CN113161730B - Orthogonal mode-based planar compact low-coupling quad-polarized MIMO antenna - Google Patents

Abstract

The invention discloses a plane compact low-coupling quad-polarized MIMO antenna based on an orthogonal mode, comprising a first radiator and a second radiator based on the orthogonal mode, and the first radiator adopts a ring structure, so the The second radiator adopts a microstrip patch structure, and the radiation modes of electric dipole (Ex) and magnetic dipole (Hz) are obtained on the first radiator, and two orthogonal TM11 are obtained on the second radiator Microstrip antenna patterns (Hx, Hy). The invention makes full use of the inner space of the first radiator, places the second radiator in the first radiator, obtains four polarization modes in the plane structure, and has the characteristics of compact structure and low coupling; The working frequency of the TM11 mode of the two radiators is in the same frequency band as the first radiator. The invention effectively utilizes the electromagnetic field vector characteristics, and can obtain a channel capacity greater than 3×3 and close to 4×4 IID Rayleigh channels in a multipath-rich propagation environment through a compact structure.

Description

Orthogonal mode-based planar compact low-coupling quad-polarized MIMO antenna

technical field

The invention relates to an antenna, in particular to a plane compact low-coupling quad-polarized MIMO antenna based on an orthogonal mode, which can be used in the fields of wireless communication, massive MIMO antenna array and the like.

Background technique

With the vigorous development of wireless communication technology, spectrum resources are becoming increasingly tight, and it has become an inevitable trend to develop and utilize existing frequency bands as much as possible and improve spectrum utilization. Multiple-Input Multiple-Output (MIMO) technology can establish multiple parallel spatial sub-channels by using multiple transmit and receive antennas at the transmitter and receiver respectively, without increasing spectrum resources and antennas. In the case of transmit power, the system channel quality can be doubled. In recent years, with the development of large-scale and ultra-large-scale MIMO technology in 5G and next-generation mobile communication systems, base stations and mobile terminals have higher and higher requirements for antenna volume and quality, and antenna designs are becoming smaller, more compact, and more portable. With the improvement of the direction, people urgently need compact and miniaturized antennas to meet the growing market demand. The multi-polarization MIMO antenna technology using polarization diversity technology has been proposed and proved to be able to solve this problem well.

Multi-polarized antennas, also known as vector antennas, can make MIMO antennas possible by exploiting all six vector components of the electromagnetic fields Ex, Ey, Ez, Hx, Hy, Hz in space to provide up to six degrees of freedom in a rich scattering environment Forming multiple independent parallel sub-channels in the form of spatial co-location is therefore an important technique for realizing compact MIMO antenna arrays. Due to the difficulty of realizing a multi-polarized antenna with a common point, orthogonality, low coupling and compact structure, the existing multi-polarized antennas mostly adopt the design of dual-polarized and tri-polarized antennas, while for quad-polarized and more heavy-duty antennas Polarized antenna designs are relatively rare.

The disadvantages of the existing technology mainly include: (1) Compared with the loop antenna, the electric dipole has a simpler structure, and it is easier to obtain a low-coupling multi-polarized antenna through different polarization directions, but it cannot be used for the antenna in space. The magnetic field component is fully utilized. In a multi-polarized antenna composed of an electric dipole and a loop antenna, the coupling between the electric dipole and the loop antenna is difficult to remove, especially in the case of coplanarity, it is usually necessary to add a decoupling network , EBG and other structures to improve port isolation, so the design of multi-polarized low-coupling electromagnetic dipole antennas composed of electric dipoles and loop antennas is more difficult. (2) In order to obtain orthogonal electric field and magnetic field components, it is usually necessary to place the electric dipole antenna and the loop antenna unit orthogonally, and the resulting three-dimensional structure will increase the difficulty of design and processing. Several quad-polarized MIMO antennas proposed at present are all three-dimensional structures, and the antenna structures and feeding networks are complex, which is not conducive to integration, and is difficult to be applied in some specific usage scenarios.

SUMMARY OF THE INVENTION

Purpose of the invention: The purpose of the present invention is to provide a plane compact low-coupling quad-polarized MIMO antenna based on orthogonal mode, which is low-coupling, compact in structure and convenient for integration.

Technical solution: the planar compact low-coupling quad-polarized MIMO antenna based on the orthogonal mode of the present invention includes a first radiator and a second radiator based on the orthogonal mode, and the first radiator adopts a ring structure , through different excitation positions and excitation methods, respectively control the surface current direction on the ring to obtain two orthogonal radiation modes, namely the radiation modes of the electric dipole (Ex) and the magnetic dipole (Hz), specifically, When the surface current on the ring is uniform and in the same direction, the radiation mode of the magnetic dipole (Hz) is obtained. At this time, there is no current zero point on the radiator, which is called an even mode; when the surface current on the first radiator is about the x-axis Symmetric, when the direction is opposite, the radiation mode of the electric dipole (Ex) is obtained. At this time, there is a current zero point on the radiator, which is called an odd mode; the second radiator adopts a microstrip patch antenna, and the second radiation After the body is miniaturized, the operating frequency of its TM11 mode can be reduced to make it work within the same bandwidth as the first radiator when its area is limited. By exciting at two orthogonal positions of the x-axis and the y-axis, the second radiator can obtain two orthogonal operating modes (Hy, Hx) of the TM11 microstrip antenna.

The first radiator consists of two concentric loop antennas based on zero-phase-shift transmission lines.

The diameter of the second radiator is smaller than the diameter of the inner circle of the first radiator ring, the second radiator is placed in the annular structure of the first radiator, and the inner space of the annular structure is fully utilized.

The second radiator and the first radiator work in the same frequency band.

The antenna also includes an antenna grounding metal plate, a dielectric plate and a microstrip feeding structure, the antenna grounding metal plate and the first radiator are placed on the upper surface of the dielectric plate, the second radiator and the microstrip feeding structure Place on the lower surface of the media plate.

The antenna further includes a feed port, the feed port includes a first feed port, a second feed port, a third feed port, and a fourth feed port, and the first feed port is fed through a lumped port. The inner loop of the first radiator is fed, the second feeding port feeds the outer loop of the first radiator through the microstrip feeding structure, and the third feeding port and the fourth feeding port are respectively in the second radiator. x-axis and y-axis position excitation.

The microstrip feeding structure adopts a T-shaped microstrip line feeding structure.

Beneficial effect: Compared with the prior art, the present invention has the following advantages:

(1) The present invention makes full use of the inner space of the annular structure of the first radiator, places the second radiator in the first radiator, and obtains the result by combining two different radiators based on mode orthogonality in the plane structure Four polarization modes, featuring compact structure and low coupling;

(2) The second radiator is miniaturized by the fractal structure, and the operating frequency of its TM11 mode can be reduced under the premise that the area of the second radiator is limited, and it operates in the same frequency band as the first radiator;

(3) The two radiators used in the present invention have simple structures, and their planar structures are easy to process, install and use;

(4) The present invention can more effectively utilize the electromagnetic field vector characteristics in space, and can obtain channels larger than 3×3 and close to 4×4 IID Rayleigh channels in a multipath-rich propagation environment with a compact structure capacity.

Description of drawings

FIG. 1 is a schematic structural diagram of a quad-polarized MIMO antenna;

Figure 2 is the S-parameter simulation result of the quad-polarized MIMO antenna;

Fig. 3 is the simulation result of coupling between each port of quad-polarized MIMO antenna;

Fig. 4 is the current distribution diagram on the first radiator 1 when the first feed port 6 and the second feed port 7 of the quad-polarized MIMO antenna are excited respectively, wherein Fig. 4a is the first feed of the quad-polarized MIMO antenna When the electrical port 6 is excited, the current distribution diagram on the first radiator 1, FIG. 4b is the current distribution diagram on the first radiator 1 when the second feed port 7 of the quad-polarized MIMO antenna is excited;

Fig. 5 is the electric field distribution diagram on the second radiator 2 when the third feed port 8 and the fourth feed port 9 of the quad-polarized MIMO antenna are excited respectively, wherein Fig. 5a is the third feed of the quad-polarized MIMO antenna When the electrical port 8 is excited, the electric field distribution diagram on the second radiator 2, FIG. 5b is the electric field distribution diagram on the second radiator 2 when the fourth feed port 9 of the quad-polarized MIMO antenna is excited;

Fig. 6 is the radiation pattern when the first feed port 6 of the quad-polarized MIMO antenna is excited, wherein, Fig. 6a is the radiation pattern of the xoy surface, and Fig. 6b is the radiation pattern of the yoz surface;

Fig. 7 is the radiation pattern when the second feed port 7 of the quad-polarized MIMO antenna is excited, wherein Fig. 7a is the radiation pattern of the xoy plane, and Fig. 7b is the radiation pattern of the yoz plane;

Fig. 8 is the radiation pattern when the third feed port 8 of the quad-polarized MIMO antenna is excited, wherein Fig. 8a is the radiation pattern of the yoz surface, and Fig. 8b is the radiation pattern of the xoz surface;

Fig. 9 is the radiation pattern when the fourth feed port 9 of the quad-polarized MIMO antenna is excited, wherein Fig. 9a is the radiation pattern of the yoz surface, and Fig. 9b is the radiation pattern of the xoz surface;

FIG. 10 is a comparison diagram of the resonance frequency when the second radiator 2 adopts the Tee-Type fractal structure and when the Tee-Type fractal structure is not adopted.

11 is the cumulative distribution result of the channel capacity actually measured by the quad-polarized MIMO antenna in the office environment according to the embodiment of the present invention, and the channel capacity comparison with the 3×3 and 4×4 IID Rayleigh channels.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

As shown in FIG. 1 , the quad-polarized MIMO antenna of this embodiment is composed of a first radiator 1 , a second radiator 2 , an antenna grounding metal plate 3 , a dielectric plate 4 , a T-shaped feeding structure 5 and a feeding port , the feed ports include a first feed port 6 , a second feed port 7 , a third feed port 8 and a fourth feed port 9 . Among them, the first feeding port 6 uses a lumped port with a characteristic impedance of 50Ω to excite the inner ring of the first radiator 1, and the second feeding port 7 uses an SMA coaxial cable with a characteristic impedance of 50Ω for feeding, and the microstrip feeding The electrical structure 5 excites the outer ring of the first radiator 1, the third feeding port 8 and the fourth feeding port 9 are fed by SMA coaxial cables with a characteristic impedance of 50Ω, and the second radiation is excited in the x-axis and y-axis respectively body 2.

In this embodiment, the dielectric board 4 is an epoxy resin board FR-4 with a dielectric constant of 4.4, which is placed on the xoy surface, the antenna grounding metal plate 3 and the first radiator 1 are placed on the upper surface of the dielectric board 4, the second The radiator 2 and the microstrip feeding structure 5 are placed on the lower surface of the dielectric plate 4 .

The first radiator 1 is composed of two concentric loop antennas based on zero-phase-shift transmission lines. The structures of the outer loop and the inner loop are basically the same. Compared with the inner loop, the outer loop is rotated clockwise by 22.5°. These zero-phase-shifted transmission lines with periodic structures can introduce series capacitance in the loop, provide little phase correction between adjacent sections, and maintain current flow along the loop even if the loop has a perimeter comparable to the operating wavelength Phase match. With two different excitations, the direction of the surface current on the loop is controlled separately. Specifically, when the feeding port 6 is excited, a surface current of equal magnitude and the same direction is excited on the first radiator 1, and the radiation characteristics of the magnetic dipole (Hz) can be obtained; when the feeding port 7 is excited, the Under the action of the microstrip feed line 5, the current flows in two opposite directions at the second feed port 7. Because of the existence of the zero-phase-shift transmission line and the complete symmetry of the structure, the currents flowing to both ends are equal in magnitude and opposite. On the first radiator 1, a surface current of equal magnitude and opposite, uniform symmetry is obtained, and the radiation characteristics of the electric dipole (Ex) in the horizontal direction can be obtained.

Among them, since the second radiator 2 needs to be placed in the annular structure of the first radiator 1, its area is limited by the size of the first radiator 1. At this time, the operating frequency of the second radiator 2 is high, and it needs to It is miniaturized to reduce the operating frequency of its TM11 mode, so that it operates in the same frequency band as the first radiator 1 . Specifically, the second radiator 2 in the present invention adopts a microstrip patch antenna based on a Tee-type fractal structure. Fractal structure is an important means of antenna miniaturization. Each segment has the characteristics of the entire structure on a smaller scale. This is the basic property of self-similarity. After a limited number of fractal geometry iterations, the number of fractal repetitions increases. , the lowest resonant frequency of the antenna decreases gradually, and finally works in the same frequency band as the first radiator 1, and can maintain two orthogonal TM11 microstrip antenna operating modes. Referring to FIG. 10 , it is a comparison diagram of the resonance frequencies of the microstrip patch antenna using the Tee-Type fractal structure and the circular microstrip antenna with the same radius without the Tee-Type structure. It can be seen from the figure that the microstrip patch antenna using the Tee-Type structure can effectively reduce the operating frequency of the microstrip patch antenna with the same radius from 2.8GHz to 2.45GHz. This enables the second radiator 2 to work in the same frequency band as the first radiator 1 under the condition of limited area, and then together form a quad-polarized MIMO antenna in the same working frequency band.

Wherein, by combining the first radiator 1 and the second radiator 2, the quad-polarized MIMO antenna with a common point orthogonal, low coupling and compact structure according to the present invention is obtained.

Further, in order to verify the performance of the MIMO system of the proposed quad-polarized antenna, we process and test the quad-polarized antenna proposed in the present invention, and analyze its channel capacity in an actual office environment. The transmitting and receiving antennas tested are all quad-polarized MIMO antennas proposed in the embodiments of the present invention. During the test, the transmitting and receiving antennas are all 1.05 meters high and the distance between the transmitting and receiving antennas is 1.71 meters. The channel capacity C is calculated by the commonly used expression of the channel capacity of the MIMO system, which can be expressed as:

其中‖·‖_F表示Frobenius范数，K表示分析容量的所有参数。通过这种归一化，可以消除计算中路径损耗对总接收信号功率的影响，并且可以很好地反映环境中多径的丰富程度对MIMO系统信道容量的影响。Among them, I represents a 4×4 unit matrix, n _T = 4 is the number of transmit ports, det( ) represents the determinant of the matrix, SNR represents the signal-to-noise ratio, here the signal-to-noise ratio SNR=20dB, and H adopts the commonly used Normalized channel matrix:

where ‖· _‖F represents the Frobenius norm, and K represents all parameters of the analytical capacity. Through this normalization, the influence of path loss on the total received signal power in the calculation can be eliminated, and the influence of the abundance of multipath in the environment on the channel capacity of the MIMO system can be well reflected.

Referring to Figure 11, it is the cumulative distribution function result of the channel capacity (signal-to-noise ratio SNR is 20dB) obtained by the quad-polarized MIMO antenna in the office environment. The channel capacity results of the IID Rayleigh channel, as shown in Figure 11, the quad-polarized MIMO antenna proposed in the present invention can obtain IID much larger than 3×3 and close to 4×4 in the real office propagation environment The channel capacity of the Rayleigh channel.

Figure 2 shows the reflection coefficient curve of the four-polarized MIMO antenna. It can be seen that the -10dB impedance common bandwidth of the antenna is 40MHz (2.41-2.45GHz).

Figure 3 shows the coupling curve of the quad-polarized MIMO antenna. In the common bandwidth of -10dB impedance, the coupling is lower than -15.5dB.

Fig. 4 is the current distribution diagram on the first radiator 1 when the first feed port 6 and the second feed port 7 of the quad-polarized MIMO antenna are excited respectively, wherein Fig. 4a is the first feed of the quad-polarized MIMO antenna When the electrical port 6 is excited, the current distribution diagram on the first radiator 1, Figure 4b is the current distribution diagram on the first radiator 1 when the second feed port 7 of the quad-polarized MIMO antenna is excited, as shown in Figure 4a As shown, the amplitudes of the currents on the first radiator 1 are equal when the first feeding port 6 is excited, and due to the relationship of the phase compensation of the zero-phase-shift transmission line, the directions of the currents are the same, thus forming on the metal ring In order to obtain the ring current of equal amplitude and phase, its radiation characteristics can be equivalent to the magnetic dipole antenna Hz in the vertical direction; as shown in Figure 4b, when the second feeding port 7 is fed, the Under the action of the feed 5, the current flows in two opposite directions at the second feed port 7. Due to the existence of the zero-phase-shift transmission line and the complete symmetry of the structure, the currents flowing to both ends are equal in amplitude and opposite in direction, and their radiation The characteristic can be equivalent to the electric dipole Ex in the horizontal direction.

Fig. 5 is the electric field distribution diagram on the second radiator 2 when the third feed port 8 and the fourth feed port 9 of the quad-polarized MIMO antenna are excited respectively, wherein Fig. 5a is the third feed of the quad-polarized MIMO antenna When the electrical port 8 is excited, the electric field distribution diagram on the second radiator 2, Figure 5b is the electric field distribution diagram on the second radiator 2 when the fourth feed port 9 of the quad-polarized MIMO antenna is excited, as shown in Figure 5a As shown, when the third feeding port 8 is feeding, it can be seen that the electric field is distributed in the z-axis direction, which is symmetric about the x-axis and anti-symmetric about the y-axis; similarly, as shown in Figure 5b, when the fourth feeding When the port 9 is feeding, it can also be seen that the electric field is distributed in the z-axis direction. The difference is that the electric field at this time is symmetric about the y-axis and anti-symmetric about the x-axis. Based on the above analysis, we can draw the conclusion that the second radiator 2 operates in two orthogonal TM11 microstrip antenna modes (Hy, Hx) when ports 8 and 9 are fed separately.

Fig. 6 is the radiation pattern when the first feed port 6 of the quad-polarized MIMO antenna is excited, wherein Fig. 6a is the radiation pattern of the xoy surface, and Fig. 6b is the radiation pattern of the yoz surface. As shown in Fig. 6, port 6 is excited When , the quad-polarized MIMO antenna obtains good horizontally polarized omnidirectional radiation on the xoy plane, and a figure-8 radiation pattern on the yoz plane, which is consistent with the radiation of a magnetic dipole (Hz) placed along the z-axis characteristic.

FIG. 7 is the radiation pattern of the quad-polarized MIMO antenna when the second feed port 7 is excited according to the embodiment of the present invention, wherein FIG. 7a is the radiation pattern of the xoy plane, and FIG. 7b is the radiation pattern of the yoz plane, as shown in FIG. 7 . The xoy plane shows a quasi-"8" radiation pattern, and good omnidirectional radiation is obtained on the yoz plane, the radiation pattern is very close to that of an ideal electric dipole (Ex) placed along the x-axis.

FIG. 8 is a radiation pattern when the third feed port 8 of the quad-polarized MIMO antenna is excited, wherein FIG. 8a is the radiation pattern of the yoz surface, and FIG. 8b is the radiation pattern of the xoz surface.

Fig. 9 is the radiation pattern when the fourth feed port 9 of the quad-polarized MIMO antenna is excited, wherein Fig. 9a is the radiation pattern of the yoz surface, and Fig. 9b is the radiation pattern of the xoz surface. As shown in Fig. 9, in the present invention The third feeding port 8 and the fourth feeding port 9 conform to the radiation characteristics of two orthogonal microstrip modes (Hy, Hx);

Figure 10 is a comparison diagram of the resonant frequency of the second radiator when the Tee-Type fractal structure is used and when the Tee-Type fractal structure is not used. It can be seen that the use of the Tee-Type fractal structure can effectively reduce the frequency of the microstrip patch antenna. working frequency.

Figure 11 is the cumulative distribution result of the channel capacity obtained by the quad-polarized MIMO antenna proposed by the present invention in the real environment of the office (signal-to-noise ratio SNR=20dB), and its independent and identical distribution with 3×3 and 4×4 Channel capacity comparison of Rayleigh channels. As shown in the figure, the quad-polarized MIMO antenna proposed by the present invention can obtain a channel capacity close to the 4×4 IID Rayleigh channel in the real environment, which is much larger than the channel capacity of the 3×3 IID Rayleigh channel. capacity.

Claims (5)

1. A planar compact low-coupling quad-polarized MIMO antenna based on an orthogonal mode, characterized in that it comprises a first radiator (1) and a second radiator (2) based on an orthogonal mode, the first The radiator (1) adopts a ring structure, the second radiator (2) is a microstrip patch antenna based on a Tee-type fractal structure, and the diameter of the second radiator (2) is smaller than that of the first radiator The inner diameter of the ring of the body (1), the second radiator (2) is placed in the annular structure of the first radiator (1); Four polarization modes are obtained by the combination of two different orthogonal mode-based radiators in the planar structure, the radiation modes of the electric dipole Ex and the magnetic dipole Hz are obtained on the first radiator, and the radiation modes of the electric dipole Ex and the magnetic dipole Hz are obtained on the second radiator. The radiator obtains two orthogonal TM11 microstrip antenna operating modes Hx and Hy; Wherein, the second radiator (2) undergoes a limited number of fractal geometric iterations, and the number of fractal repetitions increases, so that the second radiator (2) and the first radiator (1) work in the same frequency band, and can maintain two An orthogonal TM11 microstrip antenna operating mode. 2 . The quad-polarized MIMO antenna according to claim 1 , wherein the first radiator ( 1 ) consists of two concentric loop antennas based on zero-phase-shift transmission lines. 3 . 3. The quad-polarized MIMO antenna according to claim 1, characterized in that: the antenna further comprises an antenna grounding metal plate (3), a dielectric plate (4) and a microstrip feeding structure (5), the antenna The grounded metal plate (3) and the first radiator (1) are placed on the upper surface of the dielectric plate (4), and the second radiator (2) and the microstrip feeding structure (5) are placed on the dielectric plate (4) the lower surface. 4. The quad-polarized MIMO antenna according to claim 1, wherein the antenna further comprises a feeding port, the feeding port comprising a first feeding port (6) and a second feeding port (7) , a third feeding port (8) and a fourth feeding port (9), the first feeding port (6) feeds the inner loop of the first radiator (1) through the lumped port, the second feeding The electrical port (7) feeds the outer ring of the first radiator (1) through the microstrip feeding structure (5), and the third feeding port (8) and the fourth feeding port (9) are respectively connected to the second radiator The x-axis and y-axis position excitation of the body (2). 5. The quad-polarized MIMO antenna according to claim 3, wherein the microstrip feeding structure (5) adopts a T-shaped microstrip line structure.

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