Bidirectional coupler applied to high-frequency RFID system

Abstract

The invention relates to the technical field of coupler design, in particular to a bi-directional coupler applied to a high-frequency RFID (Radio Frequency Identification Device) system, which comprises the following steps: S1, respectively constructing a series transformer, a parallel transformer and a Magic-T structure hybrid network, and forming an impedance self-matching coupler core framework by adopting a plurality of Ni-Zn ferrite double-hole magnetic rings; s2, inputting an original coupling signal output by the coupler core architecture into a phase-amplitude cooperative calibration module to generate a calibrated stable coupling signal; s3, inputting the stable coupling signal into a bridging T-type attenuation network group, respectively performing accurate power adjustment on a forward coupling path and a reverse coupling path, and finally outputting a high-directivity and low-fluctuation coupling signal; s4, monitoring the impedance state of an antenna port in real time, and feeding back and adjusting a matching network structure to realize stable control of the standing-wave ratio in a full frequency band range; according to the invention, the design of an external matching circuit is simplified, the coupling efficiency and directivity are improved, and the method has important engineering value.

Description

Technical Field

[0001] This invention relates to the field of coupler design technology, and in particular to a dual directional coupler for use in high-frequency RFID systems. Background Technology

[0002] With the widespread application of high-frequency RFID systems in industrial automatic identification, smart logistics, and retail payment, higher requirements are placed on the directionality, stability, and coupling efficiency of antenna port power transmission. Traditional RFID couplers mostly use series-parallel networks built with discrete components to achieve signal coupling. Their structure is complex and bulky, and they are susceptible to impedance mismatch and frequency drift in the high-frequency band, leading to increased VSWR, deteriorated signal directionality, and increased system bit error rate. In addition, existing couplers mostly lack the ability to adaptively adjust to dynamic load changes, making it difficult to adapt to complex environments such as frequency band jumps and tag reflection intensity fluctuations in various scenarios, which limits the stability and practicality of the system.

[0003] To address the aforementioned issues, some studies have attempted to improve system integration, coupling, and directivity using multi-winding structures or magnetic ring coupling. However, these approaches still suffer from limitations such as unclear distinction between winding functions and coarse impedance matching control. Furthermore, they often lack the ability to perform fine-grained phase and amplitude calibration of the coupled signals, resulting in significant fluctuations in the directional signal output and failing to meet the requirements of high-precision applications. Therefore, there is an urgent need for a dual-directional coupler solution with high structural integration, strong directivity, and adaptive adjustment and feedback capabilities to enhance the stable operation and anti-interference performance of high-frequency RFID systems in complex environments. Summary of the Invention

[0004] This invention provides a dual directional coupler for use in high-frequency RFID systems.

[0005] A dual directional coupler for use in a high-frequency RFID system includes the following steps: S1: Construct a hybrid network of series transformers, parallel transformers and Magic-T structure respectively, and use multiple Ni-Zn ferrite double-hole magnetic rings to realize the winding structure of each transformer, forming the core architecture of the impedance self-matching coupler. S2: Input the original coupling signal output from the core architecture of the coupler to the phase-amplitude co-calibration module, and generate a calibrated stable coupling signal by detecting and adjusting the phase consistency and amplitude balance of the signal in real time; S3: The stable coupling signal is input to the bridged T-type attenuation network group. The power of the forward coupling path and the reverse coupling path are precisely adjusted through the dual-path symmetrical attenuation mechanism, and finally the coupling signal with high directivity and low fluctuation is output. S4: Input the coupling signal to the dynamic load adaptation module, and adjust the matching network structure by monitoring the impedance status of the antenna port in real time to achieve stable control of the standing wave ratio in the full frequency band.

[0006] Optionally, S1 includes: S11: Select BN-73-302 type Ni-Zn ferrite double-hole magnetic ring to construct three physically separate transformer structures respectively; S12: The series transformer functional winding is wound on the first magnetic ring, using enameled copper wire with a diameter of 0.4mm, and the primary to secondary turns ratio is 1:8; S13: Wind a parallel transformer functional winding on the second magnetic ring with a turns ratio of 16:1; S14: Construct a Magic-T hybrid network on the third magnetic ring, using three sets of winding structures with a turns ratio of 1:1:1; S15: Each winding is arranged with a short gap to achieve electromagnetic coupling and is connected to a microstrip impedance converter to form a complete coupler core architecture.

[0007] Optionally, S2 includes: S21: The original coupled signal is split into two paths and input to the phase detector and amplitude detector respectively to generate phase error signal and amplitude error signal; S22: The phase error signal and amplitude error signal are input to the digital signal processor, and a phase correction command and an amplitude balance command are generated respectively through a dual closed-loop control algorithm. These commands are used to control the adjustable phase delay line and the digitally controlled attenuator array to perform phase compensation and amplitude equalization on the coupled signal and output a stable coupled signal.

[0008] Optionally, the phase detector uses the orthogonal correlation detection principle to extract the phase difference, and the amplitude detector uses a logarithmic amplifier structure to extract the amplitude level difference, and outputs error signals respectively.

[0009] Optionally, the dual-loop control algorithm includes a phase control loop for phase compensation and an amplitude control loop for amplitude equalization. The phase control loop dynamically adjusts the adjustable phase delay line according to the phase error signal, and the amplitude control loop dynamically adjusts the numerically controlled attenuator array according to the amplitude error signal, thereby achieving synchronous adjustment of the phase and amplitude of the coupled signal.

[0010] Optionally, S3 includes: S31: The stable coupled signal is split into two paths by a power divider and input to the forward and reverse bridged T-type attenuators respectively; S32: The forward bridging T-type attenuator is a fixed attenuation structure, including a series resistor network, a parallel resistor network, and... Type-matching circuits are used for precise attenuation of transmitted signals; S33: The reverse bridging T-type attenuator is the same as the forward structure and is used to monitor the tag echo signal and feed it back to the digital control unit; S34: The digital control unit dynamically controls the digitally controlled resistor array based on the deviation between the power feedback and the preset threshold, thereby achieving adaptive attenuation adjustment of the reverse path.

[0011] Optionally, S33 includes: S331: The reverse bridging T-type attenuator adopts the same topology as the forward bridging T-type attenuator, and integrates a digitally controlled resistor array inside for dynamic attenuation control of the tag echo signal. S332: A directional power detector is installed at the output end of the reverse bridging T-type attenuator to monitor the output power of the tag echo signal in real time and feed the detection result back to the digital control unit.

[0012] Optionally, S4 includes: S41: A directional coupler is connected in series between the coupling signal output terminal and the antenna port to extract the forward and reflected power signals and input them to the impedance detection unit. S42: The impedance detection unit calculates the complex impedance based on the power vector synthesis algorithm and compares it with the matching interval, and outputs a mismatch evaluation signal. S43: Input the evaluation signal into the digital signal processor to generate coupling adjustment control instructions; S44: An adjustable device for controlling the distance between windings in a magnetic coupling structure to achieve dynamic impedance matching at the antenna port.

[0013] Optionally, the coupling strength control command includes the coupling strength adjustment direction and the coupling strength adjustment range.

[0014] Optionally, the standing wave ratio (SWR) feedback mechanism is used to continuously monitor the SWR status of the antenna port. When the SWR is detected to exceed the preset SWR upper limit threshold, the coupling strength adjustment process is automatically triggered. Impedance matching correction is achieved by adjusting the spacing of the magnetic winding group, maintaining stable coupling and low reflection operation in the full frequency band.

[0015] The beneficial effects of this invention are: This invention achieves physical integration and electromagnetic synergistic design of different functional windings by integrating series transformer functional windings, parallel transformer functional windings, and Magic-T hybrid network windings on a single Ni-Zn ferrite double-hole magnetic ring. By controlling the turns ratio and spatial coupling distance of each winding, combined with an FR4 substrate microstrip impedance transformer, a core architecture of impedance self-matching coupler is formed. This not only simplifies the design of external matching circuits and improves coupling efficiency and directionality, but also has excellent miniaturization integration potential, making it suitable for applications such as high-frequency RFID systems that are sensitive to coupling stability and size.

[0016] This invention innovatively introduces a phase-amplitude collaborative calibration module and a dynamic load adaptation module into the coupled signal transmission link. It utilizes a dual closed-loop control algorithm to compensate for phase difference and amplitude imbalance in real time. Furthermore, it achieves precise attenuation and power regulation of the forward and reverse paths through a bridging T-type attenuation network group, outputting a stable dual-directional signal. In addition, it drives an adjustable magnetic coupling mechanism through a standing wave ratio feedback mechanism to dynamically adjust the spacing of the magnetic winding group, ensuring stable coupling across the entire frequency band. This improves the robustness and adaptability of the system under varying loads and interference environments, and has significant engineering value in high-frequency RFID and other applications requiring high-stability coupling. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the adjustment process according to an embodiment of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Those skilled in the art may employ other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0020] like Figure 1-2 As shown, a dual directional coupler for use in a high-frequency RFID system includes the following steps: S1: Construct a hybrid network of series transformers, parallel transformers and Magic-T structure respectively, and use multiple Ni-Zn ferrite double-hole magnetic rings to realize the winding structure of each transformer, forming the core architecture of the impedance self-matching coupler. S1 specifically includes: S11: In the first hole of the BN-73-302 Ni-Zn ferrite double-hole magnetic ring, 0.4mm diameter enameled copper wire is used to wind the primary and secondary windings of a series transformer, respectively. The turns ratio is expressed as: ; in, This refers to the number of turns in the primary winding of the series transformer. The number of turns in the primary winding ranges from 1 to 3 turns. The primary winding is connected to the main line path. To ensure low main line attenuation, the number of turns should be controlled within a small range. Too many turns will cause increased attenuation and reflection of the main line signal. This refers to the number of turns in the secondary winding of the series transformer, ranging from 6 to 24 turns. The secondary winding is responsible for coupling the transmitted power to the coupling path. To achieve typical coupling, a relatively high number of turns is required to increase the induced energy. The turns ratio is... Considering coupling efficiency, directionality, and volume limitations, exceeding these values ​​will cause coupling imbalance or deterioration of frequency response. The diameter of the winding conductor is selected as 0.4mm to balance the current carrying capacity and the utilization rate of the magnetic ring window space. If the diameter is too large, the number of turns will be insufficient, and if it is too small, the resistance will increase and the temperature rise will increase. The BN-73-302 magnetic ring is a Ni-Zn double-hole magnetic ring with high permeability and high inductance coefficient, which is suitable for small signal transformer coupling scenarios in the medium and high frequency range. This invention constructs three transformer structures in multiple BN-73-302 type Ni-Zn ferrite double-hole magnetic rings: a series transformer functional winding is wound on the first magnetic ring, with the primary and secondary windings being the main signal path and the transformer extraction path, respectively. A turns ratio structure of 1:8 is constructed using enameled copper wire with a diameter of 0.4mm to ensure efficient transmission and voltage conversion performance. S12: In the second and third BN-73-302 double-hole magnetic rings, parallel transformer functional windings and Magic-T hybrid network windings are constructed respectively. Each structure uses an independent magnetic ring to achieve structural isolation and electromagnetic compatibility optimization. (1) The turns ratio of the functional winding of a parallel transformer is expressed as: ; in, This is the main signal path winding of the parallel transformer, connected in series with the main signal path. Its value ranges from 12 to 24. The primary winding is directly connected in series with the main signal path and has high inductive reactance to ensure signal coupling efficiency and directivity. A typical value is 16 turns. If the value is too small, the impedance transformation will be insufficient; if it is too large, it will easily cause narrowing of bandwidth and resonance mismatch. As a feedback coupling winding, it is typically used for reflection suppression and impedance compensation. The winding is arranged in two magnetic holes of the second magnetic ring. The energy coupling path is optimized by comparing the number of turns, with a value ranging from 0.5 to 2. In the integrated magnetic ring, the series winding in the main signal path needs to provide appropriate inductive reactance. The inductive reactance is used to achieve directional coupling, filtering, or impedance transformation. If the inductive reactance is too small, the signal coupling efficiency is insufficient and the directivity is poor. If the inductive reactance is too large, the bandwidth narrows and the risk of resonance mismatch increases. The inductive reactance is calculated as follows: ; in, It is the operating frequency. Let be the permeability of the magnetic core. The number of turns in the winding. This is the effective cross-sectional area of ​​the magnetic core. It is the average length of the magnetic circuit; By setting the required inductive impedance By determining the range (e.g., tens to hundreds of ohms) and substituting the magnetic ring structure parameters, a reasonable range for the number of turns can be calculated. 16 turns is the empirically optimal value while meeting the inductive reactance requirements. In mid-to-high frequency RFID systems such as 13.56MHz, using 16 turns can provide sufficient inductive reactance (tens to hundreds of ohms), avoiding signal short circuits or insufficient coupling. If the number of turns is too large, the parasitic capacitance effect is enhanced, leading to narrower bandwidth or even the formation of resonance peaks, increasing the risk of mismatch. If the number of turns is too small, the coupling efficiency is low, and the directivity deteriorates. The BN-73-302 magnetic core has a certain magnetic circuit length and effective cross-sectional area. Combined with the high permeability of ferrite material, a number of turns of approximately 16 provides a good balance in the 3MHz-30MHz range.

[0021] (2) The Magic-T hybrid network winding adopts a three-group winding structure with equal number of turns, distributed in the double holes and port lead-out cables of the third magnetic ring, forming a three-port signal mixer structure. The typical topology maintains a 1:1:1 turns ratio, which is used for power combining and symmetrical distribution of the RF reflected signal path, as shown below: ; in, , , These represent the number of turns in the windings at the three ports of the Magic-T hybrid network, used to achieve equal-amplitude signal combining and separating. The values ​​range from 4 to 10 turns each. The three windings must maintain strict consistency in the number of turns. A higher number of turns improves the common-mode rejection ratio and directivity, but excessively high numbers increase the impact of parasitic parameters. The Magic-T network is essentially an equal-amplitude power divider / combiner, requiring perfect symmetry in the inductance of each winding. Any deviation will lead to reduced directivity and increased reflection coefficient. This is a fixed configuration; S13: The output pins of the secondary winding of the series transformer and the primary winding of the parallel transformer are interconnected by short-distance welding, and the wiring spacing between the windings is kept within 0.5mm to enhance magnetic coupling efficiency, improve the consistency of electromagnetic energy transfer, suppress high-frequency crosstalk, and ensure the stability of the coupling structure. Among them, the spacing between windings Controlling the distance between the series secondary and the parallel primary helps improve magnetic coupling efficiency and suppress high-frequency crosstalk. 0.5mm is the optimal upper limit to ensure consistent performance under processing tolerance. S14: The output terminals of each winding are soldered to the FR4 material PCB board by spot welding or surface mount technology. Its microstrip structure is used to achieve impedance matching, signal guidance and power regulation of different transformers. The connection section adopts precision wiring to maintain the waveform integrity and direction control characteristics of high frequency signals. To achieve efficient connection with the subsequent RFID reader module, the outputs of all functional windings are connected to the microstrip circuit structure mounted on an FR4 printed circuit board (PCB) via soldering or pin connection. The FR4 material used possesses excellent high-frequency dielectric properties and processing stability, making it suitable for high-frequency RF module integration. At the microstrip level, three functional units are arranged, including: (1) Microstrip impedance converter: used to adjust the output impedance of each winding to the standard value required by the system (such as 50Ω) to reduce standing wave reflection; (2) Matching network and attenuation bridge: Implement detailed power distribution and attenuation control for different channels (forward coupling, reverse coupling) to improve channel isolation and directional stability; (3) Signal port structure: Set up a coupled output port and an isolation port to achieve effective extraction of highly directional coupled signals and suppression of residual signals.

[0022] S2: Input the original coupling signal output from the core architecture of the coupler to the phase-amplitude co-calibration module, and generate a calibrated stable coupling signal by detecting and adjusting the phase consistency and amplitude balance of the signal in real time; S2 specifically includes: S21: The phase detector, based on the orthogonal correlation detection principle, performs orthogonal demodulation on two coupled signals. Let the two signals be... and The phase difference between the two signals is obtained. The phase detector extracts the phase difference through a phase-locked unit constructed by a multiplier and a low-pass filter, and outputs a phase error signal, which is expressed as: ; ; ; ; in, The amplitudes of the two signals range from 0.1V to 2.0V. To maintain linear operation of the amplifier and multiplier, the input signal amplitude is generally controlled within a peak value of 1-2V. A value below 0.1V will lead to a decrease in the signal-to-noise ratio. The center angular frequency of the signal, with a value range of [value missing]. rad / s, Let be the initial phase of the two signals. Phase is a periodic quantity and is defined within the unit circle. The phase difference between the two signals is expressed in rad. This is the sensitivity constant of the phase detector, ranging from 0.5 to 2.0 V / rad. Its value depends on the multiplier gain and the bandwidth of the subsequent low-pass filter. Higher sensitivity facilitates error control but easily introduces high-frequency noise, requiring matching with the DSP's dynamic range to avoid detection failure due to excessively small errors, or amplification of noise due to excessively large errors. The output is a phase error signal. After the error signal enters the digital signal processor (DSP), it generates control commands through the phase closed-loop control algorithm to drive the adjustable phase delay line and realize real-time phase compensation of the original coupled signal. In this step, the system compares the two signals output by the coupler in real time, identifies and corrects their phase inconsistencies, and ensures that the final output signal has good phase symmetry, which is a prerequisite for achieving high directivity and low VSWR characteristics.

[0023] S22: The amplitude detector uses a logarithmic amplifier structure to detect the amplitude levels of the two coupled signals respectively, calculate their logarithmic ratio, and output an amplitude error signal, expressed as: ; ; in, These are the amplitudes of the two signals, in volts (V). It is the amplitude level difference, representing the power difference between two signals, used to determine whether equalization adjustment is needed, and the unit is dB. This is the sensitivity coefficient of the amplitude detector, with a value ranging from 0.5 to 2.0 V / dB. It represents the change in output voltage corresponding to each amplitude difference. If the sensitivity is too low, the response will be sluggish; if it is too high, it will be easily affected by noise. It is an amplitude error signal output with a value range of -10 to 10V. The actual control signal level range must be compatible with the input level of the DSP or control circuit. The amplitude error signal is also input to the DSP module, which calculates the attenuation control command through the amplitude closed-loop control algorithm, drives the subsequent digitally controlled attenuator array (DATT), and performs amplitude equalization on the compensated signal. S23: When the DSP determines the phase threshold... and amplitude threshold If the error meets the judgment condition, the signal is considered to have achieved phase consistency and amplitude balance requirements, and the output is a stable coupled signal, which is then fed into the subsequent bridging T-type attenuation network group. The judgment condition is expressed as follows: ; in, This is the phase threshold, also known as the phase consistency judgment threshold, with a value ranging from 1° to 5°. Generally, RF signal processing circuits consider a phase error within 5° to be consistent. Some high-precision systems have stricter requirements, within 1°. The amplitude threshold, also known as the amplitude balance judgment threshold, has a value range of 0.5-1.5dB. It is the error tolerance range for judging whether the amplitude is "balanced". In RF systems, a value within ±1dB is considered to indicate that the signal is symmetrical.

[0024] S3: The stable coupled signal is input to the bridged T-type attenuation network group. The power of the forward coupling path and the reverse coupling path are precisely adjusted through the dual-path symmetrical attenuation mechanism, and finally the coupled signal with high directivity and low fluctuation is output. S3 specifically includes: S31: The forward attenuation path adopts an improved bridging T-type topology, consisting of a series resistor network. Parallel bridging resistors and for impedance matching It is composed of impedance transformation units; in, It indicates two resistors in parallel. and The resulting equivalent bridging resistor possesses excellent heat distribution and low parasitic inductance, significantly improving overall heat dissipation and high-frequency stability while maintaining the same equivalent resistance value. This structure is used for sampling forward-transmitted signals. The precise attenuation ensures that the energy loss of the main signal after sample extraction is controllable and the matching error is minimal. The values ​​of each resistor are determined through precise selection and simulation optimization to meet the target attenuation characteristics and impedance consistency requirements. S32: The reverse path adopts the same bridged T-type topology as the forward path, including a digitally controlled resistor array to achieve a dynamically adjustable attenuation range. It is dynamically driven by the output signal of the control module, and is represented as follows: ; in, The attenuation amount on the reverse path is determined by controlling the variable resistor element. It enables adaptive adjustment of echo signal strength, optimizes signal-to-noise ratio and adapts to dynamic load changes in multi-tag environments, covers typical ranges of tag echo signal strength fluctuations in most RFID scenarios, and improves the dynamic adaptability of the receiver. S33: Directional power detectors are integrated at the outputs of the two attenuators to measure the output signal power in real time. The detection results are fed back to the digital control unit (such as FPGA or DSP) and compared with a preset power threshold. After comparison, a resistance adjustment signal is generated. ,according to By controlling the resistance value of the digitally controlled resistor array in the reverse attenuator, the desired effect can be achieved. The dynamic adjustment is represented as: ; ; in, This represents the actual output power measured by the power detector, in dBm, corresponding to the power level of the attenuator's output signal. This is the output signal voltage of the attenuator, with a value range of 0.05-0.5V. The load resistor in the power detection circuit is set to 50Ω to meet system impedance matching requirements (such as the uniform impedance of an RFID system). The target power threshold set for the digital control unit has a range of values. dBm is the baseline for the controller to determine whether the output power has reached the target value. It is set at around -20dBm, which can tolerate a dynamic fluctuation of 3dB to adapt to different echo intensity scenarios. The digital signal or analog voltage used to control the attenuator resistor array is expressed in V / bit and represents the quantized representation of the control signal.

[0025] S34: The final output coupled signal must meet the following performance requirements: (1) Directional indicators dB; (2) Signal fluctuation dB; (3) The output power of the forward port is stable, meeting the downstream transmission sampling requirements; (4) The reverse port output signal has a high signal-to-noise ratio and is suitable for tag echo recognition processing.

[0026] Among them, directional indicators Directivity, measured in dB, indicates the degree of energy isolation between the forward and reverse signals. It is one of the core parameters for evaluating the performance of dual-directional couplers. In high-frequency RFID systems, the tag echo signal is typically tens of dB weaker than the transmitted signal. Insufficient directionality can cause strong transmitted signals to interfere with the receiver, suppressing the weak echo signal and leading to identification failure. Directivity above 40 dB ensures that the echo signal is not overwhelmed by the main energy source and is recognized in engineering as the dividing line for high-performance couplers. (Signal fluctuation...) The amplitude stability of the coupler's output signal is crucial. In actual operation, factors such as temperature, load, and slight changes in coupling state can easily cause fluctuations in the output signal. Fluctuations within ±0.3dB indicate a relatively stable coupling path, helping to maintain system gain consistency, matching stability, and detection accuracy, and avoiding misjudgments or false triggers caused by signal jitter. The forward coupling end is used to output transmitted signal samples for use by the power detector or feedforward control module. Its stability directly affects the power loop accuracy and modulation integrity. If the forward sample power deviation is too large, it may lead to transmission control distortion and abnormal modulation waveforms, affecting system reliability. Therefore, this path requires precise attenuation and matching processing, and the output power should be controlled within a stable and linear response range. The reverse path is mainly used to extract tag echo signals. The signal strength itself is very weak, and without proper dynamic attenuation and noise suppression, it is easily covered by background noise. By finely controlling the signal amplitude through an adjustable attenuator to keep it at the optimal position in the dynamic range of the receiving front end, the signal-to-noise ratio can be significantly improved, enhancing tag identification capabilities and anti-interference performance.

[0027] S4: Input the coupling signal to the dynamic load adaptation module, monitor the impedance status of the antenna port in real time, and adjust the matching network structure to achieve stable control of the standing wave ratio in the entire frequency band. S4 specifically includes: S41: A directional coupler is connected in series between the bidirectional coupled signal output terminal and the antenna port. This coupler is used to extract the forward power signal. With reflected power signal ,Will and The synchronous input is sent to the impedance detection unit, and the complex impedance of the antenna port is calculated based on the power vector synthesis algorithm. , represented as: ; in, This is the voltage for the forward signal, ranging from 0.5V to 5V, which meets the transmission power range of the RFID reader. Let be the current of the forward signal, ranging from 10-100mA, satisfying typical transmit power, and considering the voltage-current relationship under Ohm's law. The voltage of the reflected signal ranges from 0 to 2V. Ideally, the reflected signal should be close to 0V. Maximum reflection corresponds to total internal reflection of the echo. The current for the reflected signal ranges from 0 to 50 mA, matching the reflected power. The maximum value corresponds to a completely reflective load. This is the complex impedance value (including the real and imaginary parts) of the antenna port. S42: The calculated result With preset impedance matching range Comparisons are made to generate impedance mismatch assessment signals. ,Will The input is sent to a digital signal processor (DSP), which generates coupling strength control commands based on the control strategy. The instruction includes the coupling strength adjustment amount. Adjust direction indicators Impedance mismatch assessment signal Represented as: ; in, For ideal matching impedance, the range of values ​​is: Manufacturing tolerances and temperature drift were taken into account. Impedance mismatch, less than 5 Excellent, above 15 Compensation and adjustments are required.

[0028] S43: Will The transmission is to an adjustable magnetic coupling mechanism positioned around the integrated magnetic ring, including a stepper motor-driven relative position adjustment device for adjusting the axial spacing between the series transformer functional windings and the parallel transformer functional windings. The adjustment range is The electromagnetic coupling strength can be changed by adjusting the winding spacing. This indirectly adjusts the impedance matching state of the coupler; Among them, mechanical precision is insufficient when the axial spacing is less than 0.1mm, and coupling drops sharply when it is greater than 2mm; S44: Monitor the VSWR at the antenna port and set the upper limit threshold for VSWR. When the VSWR is detected to exceed the upper limit threshold, the above-mentioned coupling strength adjustment process is immediately triggered; after the adjustment is completed, the target VSWR is maintained at [value missing]. Within this range, the control process operates continuously in a closed loop within the frequency range of 3MHz-30MHz, ensuring that the coupler achieves high stability and high directivity impedance adaptive adjustment across the entire frequency band. in, The upper limit threshold for VSWR. This is the upper limit acceptable for RFID systems. With a target VSWR, the frequency range of 3MHz-30MHz fully covers the high-frequency RFID application band and is compatible with a variety of tag protocols.

[0029] To ensure that the high-frequency RFID system can still work stably under different load conditions, this step establishes a closed-loop adjustment mechanism based on VSWR at the output of the dual directional coupler. VSWR is an important indicator for measuring the impedance matching degree of the radio frequency system. The higher the VSWR, the more severe the energy reflection, the lower the system efficiency, which may lead to coupler overheating, damage, or even signal distortion.

[0030] Therefore, this step sets an upper limit threshold for the standing wave ratio (SWR). Once the actual SWR at the antenna port is detected to exceed this value, the electromagnetic coupling strength adjustment process is immediately triggered to adjust the relative spacing between the windings from the source, thereby changing the input and output impedance matching characteristics of the coupler. To improve adjustment accuracy and stability, the control process continuously operates across the entire frequency band from 3MHz to 30MHz. Through real-time feedback and dynamic adjustment, the final VSWR is stably controlled below 1.2. This closed-loop adjustment mechanism can dynamically adapt to changes in different antenna or load conditions, improve the system's coupling efficiency, reduce reflection loss, and thus ensure the long-term stable operation of the RFID system.

[0031] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0032] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dual directional coupler for use in a high-frequency RFID system, characterized in that, Includes the following steps: S1: Construct a hybrid network of series transformers, parallel transformers and Magic-T structure respectively, and use multiple Ni-Zn ferrite double-hole magnetic rings to realize the winding structure of each transformer, forming the core architecture of the impedance self-matching coupler. S2: Input the original coupling signal output from the core architecture of the coupler to the phase-amplitude co-calibration module, and generate a calibrated stable coupling signal by detecting and adjusting the phase consistency and amplitude balance of the signal in real time; S3: The stable coupling signal is input to the bridged T-type attenuation network group. The power of the forward coupling path and the reverse coupling path are precisely adjusted through the dual-path symmetrical attenuation mechanism, and finally the coupling signal with high directivity and low fluctuation is output. S4: Input the coupling signal to the dynamic load adaptation module, and adjust the matching network structure by monitoring the impedance status of the antenna port in real time to achieve stable control of the standing wave ratio in the full frequency band.

2. The dual directional coupler for a high-frequency RFID system according to claim 1, characterized in that, S1 includes: S11: Select BN-73-302 type Ni-Zn ferrite double-hole magnetic ring to construct three physically separate transformer structures respectively; S12: The series transformer functional winding is wound on the first magnetic ring, using enameled copper wire with a diameter of 0.4mm, and the primary to secondary turns ratio is 1:8; S13: Wind a parallel transformer functional winding on the second magnetic ring with a turns ratio of 16:1; S14: Construct a Magic-T hybrid network on the third magnetic ring, using three sets of winding structures with a turns ratio of 1:1:1; S15: Each winding is arranged with a short gap to achieve electromagnetic coupling and is connected to a microstrip impedance converter to form a complete coupler core architecture.

3. A dual directional coupler for use in a high-frequency RFID system according to claim 1, characterized in that, S2 includes: S21: The original coupled signal is split into two paths and input to the phase detector and amplitude detector respectively to generate phase error signal and amplitude error signal; S22: The phase error signal and amplitude error signal are input to the digital signal processor, and a phase correction command and an amplitude balance command are generated respectively through a dual closed-loop control algorithm. These commands are used to control the adjustable phase delay line and the digitally controlled attenuator array to perform phase compensation and amplitude equalization on the coupled signal and output a stable coupled signal.

4. A dual directional coupler for use in a high-frequency RFID system according to claim 3, characterized in that, The phase detector uses the orthogonal correlation detection principle to extract the phase difference, and the amplitude detector uses a logarithmic amplifier structure to extract the amplitude level difference, and outputs error signals respectively.

5. A dual directional coupler for use in a high-frequency RFID system according to claim 3, characterized in that, The dual-loop control algorithm includes a phase control loop for phase compensation and an amplitude control loop for amplitude equalization. The phase control loop dynamically adjusts the adjustable phase delay line according to the phase error signal, and the amplitude control loop dynamically adjusts the numerically controlled attenuator array according to the amplitude error signal, thereby achieving synchronous adjustment of the phase and amplitude of the coupled signal.

6. A dual directional coupler for use in a high-frequency RFID system according to claim 3, characterized in that, S3 includes: S31: The stable coupled signal is split into two paths by a power divider and input to the forward and reverse bridged T-type attenuators respectively; S32: The forward bridging T-type attenuator is a fixed attenuation structure, including a series resistor network, a parallel resistor network, and... Type-matching circuits are used for precise attenuation of transmitted signals; S33: The reverse bridging T-type attenuator is the same as the forward structure and is used to monitor the tag echo signal and feed it back to the digital control unit; S34: The digital control unit dynamically controls the digitally controlled resistor array based on the deviation between the power feedback and the preset threshold, thereby achieving adaptive attenuation adjustment of the reverse path.

7. A dual directional coupler for use in a high-frequency RFID system according to claim 6, characterized in that, S33 includes: S331: The reverse bridging T-type attenuator adopts the same topology as the forward bridging T-type attenuator, and integrates a digitally controlled resistor array inside for dynamic attenuation control of the tag echo signal. S332: A directional power detector is installed at the output end of the reverse bridging T-type attenuator to monitor the output power of the tag echo signal in real time and feed the detection result back to the digital control unit.

8. A dual directional coupler for use in a high-frequency RFID system according to claim 1, characterized in that, S4 includes: S41: A directional coupler is connected in series between the coupling signal output terminal and the antenna port to extract the forward and reflected power signals and input them to the impedance detection unit. S42: The impedance detection unit calculates the complex impedance based on the power vector synthesis algorithm and compares it with the matching interval, and outputs a mismatch evaluation signal. S43: Input the evaluation signal into the digital signal processor to generate coupling adjustment control instructions; S44: An adjustable device for controlling the distance between windings in a magnetic coupling structure to achieve dynamic impedance matching at the antenna port.

9. A dual directional coupler for use in a high-frequency RFID system according to claim 8, characterized in that, The coupling strength control command includes the coupling strength adjustment direction and the coupling strength adjustment range.

10. A dual directional coupler for use in a high-frequency RFID system according to claim 8, characterized in that, The standing wave ratio (SWR) feedback mechanism is used to continuously monitor the SWR status of the antenna port. When the SWR is detected to exceed the preset SWR upper limit threshold, the coupling strength adjustment process is automatically triggered. Impedance matching correction is achieved by adjusting the spacing of the magnetic winding group, maintaining stable coupling and low reflection operation in the full frequency band.

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