curves in the 60° direction of the E plane, comparing the simulation and actual measurements of a tightly coupled dipole antenna array with 22 antenna elements.

[0031] In the figure, 1: Upper dielectric substrate; 2: Middle dielectric substrate; 3: Lower dielectric substrate; 4: First metal layer; 5: Second metal layer; 6: Third metal layer; 7: Fourth metal layer; 8: Balanced feed balun; 9: Tightly coupled dipole radiating patch; 10: Auxiliary log-periodic dipole arm; 11: Tightly coupled dipole corner; 12: Overlapping area of ​​radiating patches; 13: Transition section of rectangular radiating patch; 14: Rectangular radiating patch; 15: First group of dipole arms; 16: Second group of dipole arms; 17: Third group of dipole arms. Sub-arm; 18: Fourth group dipole arm; 19: Fifth group dipole arm; 15-2, 16-1, 17-2, 18-1, 19-2: Left arms of the first to fifth groups of dipole arms; 15-1, 16-2, 17-1, 18-2, 19-1: Right arms of the first to fifth groups of dipole arms; 20: Coaxial connector connecting section metal strip; 21: Trapezoidal impedance transformation section; 22: Feeder section; 23: Probe; 24: Coaxial connector connecting section metal backplate; 25: Exponential impedance transformation section. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] The present invention discloses a tightly coupled dipole antenna array loaded with a log-periodic dipole, which mainly consists of a balanced feed balun, a tightly coupled dipole radiating patch, and an auxiliary log-periodic dipole arm. The structure comprises four metal layers and a dielectric substrate between the metal layers. The first and second metal layers have one-dimensionally equally spaced tightly coupled dipole radiating patches of the same geometric size. Each tightly coupled dipole radiating patch is connected to an auxiliary log-periodic dipole arm. The arrangement of the radiating patches and arms on the first and second metal layers is rotationally symmetrical about the center line of the antenna array elements. Adjacent antenna elements have overlapping radiating patches on the first and second metal layers. An equivalent capacitance is introduced through coupling to cancel the inductance introduced by itself, enabling operation over a wide frequency band. The third and fourth metal layers are located between the first and second metal layers and have a balanced feed balun. The balanced feed balun uses a microstrip line to dielectric bifilar line with a gradient ground plane to achieve impedance transformation and reverse the feed direction.

[0034] Figures 1 to 3 illustrate a specific form of a tightly coupled dipole antenna array loaded with a log-periodic oscillator. As shown in Figure 1, the main structure of the antenna array includes an upper dielectric substrate 1, a middle dielectric substrate 2, and a lower dielectric substrate 3. The upper surface of the upper dielectric substrate 1 has a first metal layer 4, the lower surface of the lower dielectric substrate 3 has a second metal layer 5, and the upper and lower surfaces of the middle dielectric substrate 2 have a third metal layer 6 and a fourth metal layer 7, respectively. In this embodiment, the antenna circuitry is fabricated using traditional PCB technology. The metal layer on the dielectric substrate is copper with a thickness of 35 μm. The dielectric substrates are all Rogers 4003 with a thickness of 1 mm and a dielectric constant of 3.55.

[0035] As shown in Figures 2 and 3, the first metal layer 4 and the second metal layer 5 contain a plurality of one-dimensional tightly coupled dipole radiating patches 9 arranged at equal intervals, forming a one-dimensional tightly coupled dipole antenna array. The radiating patches on the first metal layer 4 and the second metal layer 5 are arranged symmetrically with the antenna element centerline rotated 180 degrees. The radiating patches on the first metal layer 4 form the right radiating arm of the tightly coupled dipole, and the radiating patches on the second metal layer 5 form the left radiating arm. The first metal layer 4 and the second metal layer 5 also contain an auxiliary log-periodic dipole matched radiation array composed of auxiliary log-periodic dipole arms 10. The arms on the first metal layer 4 and the arms on the second metal layer 5 are arranged symmetrically with the antenna element centerline rotated 180 degrees, and are staggered. For example, if the first-stage oscillator arm on the first metal layer 4 forms the left oscillator arm of the dipole structure, then the first-stage oscillator arm on the second metal layer 5 forms the right oscillator arm of the dipole structure; if the second-stage oscillator arm on the first metal layer 4 forms the right oscillator arm of the dipole structure, then the second-stage oscillator arm on the second metal layer 5 forms the left oscillator arm of the dipole structure, and so on. Each array unit in the first metal layer 4 and the second metal layer 5 has the same oscillator arm placement position and arrangement. The third metal layer 6 and the fourth metal layer 7 are equipped with a balanced feed balun 8, one end of which is directly connected to a coaxial connector, and the other end feeds the radiating patch via a probe.

[0036] As shown in Figure 4, the main structure of the antenna array is a tightly coupled dipole radiating patch 9. An auxiliary log-periodic dipole arm 10, located at the upper end of the tightly coupled dipole radiating patch 9, achieves ultra-wideband matching. The lower end of the auxiliary log-periodic dipole arm 10 is a tightly coupled dipole corner 11. The tightly coupled dipole radiating patch 9 is essentially a dipole antenna. It introduces an equivalent capacitance with adjacent dipoles through strong coupling to cancel the inductance introduced by itself, enabling it to operate over a wide frequency band. The radiating patch is segmented. The first segment is the transition segment 13 from the feed line to the rectangular radiating patch, and the second segment is the extension of the rectangular radiating patch 14. The overlap 12 of the radiating patches on the first metal layer 4 and the second metal layer 5 is located at the end of the rectangular radiating patch 14. The length of the transition section 13 from the feed line to the rectangular radiating patch should not exceed half the length of the entire radiating patch to avoid affecting the distribution of low-frequency radiated current elements. The width of the tightly coupled dipole radiating patch 9 should not be less than the width of the longest pair of arms in the auxiliary log-periodic dipole arms 10. The length of the tightly coupled dipole radiating patch 9 should not be less than the length of the longest pair of arms in the auxiliary log-periodic dipole arms 10. The coupling length of the tightly coupled dipole radiating patch 9 affects the low-frequency performance of the antenna array. In this embodiment, the tightly coupled dipole antenna does not require a reflective backplane.

[0037] The main structure of the auxiliary log-periodic dipole matched radiation array is a dipole arm with a log-periodic topological transformation. The rear end of the central feed line extends outward to form an extension body, which, together with the log-periodic dipole, forms a log-periodic dipole end-emitting radiator. The lengths and widths of the multiple sets of dipole arms in the auxiliary log-periodic dipole arm 10 gradually increase from front to back, and the distance between adjacent dipole arms also gradually increases from front to back. In specific design, the length, width, and adjacent spacing of the auxiliary log-periodic dipole arm 10 can satisfy the following relationships:

[0038] Where τ represents the scaling factor, indicating the degree of scaling of the logarithmic period; l n l n+1 These represent the lengths of the nth and (n+1)th oscillator arms, respectively, where 1 ≤ n ≤ N-1, and N is the number of oscillator arm stages; w n w n+1 These represent the widths of the nth and (n+1)th stage oscillator arms, respectively, where 1 ≤ n ≤ N-1; s n s n+1 These represent the distances between the nth and n+1th stage oscillator arms and between the n+1th and n+2th stage oscillator arms, respectively, where 1≤n≤N-2.

[0039] As shown in Figures 5 and 6, the auxiliary log-periodic dipole arm 10 includes five groups: the first group of dipole arms 15, the second group of dipole arms 16, the third group of dipole arms 17, the fourth group of dipole arms 18, and the fifth group of dipole arms 19. The left arm 15-2 of the first group of dipole oscillator arms 15 is located in the first metal layer 4, and the right arm 15-1 is located in the second metal layer 5; the left arm 16-1 of the second group of dipole oscillator arms 16 is located in the second metal layer 5, and the right arm 16-2 is located in the first metal layer 4; the left arm 17-2 of the third group of dipole oscillator arms 17 is located in the first metal layer 4, and the right arm 17-1 is located in the second metal layer 5; the left arm 18-1 of the fourth group of dipole oscillator arms 18 is located in the second metal layer 5, and the right arm 18-2 is located in the first metal layer 4; the left arm 19-2 of the fifth group of dipole oscillator arms 19 is located in the first metal layer 4, and the right arm 19-1 is located in the second metal layer 5. In this embodiment, the auxiliary log-periodic dipole arms 10 are staggered to establish relatively symmetrical boundary conditions, ensuring the balance of the radiation pattern and minimizing interference between adjacent dipole units by ensuring a 180° phase shift. The shorter end of the auxiliary log-periodic dipole arm 10 is located in the radiation direction, and the longer end is located in the feeding direction. The feeding current is fed from the shorter end of the arm rather than the longer end.

[0040] As shown in Figure 7, the balanced feed balun 8 includes a coaxial connector metal strip 20, a trapezoidal impedance transformation section 21, a feed line section 22, a coaxial connector metal backplate 24, and an exponential impedance transformation section 25. The feed line section 22 and the exponential impedance transformation section 25 form a dielectric bi-line structure. The top end of the feed line section 22 is connected to the auxiliary logarithmic periodic dipole arm 10 via a probe 23, and the bottom end is connected to the trapezoidal impedance transformation section 21. The trapezoidal impedance transformation section 21 is fed by connecting to the coaxial feed line via the coaxial connector metal strip 20. The feed connector is a coaxial feed port and can be directly fixed to the intermediate dielectric substrate 2 using a threaded fixing method. The coaxial connector metal strip 20 adopts a ground-cut microstrip line structure, while the trapezoidal impedance transformation section 21 is not a fully microstrip line structure. In this embodiment, the backplane adopts an exponential gradient line structure for impedance matching, and the frontplane adopts a trapezoidal impedance transformation structure. The exponential gradient line structure, by adjusting the slope of the gradient line, allows the balanced feed balun 8 to cover an ultra-wide frequency band. Specifically, the balanced feed balun 8 gradually changes its characteristic impedance along the transmission line length, and its characteristic impedance changes exponentially along the transmission line length: Z(z)=Z0e δz

[0041] Where Z(z) is the characteristic impedance of the transmission line at position z; Z0 is the characteristic impedance of the starting end of the transmission line (z=0); z is the distance along the length of the transmission line; δ is the impedance change coefficient, which determines the rate of change of the characteristic impedance, and can be determined by the following formula:

[0042] Where L is the total length of the transmission line; Z L It is the characteristic impedance at the end of the transmission line (z = L); In represents the natural logarithm.

[0043] In this embodiment, the balanced feed balun 8 disposed on the middle dielectric substrate 2 transmits the current of the dielectric double-wire structure in reverse to the first metal layer 4 and the second metal layer 5 through the probe 23, thus forming the radiation conditions of the tightly coupled dipole antenna. The feed probe 23 is located in the dielectric of the upper dielectric substrate 1 and the lower dielectric substrate 3. The middle dielectric substrate 2 is the transmission layer, and the feed line of this layer in the antenna part is a dielectric double-wire structure. After being matched by the balanced feed balun 8, the double-wire currents are of equal amplitude and out of phase, thus constructing the current conditions of the upper and lower dielectric substrate radiating elements. The tightly coupled dipole radiating patch 9 and the auxiliary log-periodic dipole arm 10 are fed in reverse through the balanced feed balun 8 and the probe 23. The feed line first passes through the auxiliary log-periodic dipole arm 10 and then feeds to the tightly coupled dipole radiating patch 9, forming forward unidirectional radiation to ensure that the radiation direction is towards the end-fire direction rather than the feed direction.

[0044] Figures 8(a), (b), (c), and (d) show schematic diagrams of the metal layers in a one-dimensional linear array. The antenna array is fabricated in units of subarrays. One end of the subarray has an outwardly extending protrusion that matches the tightly coupled dipole radiating patch, and the other end has a recess that matches the protrusion. The subarray in the figure consists of 8 antenna elements. After the subarray is fabricated, three dielectric substrates are fixed by passing nylon screws through fixing holes. At the same time, the extension fixing structures on both sides can extend the subarray to achieve the assembly of antennas with a number of array elements that are multiples of 8.

[0045] The effects of this invention are illustrated below with a specific design example of a tightly coupled dipole antenna array loaded with a log-periodic oscillator. In this design example, the antenna element spacing is set to 24.4 mm, the fixing screw hole spacing is 24.4 mm, the aperture is 2 mm, and the overall antenna height is 32 mm. The design operates at frequencies between 2 and 18 GHz. Based on this, the lengths of the auxiliary log-periodic dipole arms, from top to bottom, are determined to be 2.2 mm, 3.2 mm, 4 mm, 6.2 mm, and 7 mm; the widths of the auxiliary log-periodic dipole arms, from top to bottom, are 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, and 1 mm; the length of the tightly coupled dipole radiating patch is 13 mm, with a gradient transition section of 5.7 mm, a rectangular radiating patch width of 2 mm, and a patch overlap length of 4 mm; in the balanced-fed balun, the metal strip on the front plate starts with a width of 2.1 mm, undergoes a 4.5 mm trapezoidal transformation to a length of 14.42 mm and a width of 1.1 mm, while the metal back plate starts with a width of 10 mm, undergoes a 13.2 mm exponential gradient transformation to a length of 5.72 mm and a width of 1.1 mm, together with the front plate metal strip to form a dielectric bi-line structure. The coaxial power supply port is designed with a transition area for connection to the SMA connector, and holes are drilled according to the corresponding SMA model.

[0046] Figure 9 shows a comparison of the standing wave ratio (VSWR) curves of the designed antenna array. The solid line represents the measured curve, and the dashed line represents the simulated curve. It can be seen that the measured VSWR of the designed antenna matches the simulated VSWR within the impedance bandwidth of 2GHz to 18GHz. The impedance bandwidth of the designed antenna can cover 2GHz to 18GHz, satisfying the requirement that the VSWR is less than 3.

[0047] Figure 10 shows the main polarization gain curve and comparison diagram of the designed antenna array in the 0° direction of the E plane. The number of array elements is 22. The solid line is the measured curve and the dashed line is the simulated curve. It can be seen that the measured gain of the designed antenna matches the simulated gain in the range of 2GHz to 18GHz.

[0048] Figure 11 shows the main polarization gain curve and comparison diagram of the designed antenna array in the 30° direction of the E plane. The number of array elements is 22. The solid line is the measured curve and the dashed line is the simulated curve. It can be seen that the measured gain of the designed antenna matches the simulated gain in the range of 2GHz to 18GHz.

[0049] Figure 12 shows the main polarization gain curve and comparison diagram of the designed antenna array in the 60° direction of the E plane. The number of array elements is 22. The solid line is the measured curve and the dashed line is the simulated curve. It can be seen that the measured gain of the designed antenna matches the simulated gain in the range of 2GHz to 18GHz.

[0050] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning understood by those skilled in the art. It should be understood that the terms "upper," "lower," "front," "back," etc., indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, not indicating or implying that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "multiple" means two or more, unless otherwise explicitly defined; unless otherwise explicitly specified and limited, the terms "connected," "linked," etc., should be interpreted broadly, for example, referring to a fixed connection, a detachable connection, or an integral part; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or a connection within two elements or an interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some or all of the technical features. Such modifications or substitutions do not cause the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator, characterized in that: The system comprises four metal layers and a dielectric substrate between the metal layers. The first and second metal layers have one-dimensionally equally spaced tightly coupled dipole radiating patches of the same geometric size. Each tightly coupled dipole radiating patch is connected to an auxiliary log-periodic dipole arm. The arrangement of the radiating patches and arms on the first and second metal layers is rotationally symmetrical about the center line of the antenna array elements. The radiating patches of adjacent antenna array elements overlap on the first and second metal layers, and an equivalent capacitance is introduced through coupling. The third and fourth metal layers are located between the first and second metal layers and are equipped with a balanced feed balun. A microstrip line to dielectric bi-line with a gradient ground plane is used to achieve impedance transformation and reversal of the feed direction.

2. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 1, characterized in that: The auxiliary log-periodic dipole arm is located at the upper end of the tightly coupled dipole radiating patch, and the lower end of the auxiliary log-periodic dipole arm is the tightly coupled dipole corner; the radiating patches on the first metal layer and the second metal layer are segmented, the first segment is the transition segment from the feed line to the rectangular radiating patch, and the second segment is the extension of the rectangular radiating patch; the overlap of the radiating patches on the first metal layer and the second metal layer is located at the end of the rectangular radiating patch.

3. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 2, characterized in that: The length of the transition section from the first feed line to the rectangular radiating patch does not exceed that of the rectangular radiating patch, and the length of the tightly coupled dipole radiating patch is not less than the length of the longest pair of arms in the auxiliary log-periodic dipole arms.

4. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 1, characterized in that: The radiating patch on the first metal layer forms the right radiating arm of the tightly coupled dipole, and the radiating patch on the second metal layer forms the left radiating arm of the tightly coupled dipole; the first-stage oscillator arm on the first metal layer forms the left oscillator arm of the dipole structure, then the first-stage oscillator arm on the second metal layer forms the right oscillator arm of the dipole structure, the second-stage oscillator arm on the second metal layer forms the left oscillator arm of the dipole structure.

5. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 1, characterized in that: The auxiliary log-periodic dipole arms consist of five groups. The left arm of the first, third, and fifth groups of dipole arms is located in the first metal layer, and the right arm is located in the second metal layer. The left arm of the second and fourth groups of dipole arms is located in the second metal layer, and the right arm is located in the first metal layer. The length, width, and spacing of the multiple groups of dipole arms gradually increase from the radiation direction to the feeding direction.

6. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 1, characterized in that: The balanced feed balun backplane uses an exponential gradient line structure to achieve impedance matching. By adjusting the slope of the gradient line, the coverage frequency band of the balanced feed balun can be extended.

7. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 1, characterized in that: The balanced feed balun includes a coaxial connector metal strip, a trapezoidal impedance transformation section, a feed line section, a coaxial connector metal backplate, and an exponential impedance transformation section. The feed line section and the exponential impedance transformation section form a dielectric bi-wire structure. The top of the feed line section is connected to the auxiliary logarithmic periodic dipole arm via a probe, and the bottom is connected to the trapezoidal impedance transformation section. The trapezoidal impedance transformation section is fed by connecting to the coaxial feed line via the coaxial connector metal strip. The coaxial connector metal strip adopts a ground-cut microstrip line structure.

8. A tightly coupled dipole antenna array loaded with a log-periodic oscillator according to claim 1, characterized in that: The tightly coupled dipole radiating patch and the auxiliary log-periodic dipole arm are fed in opposite directions by a balanced feeding balun and a probe. The feeding line first passes through the auxiliary log-periodic dipole arm and then feeds to the tightly coupled dipole radiating patch, forming forward unidirectional radiation.

9. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 8, characterized in that: The feed probes are located in the dielectric substrate between the first and third metal layers and between the fourth and second metal layers. The current is transmitted in reverse to the first and second metal layers through the feed probes, thus forming the radiation conditions of the tightly coupled dipole antenna.

10. A tightly coupled dipole antenna array loaded with a logarithmic periodic oscillator according to claim 1, characterized in that: The tightly coupled dipole antenna array is a one-dimensional linear array, fabricated in units of subarrays. One end of the subarray has an outwardly extending protrusion that matches the tightly coupled dipole radiating patch, and the other end has a recess that matches the protrusion.

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