An ultra-wideband planar helical antenna with adjustable notch based on split ring resonator

Abstract

The present invention discloses an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring, and relates to the field of antenna technology. The helical antenna is realized by loading an open resonant ring with a step impedance characteristic on a planar composite helical antenna, and its structure includes a planar composite helical antenna structure, an absorbing back cavity, an exponentially tapered balun, and an open resonant ring with a step impedance characteristic loaded on the planar composite helical antenna structure. The present invention realizes impedance matching and unbalanced-balanced feeding by etching a planar composite helical antenna on an antenna dielectric substrate and connecting an exponentially tapered balun on a vertical surface of the helical antenna. Furthermore, a wave-absorbing back cavity is placed under the helical antenna, so that the designed helical antenna can realize unidirectional radiation. And by arranging and distributing the number, position, and direction of the open resonant rings in different ways, the characteristics of adjustable notch frequency band and depth are finally realized.

Description

Technical Field

[0001] The invention belongs to the technical field of antennas, and in particular relates to an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring. Background Art

[0002] With the development of modern wireless communications, ultra-wideband communication technology has been widely used in ultra-wideband communication systems, military radars, bioengineering and other fields due to its advantages of high transmission rate, large system capacity and high resolution. Planar spiral antennas have become one of the main forms of broadband antennas because of their good impedance and radiation characteristics in a wide bandwidth. The spiral antenna in free space can radiate circularly polarized waves in two directions perpendicular to the spiral plane. However, many communication and detection systems have some special requirements for antennas, such as wide bandwidth, small size, unidirectional radiation, stable performance, etc. These have also become topics that scholars have widely studied in recent years.

[0003] In the design of traditional helical antennas, a metal back cavity is usually placed at a quarter wavelength below the antenna to achieve unidirectional radiation, but this fixed length will cause the radiation waves reflected from the metal back cavity to cause serious interference in certain frequency bands, unstable performance, and severely limit the wideband characteristics of the helical antenna. Usually, absorbing materials are placed in the metal back cavity, but this will increase the overall weight of the antenna, and the gain and efficiency of the antenna in the working frequency band will also be greatly reduced. Therefore, it is necessary to design a better absorbing material structure to reduce the use of absorbing materials without excessively reducing the gain and efficiency of the antenna.

[0004] It should be noted that within the ultra-wideband system frequency band (3.1GHz-10.6GHz), there are also other narrowband communication system frequency bands such as wireless local area network (WLAN: 5.15~5.35GHz, 5.725~5.825GHz) and wireless metropolitan area network (WiMAX: 3.4~3.69GHz, 5.25~5.85GHz). In order to avoid mutual interference between the ultra-wideband communication system and these narrowband communication systems, there are usually three methods currently used: one is to add a filter at the front end of the antenna, use the characteristics of the filter to form a notch, and filter out unnecessary narrowband signals, but the structure is complex and not conducive to processing; the second is to etch U-shaped and C-shaped slots on the radiation patch, floor and feeder of the ultra-wideband antenna to design an ultra-wideband antenna with notch performance, change the position and length of the slot, and change the current distribution on the antenna to form a notch in the target frequency band. This method only needs to make corresponding designs and improvements to the antenna structure to effectively suppress the interference of narrowband communication signals, and its simple structure is also easy to integrate; the third is to introduce a parasitic unit into the ultra-wideband antenna so that the parasitic unit works in the frequency band that needs to be suppressed. The current direction of the parasitic unit in the notch frequency band is opposite to the current on the patch surface, thereby suppressing the radiation of the radiating unit. The latter two methods are used more frequently and are convenient for the miniaturization and integration of the system.

[0005] The notch frequency band of the traditional notch UWB antenna is fixed. When the interference signal does not exist or the interference signal of different narrowband frequency bands appears, it is not conducive to fully utilizing the UWB spectrum. In order to improve the performance of the UWB planar antenna and make full use of the UWB spectrum resources, further research is needed on the UWB planar antenna with adjustable notch. Summary of the invention

[0006] In view of the above-mentioned problems, the present invention proposes an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring. In view of the mutual interference problem between the ultra-wideband system and the narrowband communication system, a planar composite helical antenna is loaded with an open resonant ring with a stepped impedance characteristic, thereby achieving the suppression of narrowband signals in the target frequency band within the ultra-wideband frequency band; the frequency band and depth of the notch are adjustable by distributing the number, position and direction of the open resonant ring units differently; the overall design achieves the characteristics of wide bandwidth, unidirectional radiation, adjustable notch and lightweight.

[0007] The above purpose is achieved through the following technical solutions:

[0008] The invention discloses an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring, comprising a planar composite helical antenna structure, a wave-absorbing back cavity, an exponential gradient balun, and an open resonant ring with a stepped impedance characteristic loaded on the planar composite helical antenna structure;

[0009] The absorbing back cavity comprises a cylindrical metal back cavity, a stepped absorbing material is placed inside the cylindrical metal back cavity, and a hole is dug at the center of the lower surface of the cylindrical metal back cavity for connecting the SMA with the lower end of the exponential gradient balun for feeding;

[0010] The exponentially gradient balun is formed by etching an exponentially gradient signal line and an exponentially gradient ground line on the upper and lower surfaces of the balun dielectric substrate, respectively, and placed inside the absorbing back cavity along the axis of the planar spiral antenna, with the upper end connected to the center of the composite spiral arm and the lower end placed on the upper surface of the absorbing back cavity;

[0011] The planar composite helical antenna structure has two composite helical antenna arms etched on the upper surface of the antenna dielectric substrate, and a chip resistor is loaded at each end of the two composite helical antenna arms;

[0012] The open resonant ring with step impedance characteristics is a step impedance open resonant ring etched on the upper surface of an open resonant ring dielectric substrate and placed on the upper surface of a planar composite helical antenna structure.

[0013] Further, it is characterized in that the loading position of the open resonant ring with a stepped impedance characteristic is on the upper surface of the planar composite helical antenna, the number of the etched open resonant rings with stepped impedance is one, two or four, the etched position of the open resonant ring with stepped impedance is located in the radiation zone of a wavelength corresponding to the notch frequency point, and all are opened along the radius facing away from the center of the circle; the total length of each of the open resonant rings with stepped impedance is half the wavelength corresponding to the notch frequency point.

[0014] Furthermore, the two composite helical antenna arms in the planar composite helical antenna structure are obtained by rotating one of the spiral arms 180° symmetrically to obtain another spiral arm, the central part of each spiral arm is an equiangular spiral antenna, the outer circle part is an Archimedean spiral, the ends of the two spiral arms are both cut, and a chip resistor is welded at each end.

[0015] Furthermore, the equiangular spiral antenna equation of the central portion of each spiral arm in the planar composite spiral antenna structure is:

[0016] (1)

[0017] The equation of the Archimedean spiral antenna of the outer ring is:

[0018] { x = [ e 0 . 221 × 2 . 5 π + 1 . 2 × ( t − 2 . 5 π )] × cos t y = [ e 0 . 221 × 2 . 5 π + 1 . 2 × ( t − 2 . 5 π )] × sin t 2 . 5 π ≤ t ≤ 9 . 8 π (2)

[0019] Wherein, x, y respectively represent the position of the planar compound helical antenna in a planar rectangular coordinate system when the planar compound helical antenna structure center establishes the coordinate system, e is the base of the natural logarithm, π is the pi, and t represents the winding radian.

[0020] Furthermore, the exponentially gradient signal line and the exponentially gradient ground line of the exponentially gradient balun are both exponentially gradient lines; the top of the exponentially gradient balun penetrates the antenna dielectric substrate, the exponentially gradient signal line and the exponentially gradient ground line are respectively connected to the starting points of the two composite spiral antenna arms, and the bottom penetrates the center hole of the lower surface of the cylindrical metal back cavity to be connected to the SMA cable interface.

[0021] Furthermore, the exponentially gradient signal line and the exponentially gradient ground line of the exponentially gradient balun are obtained by different exponentially gradient equations respectively, and the specific structural parameters are: the balanced end line width w1=0.783mm, the unbalanced end signal line width w2=2.4mm, the unbalanced end ground line w3=6mm, and the overall length of the exponentially gradient balun is l=28mm.

[0022] Furthermore, the antenna dielectric substrate, the balun dielectric substrate and the open resonant ring dielectric substrate are all made of Rogers RT5880, and the relevant electrical parameters are ε r =2.2, tanδ =0.0009, and the thickness is 0.787mm.

[0023] Furthermore, the relative dielectric constant of the absorbing material used in the absorbing material is 9.3 and the loss tangent is 0.03; the specific structural parameters of the absorbing back cavity are: the cavity thickness of the cylindrical metal back cavity is 1 mm, the overall diameter is D =80mm, cavity height H =28mm; the height of the stepped absorbing material is h=24mm, the height of each step is Δh=6mm, the width of each step is Δw=8mm, and d=5.5mm.

[0024] Compared with the prior art, the present invention has the following significant advantages:

[0025] 1. The absorbing back cavity proposed in the present invention reduces the volume of the absorbing material by placing a stepped absorbing material inside the cylindrical metal back cavity, thereby avoiding excessive increase in antenna weight and reduction in antenna gain and efficiency.

[0026] 2. The open resonant ring structure with a stepped impedance characteristic proposed in the present invention avoids the interference of high-frequency resonance on the working frequency band caused by the multi-mode resonance of the traditional open resonant ring. Through the design of the stepped impedance characteristic, the high-frequency resonance point is moved outside the working frequency band to achieve the notch function of a single target narrowband frequency band.

[0027] 3. Currently, there are few studies on realizing notch characteristics based on spiral antennas. The ultra-wideband spiral antenna with adjustable notch proposed in the present invention realizes adjustable frequency band and depth of notch by loading stepped impedance open resonant rings with different numbers, positions and directions on a planar composite spiral antenna.

[0028] 4. The present invention proposes a planar ultra-wideband helical antenna with adjustable notch based on an open resonant ring with stepped impedance characteristics, which has the characteristics of ultra-wideband, unidirectional radiation, circular polarization and adjustable notch. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The schematic diagram of the structure of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring according to the present invention is shown in FIG. Figure 1 (a) is a three-dimensional exploded schematic diagram of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring according to the present invention; Figure 1 (b) is a three-dimensional assembly schematic diagram of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring according to the present invention; Figure 1 (c) is a cross-sectional schematic diagram of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring according to the present invention;

[0030] Figure 2 A top view of the planar composite helical antenna structure proposed by the present invention and its dimension markings;

[0031] Figure 3 A schematic diagram of an exponential gradient balun according to the present invention and its dimension markings;

[0032] Figure 4 is a schematic diagram of the structure of the wave-absorbing back cavity proposed in the present invention, Figure 4 (a) is a cross-sectional side view of the wave-absorbing back cavity proposed in the present invention and its dimension markings; Figure 4 (b) is a three-dimensional schematic diagram of the wave-absorbing back cavity proposed in the present invention;

[0033] Figure 5 is a schematic diagram of an open resonant ring with a stepped impedance characteristic carried on a planar composite helical antenna according to the present invention, Figure 5 (a) is a schematic diagram of a stepped impedance open resonant ring unit and its dimension markings according to the present invention; Figure 5 (b) is a top view of an open resonant ring with a stepped impedance characteristic loaded on a planar composite helical antenna according to the present invention and its dimension annotation, taking the arrangement of a stepped impedance open resonant ring as an example;

[0034] Figure 6is S according to the present invention taking a stepped impedance open resonant ring as an example 11 Simulation result diagram;

[0035] Figure 7 is a simulation result diagram of actual gain and axial ratio taking a stepped impedance open resonant ring as an example according to the present invention;

[0036] Figure 8 are normalized radiation patterns at several typical frequency points at Phi=0° and Phi=90°, taking a stepped impedance open resonant ring as an example according to the present invention, Figure 8 (a) shows the directional patterns of Phi=0° and Phi=90° at 2 GHz. Figure 8 (b) shows the directivity diagrams of Phi=0° and Phi=90° at 6 GHz. Figure 8 (c) shows the directivity patterns of Phi=0° and Phi=90° at 10 GHz. Figure 8 (d) shows the directivity patterns of Phi=0° and Phi=90° at 14 GHz. Figure 8 (e) shows the directivity patterns of Phi=0° and Phi=90° at 18 GHz.

[0037] Fig. 9 In order to study the influence of position dx when loading a stepped impedance open resonant ring according to the present invention, Fig. 9 (a) is the distribution of the position dx when a step impedance open resonant ring is loaded according to the present invention; Fig. 9 (b) is a study of the effect of three position dx changes on the notch when loading a step impedance open resonant ring according to the present invention, corresponding to S 11 The simulation result diagram of Fig. 9 (c) is a simulation result diagram of actual gain and axial ratio respectively, showing the influence of three position dx changes on notch when loading a stepped impedance open resonant ring according to the present invention;

[0038] Fig.10 In order to study the influence of four directions θ when loading a stepped impedance open resonant ring according to the present invention, Fig.10 (a) is a study of the changes in θ in four directions when a stepped impedance open resonant ring is loaded according to the present invention; Fig.10 (b) in the figure is a study of the effect of the change of θ in four directions on the notch when a step impedance open resonant ring is loaded according to the present invention, corresponding to S 11 The simulation result diagram of Fig.10(c) is a simulation result diagram of the influence of the change of θ in four directions on the notch when a stepped impedance open resonant ring is loaded according to the present invention, which corresponds to the actual gain and axial ratio respectively;

[0039] Fig.11 In order to study the influence of the position dx when loading two step impedance open resonant rings according to the present invention, Fig.11 (a) is a distribution of the position dx when two step impedance open resonant rings are loaded according to the present invention; Fig.11 (b) is a study of the influence of three position dx changes on the notch when two step impedance open resonant rings are loaded according to the present invention, corresponding to S 11 The simulation result diagram of Fig.11 (c) is a simulation result diagram corresponding to the actual gain, which is a study of the influence of three position dx changes on the notch when two step impedance open resonant rings are loaded according to the present invention; Fig.11 (d) is a simulation result diagram of the corresponding axial ratio when studying the influence of three position dx changes on the notch when two step impedance open resonant rings are loaded according to the present invention;

[0040] Fig.12 In order to study the influence of four directions θ when loading two step impedance open resonant rings according to the present invention, Fig.12 (a) is a study of the changes in θ in four directions when two step impedance open resonant rings are loaded according to the present invention; Fig.12 (b) is a study of the effect of four direction θ changes on the notch when two step impedance open resonant rings are loaded according to the present invention, corresponding to S 11 The simulation result diagram of Fig.12 (c) is a simulation result diagram corresponding to the actual gain, which is a study of the influence of the change of θ in four directions on the notch when two step impedance open resonant rings are loaded according to the present invention; Fig.12 (d) is a simulation result diagram of the corresponding axial ratio when two step impedance open resonant rings are loaded and the influence of the change of θ in four directions on the notch is studied according to the present invention;

[0041] Fig.13 In order to study the influence of position dx when loading four step impedance open resonant rings according to the present invention, Fig.13 (a) is a study of the distribution of positions dx when four step impedance open resonant rings are loaded according to the present invention; Fig.13 (b) is a study of the effect of four position dx changes on the notch when loading four step impedance open resonant rings according to the present invention, corresponding to S 11 The simulation result diagram of Fig.13(c) is a simulation result diagram corresponding to the actual gain, which is a study of the influence of four position dx changes on the notch when four step impedance open resonant rings are loaded according to the present invention; Fig.13 (d) is a simulation result diagram of the corresponding axial ratio when studying the influence of four position dx changes on the notch when four step impedance open resonant rings are loaded according to the present invention;

[0042] Fig.14 In order to study the influence of four directions θ when loading four step impedance open resonant rings according to the present invention, Fig.14 (a) is a study of the changes in θ in four directions when four step impedance open resonant rings are loaded according to the present invention; Fig.14 (b) is a study of the effect of the change of θ in four directions on the notch when four step impedance open resonant rings are loaded according to the present invention, corresponding to S 11 The simulation result diagram of Fig.14 (c) is a simulation result diagram corresponding to the actual gain, which is a study of the influence of the change of θ in four directions on the notch when four step impedance open resonant rings are loaded according to the present invention; Fig.14 (d) is a simulation result diagram of the corresponding axial ratio when studying the influence of the change of θ in four directions on the notch when four step impedance open resonant rings are loaded according to the present invention;

[0043] Fig.15 In order to comprehensively select the best performance of the combination of one, two and four step impedance open resonant rings for comparison according to the present invention, Fig.15 (a) in the equation corresponds to S 11 The simulation result diagram of Fig.15 (b) in the figure corresponds to the simulation result diagram of the actual gain; Fig.15 (c) The simulation result diagram of the corresponding axis ratio;

[0044] Fig.16 The optimal general models corresponding to the loading of one, two and four step impedance open resonant rings according to the present invention are as follows: Fig.16 (a) is the optimal general model corresponding to a step impedance open resonant ring loaded according to the present invention; Fig.16 (b) is the optimal general model corresponding to when two step impedance open resonant rings are loaded according to the present invention; Fig.16 (c) is the optimal general model corresponding to when four stepped impedance open resonant rings are loaded according to the present invention. DETAILED DESCRIPTION

[0045] In the following, in conjunction with the accompanying drawings, an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring proposed by the present invention is described in detail with reference to a specific embodiment.

[0046] The three-dimensional explosion diagram of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring designed by the present invention is shown in FIG. Figure 1 As shown, the antenna includes a planar composite helical antenna structure, two patch resistors, an absorbing back cavity, an exponential gradient balun, and different combinations of open resonant rings with step impedance characteristics. The planar composite helical antenna structure is to etch two centrally symmetrical composite helical antenna arms 2 on the upper surface of the antenna dielectric substrate 1, the two composite helical antenna arms 2 are composed of an equiangular spiral line in the center part and an Archimedean spiral line in the outer circle part, and the ends of the two spiral arms are cut, and a patch resistor is loaded between each spiral arm near the end and the adjacent inner arm. The exponential gradient balun includes a balun dielectric substrate 4, an exponential gradient signal line 5 and an exponential gradient ground line 6. The exponential gradient signal line 5 and the exponential gradient ground line are both exponential gradient lines. The exponential gradient balun realizes the conversion from unbalanced feeding to balanced feeding and impedance transformation. The exponential gradient balun is placed vertically on the axis, and its top passes through the antenna dielectric substrate 1. The upper ends of the exponential gradient signal line 5 and the exponential gradient ground line 6 are respectively connected to the central starting points of the two composite helical antenna arms 2, and the bottom of the exponential gradient balun is placed on the absorbing back cavity. The absorbing back cavity includes a cylindrical metal back cavity 7 and a stepped absorbing material 8. The central cylindrical part of the absorbing material 8 is hollowed out to facilitate the placement of the exponential gradient balun. A small hole is dug in the center of the bottom of the cylindrical metal back cavity 7 to facilitate the connection of the SMA feeding conductor with the bottom of the exponential gradient balun. The open resonant ring with a step impedance characteristic is an open resonant ring 10 with a step impedance etched on the upper surface of an open resonant ring dielectric substrate 9. The open resonant ring dielectric substrate 9 is placed on the upper surface of the antenna dielectric substrate 1 and aligned with its center. Different combinations of open resonant rings can be designed according to the requirements of the frequency band and depth of the notch, and the notch adjustable function can be achieved by replacing the dielectric substrate of the etched open resonant ring. In this embodiment, the plates used for the antenna dielectric substrate 1, the balun dielectric substrate 4 and the open resonant ring dielectric substrate 9 are all RogersRT5880, and its related electrical parameters are ε r =2.2, tanδ =0.0009, and the thickness of all dielectric substrates is 0.787 mm.

[0047] Embodiment 1:

[0048] Figure 1 (a) is a three-dimensional exploded schematic diagram of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring proposed by the present invention. Figure 1(b) is a schematic diagram of the assembly of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring proposed by the present invention, which includes a planar composite helical antenna structure, two patch resistors, an absorbing back cavity, an exponentially tapered balun, and open resonant rings with stepped impedance characteristics in different combinations. The planar helical antenna structure is composed of a circular antenna dielectric substrate 1, two centrally symmetrical composite helical antenna arms 2, and two patch resistors 3; the exponentially tapered balun is composed of a balun dielectric substrate 4, an exponentially tapered signal line 5, and an exponentially tapered ground line 6; the absorbing back cavity is composed of a cylindrical metal back cavity 7 and a stepped absorbing material 8; the open resonant ring with stepped impedance is composed of a stepped impedance open resonant ring 10 etched on a circular open resonant ring dielectric substrate 9.

[0049] Figure 1 (c) is a cross-sectional schematic diagram of an ultra-wideband planar helical antenna with adjustable notch based on an open resonant ring according to the present invention, Figure 1 (c) shows the specific assembly method and positional relationship of each part. The specific assembly steps are as follows: the exponential gradient balun is placed perpendicular to the plane of the planar composite helical antenna structure, and passes through the absorbing back cavity along the axial direction, and the top is inserted into the center of the antenna dielectric substrate 1 and connected to the composite helical antenna; the open resonant ring with step impedance characteristics is placed on the upper surface of the antenna dielectric substrate 1; finally, the SMA cable interface 11 passes through the bottom circular hole of the cylindrical metal back cavity 7 and is connected to the bottom of the exponential gradient balun, and the overall assembly of the antenna is completed.

[0050] like Figure 2 As shown, it is a top view of the planar composite helical antenna structure proposed according to the present invention and its dimension annotation. The two composite helical antenna arms 2 are obtained by rotating one of the spiral arms 180° symmetrically to obtain another spiral arm. The central part of each spiral arm is an equiangular spiral antenna, and the outer circle part is an Archimedean spiral line. The equation of the equiangular spiral antenna is shown in equation (1), and the equation of the Archimedean spiral antenna is shown in equation (2). The spiral arm end is truncated with a circle with a radius of 35 mm to achieve tapering of the spiral arm end. A chip resistor 3 is loaded between the two spiral arms near the end and the adjacent inner arm. The antenna dielectric substrate 1 is made of Rogers RT5880 with a dielectric constant of 2.2, with single-sided copper coating, and two composite helical antenna arms 2 are etched on the upper surface. The center groove is used to insert an exponential gradient balun. The specific parameters are: the radius of the circular antenna dielectric plate 1 is 36 mm, the thickness is 0.787 mm, and the maximum radius r of the two composite helical antenna arms 2 is 2. m =35mm, the resistance of the two chip resistors 3 are both 300Ω. The equation of the equiangular spiral antenna in the center is:

[0051] (1)

[0052] The equation of the Archimedean spiral antenna of the outer ring is:

[0053] { x = [ e 0 . 221 × 2 . 5 π + 1 . 2 × ( t − 2 . 5 π )] × cos t y = [ e 0 . 221 × 2 . 5 π + 1 . 2 × ( t − 2 . 5 π )] × sin t 2 . 5 π ≤ t ≤ 9 . 8 π (2)

[0054] Wherein, x, y respectively represent the position of the planar compound helical antenna in a planar rectangular coordinate system when the planar compound helical antenna structure center establishes the coordinate system, e is the base of the natural logarithm, π is the pi, and t represents the winding radian.

[0055] like Figure 3 As shown, it is a schematic diagram of the exponential gradient balun proposed according to the present invention and its dimension marking. The balun dielectric substrate 4 is made of Rogers RT5880, has a thickness of 0.787mm, is copper-clad on both sides, and has exponential gradient signal lines 5 and exponential gradient ground lines 6 etched on the front and back sides respectively, both of which are obtained by different exponential gradient equations. The specific structural parameters are: balanced end line width w1=0.783mm, unbalanced end signal line width w2=2.4mm, unbalanced end ground line w3=6mm, and the overall length of the balun is l=28mm.

[0056] like Figure 4 (a) and Figure 4 As shown in (b), they are respectively the cross-sectional side view of the absorbing back cavity proposed in the present invention, its dimension annotation and the three-dimensional schematic diagram. The absorbing back cavity includes a cylindrical metal back cavity 7 and a stepped absorbing material 8. Since the main radiation area of ​​the spiral antenna is a ring area with a circumference of one wavelength, the radiation area from high frequency to low frequency gradually extends from the inside to the outside. In order to avoid too much absorbing material 8 filling which will cause the antenna gain to be too low and affect the performance of the antenna, the absorbing material 8 has a stepped structure, which absorbs the back radiation in a targeted manner for the radiation area of ​​the corresponding working frequency point, which can reduce the volume of the absorbing material, minimize the loss of antenna gain, and control the weight of the entire antenna. The relative dielectric constant of the absorbing material used is 9.3 and the loss tangent is 0.03. The specific structural parameters are: the cavity thickness of the cylindrical metal back cavity 7 is 1 mm, and the overall diameter is D =80mm, cavity height H =28mm, the absorbing material 8 is a stepped structure, with a height h=24mm, a height of each step Δh=6mm, a width of each step Δw=8mm, and d=5.5mm.

[0057] like Figure 5 (a) is a schematic diagram of a stepped impedance split resonant ring unit and its dimension markings according to the present invention. The specific structural dimensions are: sl1=4.2mm, sl2=2.5mm, ss=0.3mm, ss2=0.8mm, sg=0.5mm.

[0058] like Figure 5 As shown in (b), it is a top view and dimension annotation of the open resonant ring with stepped impedance characteristics loaded on the planar composite helical antenna proposed by the present invention. The open resonant ring dielectric substrate 9 is made of RogersRT5880, with a thickness of 0.787mm, single-sided copper coating, and an open resonant ring is etched on the upper surface. The open resonant ring dielectric substrate 9 is placed on the upper surface of the antenna dielectric substrate 1 and aligned with its center. Since the effective radiation area of ​​the helical antenna is about one wavelength at the helical circumference, in order to design the notch frequency point at about 5.6GHz, it can be calculated that the radius of the main radiation area of ​​5.6GHz is about 5.6mm, that is, the distribution position of the step impedance open resonant ring 10 dx , using the physical mechanism of high Q value step impedance open resonant ring absorbing electromagnetic wave energy during resonance, to achieve the notch characteristic around 5.6GHz frequency. The unit structure of the step impedance open resonant ring 10 is Figure 5 As shown in (a), the number, position and direction of the step impedance open resonant ring are different, and the combination of the step impedance open resonant ring is different, which has different effects on the frequency band and depth of the notch. The notch reconfigurable function can be achieved by replacing the open resonant ring dielectric substrate 9 with different numbers of step impedance open resonant rings. Taking the etching of one step impedance open resonant ring as an example, the distance between the center of the circle and the center of the step impedance open resonant ring unit is dx=5.5mm.

[0059] like Figure 6 As shown, the S of a step impedance open resonant ring according to the present invention is taken as an example. 11 From the simulation result diagram, we can observe that the notch frequency of the ultra-wideband notch spiral antenna of this structure is 5.57 GHz, which can realize the notch function in the ultra-wideband 2-18 GHz frequency band.

[0060] like Figure 7 As shown in the figure, it is a simulation result diagram of the actual gain and axial ratio taking a stepped impedance open resonant ring as an example according to the present invention. It can be observed that the ultra-wideband notch spiral antenna of this structure achieves a gain notch of 4.65dBic at 5.6GHz, and the axial ratio at the corresponding notch frequency point rises sharply. It can be seen that loading the stepped impedance open resonant ring will suppress the radiation in the frequency band near 5.6GHz and realize the notch characteristic, but will not affect the normal circularly polarized radiation in other frequency bands of 2-18GHz.

[0061] like Figure 8As shown, the normalized radiation patterns of several typical frequency points at Phi=0° and Phi=90° are shown according to the present invention, taking a stepped impedance open resonant ring as an example. It can be observed that the patterns of Phi=0 and Phi=90 at high frequencies do not overlap because the placement of the stepped impedance open resonant ring interferes with the high-frequency current, thus affecting the high-frequency pattern. The antenna has a relatively regular pattern in the operating frequency band of 2-18GHz, a small backlobe level, and good unidirectional radiation performance.

[0062] like Fig. 9 (a) shows the distribution of the position dx when a step impedance open resonant ring is loaded according to the present invention; Fig. 9 (b) Fig. 9 (c) in the figure is a study of the influence of three position dx changes on the notch when loading a step impedance open resonant ring according to the present invention, corresponding to S 11 , the simulation results of actual gain and axial ratio, it can be observed that the larger the dx, the weaker the reflection coefficient, corresponding to the reduction of the gain dip at the notch; the smaller the dx, the step impedance open resonant ring affects the high-frequency radiation, the axial ratio at high frequency is greater than 3dB, that is, the axial ratio performance at high frequency deteriorates. Combined with the above research, 5.5mm is more appropriate for dx.

[0063] like Fig.10 As shown in (a) in the figure, when a step impedance open resonant ring is loaded, the change of the four directions θ is studied according to the present invention. Take dx=5.5mm, the step impedance open resonant ring is rotated counterclockwise with its center as the center of the circle, and the open resonant ring is taken to be facing the +y direction as θ=0°. The four cases of θ=0°, θ=90°, θ=180, and θ=270° are analyzed to discuss the influence of the direction of the step impedance open resonant ring on the performance of the trap antenna. Fig.10 (b) Fig.10 As shown in (c), the effect of the change of θ in four directions on the notch when loading a step impedance open resonant ring is studied according to the present invention, corresponding to S 11 , the simulation results of actual gain and axial ratio, it can be observed that θ=0° and θ=180° will destroy the axial ratio performance of high frequency, so the high frequency gain will be reduced, and the notch characteristics at the resonant frequency are also weak; in addition, the resonant frequency of θ=0° and θ=180° is higher than that of θ=90° and θ=270°, and the resonant frequency band is wider. This is because the orientation of the stepped impedance open resonant ring is different, and the current coupling with the spiral antenna arm below is also different, which affects the resonant frequency and resonant bandwidth. When θ=90° and θ=270°, the notch performance at 5.6GHz is better, and it will not destroy the broadband performance of other frequency points within 2-18GHz. In particular, when θ=270°, the gain notch characteristics are the best, and a gain notch of 4.71dBic is achieved at 5.6GHz.

[0064] like Fig.11 As shown in (a), the distribution of the position dx when two step impedance open resonant rings are loaded is studied according to the present invention; Fig.11 (b) Fig.11 (c) in the figure is the simulation result diagram of S11, actual gain and axial ratio, which respectively correspond to the influence of three positions dx changes on notch when loading two step impedance open resonant rings according to the present invention. It can be observed that the larger dx is, the weaker the reflection coefficient will be, corresponding to the reduction of the gain dip amplitude at the notch; the smaller dx is, the step impedance open resonant ring will affect the high-frequency radiation, and the axial ratio at high frequency is greater than 3dB, that is, the axial ratio performance at high frequency deteriorates. Combined with the above research, when loading two open resonant rings, dx is more suitable to be 5.5mm.

[0065] like Fig.12 As shown in (a), the change of θ in four directions when two step impedance open resonant rings are loaded is studied according to the present invention. dx=5.5mm is taken. Fig. 9 The step impedance open resonant ring in the +x-axis direction in (a) is copied and rotated 180° along the center of the coordinate origin to obtain the loading combination of two step impedance open resonant rings. Four cases of θ=0°, θ=90°, θ=180°, and θ=270° are analyzed to discuss the influence of the orientation of the two step impedance open resonant rings on the performance of the trap antenna. Fig.12 (b) Fig.12 As shown in (c), the effect of the change of θ in four directions on the notch when loading two step impedance open resonant rings is studied according to the present invention, corresponding to S 11 , the simulation results of actual gain and axial ratio. It can be observed that the notch frequency is about 6 GHz in the cases of θ=0° and θ=180°, but the orientation of the stepped impedance open resonant ring has a great influence on the high-frequency current, resulting in a sharp deterioration of the high-frequency axial ratio; the notch frequency is about 5.6 GHz in the cases of θ=90° and θ=270°, which is slightly lower than the notch frequency in the cases of θ=0° and θ=180°. The overall performance of the antenna is better in the case of θ=270°, and the antenna achieves a gain dip of 6 dBic at 5.6 GHz.

[0066] like Fig.13 As shown in (a), according to the present invention, the step impedance open resonant ring in the +x-axis direction is rotated 90° around the coordinate origin to obtain another 3 step impedance open resonant rings, forming a 4 step impedance open resonant ring loading combination placed above the helical antenna, and studying the distribution of the position (dx) when loading four step impedance open resonant rings (θ=270°); Fig.13 (b) Fig.13(c) is a study of the effect of four position dx changes on the notch when loading four step impedance open resonant rings according to the present invention, corresponding to S 11 , the simulation results of actual gain and axial ratio, it can be observed that dx has little effect on the resonant frequency. The larger dx is, the weaker the reflection coefficient will be, corresponding to a smaller gain dip at the notch. However, due to the large number of stepped impedance open resonant rings, the high-frequency current is greatly affected, and the overall high-frequency axial ratio performance deteriorates.

[0067] like Fig.14 As shown in (a), the change of θ in four directions when four step impedance open resonant rings are loaded is studied according to the present invention. dx=6.5mm is taken. Fig. 9 In (a), the stepped impedance open resonant ring in the +x-axis direction is continuously replicated along the origin of the coordinate system and rotated 90° to obtain the loading combination of four stepped impedance open resonant rings. The four cases of θ=0°, θ=90°, θ=180°, and θ=270° are analyzed to discuss the influence of the orientation of the four stepped impedance open resonant rings on the performance of the trap antenna. Fig.14 (b) Fig.14 As shown in (c), the effect of four direction (θ) changes on the notch when loading two step impedance open resonant rings is studied according to the present invention, corresponding to S 11 , the simulation results of actual gain and axial ratio, it can be observed that the notch characteristic is the weakest when θ=90°, and the gain only dips by 1.1dBic at the resonant frequency of 5.7GHz. The axial ratio of θ=180° and θ=270° in the high frequency band is greater than 3dB, and the circular polarization performance is not good enough. The notch characteristic is the best when θ=0°, and the gain dips by 11dBic at the resonant frequency of 6GHz, but the axial ratio performance deteriorates in the high frequency band after 16GHz.

[0068] like Fig.15 As shown in (a), (b), and (c), the best performance of the combination of one, two, and four stepped impedance open resonant rings (SRRs) is comprehensively selected according to the present invention for comparison, corresponding to S 11, simulation results of actual gain and axial ratio. The best antenna performance when loading one step impedance open resonant ring: dx=5.5mm, θ=270°; the best antenna performance when loading two step impedance open resonant rings: dx=5.5mm, θ=270°; the best antenna performance when loading four step impedance open resonant rings: dx=6.5mm, θ=270°. From the comparison results, it can be observed that when the structural size and direction of the step impedance open resonant ring are the same, the notch frequency remains unchanged; the notch frequency band can be adjusted by adjusting the structural size and position dx of the impedance open resonant ring; the more the number of step impedance open resonant rings loaded at the same time, the better the gain notch characteristics at the resonant frequency, the deeper the notch depth, but it will inevitably have a greater impact on the current at high frequencies, so the axial ratio characteristics at high frequencies are worse. In actual design requirements, it is necessary to take into account both the notch characteristics and the radiation characteristics in other frequency bands, and the notch characteristics should not affect the performance in other frequency bands as much as possible.

[0069] Fig.16 (a), (b), and (c) are the optimal general models corresponding to when one, two, and four step impedance open resonant rings are loaded according to the present invention, and the specific size of the open resonant ring is Figure 5 Given in, the position and direction are in Fig.15 The design method is given in the following. Summary: 1. Regarding the number: the more the number of open resonant rings loaded with stepped impedance, the deeper the notch depth, but the high-frequency axial ratio performance will deteriorate; 2. Regarding the position: the open resonant ring is placed in a ring shape in the radiation zone of a wavelength corresponding to the notch frequency (calculated to obtain dx), and the total length of the open resonant ring is half the wavelength corresponding to the notch frequency (the total length of the open resonant ring is calculated: sl1×4-sg+sl2×2). In order to avoid affecting the radiation characteristics of the helical antenna in other frequency bands, the open resonant ring is bent to achieve miniaturization; 3. Regarding the direction: the open resonant rings are all opened along the radius with their backs facing the center of the circle.

[0070] The above are only the best embodiments of the present invention, but the present invention is not limited to the above embodiments. The above specific implementation methods are only illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all within the protection of the present invention.

Claims

1. An ultra-wideband planar helical antenna with adjustable notch based on an open ring resonator, characterized in that: The invention comprises a planar composite helical antenna structure, a wave-absorbing back cavity, an exponential gradient balun and an open resonant ring with a stepped impedance characteristic loaded on the planar composite helical antenna structure; The absorbing back cavity comprises a cylindrical metal back cavity (7), a stepped absorbing material (8) is placed inside the cylindrical metal back cavity (7), and a hole is dug at the center of the lower surface of the cylindrical metal back cavity (7) for connecting the SMA with the lower end of the exponential gradient balun for feeding; The exponentially gradient balun is formed by etching an exponentially gradient signal line (5) and an exponentially gradient ground line (6) on the upper and lower surfaces of a balun dielectric substrate (4), respectively, and is placed inside the wave absorbing back cavity along the axis of the planar spiral antenna, with the upper end connected to the center of the composite spiral arm and the lower end placed on the upper surface of the wave absorbing back cavity; The planar composite helical antenna structure has two composite helical antenna arms (2) etched on the upper surface of an antenna dielectric substrate (1), and a chip resistor (3) is loaded at each of the two ends of the two composite helical antenna arms (2); The open resonant ring with a step impedance characteristic is a step impedance open resonant ring (10) etched on the upper surface of an open resonant ring dielectric substrate (9), and placed on the upper surface of a planar composite helical antenna structure; The loading position of the open resonant ring with a step impedance characteristic is on the upper surface of the planar composite helical antenna, the number of etched step impedance open resonant rings (10) is one, two or four, the etched position of the step impedance open resonant rings (10) is located in a radiation zone of a wavelength corresponding to the notch frequency point, and all are opened along the radius and facing away from the center of the circle; the total length of each step impedance open resonant ring (10) is half a wavelength corresponding to the notch frequency point; The stepped absorbing material (8) inside the absorbing back cavity is a absorbing material with a relative dielectric constant of 9.3 and a loss tangent of 0.03; the specific structural parameters of the absorbing back cavity are: the thickness of the cylindrical metal back cavity (7) is 1 mm, the overall diameter D=80 mm, the cavity height H=28 mm, the height of the stepped absorbing material (8) h=24 mm, the height Δh of each step is 6 mm, the width Δw of each step is 8 mm, and d=5.5 mm.

2. The ultra-wideband planar helical antenna with adjustable notch based on an open ring resonator according to claim 1, characterized in that: The two composite helical antenna arms (2) in the planar composite helical antenna structure are obtained by rotating one of the spiral arms 180 degrees from the center to obtain another spiral arm, the central part of each spiral arm is an equiangular spiral antenna, the outer circle part is an Archimedean spiral, the ends of the two spiral arms are both cut, and a chip resistor (3) is welded at each end.

3. The ultra-wideband planar helical antenna with adjustable notch based on an open ring resonator according to claim 2, characterized in that: The equiangular spiral antenna equation for the central portion of each spiral arm in the planar composite spiral antenna structure is: The equation of the Archimedean spiral antenna of the outer ring is: Wherein, x, y respectively represent the position of the planar compound helical antenna in a planar rectangular coordinate system when the planar compound helical antenna structure center establishes the coordinate system, e is the base of the natural logarithm, π is the pi, and t represents the winding radian.

4. The ultra-wideband planar helical antenna with adjustable notch based on an open ring resonator according to claim 1, characterized in that: The exponentially-varying signal line (5) and the exponentially-varying ground line (6) of the exponentially-varying balun are both exponentially-varying lines; The top of the exponential gradient balun penetrates the antenna dielectric substrate (1), the exponential gradient signal line (5) and the exponential gradient ground line (6) are respectively connected to the starting points of the two composite helical antenna arms (2), and the bottom penetrates the central hole of the lower surface of the cylindrical metal back cavity (7) to be connected to the SMA cable interface (11).

5. The ultra-wideband planar helical antenna with adjustable notch based on an open ring resonator according to claim 4, characterized in that: The exponentially tapered signal line (5) and the exponentially tapered ground line (6) of the exponentially tapered balun are obtained by different exponentially tapered equations, respectively. The specific structural parameters are: balanced end line width w1=0.783mm, unbalanced end signal line width w2=2.4mm, unbalanced end ground line w3=6mm, and the overall length l of the exponentially tapered balun is 28mm.

6. The ultra-wideband planar helical antenna with adjustable notch based on an open ring resonator according to claim 1, characterized in that: The antenna dielectric substrate (1), the balun dielectric substrate (4) and the open resonant ring dielectric substrate (9) are all made of Rogers RT5880, and the relevant electrical parameters are ε r =2.2, tanδ=0.0009, and the thickness is 0.787mm.

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