Multi-function co-boresight series-fed filter antenna and design method

Abstract

The application discloses a multi-service common-aperture series-fed filter antenna and a design method thereof. The antenna comprises an antenna body, N independent input ports are arranged on the antenna body, and each input port supports one working frequency band. The N input ports are arranged on different radiators for multi-frequency feeding, and a filter structure is arranged on each radiator to realize high isolation between the ports. Radio frequency signals of each working frequency band are input through the corresponding input ports and radiated to the free space by the same antenna body to realize multi-service common-aperture and common-antenna-body. The number of antennas required by a radio frequency communication device formed by the antenna and the space occupied by the antennas can be reduced to 1 / N of the split design. High-impedance feed lines and radiators are alternately connected to feed each radiator in phase as much as possible to realize the electrical characteristics of high gain and horizontal omnidirectional radiation.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication technology, and in particular to a series-fed filter antenna with multiple common apertures and its design method. Background Technology

[0002] With the development of the information age, wireless communication technology is playing an increasingly important role in social production. New concepts and technologies such as the Internet of Things, personal satellite communication, and 5G have emerged, further transforming people's lives. However, with the increasing variety of wireless communication technologies, spectrum resources are becoming increasingly scarce, and the design requirements for radio frequency (RF) front-ends are becoming more demanding. Current wireless communication devices often need to simultaneously support multiple wireless communication technologies and protocols, such as 2G / 3G / 4G / 5G, Wi-Fi, GPS, and Bluetooth. This significantly increases the complexity and size of RF front-end design, while available design space is often limited. Therefore, how to improve the integration of RF front-end design, minimize interference between different frequency bands, and maximize radiation gain within limited space are crucial issues that need to be considered in current wireless communication technology.

[0003] Antennas and filtering circuits constitute a significant portion of the RF front-end circuitry. To separate different wireless communication frequency bands, enabling transmitters and receivers to communicate in the correct bands and reducing interference from other frequency bands, filtering circuits are crucial. In traditional RF front-ends, filters and antennas are designed separately, resulting in a large size. Filtered antennas integrate the filter and antenna design, either by using the antenna as the final stage of the filter or by introducing resonant and parasitic structures onto the antenna. Currently, filtered antennas typically only achieve filtered radiation response within the operating frequency band on a single antenna. When the system needs to support multiple frequency bands, the number of antennas must be increased. For example, the three commonly used WiFi frequency bands are 2.4~2.485GHz, 5.15~5.35GHz, and 5.725~5.925GHz. If devices such as routers need to support these three frequency bands simultaneously and ensure sufficiently low crosstalk between bands, the smallest and most effective solution currently available is to use independent filtered antennas for each frequency band, maintaining sufficient spatial distance. Since routers primarily employ 2×2 MIMO technology, the number of multi-band antennas reaches six, inevitably increasing system complexity and size, leading to higher costs, and potentially limiting their use in certain special scenarios. Therefore, reducing the number of antennas while maintaining the performance of multiple frequency band wireless channels has become one of the technical challenges in the field of multi-band routers. To address this issue, a current effective solution is to integrate the filtering performance of multiple frequency bands into a single antenna element using filtering antenna technology, achieving a multi-channel, common-aperture filtering antenna. However, the technical challenge this invention aims to overcome is how to achieve multi-band filtering performance within a smaller antenna element, improving the isolation between different frequency band ports while maintaining the original antenna's radiation performance. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the first objective of the present invention is to provide a multi-channel common aperture series-fed filter antenna, specifically relating to a multi-channel common aperture common antenna body with high port isolation.

[0005] The second objective of this invention is to provide a design method for a multi-channel, common-aperture series-fed filter antenna.

[0006] A third objective of this invention is to provide a radio frequency communication device.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A multi-channel common-aperture series-fed filter antenna includes an antenna body with N independent input ports, each input port supporting one operating frequency band.

[0009] N input ports are placed on different radiators for multi-frequency feeding, and a filter structure is set on each radiator to achieve high isolation between ports;

[0010] Each operating frequency band inputs an RF signal to its input port, feeds it to the corresponding radiator, and radiates it into free space through the same antenna body, thus realizing a multi-channel, common-aperture, common-antenna-body series-fed filter antenna with high port isolation.

[0011] Furthermore, the antenna body includes a dielectric substrate, with a top metal layer on one side and a bottom metal layer on the other side. The top metal layer has M radiators, where M ≥ N, and N of the M radiators correspond one-to-one with N input ports. The dielectric substrate is embedded with N metal ground planes, which correspond one-to-one with the N radiators. The M radiators are connected by high-impedance feed lines. The bottom metal layer has microstrip lines corresponding to the N radiators, forming parallel resonators with the radiators. Each operating frequency band is fed by an independent external feed line.

[0012] Furthermore, the N radiators are partially hollowed out to accommodate short-circuit transmission lines, forming U-shaped air troughs with stepped widths;

[0013] The short-circuit transmission line, U-shaped air slot, microstrip line, and radiator constitute a filtering structure, which enables the antenna to generate transmission and radiation nulls at the upper and lower sidebands outside the passband, suppressing interference from other frequency bands and maintaining high isolation between ports of multiple frequency bands fed to the same antenna body.

[0014] Furthermore, the M radiators are connected via high-impedance feed lines, specifically alternating between radiators and high-impedance feed lines. The high-impedance feed lines are equivalent to open circuits in the circuitry, allowing each radiator to operate independently at the circuit level. At the radiation level, the alternating connection of radiators and high-impedance feed lines forms a series-fed antenna structure, increasing the antenna's radiating aperture. Secondly, the feed point for each frequency band is located at the bottom of the radiator, near its edge, at a current wave node, thus minimizing crosstalk current from other frequency band ports. For these reasons, the filtering structure for each frequency band can be designed independently without being affected by the filtering structures of other frequency bands.

[0015] Furthermore, the radiator is composed of low-impedance lines.

[0016] Furthermore, the input port of one operating frequency band is fed by M radiators of the antenna body, which together radiate to achieve multi-band multiplexing of the M radiators.

[0017] Furthermore, the length of the short-circuit transmission line is λ1 / 4, which is equivalent to an LC resonator connected in parallel between the input port and the radiation port. The center frequency is located within the passband, and λ1 is the wavelength corresponding to the resonant frequency of the short-circuit transmission line.

[0018] Furthermore, the microstrip line and the radiator form a quarter-wavelength parallel resonator, which is excited by differential mode, and the current on the microstrip line and the radiator is opposite at resonance.

[0019] Furthermore, the U-shaped air trough introduces electromagnetic coupling between the short-circuit transmission line and the radiator.

[0020] Furthermore, by adjusting the length of the high-impedance feed line, each radiator is fed in phase.

[0021] Furthermore, the above structure introduces a second-order bandpass filter response in each frequency band.

[0022] Furthermore, when antenna loss is sufficiently low, the discontinuity between the high-impedance feed line and the low-impedance radiator does not result in energy loss. When the antenna input ports are well matched, according to the principle of current continuity, the current will reach all radiators on the same antenna body through the high-impedance feed line, thus forming a series-fed array antenna structure, increasing the radiating aperture and gain. The energy input from the ports is divided into three parts: one is due to the antenna's own losses, the second is radiated into free space by the antenna, and the third is transmitted to other external ports. In the design, the high isolation between the antenna ports ensures that almost no energy is transmitted to other external ports, and the antenna loss is sufficiently low, so most of the energy is radiated into free space; therefore, high radiation efficiency can still be maintained even in the case of multiple frequency bands sharing the same antenna body.

[0023] Furthermore, when there are three input ports, a three-port common aperture series-fed filter antenna is formed, including a dielectric substrate. A top metal layer is provided on one side of the dielectric substrate, and a bottom metal layer is provided on the bottom side. Three radiators are provided on the top metal layer. The three radiators are connected through a first high-impedance feed line and a second high-impedance feed line. U-shaped air slots are provided inside the three radiators. A metal ground plane corresponding to the radiator is embedded in the dielectric substrate. A microstrip line corresponding to the radiator is provided on the bottom metal layer. The radiators are fed by external feed lines.

[0024] Furthermore, the three radiators support three operating frequency bands: 2.4–2.485 GHz, 5.15–5.35 GHz, and 5.725–5.925 GHz, respectively.

[0025] A design method for implementing the aforementioned series-fed filter antenna includes the following steps:

[0026] Define N operating frequency bands, where there is no frequency overlap between the operating frequency bands;

[0027] Select the antenna type according to the required radiation mode;

[0028] The antenna is designed as follows:

[0029] The N input ports corresponding to the N operating frequency bands are respectively fed to different radiators. The selection of the feeding position ensures that the antenna is effectively excited and radiates the required mode.

[0030] A filter structure is designed on the radiator of the corresponding input port to achieve the integration of combining, filtering and radiation functions into one, while maintaining high isolation between different input ports. Each frequency band works independently at the same time and is a series-fed filter antenna that radiates into free space through the same antenna body.

[0031] A radio frequency communication device includes the aforementioned series-fed filter antenna.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] (1) The antenna of the present invention integrates multiple working frequency bands on one antenna body. Each working frequency band uses an independent input port to feed the radiator of the corresponding frequency band. It can work simultaneously and independently, reducing the number of antennas required to 1 / N of the traditional split antenna design (N is the number of frequency bands supported by the antenna of the present invention), realizing the multi-working and common aperture function, and has the structural characteristics of a common antenna body.

[0034] (2) The antenna of the present invention is fed to the input port of one working frequency band and is radiated by M radiators of the antenna body, realizing multi-band multiplexing of M radiators. Therefore, the gain is not significantly reduced compared with the traditional discrete antenna.

[0035] (3) By setting up independent filtering structures for each frequency band, the present invention introduces a second-order bandpass filter response for each frequency band without using additional integrated filters, generating transmission and radiation nulls at the upper and lower sidebands outside the passband, thereby achieving high out-of-band suppression performance and high port isolation, and effectively reducing antenna size.

[0036] (4) The antenna structure of the present invention is simple, can be mass-produced using PCB processing technology and is inexpensive; compared with the current antenna design, it can significantly reduce the size of communication equipment, improve integration and enhance the communication performance of multi-band communication equipment. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a multi-channel common-aperture series-fed filter antenna according to Embodiment 1 of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of a three-channel common aperture series-fed filter antenna according to Embodiment 2 of the present invention;

[0039] Figure 3 This is a schematic diagram of the filtering structure in Embodiment 1 of the present invention;

[0040] Figures 4(a) and 4(b) are port S-parameter curves of Embodiment 2 of the present invention;

[0041] Figures 5(a)-5(c) are gain curves of Embodiment 2 of the present invention;

[0042] Figures 6(a) and 6(b) are radiation patterns of the E-plane and H-plane at 2.45 GHz in Embodiment 2 of the present invention;

[0043] Figures 7(a) and 7(b) are radiation patterns of the E-plane and H-plane at 5.25 GHz in Embodiment 2 of the present invention;

[0044] Figures 8(a) and 8(b) are radiation patterns of the E-plane and H-plane at 5.85 GHz in Embodiment 2 of the present invention. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0046] Example 1

[0047] In this embodiment, one side refers to the upper surface of the dielectric substrate, and the other side refers to the lower surface of the dielectric substrate.

[0048] like Figure 1 As shown, this embodiment provides a series-fed filter antenna with high port isolation, featuring a multi-port common aperture and common antenna body. It is manufactured using PCB technology and includes an antenna body with N independent input ports. Each input port supports one operating frequency band, and the antenna supports a total of N operating frequency bands.

[0049] N input ports are placed on different radiators for multi-frequency feeding. Each radiator is equipped with a filter structure to achieve high isolation between different frequencies of each port. Each frequency band inputs radio frequency signals through the corresponding input port, which can work simultaneously and independently and radiate into free space from the same antenna body, realizing the function of multiple work with a common aperture and having the structural characteristics of a common antenna body.

[0050] The series-fed filter antenna provided in this embodiment integrates combining, filtering and radiation functions into one unit, which effectively reduces system complexity, insertion loss and size compared to discrete components.

[0051] Furthermore, the multi-channel, shared-aperture, shared-antenna-body design can significantly reduce the space occupied by the antenna. When the entire system needs to support N different frequency bands to work simultaneously and independently, compared with the traditional discrete antenna design, multiple radiators on a single antenna body can reuse multiple frequency bands, reducing the number of antennas to 1 / N and the volume occupied to 1 / N, while maintaining the same radiation performance.

[0052] The series-fed filter antenna with multiple antennas of the same aperture in Embodiment 1 has the following specific structure: a dielectric substrate 3, a top metal layer 1 disposed on the upper surface of the dielectric substrate 3, a bottom metal layer 4 disposed on the lower surface of the dielectric substrate, M radiators 6 disposed on the top metal layer 1, where M ≥ N, and both M and N are greater than or equal to 1, and the number of radiators is greater than the number of frequency bands, N metal ground planes 2 embedded in the dielectric substrate, each metal ground plane 2 corresponding to one of the N radiators, the M radiators 6 being connected by high-impedance feed lines 8, and microstrip lines 9 disposed on the bottom metal layer 4, each microstrip line 9 being disposed corresponding to one of the N radiators, the number of microstrip lines being N pairs, and the microstrip lines and radiators forming a parallel resonator.

[0053] Furthermore, the other MN radiators are connected by high-impedance feed lines to form a radiating structure.

[0054] Furthermore, each operating frequency band is fed by an independent external feed line 5, which is located behind the dielectric substrate 3. The outer conductor 10 of the external feed line is connected to the metal ground plane, and the inner conductor 11 passes through the dielectric substrate and is connected to the top metal layer 1.

[0055] Furthermore, the input port of a working frequency band is fed by M radiators of the antenna body, which together radiate to achieve multi-band multiplexing of the M radiators.

[0056] Furthermore, the radiator portion corresponding to the input port is hollowed out to accommodate the short-circuit transmission line 7, forming a U-shaped air trough 12 with a stepped width.

[0057] To further explain, the bottom of the short-circuited transmission line is short-circuited by a metal ground plane, while the top is an open-circuit structure. Since there are no metal obstructions on the short-circuited transmission line, it can radiate electromagnetic waves into the air. The length of the short-circuited transmission line is λ1 / 4, equivalent to an LC resonator connected in parallel between the input signal port and the radiation port, where λ1 is the wavelength corresponding to the resonant frequency of the short-circuited transmission line. When the operating frequency equals the resonant frequency, the energy transferred to the subsequent stage is maximum, and consequently, the energy radiated into free space is also maximum; this frequency point is the radiation pole. When the operating frequency is outside the resonant frequency, the short-circuited transmission line is detuned, equivalent to an inductor or capacitor, and the energy transferred to the subsequent stage decreases rapidly, resulting in high out-of-band rejection.

[0058] To further explain, the U-shaped air trough 12 introduces electromagnetic coupling between the short-circuit transmission line 7 and the radiator 6. By changing its size parameters, the radiation null point of the lower sideband can be adjusted.

[0059] To further explain, the bottom of the microstrip line on the bottom metal layer 4 is short-circuited by the metal ground plane, and the top is an open-circuit structure. The structure formed by the microstrip line and the radiator on the top metal layer is equivalent to a parallel resonator. The length of the microstrip line is λ² / 4, where λ² is the wavelength corresponding to the resonant frequency of this parallel resonator. The parallel resonator is differentially fed, and the microstrip line is placed at the edge of the U-shaped air slot, equivalent to being connected in parallel to the inductive non-resonant node formed when the short-circuited transmission line is detuned. When the operating frequency is equal to the resonant frequency of the parallel resonator, the current in the microstrip line is out of phase with the current in the radiator, generating a radiation zero. When the operating frequency is less than the resonant frequency, a transmission pole is generated between the signal port and the radiation port.

[0060] To further explain, such as Figure 3 As shown, the filter structure, consisting of short-circuited transmission line 7, U-shaped air slot 12, microstrip line 9, and radiator 6, forms a second-order filter response. It generates radiation nulls at the upper and lower sidebands outside the passband, effectively suppressing interference from other frequency bands. This ensures high isolation between ports of multiple frequency bands fed to the same antenna body, guaranteeing independent operating performance for each frequency band.

[0061] To further explain, the M radiators 6 are connected sequentially via high-impedance feed lines 8, meaning the radiators and high-impedance feed lines are alternately arranged. First, the high-impedance feed line is equivalent to an open circuit in terms of circuitry, allowing each radiator to operate independently at the circuit level. At the radiation level, the alternating connection of radiators and high-impedance feed lines forms a series-fed antenna structure, increasing the antenna's radiating aperture. Second, the feed point 24 for each frequency band is located at the bottom of the radiator, close to its edge, at a current wave node. Therefore, crosstalk currents from other frequency band ports are minimized at this location. For these reasons, the filtering structure for each frequency band can be designed independently without being affected by the filtering structures of other frequency bands.

[0062] At the radiation level, when antenna loss is sufficiently low, the discontinuity between the high-impedance feed line and the low-impedance radiator does not result in energy loss. When the antenna input ports are well matched, according to the principle of current continuity, the current will reach all radiators on the same antenna body through the high-impedance feed line, thus forming a series-fed array antenna structure, increasing the radiating aperture and gain. The energy input from the ports is divided into three parts: one is due to the antenna's own losses, the second is radiated into free space by the antenna, and the third is transmitted to other external ports. In the design, the high isolation between the antenna ports ensures that almost no energy is transmitted to other external ports, and the antenna loss is sufficiently low, so most of the energy is radiated into free space; therefore, high radiation efficiency can still be maintained even in the case of multiple frequency bands sharing the same antenna body.

[0063] To further explain, by changing parameters such as the length and width of the short-circuit transmission line, the ratio of the length and step width of the U-shaped air slot, the position and length and width of the microstrip line, and the height of the feed point, the operating frequency, bandwidth, and radiation null position of the filter structure can be adjusted, thereby enabling the reuse of the same filter circuit in different frequency bands.

[0064] To further explain, by rationally designing the length of the high-impedance feeder and the radiator, it is possible to ensure that each radiator is in phase feeding as much as possible in different frequency bands, so that the maximum radiation direction is kept in the horizontal direction, thereby achieving electrical characteristics with horizontal omnidirectional and high-gain radiation.

[0065] Example 2

[0066] like Figure 2 As shown, this embodiment provides a series-fed filter antenna with high port isolation, sharing a common aperture and antenna body across three operating frequency bands: 2.4–2.485 GHz (2.4 GHz band), 5.15–5.35 GHz (5.2 GHz band), and 5.725–5.925 GHz (5.8 GHz band). The three operating frequency bands are fed to the same antenna body via independent input ports, allowing each band to operate simultaneously and independently, with high isolation between the ports. The antenna feeding and filtering structure can be divided into three parts: the first part designs the feeding and filtering structure for the 2.4 GHz band; the second part designs the feeding and filtering structure for the 5.2 GHz band; and the third part designs the feeding and filtering structure for the 5.8 GHz band.

[0067] The antenna is designed based on the case of a high-isolation multi-channel common-aperture common-antenna series-feed filter antenna with a frequency band number N of 3 in Embodiment 1. Specifically, it includes a dielectric substrate 21, a feeding structure and a filtering structure. A top metal layer is provided on the upper surface of the dielectric substrate 21, and three radiators 16 are provided on the top metal layer. A bottom metal layer is provided on the lower surface of the dielectric substrate. A metal ground plane 20 is embedded in the top metal layer, and a microstrip line 22 is provided on the bottom metal layer.

[0068] Furthermore, the antenna in this embodiment 2 is a series-fed filter antenna. The 2.4GHz, 5.2GHz, and 5.8GHz frequency bands can share all radiators, maximizing gain and reusing the radiation structure, while the three frequency bands operate independently. The series-fed filter antenna can be in the form of monopole, dipole, parallel double-line, patch, or other resonators, and its shape is variable. The antenna in this embodiment 2 includes three radiators 16, which are connected sequentially via high-impedance feed lines 19. The series-fed antenna operates in a high-order mode, and a short-circuited transmission line 17 is cut out in the upper part of each radiator, forming a U-shaped air slot 18.

[0069] The metal ground plane 20 is embedded in the dielectric substrate 21 and is used to provide a grounding point. Its size is adjusted according to impedance matching and power supply efficiency.

[0070] Furthermore, in this embodiment 2, feeding and filtering structures are designed on all three radiators of the antenna. A 2.4GHz filtering structure 13 is designed on the lowermost radiator, a 5.2GHz filtering structure 14 is designed on the middle radiator, and a 5.8GHz filtering structure 15 is designed on the uppermost radiating metal patch. The design method for the feeding and filtering structures is the same as that provided in embodiment 1. The filtering structure consists of a short-circuit transmission line, a U-shaped air slot, a microstrip line, and radiators. The feeding structure is implemented by an external feed line 23, which is a coaxial feed line. The inner conductor is soldered to the short-circuit transmission line, and the outer conductor is soldered to a metal ground plane, forming a closed current path that feeds the antenna through magnetic coupling.

[0071] Furthermore, the antenna in this embodiment 2 uses a dielectric substrate with a relative permittivity of 4.5 and a thickness of 30 mil. The dimensional parameters are as follows: the dielectric substrate 21 has a width w1 of 20 mm and a length l1 of 150 mm. The three metal ground planes 20 are cuboid metals with widths w2=18 mm, w3=6.2 mm, and w4=10 mm, and lengths l5=7 mm, l6=2 mm, and l7=2 mm, respectively. The lengths of the three pairs of microstrip lines 22 are l2=17.3 mm, l3=7.9 mm, and l4=7.1 mm, respectively. The widths of the three radiators 16 are w5=7.5 mm, w6=5 mm, and w7=8 mm, and the lengths are l11=40.5 mm, l13=21.1 mm, and l15=30 mm, respectively. The lengths of the two high-impedance feed lines 19 are l12=21.8 mm and l14=22.9 mm, respectively. The lengths of the three short-circuit transmission lines 17 are l8=22.4mm, l9=9.85mm, and l10=8.7mm, respectively. The above is only one applicable size for the antenna in this embodiment 2; changing only the size parameters is still within the protection scope of this invention.

[0072] Figures 4(a) and 4(b) show the S-parameter curves of the three-port common-aperture common-antenna-body series-fed filter antenna with high port isolation in Embodiment 2, where port 1 corresponds to the 2.4GHz port, port 2 corresponds to the 5.2GHz port, and port 3 corresponds to the 5.8GHz port. Figure 4(a) is the S-parameter curve of the three-port common-aperture common-antenna-body series-fed filter antenna with high port isolation in Embodiment 2. 11 S 22 and S 33The curves show good return loss at all three ports, and the 8dB bandwidth effectively covers the three operating frequency bands: 2.4–2.485 GHz, 5.15–5.35 GHz, and 5.725–5.925 GHz. Through the filter antenna design, all three bands exhibit good filtering performance, demonstrating second-order filtering response, fast edge roll-off, and high out-of-band rejection. Outside the passband, the 2.4 GHz port shows excellent SS in the 2.5–6.5 GHz wideband. 11 Approaching 0dB, the 5.2GHz port operates within a bandwidth of less than 5.15GHz. 22 Approaching 0dB, the 5.8GHz port operates within a bandwidth of less than 5.725GHz. 22 Approaching 0dB, all three ports achieve good out-of-band suppression.

[0073] Figure 4(b) shows S 12 S 13 and S 23 The graph shows that the isolation between the 2.4GHz port and the 5.2GHz port, as well as between the 2.4GHz port and the 5.8GHz port, is greater than 30dB; the isolation between the 5.2GHz port and the 5.8GHz port is greater than 25dB, demonstrating high isolation characteristics.

[0074] Figures 5(a)-5(c) show the gain curves of the three-channel, common-aperture, common-antenna-body series-fed filter antenna with high port isolation in Embodiment 2. Figure 5(a) shows the gain curve for the 2.4GHz port, Figure 5(b) shows the gain curve for the 5.2GHz port, and Figure 5(c) shows the gain curve for the 5.8GHz port. The gain curves demonstrate significant filtering characteristics. The gain in the 2.4GHz band reaches 2.5dB, and the gain in the 5.2GHz and 5.8GHz bands reaches 4.5dB. By adjusting the feeding and filtering structures, one radiating null point of the 5.2GHz port is designed to be around 5.85GHz, and one radiating null point of the 5.8GHz port is designed to be around 5.25GHz, achieving high suppression between two frequency bands with a passband frequency difference of only 0.4GHz. This ensures high port isolation. In the crossover frequency band, the out-of-band suppression can reach more than 15dB, ensuring high isolation between ports.

[0075] Figures 6(a) and 6(b) show the radiation pattern at 2.45 GHz of the three-channel, common-aperture, series-fed filter antenna with high port isolation in Embodiment 2; Figures 7(a) and 7(b) show the radiation pattern at 5.25 GHz; and Figures 8(a) and 8(b) show the radiation pattern at 5.85 GHz. Within the three operating frequency bands, the antenna of Embodiment 2 still exhibits good horizontal omnidirectional radiation characteristics when sharing the same antenna body across all three bands.

[0076] Example 3

[0077] A design method for a multi-channel, common-aperture, common-antenna-body series-fed filter antenna with high port isolation includes the following steps:

[0078] (1) Determine the number of working frequency bands N, and note that there should be no frequency overlap between the working frequency bands;

[0079] (2) Select the appropriate antenna type according to the required radiation mode. Specifically, select the antenna type according to the radiation square pattern. The antenna types include monopoles, magnetoelectric dipoles, and dual-polarized dipoles. Embodiments 1 and 2 of this invention are both series-fed monopoles.

[0080] (3) Design the antenna; First, feed N input ports to different radiators of the antenna. The selection of the feeding position needs to ensure that the antenna can be effectively excited and radiate the required mode; Then, design filtering devices on the radiators of the corresponding ports, including filters, filtering antennas and other devices that can achieve filtering performance, and ensure good out-of-band suppression through filtering performance.

[0081] (4) The antenna designed through the above steps integrates the three functions of combining, filtering and radiation into one, maintains high isolation between different input ports, and can work simultaneously and independently in each frequency band, and radiates into free space through the same antenna body;

[0082] Following the steps described above, the high-isolation multi-channel common-aperture common-antenna-body series-feed filter antenna described in the first objective of this invention can be designed.

[0083] Example 4

[0084] A radio frequency communication device includes a series-fed filter antenna as described in Embodiment 1 or Embodiment 2.

[0085] In summary, the antenna of this invention integrates multiple operating frequency bands on a single antenna body. Each frequency band uses an independent port to feed the radiator of its corresponding frequency band, enabling simultaneous and independent operation. This reduces the required number of antennas to 1 / N of that in traditional discrete antenna designs (where N is the number of frequency bands supported by the antenna of this invention), achieving multi-channel, shared-aperture functionality and possessing the structural characteristics of a shared antenna body. Since the radiators on the antenna reuse multiple frequency bands, the gain is not significantly reduced compared to traditional discrete antennas. Through a designed filtering structure, the antenna introduces a second-order bandpass filter response in each frequency band without using additional integrated filters, generating out-of-band radiation nulls, achieving high out-of-band rejection performance and high port isolation, while effectively reducing the antenna size. The antenna of this invention has a simple structure, can be mass-produced using PCB fabrication technology, and is inexpensive. Compared to current antenna designs, it can significantly reduce the size of communication equipment, increase integration, and improve the communication performance of multi-band communication equipment.

[0086] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-channel, common-aperture series-fed filter antenna, characterized in that, It includes an antenna body, on which N independent input ports are provided, each input port supporting one operating frequency band; N input ports are placed on different radiators for multi-frequency feeding, and a filter structure is set on each radiator to achieve high isolation between ports; Each operating frequency band inputs an RF signal to its input port, feeds it to the corresponding radiator, and radiates it into free space through the same antenna body, thus realizing a multi-channel, common-aperture, common-antenna-body approach. The antenna body includes a dielectric substrate. A top metal layer is disposed on one side of the dielectric substrate, and a bottom metal layer is disposed on the other side. M radiators are disposed on the top metal layer, where M ≥ N. N of the M radiators correspond one-to-one with N input ports. N metal ground planes are embedded in the dielectric substrate, and the N metal ground planes correspond one-to-one with the N radiators. The M radiators are connected by high-impedance feed lines. The bottom metal layer is disposed with microstrip lines corresponding to the N radiators, forming parallel resonators with the radiators. Each operating frequency band is fed by an independent external feed line.

2. The series-fed filter antenna according to claim 1, characterized in that, N of the radiators are partially hollowed out to accommodate short-circuit transmission lines, forming U-shaped air troughs with stepped widths; The short-circuit transmission line, U-shaped air slot, microstrip line, and radiator constitute a filtering structure, which enables the antenna to generate transmission and radiation nulls at the upper and lower sidebands outside the passband, suppressing interference from other frequency bands and maintaining high isolation between ports of multiple frequency bands fed to the same antenna body.

3. The series-fed filter antenna according to claim 1, characterized in that, The M radiators are connected by high-impedance feed lines, specifically, the radiators and high-impedance feed lines are alternately arranged. The high-impedance feed lines are equivalent to open circuits in the circuit, and each radiator works independently at the circuit level. At the radiation level, the radiators and high-impedance feed lines are alternately connected to form a series-fed antenna structure, which increases the antenna radiation aperture.

4. The series-fed filter antenna according to any one of claims 1-3, characterized in that, The radiator is composed of low-impedance lines.

5. The series-fed filter antenna according to claim 1, characterized in that, The input port of a single operating frequency band is fed by M radiators of the antenna body, which together radiate the signal, thus achieving multi-band multiplexing of the M radiators.

6. The series-fed filter antenna according to claim 2, characterized in that, The length of the short-circuit transmission line is λ1 / 4, which is equivalent to an LC resonator connected in parallel between the input port and the radiation port. The center frequency is located in the passband, and λ1 is the wavelength corresponding to the resonant frequency of the short-circuit transmission line.

7. The series-fed filter antenna according to claim 1, characterized in that, The microstrip line and the radiator form a quarter-wavelength parallel resonator, which is excited by differential mode. At resonance, the currents on the microstrip line and the radiator are in opposite directions.

8. The series-fed filter antenna according to claim 2, characterized in that, The U-shaped air trough introduces electromagnetic coupling between the short-circuit transmission line and the radiator.

9. The series-fed filter antenna according to claim 1, characterized in that, By adjusting the length of the high-impedance feed line, each radiator is fed in phase.

10. The series-fed filter antenna according to claim 1, characterized in that, When there are three input ports, a three-port common aperture series-fed filter antenna is formed, including a dielectric substrate. A top metal layer is provided on one side of the dielectric substrate, and a bottom metal layer is provided on the bottom side. Three radiators are provided on the top metal layer. The three radiators are connected through a first high-impedance feed line and a second high-impedance feed line. U-shaped air slots are provided inside the three radiators. A metal ground plane corresponding to the radiator is embedded in the dielectric substrate. A microstrip line corresponding to the radiator is provided on the bottom metal layer. The radiators are fed by external feed lines.

11. The series-fed filter antenna according to claim 10, characterized in that, The three radiators support three operating frequency bands: 2.4–2.485 GHz, 5.15–5.35 GHz, and 5.725–5.925 GHz, respectively.

12. A design method for implementing the series-fed filter antenna according to any one of claims 1-11, characterized in that, Includes the following steps: Define N operating frequency bands, where there is no frequency overlap between the operating frequency bands; Select the antenna type according to the required radiation mode; The antenna is designed as follows: The N input ports corresponding to the N operating frequency bands are respectively fed to different radiators. The selection of the feeding position ensures that the antenna is effectively excited and radiates the required mode. A filter structure is designed on the radiator of the corresponding input port to achieve the integration of combining, filtering and radiation functions into one, while maintaining high isolation between different input ports. Each frequency band works independently at the same time and is a series-fed filter antenna that radiates into free space through the same antenna body.

13. A radio frequency communication device, characterized in that, Includes the series-fed filter antenna as described in any one of claims 1-11.

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