Filtering subarray antenna for 5G Massive MIMO base station

Abstract

The invention provides a filtering sub-array antenna for a 5G Massive MIMO base station, relates to the technical field of wireless communication, solves the problem of large size of a low-frequency filtering structure by integrating serial SRR structures in a sub-array feed network, and effectively expands the working bandwidth by combining the regulation and control of a metal strip on a medium high-order mode. And meanwhile, high-frequency out-of-band rejection insensitive to array mutual coupling is realized by utilizing a natural radiation zero point of a medium high-order mode in an edge emission direction, so that a compact antenna sub-array which is low in profile, low in loss, wide in frequency band and relatively good in out-of-band rejection characteristic is realized on the premise that an external filter device is not needed.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to a filter subarray antenna for a 5G Massive MIMO base station. Background Technology

[0002] With the mature commercial deployment of fifth-generation mobile communication technology (5G), Massive MIMO (Massive Multiple-Input Multiple-Output) technology has become a key technology for improving system capacity and spectral efficiency. In 5G base stations, especially in the Sub-6GHz band, active antenna units (AAUs) typically integrate large-scale 64-channel or 128-channel antenna arrays. To balance system cost, power consumption, and beamforming performance, fully digital beamforming is usually not used; instead, subarray technology is employed, where multiple (usually three) radiating elements in the vertical direction are connected to the same RF transceiver channel through a passive power distribution feed network. Simultaneously, to meet the requirements of base station miniaturization, lightweight design, and low power consumption, the antenna system not only needs to possess good radiation characteristics but also filtering capabilities to suppress out-of-band interference signals.

[0003] For this type of subarray antenna, existing technical solutions mainly fall into two categories: one is a cascaded architecture consisting of independent broadband radiating subarray logic units and independent RF filters connected via coaxial cables or board-to-board connectors; with the development of filtering antenna technology, another approach is to directly array units with filtering capabilities, relying on the filtering characteristics of the units themselves to replace the back-end filters. Although the above solutions have been applied, there are still obvious limitations: First, in the design of traditional subarrays, the feed network only plays a role in power distribution and phase control, which occupies valuable trace space on the PCB board without contributing to filtering performance, leading to the necessity of relying on bulky external filters or sacrificing unit performance; second, some filtering antenna units have strong mutual coupling effects between adjacent units after arraying; finally, the commonly used traditional multi-layer suspended PCB board structure to expand bandwidth, the misalignment between layers will significantly affect the consistency of the subarray. Summary of the Invention

[0004] Therefore, this invention provides a filter subarray antenna for 5G Massive MIMO base stations to solve the technical problems of high insertion loss and large size caused by reliance on external filters in existing Massive MIMO base station antenna subarray technology, as well as the deterioration of high-frequency out-of-band suppression performance due to mutual coupling effect of traditional filter antenna elements under compact array conditions, and the difficulty in achieving both wide bandwidth and filtering selectivity in a limited space. The filter subarray antenna for 5G Massive MIMO base stations provided by this invention solves the problem of large size of low-frequency filter structure by integrating a series SRR structure in the subarray feed network, and effectively expands the operating bandwidth by combining the modulation of the higher-order modes of the dielectric with metal strips. At the same time, it utilizes the natural radiation null point of the higher-order modes of the dielectric in the side-firing direction to achieve high-frequency out-of-band suppression that is insensitive to array mutual coupling. Thus, without the need for external filtering devices, a compact antenna subarray with low profile, low loss, wide bandwidth and good out-of-band suppression characteristics is achieved.

[0005] The filter subarray antenna for 5G Massive MIMO base stations provided by the present invention includes: a multi-layer stacked structure, the bottom layer being a dielectric substrate with a lower layer printed with a metal reflective ground plane, an upper layer printed with a feed network and a radiating patch, the middle layer being a small rectangular dielectric block for support and energy coupling, and the top layer being a parasitic radiating dielectric patch.

[0006] Furthermore, the radiating antenna element employs a stacked design of composite metal patches and dielectric patches. The metal patch serves as the driving source, directly fed through a ±45 degree dual-polarized microstrip line to excite the fundamental mode radiation. Above the driving patch, four discrete small dielectric blocks are positioned as intermediate supports, serving not only to support the upper layer patch but also as excitation channels for exciting the top dielectric patch. A metal strip is loaded at the bottom of the dielectric patch. This metal strip, by changing the boundary conditions, independently modulates the resonant frequency of the dielectric's higher-order mode TE12, bringing it closer to the fundamental mode frequency, thereby expanding the operating impedance bandwidth of the antenna subarray. This antenna structure can excite the TE22 mode of the dielectric at high-frequency out-of-band points. Due to the centrosymmetry of the TE22 mode's field distribution, its far-field radiation in the antenna's side-firing direction cancels each other out, thus forming a natural radiation null point on the gain pattern.

[0007] Furthermore, for the feeding network, this invention employs a direct 1-to-3 power distribution feeding network to feed the three radiating elements in the subarray with equal amplitude and in-phase power. Specifically, the feeding network includes two sets of mirror-symmetric direct 1-to-3 power distribution circuits. The input end uses a 50Ω microstrip line, and broadband impedance matching is achieved through a third-order impedance step line. Phase delay is introduced in each branch path, thereby achieving a preset beam downtilt angle of 7° in the antenna subarray. An open-circuit resonant ring (SRR) structure with band-stop characteristics is connected in series on both sides near the radiating metal patch on the branch microstrip line of the feeding network. By precisely designing its geometry, its resonant frequency is located outside the low-frequency band of the antenna's operating frequency band, introducing a transmission zero and improving the out-of-band rejection capability of the subarray on the low-frequency side.

[0008] The key innovation of this invention lies in utilizing the modal characteristics of the dielectric structure itself to achieve high-frequency suppression without relying on lossy circuits, while simultaneously widening the operating bandwidth with the help of metal strips. This achieves broadband operation and high-frequency out-of-band suppression while avoiding high insertion loss. Furthermore, by using a series SRR structure in the feed network to suppress low-frequency interference, the antenna can achieve bilateral filtering, and the filtering effect after arraying is minimally affected by mutual coupling. This structure creatively integrates the filtering characteristics at the feed circuit level with the modal filtering characteristics of the radiator itself, forming a 1×3 antenna array as the basic logic unit of Massive MIMO.

[0009] The present invention has the following advantages over the prior art:

[0010] 1. The antenna of the present invention has a compact overall size, with a cross-section of only 0.1λ0 (λ0 is the center frequency wavelength of the C-band), and the upper parasitic dielectric patch can be assembled using SMT technology, which effectively improves the consistency of the array layer dimensions.

[0011] 2. The antenna array of the present invention has a -15dB impedance bandwidth of 3.3-4.0 GHz and a relative bandwidth of 19.18%, which can cover the mainstream n78 frequency band of 5G and meet the needs of mobile base station communication.

[0012] 3. The low-frequency null of the antenna of this invention is provided by SRR, and the high-frequency null is formed by utilizing the natural field cancellation characteristics of the dielectric TE22 mode in the side-emitting direction. This allows the subarray to achieve good out-of-band suppression while maintaining an average in-band radiation efficiency of over 85%. In a compact array environment, the antenna subarray of this invention can still maintain a stable radiation null position, and the filtering level does not deteriorate with the expansion of the array size. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0015] Figure 2 This is an exploded view of the structure of the present invention.

[0016] Figure 3 This is a top view of the present invention.

[0017] Figure 4 This is a diagram showing the reflection coefficient, isolation, and gain results of the present invention.

[0018] Figure 5 This is the antenna array pattern of the present invention at 3.4 GHz and 3.8 GHz.

[0019] Figure 6 This is an enlarged view of the open-ended resonant ring of the present invention.

[0020] Explanation of reference numerals in the attached figures:

[0021] 111. Parasitic dielectric patch; 121. Parasitic metal strip; 131. Supporting dielectric block; 211. One-to-three power distribution feeder network one; 212. One-to-three power distribution feeder network two; 221. Open resonant ring; 231. Radiation metal patch; 3. Dielectric substrate; 4. Metal reflective ground; 2111. Input port one; 2121. Input port two. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment provides a filtered subarray antenna for a 5G Massive MIMO system. In this embodiment, the subarray antenna includes three radiating elements arranged linearly along the y-axis (horizontal direction). These three radiating elements share a mirror-placed feed network, forming a 1×3 subarray topology. The entire antenna subarray is compact in size and low in height, making it easy to integrate on a large scale in a Massive MIMO active antenna element (AAU).

[0025] Figure 1 This is a schematic diagram of the overall structure of the filter antenna subarray provided in this embodiment. Figure 2 The exploded view of the filtered antenna subarray provided in this embodiment shows that its main structure is based on a stacked design, and from bottom to top mainly includes: a metal reflective ground 4, a dielectric substrate 3, a pair of mirror-placed 1-to-3 power distribution feed networks 211 and 212 printed on the upper surface of the dielectric substrate 3, a radiating metal patch 231, an intermediate supporting dielectric 131, and an uppermost parasitic dielectric patch 111 and a parasitic metal strip 121 for controlling the higher-order modes of the dielectric patch. The dielectric substrate 3 has a dielectric constant of 3.0 and a thickness of 0.762 mm. A complete copper foil is covered on the lower surface of the dielectric substrate 3 as the metal reflective ground 4, ensuring the unidirectional radiation characteristics of the antenna and serving as the reference ground for the radio frequency circuit. The array spacing of the 1×3 subarray is 0.64 free-space wavelengths at 3.5 GHz.

[0026] Two sets of mirror-symmetric microstrip feed networks are printed on the upper surface of the dielectric substrate 3, corresponding to dual-polarization (±45°) excitation metal patches 231 respectively. Taking one polarization as an example, the signal enters through the input port 2111 and distributes the energy to three branch lines through the first-stage 1-to-3 power divider. In order to achieve good impedance matching over a wide bandwidth, the branch lines of the power divider adopt a third-order impedance step line design. On the branch microstrip line near the oblique angle of the metal patch, an open-circuit resonator (SRR) 221 is integrated (e.g., Figure 6 (As shown in the enlarged view). The SRR structure 221 is connected in series on one side of the microstrip line, and its geometry is precisely tuned so that its resonant frequency is outside the low-frequency band of the antenna's operating frequency. When a signal passes through, the SRR structure generates a band-stop effect at low frequencies, forming a steep transmission null, thereby cutting off the transmission of low-frequency interference signals.

[0027] Furthermore, the three branch microstrip lines of the feed network have a preset physical length difference, which introduces a progressive phase delay between the three radiating elements, thereby causing the main beam of the subarray to generate a preset 7° downtilt angle in the vertical plane to meet the base station coverage optimization requirements. Each radiating element adopts a stacked coupling structure. The radiating metal patch 231 located on the upper surface of the dielectric substrate 3 serves as a driving source, directly connected to the feed microstrip line using a microstrip direct feed method, and achieving dual-polarization excitation through two sets of orthogonal feed lines. Above the radiating metal patch 231, four discrete supporting dielectric blocks 131 are arranged. These four dielectric blocks are centrally symmetrically distributed, serving not only to support the upper dielectric patch 111, but also as a transmission path for excitation energy. Parasitic metal strips 121 are attached to the lower surface of the dielectric patch 111. These metal strips serve as tuning elements, used to change the boundary conditions of the dielectric blocks, adjust the resonant frequency of the dielectric TE12 mode, and bring it closer to the fundamental mode, thereby expanding the impedance bandwidth of the antenna. The dielectric patch is excited to a higher-order mode TE22 at a specific frequency. Because the field distribution of this mode exhibits anti-symmetry along the antenna's side-firing direction, the far-field radiation cancels each other out, thus creating a high-frequency radiation null point on the gain pattern. Both the dielectric patch and the supporting dielectric block have a dielectric constant of 20.

[0028] Figure 4 The simulation results of the S-parameters and gain of the antenna subarray in this embodiment are presented. The frequency band covers 3.3 GHz-4.0 GHz. Within this operating bandwidth, the S11 return loss is below -15 dB and the S21 isolation remains below -17 dB, covering the mainstream 5G N78 frequency band. The gain curve has two obvious radiation nulls at 2.5 GHz and 4.2 GHz. Within the passband, the average gain of the antenna subarray is stable at around 10.5 dBi, and the gain flatness is good. Figure 5 The radiation patterns of the antenna at two typical frequency points, 3.4 GHz and 3.8 GHz, are shown. The antenna maintains good directional radiation characteristics and a stable main lobe shape in both cases. The vertical plane radiation pattern shows that the main beam pointing verifies the function of the preset 7° downtilt angle caused by the phase delay of the feed network.

[0029] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A filter subarray antenna for a 5G Massive MIMO base station, characterized in that, include: A dielectric substrate (3) is provided with a metal reflective ground (4) below it; a three-way power distribution feed network I (211) and a three-way power distribution feed network II (212) are provided on the dielectric substrate (3); both the three-way power distribution feed network I (211) and the three-way power distribution feed network II (212) are connected to a radiating metal patch (231) provided on the dielectric substrate (3).

2. The filter subarray antenna for a 5G Massive MIMO base station according to claim 1, characterized in that, A parasitic medium patch (111) is disposed above the radiation metal patch (231), and an intermediate support medium and a parasitic metal strip (121) are disposed between the radiation metal patch (231) and the parasitic medium patch (111).

3. The filter subarray antenna for a 5G Massive MIMO base station according to claim 2, characterized in that, The first (211) power distribution feed network and the second (212) power distribution feed network are mirror-symmetrical along the y-axis of the dielectric substrate (3).

4. The filter subarray antenna for a 5G Massive MIMO base station according to claim 3, characterized in that, The intermediate support medium and the parasitic metal strip (121) are arranged in four groups in a circumferential array with the center of the metal radiation patch as the center.

5. The filter subarray antenna for a 5G Massive MIMO base station according to claim 4, characterized in that, The supporting medium and the parasitic metal strip (121) are spaced apart.

6. The filter subarray antenna for a 5G Massive MIMO base station according to claim 5, characterized in that, The radiation metal patch is arranged in three groups along the y-axis on the dielectric substrate (3).

7. The filter subarray antenna for a 5G Massive MIMO base station according to claim 6, characterized in that, Input port 1 (2111) and input port 2 (2121) are respectively provided on the 1-to-3 power distribution feeder network 1 (211) and the 1-to-3 power distribution feeder network 2 (212).

8. The filter subarray antenna for a 5G Massive MIMO base station according to claim 7, characterized in that, The three-way power distribution feed network (211) includes three branch microstrip lines connected to the input port (2111). Each branch microstrip line is connected to one side of a set of radiating metal patches (231) at a right angle. Each branch microstrip line has an open resonant ring (221) integrated near the sharp corner.

9. The filter subarray antenna for a 5G Massive MIMO base station according to claim 8, characterized in that, The three-way power distribution feeder network 2 (212) includes three branch microstrip lines connected to the input port 2 (2121). Each branch microstrip line is connected to the other side of a set of radiating metal patches (231) at a right angle. Each branch microstrip line has an open resonant ring (221) integrated near the sharp corner area.

10. The filter subarray antenna for a 5G Massive MIMO base station according to claim 9, characterized in that, The opening of the open resonant ring (221) faces outward.

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