Single balanced mixer with integrated second harmonic extraction and self-shielding function and system

Abstract

This application relates to the field of microwave radio frequency technology, and in particular to a single-balanced mixer and system integrating second harmonic extraction and self-shielding functions. The single-balanced mixer includes: a branch-line coupler, a diode mixer unit, an RF input port, a local oscillator input port, and an intermediate frequency (IF) output port. The branch-line coupler includes two parallel transmission arms and two series transmission arms. The RF input port and the local oscillator input port are respectively connected to the input terminals of the branch-line coupler. The signal input terminal of the diode mixer unit is connected to the output terminal of the branch-line coupler, and the output terminal of the diode mixer unit is connected to the IF output port. A second harmonic extraction port is led out on the transmission line between the output terminal of the branch-line coupler and the signal input terminal of the diode mixer unit. By adopting this application, down-conversion of down-going reception and extraction of up-going second harmonic carrier are simultaneously achieved, solving the self-interference problem between transmission and reception, simplifying the circuit structure, and improving the RF energy utilization rate.

Description

Technical Field

[0001] This application relates to the field of microwave radio frequency technology, and in particular to a single-balanced mixer and system with integrated second harmonic extraction and self-shielding functions. Background Technology

[0002] Backscatter communication is a core supporting technology for passive IoT and UHF RFID systems, and a key path to achieve battery-free, low-power passive tag wireless communication. As passive IoT nodes develop towards miniaturization and large-scale deployment, frequency-shift backscatter technology has become a mainstream research and application direction in the industry because it can alleviate the problem of self-interference between transmit and receive on the same frequency. However, the circuit complexity, power consumption, and energy utilization of its tag-end RF front-end remain the core bottlenecks restricting the large-scale implementation of this technology.

[0003] The existing radio frequency front-end of frequency-shifted backscatter tags typically uses an independent mixer circuit to downconvert the downlink fundamental signal for reception. At the same time, an independent frequency multiplier, oscillator, or external auxiliary carrier source is configured to generate the uplink transmit carrier. The second harmonic generated by the nonlinearity of the diode during the mixing process is regarded as spurious interference and dissipated by the filter circuit. The isolation of the transmit and receive links relies on external duplexers and circulators. This architecture has the defects of hardware redundancy, large circuit size, and high static power consumption, and also causes serious waste of radio frequency energy. External isolation devices also have the problems of high insertion loss and high cost, which cannot meet the low power consumption and miniaturization application requirements of passive tags. Summary of the Invention

[0004] In order to solve the problems of difficulty in acquiring carrier waves of passive backscatter tag, waste of harmonic energy, and self-interference between transmit and receive, this application provides a single-balanced mixer and system that integrates second harmonic extraction and self-shielding functions.

[0005] In a first aspect, this application provides a single-balanced mixer that integrates second harmonic extraction and self-shielding functions, including: a branch line coupler, a diode mixer unit, an RF input port, a local oscillator input port, and an intermediate frequency output port;

[0006] The branch line coupler includes four transmission lines connected end to end to form a ring structure. The four transmission lines include two parallel transmission arms and two series transmission arms. The two series transmission arms are respectively connected in parallel with a first short-circuit stub and a second short-circuit stub.

[0007] The RF input port and the local oscillator input port are respectively connected to the input terminals of the branch line coupler;

[0008] The signal input terminal of the diode mixer is connected to the output terminal of the branch line coupler, and the output terminal of the diode mixer is connected to the intermediate frequency output port.

[0009] A second harmonic extraction port is led out on the transmission line between the output of the branch line coupler and the signal input of the diode mixer unit.

[0010] In one specific implementation, the two parallel transmission arms of the branch line coupler are a first parallel arm and a second parallel arm that are parallel to each other, and the two series transmission arms are a first series arm and a second series arm that are parallel to each other.

[0011] The two ends of the first series arm are connected to the first end of the first parallel arm and the first end of the second parallel arm, respectively. The two ends of the second series arm are connected to the second end of the first parallel arm and the second end of the second parallel arm, respectively, forming a closed ring coupling structure.

[0012] The radio frequency input port is connected to the first end of the first parallel arm, and the local oscillator input port is connected to the second end of the first parallel arm;

[0013] The first end of the second parallel arm constitutes the first output terminal of the branch line coupler, and the second end of the second parallel arm constitutes the second output terminal of the branch line coupler.

[0014] In one specific implementation scheme, the characteristic impedances of the first parallel arm and the second parallel arm are the same, and the characteristic impedances of the first series arm and the second series arm are the same.

[0015] The electrical lengths of the first parallel arm, the second parallel arm, the first series arm, and the second series arm are all quarter wavelengths at the fundamental frequency of the mixer's operation.

[0016] In one specific implementation scheme, the first short-circuit stub and the second short-circuit stub are fundamental quarter-wavelength short-circuit stubs with completely identical structure and electrical parameters, and are symmetrically arranged at the center of the two series transmission arms.

[0017] The electrical lengths of the first and second short-circuit stubs are one-quarter of the wavelength at the fundamental frequency of the mixer and one-half the wavelength at the second harmonic frequency corresponding to the fundamental frequency.

[0018] In one specific implementation, the diode mixer unit includes:

[0019] First diode and second diode;

[0020] The anodes of both the first and second diodes serve as signal input terminals of the diode mixer unit and are connected to the output terminals of the branch line coupler, respectively.

[0021] The cathodes of the first diode and the second diode are shorted to form a common cathode, which serves as the output terminal of the diode mixer unit and is connected to the intermediate frequency output port.

[0022] In one specific implementation, the single-balanced mixer further includes an impedance matching network connected in series between the output of the branch-line coupler and the diode mixer unit.

[0023] Impedance matching networks consist of an inductor and a capacitor connected in series on the transmission line, with the first end of the capacitor connected to the output of the inductor and the second end of the capacitor grounded.

[0024] Secondly, this application also provides a backscatter communication system, including: a reader and a passive tag, wherein the passive tag has a built-in single-balanced mixer with integrated second harmonic extraction and self-shielding functions;

[0025] Passive tags also include tag transceiver antennas, tag-end circulators, local oscillator sources, and tag intermediate frequency demodulation modules;

[0026] The tag transceiver antenna is connected to the common terminal of the tag end circulator. The first transceiver terminal of the tag end circulator is connected to the RF input port of the single-balanced mixer, and the second transceiver terminal of the tag end circulator is connected to the second harmonic extraction port of the single-balanced mixer.

[0027] The local oscillator is connected to the local oscillator input port of the single-balanced mixer, and the tag intermediate frequency demodulation module is connected to the intermediate frequency output port of the single-balanced mixer;

[0028] The reader includes a reader transceiver antenna, a power amplifier, a low-noise amplifier, a demodulation module, and a host computer. The reader transceiver antenna is used to transmit the fundamental wave signal to the passive tag and to receive the second harmonic signal returned by the passive tag.

[0029] Thirdly, this application also provides a backscatter communication method, comprising:

[0030] The reader generates and transmits a fundamental radio frequency signal;

[0031] The passive tag receives the fundamental radio frequency signal through the tag transceiver antenna and transmits the fundamental radio frequency signal to the radio frequency input port of the single balanced mixer. At the same time, the local oscillator of the passive tag generates the local oscillator signal and transmits it to the local oscillator input port of the single balanced mixer.

[0032] The single-balanced mixer uses an internal diode mixer unit to down-convert and mix the fundamental radio frequency signal and the local oscillator signal to generate an intermediate frequency signal carrying downlink data. The intermediate frequency signal is then output from the intermediate frequency output port to the intermediate frequency demodulation module for demodulation, thus completing the downlink data reception.

[0033] During the mixing process, the diode mixer unit uses its own nonlinear characteristics to generate the second harmonic signal corresponding to the fundamental radio frequency signal, and blocks the return path of the second harmonic signal to the radio frequency input port and the local oscillator input port through the short-circuit stub connected in parallel to the series transmission arm of the single balanced mixer, thereby achieving self-shielding of the transmitted and received signals.

[0034] The second harmonic signal whose return path is blocked is extracted from the second harmonic extraction port of the single-balanced mixer and used as the carrier of the uplink backscatter communication, which is then radiated to the reader through the tag transceiver antenna.

[0035] The reader receives the second harmonic signal, performs low-noise amplification and demodulation on the second harmonic signal, restores the uplink data uploaded by the passive tag, and completes bidirectional communication.

[0036] A third aspect of this application provides an electronic device, comprising: a processor and a memory; wherein the memory stores a computer program adapted to be loaded by the processor and to execute the above-described method steps.

[0037] A fourth aspect of this application provides a computer storage medium storing a plurality of instructions adapted for loading by a processor and executing the method steps described above. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a single-balanced mixer with integrated second harmonic extraction and self-shielding functions provided in an embodiment of this application;

[0039] Figure 2 This is a circuit diagram of a single-balanced mixer that integrates second harmonic extraction and self-shielding functions, provided in an embodiment of this application.

[0040] Figure 3 This is a circuit diagram of a backscatter communication system provided in an embodiment of this application;

[0041] Figure 4 This is a flowchart illustrating a backscatter communication method provided in an embodiment of this application. Detailed Implementation

[0042] The terminology used in the following embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification of this application, the singular expressions “a,” “an,” “the,” “the,” and “this” are intended to include the plural expressions as well, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this application refers to any or all possible combinations including one or more of the listed items.

[0043] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature, and in the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0044] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0045] This embodiment relates to a single-balanced mixer 203 that integrates second harmonic extraction and self-shielding functions. The single-balanced mixer 203 is mainly used in the RF front-end circuit of the tag end of passive backscatter communication system, passive IoT tag, and RFID system to simultaneously complete the down-conversion of downlink RF signal reception and the generation and extraction of uplink backscatter carrier.

[0046] Please see Figures 1 to 2 The single-balanced mixer 203, which integrates second harmonic extraction and self-shielding functions, includes: a branch line coupler 2031, a diode mixer unit 203e, a radio frequency (RF) input port 207, a local oscillator (LO) input port 208, and an intermediate frequency (IF) output port 210.

[0047] The branch line coupler 2031 is the core power distribution and phase control component of the single-balanced mixer 203. It is used to perform equal amplitude power distribution and fixed phase difference phase shift processing on the two input RF signals, and to provide two drive signals that meet the single-balanced mixing operation requirements for the downstream diode mixer unit 203e.

[0048] The branch line coupler 2031 includes four transmission lines connected end-to-end to form a ring structure. The four transmission lines are divided into two parallel transmission arms 203b and two series transmission arms 203a. The two parallel transmission arms 203b are used to carry the input signal and the output signal, while the two series transmission arms 203a are used to realize signal coupling and phase modulation within the coupler.

[0049] The two series transmission arms 203a are respectively connected in parallel with a first short-circuit stub and a second short-circuit stub. The first short-circuit stub and the second short-circuit stub are used to realize frequency-selective impedance control, providing a hardware basis for the self-shielding function of the mixer.

[0050] The RF input port 207 and the local oscillator input port 208 are respectively connected to the input terminals of the branch line coupler 2031. The RF input port 207 is used to receive the fundamental RF signal transmitted from the reader 100 by the external tag antenna. The local oscillator input port 208 is used to receive the fixed frequency local oscillator signal generated by the tag's local crystal oscillator circuit. The fundamental RF signal and the local oscillator signal are sent to the branch line coupler 2031 as two input signals for the mixing operation.

[0051] The signal input terminal of diode mixer 203e is connected to the output terminal of branch line coupler 2031, and the output terminal of diode mixer 203e is connected to intermediate frequency output port 210. Diode mixer 203e generates an intermediate frequency signal for downlink data demodulation by downconverting the fundamental radio frequency signal and the local oscillator signal, and generates the second harmonic signal corresponding to the fundamental radio frequency signal and the local oscillator signal by utilizing the nonlinear frequency doubling effect, providing a carrier source for uplink backscatter communication.

[0052] The intermediate frequency output port 210 is used to transmit the intermediate frequency signal generated by the downconversion of the diode mixer unit 203e to the back-end intermediate frequency demodulation circuit to complete the restoration of the downlink communication data.

[0053] A second harmonic extraction port 209 is led out on the transmission line between the output terminal of the branch line coupler 2031 and the signal input terminal of the diode mixer unit 203e. The lead-out position of the second harmonic extraction port 209 is set before the signal input terminal of the diode mixer unit 203e.

[0054] The second harmonic extraction port 209 can be positioned so that after the return path of the second harmonic signal is blocked by the short-circuit stub 203c, the converged second harmonic signal can be exported, preventing the second harmonic signal from entering the intermediate frequency output link of the diode mixer unit 203e. At the same time, the second harmonic energy generated during the mixing process can be recovered and reused as the uplink carrier of the backscatter communication.

[0055] In this embodiment, the single-balanced mixer 203 simultaneously achieves the dual functions of downlink reception demodulation and uplink carrier generation through a single circuit topology, eliminating the need for additional independent duplexers, frequency multipliers, oscillators, and other devices. This significantly simplifies the structure of the passive tag 200 front-end circuit, reduces the circuit's static power consumption and layout area, and achieves physical isolation between transmitted and received signals through the internal short-circuit stub 203c, thus fundamentally solving the self-interference problem in backscatter communication.

[0056] In some embodiments, the fundamental frequency of the single-balanced mixer 203 is 2.45 GHz, the second harmonic frequency corresponding to the fundamental frequency is 4.9 GHz, the frequency of the fundamental radio frequency signal received by the radio frequency input port 207 is 2.45 GHz, the frequency of the local oscillator signal received by the local oscillator input port 208 is 2.43 GHz, and the frequency of the intermediate frequency signal generated by the diode mixer unit 203e through downconversion is 20 MHz.

[0057] In some embodiments, the fundamental frequency of the single-balanced mixer 203 is 915MHz, the second harmonic frequency corresponding to the fundamental frequency is 1.83GHz, the frequency of the fundamental radio frequency signal received by the radio frequency input port 207 is 915MHz, the frequency of the local oscillator signal received by the local oscillator input port 208 is 912MHz, and the frequency of the intermediate frequency signal generated by the diode mixer unit 203e through downconversion is 3MHz.

[0058] Based on the above embodiments, as another optional embodiment, the two parallel transmission arms 203b of the branch line coupler 2031 are a first parallel arm and a second parallel arm that are parallel to each other, and the two series transmission arms 203a are a first series arm and a second series arm that are parallel to each other.

[0059] The two ends of the first series arm are connected to the first end of the first parallel arm and the first end of the second parallel arm, respectively. The two ends of the second series arm are connected to the second end of the first parallel arm and the second end of the second parallel arm, respectively. The first parallel arm, the second parallel arm, the first series arm, and the second series arm together form a closed ring coupling structure.

[0060] The parallel symmetrical arm design ensures that the signal coupling process inside the branch line coupler 2031 is uniform and stable, avoiding problems such as signal amplitude imbalance and phase offset exceeding tolerance.

[0061] The RF input port 207 is connected to the first end of the first parallel arm, and the local oscillator input port 208 is connected to the second end of the first parallel arm. Both input signals are connected to the coupler from the same parallel arm, which can simplify the wiring of the circuit and improve the isolation between the input ports, avoiding crosstalk between the local oscillator signal and the RF input signal.

[0062] The first end of the second parallel arm forms the first output terminal of the branch line coupler 2031, and the second end of the second parallel arm forms the second output terminal of the branch line coupler 2031. Both output signals are derived from the same parallel arm, which can ensure the electrical characteristics of the two output signals are consistent, facilitate the subsequent symmetrical connection with the diode mixer unit 203e, and maintain the balanced working state of the single balanced mixer 203.

[0063] The branch line coupler 2031 performs power distribution and phase shift processing on the fundamental radio frequency signal input from the radio frequency input port 207 and the local oscillator signal input from the local oscillator input port 208 through a closed ring coupling structure. After the fundamental radio frequency signal input from the radio frequency input port 207 enters the first end of the first parallel arm, part of the signal is coupled to the first end of the second parallel arm through the first series arm, and the other part of the signal is coupled to the second end of the second parallel arm through the second series arm.

[0064] The local oscillator signal input at the local oscillator input port 208 enters the second end of the first parallel arm. Similarly, power distribution and coupling are completed through the first series arm and the second series arm. Finally, two output signals with equal amplitude and fixed phase difference are formed at the first output end and the second output end of the second parallel arm. The two output signals are sent to the diode mixer unit 203e at the back end to meet the driving requirements of the single balanced mixer 203.

[0065] Based on the above embodiments, as another optional embodiment, the characteristic impedances of the first parallel arm and the second parallel arm are the same, and the characteristic impedances of the first series arm and the second series arm are the same. This symmetrical characteristic impedance design ensures that the two output signals of the branch line coupler 2031 maintain amplitude balance and stable phase difference, avoiding amplitude deviation and phase shift exceeding tolerances in the two output signals due to inconsistent arm impedances, and preventing spurious performance degradation and port isolation reduction in the subsequent diode mixer unit 203e.

[0066] The electrical lengths of the first parallel arm, the second parallel arm, the first series arm, and the second series arm are all one-quarter wavelength at the fundamental frequency of the mixer's operation. The electrical length of a transmission line is the ratio of its physical length to the wavelength of the signal within it; the electrical length directly determines the impedance transformation characteristics and phase modulation effect of the transmission line.

[0067] When the electrical length of the four transmission arms of the branch line coupler 2031 is one-quarter wavelength at the operating fundamental frequency, the branch line coupler 2031 can achieve a standard 3dB equal power distribution and form a fixed phase difference of 90 degrees between the two output signals. This is the core prerequisite for the single balanced mixer 203 to achieve high isolation and low spurious mixing.

[0068] The impedance and electrical length design in this embodiment has strong versatility. Designers can adapt to different operating frequency bands by adjusting the physical length of the transmission arm without changing the core topology. This enables applications in different ISM frequency bands such as 915MHz, 2.45GHz, and 5.8GHz, greatly improving the applicability of the circuit.

[0069] The symmetrical impedance design and quarter-wavelength electrical length design in this embodiment can also ensure that the first short-circuit stub and the second short-circuit stub have the same effect on the two series transmission arms 203a, avoiding the problems of incomplete second harmonic blocking and backflow leakage, and further improving the self-shielding effect and port isolation of the mixer.

[0070] In some embodiments, the characteristic impedance of the first parallel arm and the second parallel arm is 50Ω, and the characteristic impedance of the first series arm and the second series arm is 35.36Ω. This impedance parameter is compatible with the 50Ω characteristic impedance standard commonly used in radio frequency systems, and can be directly matched with standard radio frequency devices and antennas without transition.

[0071] In some embodiments, the electrical lengths of the first parallel arm, the second parallel arm, the first series arm, and the second series arm have a tolerance range of ±5% at the fundamental frequency of the mixer operation. This tolerance range can accommodate process deviations during microstrip line fabrication, ensuring the mass production yield and performance consistency of the mixer.

[0072] In some embodiments, the transmission line is implemented using microstrip line technology. The characteristic impedance of the transmission line is determined by the linewidth of the transmission line, the dielectric constant of the dielectric substrate, and the thickness of the dielectric substrate. Designers can adjust the linewidth of the transmission line according to the actual substrate material selected to achieve the target characteristic impedance and ensure the consistency of characteristic impedance between parallel arms and between series arms.

[0073] Based on the above embodiments, as another optional embodiment, the first short-circuit stub and the second short-circuit stub are fundamental wave quarter-wavelength short-circuit stubs 203c with completely identical structure and electrical parameters, and the first short-circuit stub and the second short-circuit stub are symmetrically arranged at the center of the two series transmission arms 203a.

[0074] The symmetrical design with identical structure and electrical parameters ensures that the impedance characteristics of the two short-circuited stubs 203c are completely identical at the same frequency, achieving the same blocking effect on the second harmonic signals on the two transmission lines. This avoids the problem of one line being completely blocked while the other line leaks signals, ensuring the integrity of the self-shielding function.

[0075] The center position of the series transmission arm 203a is the midpoint of the electrical length of the series arm. A short-circuit stub 203c is connected in parallel at this position, which can achieve uniform impedance control of the forward fundamental signal and the reverse second harmonic signal transmitted on the series arm. This will not destroy the power distribution and phase shift characteristics of the branch line coupler 2031 at the fundamental frequency. At the same time, it can maximize the blocking effect of the second harmonic signal and prevent the second harmonic signal from leaking to the RF input port 207 and the local oscillator input port 208 through the two ends of the series arm.

[0076] The electrical lengths of the first and second short-circuit stubs are one-quarter wavelength at the fundamental frequency of the mixer, and half wavelength at the second harmonic frequency corresponding to the fundamental frequency.

[0077] One end of the first and second short-circuit stubs is connected to the center of the corresponding series transmission arm 203a, and the other ends of both are grounded. The first and second short-circuit stubs utilize the impedance transformation characteristics of the transmission line to achieve frequency-selective impedance modulation. The core impedance transformation relationship is calculated using the transmission line impedance formula, which is:

[0078] Z in =Z0*(Z L +jZ0*tanθ) / (Z0+jZ L *tanθ).

[0079] Among them, Z in Z is the input impedance of the transmission line, Z0 is the characteristic impedance of the transmission line, and Z... L Let θ be the load impedance of the transmission line, and θ be the electrical length of the transmission line.

[0080] When the end of short-circuit stub 203c is grounded, the load impedance Z L =0. When the electrical length θ is 90 degrees at the fundamental frequency, which is a quarter wavelength, tanθ approaches infinity. At this time, the input impedance Z = 0. in Approaching infinity, which is the open circuit state, the short-circuited stub 203c is equivalent to not existing for the fundamental wave signal and will not affect the normal transmission of the fundamental wave signal on the series transmission arm 203a.

[0081] When the signal frequency is the second harmonic of the fundamental frequency, the electrical length θ becomes 180 degrees, which is half the wavelength, tanθ=0, and the input impedance Z... in =0, which is the short circuit state. For the second harmonic signal, the center position of the series transmission arm 203a is directly grounded. When the second harmonic signal is transmitted to this position, it will undergo total reflection and cannot continue to be transmitted to the input port of the branch line coupler 2031, thereby blocking the return path of the second harmonic signal, realizing the self-shielding function inside the mixer, and solving the self-interference problem of the transmitting and receiving signals.

[0082] The short-circuit stub 203c design in this embodiment does not require additional external filters or duplexers. By integrating a microstrip stub inside the coupler, frequency band isolation between the received fundamental signal and the transmitted second harmonic signal is achieved, significantly reducing the circuit layout area, lowering the insertion loss of signal transmission, and improving the energy utilization and communication distance of the passive tag 200.

[0083] In some embodiments, the first short-circuit stub and the second short-circuit stub are implemented using a microstrip line structure. The ground terminals of the first short-circuit stub and the second short-circuit stub are connected to the bottom ground plane of the circuit board where the mixer is located through metallized vias to ensure low impedance characteristics of the ground and improve the short-circuit blocking effect of the second harmonic.

[0084] In some embodiments, the electrical lengths of the first and second short-circuit stubs have a tolerance range of ±3% at the fundamental frequency of the mixer operation. This tolerance range can ensure the short-circuit blocking effect of the short-circuit stub 203c at the second harmonic frequency and maintain an isolation of more than 40dB between the RF input port 207, the local oscillator input port 208 and the second harmonic extraction port 209.

[0085] In some embodiments, when the fundamental frequency is 2.45 GHz, the physical length of the quarter-wavelength short-circuit stub 203c on the FR-4 dielectric substrate with a dielectric constant of 4.4 is approximately 18 mm, and when the fundamental frequency is 5.8 GHz, the physical length of the quarter-wavelength short-circuit stub 203c on the same substrate is approximately 7.5 mm.

[0086] Based on the above embodiments, as another optional embodiment, the diode mixer unit 203e includes a first diode and a second diode.

[0087] The anodes of both the first and second diodes serve as signal input terminals for the diode mixer unit 203e. The anode of the first diode is connected to the first output terminal of the branch line coupler 2031, and the anode of the second diode is connected to the second output terminal of the branch line coupler 2031. The cathodes of the first and second diodes are shorted to form a common cathode, which serves as the output terminal of the diode mixer unit 203e and is connected to the intermediate frequency output port 210.

[0088] The two equal-amplitude, fixed-phase fundamental and local oscillator signals output by the branch line coupler 2031 are fed into the anodes of the first and second diodes, respectively, and the two signals drive the first and second diodes into nonlinear operating states.

[0089] The common-cathode symmetrical connection structure adopted in this embodiment can, on the one hand, allow the difference frequency intermediate frequency signal generated after the two input signals are mixed in the diodes to be superimposed in the same direction at the common cathode, thereby increasing the output power of the intermediate frequency signal and reducing the receiving sensitivity requirements of the back-end demodulation circuit. On the other hand, it can suppress the odd-order spurious components generated during the mixing process, reduce the filtering pressure of the intermediate frequency output link, and at the same time allow the second harmonic signals generated by the two diodes to be superimposed in the same direction on the anode side, thereby increasing the output power of the second harmonic extraction port 209 and ensuring that the second harmonic signal has sufficient power for backscatter communication.

[0090] The current of a diode is exponentially related to the voltage across its terminals. When an AC signal is applied to the diode, the diode's conduction current will generate nonlinear distortion, thus generating various harmonic components of the input signal. Among them, the second harmonic component has the highest power. By utilizing the inherent nonlinear characteristics of the diode during the mixing process, the second harmonic component, which was originally regarded as spurious interference, can be recovered and reused as the carrier of uplink communication. There is no need to configure an additional independent frequency multiplier circuit, thus achieving efficient utilization of radio frequency energy.

[0091] In some embodiments, both the first diode and the second diode are Schottky barrier diodes. Schottky barrier diodes are majority carrier devices, do not have minority carrier storage effects, have fast switching speeds, small junction capacitances, low insertion loss in the microwave band, and low forward voltage drop. They are suitable for applications in low-energy scenarios of passive tag 200, and can achieve high-efficiency mixing and frequency multiplication even when the input signal power is low.

[0092] In some embodiments, the first diode and the second diode are the same type of device with identical electrical parameters to improve the balance performance and harmonic suppression effect of the mixer unit.

[0093] In some embodiments, the first diode and the second diode adopt a common anode connection structure. The cathodes of the first diode and the second diode are respectively connected to the two output terminals of the branch line coupler 2031. The anodes of the first diode and the second diode are short-circuited to form a common anode. The common anode is connected to the intermediate frequency output port 210 as the output terminal of the diode mixer unit 203e. The second harmonic extraction port 209 is led out from the cathode side of the diode. This structure can achieve the same technical effect as the common cathode structure.

[0094] Based on the above embodiments, as another optional embodiment, the single-balanced mixer 203 further includes an impedance matching network 203d, which is connected in series between the output terminal of the branch line coupler 2031 and the signal input terminal of the diode mixer unit 203e.

[0095] The impedance matching network 203d includes an inductor and a capacitor connected in series on the transmission line. The first end of the capacitor is connected to the output of the inductor, and the second end of the capacitor is grounded.

[0096] In this embodiment, the impedance matching network 203d adopts an L-shaped matching network structure with a series inductor and a parallel capacitor. The impedance matching network 203d is used to achieve impedance conjugate matching between the preceding and following circuits. That is, the output impedance of the branch line coupler 2031, after being transformed by the impedance matching network 203d, is conjugate with the input impedance of the diode mixer unit 203e. This eliminates reflection loss during signal transmission, maximizes the transmission efficiency of the fundamental signal from the branch line coupler 2031 to the diode mixer unit 203e, and maximizes the transmission efficiency of the second harmonic signal from the diode mixer unit 203e to the second harmonic extraction port 209. This reduces useless energy loss during transmission and improves the overall energy efficiency of the mixer.

[0097] In the impedance matching network 203d, the inductor connected in series on the transmission line can suppress the transmission of high-frequency spurious signals, and the parallel grounding capacitor can short-circuit out-of-band spurious signals to ground, thereby achieving a certain bandpass filtering effect, filtering out out-of-band interference in the input signal, ensuring the working stability of the mixer, and reducing the spurious components of the mixer output.

[0098] In some embodiments, the impedance matching network 203d is divided into a first impedance matching network 203d and a second impedance matching network 203d. The first impedance matching network 203d is connected in series between the first output terminal of the branch line coupler 2031 and the anode of the first diode, and the second impedance matching network 203d is connected in series between the second output terminal of the branch line coupler 2031 and the anode of the second diode. The structure and electrical parameters of the first impedance matching network 203d and the second impedance matching network 203d are completely identical, ensuring that the transmission loss and phase offset of the two signals are completely identical, maintaining the balanced working state of the mixing unit, and avoiding the deterioration of mixing performance caused by amplitude imbalance and phase deviation.

[0099] In some embodiments, the impedance matching network 203d adopts a second-order LC network structure. The second-order LC network structure can achieve good impedance matching effect in a wider frequency band, is compatible with the input parameter fluctuations of different batches of diodes, and improves the mass production performance consistency of the mixer.

[0100] In some embodiments, when the input impedance of the diode is 10-j20Ω, the designer can adjust the inductance value of the inductor and the capacitance value of the capacitor to transform the 50Ω system impedance into 10+j20Ω, which is conjugate to the diode input impedance, thereby achieving perfect impedance matching between the preceding and following stages.

[0101] In some embodiments, the single-balanced mixer 203 further includes a low-pass filter 203f disposed between the diode mixer unit 203e and the intermediate frequency output port 210.

[0102] Please refer to Figure 3Based on the above embodiments, as another optional embodiment, this application also provides a backscatter communication system, which is mainly applied to passive Internet of Things, ultra-high frequency radio frequency identification (RFID), environmental backscatter communication, low power wide area Internet of Things and other scenarios, to realize full-duplex bidirectional wireless communication between reader 100 and passive tag 200.

[0103] The backscatter communication system includes a reader 100 and a passive tag 200. The passive tag 200 has a built-in single-balanced mixer 203 with integrated second harmonic extraction and self-shielding functions.

[0104] The passive tag 200 also includes a tag transceiver antenna 201, a tag end circulator 202, a local oscillator 204, and a tag intermediate frequency demodulation module 205.

[0105] The tag transceiver antenna 201 is a radio frequency signal transceiver component of the passive tag 200. It is used to receive the spatial radiation fundamental wave signal emitted by the reader 100, and at the same time radiate the second harmonic signal generated by the single balanced mixer 203 into free space and transmit it back to the reader 100.

[0106] The tag-end circulator 202 is used to achieve signal isolation between the antenna and the receiving link, so as to prevent the high-power second harmonic signal transmitted from directly interfering with the receiving link and degrading the receiving sensitivity of the passive tag 200.

[0107] The tag transceiver antenna 201 is connected to the common terminal of the tag end circulator 202. The first transceiver terminal of the tag end circulator 202 is connected to the RF input port 207 of the single-balanced mixer 203, and the second transceiver terminal is connected to the second harmonic extraction port 209 of the single-balanced mixer 203.

[0108] The fundamental signal input from the tag transceiver antenna 201 enters the common terminal of the tag-end circulator 202 and can only be transmitted unidirectionally to the first transceiver terminal of the tag-end circulator 202 before being sent to the RF input port 207 of the single-balanced mixer 203. It will not interfere with the second transceiver terminal of the tag-end circulator 202. The second harmonic signal output from the second harmonic extraction port 209 of the single-balanced mixer 203 enters the second transceiver terminal of the tag-end circulator 202 and can only be transmitted unidirectionally to the common terminal of the tag-end circulator 202 before being radiated outward through the tag transceiver antenna 201. It will not interfere with the first transceiver terminal of the tag-end circulator 202. This achieves high isolation of the passive tag 200 transceiver link.

[0109] Local oscillator 204 is a local frequency reference device for passive tag 200, used to generate a low-power local oscillator signal at a fixed frequency, providing a stable frequency reference for the downconversion mixing operation of single balanced mixer 203.

[0110] The local oscillator 204 is connected to the local oscillator input port 208 of the single-balanced mixer 203. The local oscillator signal generated by the local oscillator 204 is directly sent to the local oscillator input port 208 of the single-balanced mixer 203, and together with the fundamental signal input from the radio frequency input port 207, enters the single-balanced mixer 203 to complete the mixing operation.

[0111] The tag intermediate frequency demodulation module 205 is the core component for downlink data processing of the passive tag 200. It is used to amplify, filter, and demodulate the intermediate frequency signal output by the single balanced mixer 203 to restore the downlink communication data sent by the reader 100.

[0112] The tag intermediate frequency demodulation module 205 is connected to the intermediate frequency output port 210 of the single balanced mixer 203. After the intermediate frequency signal generated by the down-conversion of the single balanced mixer 203 is output from the intermediate frequency output port 210, it is directly sent to the tag intermediate frequency demodulation module 205 to complete the signal demodulation. The demodulated data can be sent to the back-end microcontroller unit of the passive tag 200 for processing, storage and response execution.

[0113] The reader 100 is the main control and data processing terminal of the backscatter communication system. It is used to transmit downlink fundamental wave signals to the passive tag 200, and at the same time receive and demodulate the uplink second harmonic signal returned by the passive tag 200, so as to complete the bidirectional data interaction and system control with the passive tag 200.

[0114] The reader 100 includes a reader transceiver antenna 104, a power amplifier 102, a low-noise amplifier 105, a demodulation module 106, and a host computer 107.

[0115] The reader transceiver antenna 104 is a radio frequency signal transceiver component of the reader 100, used to transmit fundamental wave signals to the passive tag 200 and receive the second harmonic signals returned by the passive tag 200.

[0116] The power amplifier 102 is the core amplification device of the downlink transmission link of the reader 100. It is used to linearly amplify the fundamental signal generated by the fundamental signal source 101, improve the transmission power of the fundamental signal, and ensure that the passive tag 200 can stably receive the downlink fundamental signal at long distances.

[0117] The output of the power amplifier 102 is connected to the reader transceiver antenna 104, and radiates into free space through the reader transceiver antenna 104.

[0118] The low-noise amplifier 105 is the core amplification device of the uplink receiving link of the reader 100. It is used to amplify the weak second harmonic signal from the passive tag 200 received by the reader's transceiver antenna 104 with low noise. While amplifying the useful signal, it suppresses the noise introduced by the link to the maximum extent, improves the receiving sensitivity of the reader 100, and ensures stable uplink signal reception at long distances.

[0119] The input of the low-noise amplifier 105 is connected to the reader transceiver antenna 104, and the output of the low-noise amplifier 105 is connected to the input of the demodulation module 106.

[0120] The demodulation module 106 is the core component for uplink data processing of the reader 100. It is used to filter and demodulate the amplified second harmonic signal to restore the uplink communication data uploaded by the passive tag 200.

[0121] The output of the demodulation module 106 is connected to the host computer 107, and the demodulated and restored uplink data is transmitted to the host computer 107 for further processing.

[0122] The host computer 107 is the human-computer interaction and system control terminal of the reader 100. It is used to receive and display the uplink data uploaded by the passive tag 200. At the same time, it can send control commands to the reader 100 to adjust the operating parameters such as the transmission frequency, transmission power, communication rate, and modulation method of the fundamental wave signal, so as to realize the full-process control of the entire backscatter communication system.

[0123] The complete workflow of the backscatter communication system in this embodiment is divided into a downlink communication link and an uplink communication link. The two links can work synchronously to achieve full-duplex bidirectional communication.

[0124] The workflow of the downlink communication link includes: the host computer 107 of the reader 100 sends downlink communication commands, the fundamental wave signal source 101 inside the reader 100 generates a fundamental wave signal with the corresponding frequency and modulation mode, the fundamental wave signal is sent to the power amplifier 102 for power amplification, and the amplified fundamental wave signal is radiated into free space through the reader transceiver antenna 104.

[0125] After receiving the fundamental wave signal in space, the tag transceiver antenna 201 of the passive tag 200 sends the fundamental wave signal to the common terminal of the circulator. The circulator transmits the fundamental wave signal unidirectionally to the first transceiver terminal, and then sends it to the RF input port 207 of the single-balanced mixer 203. At the same time, the local oscillator source 204 of the passive tag 200 generates a local oscillator signal of a fixed frequency, which is sent to the local oscillator input port 208 of the single-balanced mixer 203.

[0126] The single-balanced mixer 203 performs down-conversion mixing on the input fundamental signal and local oscillator signal to generate an intermediate frequency signal carrying downlink data. The intermediate frequency signal is output from the intermediate frequency output port 210 and sent to the intermediate frequency demodulation module 106 to complete the demodulation and restoration of the downlink data. The back-end microcontroller unit of the passive tag 200 completes the corresponding response operation based on the demodulated downlink data.

[0127] The uplink communication link operates synchronously with the downlink communication link. While performing downconversion mixing, the single-balanced mixer 203 utilizes the nonlinear characteristics of the internal diode mixer unit 203e to generate the second harmonic signal corresponding to the fundamental signal.

[0128] The first and second short-circuit stubs inside the single-balanced mixer 203 present a short-circuit state for the second harmonic signal, blocking the return path of the second harmonic signal to the RF input port 207 and the local oscillator input port 208, thus realizing a self-shielding function inside the mixer and avoiding self-interference of the second harmonic signal on the downlink receiving link.

[0129] The second harmonic signal, whose return path is blocked, converges to the output of the second harmonic extraction port 209 of the single-balanced mixer 203 and is sent to the second transceiver terminal of the circulator. The circulator transmits the second harmonic signal unidirectionally to the common terminal, and then radiates it into free space through the tag transceiver antenna 201, sending it back to the reader 100. After receiving the second harmonic signal returned by the passive tag 200, the reader transceiver antenna 104 of the reader 100 sends the second harmonic signal to the low-noise amplifier 105 for low-noise amplification. The amplified second harmonic signal is then sent to the demodulation module 106 to complete the demodulation and restoration of the uplink data. The demodulated uplink data is then transmitted to the host computer 107 for display, storage, and analysis, thereby realizing a complete bidirectional communication closed loop between the reader 100 and the passive tag 200.

[0130] The backscatter communication system in this embodiment achieves the dual functions of downlink reception demodulation and uplink carrier generation in a single circuit through the single-balanced mixer 203 with integrated second harmonic extraction and self-shielding functions built into the passive tag 200.

[0131] In some embodiments, the fundamental frequency of the backscatter communication system is 2.45 GHz, the corresponding second harmonic frequency is 4.9 GHz, the transmit power of the fundamental signal transmitted by the reader 100 is 30 dBm, the receiving sensitivity of the passive tag 200 can reach -60 dBm, the second harmonic signal power output by the second harmonic extraction port 209 of the single balanced mixer 203 can reach -3.4 dBm, and the maximum stable communication distance of the system can reach 15 meters.

[0132] In some embodiments, the fundamental frequency of the backscatter communication system is 915MHz, and the corresponding second harmonic frequency is 1.83GHz, which is compatible with the global UHF RFID standard operating frequency band and can be compatible with the hardware architecture of existing commercial RFID readers 100.

[0133] In some embodiments, the tag transceiver antenna 201 of the passive tag 200 adopts a dual-band broadband antenna design, which can simultaneously cover the operating frequency bands of the fundamental frequency and the second harmonic frequency.

[0134] In some embodiments, the transceiver link of the reader 100 also uses a circulator to achieve same-antenna transmission and reception isolation. The reader's transceiver antenna 104 is connected to the common terminal of the circulator, the output terminal of the power amplifier 102 is connected to the transmitting terminal of the circulator, and the input terminal of the low-noise amplifier 105 is connected to the receiving terminal of the circulator, thereby realizing same-antenna transmission and reception of the reader 100, simplifying the antenna design of the reader 100, and reducing the overall size of the reader 100.

[0135] Please refer to Figure 4 Based on the above embodiments, as another optional embodiment, this application also provides a backscatter communication method applied to a backscatter communication system. The system includes a reader and a passive tag. The passive tag has a built-in single-balanced mixer with integrated second harmonic extraction and self-shielding functions. The method includes S1-S6, specifically including:

[0136] S1. The reader generates and transmits a fundamental radio frequency signal;

[0137] The host computer of the reader sends communication control commands, and the fundamental signal source generates a fundamental radio frequency signal corresponding to the ISM operating frequency band. After the fundamental radio frequency signal is linearly amplified by the power amplifier, it is radiated into free space through the reader's transceiver antenna to complete the transmission of downlink communication signals.

[0138] S2. The passive tag receives the fundamental radio frequency signal through the tag transceiver antenna and transmits the fundamental radio frequency signal to the radio frequency input port of the single balanced mixer. At the same time, the local oscillator of the passive tag generates the local oscillator signal and transmits it to the local oscillator input port of the single balanced mixer.

[0139] The passive tag's transceiver antenna receives the fundamental radio frequency signal in space. The fundamental radio frequency signal is transmitted unidirectionally to the radio frequency input port of the single-balanced mixer via a circulator. At the same time, the passive tag's low-power local oscillator generates a local oscillator signal with a fixed frequency difference from the fundamental radio frequency signal. The local oscillator signal is directly fed into the local oscillator input port of the single-balanced mixer to provide a stable frequency reference for subsequent mixing operations.

[0140] S3, the single-balanced mixer uses an internal diode mixer unit to down-convert and mix the fundamental radio frequency signal and the local oscillator signal to generate an intermediate frequency signal carrying downlink data. The intermediate frequency signal is then output from the intermediate frequency output port to the intermediate frequency demodulation module for demodulation, thus completing the downlink data reception.

[0141] The branch line coupler inside the single-balanced mixer performs equal amplitude power distribution and fixed phase offset on the input fundamental RF signal and local oscillator signal, and then sends them to the diode mixer unit. The diode mixer unit uses its own nonlinear volt-ampere characteristics to complete the down-conversion mixing of the two signals, generating an intermediate frequency signal carrying downlink data. After low-pass filtering, the intermediate frequency signal is output from the intermediate frequency output port to the intermediate frequency demodulation module to complete the demodulation and restoration of the downlink data.

[0142] S4. During the mixing process, the diode mixer unit uses its own nonlinear characteristics to generate the second harmonic signal corresponding to the fundamental radio frequency signal. It also blocks the return path of the second harmonic signal to the radio frequency input port and the local oscillator input port through the short-circuit stub connected in parallel to the series transmission arm of the single balanced mixer, thereby achieving self-shielding of the transmitted and received signals.

[0143] During the mixing process, the diode mixer unit synchronously generates the second harmonic signal corresponding to the fundamental radio frequency signal through its own nonlinear frequency doubling effect. The short-circuit stub connected in parallel on the series transmission arm of the single balanced mixer presents a short-circuit state for the second harmonic signal, causing the second harmonic signal to undergo total reflection, completely blocking its return path to the radio frequency input port and the local oscillator input port, and realizing physical isolation and self-shielding of the transmit and receive signals inside the mixer.

[0144] S5. The second harmonic signal whose return path is blocked is extracted from the second harmonic extraction port of the single-balanced mixer and used as the carrier of the uplink backscatter communication, which is then radiated to the reader through the tag transceiver antenna.

[0145] The second harmonic signal, whose return path is blocked, converges on the transmission line on the anode side of the diode and is completely exported from the second harmonic extraction port of the single-balanced mixer. It is directly used as the carrier for uplink backscatter communication and is transmitted unidirectionally to the tag transceiver antenna via the circulator, and then radiated to the reader through the tag transceiver antenna.

[0146] S6. The reader receives the second harmonic signal, performs low-noise amplification and demodulation on the second harmonic signal, restores the uplink data uploaded by the passive tag, and completes bidirectional communication.

[0147] The reader's transceiver antenna receives the second harmonic signal transmitted back by the passive tag. The second harmonic signal is sent to a low-noise amplifier for low-noise amplification and then transmitted to the demodulation module for filtering and demodulation. The uplink data uploaded by the passive tag is then restored and transmitted to the host computer, thus completing the full-duplex bidirectional communication between the reader and the passive tag.

[0148] Based on the above embodiments, as another optional embodiment, the present application embodiment may further include a computer storage medium, which may store multiple instructions adapted for loading and executing a control method of the above embodiments by a processor. For the specific execution process, please refer to the detailed description of the above embodiments, which will not be repeated here.

[0149] Based on the above embodiments, as another optional embodiment, this application embodiment may further include an electronic device. The electronic device may include: at least one processor, at least one communication bus, a user interface, at least one network interface, and a memory.

[0150] The communication bus is used to enable communication between these components.

[0151] The user interface may include a display screen and a camera. Optional user interfaces may also include standard wired interfaces and wireless interfaces.

[0152] The network interface may include standard wired interfaces and wireless interfaces (such as Wi-Fi interfaces).

[0153] The processor may include one or more processing cores. It connects to various parts of the server via various interfaces and lines, executing instructions, programs, code sets, or instruction sets stored in memory, and accessing data stored in memory to perform various server functions and process data. Optionally, the processor may be implemented using at least one of the following hardware forms: Digital Signal Processing (DSP), Field-Programmable Gate Array (FPGA), and Programmable Logic Array (PLA). The processor may integrate one or more of the following: Central Processing Unit (CPU), Graphics Processing Unit (GPU), and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content displayed on the screen; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip without being integrated into the processor.

[0154] The memory may include random access memory (RAM) or read-only memory. Optionally, the memory may include a non-transitory computer-readable storage medium. The memory can be used to store instructions, programs, code, code sets, or instruction sets. The memory may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch function, sound playback function, image playback function, etc.), instructions for implementing the above-described method embodiments, etc.; the data storage area may store data involved in the above-described method embodiments, etc. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor. As a computer storage medium, the memory may include an operating system, a network communication module, a user interface module, and an application program for a control method.

[0155] In electronic devices, the user interface is primarily used to provide an input interface for users and to acquire user input data; while the processor can be used to call an application program stored in memory for a control method. When executed by one or more processors, the electronic device performs one or more methods as described in the above embodiments. It should be noted that, for the foregoing method embodiments, for the sake of simplicity, they are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0156] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0157] In the various embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some service interface; the indirect coupling or communication connection between apparatuses or units may be electrical or other forms.

[0158] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0159] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0160] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, portable hard drives, magnetic disks, or optical disks.

[0161] The above are merely exemplary embodiments of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Other embodiments of this disclosure will readily conceive of those skilled in the art upon consideration of the specification and the disclosure of practical truths.

[0162] This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described in this disclosure. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

Claims

1. A single-balanced mixer integrating second harmonic extraction and self-shielding functions, characterized in that, include: Branch line coupler (2031), diode mixer unit (203e), RF input port (207), local oscillator input port (208) and intermediate frequency output port (210); The branch line coupler (2031) includes four transmission lines connected end to end to form a ring structure. The four transmission lines include two parallel transmission arms (203b) and two series transmission arms (203a). Each series transmission arm (203a) has a short-circuit stub (203c) connected in parallel. The radio frequency input port (207) and the local oscillator input port (208) are respectively connected to the input terminal of the branch line coupler (2031); The signal input terminal of the diode mixer unit (203e) is connected to the output terminal of the branch line coupler (2031), and the output terminal of the diode mixer unit (203e) is connected to the intermediate frequency output port (210). A second harmonic extraction port (209) is led out on the transmission line between the output terminal of the branch line coupler (2031) and the signal input terminal of the diode mixer unit (203e); The short-circuit stub (203c) includes a first short-circuit stub and a second short-circuit stub. The two short-circuit stubs (203c) are fundamental quarter-wavelength short-circuit stubs with completely identical structure and electrical parameters, and are symmetrically arranged at the center of the two series transmission arms (203a). The electrical lengths of the first short-circuit stub and the second short-circuit stub are one-quarter wavelength at the fundamental frequency of the mixer and one-half wavelength at the second harmonic frequency corresponding to the fundamental frequency.

2. The single-balanced mixer integrating second harmonic extraction and self-shielding functions according to claim 1, characterized in that, The two parallel transmission arms (203b) of the branch line coupler (2031) are a first parallel arm and a second parallel arm that are parallel to each other, and the two series transmission arms (203a) are a first series arm and a second series arm that are parallel to each other. The two ends of the first series arm are respectively connected to the first end of the first parallel arm and the first end of the second parallel arm, and the two ends of the second series arm are respectively connected to the second end of the first parallel arm and the second end of the second parallel arm, forming a closed ring coupling structure. The radio frequency input port (207) is connected to the first end of the first parallel arm, and the local oscillator input port (208) is connected to the second end of the first parallel arm; The first end of the second parallel arm constitutes the first output terminal of the branch line coupler (2031), and the second end of the second parallel arm constitutes the second output terminal of the branch line coupler (2031).

3. The single-balanced mixer integrating second harmonic extraction and self-shielding functions according to claim 2, characterized in that, The characteristic impedances of the first parallel arm and the second parallel arm are the same, and the characteristic impedances of the first series arm and the second series arm are the same. The electrical lengths of the first parallel arm, the second parallel arm, the first series arm, and the second series arm are all quarter wavelengths at the fundamental frequency of the mixer operation.

4. The single-balanced mixer integrating second harmonic extraction and self-shielding functions according to claim 1, characterized in that, The diode mixer unit (203e) includes: First diode and second diode; The anodes of the first diode and the second diode are both used as signal input terminals of the diode mixer unit (203e) and are respectively connected to the output terminal of the branch line coupler (2031); The cathodes of the first diode and the second diode are shorted to form a common cathode, which is connected to the intermediate frequency output port (210) as the output terminal of the diode mixer unit (203e).

5. The single-balanced mixer integrating second harmonic extraction and self-shielding functions according to claim 1, characterized in that, Also includes: An impedance matching network (203d) is connected in series between the output of the branch line coupler (2031) and the diode mixer unit (203e); The impedance matching network (203d) includes an inductor and a capacitor connected in series on the transmission line, with the first end of the capacitor connected to the output end of the inductor and the second end of the capacitor grounded.

6. A backscatter communication system, characterized in that, Includes a reader and a passive tag, wherein the passive tag includes a single-balanced mixer as described in any one of claims 1-5; The passive tag (200) also includes a tag transceiver antenna (201), a tag end circulator (202), a local oscillator (204), and a tag intermediate frequency demodulation module (205); The tag transceiver antenna (201) is connected to the common terminal of the tag end circulator (202), the first transceiver terminal of the tag end circulator (202) is connected to the radio frequency input port (207) of the single balanced mixer (203), and the second transceiver terminal of the tag end circulator (202) is connected to the second harmonic extraction port (209) of the single balanced mixer (203). The local oscillator (204) is connected to the local oscillator input port (208) of the single balanced mixer (203), and the tag intermediate frequency demodulation module (205) is connected to the intermediate frequency output port (210) of the single balanced mixer (203). The reader (100) includes a reader transceiver antenna (104), a power amplifier (102), a low-noise amplifier (105), a demodulation module (106), and a host computer (107). The reader transceiver antenna (104) is used to transmit a fundamental wave signal to the passive tag (200) and to receive the second harmonic signal returned by the passive tag (200).

7. A backscatter communication method, characterized in that, An application in a backscatter communication system, the system comprising a reader and a passive tag, the passive tag comprising a single-balanced mixer as described in any one of claims 1-5, the method comprising: The reader generates and transmits a fundamental radio frequency signal; The passive tag receives the fundamental radio frequency signal through the tag transceiver antenna and transmits the fundamental radio frequency signal to the radio frequency input port of the single balanced mixer. At the same time, the local oscillator of the passive tag generates a local oscillator signal and transmits it to the local oscillator input port of the single balanced mixer. The single-balanced mixer uses an internal diode mixer unit to down-convert and mix the fundamental radio frequency signal and the local oscillator signal to generate an intermediate frequency signal carrying downlink data. The intermediate frequency signal is then output from the intermediate frequency output port to the intermediate frequency demodulation module for demodulation, thus completing the downlink data reception. During the mixing process, the diode mixing unit generates the second harmonic signal corresponding to the fundamental radio frequency signal using its own nonlinear characteristics, and blocks the return path of the second harmonic signal to the radio frequency input port and the local oscillator input port through a short-circuit stub connected in parallel to the series transmission arm of the single balanced mixer, thereby achieving self-shielding of the transmitted and received signals. The second harmonic signal whose return path is blocked is extracted from the second harmonic extraction port of the single-balanced mixer and used as the carrier of uplink backscatter communication, and radiated to the reader through the tag transceiver antenna; The reader receives the second harmonic signal, performs low-noise amplification and demodulation on the second harmonic signal, restores the uplink data uploaded by the passive tag, and completes bidirectional communication.

8. An electronic device, characterized in that, It includes a processor, a memory, a user interface, and a network interface. The memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory to cause the electronic device to perform the method as described in claim 7.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores multiple instructions that are adapted to be loaded by a processor and executed as described in claim 7.

Images