CN115329792A

CN115329792A - Carrier leakage elimination device and method for high-power ultrahigh frequency radio frequency identification

Info

Publication number: CN115329792A
Application number: CN202211065596.4A
Authority: CN
Inventors: 牛建民
Original assignee: First Research Institute of Ministry of Public Security
Current assignee: First Research Institute of Ministry of Public Security
Priority date: 2022-09-01
Filing date: 2022-09-01
Publication date: 2022-11-11

Abstract

The invention discloses a carrier leakage elimination device and a carrier leakage elimination method for high-power ultrahigh frequency radio frequency identification, wherein the device comprises a power amplifier, a first directional coupler, a first 3dB bridge, a second 3dB bridge, a third 3dB bridge, two circulators and an antenna; the output end of the power amplifier is connected with the input end of the first directional coupler, the output end of the first directional coupler is connected with the first 3dB bridge, the first 3dB bridge is respectively connected with a circulator, the two circulators are both connected with the second 3dB bridge, and the second 3dB bridge is connected with the antenna; the two circulators are also connected to the 3dB bridge III, and the 3dB bridge III is connected to a signal receiving end. The invention can solve the problem of carrier leakage of the ultrahigh frequency radio frequency identification card reader or other microwave reflection communication when transmitting signals at high power.

Description

Carrier leakage elimination device and method for high-power ultrahigh frequency radio frequency identification

Technical Field

The invention relates to the technical field of radio frequency, in particular to a carrier leakage elimination device and method for high-power ultrahigh frequency radio frequency identification.

Background

RFID is an automatic identification technology which has emerged in the 90 s of the 20 th century, and uses radio frequency signals to realize contactless information transmission through spatial coupling, and achieves the purpose of identification through the transmitted information. The currently internationally common RFID frequency distribution is: the low frequency is 30-300 KHz, the typical representative frequency is 125KHz and 133KHz, and the low frequency is typically applied to animal identification, electronic locking and antitheft and the like; the high frequency is 3-30 MHz, the typical frequency is 13.56MHz, and the typical application is as second generation ID card; the frequency is 860-960 MHz (including 433MHz frequency point), typical frequency is 868MHz, typical application is such as ETC, etc.; the microwave bands are 2.45GHz and 5.8GHz.

The low-frequency and high-frequency application of the RFID works in an inductive coupling mode, the distance between the electronic tag and the card reader is several centimeters or at most dozens of centimeters, the ultrahigh-frequency and microwave application of the RFID adopts electromagnetic wave backscattering coupling, the distance between the electronic tag and the card reader can reach several meters or even dozens of meters, but simultaneously, because the card reader is integrated with a transceiver antenna, namely the transceiver antenna and a receiving antenna share one antenna, carrier signals leaked by a card reader transmitting circuit inevitably exist in a receiving circuit of the card reader, the carrier leakage forms a self-interference signal of the card reader, the self-interference signal obviously deteriorates the receiving sensitivity of the card reader, further influences the receiving distance, even blocks the card reader in serious conditions, and loses the communication capability, and the self-interference signal is inhibited in the circuit. For example, the receiving sensitivity of the integrated card reader is about-70 dBm at a carrier leakage level of 0-5 dBm, and the receiving sensitivity of the integrated card reader can reach-85 dBm at a carrier leakage level of-10 dBm, and the receiving sensitivity is different by 15dB in the two cases, which causes the communication distance to be at least two times different, so that the self-interference signal must be eliminated by using a carrier leakage suppression circuit.

The EIRP of the card reader is less than or equal to 2W according to the UHF RFID standard of China. Taking ETC as an example, the general gain of the antenna is more than 6dBi, so the power amplifier output power in the card reader is less than 0.5W. Generally speaking, increasing the transmission power is the most direct method for improving the communication distance in wireless communication, and in practical use, some UHF RFID application scenarios just need to break through the conventional distance between a card reader and an electronic tag to meet the requirement of practical communication, so that a high-power card reader is needed to transmit signals, and further a carrier leakage elimination device which can bear high power and effectively inhibit carrier leakage is required.

At present, the carrier leakage elimination technology mainly includes two types, namely an active device and a passive device in terms of device types, and an analog signal processing mode and a digital signal processing mode in terms of processing modes. At present, an application specific integrated circuit is used, and because of its high integration level, the circuit scale is small, but its development cost is high.

Passive devices do not need to be powered, such as circulators, directional couplers and the like, and do not introduce extra noise to the circuit, thereby avoiding the deterioration of the signal-to-noise ratio of a useful signal while eliminating leakage signals. The active device has stronger processing capability and can amplify signals, thereby processing stronger leakage signals.

The difference between the analog circuit and the digital circuit in eliminating the carrier leakage is the accuracy, the digital circuit can adjust the amplitude and the phase of the signal with higher accuracy, and almost all the existing carrier leakage elimination technologies are based on the principle that a cancellation signal (sometimes called a reference signal) with the same amplitude as the leakage signal but opposite phase is generated and added to cancel each other, so the error between the two signals, namely the amplitude error and the phase error of the cancellation signal and the leakage signal, is an important factor influencing the cancellation effect, the higher accuracy means a smaller error, and ideally the error is zero, and the carrier leakage signal is completely cancelled. Although the digital signal has higher precision and can be controlled more finely by analog-to-digital conversion, the digital signal brings more quantization noise and digital spurs, which are finally converted into negative factors influencing the signal-to-noise ratio of the useful signal.

The emission power of the UHF RFID card reader is smaller and is below 0.5W, the general communication distance is within 10 m, if the emission power is increased for increasing the communication distance or the emission power of microwave reflection communication based on a similar principle is increased, the carrier leakage power is inevitably increased, the leakage power which can be borne by the conventional UHF RFID card reader is below 10dBm, otherwise, a radio frequency receiving channel of the card reader is blocked.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a carrier leakage elimination device and a carrier leakage elimination method for high-power ultrahigh frequency radio frequency identification.

In order to achieve the purpose, the invention adopts the following technical scheme:

a carrier leakage elimination device for high-power ultrahigh frequency radio frequency identification comprises a power amplifier, a directional coupler I, a 3dB bridge II, a 3dB bridge III, two circulators and an antenna; the output end of the power amplifier is connected with the input end of the first directional coupler, the output end of the first directional coupler is connected with the first 3dB bridge, the first 3dB bridge is respectively connected with a circulator, the two circulators are both connected with the second 3dB bridge, and the second 3dB bridge is connected with the antenna; the two circulators are also connected to the third 3dB bridge, and the third 3dB bridge is connected to a signal receiving end.

Further, the carrier leakage elimination device further comprises a third directional coupler, a fourth directional coupler and a fifth directional coupler, wherein the third 3dB bridge, the third directional coupler, the fourth directional coupler and the fifth directional coupler are sequentially connected, and the fifth directional coupler is connected to the signal receiving end.

Furthermore, the carrier leakage elimination device also comprises a numerical control phase shifter, a directional coupler II, an attenuator I, an attenuator II, a microprocessor and an amplitude and phase comparator; the input end of the numerical control phase shifter is connected to the output end of the first directional coupler, and the output end of the numerical control phase shifter is connected to the second directional coupler; the second directional coupler is connected with the fourth directional coupler; the second directional coupler and the third directional coupler are respectively connected with the first attenuator and the second attenuator, the first attenuator and the second attenuator are both connected with the amplitude and phase comparator, the amplitude and phase comparator is connected with the microprocessor, and the microprocessor is connected with the numerical control phase shifter.

Still further, the directional coupler five is further connected to the attenuator three, the attenuator three is connected to the power detection module, and the power detection module is connected to the microprocessor.

Furthermore, in the numerical control phase shifter, 10-stage phase shifting is connected in series according to the sequence of 0.5 degrees, 1 degree, 2 degrees, 4 degrees, 8 degrees, 16 degrees, 19 degrees, 45 degrees, 90 degrees and 180 degrees, and the 10 th-stage phase shifting is also connected to the radio frequency signal attenuator; each stage of phase shift and the radio frequency signal attenuator are switched by digital logic levels.

The invention also provides a working method of the carrier leakage elimination device for high-power ultrahigh frequency radio frequency identification, which comprises the process of transmitting signals to an antenna, wherein the process of transmitting signals to the antenna comprises the following steps:

in the process of transmitting signals to an antenna, signals output by a signal source pass through a Power Amplifier (PA) to obtain carrier transmission signals (TX), and the carrier transmission signals (TX) are firstly sent to a balanced circulator isolation circuit through a directional coupler I; in the balanced circulator isolating circuit, a transmitting signal output by a directional coupler I is divided into two parts with the same amplitude and 90-degree phase difference through a 3dB bridge I and is respectively sent to a 3dB bridge II through circulators of an upper branch and a lower branch, the phase of an upper branch signal which is originally in the same phase with the transmitting signal is increased by 90 degrees at the 3dB bridge II, and the phase of a lower branch signal which is originally 90-degree phase difference with the transmitting signal is kept unchanged at the 3dB bridge II, so that the amplitude and the phase of the upper branch signal and the lower branch signal at the 3dB bridge II are the same, and the upper branch signal and the lower branch signal are superposed into a new transmitting signal which is sent to an antenna ANT to radiate to the space;

in the process of transmitting a signal TX to an antenna ANT, an upper branch signal output by the first 3dB bridge has half the power of the transmitted signal, is in phase with the transmitted signal, leaks a part of a carrier when passing through a circulator circulating counterclockwise, enters the third 3dB bridge, and remains unchanged in phase when passing through the third 3dB bridge, and a lower branch signal output by the first 3dB bridge has half the power of the transmitted signal, but lags the transmitted signal by 90 degrees in phase, also leaks a part of a carrier when passing through a circulator circulating down, enters the third 3dB bridge and lags the phase again by 90 degrees when passing through the third 3dB bridge, and the phase is accumulated by 180 degrees from the transmitted signal, so that two signals having the same amplitude but opposite phases are superposed at an output port of the third 3dB bridge, and the two signals cancel each other as a result, and thus the carrier leakage caused by the circulators of the upper branch and the lower branch is eliminated.

Further, the method also comprises a process of receiving the signal to a signal receiving end; the process of receiving the signal to the signal receiving end is as follows:

the space electromagnetic wave returned by the electronic tag is received by an antenna and converted into a weak electric signal, and the weak electric signal firstly passes through a balanced circulator isolation circuit; in the isolation circuit of the balanced circulator, the 3dB bridge II divides the weak electric signal into an upper branch signal and a lower branch signal which have the same amplitude and 90 degrees of phase difference, the upper branch signal and the lower branch signal respectively circulate through the circulator and then are converged at the three positions of the 3dB bridge, the phase of the lower branch signal which is originally in the same phase with the received signal is increased by 90 degrees at the three positions of the 3dB bridge, and the phase of the upper branch signal which is originally 90 degrees of phase difference with the received signal is kept unchanged at the three positions of the 3dB bridge, so that the upper branch signal and the lower branch signal have the same amplitude and the same phase at the three positions of the 3dB bridge, and are superposed into a new received signal which is sent to the third directional coupler and then is output to the signal receiving end through the fourth directional coupler and the fifth directional coupler in sequence.

Still further, the method further comprises a second stage leakage signal cancellation process, wherein the second stage leakage signal cancellation process comprises:

generating a reference signal, wherein the reference signal is taken from a signal output by the power amplifier and is generated by a coupling end of the first directional coupler; the second directional coupler couples a reference signal, the third directional coupler couples a leakage signal, and the reference signal and the leakage signal are respectively subjected to amplitude adjustment through the first attenuator and the second attenuator, so that the reference signal and the leakage signal reach the same amplitude as the phase comparator;

the amplitude and phase comparator judges the amplitude difference and the phase difference between the amplitude and the phase comparator and sends the amplitude difference and the phase difference to the microprocessor, the microprocessor combines the coupling degrees of the second directional coupler, the third directional coupler and the fourth directional coupler and the parameters of the first attenuator and the second attenuator after accurate quantification to obtain the amplitude difference and the phase difference of the reference signal and the leakage signal before addition, so that the microprocessor can obtain the reference signal and the leakage signal with the same amplitude and opposite phases by adjusting the numerical control phase shifter to change the amplitude and the phase of the reference signal, and the reference signal and the leakage signal with the same amplitude and opposite phases are added at four positions of the directional coupler and mutually offset.

And then, a signal obtained by adding the reference signal and the leakage signal is coupled out by one percent by using a directional coupler five and is sent to a power detection module through an attenuator three, the power detection module detects the residual carrier leakage signal after cancellation and sends a detection result to a microprocessor, if the phase difference and the amplitude difference are detected by the microprocessor to reach an expected value, otherwise, the amplitude difference and the phase difference are corrected until an expected elimination effect is achieved.

Further, the process that the microprocessor changes the amplitude and the phase of the reference signal by adjusting the numerical control phase shifter is as follows:

firstly, according to the amplitude difference between a leakage signal and a reference signal, carrying out amplitude attenuation on the reference signal in a large scale;

then the optimal phase shift value is searched: initializing the phase shift precision to be thicker stepping, comparing the amplitude of the residual leakage signal after phase shift, judging whether the amplitude is reduced, if so, judging the amplitude to be an effective phase shift value, then improving the phase shift stepping precision, and so on until the highest phase shift precision is reached;

the attenuation trimming value of the digitally controlled phase shifter is then determined: to ensure that the amplitude of the reference signal fed into the directional coupler four for addition is larger than that of the leakage signal, an optimal attenuation value is searched on the basis that: initializing an attenuation value to be a coarser step, comparing the amplitude of the residual leakage signal after attenuation, judging the residual leakage signal to be an effective attenuation value if the residual leakage signal is reduced, then improving the step precision of the attenuation, and so on until the highest precision of the attenuation is reached.

The invention has the beneficial effects that:

1. the bearing power is large. The device adopts passive radio frequency devices such as a circulator, a directional coupler, a numerical control phase shifter and the like, the carrying capacity of the power of a transmitting signal is greatly improved, theoretical calculation shows that the device can work normally when the power of the transmitting signal TX is 100 watts, experimental data shows that the device can stably inhibit carrier leakage signals within the range of the transmitting power from 1 watt to 20 watts, and the power value is far greater than the transmitting power of 0.5 watt of a common ultrahigh frequency radio frequency identification system.

2. The elimination capability to the carrier leakage is strong. The device adopts a two-stage cancellation strategy for leaked carriers, wherein the first-stage cancellation mainly eliminates carrier leakage of a circulator in a circuit, and adopts a mode that two circulators and three 3dB electric bridges form a balanced circuit, and the first-stage cancellation mainly processes leakage signals with relatively large amplitude; the second-stage cancellation aims at the total carrier leakage signals such as antenna echo and directional coupler leakage which are remained after the first-stage cancellation, a reference signal is generated firstly, phase difference and amplitude difference between the reference signal and the leakage signals are sampled and compared, then the reference signal and the leakage signals are aligned through a Digital Control Phase Shifter (DCPS) to be in equal-amplitude reversal, and finally the reference signal and the leakage signals are superposed and mutually cancelled in the directional coupler, and the second-stage processing is to process the leakage signals with relatively small amplitude. Generally speaking, through two-stage cancellation, the suppression ratio of the device to the carrier leakage signal reaches more than 70dB, when the transmitting power TX is equal to 20 watts (43 dBm), the amplitude of the carrier leakage signal leaked to a receiving link is kept below-30 dBm, the value is very safe for the receiving link, and the design target that an ultrahigh frequency radio frequency identification system can still normally work when a high-power transmitting signal is achieved.

3. The noise figure of the receiving link is small. The carrier leakage elimination device is actually a receiving and transmitting isolation device, and the influence of the device on a receiving link is mainly reflected in insertion loss and the rise of background noise, and can be represented by a noise coefficient if being uniformly expressed. The path loss from the antenna to the output end of the received signal in the device is 1.45dB, and an amplifier in the device is not used, so the noise floor is hardly raised, so the noise coefficient of the device to the receiving path is 1.45dB, and the value shows that the receiving sensitivity of the device is not obviously influenced when the device is connected into an ultrahigh frequency radio frequency identification system, and compared with the obvious increase of the transmitting power, the negative influence can be completely accepted.

In general, the invention can solve the problem of carrier leakage of an ultrahigh frequency radio frequency identification card reader or other microwave reflection communication when a high-power transmitting signal is transmitted, thereby enlarging the distance between the card reader and an electronic tag, enhancing the practicability of the system, and also improving the communication distance between a rear device and a front reflector in the microwave reflection communication, thereby increasing the detection distance.

Drawings

Fig. 1 is a schematic structural view of a carrier leakage elimination apparatus in embodiment 1 of the present invention;

FIG. 2 is a schematic structural diagram of a digitally controlled phase shifter in embodiment 1 of the present invention;

FIG. 3 is a flowchart of the second stage elimination algorithm in embodiment 2 of the present invention;

FIG. 4 is a schematic diagram of the principle of the experiment in example 3 of the present invention;

FIG. 5 is a schematic diagram of an attenuator with a resistor II connection;

fig. 6 is a schematic diagram of a transmit-receive isolation result of a carrier leakage cancellation apparatus obtained through an experiment in embodiment 3 of the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings, and it should be noted that the present embodiment is based on the technical scheme, and a detailed implementation manner and a specific operation process are provided, but the protection scope of the present invention is not limited to the present embodiment.

Example 1

If the communication distance between the UHF RFID or the similar microwave reflection communication system and the electronic tag or the front-end device is desired to be increased to meet the needs of some practical application scenarios, increasing the transmission power is an effective and simple way, but while the transmission power is increased, the power leaked from the carrier is also increased correspondingly, and even the nonlinearity is deteriorated, while the radio frequency receiving link of the UHF RFID or the similar microwave reflection communication system generally has the low noise amplifier LNA, and when the power of the signal leaked from the carrier to the receiving link exceeds 0dBm, that is, 1mW, the LNA is easy to generate saturation distortion, thereby causing the deterioration of the receiving sensitivity, and in severe cases, even blocking the receiver, so that the system cannot work normally.

The device of this embodiment is proposed for such application requirements, as shown in fig. 1, wherein a directional coupler and a circulator are applied on a path through which a large signal flows, and the directional coupler and the circulator can withstand hundreds of watts of power, and a specially designed numerical control phase shifter on the path can also withstand approximately 10W of radio frequency power, and these devices are basically passive, i.e., they hardly need to be powered and have no function of amplifying a signal, so that the carrier leakage cancellation device proposed in this embodiment does not raise the noise floor level of a receiver, and the differential loss of a received signal is controlled within 1.5dB, so that it does not significantly affect the sensitivity of the receiver. Meanwhile, the carrier leakage elimination device provided by the embodiment can suppress the carrier leakage to 70dB, so that the risk of LNA saturation distortion does not exist for the transmission signal of dozens of watts. Experimental test data shows that when the antenna is shared in transmitting and receiving, leakage generated by 0.5-20W high-power carrier signals is eliminated, and the suppression ratio is above 70 dB.

The embodiment provides a carrier leakage elimination device for high-power ultrahigh frequency radio frequency identification, which comprises a power amplifier, a first directional coupler, a first 3dB bridge, a second 3dB bridge, a third 3dB bridge, two circulators and an antenna ANT, wherein the directional coupler is connected with the first directional coupler; the output end of the power amplifier is connected with the input end of the first directional coupler, the output end of the first directional coupler is connected with the first 3dB bridge, the first 3dB bridge is respectively connected with a circulator, the two circulators are both connected with the second 3dB bridge, and the second 3dB bridge is connected with the antenna; the two circulators are also connected to the 3dB bridge three, which is connected to the receive signal terminal (RX).

Further, in this embodiment, the carrier leakage cancellation apparatus further includes a third directional coupler, a fourth directional coupler, and a fifth directional coupler, where the third 3dB bridge, the third directional coupler, the fourth directional coupler, and the fifth directional coupler are sequentially connected, and the fifth directional coupler is connected to the signal receiving end.

Furthermore, in this embodiment, the carrier leakage cancellation apparatus further includes a digital control phase shifter DCPS, a second directional coupler, a first attenuator, a second attenuator, a microprocessor MPU, and an amplitude and phase comparator GPD; the input end of the numerical control phase shifter is connected to the output end of the first directional coupler, and the output end of the numerical control phase shifter is connected to the second directional coupler; the second directional coupler is connected with the fourth directional coupler; directional coupler two and directional coupler three are connected respectively in attenuator one (II attenuate one) and attenuator two (II attenuate two), attenuator one and attenuator two all with amplitude and phase comparator are connected, amplitude and phase comparator with microprocessor connects, microprocessor connects in the numerical control looks ware.

Still further, in this embodiment, the directional coupler five is further connected to the attenuator three (ii) which is connected to the power detection module PD, and the power detection module is connected to the microprocessor.

In this embodiment, the first attenuator, the second attenuator and the third attenuator are all resistors pi-type attenuators.

Specifically, in the present embodiment, the DCPS plays a key role in the carrier leakage cancellation circuit, and the present embodiment designs a transmission line-based 10-bit digital phase shifter, as shown in fig. 2. The phase shift precision of the DCPS designed by the embodiment reaches 0.5 degree, which is superior to that of most of the existing digital phase shifters with the precision of 5.625 degrees on the market, the phase shift range is 0-364.5 degrees, whether each level of phase shift depends on the closed state of a SPDT switch, and the switches are controlled by digital logic levels, as shown in FIG. 2, 10-level phase shift networks are connected in series according to the sequence of 0.5 degrees, 1 degrees, 2 degrees, 4 degrees, 8 degrees, 16 degrees, 19 degrees, 45 degrees, 90 degrees and 180 degrees, the total insertion loss of the DCPS is 6dB in the working frequency band, the input 1dB compression point reaches 39dBm, the input 0.1dB compression point is 36.5dBm, which is higher than that of most of the digital phase shifters with the input 1dB compression point of 20-0dBm on the market, so that a high-power transmitting signal of an RFID card reader can be processed. The digital control phase shifter also comprises a digital control radio frequency signal attenuator ATT, the attenuation precision of the digital control radio frequency signal attenuator ATT is 0.25dB, the attenuation range reaches 31.75dB, and the digital control radio frequency signal attenuator ATT is switched and controlled by 7-bit logic level and is respectively 0.25dB, 0.5dB, 1dB, 2dB, 4dB, 8dB and 16dB. Aiming at the parameters of the numerical control phase shifter, such as 0.5 degree of phase precision and 0.25dB of amplitude precision, the cancellation ratio of the DCPS can reach 25dB by applying the numerical control phase shifter.

Example 2

The embodiment provides a working method of the carrier leakage elimination apparatus for high-power ultrahigh frequency radio frequency identification in embodiment 1. The working method of the embodiment comprises three parts:

(1) Procedure for transmitting a signal TX to an antenna ANT:

the Signal output by the Signal Source passes through a power amplifier PA to obtain a carrier emission Signal TX of + 27-43 dBm (0.5-20W). The carrier transmit signal TX is first sent through a directional coupler-to a balanced circulator isolation circuit, i.e., the dashed box in fig. 1. The balanced circulator isolating circuit is a core circuit specially designed in the embodiment and consists of 3dB bridges and two circulators. A transmission signal output by the first directional coupler is divided into two parts with the same amplitude and 90-degree phase difference through the first 3dB bridge, and the two parts are respectively sent to the second 3dB bridge through circulators of the upper branch and the lower branch, wherein the phase of the upper branch signal which is originally in the same phase with the transmission signal is increased by 90 degrees at the second 3dB bridge, and the phase of the lower branch signal which is originally 90-degree phase difference with the transmission signal is kept unchanged at the second 3dB bridge, so that the signals of the upper branch and the lower branch have the same amplitude and the same phase at the second 3dB bridge, and are superposed into a new transmission signal which is sent to an antenna ANT to be radiated to the space. The phase difference between the new transmitting signal and the original carrier transmitting signal TX is 90 degrees, and the amplitude difference is the sum of the difference loss of the first directional coupler and the balanced circulator. The coupling degree of the first directional coupler is 10dB, the difference loss in the working frequency band is 0.47dB, the difference loss of the isolation circuit of the balanced circulator comprises 2 3dB bridges, the difference loss of each bridge is 0.16dB, the difference loss of each circulator is 0.2dB, therefore, the path loss from the transmission signal TX to the antenna ANT is 0.47+0.16x2+0.2x2=1.19db, and relatively speaking, the value is small, and the value ensures that most of transmission power can still be sent to the antenna when the carrier leakage elimination circuit of the embodiment is used in a UHF RFID system.

(2) Procedure from antenna ANT to reception of output signal RX:

the space electromagnetic wave returned by the electronic tag is received by the antenna ANT and converted into a weak electrical signal, as shown in fig. 1, the weak electrical signal firstly passes through the balanced circulator isolating circuit, the 3dB electrical bridge two divides the weak electrical signal into an upper branch and a lower branch which have the same amplitude and 90-degree phase difference, the upper branch and the lower branch are respectively circulated by the circulator and then are converged at the three positions of the 3dB electrical bridge, the phase of the lower branch which is originally in the same phase with the received signal is increased by 90-degree at the three positions of the 3dB electrical bridge, and the phase of the upper branch which is originally 90-degree phase difference with the received signal is kept unchanged at the three positions of the 3dB electrical bridge, so that the signals of the upper branch and the lower branch have the same amplitude and the same phase at the three positions of the 3dB electrical bridge, and are superposed to form a new received signal, the new received signal is sent to the directional coupler three, and then sequentially passes through the four directional coupler and the five directional coupler to output RX received signals. The directional coupler III, the directional coupler IV and the directional coupler V have weak received electrical signals and carrier leakage signals with larger amplitudes, and the amplitudes of the two signals are different by hundred million times, so that the weak received electrical signals coupled from the directional coupler III, the directional coupler IV and the directional coupler V can be ignored, and the path loss from an antenna ANT end to a receiving output signal RX end is the through difference loss of a balanced circulator isolation circuit and a signal passing through the directional coupler III, the directional coupler IV and the directional coupler V. The difference loss of the balanced circulator isolation circuit is two 3dB bridges and two circulators, the coupling degrees of the third directional coupler and the fifth directional coupler are both 20dB, the insertion loss at the working frequency band is 0.13dB, the coupling degree of the fourth directional coupler is 10dB, and the insertion loss at the working frequency band is 0.47dB, so the path loss from an antenna ANT to a receiving output RX is 0.16x2+0.2x2+0.13+0.47+0.13=1.45dB. This value is very small for the carrier leakage cancellation circuit, which ensures that the negative effect on the original received signal is very slight and the reception sensitivity is not substantially deteriorated when the carrier leakage cancellation circuit of this embodiment is used in a UHF RFID system.

(3) And (3) a process of cancellation of a leakage signal:

as shown in fig. 1, leaked carriers mainly come from two parts, one is carrier leakage from an antenna ANT, impedance of an antenna interface is designed according to 50 ohm pure impedance, but actually port impedance of the antenna cannot be exactly 50 Ω, and reactance components exist, and objects around the antenna, especially metal materials, can cause impedance change of the antenna port, generally, return Loss of the antenna port can reach 20dB, which is well matched. The other part of carrier leakage comes from a circulator in the circuit, the circulator is a transmitting-receiving isolating device commonly used for UHF RFID, signals are generally transmitted according to the set circulating direction for transmitting and receiving separation, but the isolation degree is very limited, the isolation degree range of the ferrite circulator is generally 20-30dB, the median value can be 25dB, as shown by a dotted arrow beside the circulator in the balanced circulator isolating circuit in figure 1, when a transmitting signal passes through the circulator in normal circulation, one part enters a receiving channel along the dotted arrow due to the limited isolation degree. The two portions of the signal entering the receive path add up to form the major portion of the carrier leakage.

In order to eliminate the leaked carrier, the present embodiment adopts a two-stage elimination scheme. The first stage is a designed balanced circulator isolating circuit, and the second stage is leakage signal cancellation which takes a digital control phase shifter DCPS as a core and is carried out on a directional coupler IV.

The first stage carrier leakage elimination process is as follows: in the process of transmitting signal TX to antenna ANT, the upper branch signal output by the first 3dB bridge has half of the power of the transmitting signal, the phase of the upper branch signal is in phase with the transmitting signal, when the upper branch signal passes through the counterclockwise circulator, a part of carrier is leaked, the part of carrier enters the third 3dB bridge, the phase of the upper branch signal is kept unchanged when the upper branch signal passes through the third bridge, the lower branch signal output by the first 3dB bridge has half of the power of the transmitting signal, but the phase of the lower branch signal is 90 degrees later than that of the transmitting signal, when the lower branch signal passes through the clockwise circulator, a part of carrier is also leaked, the part of carrier enters the third 3dB bridge, the phase of the lower branch signal is 90 degrees later again when the lower branch signal passes through the third 3dB bridge, the phase accumulation of the lower branch signal is 180 degrees different from the transmitting signal, so that two signals with the same amplitude but opposite phases are superposed at the output ports of the third 3dB bridge, the two signals are mutually cancelled, and the carrier leakage caused by the circulators of the upper and lower branches can be eliminated (the two circulators have opposite electrical performance indexes which are consistent except that the transmitting and the two circulators have the same electrical performance indexes of the balanced circulator, and the balanced isolator can be independently improved by 20 compared with a single circulator.

The second stage carrier leakage elimination process is as follows: a Reference Signal is generated, the amplitude and the phase of the Reference Signal are adjusted to be the same as the amplitude of the finally leaked carrier Signal but opposite to the phase of the finally leaked carrier Signal, and the Reference Signal and the finally leaked carrier Signal are added at four positions of the directional coupler to be mutually offset, so that the purpose of further eliminating carrier leakage is achieved. As shown in fig. 1, the reference signal is taken from the signal output by the power amplifier PA and is generated by the coupled end of the first directional coupler. The GPD in fig. 1 is an amplitude and phase comparator that can compare the amplitude difference and the phase difference of two input signals. In this embodiment, a reference signal is coupled out by a second directional coupler, a carrier leakage signal is coupled out by a third directional coupler, and the amplitudes of the carrier leakage signal are adjusted by a first resistor pi-type attenuator (pi-attenuated first) and a second resistor pi-type attenuator (pi-attenuated second) respectively so that the amplitudes of the carrier leakage signal are equivalent when the carrier leakage signal reaches the GPD, so that the amplitude and phase difference between the carrier leakage signal and the GPD can be more accurately judged by a phase comparator GPD, the amplitude error a ° and the phase error β ° of the two signals are sent to a microprocessor MPU by the GPD, the amplitude difference and the phase difference between the reference signal and the leakage signal before addition can be obtained by accurately quantizing the MPU, and combining the coupling degrees of the second directional coupler, the third directional coupler and the fourth directional coupler, and the parameters of the pi-attenuated first and the pi-attenuated second, so that the amplitude and the phase of the reference signal can be changed by adjusting a numerical control phase shifter DCPS, the reference signal and the leakage signal with the same amplitude and phase can be mutually cancelled. The added signals are coupled out by one percent through a fifth directional coupler, and are sent to a power detection PD module through a third II type attenuator for detecting residual carrier leakage signals after cancellation, if the expected values are reached, phase difference and amplitude difference are stopped to be searched, otherwise, the amplitude difference and the phase difference are corrected in a small range possibly due to device and line errors until a satisfactory cancellation effect is reached, and a signal receiving end is output by a direct end of the fifth directional coupler and is used for butting a radio frequency receiving link of a subsequent UHF RFID card reader.

In this embodiment, as shown in fig. 3, the more specific second-stage elimination process is:

the first step, initialization:

and (3) resetting parameters: carrying out zero clearing on parameters including an amplitude error A, a phase error beta and a carrier residual detection value;

presetting parameters: the parameters required to be preset comprise insertion loss, II-type attenuation I, II-type attenuation II and III of the numerical control phase shifter DCPS and confidence intervals of the amplitude phase comparator GPD and the power detector PD.

Secondly, obtaining the amplitude error A degree and the phase error beta degree of the final leakage signal and the reference signal: the GPD outputs the voltage corresponding to the amplitude error A degree and the voltage corresponding to the phase error beta degree to the MPU, and after the 12-bit ADC is processed, the A degree and the beta degree are calculated according to the coupling degree, the II-type attenuation I and the II-type attenuation II of the second directional coupler and the third directional coupler. The method can quickly determine the amplitude difference and the phase difference between the leakage signal and the reference signal, and can firstly provide a relatively small phase error range compared with the method for aligning the leakage signal by traversing the phase and the amplitude of the reference signal, thereby shortening the search time of the optimal amplitude and the phase of the reference signal.

Thirdly, controlling the phase shift value and the attenuation value of the numerical control phase shifter DCPS: this step is the core of the method of the present embodiment, and the right half of fig. 3 is a specific decomposition of this step.

3.1 First, according to the amplitude difference between the leakage signal and the reference signal, the amplitude attenuation of the reference signal is carried out on a large scale;

3.2 Then search for the optimal phase shift value: initializing the phase shift precision to be thicker stepping, comparing the amplitude of the residual signal after phase shift, judging the residual signal to be an effective phase shift value if the residual signal is reduced, then improving the stepping precision of the phase shift, and so on until the highest precision of the phase shift is reached;

3.3 Next, the attenuation fine-tuning value of the DCPS is determined, because the carrier leakage cancellation device in embodiment 1 has no amplifier, and it does not introduce extra noise, but there is also a restriction that the amplitude of the reference signal must be greater than that of the leakage signal, and the coupling degree of the directional coupler four in the carrier leakage cancellation device is 10dB, so to ensure that the amplitude of the reference signal sent to the directional coupler four for addition is greater than 10dB of the leakage signal, the method for searching the optimal attenuation value is the same as the method for searching the optimal phase-shifting value, and will not be described again.

Fourthly, detecting the amplitude of the residual carrier wave after cancellation: after the optimal phase shift and the optimal attenuation are completed, a small part of residual leakage signals are coupled out by the five directional couplers, converted into direct-current voltage by the power detection circuit PD, sent to the MPU of the microprocessor, subjected to ADC, and then the output power of the actual receiving end RX is calculated according to the coupling coefficient and the II attenuation three of the five directional couplers. Because the carrier leakage elimination device formed in the embodiment is placed in front of the original UHF RFID circuit, the amplitude of the carrier leakage output only needs to meet the requirement of the UHF RFID card reader on an RX signal, the requirement is the carrier leakage elimination threshold value to be realized in the embodiment, and when the measured residual power is less than the threshold value, the cancellation process is ended.

Step five, residual signal monitoring: because the antenna is sensitive to changes of the surrounding environment or the use conditions of the UHF RFID card reader change, the performance of the radio frequency circuit is affected, the method can monitor the amplitude of the carrier residue in real time, and once the amplitude exceeds the threshold value, a new round of carrier leakage cancellation can be triggered.

Example 3

This example provides a performance test of the carrier leakage cancellation apparatus described in example 1.

As shown in fig. 4, the DUT is a carrier leakage elimination device under test, and it has 3 interfaces: TX is used for connecting a high-power transmitting signal, ANT is used for connecting a transmitting and receiving shared antenna, and RX is used for connecting a subsequent receiving circuit. In the test, a radio frequency signal source is used for generating a carrier signal, the carrier signal is sent to a tested unit after power amplification, and then the carrier signal is transmitted to a space through an antenna.

Table 1 lists the main components of the carrier leakage cancellation device tested in this embodiment, and the main printed board is an FR4 board, and 4 layers are a Top layer, a GND layer, a POWER layer and a Bottom layer. The module adopts direct current 7.5V for power supply, and the current is less than or equal to 100mA.

TABLE 1

Table 2 lists the configuration parameters of the attenuators of the tested carrier leakage cancellation apparatus of this embodiment, where 3 attenuators are all connected in a pi-type manner, as shown in fig. 5, and all resistors use the sheet resistors of the patch 0603. Because the amplitude phase comparator AD8302 and the rf power detector ADL5513 both have a confidence interval, i.e. the input range of the corresponding rf signal when the detection error is relatively small, a resistor pi-type attenuator is used in the DUT to adjust the input signal level of the AD8302 and the ADL 5513.

TABLE 2

Table 3 lists the values of the corresponding carrier residual signal RX for different carrier input signals TX of the measured carrier leakage cancellation device. The isolation of the DUT is defined as follows:

Isolatioin＝TX-RX；

table 3 lists the optimum phase shift value and attenuation value for the isolation of the carrier leakage cancellation apparatus. Fig. 6 is a graph showing the variation of the Isolation of the carrier leakage cancellation device with the carrier input signal TX. Because the carrier leakage condition of each stage in the carrier leakage elimination device is inconvenient to be tested by an instrument in real time, the isolation degree of the carrier leakage elimination device is actually characterized: when an accessed carrier transmission signal is radiated to a space through an antenna, and meanwhile, the carrier signal leaked on a receiving link, so that the Isolation of the carrier Leakage elimination device can also be considered as a high-power transmission condition, the Cancellation ratio Leakage Cancellation of the carrier Leakage elimination device is that:

TABLE 3

Table 3 and fig. 6 show that, when the input transmission power TX is equal to 0.5W to 20W, the carrier leakage cancellation apparatus in embodiment 1 suppresses the carrier at the RX receiving end by more than 70dB, and the carrier signal actually leaked to the RX receiving end is less than-30 dBm, so that the carrier leakage of this magnitude is very safe for the LNA of the receiving link, and can ensure that the receiving link can operate normally under the condition of the transmitting and receiving shared antenna.

Various corresponding changes and modifications can be made by those skilled in the art based on the above technical solutions and concepts, and all such changes and modifications should be included in the protection scope of the present invention.

Claims

1. A carrier leakage elimination device for high-power ultrahigh frequency radio frequency identification is characterized by comprising a power amplifier, a directional coupler I, a 3dB bridge II, a 3dB bridge III, two circulators and an antenna; the output end of the power amplifier is connected with the input end of the first directional coupler, the output end of the first directional coupler is connected with the first 3dB bridge, the first 3dB bridge is respectively connected with a circulator, the two circulators are both connected with the second 3dB bridge, and the second 3dB bridge is connected with the antenna; the two circulators are also connected to the 3dB bridge III, and the 3dB bridge III is connected to a signal receiving end.

2. The carrier leakage cancellation device according to claim 1, further comprising a third directional coupler, a fourth directional coupler and a fifth directional coupler, wherein the third 3dB bridge, the third directional coupler, the fourth directional coupler and the fifth directional coupler are sequentially connected, and the fifth directional coupler is connected to the receiving signal terminal.

3. The carrier leakage cancellation apparatus according to claim 2, further comprising a digitally controlled phase shifter, a second directional coupler, a first attenuator, a second attenuator, a microprocessor, and an amplitude and phase comparator; the input end of the numerical control phase shifter is connected to the output end of the first directional coupler, and the output end of the numerical control phase shifter is connected to the second directional coupler; the second directional coupler is connected with the fourth directional coupler; the second directional coupler and the third directional coupler are respectively connected with the first attenuator and the second attenuator, the first attenuator and the second attenuator are both connected with the amplitude and phase comparator, the amplitude and phase comparator is connected with the microprocessor, and the microprocessor is connected with the numerical control phase shifter.

4. The carrier leakage cancellation apparatus according to claim 3, wherein the directional coupler five is further connected to the attenuator three, the attenuator three is connected to a power detection module, and the power detection module is connected to the microprocessor.

5. The carrier leakage cancellation device according to claim 1, wherein in the digitally controlled phase shifter, 10 stages of phase shifts are connected in series in the order of 0.5 °,1 °, 2 °,4 °, 8 °, 16 °, 19 °, 45 °, 90 °, 180 °, and the 10 th stage of phase shift is further connected to the rf signal attenuator; each stage of phase shift and the radio frequency signal attenuator are switched by digital logic levels.

6. A method of operating a carrier leakage cancellation apparatus for high power uhf radio frequency identification as claimed in any one of claims 1 to 5, comprising transmitting a signal to an antenna, wherein the transmitting of the signal to the antenna comprises:

in the process of transmitting signals to an antenna, signals output by a signal source pass through a Power Amplifier (PA) to obtain carrier transmission signals (TX), and the carrier transmission signals (TX) are firstly sent to a balanced circulator isolation circuit through a directional coupler I; in the isolation circuit of the balanced circulator, a transmitting signal output by a first directional coupler is divided into two parts with the same amplitude and 90-degree phase difference through a first 3dB bridge, and the two parts are respectively sent to a second 3dB bridge through circulators of an upper branch and a lower branch, the phase of the upper branch signal which is originally in the same phase with the transmitting signal is increased by 90 degrees at the second 3dB bridge, and the phase of the lower branch signal which is originally 90-degree phase difference with the transmitting signal is kept unchanged at the second 3dB bridge, so that the amplitude and the phase of the upper branch signal and the phase of the lower branch signal at the second 3dB bridge are the same, and the upper branch signal and the lower branch signal are superposed into a new transmitting signal which is sent to an antenna ANT and radiated to the space;

7. The method of claim 6, further comprising a process of receiving the signal to a signal receiving end; the process of receiving the signal to the signal receiving end is as follows:

the space electromagnetic wave returned by the electronic tag is received by an antenna and converted into a weak electric signal, and the weak electric signal firstly passes through a balanced circulator isolation circuit; in the balanced circulator isolating circuit, the 3dB bridge II divides the weak electric signal into an upper branch signal and a lower branch signal which have the same amplitude and 90-degree phase difference, the upper branch signal and the lower branch signal respectively circulate through the circulator and then are converged at three positions of the 3dB bridge, the phase of the lower branch signal which is originally in the same phase with the received signal is increased by 90 degrees at three positions of the 3dB bridge, and the phase of the upper branch signal which is originally 90-degree phase difference with the received signal is kept unchanged at three positions of the 3dB bridge, so that the upper branch signal and the lower branch signal have the same amplitude and the same phase at three positions of the 3dB bridge, are superposed into a new received signal and are sent to the third directional coupler, and then are sequentially output to a received signal end through the fourth directional coupler and the fifth directional coupler.

8. The method of claim 7, further comprising a second stage leakage signal cancellation process, the second stage leakage signal cancellation process comprising:

9. The method of claim 8, wherein the added signal of the reference signal and the leakage signal is coupled out by one percent of a directional coupler five, and is sent to the power detection module through the attenuator three, the power detection module detects the residual carrier leakage signal after cancellation and sends the detection result to the microprocessor, if the expected value is reached, the microprocessor stops searching for the phase difference and the amplitude difference, otherwise, the amplitude difference and the phase difference are corrected until the expected cancellation effect is reached.

10. The method of claim 8, wherein the microprocessor changes the amplitude and phase of the reference signal by adjusting the digitally controlled phase shifter by:

then the optimal phase shift value is searched: initializing the phase shift precision to be thicker stepping, comparing the amplitude of the residual leakage signal after phase shift, judging the residual leakage signal to be an effective phase shift value if the residual leakage signal amplitude is reduced, and then improving the phase shift stepping precision by analogy until the highest phase shift precision is reached;

the attenuation trimming value of the digitally controlled phase shifter is then determined: and searching an optimal attenuation value on the basis of ensuring that the amplitude of the reference signal which is fed into the directional coupler IV for addition is larger than that of the leakage signal: initializing the attenuation value to be a thicker step, comparing the amplitude of the residual leakage signal after attenuation, judging the residual leakage signal to be an effective attenuation value if the residual leakage signal is reduced, then improving the step precision of the attenuation, and so on until the highest precision of the attenuation is reached.