A decoupling structure with tunable multiple frequencies between two antennas based on parasitic elements

Abstract

The present invention discloses a decoupling structure between two antennas based on a parasitic body and capable of tunable multiple frequencies. The decoupling structure is composed of a parasitic body structure and a topological structure. The main parts of the parasitic body structure and the topological structure are the capacitance, inductance and transmission line of the tunable element. In practical applications, the sizes of the chip capacitors and the chip inductors for implementing the structure are relatively small. The parasitic body structure and the topological structure are both placed between the two antennas. There are no excessive requirements for the structure of the antennas, and the influence of external factors on the capacitance and inductance is small. The parasitic body structure and the topological structure are both relatively simple and have certain regularity. The advantages are small size, small requirements on the spatial environment, and the ability to meet the current demand for miniaturization of products. The structure is simple and can be applied to the decoupling between two antennas with a single frequency point, as well as the decoupling between two antennas with dual frequencies or more, and the scalability is strong.

Description

Technical Field

[0001] The present invention relates to a decoupling structure, in particular to a decoupling structure capable of tunable multiple frequencies between two antennas based on a parasitic body. Background Art

[0002] With the full development of 5G technology, the demand for Multiple-Input Multiple-Output (MIMO) systems has become increasingly prominent. The use of MIMO antennas requires consideration of the coupling issues caused by the close proximity between antennas. Therefore, the implementation of decoupling structures is particularly important for the design of compact multi-band, multi-antenna systems. In particular, for mobile terminal devices, due to constraints such as size and the need to meet the requirements of different application frequency bands such as 2G / 3G / 4G, 5G, and Wi-Fi, multi-antenna systems require a good decoupling structure to reduce the coupling effects between antennas across multiple frequency bands. However, traditional multi-band decoupling design methods not only make it difficult to achieve decoupling simultaneously at three or more frequencies, but also often require changes to the decoupling structure to achieve antenna operating frequency band tuning.

[0003] Reference 1 (J. Prakash, R. Vijay and S. Natarajamani, "MIMO antenna for mobile terminals with enhanced isolation in LTE band," 2017 International Conference on Advances in Computing, Communications and Informatics (ICACCI), 2017, pp.) and reference 2 (S. Nandi and A. Mohan, "A Compact Dual-Band MIMO Slot Antenna for WLAN Applications," in IEEE Antennas and Wireless Propagation Letters) disclose the currently more commonly used decoupling schemes of ground branch structure and defective ground structure (DGS), which respectively decouple single frequency points and dual frequency points between antennas. However, both the ground branch structure and the defective ground structure are structural changes to the metal ground. Not only are they large in size and have high requirements for the spatial environment, they are difficult to meet the current demand for miniaturization of products. In addition, they are for specific antennas, and the decoupling between antennas is achieved at specific single or dual frequencies. The design is relatively complex, and the structure cannot be expanded to meet the decoupling requirements of two antennas with multiple frequencies, resulting in poor scalability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a tunable decoupling structure based on a parasitic body that is small in size, has low requirements on the space environment, can meet the current demand for miniaturization of products, has a simple structure, and is highly scalable. It can be used for single-frequency decoupling between two antennas, and can also be used for multi-frequency decoupling between two antennas with dual frequencies or more.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a decoupling structure based on a parasitic body that can tune multiple frequencies between two antennas. The two antennas are arranged in parallel and spaced apart on the left and right sides. The number of frequencies that need to be decoupled between the two antennas is recorded as n, where n is an integer greater than or equal to 1. The decoupling structure includes n parasitic structures and a topological structure based on a resonant circuit. The n parasitic structures are all arranged between the two antennas. The n parasitic structures are spaced apart from each other in a row from left to right, and there is a distance between each two adjacent parasitic structures.

[0006] The antenna on the left is called antenna 1, and the antenna on the right is called antenna 2. The n parasitic structures are numbered from 1 to n from left to right, wherein there is a distance between the first parasitic structure and antenna 1, and there is a distance between the nth parasitic structure and antenna 2. Each of the parasitic structures is composed of a transmission line and a load, one end of the transmission line is connected to one end of the load, and the other end of the load is grounded. The load is selected from one of capacitance and inductance. Among the n parasitic structures, the loads and load parameters of any two parasitic structures can be the same or different. After the loads and load parameters of the n parasitic structures are selected, the real part of the mutual admittance of the two antennas at each frequency point can be close to zero. When the load is a capacitor, the load parameter is the capacitance value, and when the load is an inductor, the load parameter is the inductance value.

[0007] When n is 1, that is, there is only one frequency point that needs to be decoupled between the two antennas, the topological structure includes a load, one end of the load of the topological structure is connected to antenna 1, and the other end of the load of the topological structure is connected to antenna 2, and the load of the topological structure is selected from one of a capacitor and an inductor; if n is an integer greater than or equal to 2, the topological structure includes n-1 LC circuits and a load, each LC circuit is composed of a capacitor and an inductor, and in each LC circuit, one end of the capacitor is connected to one end of the inductor, the other end of the capacitor serves as one end of the LC circuit, and the other end of the inductor serves as the end of the LC circuit. At the other end, one end of the n-1 LC circuits is connected to antenna 1, and the other end of the n-1 LC circuits is connected to antenna 2. One end of the load is connected to antenna 1, and the other end of the load is connected to antenna 2. The load is selected from one of a capacitor and an inductor. In the n-1 LC circuits, the capacitance values ​​of the capacitors in any two LC circuits can be the same or different, and the inductance values ​​of the inductors can be the same or different. After the capacitance values ​​of the capacitors, the inductance values ​​of the inductors, the selection of the loads, and the load parameters in the n-1 LC circuits are selected, the imaginary part of the mutual admittance of the two antennas at each frequency point can be zero. When the load is a capacitor, the load parameter is the capacitance value, and when the load is an inductor, the load parameter is the inductance value.

[0008] The loads in the n parasitic structures are selected as follows:

[0009] (1) When decoupling n frequency points between two antennas, a distribution port needs to be set at the back end of each antenna for excitation. A distribution port is also set at each parasitic structure for excitation. The distribution port corresponding to antenna 1 is called port 1, the distribution port corresponding to antenna 2 is called port 2, the distribution port corresponding to the first parasitic structure is called port 3, the distribution port corresponding to the second parasitic structure is called port 4, and so on. The distribution port corresponding to the nth parasitic structure is called port n+2. At this time, the two antennas and n parasitic structures form an n+2 port network. The relationship between the voltage and current of the n+2 port network is expressed by formula (1):

[0010]

[0011] In formula (1), V1 is the voltage of port 1 in the n+2 port network, V2 is the voltage between ports 2 in the n+2 port network, V3 is the voltage between ports 3 in the n+2 port network, and so on. n+2 is the voltage of the n+2 port in the n+2 port network,

[0012] I1 is the current flowing through port 1 of the n+2 port network, I2 is the current flowing through port 2 of the n+2 port network, I3 is the current flowing through port 3 of the n+2 port network, and so on. n+2 is the current flowing through the n+2 port of the n+2 port network; is the Z parameter matrix of the n+2 port network. When p=q, Z pq Indicates the input impedance of the p-port in the n+2-port network. When p≠q, Z pq represents the mutual impedance from port q to port p in the n+2-port network, where p = 1, 2, ..., n+2 and q = 1, 2, ..., n+2;

[0013] (2) For the n parasitic structures, there are n loads, which are either capacitors or inductors. At any frequency point, the impedances of the n loads are recorded as ZL1, ZL2, ..., ZL n , i=1,2,…,n,ZL i is the impedance of the load of the i-th parasitic structure. If the load is a capacitor, then C i is the capacitance value of the load. If the load is inductive, then ZL i =j×2πfL i , L i is the inductance value of the load, where f is the frequency corresponding to any frequency point, and j represents an imaginary number; at this time, V3, V4, ..., V at any frequency point can be obtained. n+2 The impedance ZL1, ZL2, ..., ZL of each load in each parasitic structuren The relationship between them can be expressed using formula (2):

[0014]

[0015] (3) According to formula (2), we can get formula (3):

[0016]

[0017] Writing formula (3) into matrix form, we get formula (4):

[0018]

[0019] (4) Order Then we can get formula (5) through formula (4):

[0020]

[0021] (6) Order From this we can get formula (6):

[0022]

[0023] According to formula (1), formula (7) can be obtained:

[0024]

[0025] Substituting formula (6) into (7) yields formula (8):

[0026]

[0027] At this point, after passing through n parasitic structures, the n+2-port network consisting of two antennas and n parasitic structures becomes a two-port network consisting of only two antennas. Antenna 1 corresponds to port 1, and antenna 2 corresponds to port 2. Equation (8) is the relationship between the voltage and current of the two-port network. Writing Equation (8) in matrix form yields Equation (9):

[0028]

[0029] In formula (9), is the Z parameter matrix of the two-port network, Z 11 ' represents the input impedance of port 1 in a two-port network, Z 11 '=Z 11 +[Z 13 Z 14 … Z 1(n+2) ]×M1,Z 22 ' represents the input impedance of the 2-port in a two-port network, Z 22 '=Z22 +[Z 23 Z 24 … Z 2(n+2) ]×M2,Z 12 ' represents the mutual impedance from port 2 to port 1 in a two-port network, Z 12 '=Z 12 +[Z 13 Z 14 … Z 1(n+2) ]×M2,Z 21 ' represents the mutual impedance from port 1 to port 2 in a two-port network, Z 21 '=Z 21 +[Z 23 Z 24 … Z 2(n+2) ]×M1;

[0030] (6) The frequency corresponding to the bth frequency point between the two antennas is recorded as f b , b=1,2,…,n, the reactance of the load in the ath parasitic structure at the first frequency between the two antennas is recorded as XL a (f1), the impedance of the load in the ath parasitic structure at the first frequency is recorded as ZL a (f1), a=1,2,…,n,ZL a (f1) = jXL a (f1), namely ZL a (f1) is XL a The imaginary part of (f1) is recorded as ZL, and the impedance of the load in the a-th parasitic structure at the b-th frequency point is recorded as ZL a (f b ), the reactance of the load in the a-th parasitic structure at the b-th frequency point is recorded as XL a (f b ), if the load in the a-th parasitic structure at the b-th frequency point is a capacitor, then the reactance of the load is at this time, If the load in the ath parasitic structure at the bth frequency point is inductive, the reactance of the load is at this time

[0031] (7) According to formula (1), two antennas and n parasitic structures form an n+2 port network. At the bth frequency point, the relationship between the voltage and current of the n+2 port network is expressed in matrix form as follows:

[0032]

[0033] In formula (10), V1(f b) is the voltage of port 1 in the n+2 port network at the bth frequency point, V2(f b ) is the voltage of port 2 in the n+2-port network at the bth frequency point, and so on, V n+2 (f b ) is the voltage of the n+2 port in the n+2 port network at the bth frequency point; I1(f b ) is the current flowing through port 1 of the n+2 port network at the bth frequency point, I2(f b ) is the current flowing through port 2 of the n+2-port network at the bth frequency point, and so on, I n+2 (f b ) is the current flowing through the n+2 port of the n+2 port network at the bth frequency point; is the Z parameter matrix of the n+2 port network at the bth frequency point. When w=v, Z wv (f b ) represents the input impedance of the w port of the n+2 port network at the bth frequency point. When w≠v, Z wv (f b ) represents the mutual impedance from port v to port w in the n+2-port network at the bth frequency, where w = 1, 2, ..., n+2, v = 1, 2, ..., n+2;

[0034] (8) The impedance ZL of the load in the a-th parasitic structure at the b-th frequency point determined in step (6) is a (f b ) corresponds to the impedance ZL in equation (2) a , we get formula (11):

[0035]

[0036] (9) According to (11), we can get formula (12):

[0037]

[0038] Writing formula (12) into matrix form gives formula (13):

[0039]

[0040] (10) Order According to formula (13), we can get formula (14):

[0041]

[0042] (11) Order From this we can get formula (15):

[0043]

[0044] According to formula (10), we can get:

[0045]

[0046] Substituting formula (15) into formula (16) yields formula (17):

[0047]

[0048] At this time, the relationship between the voltage and current of the two-port network is expressed in matrix form as follows:

[0049]

[0050] Among them, Z 11 '(f b )=Z 11 (f b )+[Z 13 (f b ) Z 14 (f b ) … Z 1(n+2) (f b )]×M1(f b ), Z 11 '(f b ) represents the input impedance of port 1 of the two-port network at the bth frequency point; Z 22 '(f b )=Z 22 (f b )+[Z 23 (f b ) Z 24 (f b ) …Z 2(n+2) (f b )]×M2(f b ), Z 22 '(f b ) represents the input impedance of the 2-port of the two-port network at the b-th frequency point;

[0051] Z 12 '(f b )=Z 12 (f b )+[Z 13 (f b ) Z 14 (f b ) … Z 1(n+2) (f b )]×M2(f b ), Z 12 '(f b) represents the mutual impedance from port 2 to port 1 of the two-port network at the bth frequency point; Z 21 '(f b )=Z 21 (f b )+[Z 23 (f b ) Z 24 (f b ) …Z 2(n+2) (f b )]×M1(f b ), Z 21 '(f b ) represents the mutual impedance from port 1 to port 2 of the two-port network at the bth frequency point; the mutual admittance from port 1 to port 2 of the two-port network at the bth frequency point is denoted as Y 12 '(f b ), Y can be obtained from the parameter conversion formula of the two-port network 12 '(f b ) is expressed as:

[0052]

[0053] (12) Set the intermediate parameter D(f b ),make Among them, Re{Y 12 '(f b )} is Y 12 '(f b ), Im{Y 12 '(f b )} is Y 12 '(f b ) of the imaginary part; give the reactance XL of the load in the a-th parasitic structure at the first frequency point a (f1) randomly assigns a value within the range (a1, a2), where the value range of a1 is (-1×10 6 ,-1×10 4 ), the value range of a2 is (1×10 -4 ,1×10 8 ), if the reactance of the load in the a-th parasitic structure is positive at this time, then the load in the parasitic structure is determined to be inductor, and then the reactance of the load in the a-th parasitic structure at the b-th frequency point is obtained as If the reactance of the load in the a-th parasitic structure is negative at this time, the load in the parasitic structure is determined to be a capacitor, and then the reactance of the load in the a-th parasitic structure at the b-th frequency point is obtained as At this time, go through step (6)-

[0054] (11) Get Y 12'(fb), take Y 12 The real and imaginary parts of '(fb) are used to obtain the intermediate parameter D(f b ), then we get D(f1) to D(f n ), D(f b ) corresponds to the bth frequency point, construct a set D for storing data, and convert the currently obtained D(f1) to D(f n ) is stored as a data of set D in set D, and then the reactance XL of the load in the a-th parasitic structure at the first frequency point is given again. a (f1) Randomly assign a value within the assignment range (a1, a2), and store a data into the set D again according to the same method as above, until Q data are stored in the set D, where Q is the number of optimizations and is an integer greater than or equal to 500; at this time, the data with the smallest value in the set D is taken and recorded as minD. The reactance of the loads in the n parasitic structures at the frequency corresponding to minD is assigned as the reactance value corresponding to each load finally selected;

[0055] (13) Determine the number of loads with reactance greater than 0 among the n parasitic structures obtained in step (12), and record this number as m. Then, among the n parasitic structures, the number of loads with inductance is m, and the number of loads with capacitance is nm. Renumber the m parasitic structures with inductance in the order of their original numbers from small to large from 1 to m. Then, the inductance value of the load in the xth parasitic structure among the m parasitic structures with inductance is XL x The reactance of the load in the xth parasitic structure among the m parasitic structures with inductive loads, x = 1, 2, ..., m, the nm parasitic structures with capacitive loads are renumbered from 1 to nm in ascending order, and the capacitance value of the load in the yth parasitic structure among the nm parasitic structures with capacitive loads is XL y is the reactance value of the capacitor in the y-th parasitic structure among the nm parasitic structures whose loads are capacitors, where y = 1, 2, …, nm.

[0056] The parameter values ​​of the capacitor and inductor in the topology are selected according to the following method:

[0057] (1) When n is 1, a single frequency point is decoupled and a capacitor or inductor is selected as the load of the topology structure. The susceptance of the load is Y = Im{Y 12 '(f1)}, after the topological structure, the imaginary part of the mutual admittance between the two antennas is Im{Y 12 " " " 1}=Im{Y 12'(f1)}-Y=0, the imaginary part is zero. If the susceptance value of the load is greater than zero, it is a capacitor, and its capacitance value is If the susceptance of the load is less than zero, it is an inductor, and its inductance is

[0058] (2) When n is an integer greater than or equal to 2, n-1 LC circuits and a load of capacitance or inductance are required. The capacitance C in the βth LC circuit of the topological structure at the first frequency point between the two antennas is β The susceptance of (f1) is denoted by XC β (f1), the capacitance of this capacitor is C β , β=1,2,…,n-1; the inductance L in the βth LC circuit of the topological structure at the first frequency point β The electrical susceptance of (f1) is XL β (f1), the inductance of the inductor is L β The capacitance of the βth LC circuit at the bth frequency is XC β (f b ), The inductance of the βth LC circuit at the bth frequency is denoted by XL β (f b ), If the other load is a capacitor, the susceptance of the capacitor C'(f1) at the first frequency point is recorded as XC'(f1), the capacitance value of the capacitor is C', and the susceptance of the capacitor at the bth frequency point is recorded as XC'(f b ), At this time, formula (20) is established:

[0059]

[0060] If the other load is an inductor, the susceptance of the inductor L'(f1) at the first frequency point is recorded as XL'(f1), and the inductance value of the inductor is L' at the bth frequency point f b The susceptance of the inductor is denoted as XL'(f b ), At this time, formula (21) is established:

[0061]

[0062] Equations (20) and (21) are both n-dimensional equations with n-1 capacitors, n-1 inductors, and a load susceptance as unknowns. Multiple solutions are obtained by calculating them respectively. Select the solution that makes XC β (f1)>0,XC'(f1)>0,XL βThe real number solution that satisfies both (f1)<0 and XL'(f1)<0 is used as the value of the unknown variable, and then the capacitance value of the capacitor in the βth LC circuit is obtained. Inductance value of the inductor When the load is a capacitor, the capacitance value of the load When the load is inductive, the inductance of the load

[0063] Compared with the prior art, the advantage of the present invention is that a decoupling structure is formed by a parasitic structure and a topological structure. The main parts of the parasitic structure and the topological structure are capacitors, inductors and transmission lines. In practical applications, the sizes of the chip capacitors and chip inductors that implement the structure are relatively small, so the volume of the entire structure is small, which can meet the current demand for miniaturization of products. In addition, since the parasitic structure and the topological structure are both placed between the two antennas, there are no excessive requirements for the structure of the antenna and the external factors have little effect on the capacitance and inductance, so the demand for the space environment is small. In addition, the parasitic structure is a transmission line connected to a load, and the other end of the load is grounded. The load can be a capacitor or an inductor, while the topological structure is mainly composed of a package. It is composed of an LC circuit including capacitors and inductors. The parasitic structure and the topological structure are relatively simple and have certain regularities. Therefore, through the two structures of the parasitic structure and the topological structure, the general rules can be used to extend the decoupling frequency from the decoupling between two antennas with a single frequency point to the decoupling between two antennas with dual frequencies or even more than three frequencies. For the decoupling of any number of frequencies, the decoupling structure adopts a parasitic structure with the same number of frequencies, and the topological structure is divided into odd-numbered frequencies and even-numbered frequencies, corresponding to their own structures. Therefore, the present invention can be applied to the decoupling between two antennas with a single frequency point, as well as the decoupling between two antennas with dual frequencies or more, and has strong scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a circuit schematic diagram of a decoupling structure with tunable single frequency between two antennas based on a parasitic body according to the present invention;

[0065] FIG2( a ) is a circuit schematic diagram of a topology of a parasitic-based decoupling structure with tunable multi-frequency points between two antennas according to the present invention, in which the load is implemented using a capacitor;

[0066] FIG2( b ) is a circuit schematic diagram of a topology structure of a parasitic-based decoupling structure with tunable multi-frequency points between two antennas according to the present invention, in which the load is implemented by an inductor;

[0067] Figure 3 This is a circuit schematic diagram of a parasitic-based decoupling structure between two antennas capable of tunable multiple frequencies when the decoupling frequency is 2;

[0068] Figure 4 This is a circuit schematic diagram of a parasitic-based decoupling structure between two antennas capable of tunable multiple frequencies when the decoupling frequency is 3;

[0069] FIG5(a) shows the S curves of the two antennas at frequencies of 2.8 GHz and 5.7 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 11 Schematic diagram;

[0070] FIG5(b) shows the S curves of the two antennas at frequencies of 2.8 GHz and 5.7 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 12 Schematic diagram;

[0071] FIG6(a) shows the S curves of the two antennas at frequencies of 2.5 GHz and 5.4 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 11 Schematic diagram;

[0072] FIG6( b ) shows the S curves of the two antennas at frequencies of 2.5 GHz and 5.4 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 12 Schematic diagram;

[0073] FIG7(a) shows the S curves of the two antennas at frequencies of 3.0 GHz, 4.7 GHz, and 5.5 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 11 Schematic diagram;

[0074] FIG7( b ) shows the S curves of the two antennas at frequencies of 3.0 GHz, 4.7 GHz, and 5.5 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 12 Schematic diagram;

[0075] FIG8(a) shows the S curves of the two antennas at frequencies of 2.4 GHz, 4.8 GHz, and 5.9 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 11 Schematic diagram;

[0076] FIG8( b ) shows the S curves of the two antennas at frequencies of 2.4 GHz, 4.8 GHz, and 5.9 GHz after decoupling the two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between the two antennas of the present invention. 12 Schematic diagram. DETAILED DESCRIPTION

[0077] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0078] Embodiment: A decoupling structure based on a parasitic body with tunable multiple frequency points between two antennas. The two antennas are arranged in parallel and spaced apart on the left and right sides. The number of frequency points that need to be decoupled between the two antennas is recorded as n, where n is an integer greater than or equal to 1. The decoupling structure includes n parasitic structures and a topological structure based on a resonant circuit. The n parasitic structures are all arranged between the two antennas. The n parasitic structures are spaced apart from each other in a row from left to right, and there is a distance between each two adjacent parasitic structures. The antenna on the left is called antenna 1, and the antenna on the right is called antenna 2. The n parasitic structures are numbered in sequence from 1 to n from left to right, where the first parasitic structure is numbered. There is a distance between the parasitic structure and antenna 1, and there is a distance between the nth parasitic structure and antenna 2. Each parasitic structure is composed of a transmission line and a load. One end of the transmission line is connected to one end of the load, and the other end of the load is grounded. The load is selected from one of capacitance and inductance. Among the n parasitic structures, the loads and load parameters in any two parasitic structures can be the same or different. After the loads and load parameters in the n parasitic structures are selected, the real part of the mutual admittance of the two antennas at each frequency point can be close to zero. When the load is a capacitor, the load parameter is the capacitance value, and when the load is an inductor, the load parameter is the inductance value; Figure 1As shown in FIG2( a ), when n is 1, that is, the number of frequency points that need to be decoupled between the two antennas is only one, the topological structure includes a load, one end of the load of the topological structure is connected to antenna 1, and the other end of the load of the topological structure is connected to antenna 2, and the load of the topological structure selects one from the capacitor and the inductor; as shown in FIG2( a ) and FIG2( b ), when n is an integer greater than or equal to 2, the topological structure includes n-1 LC circuits and a load, each LC circuit is composed of a capacitor and an inductor, and in each LC circuit, one end of the capacitor is connected to one end of the inductor, the other end of the capacitor serves as one end of the LC circuit, and the other end of the inductor serves as the other end of the LC circuit. -1 LC circuits are connected to antenna 1 at one end, and the other ends of the n-1 LC circuits are connected to antenna 2. One end of the load is connected to antenna 1, and the other end of the load is connected to antenna 2. The load is selected from one of a capacitor and an inductor. In the n-1 LC circuits, the capacitance values ​​of the capacitors and the inductance values ​​of the inductors of any two LC circuits can be the same or different. In the topological structure, the capacitance values ​​of the capacitors, the inductance values ​​of the inductors, the selection of the loads, and the load parameters in the n-1 LC circuits can make the imaginary part of the mutual admittance of the two antennas at each frequency point zero. When the load is a capacitor, the load parameter is the capacitance value, and when the load is an inductor, the load parameter is the inductance value.

[0079] In this embodiment, the loads in the n parasitic structures are selected according to the following method:

[0080] (1) When decoupling n frequency points between two antennas, a distribution port needs to be set at the back end of each antenna for excitation. A distribution port is also set at each parasitic structure for excitation. The distribution port corresponding to antenna 1 is called port 1, the distribution port corresponding to antenna 2 is called port 2, the distribution port corresponding to the first parasitic structure is called port 3, the distribution port corresponding to the second parasitic structure is called port 4, and so on. The distribution port corresponding to the nth parasitic structure is called port n+2. At this time, the two antennas and n parasitic structures form an n+2 port network. The relationship between the voltage and current of the n+2 port network is expressed by formula (1):

[0081]

[0082] In formula (1), V1 is the voltage of port 1 in the n+2 port network, V2 is the voltage between ports 2 in the n+2 port network, V3 is the voltage between ports 3 in the n+2 port network, and so on. n+2 is the voltage of port n+2 in the n+2-port network, I1 is the current flowing through port 1 in the n+2-port network, I2 is the current flowing through port 2 in the n+2-port network, I3 is the current flowing through port 3 in the n+2-port network, and so on. n+2is the current flowing through the n+2 port of the n+2 port network;

[0083] is the Z parameter matrix of the n+2 port network. When p=q, Z pq Indicates the input impedance of the p-port in the n+2-port network. When p≠q, Z pq represents the mutual impedance from port q to port p in the n+2-port network, where p = 1, 2, ..., n+2 and q = 1, 2, ..., n+2;

[0084] (2) For the n parasitic structures, there are n loads, which are either capacitors or inductors. At any frequency point, the impedances of the n loads are recorded as ZL1, ZL2, ..., ZL n , i=1,2,…,n,ZL i is the impedance of the load of the i-th parasitic structure. If the load is a capacitor, then C i is the capacitance value of the load. If the load is inductive, then ZL i =j×2πfL i , L i is the inductance value of the load, where f is the frequency corresponding to any frequency point, and j represents an imaginary number; at this time, V3, V4, ..., V at any frequency point can be obtained. n+2 The impedance ZL1, ZL2, ..., ZL of each load in each parasitic structure n The relationship between them can be expressed using formula (2):

[0085]

[0086] (3) According to formula (2), we can get formula (3):

[0087]

[0088] Writing formula (3) into matrix form, we get formula (4):

[0089]

[0090] (4) Order Then we can get formula (5) through formula (4):

[0091]

[0092] (6) Order From this we can get formula (6):

[0093]

[0094] According to formula (1), formula (7) can be obtained:

[0095]

[0096] Substituting formula (6) into (7) yields formula (8):

[0097]

[0098] At this point, after passing through n parasitic structures, the n+2-port network consisting of two antennas and n parasitic structures becomes a two-port network consisting of only two antennas. Antenna 1 corresponds to port 1, and antenna 2 corresponds to port 2. Equation (8) is the relationship between the voltage and current of the two-port network. Writing Equation (8) in matrix form yields Equation (9):

[0099]

[0100] In formula (9), is the Z parameter matrix of the two-port network, Z 11 ' represents the input impedance of port 1 in a two-port network, Z 11 '=Z 11 +[Z 13 Z 14 … Z 1(n+2) ]×M1,Z 22 ' represents the input impedance of the 2-port in a two-port network, Z 22 '=Z 22 +[Z 23 Z 24 … Z 2(n+2) ]×M2,Z 12 ' represents the mutual impedance from port 2 to port 1 in a two-port network, Z 12 '=Z 12 +[Z 13 Z 14 … Z 1(n+2) ]×M2,Z 21 ' represents the mutual impedance from port 1 to port 2 in a two-port network, Z 21 '=Z 21 +[Z 23 Z 24 … Z 2(n+2) ]×M1;

[0101] (6) The frequency corresponding to the bth frequency point between the two antennas is recorded as f b , b=1,2,…,n, the reactance of the load in the ath parasitic structure at the first frequency between the two antennas is recorded as XL a (f1), the impedance of the load in the ath parasitic structure at the first frequency is recorded as ZL a(f1), a=1,2,…,n,ZL a (f1) = jXL a (f1), namely ZL a (f1) is XL a The imaginary part of (f1) is recorded as ZL, and the impedance of the load in the a-th parasitic structure at the b-th frequency point is recorded as ZL a (f b ), the reactance of the load in the a-th parasitic structure at the b-th frequency point is recorded as XL a (f b ), if the load in the a-th parasitic structure at the b-th frequency point is a capacitor, then the reactance of the load is at this time, If the load in the ath parasitic structure at the bth frequency point is inductive, the reactance of the load is at this time

[0102] (7) According to formula (1), two antennas and n parasitic structures form an n+2 port network. At the bth frequency point, the relationship between the voltage and current of the n+2 port network is expressed in matrix form as follows:

[0103]

[0104] In formula (10), V1(f b ) is the voltage of port 1 in the n+2 port network at the bth frequency point, V2(f b ) is the voltage of port 2 in the n+2-port network at the bth frequency point, and so on, V n+2 (f b ) is the voltage of the n+2 port in the n+2 port network at the bth frequency point; I1(f b ) is the current flowing through port 1 of the n+2 port network at the bth frequency point, I2(f b ) is the current flowing through port 2 of the n+2-port network at the bth frequency point, and so on, I n+2 (f b ) is the current flowing through the n+2 port of the n+2 port network at the bth frequency point; is the Z parameter matrix of the n+2 port network at the bth frequency point. When w=v, Z wv (f b ) represents the input impedance of the w port of the n+2 port network at the bth frequency point. When w≠v, Z wv (f b ) represents the mutual impedance from port v to port w in the n+2-port network at the bth frequency, where w = 1, 2, ..., n+2, v = 1, 2, ..., n+2;

[0105] (8) The impedance ZL of the load in the a-th parasitic structure at the b-th frequency point determined in step (6) is a (f b ) corresponds to the impedance ZL in equation (2) a , we get formula (11):

[0106]

[0107] (9) According to (11), we can get formula (12):

[0108]

[0109] Writing formula (12) into matrix form gives formula (13):

[0110]

[0111] (10) Order According to formula (13), we can get formula (14):

[0112]

[0113] (11) Order From this we can get formula (15):

[0114]

[0115] According to formula (10), we can get:

[0116]

[0117] Substituting formula (15) into formula (16) yields formula (17):

[0118]

[0119] At this time, the relationship between the voltage and current of the two-port network is expressed in matrix form as follows:

[0120]

[0121] Among them, Z 11 '(f b )=Z 11 (f b )+[Z 13 (f b ) Z 14 (f b ) … Z 1(n+2) (f b )]×M1(f b ), Z 11 '(fb ) represents the input impedance of port 1 of the two-port network at the bth frequency point; Z 22 '(f b )=Z 22 (f b )+[Z 23 (f b ) Z 24 (f b ) …Z 2(n+2) (f b )]×M2(f b ), Z 22 '(f b ) represents the input impedance of the 2-port of the two-port network at the b-th frequency point;

[0122] Z 12 '(f b )=Z 12 (f b )+[Z 13 (f b ) Z 14 (f b ) … Z 1(n+2) (f b )]×M2(f b ), Z 12 '(f b ) represents the mutual impedance from port 2 to port 1 of the two-port network at the bth frequency point; Z 21 '(f b )=Z 21 (f b )+[Z 23 (f b ) Z 24 (f b ) …Z 2(n+2) (f b )]×M1(f b ), Z 21 '(f b ) represents the mutual impedance from port 1 to port 2 of the two-port network at the bth frequency point; the mutual admittance from port 1 to port 2 of the two-port network at the bth frequency point is denoted as Y 12 '(f b ), Y can be obtained from the parameter conversion formula of the two-port network 12 '(f b ) is expressed as:

[0123]

[0124] (12) Set the intermediate parameter D(f b ),make Among them, Re{Y12 '(f b )} is Y 12 '(f b ), Im{Y 12 '(f b )} is Y 12 '(f b ) of the imaginary part; give the reactance XL of the load in the a-th parasitic structure at the first frequency point a (f1) randomly assigns a value within the range (a1, a2), where the value range of a1 is (-1×10 6 ,-1×10 4 ), the value range of a2 is (1×10 -4 ,1×10 8 ), if the reactance of the load in the a-th parasitic structure is positive at this time, then the load in the parasitic structure is determined to be inductor, and then the reactance of the load in the a-th parasitic structure at the b-th frequency point is obtained as If the reactance of the load in the a-th parasitic structure is negative at this time, the load in the parasitic structure is determined to be a capacitor, and then the reactance of the load in the a-th parasitic structure at the b-th frequency point is obtained as Then, we can get Y by following steps (6)-(11) 12 '(f b ), take Y 12 '(f b ) to obtain the intermediate parameter D(f b ), then we get D(f1) to D(f n ), D(f b ) corresponds to the bth frequency point, construct a set D for storing data, and convert the currently obtained D(f1) to D(f n ) is stored as a data of set D in set D, and then the reactance XL of the load in the a-th parasitic structure at the first frequency point is given again. a (f1) Randomly assign a value within the assignment range (a1, a2), and store a data into the set D again according to the same method as above, until Q data are stored in the set D, where Q is the number of optimizations and is an integer greater than or equal to 500; at this time, the data with the smallest value in the set D is taken and recorded as minD. The reactance of the loads in the n parasitic structures at the frequency corresponding to minD is assigned as the reactance value corresponding to each load finally selected;

[0125] (13) Determine the number of loads with reactance greater than 0 among the n parasitic structures obtained in step (12), and record this number as m. Then, among the n parasitic structures, the number of loads with inductance is m, and the number of loads with capacitance is nm. Renumber the m parasitic structures with inductance in the order of their original numbers from small to large from 1 to m. Then, the inductance value of the load in the xth parasitic structure among the m parasitic structures with inductance is XL x The reactance of the load in the xth parasitic structure among the m parasitic structures with inductive loads, x = 1, 2, ..., m, the nm parasitic structures with capacitive loads are renumbered from 1 to nm in ascending order, and the capacitance value of the load in the yth parasitic structure among the nm parasitic structures with capacitive loads is XL y is the reactance value of the capacitor in the y-th parasitic structure among the nm parasitic structures whose loads are capacitors, where y = 1, 2, …, nm.

[0126] In this embodiment, the parameter values ​​of the capacitor and inductor in the topology structure are selected according to the following method:

[0127] (1) When n is 1, a single frequency point is decoupled and a capacitor or inductor is selected as the load of the topology structure. The susceptance of the load is Y = Im{Y 12 '(f1)}, after the topological structure, the imaginary part of the mutual admittance between the two antennas is Im{Y 12 " " " 1}=Im{Y 12 '(f1)}-Y=0, the imaginary part is zero. If the susceptance value of the load is greater than zero, it is a capacitor, and its capacitance value is If the susceptance of the load is less than zero, it is an inductor, and its inductance is

[0128] (2) When n is an integer greater than or equal to 2, n-1 LC circuits and a load of capacitance or inductance are required. The capacitance C in the βth LC circuit of the topological structure at the first frequency point between the two antennas is β The susceptance of (f1) is denoted by XC β (f1), the capacitance of this capacitor is C β , β=1,2,…,n-1; the inductance L in the βth LC circuit of the topological structure at the first frequency point β The electrical susceptance of (f1) is XL β (f1), the inductance of the inductor is L β The capacitance of the βth LC circuit at the bth frequency is XC β (f b ), The inductance of the βth LC circuit at the bth frequency is denoted by XL β (f b ), If the other load is a capacitor, the susceptance of the capacitor C'(f1) at the first frequency point is recorded as XC'(f1), the capacitance value of the capacitor is C', and the susceptance of the capacitor at the bth frequency point is recorded as XC'(f b ), At this time, formula (20) is established:

[0129]

[0130] If the other load is an inductor, the susceptance of the inductor L'(f1) at the first frequency point is recorded as XL'(f1), and the inductance value of the inductor is L' at the bth frequency point f b The susceptance of the inductor is denoted as XL'(f b ), At this time, formula (21) is established:

[0131]

[0132] Equations (20) and (21) are both n-dimensional equations with n-1 capacitors, n-1 inductors, and a load susceptance as unknowns. Multiple solutions are obtained by calculating them respectively. Select the solution that makes XC β (f1)>0,XC'(f1)>0,XL β The real number solution that satisfies both (f1)<0 and XL'(f1)<0 is used as the value of the unknown variable, and then the capacitance value of the capacitor in the βth LC circuit is obtained. Inductance value of the inductor When the load is a capacitor, the capacitance value of the load When the load is inductive, the inductance of the load

[0133] In order to verify the superiority of the parasitic-based decoupling structure between two antennas capable of tunable multiple frequencies, the following method is used for verification.

[0134] The present invention uses a decoupling structure based on a parasitic body with tunable multi-frequency points between two antennas to decouple two antennas with two decoupling frequency points. The circuit principle diagram is shown in FIG. Figure 3 Antenna 1 and antenna 2 are compact antennas. Since the distance between the two antennas is close, there will be a coupling effect. The present invention decouples the two antennas at two frequency points f1 and f2. The present invention uses a parasitic-based decoupling structure with tunable multiple frequencies between two antennas to decouple two antennas with three decoupling frequencies. The circuit schematic is shown in FIG. Figure 4Antenna 1 and antenna 2 are compact antennas. Since the distance between the two antennas is close, there will be a coupling effect. The present invention decouples the two antennas at three frequencies f1, f2 and f3. The isolation between the two antennas is the transmission coefficient S 12 The greater the isolation, the smaller the coupling effect between the two antennas.

[0135] Figure 3 In the A plane, the two antennas and the transmission lines in the two parasitic structures form a four-port network. At this time, S is selected for the four-port network. A 11 (f1) and S A 11 (f2) is the reflection coefficient, S A 12 (f1) and S A 12 (f2) is used as the transmission coefficient. At the B plane, the two antenna pairs form a two-port network after passing through the two parasitic structures. At this time, S is selected for the two-port network. B 11 (f1) and S B 11 (f2) is the reflection coefficient, S B 12 (f1) and S B 12 (f2) is the transmission coefficient, Y B 12 (f1) and Y B 12 (f2) as the mutual admittance. The loads in the two parasitic structures make the Re{Y B 12} are close to zero. At the C plane, select S C 11 (f1) and S C 11 (f2) is the reflection coefficient, S C 12 (f1) and S C 12 (f2) is the transmission coefficient, Y C 12 (f1) and Y C 12 (f2) as mutual admittance, the topology makes Im{Y C 12} are all zero. As a result, the mutual admittance between antenna 1 and antenna 2 at high and low frequencies is close to zero, completing the decoupling. The above is the overall structure of the decoupling method of this invention. After the decoupling is completed, matching circuits are set at port 1 and port 2 for matching. At the D plane, S D 11 (f1) and S D 11 (f2) is the reflection coefficient, S D 12 (f1) and S D 12 (f2) is used as the transmission coefficient, and the matching circuit is selected so that the reflection coefficient at high and low frequencies meets the requirement of -10dB.

[0136] Figure 4 In the A plane, the two antennas and the transmission lines in the three parasitic structures form a five-port network. At this time, S is selected for the five-port network. A 11 (f1), S A 11 (f2) and S A 11 (f3) is the reflection coefficient, S A 12 (f1), S A 12 (f2) and S A 12 (f3) is used as the transmission coefficient. At the B plane, the two antennas form a two-port network after passing through three parasitic structures. At this time, S is selected for the two-port network. B 11 (f1), S B 11 (f2) and S B 11 (f3) is the reflection coefficient, S B 12 (f1), S B 12 (f2) and S B 12 (f3) is the transmission coefficient, Y B 12 (f1), Y B 12 (f2) and Y B 12 (f3) is the mutual admittance. The three parasitic structures make Re{Y B 12} are close to zero. At the C plane, select S C 11 (f1), SC 11 (f2) and S C 11 (f3) is the reflection coefficient, S C 12 (f1), S C 12 (f2) and S C 12 (f3) is the transmission coefficient, Y C 12 (f1), Y C 12 (f2) and Y C 12 (f3) as mutual admittance. The topology makes Im{Y C 12} are all zero. Thus, decoupling is achieved at three frequency points. Finally, each port is matched through the matching circuit. At the D plane, S D 11 (f1), S D 11 (f2) and S D 11 (f3) is the reflection coefficient, S D 12 (f1), S D 12 (f2) and S D 12 (f3) is used as the transmission coefficient.

[0137] Decoupling between two antennas primarily requires high isolation, which in turn requires that the mutual admittance between the two antennas be zero or close to zero. Mutual admittance is divided into real and imaginary parts. The parasitic structure of the present invention minimizes the real part of the mutual admittance to zero, while the topological structure minimizes the imaginary part of the mutual admittance to zero.

[0138] by Figure 3 Taking the topological structure of the two frequency points decoupling as an example, according to the above-mentioned parasitic structure, the real part of the mutual admittance between the two antennas at the high and low frequency points is close to zero. At this time, the imaginary parts of the mutual admittance at the high and low frequencies are Im{Y B 12 (f1)} and Im{Y B 12 (f2)}. Assuming that the topology is an LC circuit formed by a capacitor and an inductor in series and a load in parallel, if the load is an inductor, the susceptance of the capacitor in the LC circuit at low frequency is YL1=2πf1C1, and the susceptance of the inductor in the LC circuit is The susceptance of the load is At this point you can get:

[0139]

[0140] This is a three-dimensional two-dimensional equation system, in which the capacitance and inductance are variables. According to the equation system, YL1 and YL2 are replaced by f1, f2, Im{Y B 12 (f1)}、Im{Y B 12 (f2)} and YL3 expression can be obtained:

[0141]

[0142] It is necessary to satisfy YL1>0, YL2<0, and YL3<0. Therefore, the susceptance values ​​of the other two capacitors and inductor can be obtained by determining the range of YL3. B 12 (f1)} and Im{Y B 12 There are four cases where the positive or negative value of (f2)} can be analyzed:

[0143] ①

[0144] ②

[0145] ③

[0146] ④Im{Y B 12 (f1)}<0,Im{Y B 12 (f2) < 0

[0147]

[0148] From the above analysis, we can get the range of YL3 in four cases. As long as the value of YL3 is selected within the given range, the values ​​of YL1 and YL2 can be determined, thus achieving Im{Y C 12 (f1)}=0 and Im{Y C 12 Theoretical decoupling effect of (f2)}=0.

[0149] However, in some cases, the range of YL3 is an empty set. In this case, the parallel inductor can be replaced with a capacitor. At this time, the susceptance value of the capacitor of the LC circuit at low frequency is YL1=2πf1C1>0, and the susceptance value of the inductor of the LC circuit is The load susceptance is YL3 = 2πf1C2 > 0. Consistent with the above analysis, the following YL3 ranges are obtained for the four cases:

[0150] ①

[0151] ②

[0152] ③ Im{Y B 12 (f1)}<0,Im{Y B 12 (f2) < 0

[0153]

[0154] ④ Im{Y B 12 (f1)}>0,Im{Y B 12 (f2)>0

[0155]

[0156] Therefore, the structure of connecting a capacitor in series with an inductor (LC circuit) and then connecting a capacitor or inductor in parallel to the whole structure can cover all situations of two-frequency decoupling. At the same time, it can make the imaginary part of the mutual admittance between the two antennas completely zero during the decoupling process, which is an ideal theoretical result. Similarly, the structure of three-frequency decoupling is also analyzed in this way during the derivation process for eight situations. The topology is two LC circuits composed of four capacitors and an inductor, and then a capacitor or inductor is connected in parallel. It uses five variables to solve a three-dimensional set of equations, so it can also cover all situations. To extend this structure to n-frequency decoupling, it is necessary to use n-1 LC circuits in parallel with capacitors or inductors to form a corresponding appropriate topology structure, thereby achieving decoupling at multiple frequency points.

[0157] Will Figure 3 The two antennas in the figure are implemented using a pair of F-type antennas, and the present invention is used for decoupling at two frequency points. In order to test whether the present invention can be generally applied to multi-frequency decoupling of most antennas, two sets of dual-frequency decoupling frequencies and two sets of triple-frequency decoupling frequencies are selected for the two F-type antennas for decoupling, and finally impedance matching is performed to observe the values ​​of reflection coefficient and propagation coefficient on the three planes A, C, and D. After the two antennas with two frequency points are decoupled using the tunable multi-frequency decoupling structure between two antennas based on the parasitic body of the present invention, the S of the two antennas at frequencies of 2.8 GHz and 5.7 GHz are significantly different. 11The schematic diagram is shown in FIG5 (a); after decoupling two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between two antennas of the present invention, the S of the two antennas at frequencies of 2.8 GHz and 5.7 GHz are 12 The schematic diagram is shown in FIG5(b); after decoupling the two antennas with two frequencies using the tunable multi-frequency decoupling structure between the two antennas based on the parasitic body of the present invention, the S of the two antennas at frequencies of 2.5 GHz and 5.4 GHz are 11 The schematic diagram is shown in FIG6 (a); after decoupling two antennas with two frequencies using the parasitic-based tunable multi-frequency decoupling structure between two antennas of the present invention, the S of the two antennas at frequencies of 2.5 GHz and 5.4 GHz are 12 The schematic diagram is shown in FIG6(b); after decoupling two antennas with three frequencies using the tunable multi-frequency decoupling structure between two antennas based on the parasitic body of the present invention, the S of the two antennas at frequencies of 3.0 GHz, 4.7 GHz and 5.5 GHz are 11 The schematic diagram is shown in FIG7 (a); after decoupling two antennas with three frequencies using the parasitic-based tunable multi-frequency decoupling structure between two antennas of the present invention, the S of the two antennas at frequencies of 3.0 GHz, 4.7 GHz and 5.5 GHz are 12 The schematic diagram is shown in FIG7( b ); after decoupling two antennas with three frequencies using the parasitic-based tunable multi-frequency decoupling structure between two antennas of the present invention, the S of the two antennas at frequencies of 2.4 GHz, 4.8 GHz, and 5.9 GHz are 11 The schematic diagram is shown in FIG8 (a); after decoupling two antennas with three frequencies using the parasitic-based tunable multi-frequency decoupling structure between two antennas of the present invention, the S of the two antennas at frequencies of 2.4 GHz, 4.8 GHz, and 5.9 GHz are 12 The schematic diagram is shown in Figure 8(b).

[0158] Analyzing Figure 5(a), we can see that the reflection coefficient S at the C plane after decoupling C 11 (f1) = -7.361dB and S C 11 (f2) = -5.593dB. At this time, due to decoupling, the reflection coefficient parameters are relatively poor at both high and low frequencies. Therefore, after adding the matching network, the reflection coefficient at the D plane is S D 11 (f1) = -11.816dB and S D 11(f2) = -11.823dB, which meets the requirement that the reflection coefficient after matching is less than -10dB. Now look at S in Figure 5(b) 12 Schematic diagram, for the A plane, the transmission coefficient S of the original antenna at high and low frequencies A 12 (f1) = -9.278dB and S A 12 (f2) = -12.857dB, it can be seen that the coupling degree is still relatively high; and after decoupling, the transmission coefficient at the C plane is S C 12 (f1) = -26.579 dB and S C 12 (f2) = -38.378 dB. It can be clearly seen that the transmission coefficient has dropped by about 15-20 dB, which can achieve good decoupling.

[0159] Analyzing Figure 6(a), we can get the final reflection coefficient at the D plane after decoupling matching is S D 11 (f1) = -28.167dB and S D 11 (f2) = -17.986dB, the reflection coefficient after overall matching meets the requirements. The transmission coefficient obtained after decoupling is S C 12 (f1) = -25.682dB and S C 12 (f2) = -37.523 dB. This shows that for the same test antenna, by selecting two frequency points in different groups and using the decoupling structure of the present invention to decouple each frequency point group, the coupling degree can be improved.

[0160] From the analysis of Figure 7(a), we can see that the reflection coefficient of the original antenna at these three frequency points is S A 11 (f1)=-10.621dB、S A 11 (f2) = -5.891dB and S A 11 (f3) = -9.978dB. The final reflection coefficient after decoupling and matching is S D 11 (f1)=-15.087dB、S D 11 (f2) = -13.356dB and S D 11 (f3) = -10.964dB, which meets the requirement that the reflection coefficient at the decoupling frequency is less than -10dB. Analyzing Figure 7(b), we can see that the transmission coefficient of the original antenna at the three frequencies is SA 12 (f1)=-9.944dB、S A 12 (f2) = -22.178dB and S A 12 (f3) = -13.235dB, and the transmission coefficient after decoupling is S C 12 (f1)=-23.073dB、S C 12 (f2) = -37.729dB and S C 12 (f3) = -26.078dB, and the coupling degree is improved by about 15dB.

[0161] Analyzing Figure 8(a), we can see that the reflection coefficients of the two antennas are: on plane A, S A 11 (f1)=-21.861dB、S A 11 (f2) = -6.952dB and S A 11 (f3) = -6.160dB; on the C plane, S C 11 (f1)=-10.096dB、S C 11 (f2) = -6.459dB and S C 11 (f3) = -3.038dB; on the D plane, S D 11 (f1)=-16.898dB、S D 11 (f2) = -19.999dB and S D 11 (f3) = -12.084dB. Analyzing Figure 8(b), we can see that the transmission coefficients on different planes are: On plane A, S A 12 (f1)=-8.624dB、S A 12 (f2) = -21.008dB and S A 12 (f3) = -12.259dB; on the C plane, S C 12 (f1)=-19.068dB、S C 12 (f2) = -43.904dB and S C 12(f3) = -40.631 dB. It can be seen from this that for this test antenna, selecting different decoupling frequency points can achieve a general structural rule for three-frequency decoupling.

[0162] Using the two F-type antennas as an example, this paper selected two groups of two and three frequencies for simulation. The results show that the decoupling structure of the present invention is well suited for multi-frequency tunable decoupling. Therefore, this structure can be extended to a wide range of antennas for decoupling at n frequencies.

Claims

1. A decoupling structure for tunable multiple frequencies between two antennas based on a parasitic body, wherein the two antennas are arranged in parallel and spaced apart. The number of frequencies to be decoupled between the two antennas is denoted as n, where n is an integer greater than or equal to 1. The decoupling structure includes n parasitic structures and a topological structure based on a resonant circuit. The n parasitic structures are arranged between the two antennas. The n parasitic structures are spaced apart from left to right along a row, and there is a distance between each two adjacent parasitic structures. The antenna on the left is called antenna 1, and the antenna on the right is called antenna 2. The n parasitic structures are numbered from 1 to n from left to right, wherein there is a distance between the first parasitic structure and antenna 1, and there is a distance between the nth parasitic structure and antenna 2. Each of the parasitic structures is composed of a transmission line and a load, one end of the transmission line is connected to one end of the load, and the other end of the load is grounded. The load is selected from one of capacitance and inductance. Among the n parasitic structures, the loads and load parameters of any two parasitic structures can be the same or different. After the loads and load parameters of the n parasitic structures are selected, the real part of the mutual admittance of the two antennas at each frequency point can be close to zero. When the load is a capacitor, the load parameter is the capacitance value, and when the load is an inductor, the load parameter is the inductance value. When n is 1, that is, there is only one frequency point that needs to be decoupled between the two antennas, the topological structure includes a load, one end of the load of the topological structure is connected to antenna 1, and the other end of the load of the topological structure is connected to antenna 2, and the load of the topological structure is selected from one of a capacitor and an inductor; if n is an integer greater than or equal to 2, the topological structure includes n-1 LC circuits and a load, each LC circuit is composed of a capacitor and an inductor, and in each LC circuit, one end of the capacitor is connected to one end of the inductor, the other end of the capacitor serves as one end of the LC circuit, and the other end of the inductor serves as the end of the LC circuit. At the other end, one end of each of the n-1 LC circuits is connected to antenna 1, and the other end of each of the n-1 LC circuits is connected to antenna 2. One end of the load is connected to antenna 1, and the other end of the load is connected to antenna 2. The load is selected from one of a capacitor and an inductor. In the n-1 LC circuits, the capacitance values ​​of the capacitors in any two LC circuits can be the same or different, and the inductance values ​​of the inductors can be the same or different. After the capacitance values ​​of the capacitors, the inductance values ​​of the inductors, the selection of the loads, and the selection of the load parameters in the n-1 LC circuits are selected, the imaginary part of the mutual admittance of the two antennas at each frequency point can be zero. When the load is a capacitor, the load parameter is the capacitance value, and when the load is an inductor, the load parameter is the inductance value. The loads in the n parasitic structures are selected as follows: (1) When decoupling n frequency points between two antennas, a distribution port needs to be set at the back end of each antenna for excitation. A distribution port is also set at each parasitic structure for excitation. The distribution port corresponding to antenna 1 is called port 1, the distribution port corresponding to antenna 2 is called port 2, the distribution port corresponding to the first parasitic structure is called port 3, the distribution port corresponding to the second parasitic structure is called port 4, and so on. The distribution port corresponding to the nth parasitic structure is called port n+2. At this time, the two antennas and n parasitic structures form an n+2 port network. The relationship between the voltage and current of the n+2 port network is expressed by formula (1): In formula (1), V1 is the voltage of port 1 in the n+2 port network, V2 is the voltage between ports 2 in the n+2 port network, V3 is the voltage between ports 3 in the n+2 port network, and so on. n+2 is the voltage of port n+2 in the n+2-port network, I1 is the current flowing through port 1 in the n+2-port network, I2 is the current flowing through port 2 in the n+2-port network, I3 is the current flowing through port 3 in the n+2-port network, and so on. n+2 is the current flowing through the n+2 port of the n+2 port network; is the Z parameter matrix of the n+2 port network. When p=q, Z pq Indicates the input impedance of the p-port in the n+2-port network. When p≠q, Z pq represents the mutual impedance from port q to port p in the n+2-port network, where p = 1, 2, ..., n+2 and q = 1, 2, ..., n+2; (2) For the n parasitic structures, there are n loads, which are either capacitors or inductors. At any frequency point, the impedances of the n loads are recorded as ZL1, ZL2, ..., ZL n , i=1,2,…,n,ZL i is the impedance of the load of the i-th parasitic structure. If the load is a capacitor, then C i is the capacitance value of the load. If the load is inductive, then ZL i =j×2πfL i , L i is the inductance value of the load, where f is the frequency corresponding to any frequency point, and j represents an imaginary number; at this time, V3, V4, ..., V at any frequency point can be obtained. n+2 The impedance ZL1, ZL2, ..., ZL of each load in each parasitic structure n The relationship between them can be expressed using formula (2): (3) According to formula (2), we can get formula (3): Writing formula (3) into matrix form, we get formula (4): (4) Order Then we can get formula (5) through formula (4): (6) Order From this we can get formula (6): According to formula (1), formula (7) can be obtained: Substituting formula (6) into (7) yields formula (8): At this point, after passing through n parasitic structures, the n+2-port network consisting of two antennas and n parasitic structures becomes a two-port network consisting of only two antennas. Antenna 1 corresponds to port 1, and antenna 2 corresponds to port 2. Equation (8) is the relationship between the voltage and current of the two-port network. Writing Equation (8) in matrix form yields Equation (9): In formula (9), is the Z parameter matrix of the two-port network, Z 11 ' represents the input impedance of port 1 in a two-port network, Z 11 '=Z 11 +[Z 13 Z 14 … Z 1(n+2) ]×M1,Z 22 ' represents the input impedance of the 2-port in a two-port network, Z 22 '=Z 22 +[Z 23 Z 24 … Z 2(n+2) ]×M2,Z 12 ' represents the mutual impedance from port 2 to port 1 in a two-port network, Z 12 '=Z 12 +[Z 13 Z 14 … Z 1(n+2) ]×M2,Z 21 ' represents the mutual impedance from port 1 to port 2 in a two-port network, Z 21 '=Z 21 +[Z 23 Z 24 …Z 2(n+2) ]×M1; (6) The frequency corresponding to the bth frequency point between the two antennas is recorded as f b , b=1,2,…,n, the reactance of the load in the ath parasitic structure at the first frequency between the two antennas is recorded as XL a (f1), the impedance of the load in the ath parasitic structure at the first frequency is recorded as ZL a (f1), a=1,2,…,n,ZL a (f1) = jXL a (f1), namely ZL a (f1) is XL a The imaginary part of (f1) is recorded as ZL, and the impedance of the load in the a-th parasitic structure at the b-th frequency point is recorded as ZL a (f b ), the reactance of the load in the a-th parasitic structure at the b-th frequency point is recorded as XL a (f b ), if the load in the a-th parasitic structure at the b-th frequency point is a capacitor, then the reactance of the load is at this time, If the load in the ath parasitic structure at the bth frequency point is inductive, the reactance of the load is at this time (7) According to formula (1), two antennas and n parasitic structures form an n+2 port network. At the bth frequency point, the relationship between the voltage and current of the n+2 port network is expressed in matrix form as follows: In formula (10), V1(f b ) is the voltage of port 1 in the n+2 port network at the bth frequency point, V2(f b ) is the voltage of port 2 in the n+2-port network at the bth frequency point, and so on, V n+2 (f b ) is the voltage of the n+2 port in the n+2 port network at the bth frequency point; I1(f b ) is the current flowing through port 1 of the n+2 port network at the bth frequency point, I2(f b ) is the current flowing through port 2 of the n+2-port network at the bth frequency point, and so on, I n+2 (f b ) is the current flowing through the n+2 port of the n+2 port network at the bth frequency point; is the Z parameter matrix of the n+2 port network at the bth frequency point. When w=v, Z wv (f b ) represents the input impedance of the w port of the n+2 port network at the bth frequency point. When w≠v, Z wv (f b ) represents the mutual impedance from port v to port w in the n+2-port network at the bth frequency, where w = 1, 2, ..., n+2, v = 1, 2, ..., n+2; (8) The impedance ZL of the load in the a-th parasitic structure at the b-th frequency point determined in step (6) is a (f b ) corresponds to the impedance ZL in equation (2) a , we get formula (11): (9) According to (11), we can get formula (12): Writing formula (12) into matrix form gives formula (13): (10) Order According to formula (13), we can get formula (14): (11) Order From this we can get formula (15): According to formula (10), we can get: Substituting formula (15) into formula (16) yields formula (17): At this time, the relationship between the voltage and current of the two-port network is expressed in matrix form as follows: Among them, Z 11 '(f b )=Z 11 (f b )+[Z 13 (f b ) Z 14 (f b ) …Z 1(n+2) (f b )]×M1(f b ), Z 11 '(f b ) represents the input impedance of port 1 of the two-port network at the bth frequency point; Z 22 '(f b )=Z 22 (f b )+[Z 23 (f b ) Z 24 (f b ) … Z 2(n+2) (f b )]×M2(f b ), Z 22 '(f b ) represents the input impedance of the 2-port of the two-port network at the b-th frequency point; Z 12 '(f b )=Z 12 (f b )+[Z 13 (f b ) Z 14 (f b ) … Z 1(n+2) (f b )]×M2(f b ), Z 12 '(f b ) represents the mutual impedance from port 2 to port 1 of the two-port network at the bth frequency point; Z 21 '(f b )=Z 21 (f b )+[Z 23 (f b ) Z 24 (f b ) … Z 2(n+2) (f b )]×M1(f b ), Z 21 '(f b ) represents the mutual impedance from port 1 to port 2 of the two-port network at the bth frequency point; the mutual admittance from port 1 to port 2 of the two-port network at the bth frequency point is denoted as Y 12 '(f b ), Y can be obtained from the parameter conversion formula of the two-port network 12 '(f b ) is expressed as: (12) Set the intermediate parameter D(f b ),make Among them, Re{Y 12 '(f b )} is Y 12 '(f b ), Im{Y 12 '(f b )} is Y 12 '(f b ) of the imaginary part; give the reactance XL of the load in the a-th parasitic structure at the first frequency point a (f1) randomly assigns a value within the range (a1, a2), where the value range of a1 is (-1×10 6 ,-1×10 4 ), the value range of a2 is (1×10 -4 ,1×10 8 ), if the reactance of the load in the a-th parasitic structure is positive at this time, then the load in the parasitic structure is determined to be inductor, and then the reactance of the load in the a-th parasitic structure at the b-th frequency point is obtained as If the reactance of the load in the a-th parasitic structure is negative at this time, the load in the parasitic structure is determined to be a capacitor, and then the reactance of the load in the a-th parasitic structure at the b-th frequency point is obtained as Then, we can get Y by following steps (6)-(11) 12 '(f b ), take Y 12 '(f b ) to obtain the intermediate parameter D(f b ), then we get D(f1) to D(f n ), D(f b ) corresponds to the bth frequency point, construct a set D for storing data, and convert the currently obtained D(f1) to D(f n ) is stored as a data of set D in set D, and then the reactance XL of the load in the a-th parasitic structure at the first frequency point is given again. a (f1) Randomly assign a value within the assignment range (a1, a2), and store a data into the set D again according to the same method as above, until Q data are stored in the set D, where Q is the number of optimizations and is an integer greater than or equal to 500; at this time, the data with the smallest value in the set D is taken and recorded as minD. The reactance of the loads in the n parasitic structures at the frequency corresponding to minD is assigned as the reactance value corresponding to each load finally selected; (13) Determine the number of loads with reactance greater than 0 among the n parasitic structures obtained in step (12), and record this number as m. Then, among the n parasitic structures, the number of loads with inductance is m, and the number of loads with capacitance is nm. Renumber the m parasitic structures with inductance in the order of their original numbers from small to large from 1 to m. Then, the inductance value of the load in the xth parasitic structure among the m parasitic structures with inductance is XL x The reactance of the load in the xth parasitic structure among the m parasitic structures with inductive loads, x = 1, 2, ..., m, the nm parasitic structures with capacitive loads are renumbered from 1 to nm in ascending order, and the capacitance value of the load in the yth parasitic structure among the nm parasitic structures with capacitive loads is XL y is the reactance value of the capacitor in the y-th parasitic structure among the nm parasitic structures whose loads are capacitors, where y = 1, 2, …, nm.

2. The decoupling structure for tunable multiple frequencies between two antennas based on a parasitic body according to claim 1, characterized in that The parameter values ​​of the capacitor and inductor in the topology are selected according to the following method: (1) When n is 1, a single frequency point is decoupled and a capacitor or inductor is selected as the load of the topology structure. The susceptance of the load is Y = Im{Y 12 '(f1)}, after the topological structure, the imaginary part of the mutual admittance between the two antennas is Im{Y 12 " " " 1}=Im{Y 12 '(f1)}-Y=0, the imaginary part is zero. If the susceptance value of the load is greater than zero, it is a capacitor, and its capacitance value is If the susceptance of the load is less than zero, it is an inductor, and its inductance is (2) When n is an integer greater than or equal to 2, n-1 LC circuits and a load of capacitance or inductance are required. The capacitance C in the βth LC circuit of the topological structure at the first frequency point between the two antennas is β The susceptance of (f1) is denoted by XC β (f1), the capacitance of this capacitor is C β , β=1,2,…,n-1; the inductance L in the βth LC circuit of the topological structure at the first frequency point β The electrical susceptance of (f1) is XL β (f1), the inductance of the inductor is L β The capacitance of the βth LC circuit at the bth frequency is XC β (f b ), The inductance of the βth LC circuit at the bth frequency is denoted by XL β (f b ), If the other load is a capacitor, the susceptance of the capacitor C'(f1) at the first frequency point is recorded as XC'(f1), the capacitance value of the capacitor is C', and the susceptance of the capacitor at the bth frequency point is recorded as XC'(f b ), At this time, formula (20) is established: If the other load is an inductor, the susceptance of the inductor L'(f1) at the first frequency point is recorded as XL'(f1), and the inductance value of the inductor is L' at the bth frequency point f b The susceptance of the inductor is denoted as XL'(f b ), At this time, formula (21) is established: Equations (20) and (21) are both n-dimensional equations with n-1 capacitors, n-1 inductors, and a load susceptance as unknowns. Multiple solutions are obtained by calculating them respectively. Select the solution that makes XC β (f1)>0,XC'(f1)>0,XL β The real number solution that satisfies both (f1)<0 and XL'(f1)<0 is used as the value of the unknown variable, and then the capacitance value of the capacitor in the βth LC circuit is obtained. Inductance value of the inductor When the load is a capacitor, the capacitance value of the load When the load is inductive, the inductance of the load

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