Passive chamber division monitoring system and monitoring tag for suppressing chamber division antenna intermodulation degradation

Abstract

The application provides a passive room-division monitoring system and a monitoring tag for inhibiting room-division antenna intermodulation degradation. The working frequency band of the tag antenna is designed as 920-960 MHz, so that the working frequency band of the tag antenna covers the intermodulation interference frequency band, then a duplexer is used to decouple the radio frequency signals received through the tag antenna, effectively strips the radio frequency signals of the intermodulation frequency band from the working frequency band of the monitoring tag and transmits the radio frequency signals to a resistance load for heat consumption, and decouples the radio frequency signals of the effective frequency band and transmits the radio frequency signals to an RFID tag chip, so that the invasion of the intermodulation frequency generated by the monitoring tag to the working frequency band of the room-division antenna is avoided, and the degradation influence on the intermodulation performance of the room-division antenna is fully inhibited.

Description

Technical Field

[0001] This invention relates to the field of RFID tag communication technology, specifically to a monitoring system and its monitoring tag for suppressing intermodulation degradation of indoor distributed antennas. Background Technology

[0002] A passive indoor distributed antenna system (DAS) refers to a system that connects an RFID gateway to a passive indoor distributed antenna system via a dedicated multi-frequency combiner. Passive radio frequency tags are installed on the antennas of the passive indoor distributed antenna system. The system automatically traverses and detects each radio frequency link by transmitting radio frequency identification signals through the RFID gateway. The system reads and analyzes the received signal strength indication value of the signals returned by the passive radio frequency tags to achieve high-range detection of link loss.

[0003] In passive indoor distributed antenna system (DAS) monitoring scenarios, the operating frequency band of the monitoring tag overlaps with that of the indoor distributed antenna provided by the mobile communication operator. When the monitoring tag is placed on the indoor distributed antenna, multiple carrier signals of different frequencies in the antenna simultaneously act on the monitoring tag. Due to the nonlinear electromagnetic response of the monitoring tag, the resulting intermodulation frequency components will intrude into the operating frequency band of the indoor distributed antenna, raising the Nth-order intermodulation index of the antenna and causing the N-order passive intermodulation performance of the system to degrade.

[0004] To address the aforementioned intermodulation degradation issue, one solution is to compress the operating bandwidth of monitoring tags to avoid mobile communication frequency bands. However, according to the 5G NR frequency band specifications developed by the international telecommunications standards organization 3GPP and China's current spectrum allocation framework, the Band 8 band (880-960 MHz) has been fully allocated by multiple operators, including China Mobile, China Unicom, and China Telecom, leaving only a 5MHz idle spectrum segment in the 920-925 MHz range. If the operating frequency band of the monitoring tag's antenna is directly limited to this extremely narrow bandwidth, the following difficulties will be encountered: First, the antenna of a passive RF monitoring tag is a typical electrically small antenna (its size is much smaller than the operating wavelength). Due to physical size limitations, the bandwidth must be extended to achieve high sensitivity. The overall operating bandwidth is usually maintained in a relatively wide range (the operating frequency band of ordinary RF tag antennas is usually 920–940 MHz), which is difficult to directly compress to 5MHz; Second, extremely narrow bandwidth tags have extremely high requirements for processing precision, which significantly increases manufacturing costs; Third, narrowband tags are easily affected by environmental factors (temperature changes, material deformation) during actual deployment, which can cause frequency shifts, leading to the tag deviating from the preset frequency band and becoming ineffective.

[0005] In addition, the following technical problems exist in the actual deployment of the aforementioned monitoring tags on indoor distributed antennas: Firstly, parasitic capacitance will form between the radiator of the monitoring tag and the metal ground plane of the indoor distributed antenna, causing the impedance of the tag antenna to shift and mismatch with the impedance of the RFID tag chip of the monitoring tag, thereby affecting the reading distance and wake-up sensitivity of the monitoring tag.

[0006] Secondly, after the monitoring tag is placed on the surface of the indoor distributed antenna, some of the electromagnetic energy of the radiator of the indoor distributed antenna will be absorbed or reflected by the metal structure of the monitoring tag (antenna radiator, chip circuit, etc.), resulting in a decrease in the effective radiation power of the indoor distributed antenna and affecting the original coverage distance and signal quality of the indoor distributed antenna. Summary of the Invention

[0007] Purpose of the invention: The embodiments of this application aim to provide a monitoring tag and monitoring system for suppressing intermodulation degradation of indoor distributed antennas, so as to at least partially overcome the defects of the prior art.

[0008] Summary of the Invention: To achieve the above objectives, the embodiments of this application propose the following technical solutions: In a first aspect, a monitoring tag is provided, which is mounted on the indoor distributed antenna of a passive indoor distribution system; the monitoring tag includes a tag antenna, a duplexer, an RFID tag chip, and a resistive load. The antenna end of the duplexer is connected to the tag antenna, the receiving end of the duplexer is connected to the resistive load, and the transmitting end of the duplexer is connected to the RFID tag chip. The tag antenna operates in the 920-960 MHz frequency band, which is divided into an effective frequency band and an intermodulation frequency band. The effective frequency band is 920–925 MHz, which is the operating frequency band of the RFID tag chip. The intermodulation frequency band is 934–960 MHz, which is the intermodulation interference band of mobile communication signals. The duplexer is used to decouple the radio frequency signal received through the tag antenna, transmit the radio frequency signal of the effective frequency band to the RFID tag chip, and transmit the radio frequency signal of the intermodulation frequency band to the resistive load for heat dissipation.

[0009] Optionally, the monitoring tag further includes a first to a third impedance matching network; The antenna end of the duplexer is connected to the tag antenna through the first impedance matching network, the receiving end of the duplexer is connected to the resistive load through the second impedance matching network, and the transmitting end of the duplexer is connected to the RFID tag chip through the third impedance matching network. The first to third impedance matching networks achieve conjugate matching with their respective loads, thereby maximizing signal transmission efficiency.

[0010] Optionally, the network structures of the first to third impedance matching networks are identical, and the network structures of the first to third impedance matching networks are as follows: π-type impedance matching network, or L-type impedance matching network, or T-type impedance matching network.

[0011] Optionally, the tag antenna further includes a resonant ring coupled to the radiator of the tag antenna to introduce two resonant points in the operating frequency band of the tag antenna, forming a smooth frequency band covering the 920–960 MHz band between the two resonant points.

[0012] Optionally, a tag metal ground layer is provided on the back side of the radiator of the tag antenna, near the indoor distributed antenna, and the tag metal ground layer is used to eliminate the parasitic capacitance between the metal ground plane of the indoor distributed antenna and the radiator of the tag antenna.

[0013] Optionally, the monitoring tag includes, from top to bottom, a surface protective layer, an antenna and circuit layer, a flexible substrate material layer, a tag metal ground layer, and an adhesive layer.

[0014] Optionally, a tag metal ground layer is provided on the front side of the radiator of the tag antenna, away from the indoor distributed antenna. The tag metal ground layer is used as a reflector to enhance the radiation intensity of the indoor distributed antenna.

[0015] Optionally, the monitoring tag includes, from top to bottom, a surface protective layer, a tag metal ground layer, a flexible substrate material layer, an antenna and circuit layer, and an adhesive layer.

[0016] Optionally, the monitoring tag is a flexible tag; the monitoring tag is affixed to the outer shell of the indoor distributed antenna.

[0017] Secondly, a passive indoor distribution monitoring system for suppressing intermodulation degradation of indoor distribution antennas is provided, comprising: a passive indoor distribution system, an RFID gateway, a multi-frequency combiner, and the aforementioned monitoring tag; The monitoring tag is mounted on the indoor distributed antenna of the passive indoor distribution system; The RFID gateway, as an independent signal source, is connected to the antenna feeder system of the passive indoor distributed antenna system. By sending radio frequency signals to the monitoring tags on each indoor distributed antenna and receiving the received signal strength indication value returned by the monitoring tags, the link loss of the indoor distributed antenna is monitored.

[0018] Beneficial effects: Compared with the prior art, the monitoring tag proposed in this application has the following beneficial effects: The monitoring tag described in this application has its antenna operating in the 920-960 MHz frequency band to cover the intermodulation interference band (934-960 MHz). A duplexer is then used to decouple the radio frequency signal received by the tag antenna, effectively stripping the intermodulation band radio frequency signal from the monitoring tag's operating frequency band and transmitting it to a resistive load for heat dissipation. The effective frequency band radio frequency signal is decoupled and transmitted to the RFID tag chip, thereby avoiding the intrusion of the intermodulation frequency generated by the monitoring tag into the indoor distributed antenna's operating frequency band and fully suppressing the deterioration effect on the indoor distributed antenna's intermodulation performance.

[0019] Furthermore, the monitoring tag described in this application eliminates the parasitic capacitance between the metal ground plane of the indoor distributed antenna and the radiator of the tag antenna by setting a tag metal ground layer on the back of the tag antenna radiator, so that the impedance of the tag antenna remains constant after it is attached to the indoor distributed antenna, thus ensuring the reading distance and wake-up sensitivity of the monitoring tag.

[0020] Furthermore, the monitoring tag described in this application embodiment sets a tag metal ground layer on the front side of the tag antenna radiator, away from the metal ground plane of the indoor distributed antenna, to reflect the electromagnetic waves radiated by the indoor distributed antenna in a direction away from the monitoring tag, thereby reducing the absorption and reflection loss of the energy radiated by the indoor distributed antenna by the monitoring tag, thereby enhancing the effective radiation power of the indoor distributed antenna and ensuring that the coverage performance of the indoor distributed antenna is not affected by the attachment of the monitoring tag. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the architecture of a prior art passive indoor distribution monitoring system involved in an embodiment.

[0022] Figure 2 This is a schematic diagram of the structure of a monitoring tag involved in an embodiment.

[0023] Figure 3 This is a schematic diagram illustrating the working principle of the duplexer involved in the embodiment.

[0024] Figure 4 This is a schematic diagram showing the location of the label metal layer involved in the embodiment.

[0025] Figure 5 This is a schematic diagram of the layered structure of a monitoring tag according to an embodiment.

[0026] Figure 6 This is a schematic diagram of another layered structure of a monitoring tag involved in the embodiment. Detailed Implementation

[0027] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. However, it should be understood that the present invention can be implemented in various forms. The exemplary and non-limiting embodiments shown in the drawings and described below are not intended to limit the invention to the specific embodiments illustrated.

[0028] It should be understood that, where technically feasible, the technical features listed above for different embodiments can be combined with each other to form other embodiments within the scope of this invention. Furthermore, the specific examples and embodiments described in this invention are non-limiting, and corresponding modifications can be made to the structures, steps, and order described above without departing from the protection scope of this invention.

[0029] This embodiment aims to provide a monitoring tag and monitoring system for suppressing intermodulation degradation of indoor distributed antennas. The monitoring tag is applied to a passive indoor distributed monitoring system.

[0030] Before introducing the monitoring tag described in this embodiment, we will first introduce the application scenario of the monitoring tag, namely the passive indoor distribution monitoring system.

[0031] Please refer to Figure 1 , Figure 1 The architecture diagram of a current passive indoor distribution monitoring system is shown. Figure 1 As shown, the passive indoor distribution monitoring system includes a passive indoor distribution system, an RFID gateway, a multi-frequency combiner, and monitoring tags.

[0032] The passive indoor distributed antenna system (DAS) combines multiple signals from external sources (including 2G, 3G, 4G, and 5G mobile communication sources) into a single antenna feeder system via a multi-frequency combiner. This allows the signal to be evenly distributed throughout the room via the DAS antenna, solving the problems of signal blind spots and weak coverage. The passive indoor DAS monitoring system adds an RFID gateway and monitoring tags (passive RFID tags) to the passive DAS system. The RFID gateway acts as an independent signal source, connected to the antenna feeder system via the multi-frequency combiner. The monitoring tags are mounted on the DAS antenna. The system automatically traverses and detects each RF link by transmitting RFID signals from the RFID gateway. By reading and analyzing the received signal strength indication value returned by the passive RFID tags, the system achieves high-range detection of link loss.

[0033] In practice, according to the 5G NR frequency band specifications formulated by the international telecommunications standards organization 3GPP, the n5 and n8 bands cover the frequency ranges of 869-880 MHz / 925-960 MHz and 880-915 MHz / 925-960 MHz, respectively. Under China's current spectrum allocation framework, the Band 8 band has been divided and occupied by multiple operators: China Mobile has obtained 889-904 MHz / 934-949 MHz, China Unicom has obtained 904-915 MHz / 949-960 MHz, and China Telecom's CDMA system also occupies some low-frequency resources. This multi-operator shared frequency band pattern has resulted in the 870-915 MHz and 934-960 MHz bands being completely allocated, leaving passive indoor distributed monitoring systems facing severe spectrum resource constraints.

[0034] In passive indoor monitoring scenarios, the operating frequency band of passive RFID tags overlaps with the operating frequency band of indoor antennas provided by mobile communication operators. Therefore, when multiple carrier signals of different frequencies in the indoor antenna act on the passive RFID tag simultaneously after the passive RFID tag is placed on the indoor antenna, the passive RFID tag exhibits a nonlinear electromagnetic response. The resulting intermodulation frequency components will intrude into the operating frequency band of the indoor antenna, raising the N-order intermodulation index of the indoor antenna and causing the N-order passive intermodulation performance of the system to deteriorate.

[0035] Given that passive monitoring systems must avoid interference with existing licensed spectrum from mobile operators, their operating frequency bands need to maintain necessary isolation from allocated frequency bands. Analysis of the actual occupancy of the Band 8 band revealed that the 920-925 MHz range is a currently unused segment in the spectrum allocation and has a natural isolation band from both uplink and downlink frequency bands. Therefore, in this embodiment, the 920-925 MHz band is selected as the optional operating frequency band for the passive monitoring system. However, this band has an extremely narrow bandwidth of only 5 MHz, which places stringent requirements on the quality factor (Q value) design of the RFID tags.

[0036] In practical engineering implementation, designing RFID tags with extremely high Q values ​​faces multiple challenges: 1. The precision machining process required to achieve narrowband resonance will significantly increase manufacturing costs, making it difficult to meet the economic requirements for large-scale deployment.

[0037] 2. The antenna of a passive RFID tag is a typical electrically small antenna (the size is much smaller than the operating wavelength). Due to size limitations, passive RFID tags must expand their bandwidth to achieve high sensitivity. This means that the overall operating bandwidth of passive RFID tags is usually maintained in a relatively wide range (e.g., 920-940MHz).

[0038] 3. Narrow-bandwidth tags are susceptible to frequency shifts due to environmental factors (such as temperature changes and material deformation) during actual deployment, causing the tags to deviate from the preset operating frequency band and become ineffective.

[0039] Based on the above factors, it is not possible to directly design the operating frequency band of the tag antenna to be 920-925MHz in actual operation.

[0040] In view of this, this embodiment provides a monitoring system and its monitoring tag for suppressing intermodulation degradation of indoor distributed antennas. This monitoring tag, while maintaining the "wide bandwidth" characteristic of the tag antenna, decouples the radio frequency signal received through the tag antenna into an effective frequency band (920–925 MHz) and an intermodulation frequency band (i.e., the frequency band prone to intermodulation interference, 934–960 MHz). The radio frequency signal of the effective frequency band is transmitted to the RFID tag chip of the monitoring tag, while the radio frequency signal of the intermodulation frequency band is transmitted to a resistive load for heat dissipation, thus minimizing the impact of intermodulation interference on the indoor distributed antenna.

[0041] The monitoring system for suppressing intermodulation degradation of indoor distributed antennas and its monitoring tag described in this embodiment will be specifically described below with reference to specific embodiments and accompanying drawings.

[0042] Please refer to Figure 2 , Figure 2 A schematic diagram of a monitoring tag structure is shown. (For example...) Figure 2 As shown, the monitoring tag described in this embodiment is mounted on the indoor distributed antenna of a passive indoor distribution system. The monitoring tag includes a tag antenna, a duplexer, an RFID tag chip, and a resistive load. The antenna end (Ant end) of the duplexer is connected to the tag antenna, the receiving end (Rx end) of the duplexer is connected to the resistive load, and the transmitting end (Tx end) of the duplexer is connected to the RFID tag chip. The tag antenna is used to receive the radio frequency signal sent by the RFID gateway, and the duplexer is used to decouple the radio frequency signal received through the tag antenna. For details, please refer to... Figure 3 , Figure 3 It shows Figure 2 The diagram shows the working principle of the duplexer in the monitoring tag. Figure 3 As shown, the duplexer is used to decouple the radio frequency signal received through the tag antenna, transmit the radio frequency signal in the effective frequency band to the RFID tag chip, and transmit the radio frequency signal in the intermodulation frequency band to the resistive load for heat dissipation.

[0043] The tag antenna's operating frequency band must cover at least the effective frequency band and the intermodulation frequency band. The effective frequency band refers to the operating frequency band of the RFID tag chip, while the intermodulation frequency band refers to the frequency band that contains elements prone to intermodulation interference. In practice, the tag antenna is designed to operate in the 920-960 MHz frequency band, with the effective frequency band at 920–925 MHz and the intermodulation frequency band at 934-960 MHz.

[0044] Ordinary RFID tags typically operate in the 920-940MHz frequency band. However, in this embodiment, the tag antenna is designed to operate in the 920-960MHz frequency band. This is because the 934-960MHz band includes licensed frequency bands from multiple mobile communication operators. When the monitoring system described in this embodiment is installed on an indoor distributed antenna, it will inevitably be exposed to signals in this frequency band. If the tag antenna's operating frequency band does not fully encompass this band (934-960 MHz), i.e., assuming the tag antenna's operating frequency band is 920-940 MHz, then when communication signals in the 941-960MHz band reach the tag antenna, reflection will occur. The resulting N-order intermodulation products will then intrude back into the indoor distributed system, exacerbating the intermodulation interference problem. Therefore, in this embodiment, ordinary 920-940MHz RFID tags cannot be used.

[0045] In this embodiment, the operating frequency band of the tag antenna is designed to cover the intermodulation band and the effective frequency band of 920-960MHz. This allows the communication signals in the intermodulation band to be received by the tag antenna and fed into the resistive load for heat dissipation, rather than being reflected back to the indoor distribution system at the tag antenna end. This eliminates the N-order intermodulation products excited by the reflected signal from the root cause, effectively solving the problem of intermodulation degradation caused by insufficient tag bandwidth in the prior art.

[0046] For details, please continue to refer to [the website / information]. Figure 3 The duplexer receives RF signals in the 920-960 MHz band via the tag antenna, then decouples the RF signals in the 934-960 MHz band and transmits them to a resistive load for heat dissipation. At the same time, it decouples the RF signals in the 920–925 MHz band and transmits them to the RFID tag chip.

[0047] Please continue to refer to this. Figure 2 In one embodiment, the monitoring tag may further include first to third impedance matching networks. The antenna end of the duplexer is connected to the tag antenna through the first impedance matching network, the receiver end of the duplexer is connected to a resistive load through the second impedance matching network, and the transmitter end of the duplexer is connected to the RFID tag chip through the third impedance matching network; the first to third impedance matching networks achieve conjugate matching with the corresponding loads, thereby maximizing signal transmission efficiency.

[0048] The first impedance matching network achieves conjugate matching between the tag antenna and the antenna end of the duplexer, ensuring that the RF signal can be fed into the duplexer from the tag antenna with high transmission efficiency. The output end of the duplexer is conjugate matched with a resistive load through a second impedance matching network, ensuring impedance consistency along the transmission path from the duplexer's output end to the resistive load within the intermodulation band. This effectively suppresses signal reflection, ensuring the resistive load fully consumes the intermodulation signal and significantly reduces the generation of intermodulation products. The transmitter end of the duplexer is conjugate matched with the RFID tag chip through a third impedance matching network, achieving maximum power transfer from the duplexer to the RFID chip while suppressing signal reflection. This ensures the tag chip receives sufficient wake-up energy and operational stability within a very narrow operating frequency band (920-925MHz).

[0049] The network structures of the first to third impedance matching networks described above are identical. Optionally, the first to third impedance matching networks can be π-type, L-type, or T-type impedance matching networks. It should be noted that other impedance matching networks capable of achieving impedance matching of corresponding branches can also be applied to the embodiments of this application, and this embodiment does not impose any limitations on them.

[0050] In one embodiment, the operating bandwidth of a standard RFID tag (typically operating in the 920-940MHz band) can be extended by adding a resonant ring to its antenna. This resonant ring is coupled to the radiator of the tag antenna to introduce two resonant points within the operating band, forming a smooth frequency band covering 920-960MHz. In this case, the standard RFID tag has an operating bandwidth of 920-960 MHz, covering both the effective and intermodulation bands. After this resonant ring-based bandwidth extension, the standard RFID tag can be used as the passive indoor monitoring tag described above.

[0051] In one embodiment, the tag antenna described above can be a dipole antenna. It should be noted that the tag antenna can also employ other structures capable of achieving the corresponding functions of the tag antenna in this embodiment; this embodiment does not impose any limitations on this.

[0052] In one embodiment, a tag metal ground layer can also be provided on the back side of the tag antenna radiator, near the indoor distributed antenna, such as... Figure 4 As shown, taking a dipole antenna as an example, the tag's metallic ground layer is placed on the back side of the dipole antenna's radiator, closer to the indoor distributed antenna. Using a tag's metallic ground layer can eliminate the parasitic capacitance between the indoor distributed antenna's metallic ground plane and the tag antenna's radiator. The specific principle is as follows: When a standard dipole tag antenna is directly attached to the metal ground plane of an indoor distributed antenna, a parallel-plate capacitor structure is formed between them: the radiator of the tag antenna forms one plate of the capacitor, the metal ground plane of the indoor distributed antenna forms the other plate, and the dielectric between them (such as the antenna substrate, air layer, or plastic shell) forms the capacitor's dielectric. This structure introduces a parasitic capacitance. The tag antenna's originally designed impedance (e.g., 50 ohms or the conjugate matching value required by the chip) is "pulled off" by this parasitic capacitance, resulting in impedance mismatch. The chip cannot obtain enough power to start, the reading distance drops sharply, or it may even become unable to read.

[0053] A metal ground layer is inserted on the back of the tag antenna, which serves as an electrostatic shield.

[0054] According to the principles of electromagnetism, metal is an equipotential body. When the tag's metal ground layer is present on the back, the electric field lines generated by the tag antenna radiator will terminate at this metal ground layer on the back, instead of extending through the medium to the indoor distributed antenna metal ground plane below. In other words, the indoor distributed antenna metal ground plane is "blocked" by this metal ground plane.

[0055] Therefore, parasitic capacitance no longer exists between the tag antenna radiator and the indoor distributed antenna's metal ground plane. Instead, there is a fixed capacitance between the tag antenna's own radiator and the tag's metal ground layer on the back. Since this tag metal ground layer is part of the tag antenna design, this capacitance can be fixed and compensated for during the design phase, thus ensuring that the tag antenna's impedance remains constant before and after being attached to the indoor distributed antenna, guaranteeing the consistency and reliability of the monitoring tag's performance.

[0056] In one embodiment, a tag metal ground layer can be provided on the front of the tag antenna radiator, on the side away from the indoor distributed antenna. This tag metal ground layer acts as a reflector, reflecting the electromagnetic waves radiated backward by the tag antenna radiator (i.e., the radiation component facing away from the RFID gateway) to the front, so that they are superimposed in phase with the forward radiation component. This achieves secondary utilization of the backward radiated energy of the tag antenna, significantly improving the forward radiation gain and receiving sensitivity of the tag antenna, thereby effectively extending the effective reading distance of the RFID gateway for passive monitoring tags.

[0057] In one embodiment, the monitoring tag can be designed as a flexible tag so that it can be easily attached to the housing of an indoor distributed antenna with a certain curvature.

[0058] With the tag's metallic ground layer positioned behind the tag antenna radiator, near the indoor distributed antenna, the monitoring tag can be used as follows: Figure 5 The layered design structure is shown. (Example) Figure 5As shown, the monitoring tag comprises, from top to bottom, a surface protective layer, an antenna and circuit layer, a flexible substrate material layer, a tag metal ground layer, and an adhesive layer. The monitoring tag is attached to the outer shell of the indoor distributed antenna via the adhesive layer.

[0059] With the tag's metallic ground layer positioned in front of the tag antenna's radiator, away from the indoor distributed antenna, the monitoring tag can be used as follows: Figure 6 The layered design structure is shown. (Example) Figure 6 As shown, the monitoring tag comprises, from top to bottom, a surface protective layer, a tag metal ground layer, a flexible substrate material layer, an antenna and circuit layer, and an adhesive layer. The monitoring tag is attached to the outer shell of the indoor distributed antenna via the adhesive layer.

[0060] Corresponding to the aforementioned monitoring tags, this application also provides a passive indoor distribution monitoring system for suppressing intermodulation degradation of indoor distribution antennas. The system includes: a passive indoor distribution system, an RFID gateway, a multi-frequency combiner, and the aforementioned monitoring tags. The monitoring tags are mounted on the indoor distribution antennas of the passive indoor distribution system. The RFID gateway, acting as an independent signal source, is connected to the antenna feeder system of the passive indoor distribution system. By sending radio frequency signals to the monitoring tags on each indoor distribution antenna and receiving the received signal strength indication value returned by the monitoring tags, the link loss of the indoor distribution antennas is monitored.

[0061] In this passive indoor distributed antenna monitoring system, the principle of the monitoring tag in suppressing intermodulation degradation of the indoor distributed antenna can be referred to the above introduction on the monitoring tag, and will not be repeated here in this embodiment.

[0062] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A monitoring tag, characterized by The monitoring tag is mounted on the indoor distributed antenna of the passive indoor distribution system; the monitoring tag includes a tag antenna, a duplexer, an RFID tag chip, and a resistive load. The antenna end of the duplexer is connected to the tag antenna, the receiving end of the duplexer is connected to the resistive load, and the transmitting end of the duplexer is connected to the RFID tag chip. The tag antenna operates in the 920-960 MHz frequency band, which is divided into an effective frequency band and an intermodulation frequency band. The effective frequency band is 920–925 MHz, which is the operating frequency band of the RFID tag chip. The intermodulation frequency band is 934–960 MHz, which is the intermodulation interference band of mobile communication signals. The duplexer is used to decouple the radio frequency signal received through the tag antenna, transmit the radio frequency signal of the effective frequency band to the RFID tag chip, and transmit the radio frequency signal of the intermodulation frequency band to the resistive load for heat dissipation.

2. The monitoring tag of claim 1, wherein, The monitoring tag also includes first to third impedance matching networks; The antenna end of the duplexer is connected to the tag antenna through the first impedance matching network, the receiving end of the duplexer is connected to the resistive load through the second impedance matching network, and the transmitting end of the duplexer is connected to the RFID tag chip through the third impedance matching network. The first to third impedance matching networks achieve conjugate matching with their respective loads, thereby maximizing signal transmission efficiency.

3. The monitoring tag according to claim 1, characterized in that, The network structures of the first to third impedance matching networks are identical, and the network structures of the first to third impedance matching networks are as follows: π-type impedance matching network, or L-type impedance matching network, or T-type impedance matching network.

4. The monitoring tag according to claim 1, characterized in that, The tag antenna also includes a resonant ring, which is coupled to the radiator of the tag antenna to introduce two resonant points in the operating frequency band of the tag antenna, forming a smooth frequency band covering the 920–960 MHz band between the two resonant points.

5. The monitoring tag according to claim 1, characterized in that, A tag metal ground layer is provided on the back of the radiator of the tag antenna, on the side close to the indoor distributed antenna. The tag metal ground layer is used to eliminate the parasitic capacitance between the metal ground plane of the indoor distributed antenna and the radiator of the tag antenna.

6. The monitoring tag according to claim 5, characterized in that, The monitoring tag includes, from top to bottom, a surface protective layer, an antenna and circuit layer, a flexible substrate material layer, a tag metal ground layer, and an adhesive layer.

7. The monitoring tag according to claim 1, characterized in that, A tag metal ground layer is provided on the front side of the radiator of the tag antenna, away from the indoor distributed antenna. The tag metal ground layer is used as a reflector to enhance the radiation intensity of the indoor distributed antenna.

8. The monitoring tag according to claim 7, characterized in that, The monitoring tag includes, from top to bottom, a surface protective layer, a tag metal ground layer, a flexible substrate material layer, an antenna and circuit layer, and an adhesive layer.

9. The monitoring tag according to claim 1, characterized in that, The monitoring tag is a flexible tag; the monitoring tag is affixed to the outer shell of the indoor distributed antenna.

10. A passive indoor distributed antenna monitoring system for suppressing intermodulation degradation, characterized in that, include: Passive indoor distribution system, RFID gateway, multi-frequency combiner and monitoring tag as described in any one of claims 1 to 9; The monitoring tag is mounted on the indoor distributed antenna of the passive indoor distribution system; The RFID gateway, as an independent signal source, is connected to the antenna feeder system of the passive indoor distributed antenna system. By sending radio frequency signals to the monitoring tags on each indoor distributed antenna and receiving the received signal strength indication value returned by the monitoring tags, the link loss of the indoor distributed antenna is monitored.

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