Ultra-wideband miniaturized dual-mode end-on-fire antenna

Abstract

The invention provides an ultra-wideband miniaturized dual-mode end-on-fire antenna. The ultra-wideband miniaturized dual-mode end-on-fire antenna comprises a microstrip line-to-slot line structure, an SSPPs structure on the outer side of the antenna and a Vivaldi structure on the inner side of the antenna, the microstrip line-to-slot line structure is used for exciting the SSPPs structure and the Vivaldi structure; the SSPPs structure is used for excitation, transmission and radiation of SSPPs mode electromagnetic waves, and is used for suppressing interference between modes; the Vivaldi structure is used for transmission and radiation of Vivaldi mode electromagnetic waves; through a new method of combining an SSPPs end-fire mode and a Vivaldi end-fire mode, the compatibility of ultra wide band and miniaturization requirements in the end-fire antenna is realized, the aperture of the antenna is fully utilized, stable end-fire is realized in a working frequency band from 2.04 GHz to 23.1 GHz, the gain can be realized from 8.5 to 16.96 dBi, and the effects of ultra wide band, high gain, miniaturization and high aperture efficiency are achieved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of end-fire antennas, and in particular, to an ultra-wideband and miniaturized dual-mode end-fire antenna. Background Art

[0002] Ultra-wideband and miniaturization are core requirements in fields such as 5G / 6G communications, Internet of Things (IoT), automotive radar, and medical imaging. Ultra-wideband miniaturized end-fire antenna technology is developing towards high performance, high integration, and low cost. Miniaturization requires the electrical size of the antenna to be as small as possible, but ultra-wideband performance requires a relatively large electrical size to cover multiple octave operating bandwidths. Therefore, there is a serious constraint between the two characteristics. Most traditional antennas broaden the impedance bandwidth by optimizing the antenna shape, loading additional structures, increasing the dielectric constant of the dielectric material, etc. They are still limited to achieving end-fire using a single radiation mode and have not carried out a detailed exploration and effective combination of the two radiation modes. There are still significant defects and important challenges in simultaneously achieving ultra-wideband, miniaturization, and gain enhancement. Therefore, developing an ultra-wideband miniaturized dual-mode end-fire antenna to effectively overcome the above-mentioned defects in related technologies has become an urgent technical problem in the industry. Summary of the Invention

[0003] In view of the above problems existing in the prior art, the embodiments of the present invention provide an ultra-wideband miniaturized dual-mode end-fire antenna.

[0004] The embodiments of the present invention provide an ultra-wideband miniaturized dual-mode end-fire antenna, comprising:

[0005] A microstrip-to-slotline structure, as a feeding part, for connecting a radio frequency excitation signal;

[0006] An antenna structure, including a Vivaldi structure and spoof surface plasmon polaritons (SSPPs) structures located on both sides of the Vivaldi structure, and the antenna structure is connected to the microstrip-to-slotline structure;

[0007] The SSPPs structure is used to achieve end-fire in the first frequency band under the excitation of the radio frequency excitation signal;

[0008] The Vivaldi structure is used to achieve end-fire in the second frequency band under the excitation of the radio frequency excitation signal;

[0009] Wherein, the frequency in the second frequency band is higher than the frequency in the first frequency band.

[0010] According to the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, the microstrip-to-slotline structure includes a microstrip line and a dielectric substrate;

[0011] The microstrip line includes a conductor strip and a microstrip line ground plane. The conductor strip is located on the lower layer of the dielectric substrate, and the microstrip line ground plane is located on the upper layer of the dielectric substrate;

[0012] The width of the conductor strip decreases exponentially from one end away from the antenna structure to the other end to achieve the coupling between the microstrip line and the slot line in the Vivaldi structure.

[0013] For the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, the SSPPs structure on each side includes a plurality of periodically arranged U-shaped SSPPs units, and the U-shaped openings of the U-shaped SSPPs units face outward;

[0014] The U-shaped SSPPs units on each side are divided into a mode excitation section, a wave guiding section, and a radiation section. The mode excitation section, the wave guiding section, and the radiation section are connected in sequence, and the mode excitation section is connected to the microstrip line-to-slot line structure;

[0015] The mode excitation section is used for the coupled excitation of electromagnetic waves in the SSPPs mode, the wave guiding section is used for the transmission of electromagnetic waves in the SSPPs mode, and the radiation section is used for the radiation of electromagnetic waves in the SSPPs mode.

[0016] For the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, each mode excitation section includes a matching sub-section, an excitation sub-section, and a transition sub-section;

[0017] Among them, the matching sub-section is used for impedance matching. The slot depth of the U-shaped SSPPs units in the matching sub-section gradually increases. Correspondingly, the distance between the bottom of the slot and the nearest slot line in the Vivaldi structure gradually decreases;

[0018] The excitation sub-section is used for the coupled excitation of electromagnetic waves in the SSPPs mode, and the length of the excitation sub-section is half of the wavelength of the electromagnetic waves in the SSPPs mode at the lowest operating frequency of the dual-mode antenna;

[0019] The distance between the bottom of the slot of the U-shaped SSPPs units in the transition sub-section and the nearest slot line in the Vivaldi structure gradually widens to reduce the influence of the electromagnetic waves in the Vivaldi mode and the SSPPs mode in the wave guiding section, and provides space for the widening of the distance between the slot lines in the Vivaldi structure.

[0020] For the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, the slot depth h0 of the U-shaped SSPPs units in the excitation sub-section is greater than the slot depth h of the U-shaped SSPPs units in the wave guiding section, so that the SSPPs cut-off frequency of the mode excitation section is less than the SSPPs cut-off frequency of the wave guiding section, covering the mode interference frequency band and suppressing the impedance matching deterioration, radiation beam splitting, and gain reduction caused by mode interference.

[0021] According to the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, the slot depth of the U-shaped SSPPs unit in the transition sub-segment gradually decreases from h0 to h.

[0022] According to the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, the slot depth of the U-shaped SSPPs unit in the radiation segment decreases exponentially from the slot depth h of the U-shaped SSPPs unit in the waveguide band to 0 mm, realizing the transition and conversion between the SSPPs wave and the free-space wave.

[0023] According to the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, one end of the slot line in the Vivaldi structure is connected to the slot line in the microstrip line to slot line structure to form a continuous gradual transition, and the other end of the slot line in the Vivaldi structure extends to the end of the SSPPs structure;

[0024] The slot line spacing in the Vivaldi structure widens exponentially from one end close to the microstrip line to slot line structure to the other end, realizing the transmission and radiation of the Vivaldi mode electromagnetic wave.

[0025] According to the ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention, the SSPPs structure provides end-fire in the SSPPs mode, the Vivaldi structure provides end-fire in the Vivaldi mode, and there is no frequency break point between the first frequency band and the second frequency band corresponding to the two end-fire modes, jointly covering the complete operating frequency band.

[0026] The ultra-wideband miniaturized dual-mode end-fire antenna provided by the embodiments of the present invention combines the SSPPs end-fire mode and the Vivaldi end-fire mode in a new way to meet the requirements of ultra-wideband and miniaturization in end-fire antennas, makes full use of the antenna aperture, and suppresses the interference between the dual modes by deepening the groove depth of the SSPPs unit in the mode excitation segment. The aperture efficiency of the dual-mode antenna at the lowest frequency point is as high as 91.72%. The dual-mode antenna realizes stable end-fire in the frequency range of the ultra-wideband frequency band from 2.04 GHz to 23.1 GHz (11.3 times frequency). The achievable gain of the dual-mode antenna is 8.5 to 16.96 dBi, which is up to 6.9 dB higher than that of the Vivaldi antenna of the same size. The dual-mode antenna is small in size and low in profile, only 0.41λ0×1.71λ0×0.0035λ0 (λ0 is the wavelength of the free-space wave at the lowest operating frequency point). Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 Schematic diagram of the ultra-wideband miniaturized dual-mode end-fire antenna structure provided by the embodiment of the present invention;

[0029] Figure 2 Schematic diagram of the mode interference and suppression effect provided by the embodiment of the present invention;

[0030] Figure 3 Schematic diagram of the measured S-parameter effect of the dual-mode end-fire antenna provided by the embodiment of the present invention;

[0031] Figure 4 Schematic diagram of the measured achievable gain effect of the dual-mode end-fire antenna provided by the embodiment of the present invention;

[0032] Figure 5 Schematic diagram of the measured normalized direction effect of the dual-mode end-fire antenna provided by the embodiment of the present invention. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. In addition, the technical features in each embodiment or individual embodiment provided by the present invention can be combined with each other arbitrarily to form a feasible technical solution. This combination is not restricted by the order of steps and / or the structure composition mode, but must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0034] The embodiment of the present invention provides an ultra-wideband miniaturized dual-mode end-fire antenna. Refer to Figure 1 , the device includes:

[0035] A microstrip-to-slotline structure, as the feeding part, for connecting the radio frequency excitation signal;

[0036] An antenna structure, comprising a Vivaldi structure and SSPPs structures located on both sides of the Vivaldi structure, and the antenna structure is connected to a microstrip line to slot line structure;

[0037] The SSPPs structure is configured to achieve end-fire of a first frequency band under the excitation of the radio frequency excitation signal;

[0038] The Vivaldi structure is configured to achieve end-fire of a second frequency band under the excitation of the radio frequency excitation signal;

[0039] Wherein, the frequency in the second frequency band is higher than the frequency in the first frequency band.

[0040] See Figure 1 , the ultra-wideband miniaturized dual-mode end-fire antenna provided in the embodiment of the present invention includes upper and lower metal conductors and a dielectric substrate in the middle layer. Among them, the metal conductor material is generally copper, and the thickness can be 0.018 mm. The dielectric substrate can adopt Rogers RT5880, with a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of 0.508 mm. The length of the dielectric substrate is 252 mm, and the width is 60 mm.

[0041] The first frequency band can be 2.04 to 4.1 GHz, and the second frequency band can be 4.1 to 23.1 GHz. The Vivaldi structure and the SSPPs structure jointly complete end-fire from 2.04 to 23.1 GHz.

[0042] See Figure 1 , on the basis of the above embodiment, the microstrip line to slot line feeding structure L1 is a microstrip line to slot line structure for connecting a radio frequency excitation signal. The microstrip ground plane is located on the upper layer of the dielectric substrate, and the conductor strip is located on the lower layer of the dielectric substrate. In order to achieve efficient coupling between the microstrip line and the slot line, the width of the conductor strip of the microstrip line is exponentially transformed from 1.53 mm to 0.8 mm, and the exponential expressions are as shown in formulas (1) to (3), and the exponential coefficients α of y1 = f(x1) and y2 = f(x2) are both set to 0.2.

[0043] y = c1e αx +c2 (x1≤x≤x2) (1)

[0044]

[0045] Wherein, (x1, y1) and (x2, y2) are the two endpoints of the line segment y = f(x), e is the exponential symbol, c1 and c2 are both intermediate parameters, y is the exponential function, and x is the independent variable.

[0046] See Figure 1, on the basis of the above embodiments, the SSPPs structure is distributed outside the antenna and is composed of U-shaped SSPPs units (slot width a = 1.7 mm, period p = 3 mm). It can be divided into a mode excitation section L2, a guiding section L3, and a radiation section L4, where L2 = 72 mm, L3 = 105 mm, and L4 = 75 mm.

[0047] In the mode excitation section L2, it includes three sub-sections: a matching sub-section, an excitation sub-section, and a transition sub-section. Among them, the matching sub-section is used for impedance matching and is composed of 5 U-shaped units with increasing slot depths; the excitation sub-section is composed of 10 U-shaped units arranged in a period, with a slot depth h0 = 14 mm, and the distance between the bottom of the groove and the slot line is d0 - h0 = 7 mm, ensuring that the SSPPs mode electromagnetic wave is efficiently coupled and excited; the transition sub-section is used for the transition between the SSPPs units in the excitation sub-section of the mode excitation section L2 and the SSPPs units in the guiding section L3. The slot depth of the unit decreases from 14 mm to 12 mm, and the distance between the bottom of the unit slot and the slot line increases from d0 - h0 = 7 mm to d - h = 18 mm.

[0048] In the guiding section L3, the distance between the bottom of the groove and the slot line is d–h = 18 mm, reducing the influence of the Vivaldi mode electromagnetic wave and the SSPPs mode electromagnetic wave in the guiding section, and providing space for widening the slot line structure into a Vivaldi radiator.

[0049] In the radiation section L4, in order to achieve the transition and conversion between the strongly confined SSPPs wave and the free-space wave, the slot depth of the U-shaped SSPPs unit decreases exponentially from 12 mm to 0 mm. The exponential expressions are shown in formulas (1) to (3), and the exponential coefficient α of y3 = f(x3) is set to -0.01.

[0050] See Figure 1 , on the basis of the above embodiments, for the SSPPs structure outside the antenna, the slot depth h0 of the unit in the mode excitation section L2 and the slot depth h of the unit in the guiding section L3 are respectively set to 14 mm and 12 mm to demonstrate in this embodiment the ability of enhancing the SSPPs low-pass characteristic of the mode excitation section L2 to suppress the dual-mode interference, so that the SSPPs cut-off frequency of the mode excitation section L2 is lower than the SSPPs cut-off frequency of the guiding section L3, achieving the effect of being able to cover the mode interference and suppressing the deterioration of impedance matching, radiation beam splitting, and gain reduction caused by the mode interference.

[0051] See Figure 1, based on the above embodiments, the Vivaldi structure is distributed inside the antenna. The slot line of the inner Vivaldi structure forms a continuous gradual transition with the slot line of the microstrip line to slot line feeding structure. The width of the slot line exponentially broadens from 0.22 mm to 15 mm, realizing the transmission and radiation of Vivaldi-mode electromagnetic waves. The exponential expression is as shown in formulas (1) to (3), and the exponential coefficient α of y4 = f(x4) is set to 0.02.

[0052] Specifically, as Figure 2 (where part (a) is the impedance matching comparison, part (b) is the gain comparison, part (c) is the beam lobes, and part (d) is the beam concentration) shows, during the mode combination process, within the frequency band where the two modes work simultaneously, due to the mutual interference between the two modes, the impedance matching deteriorates (corresponding to Figure 2 (a) h0 = 12 mm), the gain decreases (corresponding to Figure 2 (b) h0 = 12 mm), and the radiation beam splits (corresponding to Figure 2 (c)). By enhancing the low-pass characteristic of the mode excitation section of SSPPs, the mode interference is effectively suppressed: that is, the slot depth (h0 = 14 mm) of the SSPPs unit in the mode excitation section L2 is greater than the slot depth (h = 12 mm) of the SSPPs unit in the waveguide section L3, so that the cut-off frequency of SSPPs is reduced from 5 GHz to 4.1 GHz, achieving the effect of covering the interference frequency band, effectively suppressing the mode interference, and bringing about an improvement in impedance matching (corresponding to Figure 2 (a) h0 = 14 mm), an increase in gain (corresponding to Figure 2 (b) h0 = 14 mm), and the disappearance of the radiation beam split (corresponding to Figure 2 (d)).

[0053] Furthermore, the impedance matching characteristic of the ultra-wideband miniaturized dual-mode end-fire antenna with the ability to suppress mode interference (h0 = 14 mm) provided in this embodiment is as Figure 3 shown, and the achievable gain is as Figure 4 shown. The normalized radiation pattern within the operating frequency band is as Figure 5 shown (where part (a) is 2.1 GHz, part (b) is 3 GHz, part (c) is 4 GHz, part (d) is 5 GHz, part (e) is 8 GHz, part (f) is 13 GHz, part (g) is 18 GHz, and part (h) is 23 GHz). It can be seen from this that thanks to the combination of the SSPPs end-fire mode and the Vivaldi end-fire mode, this dual-mode end-fire antenna can achieve stable end-fire within the entire operating frequency band of 2.04 - 23.1 GHz (167.5%), and the achievable gain can be increased to 8.56 - 16.96 dBi.

[0054] The ultra-wideband miniaturized dual-mode end-fire antenna provided by the present invention combines the SSPPs end-fire mode and the Vivaldi end-fire mode in a new way to meet the requirements of ultra-wideband and miniaturization in end-fire antennas, makes full use of the antenna aperture, and suppresses the interference between the dual modes by deepening the groove depth of the SSPPs structure in the excitation section. The aperture efficiency of the dual-mode antenna at the lowest frequency point is as high as 91.72%. The dual-mode antenna achieves stable end-fire within the frequency range of the ultra-wideband frequency band from 2.04 GHz to 23.1 GHz (11.3 times frequency). The achievable gain of the dual-mode antenna is 8.5 to 16.96 dBi, which is increased by up to 6.9 dB compared with the Vivaldi antenna of the same size. At the same time, the antenna has an aperture efficiency as high as 91.72% at the lowest frequency, and is small in size and low in profile, being 0.41λ0×1.71λ0×0.0035λ0 (λ0 is the wavelength of the free-space wave at the lowest operating frequency point).

[0055] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative labor.

[0056] It should be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "including..." do not exclude the existence of additional identical elements in the process, method, article or device including the said elements. For any "predetermined threshold", "preset threshold" or similar expressions, if no specific value is marked, a person of ordinary skill in the art can determine its specific value through simple experiments or corresponding debugging.

[0057] It should also be noted that unless otherwise clearly specified and limited, the terms "set", "installed", "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements. For a person of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A miniaturized ultra-wideband dual-mode end-fire antenna, characterized in that, Comprising: A microstrip-to-slotline structure, as a feeding part, for connecting a radio frequency excitation signal; An antenna structure, including a Vivaldi structure and SSPPs structures located on both sides of the Vivaldi structure, and the antenna structure is connected to the microstrip-to-slotline structure; The SSPPs structure is used to achieve end-fire radiation in the first frequency band under the excitation of the radio frequency excitation signal; The Vivaldi structure is used to achieve end-fire radiation in the second frequency band under the excitation of the radio frequency excitation signal; Wherein, the frequency in the second frequency band is higher than the frequency in the first frequency band.

2. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 1, wherein The microstrip-to-slotline structure includes a microstrip line and a dielectric substrate; The microstrip line includes a conductor strip and a microstrip line ground plane, the conductor strip is located on the lower layer of the dielectric substrate, and the microstrip line ground plane is located on the upper layer of the dielectric substrate; The width of the conductor strip decreases exponentially from one end far away from the antenna structure to the other end, so as to realize the coupling between the microstrip line and the slotline in the Vivaldi structure.

3. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 1, characterized in that, Each side of the SSPPs structure includes a plurality of periodically arranged U-shaped SSPPs units, and the U-shaped opening of the U-shaped SSPPs unit faces outward; Each side of the U-shaped SSPPs units is divided into a mode excitation section, a guiding section and a radiation section, the mode excitation section, the guiding section and the radiation section are connected in sequence, and the mode excitation section is connected to the microstrip-to-slotline structure; The mode excitation section is used for the coupled excitation of electromagnetic waves in the SSPPs mode, the guiding section is used for the transmission of electromagnetic waves in the SSPPs mode, and the radiation section is used for the radiation of electromagnetic waves in the SSPPs mode.

4. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 3, characterized in that, Each mode excitation section includes a matching sub-section, an excitation sub-section and a transition sub-section; Wherein, the matching sub-section is used for impedance matching, and the groove depth of the U-shaped SSPPs unit in the matching sub-section gradually increases. Correspondingly, the distance between the bottom of the groove and the nearest slotline in the Vivaldi structure gradually decreases; The excitation sub-section is used for the coupled excitation of electromagnetic waves in the SSPPs mode, and the length of the excitation sub-section is half of the wavelength of the electromagnetic wave in the SSPPs mode at the lowest operating frequency of the dual-mode antenna; The distance between the bottom of the groove of the U-shaped SSPPs unit in the transition sub-section and the nearest slotline in the Vivaldi structure gradually widens, so as to reduce the influence of the electromagnetic waves in the Vivaldi mode and the SSPPs mode in the guiding section, and provide space for the widening of the distance between the slotlines in the Vivaldi structure.

5. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 4, wherein The groove depth h0 of the U-shaped SSPPs unit in the excitation sub-section is greater than the groove depth h of the U-shaped SSPPs unit in the guiding section, so that the SSPPs cut-off frequency of the mode excitation section is less than the SSPPs cut-off frequency of the guiding section, covering the mode interference frequency band and suppressing the impedance matching deterioration, radiation beam splitting and gain decrease caused by mode interference.

6. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 5, characterized in that, The groove depth of the U-shaped SSPPs unit in the transition sub-section gradually decreases from h0 to h.

7. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 3, characterized in that, The groove depth of the U-shaped SSPPs unit in the radiation section decreases exponentially from the groove depth h of the U-shaped SSPPs unit in the guiding section to 0 mm, realizing the transition and conversion between the SSPPs wave and the free-space wave.

8. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 1, characterized in that, One end of the slot line in the Vivaldi structure is connected to the slot line in the microstrip-to-slotline structure to form a continuous and gradual transition, and the other end of the slot line in the Vivaldi structure extends to the end of the SSPPs structure; The slot line spacing in the Vivaldi structure widens exponentially from one end close to the microstrip-to-slotline structure to the other end, realizing the transmission and radiation of the Vivaldi-mode electromagnetic wave.

9. The ultra-wideband miniaturized dual-mode end-fire antenna according to claim 1, characterized in that, The SSPPs structure provides end-fire of the SSPPs mode, and the Vivaldi structure provides end-fire of the Vivaldi mode, and there is no frequency break point between the first frequency band and the second frequency band corresponding to the two end-fire modes, jointly covering the complete working frequency band.

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