A single plane electrically small quasi-isotropic antenna

Abstract

The application discloses a single-plane electrically small quasi-isotropic antenna, which comprises a dielectric substrate, an antenna patch radiation unit attached to the upper surface of the dielectric substrate, the antenna patch radiation unit comprising a symmetrical folded dipole and a pair of parallel transmission lines, the folded dipole being formed by twice bending two arms of a dipole microstrip line, wherein the two arms of the dipole are bent once so that the bent part is perpendicular to the unbent stub, and the ends of the two arms of the dipole are bent again so that the bent part is parallel to the unbent stub, and the parallel transmission lines are placed in the middle of the folded dipole. The application can realize good quasi-isotropic radiation characteristics while realizing antenna miniaturization, and can effectively emit or receive signals from all directions.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, and specifically relates to a single-plane electrically small quasi-isotropic antenna. Background Technology

[0002] With the rapid development of IoT technology, more and more devices are achieving interconnectivity. In practical applications, such as RFID and radio frequency energy harvesting systems, the location of terminal devices has a certain degree of randomness, leading to uncertainty in the direction of their transmitted or received signals. To maintain good communication between devices, it is desirable for them to effectively receive electromagnetic wave signals from all directions in space. Therefore, it is essential to design an antenna with full space coverage, i.e., a quasi-isotropic antenna, to establish stable connections for various communication scenarios. Furthermore, considering the trend of device miniaturization, quasi-isotropic antennas with miniaturized features will have even greater application prospects.

[0003] Most existing quasi-isotropic antennas employ complementary structures to achieve quasi-isotropic radiation patterns, combining multiple complementary basic antenna elements to achieve quasi-isotropic radiation across the entire space. One common approach is to arrange multiple monopole antennas regularly on a circle and excite them using an equal-amplitude orthogonal feed network to achieve quasi-isotropic radiation characteristics. A second common approach is to combine orthogonal electric and magnetic dipoles and set appropriate excitation methods, which can also form a quasi-isotropic radiation pattern. However, quasi-isotropic antennas designed using these methods generally suffer from complex structures and large sizes. Therefore, designing a quasi-isotropic antenna with a simple structure and small size is of significant research importance. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a single-plane electrically small quasi-isotropic antenna, which can achieve antenna miniaturization while realizing good quasi-isotropic radiation characteristics, and can effectively transmit or receive signals from all directions.

[0005] The technical solution of the present invention is implemented as follows: a single-plane electrically quasi-isotropic antenna, comprising a dielectric substrate; an antenna patch radiating element attached to the upper surface of the dielectric substrate, wherein the antenna patch radiating element comprises a symmetrical folded dipole and a pair of parallel transmission lines.

[0006] The folded dipole is formed by bending the two arms of a dipole microstrip line twice. The two arms of the dipole are bent once, so that the bent part is perpendicular to the unbent branch, which can be equivalent to a pair of reverse current sources and an orthogonal current source. The radiation patterns of the reverse current source and the orthogonal current source are complementary, which can achieve full space radiation coverage. On this basis, the ends of the two arms of the dipole are bent again, so that the bent part is parallel to the unbent branch, so as to achieve a compact antenna structure.

[0007] The parallel transmission line is placed in the middle of the folded dipole to excite the folded dipole to work.

[0008] Preferably, the current on each branch of the folded dipole is determined based on the current on the dipole before bending. In a three-dimensional rectangular coordinate system, assuming the current direction on the dipole before bending is the y-axis direction, the expression for the current is:

[0009] ;

[0010] Where I0 is the amplitude of the current, k is the wave number, l is the distance between any point on the dipole and the center of the dipole, and L0 is half the length of the dipole. y is the unit vector in the y-axis direction of the coordinate system;

[0011] The dipole's two arms are bent twice, each arm dividing into three segments, resulting in a total of six stubs. The magnitude of the current in each stub can be determined based on its distance from the dipole's center, i.e.:

[0012] ;

[0013] Where I1(l), I2(l), I3(l), I4(l), I5(l), and I6(l) represent the currents on the six stubs of the folded dipole, respectively. 01 l 02 and l 03 These are the lengths of the initial branch segment, the first bending branch segment, and the second bending branch segment, respectively. is the unit vector along the x-axis in the coordinate system;

[0014] Correspondingly, the electric field generated by the current on each branch segment It can be written as:

[0015] ;

[0016] Where r is the distance from the dipole center to the far-field observation point. Let r be the unit vector, and η be the wave impedance. The current distribution on each branch, Current distribution on each branch The vector form, where j is the imaginary unit. Let l be a vector form of length l, and n be the branch number;

[0017] Therefore, the total electric field produced by the folded dipole for:

[0018] ;

[0019] The current on the first bent stub forms a pair of reverse current sources, while the current on the initial stub is orthogonal to the reverse current sources, thus forming orthogonal current sources. The second bent stub is shorter and has a smaller current, which can be ignored. Calculations using the above formula show that the radiation patterns of the reverse and orthogonal current sources are complementary, achieving a quasi-isotropic radiation pattern.

[0020] Preferably, the total length of the folded dipole is at least half the working wavelength; the width is at least one three-hundredth of the working wavelength; the distance from the first bend to the center of the dipole is at least one-fifteenth of the working wavelength; the distance from the second bend to the first bend is at least one-eighth of the working wavelength; and the length of the end branch is at least one-twentieth of the working wavelength.

[0021] The parallel transmission line consists of two parallel microstrip lines with identical shapes. One end of the parallel transmission line is connected to the center of the folded dipole, and the other end extends to the edge of the dielectric substrate for easy power feeding. A comb structure, i.e. a capacitor structure, is introduced into the parallel transmission line to adjust the impedance of the antenna and achieve impedance matching.

[0022] Preferably, the total length of the parallel transmission lines is at least one-seventh of the operating wavelength, wherein the length of the comb structure is at least one-thirtieth of the operating wavelength, the width of each parallel microstrip line is at least one two-hundredth of the operating wavelength, and the spacing is at least one six-hundredth of the operating wavelength.

[0023] Optionally, the dielectric substrate may be a low-loss dielectric substrate with a thickness of 0.5-5mm.

[0024] Optionally, the single-plane electrically quasi-isotropic antenna operates at a frequency of 915 MHz.

[0025] The present invention has the following beneficial technical effects:

[0026] 1) The overall dimensions of this single-plane electrically small quasi-isotropic antenna are 0.21λ0×0.2λ0×0.003λ0 (ka=0.91<1, meeting the requirements for electrically small size), where λ0 is the operating frequency, which is the wavelength corresponding to 915MHz; the antenna has good impedance matching characteristics, with a maximum gain of 1.33dBi and a minimum gain of -0.29dBi at the operating frequency (915MHz), and a gain difference of only 1.62dB;

[0027] 2) This single-plane electrically small quasi-isotropic antenna has advantages such as simple structure, small size, low cost and easy manufacturing. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of the single-plane electrically quasi-isotropic antenna of the present invention;

[0030] Figure 2 This is a planar structural diagram of the single-plane electrically quasi-isotropic antenna patch of the present invention;

[0031] Figure 3 The reflection coefficient of the single-plane electrically quasi-isotropic antenna of the present invention;

[0032] Figure 4 This is a schematic diagram of the current distribution on the surface of the single-plane electrically quasi-isotropic antenna of the present invention;

[0033] Figure 5 This is the three-dimensional radiation pattern of the single-plane electrically quasi-isotropic antenna of the present invention at the operating frequency (915MHz);

[0034] Figure 6 It is the radiation pattern of a single-plane electrically quasi-isotropic antenna in the xoy plane;

[0035] Figure 7 It is the radiation pattern of a single-plane electrically quasi-isotropic antenna in the xoz plane;

[0036] Figure 8 It is the radiation pattern of a single-plane electrically quasi-isotropic antenna in the yoz plane.

[0037] In the figure: 1-Dielectric substrate; 2-Folded dipole; 201-Initial stub; 202-First bending stub; 203-Second bending stub; 3-Parallel transmission line; 301-Front-end parallel microstrip line; 302-Comb structure; 303-Rear-end parallel microstrip line; 4-Opening; 5-Excitation port. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] This invention discloses a single-plane electrically small quasi-isotropic antenna. Figure 1 and Figure 2 This is a schematic diagram of a single-plane electrically quasi-isotropic antenna operating at 915MHz, according to an embodiment, including a dielectric substrate 1 and an antenna patch radiating element attached to the upper surface of the dielectric substrate.

[0040] The dielectric substrate 1 is made of polytetrafluoroethylene (PTFE), with a relative permittivity of 2.2, a relative permeability of 1.0, a loss tangent of 0.0009, and a thickness of 1 mm.

[0041] like Figure 1 As shown, the antenna patch radiating element includes a folded dipole 2 and a parallel transmission line 3, featuring a simple structure. The folded dipole 2 is formed by bending the two arms of a dipole microstrip line twice, creating three segments: an initial stub 201, a first-bend stub 202, and a second-bend stub 203. The first bend of the dipole's arms ensures that the first-bend stub 202 is perpendicular to the unbendable initial stub 201, effectively realizing a pair of reverse current sources and an orthogonal current source. The radiation patterns of the reverse and orthogonal current sources are complementary, achieving full-space radiation coverage. Furthermore, a second bend is applied to the ends of the dipole's arms, making the second-bend stub 203 parallel to the unbendable initial stub 201, thus achieving a compact antenna structure. The parallel transmission line consists of two parallel microstrip lines with a comb-like structure, comprising three parts: a front parallel microstrip line 301, a comb-like structure 302, and a rear parallel microstrip line 303. The parallel transmission line 3 is placed in the middle of the symmetrical folded dipole 2, connects to the excitation port 5, and is used to excite the folded dipole 2 to operate.

[0042] The current in each branch of the folded dipole can be determined based on the current in the dipole before bending. In a three-dimensional rectangular coordinate system, assuming the direction of the current in the dipole before bending is the y-axis, the expression for the current is:

[0043] ;

[0044] Where I0 is the amplitude of the current, k is the wave number, l is the distance between any point on the dipole and the center of the dipole, and L0 is half the length of the dipole. y is the unit vector along the y-axis in the coordinate system.

[0045] The dipole's two arms are bent twice, each arm dividing into three segments, resulting in a total of six stubs. The magnitude of the current in each stub can be determined based on its distance from the dipole's center, i.e.:

[0046] ;

[0047] Where I1(l), I2(l), I3(l), I4(l), I5(l), and I6(l) represent the currents on the six stubs of the folded dipole, l 01 l 02 and l 03 These are the lengths of the initial branch segment, the first bending branch segment, and the second bending branch segment, respectively. is the unit vector along the x-axis in the coordinate system.

[0048] Correspondingly, the electric field generated by the current on each branch segment It can be written as:

[0049] ;

[0050] Where r is the distance from the dipole center to the far-field observation point. Let r be the unit vector, and η be the wave impedance. The current distribution on each branch, Current distribution on each branch The vector form, where j is the imaginary unit. Let l be a vector form of length l, and n be the branch number.

[0051] Therefore, the total electric field produced by the folded dipole for:

[0052] ;

[0053] Preferably, the total length of the folded dipole 2 is at least half the working wavelength; the width is at least one three-hundredth of the working wavelength; the distance from the first bend to the center of the dipole is at least one-fifteenth of the working wavelength; the distance from the second bend to the first bend is at least one-eighth of the working wavelength; and the length of the end branch is at least one-twentieth of the working wavelength.

[0054] Preferably, the total length of the parallel transmission lines 3 is at least one-seventh of the operating wavelength, wherein the length of the comb structure 303 is at least one-thirtieth of the operating wavelength, the width of each parallel microstrip line is at least one two-hundredth of the operating wavelength, and the spacing is at least one six-hundredth of the operating wavelength.

[0055] After the initial design, high-frequency electromagnetic simulation software was used for simulation. The optimized parameters and dimensions are shown in the table below:

[0056] Table 1 Optimal dimensions for each parameter of the present invention

[0057]

[0058] Where L is the overall length of the antenna, l1 is the distance between the first bends on the left and right, l2 is the length of the initial stub 201 in the folded dipole 2, l3 is the length of the first bend stub 202 in the folded dipole 2, l4 is the length of the second bend stub 203 in the folded dipole 2, l5 is the length of the parallel transmission line 3, l6 is the length of the front parallel microstrip line 301 in the parallel transmission line 3, l7 is the length of the comb structure 302 in the parallel transmission line 3, l8 is the length of the rear parallel microstrip line 303 in the parallel transmission line 3, W is the overall width of the antenna, w1 is the width of the initial stub 201 in the folded dipole 2, w2 is the width of the first bend stub 202 in the folded dipole 2, w3 is the width of the parallel transmission line 3, w4 is the width of the slot in the comb structure 302, and w5 is the spacing between the parallel transmission lines 3.

[0059] Based on the above parameters, the reflection coefficient |S| of the designed single-plane electrically quasi-isotropic antenna is... 11 Simulation analysis was performed on the current distribution and radiation pattern, and the results are as follows:

[0060] from Figure 3 As can be seen from the simulation (actual measurement), the resonant frequency of the single-plane electrically quasi-isotropic antenna is 915MHz (900MHz), and the corresponding reflection coefficient is -19.04dB (-22dB). The single-plane electrically quasi-isotropic antenna has good impedance matching characteristics.

[0061] from Figure 4 As can be seen, on folded dipole 2, the current amplitude gradually decreases with increasing distance from the center. From... Figure 4 It can also be observed that the structure of the dipole after one bend does indeed form a pair of opposite currents and a current orthogonal to them, thus achieving a quasi-isotropic radiation pattern. In order to reduce the size of the antenna, the dipole is bent twice. The current at the end after the second bend is very small, and it has little impact on the overall radiation of the folded dipole 2. By optimizing the bending position, the antenna can maintain a good quasi-isotropic radiation pattern.

[0062] from Figure 4 It can be further seen that the current amplitude on the parallel transmission line 3 is large, but the currents on it are opposite in direction, and the radiation cancels each other out, so it hardly affects the quasi-isotropic radiation pattern generated by the folded dipole 2.

[0063] Figure 5 This is the three-dimensional radiation pattern of a single-plane electrically small quasi-isotropic antenna at the resonant frequency of 915MHz. Its maximum radiation direction is in the -x-axis direction with a magnitude of 1.33dBi, and its minimum radiation direction is in the z-axis direction with a magnitude of -0.29dBi. The gain difference is 1.62dB. Therefore, the antenna radiation pattern has the characteristic of low gain difference.

[0064] Figures 6-8 The image shows the two-dimensional radiation pattern of a single-plane electrically quasi-isotropic antenna at its resonant frequency of 915 MHz. Figure 6 It is the radiation pattern of a single-plane electrically quasi-isotropic antenna in the xoy plane; Figure 7 It is the radiation pattern of a single-plane electrically quasi-isotropic antenna in the xoz plane; Figure 8 This is the radiation pattern of a single-plane electrically quasi-isotropic antenna in the yoz plane. The magnitude of the electric field, Let θ be the θ component of the electric field. Let θ be the θ component of the electric field. Simulation data shows that the gain difference on the xoy plane is 1.49 dB, on the xoz plane is 1.61 dB, and on the yoz plane is 0.5 dB. Figures 6-8 It can be seen that the three working surfaces (xoy plane, xoz plane and yoz plane) of the single-plane electrically small quasi-isotropic antenna all exhibit good omnidirectional radiation characteristics.

[0065] In summary, this invention utilizes a folded dipole to fabricate a quasi-isotropic single-plane microstrip antenna. By introducing a parallel transmission line with a comb-like structure to feed the folded dipole, impedance matching is achieved. The designed antenna features a simple structure, small size, low manufacturing cost, and excellent performance, making it highly promising for a wide range of applications.

[0066] Of course, those skilled in the art should be able to make various corresponding changes and modifications based on the present invention without departing from its spirit and essence, but all such changes and modifications should fall within the protection scope of the appended claims.

Claims

1. A single-planar electrically quasi-isotropic antenna, comprising a dielectric substrate; and an antenna patch radiating element attached to the upper surface of the dielectric substrate, characterized in that, The antenna patch radiating element includes a symmetrical folded dipole and a pair of parallel transmission lines; The folded dipole is formed by bending the two arms of a dipole microstrip line twice. The first bending of the two arms of the dipole makes the bent part perpendicular to the unbent branch, which is equivalent to a pair of reverse current sources and an orthogonal current source. The radiation patterns of the reverse current source and the orthogonal current source are complementary. The ends of the two arms of the dipole are bent a second time in the direction of the parallel transmission line, so that the second bending part is parallel to the unbent branch. The parallel transmission line is placed in the middle of the folded dipole. The parallel transmission line consists of two parallel microstrip lines with the same shape. One end of the parallel transmission line is connected to the center of the folded dipole, and the other end extends to the edge of the dielectric substrate for easy power feeding. A comb-like structure is introduced into the parallel transmission line to adjust the impedance of the antenna and achieve impedance matching.

2. The single-plane electrically quasi-isotropic antenna according to claim 1, characterized in that, The current in each branch of the folded dipole is determined based on the current in the dipole before bending. In a three-dimensional rectangular coordinate system, with the direction of the current in the dipole before bending as the y-axis, the expression for the current is: ； Where I0 is the amplitude of the current, and k is the wave number. Let L be the distance between any point on the dipole and the center of the dipole, and let L0 be half the length of the dipole. y is the unit vector in the y-axis direction of the coordinate system; The dipole's two arms are bent twice, each arm dividing into three segments, resulting in a total of six stubs. The magnitude of the current in each stub is determined based on its distance from the dipole's center. ； Where I1(l), I2(l), I3(l), I4(l), I5(l), and I6(l) represent the currents on the six stubs of the folded dipole, respectively. 01 l 02 and l 03 These are the lengths of the initial branch segment, the first bending branch segment, and the second bending branch segment, respectively. is the unit vector along the x-axis in the coordinate system; Correspondingly, the electric field generated by the current on each branch segment for: ； Where r is the distance from the dipole center to the far-field observation point. Let r be the unit vector, and η be the wave impedance. The current distribution on each branch, Current distribution on each branch The vector form, where j is the imaginary unit. Let l be a vector form of length l, and n be the branch number; Therefore, the total electric field produced by the folded dipole for: 。 3. The single-plane electrically quasi-isotropic antenna according to claim 1, characterized in that, The total length of the folded dipole is at least half the working wavelength; the width is at least one three-hundredth of the working wavelength; the distance from the first bend to the center of the dipole is at least one-fifteenth of the working wavelength; the distance from the second bend to the first bend is at least one-eighth of the working wavelength; and the length of the terminal stub is at least one-twentieth of the working wavelength.

4. The single-plane electrically quasi-isotropic antenna according to claim 1, characterized in that, The total length of the parallel transmission lines is at least one-seventh of the operating wavelength, wherein the length of the comb structure is at least one-thirtieth of the operating wavelength, the width of each parallel microstrip line is at least one two-hundredth of the operating wavelength, and the spacing is at least one six-hundredth of the operating wavelength.

5. The single-plane electrically quasi-isotropic antenna according to claim 1, characterized in that, The thickness of the dielectric substrate is 0.5-5 mm.

6. The single-plane electrically quasi-isotropic antenna according to claim 1, characterized in that, The single-plane electrically quasi-isotropic antenna operates at a frequency of 915MHz.

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