A broadband decoupling structure for multi-antenna communication systems

Abstract

The present invention proposes a broadband decoupling structure for a multi-antenna communication system, comprising n decoupling units; each decoupling unit comprises N C-shaped metal wires, each type of C-shaped metal wire is connected through a metallized through hole, and each type of C-shaped metal wire of the decoupling unit does not contact the metal surface of the same layer; the opening of the C-shaped metal wire is in the same direction as the dipole arm connected to it; the projections of the C-shaped metal wires in the same direction on the bottom metal surface overlap; the projection of each decoupling unit on the bottom metal surface constitutes an open ring. The present invention adopts a multi-layer distribution technology, which can greatly improve the isolation between units without affecting the impedance matching and bandwidth, thereby improving the radiation pattern and suppressing the back lobe. The present invention can be processed by standard PCB technology, with low cost, low profile, and easy integration. It can be applied not only to multi-layer antenna arrays, but also to single-layer antenna arrays and other broadband multi-antenna communication systems.

Description

Technical Field

[0001] The present invention belongs to the field of antenna technology, and in particular relates to a broadband decoupling structure applied to a multi-antenna communication system. Background Art

[0002] As one of the core contents of the development of MIMO communication technology, the research and design of MIMO antennas has also become a research hotspot in recent years. Although MIMO technology has incomparable advantages in improving channel capacity and data transmission reliability, the antennas in an ideal MIMO system are completely independent, while in reality the antennas are coupled with each other, which reduces the signal-to-noise ratio of the system and causes certain errors in signal processing. Therefore, studying how to remove the coupling between MIMO antenna units has a direct impact and practical significance on improving antenna performance and even the communication capabilities of the entire communication system. For communication systems with limited available space and working in a wider millimeter wave frequency band, antenna decoupling is a very big challenge.

[0003] Adding a resonant structure in the middle of the antenna unit to directly suppress the antenna surface wave and achieve high isolation is considered a feasible way to solve this problem. This is a decoupling technology that uses circuit methods to improve the isolation between two close antennas. Its decoupling mechanism is that the resonant structure introduces an additional coupling path between the antennas. When the coupling current of the resonant structure connected between the units is equal to the reverse of the coupling current between the original units, it can cancel out the original coupling between the antennas.

[0004] The existing decoupling methods mainly include defective ground, electromagnetic band gap, metasurface, neutralization line and resonant decoupling network. The defective ground has various forms and simple design. It can be designed into periodic or symmetrical arrangement according to the actual application, but this method has the disadvantage of destroying the integrity of the floor and worsening the front-to-back ratio of the antenna; the metasurface method does not need to destroy the integrity of the floor, but it occupies a large space and has a high profile; the neutralization line can achieve decoupling of different frequency bands, thereby expanding the decoupling bandwidth, but its implementation and adjustment process is very complicated. At present, there are methods that use defective ground methods and resonator principles to etch two open rings on the rectangular floor to form a floor CSRR structure; there are methods that use neutralization lines and resonant decoupling networks to use independent parasitic structures such as C-type parasitic structures, M-type parasitic structures, and dense zigzag lines to solve the mutual coupling between different polarization ports; or connect a neutralization line or open ring structure at the ends of two monopoles to achieve high isolation of extremely small spacing MIMO antennas. However, these studies have not achieved decoupling within a wide bandwidth, and most of them have a high isolation bandwidth of only a few hundred megahertz. Summary of the invention

[0005] The first purpose of the present invention is to meet the challenges of the prior art and propose a broadband decoupling structure based on an electromagnetic resonant ring that can be applied to a multi-antenna communication system. The decoupling structure is connected across the ends of the two antenna units, which is also the place where the coupling of the two antenna units is the strongest. It can be equivalent to a parallel circuit of resistance, inductance and capacitance, and introduces an additional coupling path between the antennas. By adjusting the equivalent capacitance and inductance values ​​of the decoupling structure, the coupling current of the resonant structure connected between the units is equal in amplitude and opposite to the coupling current between the original units, thereby offsetting the strong coupling between the original antenna units. The present invention uses this structure for a dipole three-unit array to achieve broadband decoupling of multiple antennas. This structure is easy to realize through PCB processing and has a low profile.

[0006] A broadband decoupling structure applied to a multi-antenna communication system of the present invention is a multi-layer vertical arrangement structure, including n decoupling units, n=m-1, m is the number of antenna units, m≥2;

[0007] Each decoupling unit is composed of N C-shaped metal wires and a metallized through hole, where N = the number of dipole arms of the feeding dipole in the antenna unit where the decoupling unit is located; various C-shaped metal wires in the same decoupling unit are connected through metallized through holes, and various C-shaped metal wires of the decoupling unit do not contact the metal surface of the same layer.

[0008] The C-shaped metal wire has an opening in the same direction as the connected dipole arm; it includes a first L-shaped line segment and a second L-shaped line segment; the connecting end of the first L-shaped line segment and the second L-shaped line segment is connected to the end of the dipole arm in the antenna unit where the current decoupling unit is located, and is not connected to the metal surface; the projections of the C-shaped metal wires facing the same direction on the bottom metal surface overlap;

[0009] The projection of each decoupling unit on the bottom metal surface forms an open ring.

[0010] The second object of the present invention is to provide a broadband multi-antenna communication system, comprising a first metal surface M1, a first dielectric substrate S1, a second metal surface M2, a third dielectric substrate S3, a second dielectric substrate S2, a third metal surface M3, m antenna units, and n decoupling units; n = m-1, m is the number of antenna units, and m ≥ 2;

[0011] Each decoupling unit is composed of N C-shaped metal wires and a metallized through hole, where N = the number of dipole arms of the feeding dipole in the antenna unit where the decoupling unit is located; various C-shaped metal wires in the same decoupling unit are connected through metallized through holes, and various C-shaped metal wires of the decoupling unit do not contact the metal surface of the same layer.

[0012] The C-shaped metal wire has an opening in the same direction as the connected dipole arm; it includes a first L-shaped line segment and a second L-shaped line segment; the connecting end of the first L-shaped line segment and the second L-shaped line segment is connected to the end of the dipole arm in the antenna unit where the current decoupling unit is located; the projections of the C-shaped metal wires in the same direction on the bottom metal surface overlap;

[0013] The projection of each decoupling unit on the bottom metal surface forms an open ring.

[0014] The antenna unit adopts a three-layer distributed substrate integrated coaxial line (SICL) feeding dipole, including a first and a third dipole arm connected to the first metal surface M1 and the third metal surface M3 respectively, and a second dipole arm connected to the second metal surface M2; the first and the third dipole arms have the same orientation, and the second dipole arm has an opposite orientation to the first and the third dipole arms;

[0015] The first metal surface M1 is located on the upper surface of the first dielectric substrate S1 and serves as a metal reflector of the unit antenna; the top dipole arm of the dipole antenna and the grounded coplanar waveguide (GCPW) to double-sided parallel microstrip line (DPSPL) structure are printed on the first metal surface M1;

[0016] The third dielectric substrate S3 is located on the lower surface of the first dielectric substrate S1 and is used to bond the first dielectric substrate S1 and the second dielectric substrate S2;

[0017] The second metal surface M2 is located on the lower surface of the first dielectric substrate S1 and the upper surface of the third dielectric substrate S3, and serves as a ground plane of the unit antenna; m feeding networks are provided at the front end of the second metal surface M2; the feeding networks connect the m second dipole arms with the first and third dipole arms connected to the first metal surface M1 and the third metal surface M3 to form a complete dipole array; a number of periodically distributed metallized through holes constituting a SICL structure are provided on both sides of each feeding network; the metallized through holes penetrate the three dielectric substrates and connect the first metal surface M1 and the third metal surface M3; two guide oscillators of different lengths and arranged in parallel are provided in front of the second dipole arm;

[0018] The feeding network connected to the m second dipole arms has m signal input terminals and m signal output terminals; the m signal output terminals are respectively connected to the signal input terminals of the corresponding dipole antenna units;

[0019] The third metal surface M3 is located on the lower surface of the second dielectric substrate S2 and is connected to the bottom dipole arm of the dipole antenna;

[0020] Preferably, the distance L1 between the antenna units satisfies L1≤0.6λ0; λ0 is the wavelength corresponding to the central operating frequency of the antenna unit.

[0021] Preferably, the connecting part of the metal wire of the decoupling unit and the end of the dipole arm is smaller than the line width of the decoupling metal wire.

[0022] Preferably, one end of the first L-shaped line segment of the decoupling unit is connected to one end of the second L-shaped line segment, and the other ends of the first L-shaped line segment and the second L-shaped line segment are bent inward.

[0023] Preferably, the projections of all the decoupling units on the bottom metal surface form n open rings, the open rings are axisymmetric structures, and the centers of the metallized vias connecting to form the same open ring are located on the axis of symmetry of the open ring.

[0024] Preferably, the line width of the metal wire of the decoupling unit is less than half of the line width of the dipole arm.

[0025] Preferably, the distance Lst from the dipole antenna arm to the metal reflector satisfies Lst ≤ λ0 / 4; the wire length R2 of the metal wire of the decoupling unit to the metal reflector satisfies R2 < Lst; λ0 is the wavelength corresponding to the center operating frequency of the dipole antenna.

[0026] Preferably, the transverse length Li1 of the L-shaped line segment of the C-shaped-like metal wire on the side of the dipole arm end satisfies Li1 < (L1 - Ld) / 2, and the longitudinal length Li2 satisfies Li2 < R2 - w1; where L1 is the spacing of the antenna units, Ld is the length of the dipole arm, and w1 is the line width of the C-shaped-like metal wire.

[0027] Specific working principle: When any one antenna unit works alone, the signal is transmitted from the corresponding GCPW to DSPSL to the dipole antenna. There is a decoupling unit connected between each antenna unit and the nearest antenna unit. The metal wire connected by the metallized via can be equivalent to a resistor and an inductor, and the metal wire with the other end bent inward is equivalent to two capacitor plates and can be equivalent to a capacitor. By adjusting the metal wire length R2 to change the inductance value, when the spacing between the two units and the length of the dipole arm are fixed, the larger R2 is, the larger the equivalent inductance of the decoupling unit is. By adjusting the wire lengths Li1 and Li2 of the bent part to change the capacitance value, Li1 determines the gap of the capacitive coupling gap. The larger the value of Li1 is, the smaller the gap of the capacitive coupling gap is, and the stronger the coupling is, so the equivalent capacitance value is larger, and the larger the length value Li2 of the capacitor wire is, the larger the equivalent capacitance value is. Appropriate capacitance and inductance values can make the mutual impedance between adjacent two units approach zero in a very wide frequency band, thereby canceling the original coupling between adjacent units and achieving high isolation in a wide frequency band.

[0028] The present invention has the following advantages:

[0029] (1) The structure achieves decoupling effect by printing metal wires of appropriate size at the end of the antenna unit. It can be distributed in multiple layers, has low cost, and is easy to implement a low-profile multi-antenna communication system. It does not occupy additional space between antenna units.

[0030] (2) This structure can achieve high isolation of more than 25dB within a very wide bandwidth without affecting the impedance bandwidth of the antenna unit.

[0031] (3) The structure can suppress the backward radiation of the radiation pattern and easily achieve low cross-polarization. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention;

[0033] Figure 2 is a side view of the present invention;

[0034] Figure 3 is a front plan view of the present invention;

[0035] Figure 4 is a back plan view of the present invention;

[0036] Figure 5 is a schematic diagram of a three-element antenna array feeding network of the present invention;

[0037] Figure 6 is a comparison of S parameter simulation results of the present invention and a reference antenna without a decoupling structure;

[0038] Figure 7 It is a comparison of the simulation results of the main polarization and cross polarization of the normalized E-plane and H-plane at 24GHz of the present invention;

[0039] Figure 8 It is the comparison of the simulation results of the main polarization and cross polarization of the reference antenna at 24GHz in the normalized E-plane and H-plane;

[0040] Fig. 9 It is a comparison of the simulation results of the main polarization and cross polarization of the normalized E-plane and H-plane at 35GHz of the present invention;

[0041] Fig.10 It is the comparison of the simulation results of the main polarization and cross polarization of the reference antenna at 35GHz in the normalized E-plane and H-plane;

[0042] Fig.11 It is a comparison of the simulation results of the main polarization and cross polarization of the normalized E-plane and H-plane at 42GHz of the present invention;

[0043] Fig.12 It is the comparison of the simulation results of the main polarization and cross polarization of the reference antenna at 42GHz in the normalized E-plane and H-plane;

[0044] Markings in the figure: first metal surface M1, first dielectric substrate S1, second dielectric substrate S2, second metal surface M2, third dielectric substrate S3, third metal surface M3, GCPW to SICL 1, metallized through holes on both sides of SICL structure 2, metallized blind vias of GCPW to SICL 3, metallized through holes of decoupling unit 4, guide oscillator 5, antenna array 6, SICL structure 7, multi-layer decoupling unit 8, feeding network 9, antenna unit one 10, antenna unit two 11, antenna unit three 12. DETAILED DESCRIPTION

[0045] The present invention is further analyzed below in conjunction with specific embodiments.

[0046] like Figure 1 As shown, the multi-antenna communication system using the broadband decoupling unit is a multi-layer vertical arrangement structure, including a first metal surface M1, a first dielectric substrate S1, a second metal surface M2, a third dielectric substrate S3, a second dielectric substrate S2, and a third metal surface M3; wherein the first dielectric substrate S1 and the second dielectric substrate S2 adopt Rogers 5880, with a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of 0.254 mm, and the third dielectric substrate S3 adopts Rogers 4450F, with a dielectric constant of 3.52, a loss tangent of 0.004, and a thickness of 0.1 mm;

[0047] like Figure 2 , 3 As shown, the antenna unit is a dipole with two guide oscillators 5, and the dipole antenna is excited by a 50Ω double-sided parallel strip line (DPSPL); the antenna array 6 is composed of three dipole units, which are placed at equal intervals with a spacing of L1 and are all fed by SICL, the middle one is unit one 10, the right one is unit two 11, and the left one is unit three 12;

[0048] The first metal surface M1 is located on the upper surface of the first dielectric substrate S1, and includes the top dipole arm of the dipole antenna, the top decoupling metal line contacting the end of the dipole arm, and the grounded coplanar waveguide (GCPW) to double-sided parallel microstrip line (DPSPL) structure 1. The large metal plate serves as a reflector for the unit antenna; wherein the dipole arm length Ld is 3.7 mm, the distance Lst from the dipole arm to the reflector is 1.7 mm; and the unit spacing L1 is 5 mm;

[0049] The third dielectric substrate S3 is located on the lower surface of the first dielectric substrate S1 and is used to bond the first dielectric substrate S1 and the second dielectric substrate S2;

[0050] like Figure 4 , 5As shown, the decoupling unit and the dipole unit both adopt a three-layer structure, and the dipole arms of the same angle are printed face to face on the first metal surface M1 and the third metal surface M3, and the ends of the dipole arms of the two layers are connected to the first and third types of C-shaped metal wires of the same structure in the extension direction. The openings of the first and third types of C-shaped metal wires are in the same direction as the connected dipole arms; they include a first L-shaped line segment and a second L-shaped line segment; the connecting end of the first L-shaped line segment and the second L-shaped line segment is connected to the end of the dipole arm in the antenna unit where the current decoupling unit is located; the projections of the two types of C-shaped metal wires on the bottom metal surface overlap.

[0051] The second metal surface M2 is located on the lower surface of the first dielectric substrate S1 and the upper surface of the third dielectric substrate S3. The feed network 9 on the second metal surface M2 can be directly connected to the dipole arm in the opposite direction to the first and third metal surfaces. The end of the half-arm extension direction of this layer is connected to a second type of C-shaped metal wire with the same structure and opposite direction to the first and third types of C-shaped metal wires. The guide vibrator 5 is printed on the second metal surface M2 and is located directly in front of the dipole arm. The guide vibrator 5, the dipole half-arm connected to it, the half-arms of the first metal surface M1 and the third metal surface M3, the feed network 9 and the multi-layer decoupling unit 8 constitute a complete multi-antenna array 6; the two sides of the feed network 9 are provided with metallized through holes 2 that constitute a periodic distribution of the SICL structure; the metallized through holes 2 penetrate the three dielectric substrates and connect the first metal surface M1 and the third metal surface M3; the spacing Wout of the metallized through holes 2 on both sides of the SICL is 2.1mm; the spacing L5 between the first guide vibrator and the second guide vibrator is 1.4mm;

[0052] The projection of each decoupling unit on the bottom metal surface forms an open square ring.

[0053] The dipole three-unit feeding network has three signal input terminals and three signal output terminals; the three signal output terminals are respectively connected to the signal input terminals of the corresponding dipole antenna units;

[0054] Figure 6The S parameter simulation comparison diagram of the middle unit of the dipole antenna array using the design of the present invention and the dipole antenna array without the decoupling unit is shown. The -10dB band is around 26.5-42.2GHz and 27.3-43.2GHz, respectively, indicating that the decoupling unit designed by the present invention will not affect the impedance bandwidth. After the dipole antenna is loaded with the decoupling unit designed by the present invention, its isolation is better than 25dB in the entire working frequency band, which is better than the isolation of the dipole antenna without the decoupling unit. In the low-frequency working frequency band before 34GHz, the isolation of the reference antenna without the decoupling unit is less than 20dB. The isolation between unit 1 and unit 2 and the isolation between unit 2 and unit 3 of the dipole antenna loaded with the decoupling unit are better than 30dB at around 26-33.6GHz and 27.8-34GHz, respectively.

[0055] Figure 7 , Fig. 9 , Fig.11 The comparison of the simulation results of the normalized main polarization and cross polarization of the E-plane and H-plane loaded with the dipole unit of the present invention at low frequency (27GHz), center frequency (35GHz), and high frequency (42GHz); Figure 8 , Fig.10 , Fig.12 The comparison of the simulation results of the normalized main polarization and cross polarization of the E-plane and H-plane at low frequency (27GHz), center frequency (35GHz), and high frequency (42GHz) of the reference antenna without the present invention is shown. It can be seen that the reference antenna without the present decoupling unit has strong coupling with the adjacent antenna units on both sides, and the radiation pattern will produce two back lobes, and the backward radiation is strong; the antenna loaded with the present decoupling unit has two back lobes disappear, and the backward radiation is significantly reduced.

Claims

1. A broadband decoupling structure for a multi-antenna communication system, which is a multi-layer vertically arranged structure, characterized in that It includes n decoupling units, where n = m - 1, m is the number of antenna units, and m ≥ 2; Each decoupling unit includes N C-shaped metal wires and a metallized via hole, where N is the number of dipole arms of the feeding dipole in the antenna unit where the decoupling unit is located; all the C-shaped metal wires in the same decoupling unit are connected through the metallized via hole, and the C-shaped metal wires of the decoupling unit do not contact the metal surface of the same layer; The opening of the C-shaped metal wire faces the same direction as the dipole arm it is connected to, and includes a first L-shaped line segment and a second L-shaped line segment; the connecting ends of the first L-shaped line segment and the second L-shaped line segment are connected to the end of the dipole arm in the antenna unit where the current decoupling unit is located; the projections of the C-shaped metal wires facing the same direction on the bottom metal surface coincide; The projection of each decoupling unit on the bottom metal surface forms an open loop.

2. A broadband decoupling structure for a multi-antenna communication system as claimed in claim 1, characterized in that The open loop is an axisymmetric structure, and the centers of the metallized via holes connected to form the same open loop are located on the axis of symmetry of the open loop.

3. A broadband decoupling structure for a multi-antenna communication system as claimed in claim 1, characterized in that The line width of the C-shaped metal wire of the decoupling unit is less than half of the line width of the dipole arm.

4. A broadband decoupling structure for a multi-antenna communication system as claimed in claim 1, characterized in that The wire length R2 of the metal wire from the decoupling unit to the metal reflector satisfies R2 < Lst, where Lst represents the distance from the dipole antenna arm to the metal reflector, and satisfies Lst ≤ λ0 / 4, and λ0 represents the wavelength corresponding to the center operating frequency of the dipole antenna.

5. A broadband decoupling structure for a multi-antenna communication system as claimed in claim 1, characterized in that The transverse length Li1 of the L-shaped line segment of the C-shaped metal wire on the side of the dipole arm end satisfies Li1 < (L1 - Ld) / 2, and the longitudinal length Li2 satisfies Li2 < R2 - w1; where L1 is the spacing of the antenna units, Ld is the length of the dipole arm, and w1 is the line width of the C-shaped metal wire.

6. A broadband multi-antenna communication system, comprising a first metal surface M1, a first dielectric substrate S1, a second metal surface M2, a third dielectric substrate S3, a second dielectric substrate S2, a third metal surface M3, and m antenna units, m ≥ 2; characterized in that It also includes the broadband decoupling structure according to any one of claims 1-5; The antenna unit uses a substrate integrated coaxial line-fed dipole with three-layer distribution, including a first dipole arm and a third dipole arm respectively connected to the first metal surface M1 and the third metal surface M3, and a second dipole arm connected to the second metal surface M2; the first dipole arm and the third dipole arm face the same direction, and the second dipole arm faces the opposite direction to the first dipole arm and the third dipole arm; The first metal surface M1 is located on the upper surface of the first dielectric substrate S1 and serves as the metal reflector of the unit antenna; the top dipole arm of the dipole antenna and the grounded coplanar waveguide-to-dual-sided parallel microstrip line structure are printed on the first metal surface M1; The third dielectric substrate S3 is located on the lower surface of the first dielectric substrate S1 and is used to bond the first dielectric substrate S1 and the second dielectric substrate S2; The second metal surface M2 is located on the lower surface of the first dielectric substrate S1 and the upper surface of the third dielectric substrate S3, and serves as a ground plane of the unit antenna; m feeding networks are provided at the front end of the second metal surface M2; the feeding networks connect the m second dipole arms with the first and third dipole arms connected to the first metal surface M1 and the third metal surface M3 to form a complete dipole array; a number of periodically distributed metallized through holes constituting a substrate integrated coaxial line structure are provided on both sides of each feeding network; the metallized through holes penetrate the three dielectric substrates and connect the first metal surface M1 and the third metal surface M3; two guide oscillators of different lengths and arranged in parallel are provided in front of the second dipole arm; The feeding network connected to the m second dipole arms has m signal input terminals and m signal output terminals; the m signal output terminals are respectively connected to the signal input terminals of the corresponding dipole antenna units; The third metal surface M3 is located on the lower surface of the second dielectric substrate S2 and is connected to the bottom dipole arm of the dipole antenna.

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