Broadband high-gain flatness near-field tangential electric field probe integrated with balance transition structure

Abstract

The invention discloses a broadband high-gain flatness near-field tangential electric field probe integrated with a balance transition structure, and relates to the field of electromagnetic compatibility and electromagnetic field near-field testing. The probe is designed based on four layers of printed circuit boards, and at least comprises a coupling tip, a balance transition structure, a ferry edge structure, a signal via hole and a side plug-in connector. The hook type metal patch is connected to the twisted crossed dipole through the via hole array to form a capacitive loading effect, so that the sensitivity of the probe is improved; a balanced transition structure based on microstrip-slot transition converts differential mode current generated by the twisted and crossed dipoles into single-ended common mode output current, and the test is simplified; the edge transition structure based on Chebyshev gradual transition design reduces impedance mismatch between the balance transition structure and the side plug-in connector, and inhibits ringing ripples in probe frequency response. The tangential electric field probe disclosed by the invention has the advantages of wide frequency band, high gain flatness, low cost and the like, and is convenient for engineering popularization.

Description

Technical Field

[0001] This invention relates to a broadband high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure, used for measuring the near-field tangential electric field on the surface of radio frequency integrated circuits and high-speed digital circuits, belonging to the fields of electromagnetic compatibility and electromagnetic field near-field testing. Background Technology

[0002] With the rapid development of modern electronic systems towards higher integration, higher operating frequencies, and miniaturization, electromagnetic interference (EMI) problems caused by their internal integrated circuits and wiring structures are becoming increasingly severe. This interference not only manifests as a complex superposition of common-mode and differential-mode radiation, but also forms high-gradient electromagnetic coupling in the near-field region due to bandwidth broadening and increased power density. By constructing an equivalent dipole array to characterize actual radiated electromagnetic coupling, the location of interference sources can be predicted, avoiding multiple far-field tests and significantly reducing the EMC design cycle. However, the accuracy of dipole model reconstruction is highly dependent on the accurate capture of the electromagnetic distribution in the near-field region, especially the high-sensitivity testing of the tangential electric field component.

[0003] Currently, there are two main approaches to measuring the tangential electric field component: the first is a back-end processing approach based on a vector network analyzer (VNA), which obtains the true tangential electric field value by post-processing the tangential electric field captured by the dipole. This approach places extremely high demands on the VNA, requiring an expensive three-port VNA and complex post-processing algorithms, which is not conducive to rapid diagnosis. The second approach is a front-end integrated approach, which integrates a balun structure inside the electric field probe to achieve real-time conversion and common-mode rejection of differential-mode dual-ended signals to single-ended signals. However, traditional narrowband baluns are limited by their inherent frequency response characteristics, making it difficult to achieve high flatness over an ultra-wideband range. This restricts the gain flatness and bandwidth coverage of the entire near-field testing system, failing to meet the current requirements of high-speed, high-density integrated circuits for accurate interference tracing. Therefore, designing a tangential electric field probe that can maintain high response flatness over a wide bandwidth while possessing miniaturization characteristics is of significant engineering importance for improving near-field electromagnetic scanning capabilities and supporting high-precision reconstruction of dipole models. Summary of the Invention

[0004] To address the aforementioned technical challenges, overcome the shortcomings of existing technologies, and meet the development needs of the electronics industry, this invention designs a broadband, high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure. The aim is to effectively detect the tangential electric field on the surface of integrated circuits within an ultra-wide frequency band, suppressing unwanted common-mode electrical components, reducing ringing ripples in the frequency response curve, improving the gain flatness of the tangential electric field probe, and maintaining good sensitivity and other electromagnetic characteristics. This assists engineers in quickly diagnosing faults in radio frequency electronic equipment and provides a valuable testing method for improving the electromagnetic robustness of electronic systems.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A broadband, high-gain, flat near-field tangential electric field probe with an integrated balanced transition structure is designed and fabricated based on a four-layer printed circuit board stack structure, wherein the stack structure consists of a top layer, a middle layer 1, a middle layer 2, and a bottom layer from the orientation down. The electric field probe is composed of at least a coupling tip, a balanced transition structure, a flanking structure, a signal via, and a side-mounted connector. The coupling tip, the balanced transition structure, the flanking structure, the signal via, and the side-mounted connector are cascaded in sequence.

[0007] The coupling tip consists of a twisted cross dipole, a hook-shaped metal patch, and a via array; the via array connects the hook-shaped metal patch to the twisted cross dipole.

[0008] The balanced transition structure has two balanced ports and one unbalanced port. The two balanced ports are connected to the dipole arms of the twisted cross dipole, and the one unbalanced port is connected to the wadering structure. The balanced transition structure adopts an embedded microstrip-slot transition structure, and the signal transmission path of the balanced structure is located between the intermediate layer 1 and the intermediate layer 2. Within the orthographic projection of the balanced transition structure, large rectangular openings are etched on the top and bottom layers to form electromagnetic decoupling windows. A symmetrically distributed unbalanced conversion slot line is etched on the intermediate layer 2, and two structurally identical and centrally symmetrical balanced strip lines are arranged on the intermediate layer 1. The unbalanced conversion slot line is composed of a middle slot line and two square slot lines, with the width of the middle slot line being smaller than the width of the square slot lines. The balanced strip line is composed of a main strip line and a square coupling plate, with the width of the square coupling plate being much larger than the width of the main strip line.

[0009] The waving structure is composed of striplines with multiple Chebyshev transitions, with its central conductor located in the middle layer 1, and the impedance reference planes being the top and bottom layers; the waving structure is directly connected to the signal via.

[0010] The beneficial effects of the broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure of this invention are:

[0011] This invention presents a broadband, high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure. This probe offers the combined advantages of high gain flatness, high sensitivity, and wide bandwidth. The waving-edge structure reduces the impedance mismatch between the unbalanced port of the balanced transition structure and the side-mounted connector, suppressing ringing ripple in the frequency response of the tangential electric field probe and ensuring gain flatness across an ultra-wide bandwidth. This has significant engineering implications for the accurate measurement of tangential electric field components in complex electromagnetic environments. The entire tangential electric field probe body is manufactured using standard printed circuit board technology, which is technologically mature, easy for engineers to master, and readily mass-produced, making it highly valuable for widespread application. Attached Figure Description

[0012] Figure 1 Printed circuit board stack-up diagram for a broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure.

[0013] Figure 2 The overall structure diagram of the broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure.

[0014] Figure 3 A 3D unfolded diagram of a broadband, high-gain, flat near-field tangential electric field probe with an integrated balanced transition structure.

[0015] Figure 4 Gain flatness calibration test diagram for a broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure.

[0016] Figure 5 Simulation and test results of the frequency characteristics of a broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure.

[0017] Explanation of icon numbers:

[0018] 1-1: Top layer, 1-2: Middle layer 1, 1-3: Middle layer 2, 1-4: Bottom layer, 2-1: Watanabe structure, 2-2: Rectangular opening, 2-3: Balanced stripline, 2-4: Via array, 2-5: Twisted cross dipole, 2-6: Balanced port, 2-7: Unbalanced port, 2-8: Side-mounted connector, 3-1: Signal via, 3-2: Square coupling plate, 3-3: Main stripline, 3-4: Middle slot line, 3-5: Square slot line, 3-6: Hook-shaped metal patch, 3-7: First cross dipole arm, 3-8: Second cross dipole arm, 3-9: Bottom layer electromagnetic decoupling window, 3-10: Via, 3-11: Top layer electromagnetic decoupling window, 4-1: Vector network analyzer, 4-2: Coaxial line, 4-3: Calibration microstrip line, 4-4: Tangential electric field probe, 4-5: 50 Ω matched load. Detailed Implementation

[0019] With reference to the accompanying drawings, the specific structure of a broadband high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure, the positional relationship of each component, and the function of each component are further explained.

[0020] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application.

[0022] It should be noted that the terms "top", "bottom", "upper", "lower" and similar expressions used herein are based on the orientation or relative positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description.

[0023] like Figure 1 One embodiment shown provides a printed circuit board stack structure for a broadband high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure designed according to the present invention. From top to bottom, the stack consists of a top layer 1-1, a middle layer 1-2, a middle layer 2-3, and a bottom layer 1-4. In this embodiment, the copper thickness of the bottom layer 1-1 and the top layer 1-4 in the four-layer printed circuit board is 1 oz, the copper thickness of the middle layer 1-2 and the middle layer 2-3 is 0.5 oz, a 0.2 mm FR-4 substrate (Core) is located in the middle of the printed circuit board stack structure, and two 0.198 mm PP boards are located at the top and bottom of the printed circuit board stack structure, respectively.

[0024] Figure 2This invention relates to the overall structure of a broadband high-gain flat near-field tangential electric field probe with an integrated balanced transition structure. The tangential electric field probe comprises a coupling tip, a balanced transition structure, a flanking structure, and a side-mounted connector, cascaded sequentially. The coupling tip, balanced transition structure, flanking structure 2-1, signal via 3-1, and side-mounted connector 2-8 are connected in sequence. The coupling tip consists of a twisted cross dipole 2-5, a hook-shaped metal patch 3-6, and a via array 2-4. The twisted cross dipole 2-5 is composed of a first cross dipole arm 3-7 and a second cross dipole arm 3-8. The twisted cross dipole 2-5 couples the tangential electric field, generating a differential-mode induced current dominated by the coupling capacitance. The via array 2-4 connects the hook-shaped metal patch 3-6 to the twisted cross dipole 2-5, producing a capacitive loading effect, enhancing the coupling capability of the twisted cross dipole 2-5, and thus improving the sensitivity of the tangential electric field probe. The spatial distribution of the first cross dipole arm 3-7 and the second cross dipole arm 3-8 introduces a significant phase imbalance, thereby effectively suppressing the transmission of common-mode signals and improving the anti-interference capability of the tangential electric field probe. In one embodiment of the present invention, a total of six hook-shaped metal patches 3-6 are loaded onto the twisted cross dipole 2-5, of which two are located at the top layer 1-1, one at the middle layer 1-2, one at the middle layer 2-3, and two at the bottom layer 1-4. The hook-shaped metal patches 3-6 are 3 mm long and 2 mm wide in the horizontal direction, and the upwardly extended portion is 3 mm high and 2 mm wide. The symmetrically distributed hook-shaped metal patches 3-6 are spaced 0.4 mm apart. The first cross dipole arm 3-7 is located in the middle layer 1-2, and the second cross dipole arm 3-8 is located in the middle layer 2-3. The first cross dipole arm 3-7 and the second cross dipole arm 3-8 are distributed at a 45-degree angle, thus presenting a 90-degree "X-shaped" physical layout in the middle layer 1-2 and the middle layer 2-3. In one embodiment of the present invention, the via array 2-4 consists of 6 vias 3-10. Each via 3-10 is located at the center of the hook-shaped metal patch 3-6, penetrating the top layer 1-1, the middle layer 1-2, the middle layer 2-3, and the bottom layer 1-4. The radius of the via 3-10 is 0.125 mm, and the spacing between adjacent vias 3-10 is 1 mm.

[0025] To simplify testing, an embedded microstrip-slot transition structure is used to implement the balanced transition structure in this embodiment, converting the differential-mode induced current into a single-ended common-mode current. The twisted cross dipole 2-5 is connected to the two balanced ports 2-6 of the balanced transition structure. Large rectangular openings 2-2 are etched in the region corresponding to the orthographic projection of the balanced transition structure, forming a top-layer electromagnetic decoupling window 3-11 and a bottom-layer electromagnetic decoupling window 3-9. These windows effectively reduce parasitic capacitance, providing the necessary space for the field transition between the embedded microstrip and slot layers, ensuring effective transmission and mode conversion from differential to single-ended signals. A symmetrically distributed unbalanced conversion slot line is etched in the middle two layers 1-3. This unbalanced conversion slot line consists of one intermediate slot line 3-4 and two square slot lines 3-5, ensuring that the width of the intermediate slot line 3-4 is much smaller than the width of the square slot lines 3-5. Two identical and centrally symmetrical balanced striplines 2-3 are arranged in the middle layer 1-2. Each balanced stripline 2-3 consists of a main stripline 3-3 and a square coupling plate 3-2, with the width of the square coupling plate 3-2 significantly larger than that of the main stripline 3-3. The square coupling plate 3-2 not only increases the coupling area with the square slot line 3-5, but also introduces parasitic capacitance and parasitic inductance in the transition structure to form a matching network, compensating for the parasitic reactance components introduced by the transition structure and the terminal, thereby improving mode conversion efficiency and operating bandwidth. In one embodiment of the invention, the width of the middle slot line 3-4 is 0.1 mm, the width of the square slot line 3-5 is 2 mm, the width of the main stripline 3-3 is 0.285 mm, and the width of the square coupling plate 3-2 is 2.5 mm. The top-layer electromagnetic decoupling window 3-11 and the bottom-layer electromagnetic decoupling window 3-9 are 20 mm long and 15 mm wide. The Watanabe structure 2-1, located in the middle layer 1-2, is designed as a stripline based on a multi-stage Chebyshev transition. The impedance reference planes of the center conductor are the top layer 1-1 and the bottom layer 1-4. The Watanabe structure 2-1 is connected to the unbalanced port 2-7 of the balanced transition structure to reduce the impedance mismatch between the balanced transition structure and the side-mounted connector 2-8 and suppress ringing ripples in the frequency response of the tangential electric field probe. In one embodiment of the invention, the Watanabe structure 2-1 implements a three-stage transition, with the width of the center conductor gradually changing from 0.285 mm to 0.15 mm. The differential-mode current induced by the twisted cross dipole 2-5 enters the balanced transition structure through the two balanced ports 2-6 and is coupled to both sides of the middle slot line 3-4 by the square coupling piece 3-2 at the end of the balanced stripline 2-3. A common-mode single-ended voltage is induced on the Watanabe structure 2-1, which is connected to the side-mounted connector 2-8 through the signal via 3-1, ultimately generating a common-mode single-ended output voltage on the side-mounted connector 2-8.

[0026] An embodiment of a broadband high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure designed in this invention was tested. The test calibration system is as follows: Figure 4 As shown. Before testing, the vector network analyzer 4-1 undergoes a standard two-port calibration. The calibration microstrip line 4-3 provides electric field information as a calibration component. Port 1 of the vector network analyzer 4-1 is connected to one end of the calibration microstrip line 4-3 via a coaxial line 4-2, and port 2 of the vector network analyzer 4-1 is connected to the tangential electric field probe 4-4 via the coaxial line 4-2. The other end of the calibration microstrip line 4-3 is terminated with a 50 Ω matched load 4-5. In this embodiment, the characteristic impedance of the calibration microstrip line 4-3 is 50 Ω, and the tangential electric field probe 4-4 is positioned 1.5 mm directly above the center of the calibration microstrip line 4-3.

[0027] Figure 5 The simulation and test results of the frequency characteristics of the broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure are shown in the figure. The results show that the tangential electric field probe designed in this invention has high gain flatness across the entire frequency band, stable amplitude in the mid-to-high frequency band, and no resonance, obvious ringing-like ripples, or surge ripples. The effective operating frequency band is 4.5 GHz-20 GHz, the average gain is approximately -27.6 dB, the maximum fluctuation is approximately 3.45 dB, and the average fluctuation is approximately 1.18 dB. The test results curves and simulation results curves show a high degree of agreement. Multiple field measurements of this embodiment show that when the bottom of the tangential electric field probe 4-4 is 1.5 mm above the surface of the center conductor of the calibration microstrip line 4-3, the measured cross-polarization is approximately 20.57 dB, indicating that the tangential electric field probe 4-4 has good polarization purity and can effectively suppress interference signals from non-dominant polarization directions, thereby ensuring the accuracy of the measurement of the target tangential electric field component.

[0028] It should be noted that the technical means and design methods disclosed in this invention are not limited to this invention, but also applicable to other solutions, invention methods, and invention products derived from the design ideas, invention methods, technical means, and technical features described in this invention. Therefore, these other derived solutions, invention methods, and invention products should all be considered within the scope of protection of this invention.

Claims

1. A broadband high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure, characterized in that: The tangential electric field probe is composed of at least a coupling tip, a balanced transition structure, a fencing structure, a signal via, and a side-mounted connector; the coupling tip, the balanced transition structure, the fencing structure, the signal via, and the side-mounted connector are cascaded in sequence; the coupling tip consists of a twisted cross dipole, a hook-shaped metal patch, and a via array, and the via array connects the hook-shaped metal patch to the twisted cross dipole; the design and fabrication of the tangential electric field probe is based on a four-layer printed circuit board stack-up structure, consisting of a top layer, a middle layer 1, and a middle layer 2 from top to bottom. The balanced transition structure is an embedded microstrip-slot transition structure. Within the orthographic projection of the balanced transition structure, large rectangular openings are etched on the top and bottom layers to form electromagnetic decoupling windows. A symmetrically distributed unbalanced transition slot line is etched on the middle two layers, and two structurally identical and centrally symmetrical balanced striplines are arranged on the middle one layer. The wadering structure is composed of multi-stage Chebyshev transition striplines, with its central conductor located on the middle one layer, and the impedance reference planes being the top and bottom layers. The wadering structure is directly connected to the signal via.

2. The broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure according to claim 1, characterized in that: The balanced transition structure has two balanced ports and one unbalanced port. The two balanced ports are connected to the dipole arms of the twisted cross dipole, and the one unbalanced port is connected to the Watanabe structure.

3. The broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure according to claim 1, characterized in that: The unbalanced conversion groove is composed of one intermediate groove and two square grooves, wherein the width of the intermediate groove is smaller than the width of the square groove.

4. The broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure according to claim 1, characterized in that: The balanced stripline consists of a main stripline and a square coupling plate, the width of which is much larger than the width of the main stripline.

5. The broadband high-gain flatness near-field tangential electric field probe with integrated balanced transition structure according to claim 1, characterized in that: The signal transmission path of the balanced structure is located between the middle layer 1 and the middle layer 2.

6. The broadband high-gain flatness near-field tangential electric field probe with an integrated balanced transition structure according to claim 1 or 2, characterized in that: The twisted cross dipole has two dipole arms, namely the first cross dipole arm and the second cross dipole arm.

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