A microstrip line tuning circuit and a base station antenna

Abstract

The present invention discloses a microstrip line tuning circuit. The tuning circuit is composed of a single-layer PCB circuit board, and the single-layer PCB circuit board consists of three parts: a front copper-clad microstrip line, a dielectric board, and a back copper-clad ground plane. The front copper-clad microstrip line includes: an input pad, an output pad, an input impedance transformation section, an output impedance transformation section, and a resonator composed of a plurality of parallel open stubs. The above resonator eliminates the impedance discontinuity phenomenon caused by electromagnetic mode conversion near the corresponding frequency point of the ultra-wideband radiation unit through "anti-resonance", so as to achieve the purpose of expanding the impedance bandwidth. Considering that the most widely used base station antenna radiation units currently basically operate below the third-order mode, the above microstrip line tuning circuit is optimized to a suitable resonance frequency, and theoretically adapts to almost all radiation units, significantly improving the impedance bandwidth. The present invention also provides a base station antenna.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency tuning circuits, and particularly to an impedance matching circuit and implementation method for a radiation element of an ultra-wideband base station antenna (sub-6GHz) with universality. Background Art

[0002] Wireless communication has entered the 5G era. With the development and utilization of new spectrum resources such as n74 (1427 - 1518 MHz) and n71 (617 - 698 MHz), higher requirements are put forward for the operating bandwidth of base station antennas (sub-6GHz). At the same time, the miniaturization and integration of base station antennas are the only way to solve the increasingly serious sector crosstalk and site resource tension problems in dense networking environments. Base station antennas must meet relatively strict pattern indicators and circuit indicators such as standing wave, isolation, and passive intermodulation within the operating bandwidth. On the one hand, the ultra-wideband makes the impedance matching of the radiation elements of base station antennas extremely difficult. By designing multiple resonances, the impedance bandwidth can be extended to achieve a wider frequency band matching, which is the main method for designing ultra-wideband radiation elements in the current base station antenna industry. However, the above method has limitations: 1) Designing multiple resonances is not easy because the resonance modes do not simply correspond to the radiation surface structure and feeding method of the antenna, and the interaction between different resonance modes is very sensitive; 2) Multiple resonances are not a sufficient condition for full-band impedance matching. Each resonance corresponds to a specific distribution pattern of voltage / current on the oscillator. If the conversion between different modes is discontinuous, impedance mutation may be triggered and the matching may fail. On the other hand, more arrays are integrated in the increasingly cramped antenna interior, and the crosstalk between radiation elements will become more and more serious. Complex electromagnetic coupling occurs between radiation elements through mechanisms such as common ground current, parasitic capacitance / inductance, scattering, and secondary radiation, resulting in the destruction of isolation. They emit and receive from each other, and each other is the boundary. The matching and reception / transmission signals of each radiation element are affected by other radiation elements. This not only makes it difficult to meet the circuit parameters such as standing wave and isolation, but also the radiation pattern will be seriously affected, causing problems such as gain reduction, waveform distortion, sidelobe suppression, and front-to-back ratio deterioration. Summary of the Invention

[0003] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a microstrip line tuning circuit that can eliminate the impedance discontinuity phenomenon caused by electromagnetic mode conversion near the corresponding frequency points of ultra-wideband radiation elements (sub-6GHz), thereby expanding the impedance bandwidth.

[0004] The present invention also provides an ultra-wideband base station antenna.

[0005] To achieve the above object, the present invention adopts the following technical solutions.

[0006] A microstrip line tuning circuit, characterized in that it is composed of a single-layer PCB circuit board, and the single-layer PCB circuit board is composed of a front copper-clad microstrip line, a dielectric board and a back copper-clad ground plane; the front copper-clad microstrip line includes: an input pad, an output pad, an input impedance transformation section, an output impedance transformation section, and a resonator composed of a plurality of parallel open stubs, the resonator is connected between the input impedance transformation section and the output impedance transformation section, and each of the open stubs constitutes an LC resonance circuit, and the open stubs cooperate with the input impedance transformation section and the output impedance transformation section to achieve resonance near the corresponding frequency.

[0007] More preferably, the third-order intermodulation index of the single-layer PCB circuit board within the designed operating frequency is better than -120 dBm, the thickness of the dielectric board is 0.5 - 1.5 mm, and the copper-clad thickness is 0.035 ± 0.005 mm.

[0008] More preferably, the back copper-clad ground plane is electrically connected to the input pad and the output pad through metal vias.

[0009] More preferably, the number of the open stubs is one, two or more than three.

[0010] A base station antenna, including a plurality of radiation units, characterized in that a microstrip line tuning circuit is connected to each of the radiation units, and the resonance occurring near the corresponding frequency of the microstrip line tuning circuit is used to eliminate the impedance mutation caused by the discontinuous mode conversion; the corresponding frequency is the standing wave peak frequency of the radiation unit, and the resonance is an anti-resonance that flattens the standing wave peak.

[0011] More preferably, the microstrip tuning circuit is as described above.

[0012] More preferably, the input pad of the microstrip line tuning circuit is connected to the oscillator pin or PCB feeder of the radiation unit through a radio frequency cable, and the output pad of the microstrip line tuning circuit is connected to the phase shifter or connector of the radiation unit through a radio frequency cable.

[0013] More preferably, the number of the open stubs is the same as and corresponds one by one to the number of standing wave peaks of the radiation unit.

[0014] More preferably, the radiation unit is a half-wave dipole oscillator, a full-wave folded oscillator, a die-cast metal oscillator or a PCB oscillator.

[0015] More preferably, the operating frequency band of the radiation unit includes: 1427 - 1518 MHz, 617 - 698 MHz and sub-6 GHz frequency band.

[0016] The beneficial effects of the present invention are:

[0017] 1. A microstrip tuning circuit provided by the present invention, when combined with an ultra-wideband radiation element, can eliminate the impedance discontinuity phenomenon caused by electromagnetic mode conversion near the corresponding frequency points of the ultra-wideband radiation element (sub-6GHz), thereby expanding the impedance bandwidth; at the same time, this circuit adopts a common single-layer PCB microstrip line circuit, which has the advantages of simple process, low cost, and easy batch implementation.

[0018] 2. A base station antenna provided by the present invention uses a microstrip tuning circuit for "anti-resonance", thereby achieving the purpose of eliminating the impedance mutation caused by discontinuous mode conversion of the ultra-wideband radiation element, flattening the wave peak, and improving the standing wave; this method is universal and applicable to antenna oscillators of different frequencies, different types, and different forms. At the same time, the anti-resonance adopts a single-layer PCB microstrip line circuit form that is easy to batch implement, effectively shortening the design cycle of the ultra-wideband radiation element.

[0019] 3. The above-mentioned microstrip tuning circuit can be used in a multi-frequency compact antenna array to achieve in-situ matching of the radiation element, eliminate the influence of the adapter on the power / phase distribution of the antenna array, and improve the radiation pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The three-dimensional schematic diagram of the microstrip tuning circuit provided by Embodiment 1 of the present invention is shown.

[0021] Figure 2 The front schematic diagram of the microstrip tuning circuit provided by Embodiment 1 of the present invention is shown.

[0022] Figure 3 The back schematic diagram of the microstrip tuning circuit provided by Embodiment 1 of the present invention is shown.

[0023] Figure 4 The standing wave diagram of the radiation element of the base station antenna without using the microstrip line tuning circuit is shown.

[0024] Figure 5 The standing wave diagram of the radiation element of the base station antenna using the microstrip line tuning circuit is shown.

[0025] Figure 6 The application schematic diagram of the microstrip line tuning circuit is shown.

[0026] DESCRIPTION OF THE REFERENCE NUMERALS:

[0027] 1: Front copper-clad microstrip line, 2: Dielectric plate, 3: Back copper-clad floor, 4: Metal via, 5: Radiation element.

[0028] 1-1: Input pad, 1-2: Output pad, 1-3: Input impedance transformation section, 1-4: Output impedance transformation section, 1-5: Third-order resonator. Detailed implementation manners

[0029] The following will further describe the detailed implementation manners of the present invention in conjunction with the accompanying drawings of the specification, making the technical solutions and their beneficial effects of the present invention clearer and more definite. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0030] The additional aspects and advantages of the present invention will become apparent in the following description part, or will be learned through the practice of the present invention.

[0031] Embodiment 1

[0032] As Figure 1 shown, a microstrip line tuning circuit is a single-layer PCB circuit board, which is composed of a front copper-clad microstrip line 1, a dielectric board 2, and a back copper-clad ground plane 3. The third-order intermodulation index of the PCB circuit board within the designed operating frequency is better than -120 dBm (two-way 43 dBm carrier input), the thickness of the dielectric board is 0.5 - 1.5 mm, and the copper-clad thickness is 0.035 ± 0.005 mm to meet the requirements of the base station antenna for power capacity and passive intermodulation index. In addition, to improve the consistency of mass production, the dielectric board 2 adopts a board material and manufacturing process with higher stability and smaller batch differences.

[0033] Combined with Figure 2 shown, the front copper-clad microstrip line 1 is composed of an input pad 1-1, an output pad 1-2, an input impedance transformation section 1-3, an output impedance transformation section 1-4, and a third-order resonator 1-5 composed of three open stubs of low-frequency f1, medium-frequency f2, and high-frequency f3 connected in parallel. Each open stub constitutes an LC resonance circuit, and by optimizing the open stubs and the input / output impedance transformation sections, resonance occurs near the corresponding frequencies.

[0034] The specific optimization process and optimization method for optimizing the above open stubs and input / output impedance transformation sections are all common technical knowledge mastered by those skilled in the art and will not be elaborated here.

[0035] When the above microstrip line tuning circuit is used for impedance matching of the base station antenna radiation unit, the input end is connected to the oscillator pin or the PCB feeder through a radio frequency cable, and the output end is connected to the phase shifter or the connector through a radio frequency cable, as Figure 6As shown. Considering that the most widely used base station antenna radiation units (such as half-wave dipoles and full-wave folded dipoles) basically operate below the third-order mode, after the above microstrip line tuning circuit is optimized to the appropriate resonant frequency, it theoretically adapts to almost all radiation units, significantly improving the impedance bandwidth. And its physical meaning is clear and can be realized by processing on a single-layer PCB board, undoubtedly providing a universal and inexpensive solution for the increasing bandwidth requirements of base station antennas. In addition, it should be noted that: the microstrip line tuning circuit described in this embodiment is only an example form. By increasing / decreasing the number of open stubs and modifying the impedance transformation section, the microstrip line tuning circuit described in the present invention can theoretically achieve first-order, second-order, third-order and even higher-order resonances.

[0036] Combined with Figure 3 As shown, the copper-clad floor 3 on the back realizes electrical connection with the input pad 1-1 and the output pad 1-2 through metal vias 4 for easy soldering. It should be noted that: the microstrip line tuning circuit described in this patent is applicable to various cable outer conductor soldering methods, Figure 3 The metal via grounding shown is only one example.

[0037] To demonstrate the effectiveness of the above microstrip line tuning circuit in impedance matching of base station antenna radiation units, Figure 4 and Figure 5 respectively simulate the standing wave measurement result diagrams before and after using the above microstrip line tuning circuit.

[0038] From Figure 4 it can be seen that: the overall standing wave value is relatively large, the standing waves at both ends f1 and f3 of the working frequency range are around 2, and the standing wave at the f2 frequency point is even as high as 2.6. From the standing wave curve, it can be seen that the antenna operates in the second-order resonance mode. To reduce the overall standing wave below 1.5, "peak clipping" should be performed on the three frequency points f1 / f2 / f3.

[0039] Figure 5 is the standing wave after matching using the above microstrip line tuning circuit. From Figure 5 it can be clearly seen that: through the "anti-resonance" realized by the microstrip line tuning circuit, the standing wave curves near f2 and f3 drop from the peaks to near the valleys. It can be seen that the "anti-resonance" successfully eliminates the mismatch caused by the discontinuous mode conversion of the oscillator itself at the corresponding frequencies; at the same time, the standing wave at f1 also drops below 1.5. This demonstration example fully demonstrates the significant effectiveness of the microstrip line tuning circuit described in the present invention in impedance matching of base station antenna radiation units.

[0040] In actual application, as Figure 6 shown, the above microstrip line tuning circuit can be used in a multi-frequency compact antenna array to achieve in-situ matching of the radiation unit 5, eliminate the influence of the matching on the power / phase distribution of the antenna array, and improve the radiation pattern.

[0041] It should be emphasized that: Figures 1 to 5 The demonstration example only provides a typical implementation form of the microstrip line tuning circuit disclosed in the present invention. The core principle of the present invention is to generate an anti-resonance near a specific frequency through a parallel LC tuning circuit and an impedance transformation section, so as to eliminate or improve the mismatch caused by the ultra-wideband antenna oscillator itself during the discontinuous multi-mode conversion process. Starting from this principle, the tuning circuit design, regardless of its resonance order and the implementation form adopted by the circuit, should be regarded as an embodiment of the invention. The protection scope of the present invention shall be defined by each claim item and its equivalents. The parts not described in the specific implementation manners are all prior art or common general knowledge.

Claims

1. A base station antenna, comprising a plurality of radiation units, characterized in that, A microstrip line tuning circuit is connected to each of the radiation units, and the resonance occurring in the microstrip line tuning circuit near the corresponding frequency is used to eliminate the impedance mutation caused by the discontinuous mode conversion; the corresponding frequency is the standing wave peak frequency of the radiation unit, and the resonance is an anti-resonance that flattens the standing wave peak. The microstrip line tuning circuit is composed of a single-layer PCB circuit board, and the single-layer PCB circuit board consists of three parts: a front copper-clad microstrip line, a dielectric board, and a back copper-clad ground plane; the front copper-clad microstrip line includes: an input pad, an output pad, an input impedance transformation section, an output impedance transformation section, and a resonator composed of a plurality of parallel open stubs, the resonator is connected between the input impedance transformation section and the output impedance transformation section, each of the open stubs forms an LC resonance circuit, and each of the open stubs cooperates with the input impedance transformation section and the output impedance transformation section to achieve resonance near the corresponding frequency.

2. The base station antenna according to claim 1, wherein The third-order intermodulation index of the single-layer PCB circuit board within the designed operating frequency is better than -120 dBm, the thickness of the dielectric board is 0.5 - 1.5 mm, and the copper-clad thickness is 0.035 ± 0.005 mm.

3. The base station antenna according to claim 1, characterized in that, The back copper-clad ground plane is electrically connected to the input pad and the output pad through metal vias.

4. The base station antenna according to claim 1, characterized in that, The number of the open stubs is one, two, or more than three.

5. An antenna for a base station according to claim 1, characterized in that, The input pad of the microstrip line tuning circuit is connected to the oscillator pin or the PCB feeder of the radiation unit through a radio frequency cable, and the output pad of the microstrip line tuning circuit is connected to the phase shifter or the connector of the radiation unit through a radio frequency cable.

6. The base station antenna according to claim 1, wherein The number of the open stubs is the same as and corresponds one by one to the number of standing wave peaks of the radiation unit.

7. The base station antenna according to claim 1, characterized in that, The radiation unit is a half-wave dipole oscillator, a full-wave folded oscillator, a die-cast metal oscillator, or a PCB oscillator.

8. An antenna for a base station according to claim 1, characterized in that, The operating frequency band of the radiation unit includes: 1427 - 1518 MHz, 617 - 698 MHz, and the sub-6GHz band.

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