Electromagnetic characteristic optimization method for radio frequency signal transmission channel in tile-type phased array system

Abstract

The invention discloses a method for optimizing electromagnetic characteristics of a radio frequency signal transmission channel in a tile type phased array system, and belongs to the field of radio frequency and microwaves. The method comprises the following steps: establishing a three-dimensional electromagnetic field numerical calculation model of a radio frequency signal transmission channel; simulating and analyzing TDR parameters of the radio frequency signal transmission channel, and calculating an impedance abrupt change point of the signal transmission channel; and optimizing the characteristic impedance of the impedance abrupt change point based on an anti-pad, a trapezoidal pad and a reference plane slotting compensation mode, and completing optimization of the radio frequency signal transmission channel. The signal integrity of the electronic equipment and the system can be improved by adopting a mode of combining simulation analysis and experimental test.

Description

Technical Field

[0001] This invention relates to the fields of radio frequency and microwave, and in particular to a method for optimizing the electromagnetic characteristics of radio frequency signal transmission channels in a tile-type phased array system. Background Technology

[0002] Tile-type phased array antennas are one of the key technologies widely used in modern radar and communication systems. The tile structure integrates a large number of high-density transceiver components, high-speed digital control circuits, power management units, and multi-layer high-density interconnect substrates into tiny "tiles" and assembles them tightly. This high-density integration leads to an increasingly complex internal electromagnetic environment and significantly enhanced electromagnetic coupling effects. Furthermore, the high density development has drastically increased the number of impedance discontinuities within the system (such as coaxial-microstrip transition structures, interlayer vertical interconnects, interfaces between different materials, vias, chip-to-package interfaces, and blind-mating connectors between tiles). Moreover, in the radio frequency range, the size of the interconnect structure can be comparable to the wavelength of electromagnetic waves. The combined effect of these factors makes the impedance mismatch problem in the entire signal transmission channel prominent, leading to increased signal reflection, decreased signal integrity, and reduced channel isolation. Even more seriously, under high-power operation, reflected power may be converted into heat, exacerbating localized heat generation in the system, increasing the heat dissipation burden, and affecting system reliability. Research on the electromagnetic characteristics of tile-type phased array systems is one of the key technologies for solving electromagnetic compatibility problems caused by the complex electromagnetic environment inside the system and ensuring reliable operation.

[0003] Currently, most research on tile-type phased array systems focuses on the design of phased array radar antenna structures and beam control circuits, while research on the electromagnetic characteristics and optimization design of tile-type phased array systems is relatively limited. Furthermore, impedance compensation for channel traces focuses more on optimizing line width and spacing, but these methods face practical limitations such as layout space and fabrication tolerance. Summary of the Invention

[0004] In view of this, this invention proposes a method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tiled phased array system. Under the constraint of layout space, this invention effectively avoids the electromagnetic interference problems caused by traditional optimization designs and can significantly improve the signal integrity of the tiled phased array system.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system includes the following steps:

[0007] Step 1: Establish a three-dimensional electromagnetic field numerical calculation model for the radio frequency signal transmission channel;

[0008] Step 2: Simulate and analyze the TDR parameters of the RF signal transmission channel, and calculate the impedance abrupt change points of the signal transmission channel;

[0009] Step 3: Based on anti-pad, trapezoidal pad, and reference plane slotting compensation method, optimize the characteristic impedance of impedance change point to complete the optimization of RF signal transmission channel.

[0010] Furthermore, the radio frequency signal transmission channel is a four-layer circuit board carrying a radio frequency connector, peripheral radio frequency circuits, a packaging structure, and a radio frequency chip. The peripheral radio frequency circuits include coplanar waveguides, pads, vias, blind vias, and a coaxial-coplanar waveguide transition structure. The packaging structure is a ball grid array packaging structure.

[0011] Furthermore, the four-layer circuit board includes a top layer, a first intermediate layer, a second intermediate layer, and a bottom layer, with adjacent layers separated by a dielectric substrate;

[0012] The coplanar waveguide includes a signal conductor located in the first intermediate layer, a ground conductor located in the top layer, the first intermediate layer, the second intermediate layer, and the bottom layer, a dielectric substrate located between the top layer, the first intermediate layer, the second intermediate layer, and the bottom layer, and a ground via penetrating all layers.

[0013] The coaxial-coplanar waveguide adapter structure includes a coaxial connector, a signal pad, and a blind via connecting the signal pad and the signal conductor;

[0014] The ball grid array packaging structure is used to connect peripheral radio frequency circuits and radio frequency chips.

[0015] Furthermore, the three-dimensional electromagnetic field numerical calculation model is established using electromagnetic field simulation software. The electromagnetic field simulation software has a pre-established library of dimensions and material parameters for each structure in the radio frequency signal transmission channel. When establishing the three-dimensional electromagnetic field numerical calculation model, similar structures in the three-dimensional electromagnetic field numerical calculation model are established in batches according to the corresponding structural parameters.

[0016] Furthermore, the impedance abrupt change point is located at the solder balls of the coaxial-coplanar waveguide transition structure, via, coplanar waveguide, and ball grid array packaging structure.

[0017] Furthermore, step 3 is performed as follows:

[0018] For the coaxial-coplanar waveguide transition structure, trapezoidal gradient pads are used instead of rectangular pads; the length-to-width ratio of the trapezoidal gradient pads is scanned, and optimization is performed with the interface impedance as close to 50 ohms as the target, to determine the optimal parameter combination;

[0019] Based on the model that already includes the optimal trapezoidal gradient pad, different shapes of anti-pad structures are introduced for the solder balls of the coaxial-coplanar waveguide transition structure, blind via, and ball grid array package structure; the length, width, radius and size of the anti-pad at different positions are optimized in a coordinated manner, so that the characteristic impedance at the coaxial-coplanar waveguide transition structure, via and solder ball is adjusted to a range of 50Ω±5%;

[0020] In the electromagnetic field model of the complete signal channel that includes the optimization results of the first two steps, a slot is etched on the reference ground plane below the coplanar waveguide. The ground via array around the channel is used as an electromagnetic interference isolation barrier. The shape and layout of the slot are consistent with the coplanar waveguide traces. The slot width is scanned, with the primary goal of achieving the system's voltage standing wave ratio across the entire frequency band and maximizing the S21 parameter across the entire frequency band, and the secondary goal of achieving the flattest characteristic impedance of the channel, to determine the optimal slot width.

[0021] Furthermore, the voltage standing wave ratio is obtained by converting the S-parameters obtained through vector network analysis.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. Under the constraints of layout space, the present invention effectively avoids the electromagnetic interference problems caused by traditional optimization design, and can also significantly improve the signal integrity of tile-type phased array systems.

[0024] 2. This invention uses a combination of simulation analysis and experimental testing to improve the signal integrity of electronic devices and systems. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a radio frequency signal transmission channel. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings.

[0027] A method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system is proposed. This method first establishes a three-dimensional electromagnetic field numerical calculation model of the unoptimized radio frequency transmission channel based on the size parameters and material properties of the packaging structure, peripheral circuits, and chips. Then, the TDR parameters of the signal transmission channel are simulated and analyzed, and the impedance abrupt change points of the signal transmission channel are calculated. Finally, based on the reference plane slotting compensation technique, the characteristic impedance of the impedance abrupt change points is optimized to obtain the optimal compensation optimization scheme.

[0028] Specifically, it includes the following steps:

[0029] Based on the structural, material, and dimensional parameters of the peripheral RF circuit, packaging structure, and chip, a three-dimensional electromagnetic field numerical calculation model of the unoptimized RF transmission channel is established to simulate and analyze the voltage standing wave ratio (VSWR) of the signal transmission channel. The peripheral RF circuit consists of a four-layer board circuit composed of a coaxial-coplanar waveguide transition structure, a coplanar waveguide-via-coplanar waveguide transition structure, and a coplanar waveguide-via-pad transition structure, with a ball grid array (BGA) package.

[0030] The TDR parameters of the signal transmission channel were simulated and analyzed. The impedance mutation points of the signal transmission channel were calculated to be located in the coaxial-coplanar waveguide transition structure, via, intermediate layer coplanar waveguide structure and solder ball. The impedance of all impedance mutation points is less than 50 ohms, which indicates that the impedance mutation of the circuit is capacitive.

[0031] The characteristic impedance at the coaxial-coplanar waveguide transition was optimized by using anti-pad design and trapezoidal pad structure. The via and solder ball design were optimized by using anti-pad structure. The characteristic impedance of the intermediate layer coplanar waveguide was optimized by changing the trace width and the distance between the trace and the ground plane. The TDR parameters of the signal transmission channel after optimization were obtained by simulation. It was found that the characteristic impedance at the coplanar waveguide position after optimization is still much less than 50 ohms.

[0032] Impedance compensation for the coplanar waveguide in the middle layer is achieved using a reference plane slotting compensation technique. Specifically, the technique involves: first, etching slots on the reference ground plane corresponding to the coplanar waveguide in middle layer 2, with a slot width set to w mm, and maintaining the same slot length and layout as the upper layer traces; second, scanning parameter w in 3D electromagnetic simulation software to simulate voltage standing wave ratio (VSWR) and total current draw ratio (TDR) results for different trace widths to evaluate the impact of slot width on impedance compensation; and finally, selecting the optimal w parameter based on the simulated VSWR and TDR results.

[0033] Based on the optimized design scheme, the signal transmission channels before and after optimization were processed, and the S-parameters of the signal transmission channels before and after optimization were tested using a vector network analyzer. Based on the S-parameters obtained from the test, the voltage standing wave ratio of the signal transmission channels before and after optimization was calculated.

[0034] By comparing the voltage standing wave ratio (VSWR) obtained from simulation with that obtained from testing, the effectiveness of the optimized design and the error between simulation and testing are evaluated.

[0035] Here is a more specific example:

[0036] Methods for optimizing the electromagnetic characteristics of radio frequency signal transmission channels in tile-type phased array systems include:

[0037] Step 101: Based on parameters such as the material and dimensions of the signal transmission channel, establish a three-dimensional electromagnetic field numerical calculation model of the unoptimized signal transmission channel. This signal transmission channel is as follows: Figure 1 As shown, it includes: peripheral radio frequency circuitry, ball grid array package structure, and chip.

[0038] Step 102: Simulate and analyze the TDR and voltage standing wave ratio parameters of the unoptimized signal transmission channel.

[0039] Step 103: Calculate the propagation speed of electromagnetic waves in the signal transmission channel based on the dielectric constant of the dielectric layer. Then, based on the TDR parameters of the unoptimized signal transmission channel and the calculated propagation speed of electromagnetic waves, calculate the locations corresponding to impedance discontinuities in the channel.

[0040] Step 104: Since trapezoidal pads are used in the coaxial-coplanar waveguide transition structure to improve the characteristic impedance of the structure, trapezoidal anti-pad structures are etched on the adjacent ground plane to compensate for the impedance of the coaxial-coplanar waveguide transition structure.

[0041] Step 105: Vias are used to achieve vertical interconnection between layers and represent impedance discontinuities in the signal transmission channel. A circular anti-pad structure is used to compensate for the impedance of the via structure. By changing the radius of the circular anti-pad structure, a better impedance compensation effect is obtained through comparison.

[0042] Step 106: Since the diameter of the ball grid array pad is wider than the width of the trace, the impedance at the pad is low. Therefore, a circular anti-pad structure is designed to compensate for the impedance of the pad corresponding to the signal solder ball.

[0043] Step 107: Scan the trace width of the coplanar waveguide structure and the spacing between the trace and the ground plane to evaluate the optimization effect of the trace width and the spacing between the trace and the ground plane.

[0044] Step 108: Due to space constraints, optimizing the trace width and the distance between the trace and the ground plane still cannot achieve impedance matching. Therefore, a reference plane slotting compensation technique is used to compensate the coplanar waveguide structure. Specifically: First, a slot is etched in the middle layer 2, with a width of w mm. The slot length and layout are consistent with the upper layer trace. Second, the parameter w is scanned in a 3D electromagnetic simulation software to simulate the voltage standing wave ratio (VSWR) and TDR results corresponding to different trace widths to evaluate the impact of the slot width on the impedance compensation effect. Finally, the optimal slot width w corresponding to the compensation effect is selected based on the simulated VSWR and TDR results.

[0045] Step 109: Simulate and analyze the TDR parameters and voltage standing wave ratio parameters of the optimized signal transmission channel.

[0046] Step 110: Design and fabricate high-frequency test samples before and after optimization. The structure, materials, and dimensions of the test samples, including traces, vias, grounding layers, and dielectric layers, are all consistent with the electromagnetic field model.

[0047] Step 111: Design a high-frequency test platform. Connect the two SMA connectors of the test sample to the high-frequency test cable, and use a vector network analyzer to perform high-frequency testing on the test sample. Calibration is required before the experiment to eliminate the influence of the test cable on the results.

[0048] Step 112: Calculate the voltage standing wave ratio (VSWR) parameters of the signal transmission channels before and after optimization based on the S-parameters obtained from experimental tests.

Claims

1. A method for optimizing the electromagnetic characteristics of a radio frequency signal transmission channel in a tile-type phased array system, characterized in that, Includes the following steps: Step 1: Establish a three-dimensional electromagnetic field numerical calculation model for the radio frequency signal transmission channel; Step 2: Simulate and analyze the TDR parameters of the RF signal transmission channel, and calculate the impedance abrupt change points of the signal transmission channel; Step 3: Based on anti-pad, trapezoidal pad, and reference plane slotting compensation method, optimize the characteristic impedance of impedance change point to complete the optimization of RF signal transmission channel.

2. The method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system according to claim 1, characterized in that, The radio frequency signal transmission channel is a four-layer circuit board that carries a radio frequency connector, peripheral radio frequency circuit, packaging structure and radio frequency chip. The peripheral radio frequency circuit includes coplanar waveguides, pads, vias, blind vias and coaxial-coplanar waveguide transition structures. The packaging structure is a ball grid array packaging structure.

3. The method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system according to claim 2, characterized in that, The four-layer circuit board includes a top layer, a first intermediate layer, a second intermediate layer, and a bottom layer, with adjacent layers separated by a dielectric substrate; The coplanar waveguide includes a signal conductor located in the first intermediate layer, a ground conductor located in the top layer, the first intermediate layer, the second intermediate layer, and the bottom layer, a dielectric substrate located between the top layer, the first intermediate layer, the second intermediate layer, and the bottom layer, and a ground via penetrating all layers. The coaxial-coplanar waveguide adapter structure includes a coaxial connector, a signal pad, and a blind via connecting the signal pad and the signal conductor; The ball grid array packaging structure is used to connect peripheral radio frequency circuits and radio frequency chips.

4. The method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system according to claim 2, characterized in that, The three-dimensional electromagnetic field numerical calculation model is established using electromagnetic field simulation software. The electromagnetic field simulation software has a pre-established library of dimensions and material parameters for each structure in the radio frequency signal transmission channel. When establishing the three-dimensional electromagnetic field numerical calculation model, similar structures in the three-dimensional electromagnetic field numerical calculation model are established in batches according to the corresponding structural parameters.

5. The method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system according to claim 2, characterized in that, The impedance abrupt change point is located at the solder balls of the coaxial-coplanar waveguide transition structure, via, coplanar waveguide, and ball grid array packaging structure.

6. The method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system according to claim 1, characterized in that, The specific method for step 3 is as follows: For the coaxial-coplanar waveguide transition structure, trapezoidal gradient pads are used instead of rectangular pads; the length-to-width ratio of the trapezoidal gradient pads is scanned, and optimization is performed with the interface impedance as close to 50 ohms as the target, to determine the optimal parameter combination; Based on the model that already includes the optimal trapezoidal gradient pad, different shapes of anti-pad structures are introduced for the solder balls of the coaxial-coplanar waveguide transition structure, blind via, and ball grid array package structure; the length, width, radius and size of the anti-pad at different positions are optimized in a coordinated manner, so that the characteristic impedance at the coaxial-coplanar waveguide transition structure, via and solder ball is adjusted to a range of 50Ω±5%; In the electromagnetic field model of the complete signal channel that includes the optimization results of the first two steps, a slot is etched on the reference ground plane below the coplanar waveguide. The ground via array around the channel is used as an electromagnetic interference isolation barrier. The shape and layout of the slot are consistent with the coplanar waveguide traces. The slot width is scanned, with the primary goal of achieving the system's voltage standing wave ratio across the entire frequency band and maximizing the S21 parameter across the entire frequency band, and the secondary goal of achieving the flattest characteristic impedance of the channel, to determine the optimal slot width.

7. The method for optimizing the electromagnetic characteristics of the radio frequency signal transmission channel in a tile-type phased array system according to claim 6, characterized in that, The voltage standing wave ratio is obtained by converting the S-parameters obtained through vector network analysis.

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