Ultra-wideband folded dipole antenna device based on multiple loading

Abstract

The present application relates to broadband antenna device design and beam control technology, specifically, a kind of ultra-wideband folded dipole antenna device based on multiple loading for radio system in radar and communication, it is characterized in that, there is folded dipole logarithmic periodic antenna radiator, ultra-thin semi-open metal cavity, local loading microwave wave-absorbing material, high dielectric constant covering medium, concentrated loading resistance, wherein folded dipole logarithmic periodic antenna radiator is placed in metal cavity, microwave wave-absorbing material is partially filled in metal cavity, high dielectric constant covering medium is covered at low-frequency vibrator, and the coverage range is greater than the area corresponding to low-frequency vibrator;The broadband antenna design scheme based on multiple loading in the present application is suitable for being applied to ultra-wideband radar system, passive direction finding system, electronic countermeasure system, electronic reconnaissance system and ultra-wideband communication system, and has important application value and practical significance.

Description

Technical fields:

[0001] This invention relates to broadband antenna device design and beam control technology, specifically to an ultra-wideband folded dipole antenna device based on multiple loading that can be used in radio systems such as radar and communications. Background technology:

[0002] In fields such as missile passive guidance radar, electronic reconnaissance, and ultra-wideband wireless communication, broadband antennas and their arrays play a crucial role as sensors for electromagnetic signals. In practical applications, antenna installation space is typically extremely limited, especially when the platform is an aircraft. Antennas and their arrays often need to be sized and shaped to fit the available space, maintaining aerodynamic characteristics while simultaneously ensuring that radiation and circuit performance are not significantly degraded. Therefore, broadband antennas on carrier platforms require miniaturization, low profile, and wide-bandgap radiation performance. Under special conditions, the antenna should also have beamforming capabilities to achieve the desired beam pointing.

[0003] Ultra-wideband antennas are typically used in passive receiving applications, requiring wide impedance and radiation performance to achieve signal reception and parameter measurement within the desired spatial range. Therefore, the directional characteristics of the antenna's radiation pattern are often important, and a wider beamwidth is generally more advantageous. The principles and methods of wideband antennas include angular antenna structures, self-complementary antenna structures, self-similar antennas, increasing the current radiating area, compensation, and loading.

[0004] In practical applications of traditional antennas, they are mostly directly exposed to the air, making them susceptible to oxidation and corrosion, and compromising their concealment. Harsh environments, in particular, have a greater impact on antenna damage and performance. Dielectric-buried antennas, due to their small size, high concealment, good stability, better antenna protection, and extended bandwidth, are receiving increasing attention from scholars both domestically and internationally. However, because the entire antenna is covered by a dielectric material, which contains dielectric losses, radiation losses, and surface wave losses, the radiation efficiency of dielectric-buried antennas is reduced. Summary of the Invention:

[0005] This invention addresses the antenna sensor technology requirements of ultra-wideband passive radar systems for aircraft platforms by proposing a miniaturized and low-profile broadband antenna based on multiple loading technology and beamforming technology, as well as an ultra-wideband folded dipole antenna device.

[0006] This invention achieves its purpose through the following measures:

[0007] An ultra-wideband folded dipole antenna device based on multiple loading is characterized by comprising a folded dipole log-periodic antenna radiator, an ultra-thin semi-open metal cavity, locally loaded microwave absorbing material, a high dielectric constant covering medium, and a concentrated loading resistor. The folded dipole log-periodic antenna radiator is placed in the metal cavity, the microwave absorbing material is locally filled in the metal cavity, and the high dielectric constant covering medium covers the low-frequency vibrator, with a coverage area larger than the region corresponding to the low-frequency vibrator.

[0008] The folded dipole log-periodic antenna radiator uses folded dipoles as its element type and a broadband balun structure for feeding. Assume the lengths of the nth element and the (n-1)th element are L... n and L n-1 The widths of the nth oscillator and the (n-1)th oscillator are W respectively. n and W n-1 The positions of the nth oscillator and the (n-1)th oscillator are R respectively. n and R n-1 Therefore:

[0009]

[0010]

[0011]

[0012] The excitation end of the folded dipole log-periodic antenna radiator is a coplanar stripline, which is a transmission line with a balanced structure and a broadband balun is introduced.

[0013] This invention employs an integrated broadband balun with a coplanar stripline output and a microstrip line with a characteristic impedance of 50 ohms at the input. Impedance matching is achieved using fan-shaped stubs and a gradient impedance transformation segment is introduced to jointly realize impedance transformation and balanced-to-unbalanced transformation, thus achieving impedance matching at the input. To reduce the balun's obstruction of the folded dipole log-periodic antenna and thus minimize its impact on the radiation pattern, this invention uses an irregularly shaped copper foil ground plane, which is hexagonal. The top edge is parallel to the bottom edge of the dielectric substrate. The opposite side of the bottom edge is the top edge. The top edge is parallel to the bottom edge. One end of the top edge is connected to the upper end of the vertical extension section, and the other end of the top edge is connected to the upper end of the first inclined edge. The angle between the top edge and the vertical extension section is 90°, and the angle between the top edge and the first inclined edge is greater than 90°. The lower end of the vertical extension section is connected to the upper end of the second inclined edge. The lower end of the second inclined edge is connected to one end of the bottom edge, and the other end of the bottom edge is connected to the lower end of the first inclined edge. The first and second inclined edges are parallel to each other.

[0014] The folded dipole log-periodic broadband antenna of the present invention has a low-frequency vibrator length of 53 mm, a number of 14 vibrators, a loading covering medium with a relative permittivity of 9.8, a dielectric substrate thickness of 10 mm, a length of 120 mm, covering the low-frequency vibrator, and extending beyond the area corresponding to the low-frequency vibrator; the metal cavity has a depth of 10 mm, and the bottom of the cavity is filled with conventional microwave absorbing material with a loss tangent of approximately 0.5, and the absorbing material is locally loaded.

[0015] This invention involves locally filling the bottom of an ultra-thin metal cavity with microwave material. The thickness, loss tangent, and dimensions of the microwave absorbing material are designed to adjust the beamform of the broadband antenna while maintaining antenna gain. At the low-frequency vibrator of the antenna, a distributed loading of lumped resistance is used to absorb reflected electromagnetic wave energy at low frequencies, reducing return loss. A high-dielectric-constant dielectric material is loaded above the entire folded dipole log-periodic antenna radiator, achieving a dielectric burial effect. Due to the slow-wave effect, the electrical dimensions of the antenna are reduced, achieving miniaturization. In the dielectric burial technology designed in this invention, the buried dielectric consists of a low-loss, high-dielectric-constant dielectric material at the top and a high-dielectric-constant, high-loss material at the bottom, along with a metal boundary. Its dimensions and performance are determined through full-wave electromagnetic simulation and optimization.

[0016] This invention addresses the needs of aircraft platform environments and proposes a multi-loading-based broadband antenna design and device based on the beam control requirements of broadband antennas. The antenna device employs a folded dipole log-periodic antenna as the basic radiator. Considering the actual situation where the antenna mounting platform is a metallic conductor, multi-loading techniques such as partial absorption boundary, dielectric burial, and concentrated resistance are introduced to improve the antenna's low-frequency performance and control its radiation pattern, achieving the requirements for antenna beam coverage and detection / signal measurement. This invention designs a folded dipole log-periodic antenna radiator with integrated balun feeding, resulting in stable performance, a wide beam, low cost, and ease of fabrication and assembly. The introduction of multi-loading technology makes the broadband antenna design more flexible and offers greater freedom, providing a technical approach for antenna design with special performance requirements in practical applications. The multi-loading-based broadband antenna design of this invention is suitable for application in ultra-wideband radar systems, passive direction finding systems, electronic countermeasures systems, electronic reconnaissance systems, and ultra-wideband communication systems, demonstrating significant application value and practical significance. Attached image description:

[0017] Appendix Figure 1 This is a schematic diagram of the structure of the present invention, wherein... Figure 1 (a) Overall structural diagram. Figure 1 (b) is a diagram of the antenna structure after the covering medium has been removed. Figure 1 (c) is a schematic diagram of the antenna's metal boundary and the absorbing material boundary.

[0018] Appendix Figure 2 This is an exploded schematic diagram of the folded dipole log-periodic antenna radiator in this invention, wherein... Figure 2 (a) is a schematic diagram of the structure of a folded dipole log-periodic antenna radiator; Figure 2 (b) is the front view of the radiator. Figure 2 (c) is a rear view of the radiator.

[0019] Appendix Figure 3 This is a structural diagram of the inherited printing balun in this invention, wherein... Figure 3 (a) is a 3D diagram. Figure 3 (b) is the front view. Figure 3 (c) is the rear view.

[0020] Appendix Figure 4 This is a schematic diagram of the parameters of the folded dipole log-periodic antenna radiator in this invention.

[0021] Appendix Figure 5 These are the simulation results of the return loss at the antenna port.

[0022] Appendix Figure 6 These are the simulation results of the antenna radiation characteristics at a frequency of 1.2 GHz. Figure 6 (a) Three-dimensional gain pattern Figure 6 (b) Three-dimensional axis ratio pattern Figure 6 (c) Gain pattern in the xoz plane. Figure 6 (d) In the axial ratio direction of the xoz plane, Figure 6 (e) Gain pattern in the yoz plane. Figure 6 (f) Axial ratio pattern in the yoz plane. (See attached diagram) Figure 7 Simulation results of antenna radiation characteristics at a frequency of 2 GHz. Figure 7 (a) Three-dimensional gain pattern

[0023] Figure 7 (b) Three-dimensional axis ratio pattern Figure 7 (c) Gain pattern in the xoz plane. Figure 7 (d) Axial ratio pattern in the xoz plane. Figure 7 (e) Gain pattern in the yoz plane. Figure 7 (f) Axial ratio pattern in the yoz plane.

[0024] Appendix Figure 8 Simulation results of antenna radiation characteristics at a frequency of 3 GHz. Figure 8 (a) Three-dimensional gain pattern Figure 8 (b) Three-dimensional axis ratio pattern Figure 8 (c) Gain pattern in the xoz plane. Figure 8 (d) Axial ratio pattern in the xoz plane. Figure 8 (e) Gain pattern in the yoz plane. Figure 8 (f) Axial ratio pattern in the yoz plane.

[0025] Appendix Figure 9 Simulation results of antenna radiation characteristics at a frequency of 4 GHz. Figure 9 (a) Three-dimensional gain pattern Figure 9 (b) Three-dimensional axis ratio pattern Figure 9 (c) Gain pattern in the xoz plane. Figure 9 (d) Axial ratio pattern in the xoz plane. Figure 9 (e) Gain pattern in the yoz plane. Figure 9 (f) Axial ratio pattern in the yoz plane.

[0026] Appendix Figure 10 Simulation results of antenna radiation characteristics at a frequency of 5 GHz. Figure 10 (a) Three-dimensional gain pattern Figure 10 (b) Three-dimensional axis ratio pattern Figure 10 (c) Gain pattern in the xoz plane. Figure 10 (d) Axial ratio pattern in the xoz plane. Figure 10 (e) Gain pattern in the yoz plane. Figure 10 (f) Axial ratio pattern in the yoz plane.

[0027] Appendix Figure 11 Simulation results of antenna radiation characteristics at a frequency of 6 GHz, among which Figure 11 (a) is the three-dimensional gain pattern. Figure 11 (b) Three-dimensional axis ratio pattern Figure 11 (c) Gain pattern in the xoz plane. Figure 11 (d) Axial ratio pattern in the xoz plane. Figure 11 (e) Gain pattern in the yoz plane. Figure 11 (f) Axial ratio pattern in the yoz plane.

[0028] Figure reference numerals: 1 is the covering medium, 2 is the folded dipole log-periodic antenna radiator, 3 is the coaxial cable, 4 is the absorbing material, 5 is the lumped resistor, 6 is the printed reflector element, 7 is the printed folded dipole array, 8 is the integrated printed balun, 9 is the coplanar stripline, 10 is the fan-shaped tuned stub, 11 is the tapered line impedance transformer, 12 is the microstrip transmission line with a characteristic impedance of 50 ohms, and 13 is the irregularly shaped metal ground plane. Detailed implementation method:

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] This invention addresses the antenna sensor technology requirements of ultra-wideband passive radar systems for aircraft platforms by proposing a miniaturized and low-profile broadband antenna design scheme and beam control technology employing multiple loading techniques.

[0031] On typical aircraft platforms, passive radar antennas need to be mounted on the surface of a metal platform. Therefore, the aircraft surface can be considered as the boundary condition of an electric barrier. In radar detection and guidance or electronic reconnaissance modes, the antenna beam should cover the axial front end region of the aircraft as much as possible, i.e., it should be as end-firing as possible. When a conventional broadband antenna is placed on the aircraft surface, the antenna beam will shift due to the boundary condition of the metal surface, changing its coverage range. On the other hand, due to the space constraints of the aircraft platform, the antenna is required to have a low-profile structure to occupy as little space as possible. Therefore, when designing broadband antennas to be mounted on aircraft platforms, the antenna is often required to have low-profile and miniaturized structural characteristics. At the same time, the antenna should also meet the required beam pointing and coverage range.

[0032] This invention, based on a folded dipole log-periodic antenna radiator structure, introduces dielectric burial technology, lumped resistance loading, and local absorption loading technology within a metal cavity to improve the antenna's low-frequency performance and achieve beam control. The broadband antenna structure model based on multiple loading designed in this invention is as follows: Figure 1 As shown. Figure 2 This is a structural model diagram of a folded dipole log-periodic antenna radiator. Figure 3 A schematic diagram of a Balun structure for feeding a folded dipole log-periodic antenna radiator. Figure 4 This is a schematic diagram of the parameters of a folded dipole log-periodic antenna radiator.

[0033] The multi-loaded broadband antenna structure designed in this invention mainly includes a folded dipole log-periodic antenna radiator, an ultrathin semi-open metal cavity, locally loaded microwave absorbing material, a high dielectric constant covering medium, and a concentrated loading resistor, such as... Figure 1As shown. The Eleven antenna is a tenth-harmonic bandwidth log-periodic dipole array. A complete Eleven feed consists of three parts: four log-periodic dipole lobes (i.e., the Eleven antenna), a central reflector (attached to the front and rear sides of the ground plane), and a rear feed network (balun and power divider). The Eleven antenna has excellent characteristics: a nearly constant beamwidth, directivity, and fixed phase center position throughout its bandwidth, a low profile, and a simple geometry. Therefore, the Eleven antenna is very suitable as a reflector feed. The Eleven feed can receive bilinearly polarized waves. For each linear polarization, the antenna consists of two log-periodic dipole arrays in opposite positions, i.e., two dipole lobes. At the geometric center, each dipole lobe is connected to a balanced bilinear transmission line with a characteristic impedance of 200Ω. The two bilinear transmission lines in opposite positions must combine with the same amplitude and phase to form a linear polarization. Similarly, the dipole lobes in the remaining two opposite positions are combined in the same way to form orthogonal linear polarizations. Two orthogonal linear polarization ports can be used to form circular polarization in a linearly orthogonal manner.

[0034] The folded dipole log-periodic antenna radiator in this invention is as follows: Figure 2 As shown, the oscillator type is a folded dipole, and the feeding method adopts a broadband balun structure, as follows. Figure 3 As shown, the folded dipole log-periodic antenna radiator uses a printed circuit, with the element length, element width, and element spacing all exhibiting periodic variations. Given its log-periodic structure, it operates on a similar principle to other log-periodic antennas.

[0035] Assuming a folded dipole arm is in a resonant state, the folded dipole arm closer to the feed point (with a shorter physical size) exhibits a large capacitive reactance at the input, resulting in a small current and, due to its small size, very weak radiation. When the size of the folded dipole arm increases to that of the resonant dipole arm, the input impedance becomes purely resistive, the current in the folded dipole arm increases, radiation intensifies, and it captures most of the energy on the transmission line, becoming the main radiation region of the folded dipole array. Further increases in the size of the folded dipole arm are not sufficient, as most of the energy has already been captured by the resonant dipole arm, resulting in very little energy and weak radiation. At each operating frequency, the radiating dipoles consist of 2-4 short folded dipole arms smaller than the resonant frequency folded dipole arm and one larger folded dipole arm, which together form the "operating region" of the folded dipole array.

[0036] Therefore, the folded dipole array can be divided into three regions according to the principle of logarithmic periodicity, arranged from shortest to longest folded dipole arm size (operating frequency from highest to lowest): the "transmission region," the "operating region (active region)," and the "reflection region (cutoff region)." Each operating frequency corresponds to a folded dipole arm of a corresponding length, and the two adjacent folded dipole arms also participate in the main radiation. Therefore, at each operating frequency, the current is mainly concentrated on the three folded dipole arms, which is the active region; the cutoff region consists of folded dipoles with slightly longer physical dimensions than those in the operating region, carrying extremely weak current and primarily serving a reflection function; the transmission region consists of folded dipoles with slightly shorter physical dimensions than those in the operating region, primarily serving a current transmission function. As the frequency decreases, the active region shifts from the inside out.

[0037] In this invention, the length of the antenna element, the width and position of the folded element are varied according to different proportions. This design facilitates flexible optimization of the antenna's impedance and radiation characteristics. Assume the lengths of the nth element and the (n-1)th element are L... n and L n-1 The widths of the nth oscillator and the (n-1)th oscillator are W respectively. n and W n-1 The positions of the nth oscillator and the (n-1)th oscillator are R respectively. n and R n-1 Therefore:

[0038]

[0039]

[0040]

[0041] The excitation end of the radiator of the folded dipole log-periodic antenna is a coplanar stripline, which is a transmission line with a balanced structure. Therefore, when using coaxial line feeding, a broadband balun is required. In this invention, an integrated broadband balun is designed. The output end of the balun is a coplanar stripline, and the input end is a microstrip line with a characteristic impedance of 50 ohms. Impedance matching is achieved using fan-shaped stubs, and a gradient impedance transformation section is introduced to jointly realize impedance transformation and balanced-to-unbalanced transformation, achieving impedance matching at the input end. To reduce the balun's obstruction of the folded dipole log-periodic antenna and thus reduce the impact on the radiation pattern, this invention designs an irregularly shaped copper foil ground plane. Based on the current distribution, the original copper foil ground plane is reshaped. The specific copper foil ground plane is as follows: Figure 2 As shown in (c).

[0042] In this invention, the broadband folded dipole log-periodic antenna radiator needs to be placed in an ultra-thin metal cavity so that the antenna can be mounted on the metal surface of the aircraft. Therefore, a beam control scheme for the broadband antenna needs to be designed. Considering the requirements of beam control, miniaturization, and low profile for the broadband antenna, this invention introduces a multi-loading technique: high dielectric constant dielectric burial, local loading of microwave absorbing material, and lumped resistance loading, to comprehensively achieve the desired electromagnetic control effect. The low-frequency vibrator corresponds to the longer folded dipole; therefore, the loading part of this invention corresponds to the region where the long vibrator is located. At the bottom of the ultra-thin metal cavity, a microwave material with certain absorption properties is locally filled. The thickness, loss tangent, and size of the microwave absorbing material are designed to adjust the beam shape of the broadband antenna while ensuring antenna gain. At the low-frequency vibrator of the antenna, distributed loading with lumped resistance is used to absorb the reflected electromagnetic wave energy at low frequencies, reducing return loss at low frequencies. A high dielectric constant dielectric material is loaded above the entire folded dipole log-periodic antenna radiator to achieve the effect of dielectric burial. Due to the slow wave effect, the electrical size of the antenna is reduced, achieving miniaturization. In the dielectric burial technology scheme designed in this invention, the burial medium is composed of a low-loss, high-dielectric-constant dielectric material at the top and a high-dielectric-constant, high-loss material at the bottom, together with a metal boundary. Its size and performance are determined by full-wave electromagnetic simulation and optimization.

[0043] Example:

[0044] This invention designs a multi-loaded folded dipole log-periodic broadband antenna device, focusing on the radiation pattern characteristics at low frequencies. The performance of the designed antenna was simulated using full-wave electromagnetic simulation technology, and the results demonstrate the miniaturization and beam control effects achieved by multi-loading.

[0045] The low-frequency dipole log-periodic broadband antenna designed in this invention has a low-frequency element length of 53 mm and 14 elements. The relative permittivity of the loading covering medium is 9.8, the dielectric substrate thickness is 10 mm, and the length is 120 mm. The medium covers the low-frequency element, with a range slightly larger than the corresponding area. The metal cavity depth is 10 mm, and the bottom of the cavity is filled with conventional microwave absorbing material with a loss tangent of approximately 0.5. The absorbing material is locally loaded. The simulated return loss characteristics are as follows: Figure 7 As shown in the figure, the average return loss of the antenna port is approximately -7dB in the operating frequency range of 1.2GHz to 6GHz. At lower frequencies, i.e., 1.2GHz to 2GHz, the return loss is improved.

[0046] Figures 5 to 11Simulation results of the antenna radiation characteristics at six frequency points from 1.2 GHz to 6 GHz are presented. For each frequency point, the three-dimensional gain pattern, three-dimensional axial ratio pattern, gain pattern in the xoz plane, axial ratio pattern in the xoz plane, gain pattern in the yoz plane, and axial ratio pattern in the yoz plane are all given. The simulation results show that the antenna exhibits improved radiation performance at low frequencies, the beam is controlled as expected, and the main beam direction is improved towards the end-fire direction. The axial ratio of the antenna varies significantly with space, indicating that the antenna's polarization characteristics change considerably and require compensation in application.

Claims

1. A multi-load-based ultrawideband folded dipole antenna device, characterized in that, It is equipped with a folded dipole log-periodic antenna radiator, an ultra-thin semi-open metal cavity, locally loaded microwave absorbing material, a high dielectric constant covering medium, and a concentrated loading resistor. The folded dipole log-periodic antenna radiator is placed in the metal cavity, the microwave absorbing material is locally filled in the metal cavity, and the high dielectric constant covering medium covers the low-frequency vibrator, with a coverage area larger than the area corresponding to the low-frequency vibrator. The folded dipole log-periodic antenna radiator uses folded dipoles as its element type and a broadband balun structure for feeding. Assume the lengths of the nth element and the (n-1)th element are respectively... and The widths of the nth oscillator and the (n-1)th oscillator are respectively and The positions of the nth oscillator and the (n-1)th oscillator are respectively and Therefore: (1)， (2)， (3)， The excitation end of the folded dipole log-periodic antenna radiator is a coplanar stripline, which is a transmission line of a balanced structure and a broadband balun is introduced. The broadband balun employs an integrated broadband balun with a coplanar stripline output and a microstrip line with a characteristic impedance of 50 ohms at the input. Impedance matching is achieved using fan-shaped stubs and a tapered impedance transformation section, collectively realizing impedance transformation and balanced-to-unbalanced transformation, thus achieving impedance matching at the input. To reduce the balun's obstruction of the folded dipole log-periodic antenna and thus minimize its impact on the radiation pattern, an irregularly shaped hexagonal copper foil ground plane is used. The bottom edge is flush with the edge of the dielectric substrate. The opposite side of the bottom edge is the top edge. The top edge is parallel to the bottom edge. One end of the top edge is connected to the upper end of the vertical extension section, and the other end of the top edge is connected to the upper end of the first inclined edge. The angle between the top edge and the vertical extension section is 90°, and the angle between the top edge and the first inclined edge is greater than 90°. The lower end of the vertical extension section is connected to the upper end of the second inclined edge. The lower end of the second inclined edge is connected to one end of the bottom edge, and the other end of the bottom edge is connected to the lower end of the first inclined edge. The first inclined edge and the second inclined edge are parallel to each other. It also includes a printed reflector element, wherein the concentrated load resistor is applied to the low-frequency element of the antenna.

2. The ultra-wideband folded dipole antenna device based on multiple loading according to claim 1, characterized in that, The low-frequency vibrator of the folded dipole log-periodic broadband antenna is 53 mm long and has 14 vibrators. The relative permittivity of the loaded covering medium is 9.8, the dielectric substrate is 10 mm thick and 120 mm long, covering the low-frequency vibrator and extending beyond the area corresponding to the low-frequency vibrator. The metal cavity is 10 mm deep, and the bottom of the cavity is filled with conventional microwave absorbing material with a loss tangent of 0.

5. The absorbing material is locally loaded.

Images