A terahertz planar reflectarray antenna based on square ring nested structure

Abstract

The present invention discloses a terahertz planar reflector array antenna based on a square ring nested structure, belonging to the field of terahertz technology. The novel reflector array unit structure proposed in the present invention takes into account the design requirements of full phase modulation, wide bandwidth, anti-polarization sensitivity and other characteristics, breaking through the difficulty that the traditional scheme cannot take into account phase, frequency band and polarization. The present scheme adopts a rotationally symmetric structure, has no polarization sensitivity, and has a wider effective bandwidth; the novel reflector array unit structure proposed in the present invention avoids the dependence of phase modulation capability on fine structure, introduces a broadband array to realize broadband phase modulation, and reduces the requirements for processing accuracy, so it is suitable for applications in millimeter wave and terahertz frequency bands, has a simple structure, is easy to process, has stable performance and high yield; the terahertz reflector array antenna is easy to process, has low cost, small size and excellent radiation performance, and can make up for the shortcomings of existing terahertz antennas, such as limited gain, high processing difficulty, high side lobe and cross-polarization levels, etc.

Description

Technical Field

[0001] The invention belongs to the field of terahertz technology, and in particular relates to a terahertz planar reflectarray antenna based on a square ring nested structure. Background Art

[0002] Planar reflectarray antennas are based on metasurface structures, with planar periodic arrays replacing array units. They have the advantages of simple structure, low cost, small size, and flexible beam control. For millimeter-wave and terahertz antennas, high processing accuracy is required, and many antenna forms with complex and precise structures cannot be realized. Planar reflectarray antennas are a good solution that can meet the radiation characteristics requirements such as high-gain beams, multiple beams, and beams of specific shapes, without the need for complex three-dimensional structures. For millimeter-wave and terahertz frequency bands, in order to obtain broadband, low sidelobe, low cross-polarization and other performance, planar reflectarray units are required to have a wide phase modulation range, be insensitive to the polarization mode and incident angle of the incident wave, have good broadband consistency of phase modulation, and avoid using fine structures to modulate the phase to reduce the impact of processing accuracy errors on antenna performance.

[0003] The existing planar reflector array unit structures have different shapes. There are a wide variety of reflector array antenna forms in the microwave band, but there is a lack of consideration for processing accuracy. This problem can be ignored in the microwave band, but in the millimeter wave and terahertz bands, due to the high frequency and short wavelength, many fine structures have exceeded the limit of processing accuracy. Therefore, although many reflector array antennas in the microwave band have a wide enough phase modulation range and good broadband consistency, they mostly use complex unit structures, which are no longer applicable in the millimeter wave and terahertz bands. Due to limited processing accuracy, many fine structures are difficult to ensure that they are consistent with the design. Processing errors will cause the modulation phase to deviate far from the preset value, thereby causing the radiation performance of the antenna to deteriorate, and problems such as reduced gain, increased side lobes, and increased cross-polarization levels will occur. For planar reflector array antennas in the millimeter wave and terahertz frequency bands, the design of the reflector array unit should fully consider the impact of processing accuracy, adopt a unit structure that is as simple as possible, and avoid the dependence of phase modulation on fine structures.

[0004] The unit structure used in existing planar reflectarray designs makes it difficult to take into account both a wide phase modulation range and arbitrary incident wave polarization. When the incident wave polarization is fixed, the unit design has good freedom, and the unit structure only needs to change in one dimension, so it is relatively easy to design the structure to meet the requirements of full phase coverage. When the incident wave polarization is in any direction, the unit needs to adopt a 90-degree rotationally symmetrical structure, which reduces the freedom of unit structure design and often results in insufficient modulation phase range. Therefore, a wide phase modulation range needs to rely on subtle structural changes. In the design of reflectarray antennas, the position and angle of the feed source irradiating each unit are different. Therefore, in order to improve antenna performance, the reflectarray unit needs to have polarization-insensitive characteristics and should also meet full phase coverage, thereby reducing the deterioration of the overall performance of the array due to modulation phase errors.

[0005] Due to limited process capabilities, many antenna forms are difficult to process in the millimeter wave and terahertz frequency bands. The development of millimeter wave and terahertz technology has higher and higher requirements for beam modulation, such as highly directional beams, multi-beams, interference suppression at specific angles, etc., which pose great challenges to antenna design. Planar reflectarray antennas have the characteristics of flexible beam modulation, simple structure, easy processing, small size, and low cost. They have replaced many traditional antenna forms in the microwave frequency band. However, for the millimeter wave and terahertz frequency bands, the reflectarray unit structure is used to compensate for the spatial phase to achieve beam modulation, which requires high-precision micro-surface processing technology. For many design schemes, the processing error causes the antenna performance to deteriorate seriously, and it is impossible to directly introduce the millimeter wave and terahertz frequency bands from the microwave band. Therefore, although the design principle of millimeter wave and terahertz planar reflectarray antennas is similar to that of the microwave band, the practical design schemes are still very limited, and the antenna performance is difficult to improve.

[0006] Figure 1 This is a basic planar reflector array design. The reflector array unit adopts a basic square patch periodic structure. The lower surface of the dielectric substrate is a full metal ground, and the upper surface of the dielectric substrate is etched with a designed metal pattern. When the electromagnetic wave irradiates the reflector array unit, the electromagnetic wave cannot be transmitted due to the existence of the full metal ground. A small part of the energy is absorbed by the metal and the dielectric substrate, and most of the energy is reflected. By adjusting the size of the periodic surface unit, that is, changing the side length of the square periodic surface, the reflection phase can be regulated. Furthermore, the designed reflector array units are arranged periodically to form a reflection surface. When the feed source irradiates the reflection surface, the phase difference between the received incident wave and the predetermined reflected wave at each unit position is calculated. The size of the metal pattern of each array element is adjusted by modulating the relationship between the phase and the size of the periodic structure, thereby realizing the control of the spatial phase on the entire reflection surface. The feed source adopts an offset feed method to effectively avoid the influence of the feed source shielding on the antenna aperture efficiency. The metal pattern form of the design periodic unit can obtain better antenna radiation performance.

[0007] In the actual design of planar reflectarray antennas, in order to meet the requirements of broadband, low sidelobe, high gain, low cross-polarization, etc., different periodic surface unit forms need to be adopted. Figure 2 This is a terahertz reflector array design similar to this scheme. It is based on a double open square ring reflector unit and the antenna operates at 220GHz. The substrate is made of foam, and gold patches are used on the upper and lower surfaces of the substrate to design a double open square ring structure and a floor. Changing the size of the open ring can achieve full phase range modulation. When the electromagnetic wave irradiates the metasurface vertically, if the electric field polarization direction is in the x direction, a resonance effect will occur on the open double ring. The reflection phase at the resonant frequency is zero, and the reflection phase at the offset resonant frequency is between 0° and 180°. When the frequency of the incident wave is fixed, the inherent resonant frequency can be changed by changing the size of the annular gap, thereby realizing the regulation of the reflection phase. According to the design structure characteristics, the reflector array is insensitive to the deflection angle at oblique incidence. Due to the lack of rotational symmetry, it is more sensitive to the electric field polarization direction of the incident wave. In addition, the modulation phase is more sensitive to the change in the gap width, and the processing accuracy is required to be high. The reflector array antenna uses normal direction vertical irradiation feeding, and each array element structure selects the corresponding size according to the reflection phase compensation error.

[0008] By analyzing domestic and foreign published literature, patents and products, most of the existing planar reflector array design solutions are aimed at the microwave frequency band. Although relevant scholars have proposed a variety of complex reflector array unit structures, it is unrealistic to use various fine structures to achieve phase control in the millimeter wave and terahertz frequency bands due to the limitation of processing accuracy. Many structures cannot be directly moved to the high frequency band. The existing feasible design solutions for millimeter wave and terahertz reflector arrays are relatively limited. The selection of reflector array unit structures is mostly based on traditional ring or patch forms. Improved design solutions are difficult to take into account multiple characteristics such as bandwidth, polarization sensitivity, processing accuracy sensitivity, and wide phase modulation range. Related research needs to be deepened.

[0009] The use of traditional patches or ring structures to achieve phase control has a good effect only in narrow frequency bands. Since such structures have strong resonance, they only have obvious phase modulation capabilities at the resonant frequency point. The phase modulation function quickly fails after the operating frequency shifts from the resonant frequency. The terahertz reflectarray antenna designed based on traditional patch or ring structure reflectarray units has a simple structure, low requirements for processing accuracy, and is relatively easy to design. It is more suitable for narrow-band millimeter wave or terahertz antenna design, but cannot meet the requirements for antenna working performance in a wide frequency band.

[0010] The improved multiple reflector array unit structure can utilize the multi-resonance characteristics to meet the phase modulation requirements of different operating frequencies and achieve broadband coverage based on multi-resonance frequencies. However, the design freedom of the multi-resonance unit is low in a limited space. For example, the typical value of the period is λ / 2 (λ is the free space wavelength). At this time, the length of the resonant unit is at the same order of magnitude as the period length, and the design of the multi-resonance structure is relatively complex. The design scheme that can be checked generally adopts two design ideas. The first is to use a slender multi-branch structure as the phase delay line of the resonant unit, such as a tree branch type or a logarithmic periodic type structure. At this time, the metal wire is generally very thin and the resonant frequency is very sensitive to the change of the branch size, which puts forward high requirements on the processing accuracy. In order to meet the polarization insensitive characteristics, a 90-degree rotational symmetric pattern needs to be adopted, which further increases the complexity of the structure. Another idea is to use multiple arrays as the resonant unit itself. At this time, most of the arrays can only be arranged in one dimension, and can only have effective phase modulation capabilities for incident waves polarized in a single direction, but fail to work in the other polarization direction. The polarization-sensitive characteristics add difficulties to the design of planar reflector array antennas and have a great impact on the radiation performance of the antenna. Summary of the invention

[0011] In view of the above technical problems existing in the prior art, the present invention proposes a terahertz planar reflective array antenna based on a square ring nested structure, which has a reasonable design, overcomes the shortcomings of the prior art, and has good effects.

[0012] In order to achieve the above object, the present invention adopts the following technical solution:

[0013] A terahertz planar reflector array antenna based on a square ring nested structure comprises a waveguide feed and a square ring nested reflector array unit. The waveguide feed deviates from the normal line by a certain angle to illuminate the reflective surface, and the antenna radiation direction is mirror-symmetrical to the feed incident direction.

[0014] Preferably, the square ring nested reflective array unit adopts a three-layer structure, including a square ring nested metal surface, a dielectric substrate and a metal floor; the square ring nested metal surface is located in the upper layer, the dielectric substrate is located in the middle layer, and the metal floor is located in the lower layer.

[0015] Preferably, the square ring nested reflective array unit has 90° rotational symmetry and non-polarization sensitive characteristics, and can achieve effective phase modulation for incident waves with different polarizations.

[0016] Preferably, the square ring nested metal surface and the metal floor are made of low-loss metal materials including gold plating and silver plating, and the dielectric substrate is made of low-loss dielectric materials including quartz and high molecular polymer.

[0017] Preferably, the square ring nested reflective array unit is a cube, and the thickness of the square ring nested metal surface is much smaller than the thickness of the dielectric substrate.

[0018] Preferably, the square ring nested metal surface includes six square rings to form a nested ring structure, which includes five small metal rings inside. The central ring of the five small metal rings overlaps with the other four rings, and the line width of all the ring structures is consistent.

[0019] Preferably, the square ring nested reflective array unit is formed by combining six square rings to form a broadband resonance unit, using the outer ring to generate low-frequency narrowband resonance and the inner combined ring to form broadband resonance to meet broadband coverage requirements.

[0020] Beneficial technical effects brought by the present invention:

[0021] The novel reflective array unit structure proposed in the present invention takes into account the design requirements of full phase modulation, wide bandwidth, anti-polarization sensitivity and other characteristics, breaking through the difficult problem that traditional solutions cannot take into account phase, frequency band and polarization. Compared with other structures with wide bandwidth and wide phase modulation range, this solution adopts a rotationally symmetric structure and has no polarization sensitivity. Compared with other design solutions based on rotationally symmetric structures, the present invention has a wider effective bandwidth.

[0022] The novel reflective array unit structure proposed in the present invention avoids the dependence of phase modulation capability on fine structure, introduces a broadband array to achieve broadband phase modulation, and reduces the requirements for processing accuracy. Therefore, it is suitable for applications in millimeter wave and terahertz frequency bands. Compared with other broadband reflective array units, it has a simple structure, is easy to process, has stable performance, and has a high yield rate.

[0023] The terahertz reflectarray antenna based on the novel reflectarray unit proposed in the present invention is easy to process, low in cost, small in size, and has excellent radiation performance, and can make up for the shortcomings of existing terahertz antennas, such as limited gain, great processing difficulty, high side lobes and cross-polarization levels, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The basic design scheme of the planar reflector array antenna is shown in FIG. 1 ; wherein (a) is a schematic diagram of the structure of the reflector array unit; (b) is a schematic diagram of the structure of the reflector array antenna;

[0025] Figure 2 The following is a design diagram of a terahertz planar reflective array; (a) is a schematic diagram of the reflective array unit structure; (b) is a schematic diagram of the reflective array surface structure;

[0026] Figure 3 The square ring nested reflective array unit structure diagram; (a) is a three-dimensional diagram; (b) is a top view;

[0027] Among them, 1-square ring nested metal surface; 2-dielectric substrate; 3-metal floor;

[0028] Figure 4 This is a graph showing the relationship between the reflection phase of a square ring nested reflectarray unit and the size of the unit structure;

[0029] Figure 5 The induced current distribution diagrams on the nested square ring metal pattern when the operating frequencies are 200 GHz, 300 GHz, and 400 GHz respectively; (a) is the induced current distribution diagram when the operating frequency is 200 GHz; (b) is the induced current distribution diagram when the operating frequency is 300 GHz; (c) is the induced current distribution diagram when the operating frequency is 400 GHz;

[0030] Figure 6 The terahertz reflector array antenna diagram based on the square ring nested structure; (a) is the overall structure diagram; (b) is a partial schematic diagram of the reflector surface;

[0031] Figure 7 is the radiation pattern of the proposed terahertz reflectarray antenna at different frequencies;

[0032] Figure 8 Comparison diagram of the main polarization and cross-polarization levels of the proposed reflectarray antenna; DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0034] The square ring nested reflective array unit proposed in the present invention has a structure as follows: Figure 3 As shown, it includes a square ring nested metal surface 1, a dielectric substrate 2 and a metal floor 3. Among them, the square ring nested metal surface 1 and the metal floor 3 are made of low-loss metal materials such as gold plating and silver plating, and the dielectric substrate 2 is made of low-loss dielectric materials such as quartz and high polymer. The reflective array unit is a cube with a side length of p and a thickness of t. The thickness of the metal surface is much smaller than the thickness of the dielectric substrate. The square ring nested metal surface 1 contains six square rings, forming a nested ring structure. The outermost large metal square ring has a side length of a, and contains five small metal rings. The center ring overlaps with the other four rings, and the line width of all ring structures is consistent.

[0035] By changing the size of a, the size of the square ring nested metal surface 1 is adjusted to form a series of reflective array units with metal patterns of different sizes. All units are closely arranged according to the period p to form a periodic structure, forming a reflective array. When a is changed, the line width of the metal pattern remains unchanged, and the pattern is enlarged or reduced in proportion. Controlling the size of a can change the size of the reflection phase. The simulation results of the relationship between the reflection phase and the side length a of the proposed reflective array unit are shown in Figure 4As shown. When the center frequency is set to 300GHz, a varies between 50μm and 300μm at the center frequency, and the reflection phase control range exceeds 500°, which can meet the needs of 360° full phase coverage. When the operating frequency is changed, the phase change curve remains basically consistent, and the phase curves of different frequencies are relatively parallel. Selecting the middle segment with better linearity can meet the needs of wide bandwidth and wide phase modulation range. In addition, since the reflection phase depends on structural changes, the line width selection has little effect on the reflection phase curve, thus reducing the strict requirements for processing accuracy.

[0036] In order to illustrate the design idea of ​​this scheme, the working mechanism of the proposed new structure is elaborated in depth, and the induced current at different working frequencies is analyzed. The incident wave is irradiated vertically along the normal direction of the reflective array unit, and the polarization mode is horizontal line polarization. From the symmetry of the structure, it can be seen that no matter whether the incident field polarization mode is vertical polarization or horizontal polarization, there is the same current distribution, so only one of them needs to be analyzed. Figure 5 The induced current distribution diagram on the nested square ring metal pattern when the operating frequencies are 200 GHz, 300 GHz, and 400 GHz respectively.

[0037] It can be seen that when the operating frequency is at the low end of 200GHz, the induced current is mainly distributed in the outermost large metal ring, and the five small metal rings inside are almost not involved in the work. The current presents a 1-λ resonance mode on the outer ring, which is the same as the working principle of the traditional single ring structure. When the operating frequency increases to 300GHz or even 400GHz, the induced current is mainly distributed in the five inner square rings, while the current on the outermost large ring is relatively weak. At this time, the five inner small square rings are nested to form a petal-like structure, which actually constitutes a broadband resonant unit with no polarization selection characteristics, which is similar to the working principle of a broadband antenna. The upper and lower arms of the central small square ring form two parallel resonant arrays, and a metal ring structure is connected to each of the four ends of the array for extension, which greatly expands the bandwidth of the original array. Therefore, when the frequency increases, the five inner small rings participate in the work, the working mode does not change, and there is a similar mode current distribution. The combined structure of multiple metal rings can resonate in a broadband, thereby realizing broadband phase modulation. It is worth mentioning that when the inner and outer metal rings are combined, an equivalent parasitic capacitance can be formed between the inner and outer rings, which helps to expand the coverage of the modulation phase to more than 360°.

[0038] Based on the new reflector array unit, a terahertz reflector array antenna with a center frequency of 300GHz is designed to illustrate the application value of the proposed reflector array in antenna design, and provide a terahertz reflector array antenna design scheme with excellent performance. Figure 6As shown, it is mainly composed of two parts: waveguide feed and reflector. The waveguide feed deviates from the normal line by a certain angle to illuminate the reflector, and the reflector units at different positions select the appropriate structure size according to the phase compensation condition. Here, the feed is designed to deviate from the normal line by 20°, and the antenna radiation direction is mirror-symmetrical with the feed incident direction.

[0039] Figure 7 and Figure 8 The two-dimensional radiation patterns at different simulated frequencies and the comparison diagram of the main polarization and cross-polarization levels at the center frequency are shown respectively. From the simulation results, we can see that within the 250-350GHz broadband range, the antenna patterns maintain a high degree of consistency, the pattern shape remains almost unchanged, the maximum radiation direction is consistent with the designed radiation direction (θ=-20°), and the antenna performance remains stable within the broadband. At the same time, the antenna has a cross-polarization level of less than -35dB at the center frequency, with high polarization purity, which can meet the needs of high-performance terahertz antennas.

[0040] The key points of the present invention are as follows:

[0041] The present invention proposes a square ring nested reflective array unit structure, which generates multi-resonance characteristics based on a broadband resonant unit to achieve broadband coverage, and introduces effective parasitic capacitance to achieve 360° full-phase modulation.

[0042] The novel reflective array unit structure proposed in the present invention has 90° rotational symmetry and thus has no polarization-sensitive characteristics, and can achieve effective phase modulation for incident waves with different polarizations.

[0043] Based on a novel reflective array structure, the present invention proposes a terahertz planar reflective array antenna, which has the characteristics of wide bandwidth, low side lobe and low cross-polarization.

[0044] The protection points are as follows:

[0045] A square ring nested reflectarray unit structure model is proposed. The model has 90° rotational symmetry and is resistant to polarization sensitivity.

[0046] A square ring nested reflector array unit structure model is proposed. The model uses six square rings to form a broadband resonance unit. The outer ring generates low-frequency narrowband resonance, and the internal combined ring forms broadband resonance to meet the broadband coverage requirements.

[0047] A square ring nested reflectarray unit structure model is proposed. The structural feature is that the modulation reflection phase depends on the overall size of the structure rather than the local subtle structure changes, and is insensitive to the changes in metal line width, thus reducing the strict requirements on processing accuracy.

[0048] A terahertz planar reflectarray antenna design based on square ring nested reflectarray units is proposed. The anti-polarization sensitivity, broadband stability, and wide phase modulation of the reflectarray units are combined to realize a high-performance terahertz antenna that meets the needs of wide bandwidth, low sidelobe, and low cross-polarization level.

[0049] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A terahertz planar reflectarray antenna based on a square ring nested structure, characterized in that: It includes two parts: a waveguide feed source and a square ring nested reflective array unit; the waveguide feed source deviates from the normal line by a certain angle to illuminate the reflective surface, and the antenna radiation direction is mirror-symmetrical with the feed source incident direction; The square ring nested reflective array unit adopts a three-layer structure, including a square ring nested metal surface, a dielectric substrate and a metal floor; the square ring nested metal surface is located in the upper layer, the dielectric substrate is located in the middle layer, and the metal floor is located in the lower layer; The square ring nested reflective array unit has 90° rotational symmetry and is non-polarization sensitive, and can achieve effective phase modulation for incident waves with different polarizations. The square ring nested reflective array unit is a cube, and the thickness of the square ring nested metal surface is much smaller than the thickness of the dielectric substrate; The square ring nested metal surface includes six square rings, forming a nested ring structure, which includes five small metal rings inside. The central ring of the five small metal rings overlaps with the other four rings, and the line width of all ring structures is consistent.

2. The terahertz planar reflectarray antenna based on a square ring nested structure according to claim 1, characterized in that: The square ring nesting metal surface and the metal floor adopt low-loss metal materials including gold plating and silver plating, and the dielectric substrate adopts low-loss dielectric materials including quartz and high molecular polymer.

3. The terahertz planar reflectarray antenna based on a square ring nested structure according to claim 1, characterized in that: The square ring nested reflective array unit uses six square rings to form a broadband resonance unit, uses the outer ring to generate low-frequency narrowband resonance, and uses the internal combination ring to form broadband resonance to meet broadband coverage requirements.

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