Compact broadband low-sidelobe omnidirectional antenna

Abstract

The invention belongs to the technical field of microwave antennas, and discloses a compact broadband low-sidelobe omnidirectional antenna, which comprises a dielectric substrate and a coaxial feed line, and also comprises an 8-element broadband printed oscillator antenna array and a miniaturized planar feed network which are printed on the front and back surfaces of the dielectric substrate in a center staggered symmetrical form, according to the 8-element broadband printed oscillator antenna array, broadband antenna units are symmetrically printed on the two sides of a miniaturized planar feed network in a 2 * 4 scale arrangement mode, one pair of broadband antenna units is symmetrically and compactly arranged in the horizontal direction to form one group, and four groups of broadband antenna units are arranged in the vertical direction. The miniaturized planar feed network comprises a one-to-two primary parallel double-wire network which is excited by a coaxial feed line and is located in the center and a one-to-one four-secondary series-parallel coupling microstrip network which is connected with the one-to-two primary parallel double-wire network. Signals are divided into two paths by the coaxial feeder line through the one-to-two primary parallel double-wire network, and the two paths of signals enter the one-to-four secondary series-parallel coupling microstrip network, and low-sidelobe weighted excitation of the 8-element broadband printed oscillator antenna array is realized through the control of the coupling amount.

Description

Technical Field

[0001] The invention mainly relates to the technical field of microwave antennas, and in particular to a compact broadband low-sidelobe omnidirectional antenna. Background Art

[0002] With the development of modern wireless communication systems, vertically polarized omnidirectional antennas are widely used due to their low signal attenuation. In practical applications, high-gain vertically polarized antennas with broadband performance can meet the needs of various mobile communication systems (such as 3G, LTE and WLAN), which is conducive to reducing the number of integrated antennas in the system and achieving a more compact structure.

[0003] In practical applications, vertically polarized omnidirectional antennas usually need to have not only broadband working conditions, low horizontal non-circularity levels, and easy formation of high-gain arrays, but also low cost and easy processing and preparation. However, it is difficult to meet the above characteristics at the same time. For example, the coaxial collinear (COCO) antenna adopts a colinear arrangement. By staggering the inner core and the outer skin of the coaxial line with a period of half the wavelength, a gain of more than 10dBi can be achieved. However, due to its inherent resonant characteristics, its bandwidth is limited, which limits its application. The microstrip line array antenna realized by staggered microstrip lines and the slot array antenna realized by slotting the strip line can both be considered as variations of the COCO antenna.

[0004] Conventional series-fed vertically polarized dipole array antennas can achieve good omnidirectional performance, but due to the narrowband characteristics of the series-fed network itself, its operating bandwidth is also limited. In order to improve the impedance bandwidth, many measures have been proposed. For example, broadband high-gain omnidirectional performance can be achieved by rotating the broadband dipole antenna, but the structure is complex and the production and assembly costs are high. For example, a horizontal omnidirectional pattern is formed by setting broadband directional antennas on both sides of the planar network. However, broadband feeding networks usually have large lateral dimensions, which brings about the problem of large gain fluctuations in the horizontal direction of the antenna. In general, there are many ways to improve the performance of vertically polarized array antennas, including expanding the operating bandwidth, achieving good omnidirectional radiation patterns, achieving high gain, and maintaining a simple and compact structure. However, few antennas can meet these requirements at the same time. Summary of the invention

[0005] In order to overcome the above-mentioned shortcomings, the purpose of the present invention is to provide a compact broadband low sidelobe omnidirectional antenna, which has the advantages of broadband, low sidelobe, good omnidirectionality and easy industrial production. It utilizes the splicing of wide-beam directional antennas, shortens the distance between antenna phase centers, and cooperates with a miniaturized planar feeding network to design a compact structure to achieve good broadband omnidirectional radiation performance, that is, a broadband antenna unit is used as a radiation unit to meet the broadband performance; a miniaturized planar feeding network is designed to maintain the compactness of the structure while meeting the excitation of the antenna array to achieve a lower level of horizontal radiation pattern gain non-circularity; the antenna and network are integrated into a design to reduce processing and assembly costs to meet industrial needs.

[0006] To achieve the above object, the present invention is achieved through the following technical solutions:

[0007] A compact broadband low-sidelobe omnidirectional antenna comprises a dielectric substrate and a coaxial feed line, and also comprises an 8-element broadband printed dipole antenna array and a miniaturized planar feeding network printed in a central staggered symmetrical form on both sides of the dielectric substrate. The 8-element broadband printed dipole antenna array is composed of broadband antenna units arranged in a 2*4 scale and symmetrically printed on both sides of the miniaturized planar feeding network. A pair is symmetrically and compactly arranged in the horizontal direction as a group, and four groups are arranged in the vertical direction. The miniaturized planar feeding network comprises a one-to-two primary parallel two-wire network in the center excited by the coaxial feed line and a one-to-four secondary series-parallel coupled microstrip network connected thereto. A signal is evenly divided into two paths by the coaxial feed line through the one-to-two primary parallel two-wire network and enters the one-to-four secondary series-parallel coupled microstrip network respectively, and low-sidelobe weighted excitation of the 8-element broadband printed dipole antenna array is realized by controlling the coupling amount.

[0008] Furthermore, the broadband antenna unit is composed of a broadband coupled balun, a radiating element and a parasitic element. The radiating element is coupled and excited by the broadband coupled balun, the broadband coupled balun is connected to a miniaturized planar feeding network, and the parasitic element is arranged on the outside of the radiating element.

[0009] Furthermore, the one-to-two primary parallel two-wire network includes a circular pad and a one-to-two parallel two-wire network, the circular pad is arranged at the primary input end in the center of the one-to-two parallel two-wire network, and the primary output ends at both ends of the one-to-two parallel two-wire network are respectively connected to a one-to-four secondary series-parallel coupled microstrip network.

[0010] Furthermore, the one-to-four secondary series-parallel coupled microstrip network includes a phase shifting section, an impedance transformation section, a one-to-three coupled microstrip power divider and a one-to-two coupled microstrip power divider; one side of the phase shifting section is connected to the primary output end of the one-to-two parallel two-wire network and the other side is connected to the one-to-three coupled microstrip power divider, the one-to-three coupled microstrip power divider generates three groups of output signals, two groups of equal-amplitude and in-phase signals excite the middle broadband antenna unit, and the other group of signals is fed into the impedance transformation section and then connected to the one-to-two coupled microstrip power divider for equal-amplitude and in-phase power division to excite the broadband antenna unit at the end.

[0011] Furthermore, the coaxial feed line is welded on the metal floor of the dielectric substrate, one end of which is welded to the circular pad of the one-to-two primary parallel two-wire network of the miniaturized planar feed network, and the other end is provided with a feed port.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. Simple structure and easy processing: Common broadband omnidirectional antennas usually have a three-dimensional rotationally symmetrical structure or a larger plane size. The radiating antenna of the present invention is arranged on a single-layer dielectric substrate, and broadband antenna units are closely arranged on both sides of a miniaturized planar feeding network to achieve a compact design. The antenna only uses coaxial welding feeding, and the processing cost is low.

[0014] 2. Good broadband omnidirectional performance: The relative working bandwidth of this antenna is 35.6%, which benefits from the broadband antenna design loaded with parasitic oscillators and the broadband network design based on coupled microstrip lines. Within the working bandwidth, the simulated non-circularity of the antenna horizontal plane is less than 1.6dB. In the frequency band of 2GHz to 2.5GHz (22.2%), the gain fluctuation is only 0.5dBi. This is due to the stable phase output of the network within the frequency band. The antenna maintains good omnidirectional characteristics and stable gain characteristics on the horizontal plane under broadband working conditions.

[0015] 4. Low sidelobe characteristics: The miniaturized planar feeding network of this antenna can achieve low sidelobe weighting of the output signal, which is beneficial to improving the anti-interference performance of the antenna system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0017] Figure 2 is an overall side view of the present invention;

[0018] Figure 3 is an overall top view of the present invention;

[0019] Figure 4 It is a connection diagram of the one-to-two primary parallel two-wire network and the phase shifting section of the present invention;

[0020] Figure 5 It is an overall rear view of the present invention;

[0021] Figure 6 is a schematic structural diagram of an impedance transformation section of the present invention;

[0022] Figure 7 It is a port schematic diagram of the one-to-three coupled microstrip power divider of the present invention;

[0023] Figure 8 It is a structural schematic diagram of a one-to-two coupled microstrip power divider of the present invention;

[0024] Fig. 9 It is a simulation curve diagram of a compact broadband low sidelobe omnidirectional antenna |S11| of the present invention;

[0025] Fig.10 It is a simulation curve diagram of gain and horizontal plane non-circularity of a compact broadband low sidelobe omnidirectional antenna of the present invention;

[0026] Fig.11 The invention discloses a compact broadband low sidelobe omnidirectional antenna with intermediate frequency elevation gain pattern.

[0027] Wherein: 1. dielectric substrate; 2. coaxial feed line; 201. feed port;

[0028] 10. 8-element broadband printed dipole antenna array; 101. broadband coupled balun; 102. radiating dipole; 103. parasitic dipole;

[0029] 11. Miniaturized planar feeding network; 111. Circular pad; 112. One-to-two parallel two-wire network; 113. Phase shift section; 114. Impedance transformation section; 115. One-to-three coupled microstrip power divider; 1151. Secondary first input port; 1152. Secondary first output port; 1153. Secondary second output port; 1154. Secondary third output port; 116. One-to-two coupled microstrip power divider. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] The structure of the present invention is described in detail below in conjunction with the accompanying drawings.

[0032] like Figures 1 to 8The invention relates to a compact broadband low sidelobe omnidirectional antenna, which works in the LTE and WLAN working bands, and comprises a dielectric substrate 1, a coaxial feed line 2, an 8-element broadband printed dipole antenna array 10, and a miniaturized planar feed network 11. The 8-element broadband printed dipole antenna array 10 and the miniaturized planar feed network 11 are printed on the front and back surfaces of the same dielectric substrate in a central staggered symmetrical form, and are excited by the coaxial feed line 2 welded on the dielectric substrate 1.

[0033] The coaxial feed line 2 is welded on the metal floor on the dielectric substrate 1, one end of the coaxial feed line 2 is welded to the circular pad 111 of the one-to-two primary parallel two-line network of the miniaturized planar feeding network 11, and the other end is provided with a feeding port 201. The advantage of such a setting is that since the antenna is excited perpendicular to the earth, in the prior art, the state in which one end of the coaxial feed line 2 is fixed and the other end is free will cause interference to the antenna. Therefore, the coaxial feed line 2 is welded on the dielectric substrate 1 to reduce interference. At the same time, by providing the feeding port 201 at the end of the coaxial feed line 2, the final feeding point of the coaxial feed line 2 is transferred to the edge of the compact broadband low sidelobe omnidirectional antenna described in this embodiment, thereby achieving excitation of the entire antenna.

[0034] The 8-element broadband printed dipole antenna array 10 is composed of broadband antenna units arranged in a 2*4 scale and symmetrically printed on both sides of a miniaturized planar feed network 11 on a dielectric substrate 1, wherein a pair of broadband antenna units are symmetrically and compactly arranged in the horizontal direction as a group of omnidirectional antenna radiation units, and four groups of omnidirectional antenna radiation units are arranged in the vertical direction to provide high-gain beam coverage and achieve high-gain radiation; the broadband antenna unit is composed of a broadband coupled balun 101, a radiating dipole 102 and a parasitic dipole 103, wherein the radiating dipole 102 is coupled and excited by the broadband coupled balun 101, and the broadband coupled balun 101 is connected to the miniaturized planar feed network 11. In addition, the parasitic dipole 103 is arranged on the outside of the radiating dipole 102, and the coupling effect of the two generates a new high-frequency resonance point. The broadband antenna units are compactly arranged in the horizontal direction to achieve a higher omnidirectional radiation level, and a new high-frequency resonance point is generated by the parasitic dipole 103 to alleviate the bandwidth reduction caused by strong mutual coupling and expand the working bandwidth of the antenna.

[0035] like Figure 1 As shown, the two groups in the middle are middle broadband antenna units, and the two groups at both ends are end broadband antenna units.

[0036] The miniaturized planar feeding network 11 is symmetrically printed on the dielectric substrate 1 and adopts a series-parallel combination form, including a one-to-two primary parallel two-wire network and a one-to-one-to-four secondary series-parallel coupled microstrip network.

[0037] The one-to-two primary parallel two-wire network includes a circular pad 111 and a one-to-two parallel two-wire network 112, wherein the circular pad 111 is arranged at the primary input end at the center of the one-to-two parallel two-wire network 112, and the primary output ends at both ends of the one-to-two parallel two-wire network 112 are respectively connected to a one-to-four secondary series-parallel coupled microstrip network.

[0038] The one-to-four secondary series-parallel coupled microstrip network includes a phase shift section 113 , an impedance transformation section 114 , a one-to-three coupled microstrip power divider 115 , and a one-to-two coupled microstrip power divider 116 .

[0039] The one-to-three coupled microstrip power divider 115 includes a secondary first input port 1151, a secondary first output port 1152, a secondary second output port 1153, and a secondary third output port 1154; the one-to-two coupled microstrip power divider 116 includes a secondary second input port, a secondary fourth output port, and a secondary fifth output port.

[0040] The signal at the primary output end of one end of the one-to-two parallel two-line network 112 enters the primary network output end and is connected to the phase shift section 113 and then fed into the secondary first input port 1151 of the one-to-three coupled microstrip power divider 115. After power division by the one-to-three coupled microstrip power divider 115, a portion of the energy is connected to the broadband coupled balun 101 of the broadband antenna unit in the middle through the secondary first output port 1152 and the secondary second output port 1153 symmetrical on both sides, and the other portion of the energy is fed into the impedance transformation section 114 through the secondary third output port 1154 and then connected to the secondary second input port of the one-to-two coupled microstrip power divider 116 after impedance transformation, for equal amplitude and in-phase power distribution, and the secondary fourth output port and the secondary fifth output port of the one-to-two coupled microstrip power divider 116 are connected to the broadband coupled balun 101 of the broadband antenna unit at the end.

[0041] The working process of the compact broadband low sidelobe omnidirectional antenna of this embodiment is as follows:

[0042] The signal enters from the feeding port 201 of the coaxial feed line 2, enters the one-to-two parallel two-line network 112 through the circular pad 111, and then is evenly divided into two paths by the one-to-two parallel two-line network 112 to enter the phase shift section 113 for power division and phase shifting, and then excites the one-to-three coupled microstrip power divider 115. The signal is fed into the input port 1151 of the one-to-three coupled microstrip power divider 115, and a part of it excites the broadband antenna unit in the middle through the secondary first output port 1152 and the secondary second output port 1153, and the other part of the energy continues to propagate through the secondary third output port 1154, excites the one-to-two coupled microstrip power divider 116 after passing through the impedance transformation section 114, and finally excites the broadband antenna unit at the end.

[0043] In this embodiment, the miniaturized planar feeding network 11 adopts a center staggered feeding form to provide low sidelobe amplitude weighted in-phase excitation to the 8-element broadband printed dipole antenna array 10; correspondingly, the 8-element broadband printed dipole antenna array is symmetrically printed on the front and back surfaces of the dielectric substrate in the vertical direction to offset the 180° phase difference caused by the center feeding and achieve in-phase radiation.

[0044] The one-to-three coupled microstrip power divider 115 can achieve unequal power division output by adjusting the spacing and width of the coupled microstrip lines, thereby achieving antenna amplitude low sidelobe weighting.

[0045] The phase shift section 113 and the impedance transformation section 114 are used to achieve circuit matching and maintain the in-phase excitation of the broadband antenna unit. By adjusting the microstrip line spacing and width of the one-to-three coupled microstrip power divider 115, different proportional power distribution of the output port can be achieved to achieve low sidelobe weighting.

[0046] The implementation of multiple technologies enables the present invention to achieve broadband horizontal omnidirectional radiation and low sidelobe performance in elevation under the premise of compact structure. In addition, the single-layer dielectric substrate reduces the antenna processing cost and meets the requirements of industrialization.

[0047] The application effect of the present invention is described in detail below in conjunction with simulation.

[0048] 1. Simulation content

[0049] like Figures 9 to 11 As shown, the simulation software is used to simulate the |S11|, the in-band gain and the horizontal gain non-circularity, and the intermediate frequency elevation gain pattern of the antenna in the above embodiment.

[0050] 2. Simulation results

[0051] Fig. 9 This is the |S11| curve obtained by simulating the antenna of the embodiment. The result shows that the |S11| of the antenna is less than -10dB within the bandwidth of 1.87GHz to 2.68GHz (relative working bandwidth 35.6%), achieving good broadband matching.

[0052] Fig.10 The antenna gain and horizontal plane gain non-circularity curves are obtained by simulating the antenna of the embodiment. The results show that within the working bandwidth, the simulated non-circularity of the antenna horizontal plane is less than 1.6dB, and the simulated gain is between 5.9 and 7.3dBi. Especially in the 2GHz to 2.5GHz (22.2%) frequency band, the gain fluctuation is only 0.5dBi, which is due to the stable phase output within the network frequency band. It can be seen that the antenna maintains good omnidirectional characteristics and stable gain characteristics in the horizontal plane under broadband working conditions.

[0053] Fig.11It is the intermediate frequency elevation plane gain pattern obtained by simulating the antenna of the embodiment. The antenna simulated sidelobe level is -22.5dB, realizing the characteristic of low sidelobe in the elevation plane. The simulated half-power beamwidth of the antenna in the elevation plane is 24.6°, indicating that the antenna realizes narrow beam radiation in the vertical plane. In addition, the simulated cross-polarization of the E-plane and H-plane of the antenna are both lower than -50dB. It can be seen that the antenna realizes good narrow beam, low sidelobe and low cross-polarization characteristics in the elevation plane.

[0054] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. However, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A compact broadband low sidelobe omnidirectional antenna, comprising a dielectric substrate (1) and a coaxial feed line (2), It is characterized in that It also comprises an 8-element broadband printed dipole antenna array (10) and a miniaturized planar feeding network (11) printed on both sides of a dielectric substrate in a central staggered symmetrical form. The 8-element broadband printed dipole antenna array (10) is composed of broadband antenna units arranged in a 2*4 scale and symmetrically printed on both sides of the miniaturized planar feeding network (11). A pair of broadband antenna units are symmetrically and compactly arranged in the horizontal direction as a group, and four groups are arranged in the vertical direction. The miniaturized planar feeding network (11) comprises a one-to-two primary parallel two-wire network in the center and a one-to-four secondary series-parallel coupled microstrip network connected thereto, which is excited by a coaxial feed line (2). The signal is evenly divided into two paths by the coaxial feed line (2) through the one-to-two primary parallel two-wire network and enters the one-to-four secondary series-parallel coupled microstrip network respectively. Low sidelobe weighted excitation of the 8-element broadband printed dipole antenna array (10) is achieved by controlling the coupling amount.

2. A compact broadband low sidelobe omnidirectional antenna according to claim 1, It is characterized in that The broadband antenna unit is composed of a broadband coupling balun (101), a radiating oscillator (102) and a parasitic oscillator (103); the radiating oscillator (102) is coupled and excited by the broadband coupling balun (101); the broadband coupling balun (101) is connected to a miniaturized planar feeding network (11); and the parasitic oscillator (103) is arranged outside the radiating oscillator (102).

3. A compact broadband low sidelobe omnidirectional antenna according to claim 1, It is characterized in that The one-to-two primary parallel two-wire network comprises a circular pad (111) and a one-to-two parallel two-wire network (112); the circular pad (111) is arranged at a primary input end at the center of the one-to-two parallel two-wire network (112); and primary output ends at both ends of the one-to-two parallel two-wire network (112) are respectively connected to a one-to-four secondary series-parallel coupled microstrip network.

4. A compact broadband low sidelobe omnidirectional antenna according to claim 3, It is characterized in that The one-to-four secondary series-parallel coupled microstrip network comprises a phase shift section (113), an impedance transformation section (114), a one-to-three coupled microstrip power divider 115 and a one-to-two coupled microstrip power divider (116); one side of the phase shift section (113) is connected to the primary output end of the one-to-two parallel two-wire network (112), and the other side is connected to the one-to-three coupled microstrip power divider (115); the one-to-three coupled microstrip power divider (115) generates three groups of output signals, two groups of equal-amplitude and in-phase signals excite the middle broadband antenna unit, and the other group of signals is fed into the impedance transformation section (114) and then connected to the one-to-two coupled microstrip power divider (116) to excite the broadband antenna unit at the end after equal-amplitude and in-phase power division.

5. A compact broadband low sidelobe omnidirectional antenna according to claim 3, It is characterized in that The coaxial feed line (2) is welded on the metal floor of the dielectric substrate (1), one end of which is welded to a circular pad (111) of a one-to-two primary parallel two-wire network of a miniaturized planar feed network (11), and the other end is provided with a feed port (201).

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