Mitigating beam skew in multi-beamforming networks

Abstract

Systems and methods are provided for a multi-beamforming network using an antenna array. A matrix circuit is provided for feeding elements of the antenna array to generate multiple beams. To address beam skew, a series of phase shifters with specific phase delay characteristics are used between the matrix circuit and the antenna array elements to mitigate beam skew. Linearly increasing or decreasing phase differences between signals fed to adjacent antenna array elements across the antenna array mitigate or eliminate beam skew in the resulting multi-beams. The phase shifters are programmed to provide this increasing or decreasing phase difference.

Description

[0001] Related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 923,352, filed October 18, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to antenna-related circuits, and more particularly, to circuits for reducing beam skew in a multi-beamforming network. Background Art

[0004] To increase the communication capacity of a base station, a multi-beam base station antenna array is needed to divide the base station's coverage area from the entire area into several smaller cells. In addition, it is desirable to keep the coverage of each beam the same across the entire operating frequency band.

[0005] This beam coverage can become a problem, especially with multi-beam antenna arrays.

[0006] Multibeam antenna arrays can be divided into two categories: multibeam antennas built on the lens principle and multibeam antennas formed by ordinary antenna arrays fed by a multibeam forming network (MBFN).

[0007] For lens-based antennas, such as Luneburg lens antennas, multiple beams can be generated by multiple feeds located at different positions. These positions can be calculated using principles such as lens or parabolic focusing. These multibeam antennas typically offer satisfactory performance in terms of broadband matching and beam isolation. Furthermore, in theory, they are free of beam skew.

[0008] Simply put, the main problem with lens-based antennas is their size. They require relatively large lenses / reflectors, which are bulky, expensive, and difficult to manufacture. The large size of the lenses / reflectors stems from the requirement that they must be larger than multiple electrical wavelengths. Reducing the size of these reflectors is theoretically difficult, especially for lower frequencies, such as 1 GHz to 3 GHz.

[0009] For antennas fed / generated by multi-beam forming networks (MBFNs), there are two subtypes of MBFNs. The first subtype is based on a primary lens, such as a Rotman lens. Due to the similarity in operating principles, this subtype of MBFN has the same advantages and disadvantages as lens-based multi-beam antennas: these antennas provide satisfactory performance but are physically quite large.

[0010] The second subtype of MBFN is typically constructed using directional couplers, phase shifters, and frequency dividers. The characteristics of the components depend solely on the electrical length of the transmission lines used to construct them. Because the components can be implemented using planar circuits and their size can be reduced by using meander lines or high-dielectric laminates, the network is typically much smaller than lens-based multibeam antennas. However, almost all antenna systems generated using MBFNs (including those using Butler matrices, Blass matrices, Nolen matrices, etc.) suffer from beam skew.

[0011] A problem with most multi-beam antenna arrays based on multi-beam forming networks is that the beam direction will undesirably but inevitably sweep with frequency. The beam direction changes when the frequency changes, but it is desirable or desired that the beam point in the same direction. This is particularly problematic for some communication systems, such as 3G, 4G, and 5G mobile communications, where the uplink and downlink operate in different frequency bands. Due to this variation in beam direction (called beam skew), the area covered by the beam will be different at various frequencies, and therefore, the antenna array cannot achieve closed-loop communication. This problem is exacerbated as the fractional bandwidth increases, for example, beyond 30%.

[0012] Therefore, there is a need for methods and systems that address the beam-steering problem in antenna systems generated by such MBFNs. Summary of the Invention

[0013] The present invention provides systems and methods for a multi-beamforming network using an antenna array. A matrix circuit is provided for feeding elements of the antenna array to generate multiple beams. To address beam skew, a series of phase shifters with specific phase delay characteristics are used between the matrix circuit and the antenna array elements to mitigate beam skew. Linearly increasing or decreasing phase differences between signals fed to adjacent antenna array elements across the antenna array mitigate or eliminate beam skew in the resulting multi-beams. The phase shifters are programmed to provide this increasing or decreasing phase difference.

[0014] In a first aspect, the present invention provides a circuit for simultaneously generating multiple beams using an antenna array having a plurality of antenna array elements, the circuit comprising:

[0015] a matrix circuit comprising a plurality of hybrid couplers and delay lines, wherein the matrix circuit is coupled between a plurality of loads and the antenna array;

[0016] a plurality of phase shifters coupled between the matrix circuit and the antenna array;

[0017] in,

[0018] Each row of the matrix circuit includes a plurality of hybrid couplers coupled in series in a row direction, wherein each pair of hybrid couplers in the row direction is connected by at least one delay line;

[0019] Each column of the matrix circuit includes a plurality of hybrid couplers coupled in series in the column direction;

[0020] A top row of the matrix circuit is coupled to antenna elements of the antenna array, such that each hybrid coupler of the top row is coupled to the antenna elements of the antenna array via one of the plurality of phase shifters, and each hybrid coupler of the top row is coupled in a column direction between one of the plurality of phase shifters and a hybrid coupler of a previous row of the matrix circuit;

[0021] A bottom row of the matrix circuit is coupled to a plurality of matched loads such that each hybrid coupler of the bottom row is coupled in a column direction between one of the plurality of matched loads and a hybrid coupler of an immediately next row of the matrix circuit; and

[0022] The phase shifter is used to generate a linearly increasing phase difference between adjacent antenna array elements for a signal from the matrix circuit.

[0023] In a second aspect, the present invention provides a circuit for simultaneously generating multiple beams using an antenna array having a plurality of antenna array elements, the circuit comprising:

[0024] a matrix circuit comprising a plurality of hybrid couplers and delay lines, wherein the matrix circuit is coupled between a plurality of loads and the antenna array;

[0025] a first plurality of phase shifters coupled between adjacent rows of the matrix circuit;

[0026] a second plurality of phase shifters coupled between the matrix circuit and the antenna array;

[0027] in,

[0028] Each row of the matrix circuit includes a plurality of hybrid couplers coupled in series in a row direction, wherein each pair of hybrid couplers in the row direction is connected by at least one delay line;

[0029] a top row of the matrix circuit coupled to antenna elements of the antenna array, such that each hybrid coupler of the top row is coupled to the antenna elements of the antenna array via one of the second plurality of phase shifters, and each hybrid coupler of the top row is coupled in a column direction between one of the second plurality of phase shifters and one of the first plurality of phase shifters;

[0030] A bottom row of the matrix circuit is coupled to a plurality of matched loads, such that each hybrid coupler of the bottom row is coupled between one of the plurality of matched loads and one of the first plurality of phase shifters in a column direction;

[0031] each phase shifter of the first plurality of phase shifters is coupled between hybrid couplers in adjacent rows in the matrix circuit, such that each hybrid coupler of the matrix circuit is serially coupled to at least one phase shifter of the first plurality of phase shifters in a column direction; and

[0032] The phase shifters of the first and second pluralities of phase shifters are operable to generate linearly increasing phase differences between adjacent antenna array elements for signals from the matrix circuit.

[0033] In a third aspect, the present invention provides a circuit for simultaneously generating multiple beams using an antenna array having a plurality of antenna array elements, the circuit comprising:

[0034] a matrix circuit comprising a plurality of hybrid couplers and delay lines, wherein the matrix circuit is coupled between a plurality of loads and the antenna array;

[0035] a plurality of phase shifters, wherein each phase shifter is coupled to at least one hybrid coupler;

[0036] in,

[0037] Each row of the matrix circuit includes a plurality of hybrid couplers coupled in series in a row direction, wherein each pair of hybrid couplers in the row direction is connected by at least one delay line;

[0038] - the bottom row of the matrix circuit is coupled to a plurality of matched loads; and

[0039] - the phase shifter is used to generate a linearly increasing phase difference between adjacent antenna array elements for the signal from the matrix circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the present invention will now be described with reference to the following drawings, in which like reference numerals in different drawings represent like elements, and in which:

[0041] Figure 1 The concept of beam deflection is schematically illustrated;

[0042] Figure 2 Schematically illustrates one aspect of the present invention;

[0043] Figure 3 The effect of beam deflection on beam direction is shown;

[0044] Figures 4A to 4D shows beam patterns produced using a conventional Blass matrix and an embodiment of the present invention;

[0045] Figures 5A to 5F A 12-element, 6-beam embodiment of the present invention is shown;

[0046] Figure 6 Shown by Figures 5A-5F The measured radiation pattern produced by the illustrated embodiment; and

[0047] Figure 7 A variation of one aspect of the invention is schematically shown. DETAILED DESCRIPTION

[0048] In one aspect, the present invention provides an antenna system based on a coupler and a phase shifter in terms of the composition of functional components. The resulting antenna system is compact, lightweight, and low-cost.

[0049] In another aspect, the present invention utilizes circuitry for use with an antenna array and provides circuitry for eliminating beam skew in the multiple beams generated. To eliminate beam skew, each output port of a multi-beam network connected to an antenna array element requires a linear phase delay. All output ports require a progressively increasing linear phase delay. A Blass matrix can be used to provide a basis for acceptable performance with approximately linear phase delay. Utilizing the Blass matrix, a series of phase shifters are used and placed between the Blass matrix and the antenna array elements to cancel out errors and thereby achieve the desired linear phase delay.

[0050] Regarding the theoretical basis of the present invention, in order to generate a wave with a tilt from the normal direction at a given frequency f0 A beam in a specific direction, such as Figure 1 As shown, the progressive phase difference ΔPha between adjacent elements should be (Equation 1):

[0051]

[0052] where λ0 is the wavelength of frequency f0 in free space.

[0053] It can be seen that if the beam direction To maintain a constant value within a specific frequency bandwidth, the phase difference must be a linearly increasing value because λ0 increases linearly.

[0054] However, due to the principle of directional coupling, almost all directional couplers (e.g., 3-dB 90-degree quadrature couplers, ring couplers, Magic-T, etc.) cannot provide a linearly increasing (or decreasing / lowering) phase difference between the coupled port and the through port. Instead, the coupler will generate a constant phase difference between the coupled port and the through port within a given bandwidth.

[0055] From equation (1), it is clear that ΔPha is a constant value and when λ0 increases linearly with frequency variation / increase, the value This explains the existence of beam skew in MBFNs. Moreover, since all second-type MBFNs are built based on directional couplers, the beam skew problem is inevitable if a linear phase difference cannot be generated.

[0056] To solve this beam deflection problem, a series of phase shifters or phase shifter groups are placed between the antenna array and the conventional Blass matrix to generate the required linear phase difference at the ports connected to the antenna array elements. Figure 2 shown.

[0057] Figure 2 A conventional Blass matrix is shown, in which the hybrid couplers in each row are coupled in series via a delay line. Each hybrid coupler in the bottom row is coupled in the column direction between a matched load and the hybrid coupler in the next row. Furthermore, each hybrid coupler in the top row is coupled between the hybrid coupler in the previous row and a phase shifter. Each phase shifter is coupled between the hybrid coupler in the top row and an antenna array element.

[0058] Figure 2 The schematic diagram in FIG2 is an example of a 12-element, 6-beam MBFN for beam-free applications. As described above, a series of phase shifters, shown in red in the figure, are used to eliminate beam skew. These phase shifters generate the required linearly increasing phase difference, which conventional couplers cannot generate. The linearly increasing phase difference can be designed and configured as needed. For further details on this phase difference, see the following reference: K. Ding and A.A. K. Shik, “2-D Butler Matrix and Phase-Shifter Group,” IEEE Trans. Microw. Theory Techn., Vol. 66, No. 12, pp. 5554-5562, December 2018. The entire contents of this reference are hereby incorporated by reference.

[0059] from Figure 2As can be seen in the figure, each row of the matrix circuit has a plurality of hybrid couplers coupled in series in the row direction. Each pair of hybrid couplers in the row direction is connected by at least one delay line. The top row of hybrid couplers is coupled to the antenna elements of the antenna array. This is done so that each hybrid coupler in the top row is coupled to an antenna element via a phase shifter. In this embodiment, the bottom row of the matrix circuit is coupled to a matched load, so that each hybrid coupler in the bottom row is coupled in the column direction between the matched load and a hybrid coupler from the next row.

[0060] refer to Figure 3 , the figure shows Figure 2 The simulation results of the phase difference on each path of the phase shifter in . Figure 3 It can be seen that although the 12 phase shifters have the same phase delay at the center frequency, the phase shifters have different gradients (slopes) when the frequency changes. The gradient on each path will gradually increase (or decrease) with the same difference between adjacent paths.

[0061] from Figure 3 As can be seen from the figure, multiple points can be extracted based on the preferred configuration. These points are: 1. At a given frequency, the phase delay on each path is preferably equal; 2. The phase delay gradients on each path are preferably coordinated to eliminate beam skew; and 3. The required phase delay gradient on each path is related not only to the phase shifter group itself but also to the Blass matrix. Therefore, as the beam sweeps across different frequencies, the phase delay increases with increasing frequency.

[0062] refer to Figures 4A-4D , showing the effect of eliminating or mitigating beam deflection compared to minimal or no beam deflection mitigation. Figure 4A and Figure 4C Figure 2 shows the radiation patterns of beams 2 and 3 generated by a 6-beam conventional Blass matrix when the frequency changes from 1.7 GHz to 2.7 GHz. It can be seen that without mitigating the beam deflection effect, the beam direction will shift with frequency, resulting in a reduction in beam coverage overlap across the entire frequency band. However, eliminating or mitigating beam deflection will effectively suppress the movement of the beam direction, as shown in Figure 2. Figure 4B and Figure 4D shown. Figure 4A Beam 2 from a conventional Blass matrix is shown. Figure 4B A beam 2 from a system according to the invention is shown. Figure 4C shows beam 3 from a conventional Blass matrix, while Figure 4D A beam 3 from a system according to the invention is shown.

[0063] It should be clear that one embodiment of the present invention inherits some of the inherent advantages of the Blass matrix. For example, this embodiment of the present invention can generate any number of beams for any number of elements. This is in contrast to the Butler matrix, in which the number of beams must equal the number of elements in the antenna array, and the number of beams and the number of antenna array elements must be an integer power of 2. Furthermore, this embodiment allows the direction, beamwidth, and sidelobe level of each beam to be independently designed and configured.

[0064] That is, this embodiment of the present invention differs from the Blass matrix in one important respect. It is designed based on a number of functional components, such as couplers and phase shifters, and unlike the Blass matrix, which is a monolithic whole, this embodiment of the present invention can be divided into multiple circuit boards connected by cables. While this structural separation does not improve beamforming performance, it significantly increases design flexibility and adaptability, thereby miniaturizing the overall MBFN design.

[0065] In addition to the aforementioned advantages, in this embodiment, each phase shifter in the phase shifter group can be expanded into multiple sections or constructed with multiple parts or components. This means that, in theory, there is no limit to beam skew reduction, provided there is sufficient space to accommodate the phase shifter group / multiple phase shifters. Furthermore, each phase shifter has excellent broadband matching potential to meet other possible requirements.

[0066] According to another aspect of the present invention, the design and construction of an MBFN can be divided into two discrete steps. The first step is to design a conventional Blass matrix based on the desired number of beams and the number of antenna array elements. This step involves designing the Blass matrix to account for the desired beam direction, beamwidth, and sidelobe level for each beam. Once completed, the second step is to design a phase shifter bank or banks to eliminate beam skew. It should be understood that phase shifters can be implemented using specially configured phase shifters, but programmable phase shifters can be created using electronically controllable switches with specific length segments.

[0067] According to one aspect of the present invention, a sample of a 12-element 6-beam MBFN without beam skew is shown in FIG5 . Figures 5A to 5F The overall configuration of the example, the locations of ports and loads, the layout of each layer, and cross-sectional views are shown. Figure 5A The overall configuration of the system is shown, detailing the definitions of beam ports, element ports, and loads. Figure 5B A top view of the copper layers of a simplified system. Figure 5C It is the top-level layout. Figure 5D It is the middle layer layout. Figure 5E It is the bottom layer layout. Figure 5Fis a cross-sectional view of the system's circuit board.

[0068] from Figures 5A to 5F It can be seen that the coupler matrix and the meander lines between the couplers form a Blass matrix. In addition, it can be seen that Figure 5C The 12 curved lines with curved open-ended stubs on the upper side form a phase shifter group. In one embodiment, this example configuration operates in the frequency band of 1.695 GHz - 2.69 GHz. Figure 6 , shows the measured radiation pattern of this example configuration. Figure 6 The radiation pattern on the left is for the elevation plane, while Figure 6 The radiation pattern on the right side of the center is for the azimuth plane. As can be seen, the six central beams show satisfactory performance in terms of beam stability within the band.

[0069] Although Figures 5A to 5F The configuration in shows one possible implementation, but it uses only a single row or set of phase shifters. Figures 5A to 5F The configuration in

[15] uses a single row of phase shifters, and these are placed outside the Blass matrix to eliminate beam deflection. A variation is to place multiple rows of phase shifters in the matrix. This variation is shown in

[15] . Figure 7 shown.

[0070] like Figure 7 As shown, each row of hybrid couplers in the matrix circuit is sandwiched between multiple rows of phase shifters. The bottom row of hybrid couplers is sandwiched between a row of matched loads and a row of phase shifters. Therefore, each hybrid coupler in the bottom row is coupled between a phase shifter and a matched load. Except for these bottom row hybrid couplers, each hybrid coupler is coupled between two phase shifters. For the top row of phase shifters, each phase shifter is coupled between a hybrid coupler from the top row of hybrid couplers and an antenna array element. In theory, this configuration will be better than Figures 5A-5F The configuration in shows better performance.

[0071] In this variation, there are two sets of phase shifters: the first set is located between the top row of hybrid couplers and the antenna elements, and the second set is located between adjacent rows of hybrid couplers in the matrix circuit. In the top row of hybrid couplers, each hybrid coupler is coupled in the column direction between one phase shifter of the second set and one phase shifter of the first set. In the bottom row of this variation, the bottom row is coupled to a matched load, such that each hybrid coupler in the bottom row is coupled in the column direction between the matched load and the phase shifter.

[0072] The configuration of the phase shifters in this variation has each phase shifter of the second set of phase shifters coupled between hybrid couplers in adjacent rows of the matrix circuit. This is configured such that each hybrid coupler is serially coupled to at least one phase shifter of the second set of phase shifters in the column direction. It should be understood that while this embodiment currently uses phase shifters with fixed parameters, programmable phase shifters (or phase shifters with varying parameters) are also possible.

[0073] Those who understand the invention may now envision alternative configurations and embodiments or variations to the above, all of which are intended to fall within the scope of the invention as defined in the appended claims.

Claims

1. A circuit for simultaneously generating multiple beams using an antenna array having a plurality of antenna array elements, the circuit comprising: a matrix circuit comprising a plurality of hybrid couplers and delay lines, the matrix circuit being coupled between a plurality of loads and the antenna array, and forming a multi-beamforming network; a plurality of phase shifters coupled between the matrix circuit and the antenna array; in, - each row of the matrix circuit comprises a plurality of hybrid couplers coupled in series in the row direction, wherein each pair of hybrid couplers in the row direction is directly connected by at least one delay line; Each column of the matrix circuit includes a plurality of hybrid couplers coupled in series in the column direction; A top row of the matrix circuit is coupled to antenna elements of the antenna array, such that each hybrid coupler of the top row is coupled to the antenna elements of the antenna array via one of the plurality of phase shifters, and each hybrid coupler of the top row is coupled in a column direction between one of the plurality of phase shifters and a hybrid coupler of a previous row of the matrix circuit; A bottom row of the matrix circuit is coupled to a plurality of matched loads such that each hybrid coupler of the bottom row is coupled in a column direction between one of the plurality of matched loads and a hybrid coupler of an immediately next row of the matrix circuit; and - the phase shifter is used to generate a linearly increasing phase difference between adjacent antenna array elements for the signal from the matrix circuit.

2. The circuit according to claim 1, wherein The phase of a signal sent from a particular hybrid coupler to a particular antenna element in the antenna array is controlled by a particular phase shifter to which the particular hybrid coupler is coupled, the particular hybrid coupler being located in the top row of the matrix circuit.

3. A circuit for simultaneously generating multiple beams using an antenna array having a plurality of antenna array elements, the circuit comprising: a matrix circuit comprising a plurality of hybrid couplers and delay lines, the matrix circuit being coupled between a plurality of loads and the antenna array, and forming a multi-beamforming network; a plurality of first phase shifters coupled between adjacent rows of the matrix circuit; a plurality of second phase shifters, the plurality of second phase shifters being coupled between the matrix circuit and the antenna array; in, Each row of the matrix circuit includes a plurality of hybrid couplers coupled in series in a row direction, wherein each pair of hybrid couplers in the row direction is directly connected by at least one delay line; a top row of the matrix circuit coupled to antenna elements of the antenna array, such that each hybrid coupler of the top row is coupled to the antenna elements of the antenna array via one of the second plurality of phase shifters, and each hybrid coupler of the top row is coupled in a column direction between one of the second plurality of phase shifters and one of the first plurality of phase shifters; A bottom row of the matrix circuit is coupled to a plurality of matched loads, such that each hybrid coupler of the bottom row is coupled between one of the plurality of matched loads and one of the first plurality of phase shifters in a column direction; each phase shifter of the first plurality of phase shifters is coupled between hybrid couplers in adjacent rows in the matrix circuit, such that each hybrid coupler of the matrix circuit is serially coupled to at least one phase shifter of the first plurality of phase shifters in a column direction; and The phase shifters of the first and second pluralities of phase shifters are operable to generate linearly increasing phase differences between adjacent antenna array elements for signals from the matrix circuit.

4. The circuit according to claim 3, wherein The phase of a signal sent from a particular hybrid coupler to a particular antenna element in the antenna array is at least partially controlled by a particular phase shifter of the second plurality of phase shifters, the particular phase shifter being the phase shifter to which the particular hybrid coupler is coupled, the particular hybrid coupler being located in the top row of the matrix circuit.

5. A circuit for simultaneously generating multiple beams using an antenna array having a plurality of antenna array elements, the circuit comprising: a matrix circuit comprising a plurality of hybrid couplers and delay lines, the matrix circuit being coupled between a plurality of loads and the antenna array, and forming a multi-beamforming network; a plurality of phase shifters, wherein each phase shifter is coupled to at least one hybrid coupler; in, Each row of the matrix circuit includes a plurality of hybrid couplers coupled in series in a row direction, wherein each pair of hybrid couplers in the row direction is directly connected by at least one delay line; A bottom row of the matrix circuit is coupled to a plurality of matched loads such that each hybrid coupler of the bottom row is coupled in a column direction between one of the plurality of matched loads and a hybrid coupler of an immediately next row of the matrix circuit; and The phase shifter is used to generate a linearly increasing phase difference between adjacent antenna array elements for a signal from the matrix circuit.

6. The circuit according to claim 5, wherein Each column of the matrix circuit includes a plurality of hybrid couplers, which are serially coupled to at least one phase shifter or at least one hybrid coupler in a column direction.

7. The circuit according to claim 5, wherein The top row of the matrix circuit is coupled to the antenna elements of the antenna array, so that each hybrid coupler in the top row is coupled to the antenna elements of the antenna array through one of the plurality of phase shifters, and each hybrid coupler in the top row is coupled between one of the plurality of phase shifters and the hybrid coupler of the previous row of the matrix circuit in a column direction.

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