Hybrid cascade band-pass frequency selective surface with flexibly designed pass-stop band

Abstract

The invention discloses a hybrid cascade band-pass frequency selective surface with flexibly designed pass-stop bands, and belongs to the technical field of electromagnetic fields and microwaves. The frequency selective surface is composed of two layers of structures, wherein the upper layer is of a grid square ring structure, and the lower layer is of a double-square ring structure. Under the condition that an additional electromagnetic structure is not introduced, the equivalent interlayer spacing of the upper-layer structure and the lower-layer structure is increased through staggered design of the upper-layer unit and the lower-layer unit, and the large-angle stability of the frequency selective surface is improved. According to the frequency selective surface, stable transmission performance of electromagnetic waves can be achieved within the frequency band of 3.3-3.8 GHz under the condition of different polarization and angle incidence, meanwhile, the frequency band where the pass-stop band of the frequency selective surface is located can adjust the side length size of the related square ring structure to achieve flexible design, and the frequency selective surface has the advantages of being simple in structure, low in cost and easy to popularize. The frequency selective surface has a transmission zero point outside a passband, so that a good stop-band characteristic can be realized.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic field and microwave technology, and in particular relates to a hybrid cascade bandpass frequency selective surface with flexibly designed pass / stop bands. Background Art

[0002] The fifth generation (5G) communication system will be widely used in various fields due to its high data transmission rate and low latency. However, its predecessors, such as 4G, 3G or even 2G, will still play a role for quite a long time. Even though some older generation networks may be cancelled in the future, the frequency bands allocated for them may still be used. Therefore, the 5G era requires dual-band / multi-band base station antenna arrays to cover these frequency bands. In order to save installation space and cost, antennas usually work on different frequency bands, which are usually intertwined with each other. However, in a multi-band antenna array, the electromagnetic environment of the antennas of each frequency band becomes quite complicated. Electromagnetic coupling in multi-band antenna arrays always affects the radiation pattern, input impedance and port isolation of antennas working in different frequency bands. In multi-antenna solutions, multiple antennas need to be developed to cover the required frequency bands, where the size of the low-frequency antenna is usually larger than that of the high-frequency antenna. When the high-frequency antenna is working, due to the obstruction of the low-frequency antenna, the electromagnetic waves radiated by the high-frequency antenna will excite induced current on its metal structure when passing through the low-frequency antenna, generating secondary radiation, thereby distorting the radiation pattern of the high-frequency antenna and affecting the matching effect. Therefore, it is often necessary to specially design the low-frequency antenna to improve its influence on the antenna working in the high-frequency band. The introduction of frequency selective surfaces in multi-band antennas can achieve the cross-band decoupling effect of multi-band antennas without changing the structure of the low-frequency antenna.

[0003] A frequency selective surface is a single-layer or multi-layer planar structure or three-dimensional structure formed by a periodic arrangement of scattering units or aperture structures. Due to its filtering characteristics for electromagnetic waves of different operating frequency bands, incident angles and polarization states, based on this characteristic, the frequency selective surface can be regarded as a spatial filter and is widely used in radar antenna cover applications. An ideal frequency selective surface antenna cover can not only protect the internal antenna from the influence of the external physical environment, but also fully scatter electromagnetic waves outside the antenna operating frequency band, and allow electromagnetic waves within the operating frequency band to pass with low loss, while being able to meet the normal scanning of the antenna array. This requires that the design of the frequency selective surface needs to meet the requirements of low loss in the passband, wide-angle stability, and easy to achieve flexible design adjustments in different frequency bands to adapt to the same type of applications in different frequency bands, thereby reducing design costs.

[0004] In order to enhance the wide-angle stability of the frequency selective surface, the document “Compact Ultra-Wide Band Frequency Selective Surface With High Selectivity” uses meander lines to achieve the miniaturization of the frequency selective surface and thus improve the wide-angle stability. The document “A Novel Fractal Inspired Iterated Four-Legged Loaded Loop Elements Based 2.5-D Miniaturized Frequency Selective Surface” enhances the wide-angle stability of the frequency selective surface by introducing metal through holes on the dielectric substrate. The document “On the improvement of angular stability of the 2nd-order miniaturized FSS structure” achieves the scanning-independent characteristics of the frequency selective surface by introducing a thick dielectric layer. In order to achieve the wide-angle stability of the frequency selective surface, the existing frequency selective surfaces will introduce additional physical structures or complex graphic structures, which increases the design and manufacturing costs, and their angular stability is often manifested in that the design frequency point does not shift when the electromagnetic wave is incident from different angles, rather than the transmission characteristics in the required frequency band remain stable when the electromagnetic wave is incident at different angles.

[0005] In view of the above problems, the present invention discloses a hybrid cascaded bandpass frequency selective surface with flexibly designed passbands and stopbands. Summary of the invention

[0006] Based on the above background technology, the present invention proposes a hybrid cascade bandpass frequency selective surface with flexible pass / stop band design, which is composed of two layers of printed metal dielectric plates. It has good wave transmission characteristics for electromagnetic waves with different polarizations and incident angles within the working frequency band, and has good reflection characteristics for electromagnetic waves outside the working frequency band. The design frequency band of this invention covers the n78 frequency band of 5G communication and can be used in 5G communication multi-band common aperture antennas.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A hybrid cascade bandpass frequency selective surface with flexibly designed pass / stop bands comprises a dielectric substrate with a printed grid square ring structure and a dielectric substrate with a printed square square ring structure.

[0009] Furthermore, the dielectric substrate of the printed grid square ring, the etched composite square ring is composed of the square ring and the short branches perpendicular to the edge at the center of each edge.

[0010] Furthermore, the two square rings printed on the medium substrate for printing the two square rings are designed to be staggered, and appear as double right-angle structures distributed on the four corners of the substrate unit in the same period as the grid square ring. After periodic arrangement, the double right-angle structure can be spliced ​​with the double right-angle structure of the adjacent unit to restore the double square ring structure.

[0011] The frequency selective surface of the present invention has the following beneficial effects: 1. It has good transmission characteristics for electromagnetic waves in the designed frequency band of 3.3-3.8GHz, and has good reflection characteristics outside the band. 2. Under the conditions of different polarizations and different angles of oblique incidence, the FSS still has good transmission characteristics within the designed frequency band. When the incident angle is 60°, the minimum transmission coefficient of the FSS is -0.8dB. 3. The FSS adopts two layers of dielectric plates with a simple structure, which is easy to manufacture and has low production cost. 3. For the same type of applications requiring other frequency bands, the side lengths of the square rings of the grid square ring structure and the square square ring structure can be adjusted to achieve flexible design of the passband and stopband frequency bands and reduce design costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the frequency selective surface structure of the present invention;

[0013] Figure 2 A top view of the square ring layer structure of the frequency selective surface grid of the present invention;

[0014] Figure 3 A top view of the double-square ring layer structure of the frequency selective surface of the present invention;

[0015] Figure 4 This is a transmission characteristic curve diagram of the frequency selective surface TE and TM polarized waves at 0° incidence in the 1.0-4.5 GHz frequency band in an embodiment of the present invention;

[0016] Figure 5 This is a transmission characteristic curve diagram of the frequency selective surface TE and TM polarized waves at 60° incidence in the 1.0-4.5 GHz frequency band in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the implementation examples.

[0018] like Figure 1As shown, a hybrid cascade bandpass frequency selective surface unit with flexible pass / stop band design has a period of 30 mm and is composed of two layers of printed pattern dielectric substrates. The upper structure is a dielectric substrate with a printed grid square ring structure, with a thickness of 1 mm and a dielectric constant of 3.0. The dielectric substrate with a printed grid square ring structure, the composite square ring structure etched on the substrate is composed of a square ring 1 and four rectangular short branches 2 located at the center of each side of the square ring and perpendicular to the square ring edge. The lower structure is a dielectric substrate with a printed square rectangular ring structure, with a thickness of 1 mm and a dielectric constant of 3.0. The dielectric substrate with a printed square rectangular ring structure, the square rectangular rings printed on the substrate are double right-angle structures distributed at the four corners of the dielectric substrate, the double right-angle structure is composed of an inner right angle 3 and an outer right angle 4, and the double right-angle structure will be merged with the double right-angle structure of the adjacent unit into a double right-angle structure after periodic arrangement. There is air medium between the upper and lower dielectric substrates, and the thickness of the air medium layer is 18 mm.

[0019] like Figure 2 As shown, the first layer of the grid square ring structure, the etched composite square ring structure has an outer side length of l1 = 22mm, an inner side length of l2 = 18mm, a rectangular short branch length of l3 = 3mm, and a width of l4 = 1mm. The grid square ring structure can be equivalent to a parallel LC circuit. Adjusting the side length of the grid square ring can change the resonant frequency of the equivalent parallel LC circuit, and has a certain degree of wave transmission performance within the designed frequency band.

[0020] like Figure 3As shown, the second layer of the double square ring structure is a double right-angle structure distributed in the four corners of the dielectric plate. The outer side length of the outer right angle is L1 = 13.75 mm, the width of the right angle is L2 = 0.5 mm, the outer side length of the inner right angle is L3 = 8.25 mm, and the width of the right angle is L4 = 2.1 mm. The equivalent circuit of the double square ring structure is two parallel series LC circuits. The resonant frequencies of the two series LC circuits are different due to the size difference between the inner and outer square rings. When the two series LC circuits resonate, two transmission zeros will be generated at their resonant frequencies. The inner and outer rings regulate the transmission zeros at high and low frequencies respectively, and stopbands will be formed around these two resonant frequencies. In addition, since the reactance of the series LC circuit is capacitive before resonance and inductive after resonance, in the frequency band between the two transmission zeros, the outer ring of the double square ring structure is in a resonant state, while the inner ring has not yet resonated. At this time, its equivalent circuit can be simplified to a parallel LC circuit to form a passband. Adjusting the side length of the double square ring can change the resonant frequency of the series LC circuit in the equivalent parallel branch, thereby adjusting the passband and stopband frequency band of the double square ring structure. The bandwidth formed by the grid square ring layer and the double square ring layer is relatively narrow, and the bandwidth can be expanded when cascaded, thereby realizing the passband design within the required frequency band. At the same time, the parallel series LC circuit equivalent to the double square ring structure can also introduce a transmission zero outside the passband to achieve out-of-band suppression.

[0021] Figure 4 and Figure 5 The transmission characteristic curves of TE and TM polarized waves of the frequency selective surface in the specific implementation example of the present invention when the electromagnetic wave is incident at 0° and 60° respectively. It can be seen that under the conditions of 0° and 60° incidence, in the range of 3.3-3.8GHz, the transmission coefficients of TE and TM polarized waves remain above -0.8dB, indicating that the invented frequency selective surface has good angular stability and polarization stability, and has good passband characteristics for both TE and TM polarized waves under large angle incidence. Outside the passband, due to the existence of the transmission zero point, the frequency selective surface also has a strong out-of-band suppression effect.

[0022] The above description and implementation methods are only some preferred examples of the present invention and do not constitute any limitation to the present invention. For professionals in this field, the present application may have various modifications and changes, but the modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A hybrid cascaded bandpass frequency selective surface with flexibly designed pass / stop bands, characterized in that: The frequency selective surface is composed of a layer of grid square ring structure and a layer of double square ring structure which are mixed and cascaded, and the double square ring layer is cascaded below the grid square ring layer after being staggered.

2. A hybrid cascaded bandpass frequency selective surface with flexibly designed pass / stop bands according to claim 1, characterized in that: The grid square ring structure is a structure formed by etching a composite square ring groove on a single-sided copper-clad dielectric board. The composite square ring is composed of a square ring and short branches perpendicular to each side at the center of the square ring.

3. The hybrid cascaded bandpass frequency selective surface with flexibly designed pass / stop bands according to claim 1, characterized in that: The double square ring structure is a double right-angle structure distributed at the four corners of the dielectric substrate. After periodic arrangement, the double right-angle structure and adjacent units can be spliced ​​to form a double square ring structure.

4. The hybrid cascaded bandpass frequency selective surface with flexibly designed pass / stop bands according to claim 1, characterized in that: The thickness of the upper and lower dielectric plates is 1 mm, and the space between the dielectric plates is air with a thickness of 18 mm.

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