A near-field feedback system for dual-polarized millimeter-wave phased arrays

Abstract

The present invention discloses a near-field feedback system for a dual-polarized millimeter-wave phased array, which is composed of a dual-polarized feedback architecture and a dual-polarized radiating antenna located in the antenna plane. The feedback architecture can achieve stable broadband coupling with the radiating antenna without affecting its normal operation. The present invention discloses a self-calibration system for a dual-polarized millimeter-wave phased array, which calculates the near-field coupling coefficient through electromagnetic simulation, calculates the calibration coefficient according to the near-field feedback signal, the near-field coupling coefficient and the reference signal, and realizes self-calibration by digitally controlling the amplitude and phase. The present invention also discloses a digital pre-distortion system for a dual-polarized millimeter-wave phased array, which first collects feedback signals in the far-field main lobe direction for digital pre-distortion training, then collects ideal pre-distortion signals of corresponding polarization and scanning angles in the near field, establishes a corresponding lookup table, and finally uses iterative learning to train the digital pre-distortion function to minimize the difference between the actual near-field signal and the near-field ideal pre-distortion signal, thereby realizing the linearization of the far-field beam.

Description

Technical Field

[0001] The present invention relates to the technical fields of dual-polarization phased array, self-calibration and digital predistortion, and in particular to a near-field feedback system for a dual-polarization millimeter-wave phased array. Background Art

[0002] Compared to sub-6 GHz, millimeter-wave (mmWave) transmissions, due to their large bandwidth, support higher data rates and lower latency. To compensate for the high path loss of mmWave and enable flexible beamforming, the fifth-generation (5G) standard proposes corresponding phased array systems. Many countries and regions have allocated commercial communication bands for the 5G frequency range (FR2). Polarization diversity can easily increase the transmission data rate by using two beams, such as horizontal (H) and vertical (V) polarizations, without increasing system complexity. Dual-polarized mmWave phased array transmitters combine the advantages of both technologies. To improve the performance of dual-polarized phased array transmitters, array self-calibration and digital pre-distortion (DPD) techniques are required to enhance overall transmitter performance. Calibration requires feedback signals to calculate calibration coefficients. Similarly, DPD requires feedback signals to train the DPD coefficients. Traditional phased array calibration methods require placing a reference antenna in the far field of the antenna in an anechoic chamber to obtain feedback signals. This method not only makes on-site calibration impossible but also increases the production and supporting costs of the phased array. Similarly, traditional digital pre-distortion (DPD) feedback architectures for phased array transmitters can be divided into two types based on location: at the power amplifier (PA) and at the far-field antenna. The former significantly increases the design cost of millimeter-wave beamforming chips, while the latter hinders field deployment and high-level integration of phased arrays. Extracting the feedback signal from the antenna's near-field provides a balance between cost and implementation difficulty. Summary of the Invention

[0003] Technical problem: The purpose of the present invention is to provide a feedback structure for a dual-polarization millimeter-wave phased array transmitter to solve the problem that it is difficult to integrate the feedback structure for self-calibration and digital pre-distortion of existing millimeter-wave phased array transmitters, and to achieve calibration and linearization of each channel of the phased array at a lower cost and lower difficulty.

[0004] Technical Solution: To achieve this objective, the present invention provides a near-field feedback system for a dual-polarized millimeter-wave phased array, comprising a multi-layer printed circuit board, an integrated dual-polarized radiating antenna, and a dual-polarized feedback architecture. This dual-polarized millimeter-wave phased array near-field calibration and near-field digital predistortion system are implemented based on the dual-polarized feedback architecture.

[0005] The integrated dual-polarization feedback architecture and the near-field feedback system of the dual-polarization radiating antenna are sequentially arranged from top to bottom through the first substrate, the first adhesive sheet, the middle first metal layer, the second substrate, the second adhesive sheet, the middle second metal layer, the bottom substrate, and the bottom metal layer;

[0006] A top metal layer is provided on the first substrate, including a top cross metal patch, a top circular metal patch, a top square metal patch, an H-polarized circular patch, and a V-polarized circular patch;

[0007] The first middle metal layer is a square patch;

[0008] The dual-polarized radiating antenna passes through the first substrate, the first adhesive sheet, the second substrate, the second adhesive sheet, the bottom substrate, the H-polarized grounded coplanar waveguide, and the V-polarized grounded coplanar waveguide in sequence from top to bottom;

[0009] A top metal layer is provided on the first substrate, including a top cross metal patch, a top circular metal patch, a top square metal patch, an H-polarized circular patch, and a V-polarized circular patch.

[0010] In the dual-polarized radiating antenna, there are four top-level square metal layer patches, and each top-level square metal layer patch is etched with two circular prohibited copper areas, namely, an H-polarized circular prohibited copper area along the y direction and a V-polarized circular prohibited copper area along the x direction; an H-polarized circular patch and a V-polarized circular patch along the y direction are placed in the center of each circular prohibited copper area; the arrangement of each top-level square metal layer patch and the H-polarized circular patch and the V-polarized circular patch are completely centrally symmetrical about the center of the top-level cross metal patch; the middle first metal layer has a total of four square metal pieces, which are connected to the top-level square metal layer patch through H-polarized vias and V-polarized vias.

[0011] In the dual-polarized radiating antenna, the H-polarized grounded coplanar waveguide and the V-polarized grounded coplanar waveguide are connected to the middle first metal layer, the H-polarized circular patch, and the V-polarized circular patch through H-polarized vias and V-polarized vias, respectively. The third metallized vias are circular and evenly distributed around the H-polarized vias and the V-polarized vias.

[0012] In the dual-polarization feedback architecture, the top cross metal patch and the top circular metal layer patch are completely centrally symmetrical about the center of the top cross metal patch. At the same time, there are four corresponding second metal vias, which are placed completely symmetrically around the center of the dual-polarization feedback architecture, and each top circular metal layer patch is connected to the middle second metal layer and the bottom metal layer through the second metal via.

[0013] The dual-polarized millimeter-wave phased array near-field self-calibration system calculates the near-field coupling coefficient through electromagnetic simulation, selects the near-field output signal of only one RF channel as a reference signal, derives a calibration coefficient based on the near-field feedback signal corresponding to only one RF channel being turned on each time, the near-field coupling coefficient, and the reference signal, and calibrates the millimeter-wave phased array by digitally controlling the amplitude and phase of each RF channel.

[0014] The calibration coefficient formula for the dual-polarized millimeter-wave phased array near-field self-calibration system is obtained as follows:

[0015]

[0016] In formula (1), β i is the coupling coefficient between the i-th dual-polarization radiating antenna and the dual-polarization near-field feedback structure, β ref The coupling coefficient between the radiating antenna and the near-field feedback structure corresponding to the reference RF channel, They represent the near-field output signals of the radiating antenna corresponding to the reference RF channel and the i-th radiating antenna, respectively. It is the amplitude and phase calibration coefficient of the i-th RF channel.

[0017] The dual-polarization millimeter-wave phased array near-field self-calibration system includes:

[0018] S1: Obtain the near-field channel coefficient of the i-th H-polarized or V-polarized radiating antenna and feedback structure by performing electromagnetic simulation on the dual-polarized antenna array integrated with the dual-polarized feedback structure;

[0019] S2: Use a vector network analyzer to inject a single-tone signal into the H-polarized or V-polarized input port of the array. Select an appropriate RF channel to turn on, and keep the other channels closed. The power amplifier needs to operate in a linear state, and the signal obtained from the feedback structure is used as the reference signal.

[0020] S3: Open the remaining RF channels one at a time to obtain the output signals corresponding to different H-polarization or V-polarization channels. The power amplifier needs to work in a linear state. The near-field calibration coefficient is obtained by the input signal and the output signal of the near-field feedback structure.

[0021] S4: deriving a calibration coefficient of the radio frequency channel according to the near-field channel coefficient of the i-th H-polarization or V-polarization radio frequency channel and the corresponding near-field calibration coefficient;

[0022] S5: deriving the amplitude and phase control coefficients of each RF channel according to the calibration coefficients of each H-polarization or V-polarization channel, and achieving calibration of each RF channel by controlling the attenuator and phase shifter of each RF channel.

[0023] In the dual-polarized millimeter-wave phased array near-field digital predistortion system, an input signal is beamformed through a beamforming network and an antenna array, and a nonlinear signal of the phased array transmitter is collected in the far-field mainlobe direction as a feedback signal for digital predistortion training. After the far-field digital predistortion is completed, an ideal predistortion signal corresponding to the polarization and scanning angle is collected in the near field, and a lookup table corresponding to the polarization and scanning angle is established. In actual working conditions, an iterative learning method is used to train the digital predistortion function to minimize the difference between the actual near-field nonlinear distortion signal and the near-field ideal predistortion signal. Based on the correlation between the near field and the far field, linearization of the far-field corresponding polarization and scanning angle beam is achieved.

[0024] The dual-polarized millimeter-wave phased array near-field digital predistortion system, after digital predistortion has been performed in the far-field phased array main lobe direction, obtains:

[0025]

[0026] In formula (2), is the main lobe signal of the far-field receiving transmitter, N and M are the number of elements of the array antenna along the x-axis and along the y-axis respectively, is the optimal predistortion signal, is the total nonlinear distortion of the baseband signal, It is the desired ideal input signal;

[0027] Furthermore, the ideal predistortion signal acquired in the near field is:

[0028]

[0029] In formula (3), It is an ideal near-field signal. It is the direct phase and amplitude relationship between the nth and mth RF channels and the near-field feedback structure. is the nonlinear distortion of the nth and mth RF channels.

[0030] In the dual-polarized millimeter-wave phased array near-field digital predistortion system, the iterative learning method trains the digital predistortion function to minimize the difference between the actual near-field nonlinear distortion signal and the near-field ideal predistortion signal, which is:

[0031]

[0032] x k+1 [n] = x k [n]+Γe k [n] (4)

[0033] In formula (4), k is the number of iterations, e k[n] is the difference between the ideal near-field predistortion signal and the actual near-field signal after the kth iteration, is the actual near-field output signal, x k+1 [n],x k [n] is the input signal, and Γ is the learning matrix that controls the convergence speed.

[0034] Furthermore, the linearization of the far field corresponding angle and polarization is:

[0035]

[0036] In formula (5), It is the output signal received in the far-field main lobe direction. It eliminates the nonlinear distortion of the original phased array transmitter beam signal through near-field digital distortion, and can achieve an effect close to far-field beam pre-distortion.

[0037] The dual-polarization millimeter-wave phased array near-field digital predistortion system includes:

[0038] S1: The H-polarized or V-polarized 5G NR broadband baseband signal generated by the baseband signal processing unit is fed into the dual-polarized beamforming network and then fed into the dual-polarized antenna array respectively;

[0039] S2: Based on the far-field air interface reference antenna, it collects nonlinear signals in the main lobe direction of the H-polarized or V-polarized transmit beam, down-converts the signals to obtain far-field feedback signals, and performs digital pre-distortion on the input signals to obtain the ideal pre-distorted input signals.

[0040] S3: Collect the pre-distorted near-field coupling signal in the H-polarization or V-polarization transmit beam direction at the dual-polarization near-field feedback port as the near-field ideal pre-distortion signal, and store the corresponding angles to establish a lookup table;

[0041] S4: The H-polarized or V-polarized 5G NR broadband baseband signal generated by the baseband signal processing unit is re-fed into the dual-polarized beamforming network and then fed into the dual-polarized antenna array accordingly.

[0042] S5: The near-field coupling signal in the direction of the H-polarized or V-polarized transmit beam after pre-distortion is collected at the dual-polarized near-field feedback port as the near-field nonlinear distortion signal. The DPD function is trained using an iterative learning control method to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal pre-distortion signal.

[0043] S6: The H-polarized or V-polarized baseband signal after near-field pre-distortion processing is fed back into the 5G millimeter-wave active phased array antenna array to achieve far-field linearization of the transmit beam signal.

[0044] Beneficial effects: The present invention discloses a feedback structure for a dual-polarization millimeter-wave phased array transmitter, which has the following beneficial effects compared with the prior art:

[0045] 1) The feedback structure of the dual-polarized millimeter-wave phased array transmitter provided by the present invention adopts a combination of cross patches and circular patches. The dual-polarized antenna array uses a dual-polarized antenna with stacked patches and coaxial feed, and utilizes coupling with the radiating antenna to obtain feedback signals. In the broadband (24-27GHz) range, relatively stable vertically polarized and horizontally polarized coupled signals can be obtained. This near-field feedback architecture can achieve high integration with the antenna structure, and its structure has almost no effect on the radiation performance of the original array antenna. This hardware design can be extended to large-scale dual-polarized millimeter-wave phased arrays.

[0046] 2) The present invention provides a near-field self-calibration solution for a dual-polarized millimeter-wave phased array transmitter based on a feedback architecture. This solution extracts calibration coefficients for the RF channels using feedback signals from the near-field feedback architecture and near-field coupling coefficients derived from electromagnetic simulation. This calibration coefficients are then used to digitally control the amplitude and phase of each RF channel to achieve phased array self-calibration. Compared to traditional far-field calibration, this solution not only eliminates the need for additional test antennas but also allows for on-site recalibration at any time, significantly reducing the cost and time required for dual-polarized millimeter-wave phased array calibration.

[0047] 3) The present invention provides a near-field digital predistortion scheme for a dual-polarized millimeter-wave phased array transmitter based on a feedback architecture. A lookup table of ideal predistortion signals corresponding to scanning angles and polarizations is obtained in the near field through pre-far-field digital predistortion. The digital predistortion function is trained by an iterative learning method to achieve linearization of the phased array transmitter beam. The proposed near-field feedback structure greatly reduces the design cost and difficulty of the RF end compared to traditional power amplifier coupling. Compared with traditional far-field reference antenna feedback, only far-field reference antenna far-field digital predistortion is required in advance, and no far-field reference antenna is required in actual operation. This feedback system can achieve integration with the millimeter-wave phased array and relatively good linearization performance with low design complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the structure layering of the dual-polarized antenna array and feedback architecture of the present invention;

[0049] Figure 2 A structural side view of the dual-polarized antenna array and feedback architecture of the present invention;

[0050] Figure 3 Schematic diagram of the structure of the top metal layer of the dual-polarized antenna array and feedback architecture of the present invention;

[0051] Figure 4 Schematic diagram of the structure of the first metal layer of the dual-polarized antenna array and feedback architecture of the present invention;

[0052] Figure 5Schematic diagram of the structure of the second metal layer of the dual-polarized antenna array and feedback architecture of the present invention;

[0053] Figure 6 Schematic diagram of the structure of the bottom metal layer of the dual-polarized antenna array and feedback architecture of the present invention;

[0054] Figure 7 is the return loss curve (H polarization / V polarization) of the dual-polarization antenna array unit of the present invention;

[0055] Figure 8 is a return loss curve of the dual-polarization feedback architecture of the present invention;

[0056] Figure 9 The direct coupling coefficient (H polarization / V polarization) between the dual-polarization feedback architecture of the present invention and each antenna unit;

[0057] Figure 10 The simulated radiation patterns of the vertically polarized radiation antenna array of the present invention with the beam pointing in the z direction in the xoz (E plane) and yoz (H plane) planes at 26 GHz (with or without feedback structure);

[0058] Figure 11 The simulated radiation patterns of the horizontally polarized radiation antenna array of the present invention with the beam pointing in the z direction in the yoz (E plane) and xoz (H plane) planes at 26 GHz (with or without feedback structure);

[0059] Figure 12 This is a system block diagram for the specific implementation of the present invention (dual-polarization millimeter-wave phased array near-field calibration and digital predistortion system);

[0060] Figure 13 Directivity diagram of xoz at 26 GHz with the vertically polarized radiating antenna array beam pointing to -30°, 0°, and +30° during the specific implementation of the present invention (far-field calibration and near-field calibration);

[0061] Figure 14 The directional pattern of the horizontally polarized radiating antenna array beam pointing to -30°, 0° and +30° at 26GHz (far-field calibration and near-field calibration) during the specific implementation of the present invention;

[0062] Figure 15The figures are power spectral density curves of H polarization and V polarization at 26 GHz corresponding to three azimuth scanning angles during the specific implementation of the present invention; wherein: a is a curve diagram of H polarization when the beam is scanned and the observation angle is -30°; b is a curve diagram of V polarization when the beam is scanned and the observation angle is -30°; c is a curve diagram of H polarization when the beam is scanned and the observation angle is 0°; d is a curve diagram of V polarization when the beam is scanned and the observation angle is 0°; e is a curve diagram of H polarization when the beam is scanned and the observation angle is +30°; and f is a curve diagram of V polarization when the beam is scanned and the observation angle is +30°.

[0063] Marked in the figure are: top cross metal patch 1, top circular metal layer patch 2, top square metal layer patch 3, H-polarized circular patch 4, V-polarized circular patch 5, first layer substrate 6, first layer adhesive patch 7, middle first metal layer 8, H-polarized via 9, V-polarized via 10, second layer substrate 11, second layer adhesive patch 12, first metal via 13, second metal via 14, middle second metal layer 15, bottom substrate 16, H-polarized circular metal hole ring 17, V-polarized circular metal hole ring 18, third metal via 19, fourth metal via 20, square metal hole 21, circular metal hole 22, H-polarized grounded coplanar waveguide 23, V-polarized grounded coplanar waveguide 24, bottom metal layer 25. DETAILED DESCRIPTION

[0064] In order to better understand the purpose, structure and function of the present invention, a dual-polarization phased array with an integrated dual-polarization feedback structure in the present invention is further described in detail below with reference to the accompanying drawings.

[0065] The present invention provides a near-field feedback system for a dual-polarized millimeter-wave phased array, comprising a multi-layer printed circuit board, an integrated dual-polarized radiating antenna, and a dual-polarized feedback architecture. The dual-polarized millimeter-wave phased array near-field calibration and near-field digital predistortion system are implemented based on the dual-polarized feedback architecture.

[0066] The integrated dual-polarization feedback architecture and the near-field feedback system of the dual-polarization radiating antenna are sequentially arranged from top to bottom through the first substrate 6, the first adhesive sheet 7, the middle first metal layer 8, the second substrate 11, the second adhesive sheet 12, the middle second metal layer 15, the bottom substrate 16, and the bottom metal layer 25;

[0067] A top metal layer is provided on the first substrate 6, including a top cross metal patch 1, a top circular metal patch 2, a top square metal patch 3, an H-polarized circular patch 4, and a V-polarized circular patch 5;

[0068] The middle first metal layer 8 is a square patch;

[0069] The dual-polarized radiating antenna passes through the first substrate 6, the first adhesive sheet 7, the second substrate 11, the second adhesive sheet 12, the bottom substrate 16, the H-polarized grounded coplanar waveguide 23, and the V-polarized grounded coplanar waveguide 24 in sequence from top to bottom;

[0070] A top metal layer is provided on the first substrate 6 , including a top cross metal patch 1 , a top circular metal patch 2 , a top square metal patch 3 , an H-polarized circular patch 4 , and a V-polarized circular patch 5 .

[0071] Furthermore, there are four square metal sheets on the top layer, each of which is etched with two circular copper-free zones: an H-polarized circular copper-free zone along the y-direction and a V-polarized circular copper-free zone along the x-direction. A circular metal sheet with H polarization along the y-direction and a circular metal sheet with V polarization along the x-direction are placed in the center of each circular copper-free zone. The arrangement of each square patch and circular metal sheet is completely centrosymmetrical about the center of the cross metal patch.

[0072] Furthermore, the middle first metal layer has a total of four square metal sheets, which are connected to the top square metal sheet through H-polarized metal vias and V-polarized metal vias.

[0073] Furthermore, H-polarized and V-polarized grounded coplanar waveguides are provided on the bottom metal layer as H-polarized and V-polarized excitation feed lines, respectively, which are connected to the H-polarized and V-polarized radiating antennas through H-polarized and V-polarized metalized vias.

[0074] Furthermore, the top cross metal sheet is placed at the geometric center of the 2×2 dual-polarization phased array and is connected to the feed structure through metallized vias. Four circular metal sheets are arranged around the cross metal sheet and are connected to the middle first metal layer and the bottom metal layer through metallized vias.

[0075] The present invention proposes a dual-polarization millimeter-wave phased array near-field calibration system and a dual-polarization millimeter-wave phased array near-field digital predistortion system based on a dual-polarization near-field feedback structure.

[0076] The dual-polarization millimeter wave phased array near-field calibration system of the present invention includes electromagnetic simulation near-field channel coefficients, reference channel selection, calibration coefficient calculation and digital amplitude and phase control.

[0077] Furthermore, the coupling coefficient β between the i-th radiating antenna and the near-field feedback structure is obtained through HFSS electromagnetic simulation. i .

[0078] Furthermore, a suitable RF channel is selected to be turned on (the other channels are closed), the power amplifier needs to work in a linear state, and the signal obtained from the feedback structure is recorded as the reference output signal. Where a represents the amplitude, Indicates phase.

[0079] Furthermore, the remaining RF channels are opened one by one (the remaining channels are in the closed state) to obtain the output signals corresponding to different channels. The power amplifier needs to work in a linear state, and the near-field calibration coefficient is obtained through the input signal and the output signal of the near-field feedback structure.

[0080]

[0081] In formula (2), β i is the coupling coefficient between the ith radiating antenna and the near-field feedback structure, β ref The coupling coefficient between the radiating antenna and the near-field feedback structure corresponding to the reference channel, They represent the output signals of the radiating antenna corresponding to the reference channel and the i-th radiating antenna, respectively. It is the amplitude and phase calibration coefficient of each channel.

[0082] Furthermore, the amplitude and phase of each radio frequency channel are digitally controlled according to the calibration coefficient to achieve self-calibration of each radio frequency channel of the dual-polarization millimeter wave phased array.

[0083] The dual-polarization millimeter-wave phased array near-field calibration system of the present invention comprises the following steps:

[0084] S1: Obtain the near-field channel coefficients of the i-th radiating antenna (H polarization / V polarization) and the dual-polarization feedback structure by performing electromagnetic simulation on the dual-polarization antenna array integrated with the dual-polarization feedback structure;

[0085] S2: Use a vector network analyzer to inject a single-tone signal into the array's input port (H polarization / V polarization), select an appropriate RF channel to open (the rest of the channels are closed), and use the signal obtained from the feedback structure as the reference signal;

[0086] S3: Turn on the remaining RF channels one by one (the other channels are in the closed state), obtain the output signals corresponding to different channels, and obtain the near-field calibration coefficients based on the input signals and the output signals of the near-field feedback structure;

[0087] S4: deriving a calibration coefficient of the radio frequency channel according to the near-field channel coefficient of the i-th radio frequency channel (H polarization / V polarization) and the corresponding near-field calibration coefficient;

[0088] S5: derive the amplitude and phase control coefficients of each RF channel based on the calibration coefficients (H polarization / V polarization) of each channel, and calibrate each RF channel by controlling the attenuator and phase shifter of each RF channel.

[0089] The dual-polarization phased array near-field digital pre-distortion system for dual-polarization phased array transmitters includes three parts: far-field digital pre-distortion training, near-field ideal pre-distortion signal extraction, and near-field digital pre-distortion training. The input signal forms a free-space beam through the beamforming network and antenna array, and the transmitter's nonlinear signal is collected in the far-field mainlobe direction as a feedback signal for digital pre-distortion training. After completing the far-field digital pre-distortion, the ideal pre-distortion signal corresponding to the polarization and scanning angle is collected in the near field, and a lookup table corresponding to the polarization and scanning angle is established. In actual working conditions, the DPD function is trained using an iterative learning method to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal pre-distortion signal, thereby achieving linearization of the far-field corresponding polarization and scanning angle beam.

[0090] Furthermore, the nonlinear signal of the transmitter is collected in the far-field main lobe direction and used as a feedback signal for digital predistortion to obtain:

[0091]

[0092] In formula (2), is the main lobe signal of the far-field receiving transmitter, N and M are the number of elements of the array antenna along the x-axis and along the y-axis respectively, is the optimal predistortion signal, is the total nonlinear distortion of the baseband signal, is the desired ideal input signal.

[0093] Furthermore, the ideal predistortion signal acquired in the near field is:

[0094]

[0095] In formula (3), It is an ideal near-field signal. It is the direct phase and amplitude relationship between the nth and mth RF channels and the near-field feedback structure. is the nonlinear distortion of the nth and mth RF channels.

[0096] Furthermore, the iterative learning method trains the DPD function to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal predistortion signal to be:

[0097]

[0098] x k+1 [n] = x k [n]+Γe k [n] (4)

[0099] In formula (4), k is the number of iterations, e k[n] is the difference between the ideal near-field predistortion signal and the actual near-field signal after the kth iteration, is the actual near-field output signal, x k+1 [n],x k [n] is the input signal, and Γ is the learning matrix that controls the convergence speed.

[0100] Furthermore, the linearization of the far field corresponding angle and polarization is:

[0101]

[0102] In formula (5), It is the output signal received in the far-field main lobe direction. It eliminates the nonlinear distortion of the original beam signal through near-field digital distortion, and can achieve an effect close to far-field beam pre-distortion.

[0103] The dual-polarized millimeter-wave phased array near-field digital predistortion solution system of the present invention includes a dual-polarized beamforming network, a dual-polarized antenna array with an integrated dual-polarized feedback structure, a baseband signal processing unit capable of implementing transmit nonlinear modeling and digital predistortion, and a reference antenna for a far-field air interface. The solution includes the following steps:

[0104] S1: The (H-polarization / V-polarization) 5G NR broadband baseband signal generated by the baseband signal processing unit is fed into the dual-polarization beamforming network and correspondingly fed into the dual-polarization antenna array.

[0105] S2: Based on the far-field air interface reference antenna, it collects the (H-polarization / V-polarization) nonlinear signal in the main lobe direction of the transmit beam, down-converts it to obtain the far-field feedback signal, and performs digital pre-distortion to obtain the ideal pre-distorted input signal;

[0106] S3: The near-field coupling signal (H polarization / V polarization) in the transmit beam direction after predistortion is collected at the dual-polarization near-field feedback port as the near-field ideal predistortion signal, and stored corresponding to the angle and polarization.

[0107] S4: The (H-polarization / V-polarization) 5G NR wideband baseband signal generated by the baseband signal processing unit is re-fed into the dual-polarization beamforming network and then fed into the dual-polarization antenna array accordingly.

[0108] S5: The pre-distorted (H-polarization / V-polarization) near-field coupling signal in the transmit beam direction is collected at the dual-polarization near-field feedback port as the near-field nonlinear distortion signal. The digital predistortion function is trained using an iterative learning method to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal predistortion signal.

[0109] S6: The baseband signal (H polarization / V polarization) after near-field pre-distortion processing is fed back into the 5G millimeter-wave active phased array antenna array to achieve far-field linearization of the transmitted beam signal.

[0110] The present invention discloses a dual-polarization phased array with an integrated dual-polarization feedback structure. Figure 1 and Figure 2 As shown, the dual-polarization antenna unit includes an upper radiation structure and a lower unit feeding structure. The dual-polarization feedback structure includes an upper coupling structure and a lower feeding structure.

[0111] like Figure 3 As shown, on the top metal layer, four top circular metal layer patches 2 are symmetrically distributed along the geometric center of the top cross metal patch 1. Two circular prohibited copper areas are etched on each square metal patch, namely the H-polarized circular prohibited copper area along the y direction and the V-polarized circular prohibited copper area along the x direction. In the center of each circular prohibited copper area, an H-polarized circular patch 4 in the y direction and a V-polarized circular patch 5 in the x direction are placed. The two polarized radiations are excited by the H-polarized via 9 and the V-polarized via 10, respectively. The subarray structure of the rotating feed can suppress the cross-polarization of the far-field beam. The top cross metal patch 1 is distributed at the geometric center of the array, and an arc is etched near the center to adjust the resonance point. Connected by the first metal via 13 and the circular metal hole 22, there are four top circular metal layer patches 2 around the cross metal sheet, which are connected to the second metal layer and the bottom metal layer through the second metal via 14. The setting of the top circular metal layer patch 2 is conducive to maintaining the stability of coupling in the broadband and adjusting the return loss of the feedback structure, which is one of the key points to achieve broadband feedback.

[0112] like Figure 4 As shown, on the middle first metal layer, four square middle first metal layers 8 are symmetrically distributed around the geometric center of the top cross metal patch 1, which are respectively connected to the H-polarized circular patch 4 placed in the y direction and the V-polarized circular patch 5 along the x direction by H-polarized vias 9 and V-polarized vias 10, and are also connected to the H-polarized grounded coplanar waveguide 23 and the V-polarized grounded coplanar waveguide 24.

[0113] like Figure 5 and Figure 6As shown, eight circular copper-free zones are etched in the second metal layer. These eight zones are distributed around the periphery, namely, H-polarized circular metal rings 17 along the y-direction and V-polarized circular metal rings 18 along the x-direction. H-polarized grounded coplanar waveguides 23 and V-polarized grounded coplanar waveguides 24 are provided in the bottom metal layer to transmit electromagnetic energy through H-polarized vias 9 and V-polarized vias 10, respectively. The feedback structure directly feeds circular metal vias 22 through first metal vias 13. Second metal vias 14 connect the top and bottom metal layers. Square metal vias 21 and circular metal vias 22 are used to adjust the impedance matching of the output feedback signal.

[0114] like Figure 7-11 As shown, Figure 7 It shows that the H-polarized and V-polarized radiating antennas have an impedance bandwidth of 24-28 GHz (|S11|<-10dB), covering the 5G N258 frequency band (24.25-27.5 GHz). Figures 8 to 9 The display feedback architecture can maintain a coupling degree of -13.5-15.5dB for H-polarized signals and V-polarized signals within a bandwidth of 24-27GHz, and the coupling fluctuation within the bandwidth is small. Figure 10-11 The feedback structure demonstrates a minimal impact on the array's radiation performance, but does not affect the proper functioning of the radiating antenna. Combined with the system's multi-layer PCB integrated feed scheme, its potential for application in dual-polarized millimeter-wave phased arrays is foreseeable. In particular, its relatively simple design maintains stable coupling across a wide bandwidth, suggesting potential application in dual-polarized millimeter-wave phased array communications technology across other frequency bands.

[0115] The block diagram of the feedback system is as follows Figure 12 As shown in the figure, the feedback system is demonstrated using a 2×2 dual-polarization millimeter-wave phased array RF front-end as an example. The feedback signal is collected and down-converted through the dual-polarization feedback structure, and then signal processing is performed to optimize the system performance of the millimeter-wave phased array. To further illustrate the significance of the feedback system, two specific implementation examples are used to describe it, namely the near-field calibration system of the dual-polarization millimeter-wave phased array and the digital predistortion system of the dual-polarization millimeter-wave phased array transmitter.

[0116] This specific embodiment discloses a near-field calibration system for a dual-polarization millimeter-wave phased array based on a dual-polarization feedback structure. Figure 12 As shown, it includes electromagnetic simulation near-field channel coefficients, reference channel selection, calibration coefficient calculation and digital control of amplitude and phase. Electromagnetic simulation obtains the coupling coefficient β between the i-th RF channel and the feedback end i , select the appropriate channel as the reference RF channel and ensure that the power amplifier works in a linear state, and the output signal is recorded as the reference signal Open each RF channel (H polarization / V polarization) separately, and according to the output signal of each RF channel The calibration coefficient of each RF channel is calculated by the reference signal and the near-field coupling coefficient. The amplitude and phase of each channel are digitally controlled according to the calibration coefficient to achieve channel calibration, as follows:

[0117]

[0118] The specific method includes the following steps:

[0119] S1: Obtain the near-field channel coefficients of the i-th radiating antenna (H polarization / V polarization) and the feedback structure by performing electromagnetic simulation on a dual-polarization antenna array with integrated dual-polarization feedback structure;

[0120] S2: Use a vector network analyzer to inject a single-tone signal into the array's input port (H polarization / V polarization), select an appropriate RF channel to open (the rest of the channels are closed), and use the signal obtained from the feedback structure as the reference signal;

[0121] S3: Turn on the remaining RF channels one by one (the other channels are in the off state) to obtain the output signals corresponding to different channels (H polarization / V polarization), and obtain the near-field calibration coefficient based on the input signal and the output signal of the near-field feedback structure;

[0122] S4: deriving a calibration coefficient of the radio frequency channel according to the near-field channel coefficient of the i-th radio frequency channel (H polarization / V polarization) and the corresponding near-field calibration coefficient;

[0123] S5: deriving the amplitude and phase control coefficients of each RF channel according to the calibration coefficients (H polarization / V polarization) of each channel, and achieving calibration of each RF channel by controlling the attenuator and phase shifter of each RF channel.

[0124] The effect of dual-polarization near-field calibration is compared with the traditional far-field calibration method. The dual-polarization near-field calibration method proposed by the present invention can achieve performance close to that of traditional far-field calibration. In the process of implementing near-field calibration, no far-field reference antenna is required at all, which solves the pain points of traditional calibration, such as being expensive, time-consuming, and unable to be calibrated on-site. This greatly reduces the calibration cost of millimeter-wave phased arrays, which is of great significance for future commercial millimeter-wave phased arrays. The directional patterns of near-field calibration and far-field calibration are compared as follows: Figure 13-14 express.

[0125] This specific implementation scheme also discloses a dual-polarization phased array near-field digital pre-distortion scheme for a dual-polarization phased array transmitter, which includes three parts: far-field digital pre-distortion training, near-field ideal pre-distortion signal extraction, and near-field distortion pre-distortion training. The input signal is formed into a beam through a beamforming network and an antenna array, and the nonlinear signal of the transmitter is collected in the far-field main lobe direction as a feedback signal for digital pre-distortion training. After the far-field digital pre-distortion is completed, the ideal pre-distortion signal corresponding to the polarization and scanning angle is collected in the near field, and a lookup table corresponding to the polarization and scanning angle is established. In actual working conditions, the digital pre-distortion function is trained using an iterative learning method to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal pre-distortion signal, thereby achieving linearization of the far-field corresponding polarization and scanning angle beam.

[0126] Furthermore, the nonlinear signal of the transmitter is collected in the far-field main lobe direction and used as a feedback signal for digital predistortion to obtain:

[0127]

[0128] In formula (2), is the main lobe signal of the far-field receiving transmitter, N and M are the number of elements of the array antenna along the x-axis and along the y-axis respectively, is the optimal predistortion signal, is the total nonlinear distortion of the baseband signal, is the desired ideal input signal.

[0129] Furthermore, the ideal predistortion signal acquired in the near field is:

[0130]

[0131] In formula (3), It is an ideal near-field signal. It is the direct phase and amplitude relationship between the nth and mth RF channels and the near-field feedback structure. is the nonlinear distortion of the nth and mth RF channels.

[0132] Furthermore, the iterative learning method trains the DPD function to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal predistortion signal to be:

[0133]

[0134] x k+1 [n] = x k [n]+Γe k [n] (4)

[0135] In formula (4), k is the number of iterations, e k[n] is the direct difference between the ideal near-field signal and the actual near-field signal after the kth iteration, is the actual near-field output signal, x k+1 [n],x k [n] is the input signal, and Γ is the learning matrix that controls the convergence speed.

[0136] Furthermore, the linearization of the far field corresponding angle and polarization is:

[0137]

[0138] In formula (5), It is the output signal received in the far-field main lobe direction. It eliminates the nonlinear distortion of the original beam signal through near-field digital distortion, and can achieve an effect close to far-field beam pre-distortion.

[0139] The dual-polarization phased array near-field digital predistortion method of the present invention includes a dual-polarization beamforming network, a dual-polarization antenna array with an integrated dual-polarization feedback structure, a baseband signal processing unit capable of implementing nonlinear modeling and digital predistortion of the transmit RF channel, and a reference antenna for the far-field air interface. The method includes the following steps:

[0140] S1: The (H-polarization / V-polarization) 5G NR broadband baseband signal generated by the baseband signal processing unit is fed into the dual-polarization beamforming network and correspondingly fed into the dual-polarization antenna array.

[0141] S2: Based on the far-field air interface reference antenna, it collects the (H-polarization / V-polarization) nonlinear signal in the main lobe direction of the transmit beam, down-converts it to obtain the far-field feedback signal, and digitally predistorts the input signal to obtain the ideal predistorted input signal;

[0142] S3: The near-field coupling signal (H polarization / V polarization) in the transmit beam direction after predistortion is collected at the dual-polarization near-field feedback port as the near-field ideal predistortion signal and stored at the corresponding angle.

[0143] S4: The (H-polarization / V-polarization) 5G NR wideband baseband signal generated by the baseband signal processing unit is re-fed into the dual-polarization beamforming network and then fed into the dual-polarization antenna array accordingly.

[0144] S5: The pre-distorted (H-polarization / V-polarization) near-field coupling signal in the transmit beam direction is collected at the dual-polarization near-field feedback port as the near-field nonlinear distortion signal. The digital predistortion function is trained using an iterative learning method to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal predistortion signal.

[0145] S6: The baseband signal (H polarization / V polarization) after near-field pre-distortion processing is fed back into the 5G millimeter-wave active phased array antenna array to achieve far-field linearization of the transmitted beam signal.

[0146] Taking the 5G NR input signal with a bandwidth of 100MHz as an example, the dual-polarization near-field digital pre-distortion technology proposed in this invention achieves a good beam linearization effect. The power spectrum density of the far-field beam main lobe direction before and after linearization of the H-polarization and V-polarization arrays at different azimuth scanning angles (-30°, 0°, +30°) is as follows: Figure 14 As shown in the figure, it can be seen that dual-polarization near-field digital pre-distortion technology can achieve relatively good linearization effects. Compared with traditional millimeter-wave phased array linearization methods, it can realize the integration of feedback architecture and millimeter-wave phased array transmitter with lower design difficulty, thus facilitating its application in larger-scale dual-polarization millimeter-wave phased array communication systems.

[0147] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A near-field feedback system for a dual-polarized millimeter-wave phased array, comprising a multi-layer printed circuit board, characterized in that: It includes an integrated dual-polarization radiating antenna and a dual-polarization feedback architecture, and implements a dual-polarization millimeter-wave phased array near-field calibration and near-field digital pre-distortion system based on the dual-polarization feedback architecture; The integrated dual-polarization feedback architecture and the near-field feedback system of the dual-polarization radiating antenna are sequentially arranged from top to bottom through a first substrate (6), a first adhesive sheet (7), a middle first metal layer (8), a second substrate (11), a second adhesive sheet (12), a middle second metal layer (15), a bottom substrate (16), and a bottom metal layer (25); A top metal layer is provided on the first substrate (6), including a top cross metal patch (1), a top circular metal patch (2), a top square metal patch (3), an H-polarized circular patch (4), and a V-polarized circular patch (5); The first intermediate metal layer (8) is a square patch; The dual-polarized radiating antenna passes through the first substrate (6), the first adhesive sheet (7), the second substrate (11), the second adhesive sheet (12), the bottom substrate (16), the H-polarized grounded coplanar waveguide (23), and the V-polarized grounded coplanar waveguide (24) in sequence from top to bottom; A top metal layer is provided on the first substrate (6), including a top cross metal patch (1), a top circular metal patch (2), a top square metal patch (3), an H-polarized circular patch (4), and a V-polarized circular patch (5); In the dual-polarized radiation antenna, there are four top-level square metal layer patches (3), and each top-level square metal layer patch (3) is etched with two circular prohibited copper-plating areas, namely, an H-polarized circular prohibited copper-plating area along the y direction and a V-polarized circular prohibited copper-plating area along the x direction; an H-polarized circular patch (4) and a V-polarized circular patch (5) along the x-direction and the y-direction are placed in the center of each circular prohibited copper-plating area; each top-level square metal layer patch (3) and the H-polarized circular patch (4) and the V-polarized circular patch (5) are arranged completely symmetrically with respect to the center of the top-level cross metal patch (1); the middle first metal layer (8) has four square metal pieces, which are connected to the top-level square metal layer patch (3) through an H-polarized via hole (9) and a V-polarized via hole (10); In the dual-polarization feedback architecture, the top cross metal patch (1) and the top circular metal layer patch (2) are completely centrally symmetrical about the center of the top cross metal patch (1), and there are four corresponding second metal vias (14), which are completely symmetrically placed around the center of the dual-polarization feedback architecture, and each top circular metal layer patch (2) is connected to the middle second metal layer (15) and the bottom metal layer (25) through the second metal via (14).

2. The near-field feedback system for dual-polarization millimeter-wave phased array according to claim 1, characterized in that: In the dual-polarized radiating antenna, the H-polarized grounded coplanar waveguide (23) and the V-polarized grounded coplanar waveguide (24) are connected to the middle first metal layer (8), the H-polarized circular patch (4), and the V-polarized circular patch (5) through the H-polarized via (9) and the V-polarized via (10), respectively; and the third metalized via (19) is uniformly distributed in a circular shape around the H-polarized via (9) and the V-polarized via (10).

3. The near-field feedback system for dual-polarization millimeter-wave phased array according to claim 1, characterized in that: The dual-polarized millimeter-wave phased array near-field self-calibration system calculates the near-field coupling coefficient through electromagnetic simulation, selects the near-field output signal of only one RF channel as the reference signal, derives the calibration coefficient based on the near-field feedback signal corresponding to only one RF channel being turned on each time, the near-field coupling coefficient, and the reference signal, and calibrates the millimeter-wave phased array by digitally controlling the amplitude and phase of each RF channel. The calibration coefficient formula for the dual-polarized millimeter-wave phased array near-field self-calibration system is obtained as follows: In formula (1), β i is the coupling coefficient between the i-th dual-polarization radiating antenna and the dual-polarization near-field feedback structure, β ref The coupling coefficient between the radiating antenna and the near-field feedback structure corresponding to the reference RF channel, They represent the near-field output signals of the radiating antenna corresponding to the reference RF channel and the i-th radiating antenna, respectively. It is the amplitude and phase calibration coefficient of the i-th RF channel.

4. The near-field feedback system for dual-polarization millimeter-wave phased array according to claim 3, characterized in that: The dual-polarization millimeter-wave phased array near-field self-calibration system includes: S1: Obtain the near-field channel coefficient of the i-th H-polarized or V-polarized radiating antenna and feedback structure by performing electromagnetic simulation on the dual-polarized antenna array integrated with the dual-polarized feedback structure; S2: Use a vector network analyzer to inject a single-tone signal into the H-polarized or V-polarized input port of the array. Select an appropriate RF channel to turn on, and keep the other channels closed. The power amplifier needs to operate in a linear state, and the signal obtained from the feedback structure is used as the reference signal. S3: Open the remaining RF channels one at a time to obtain the output signals corresponding to different H-polarization or V-polarization channels. The power amplifier needs to work in a linear state. The near-field calibration coefficient is obtained by the input signal and the output signal of the near-field feedback structure. S4: deriving a calibration coefficient of the radio frequency channel according to the near-field channel coefficient of the i-th H-polarization or V-polarization radio frequency channel and the corresponding near-field calibration coefficient; S5: deriving the amplitude and phase control coefficients of each RF channel according to the calibration coefficients of each H-polarization or V-polarization channel, and achieving calibration of each RF channel by controlling the attenuator and phase shifter of each RF channel.

5. The near-field feedback system for a dual-polarized millimeter-wave phased array according to claim 1, wherein: In the dual-polarized millimeter-wave phased array near-field digital predistortion system, an input signal is beamformed through a beamforming network and an antenna array, and a nonlinear signal of the phased array transmitter is collected in the far-field mainlobe direction as a feedback signal for digital predistortion training. After the far-field digital predistortion is completed, an ideal predistortion signal corresponding to the polarization and scanning angle is collected in the near field, and a lookup table corresponding to the polarization and scanning angle is established. In actual working conditions, an iterative learning method is used to train the digital predistortion function to minimize the difference between the actual near-field nonlinear distortion signal and the near-field ideal predistortion signal. Based on the correlation between the near field and the far field, linearization of the far-field corresponding polarization and scanning angle beam is achieved.

6. The near-field feedback system for a dual-polarized millimeter-wave phased array according to claim 5, characterized in that: The dual-polarized millimeter-wave phased array near-field digital predistortion system, after digital predistortion has been performed in the far-field phased array main lobe direction, obtains: In formula (2), is the main lobe signal of the far-field receiving transmitter, N and M are the number of elements of the array antenna along the x-axis and along the y-axis respectively, is the optimal predistortion signal, is the total nonlinear distortion of the baseband signal, It is the desired ideal input signal; Furthermore, the ideal predistortion signal acquired in the near field is: In formula (3), It is an ideal near-field signal. It is the direct phase and amplitude relationship between the nth and mth RF channels and the near-field feedback structure. is the nonlinear distortion of the nth and mth RF channels.

7. The near-field feedback system for a dual-polarized millimeter-wave phased array according to claim 6, wherein: In the dual-polarized millimeter-wave phased array near-field digital predistortion system, the iterative learning method trains the digital predistortion function to minimize the difference between the actual near-field nonlinear distortion signal and the near-field ideal predistortion signal, which is: x k+1 [n]=x k [n]+Γe k [n] (4) In formula (4), k is the number of iterations, e k [n] is the difference between the ideal near-field predistortion signal and the actual near-field signal after the kth iteration, is the actual near-field output signal, x k+1 [n],x k [n] is the input signal, Γ is the learning matrix that controls the convergence speed; Furthermore, the linearization of the far field corresponding angle and polarization is: In formula (5), It is the output signal received in the far-field main lobe direction. It eliminates the nonlinear distortion of the original phased array transmitter beam signal through near-field digital distortion, and can achieve an effect close to far-field beam pre-distortion.

8. The near-field feedback system for dual-polarization millimeter-wave phased array according to claim 7, characterized in that: The dual-polarization millimeter-wave phased array near-field digital predistortion system includes: S1: The H-polarized or V-polarized 5GNR broadband baseband signal generated by the baseband signal processing unit is fed into the dual-polarized beamforming network and then fed into the dual-polarized antenna array respectively; S2: Based on the far-field air interface reference antenna, it collects nonlinear signals in the main lobe direction of the H-polarized or V-polarized transmit beam, down-converts the signals to obtain far-field feedback signals, and performs digital pre-distortion on the input signals to obtain the ideal pre-distorted input signals. S3: Collect the pre-distorted near-field coupling signal in the H-polarization or V-polarization transmit beam direction at the dual-polarization near-field feedback port as the near-field ideal pre-distortion signal, and store the corresponding angles to establish a lookup table; S4: The H-polarized or V-polarized 5GNR broadband baseband signal generated by the baseband signal processing unit is re-fed into the dual-polarized beamforming network and correspondingly fed into the dual-polarized antenna array; S5: The near-field coupling signal in the direction of the H-polarized or V-polarized transmit beam after pre-distortion is collected at the dual-polarized near-field feedback port as the near-field nonlinear distortion signal. The DPD function is trained using an iterative learning control method to minimize the difference between the near-field nonlinear distortion signal and the near-field ideal pre-distortion signal. S6: The H-polarized or V-polarized baseband signal after near-field pre-distortion processing is fed back into the 5G millimeter-wave active phased array antenna array to achieve far-field linearization of the transmit beam signal.

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