阅读说明：本技术 一种设计遥感扫描天线的新方法 (New method for designing remote sensing scanning antenna ) 是由 刘小明 俞硕 甘露 于 2019-09-09 设计创作，主要内容包括：本发明公布了一种基于准光技术的用于设计遥感扫描天线的新方法。扫描天线是毫米波及太赫兹波段遥感系统中的重要探测器件。扫描天线主要由一个改进的主反射面以及馈源阵列组成。目前,反射式扫描天线的设计方法主要有物理光学法、几何光学法。物理光学法的缺点在于计算效率太低；而几何光学法的缺点在于计算精度不高。本发明提出的基于准光技术的设计方法可以兼顾效率和精度的要求,大大提高系统的设计效率。该方法要求反射面为二次曲面,馈源为高斯馈源,主要针对但不限于毫米波与太赫兹频段辐射计系统应用。(The invention discloses a novel method for designing a remote sensing scanning antenna based on a quasi-optical technology. The scanning antenna is an important detecting device in millimeter wave and terahertz wave band remote sensing systems. The scanning antenna mainly comprises an improved main reflecting surface and a feed source array. At present, the design methods of the reflective scanning antenna mainly include a physical optical method and a geometric optical method. The disadvantage of physical optics is that the computational efficiency is too low; the geometrical optics method has the disadvantage of low calculation accuracy. The design method based on the quasi-optical technology can meet the requirements of efficiency and precision, and greatly improves the design efficiency of the system. The method requires that the reflecting surface is a quadric surface and the feed source is a Gaussian feed source, and is mainly applied to but not limited to millimeter wave and terahertz frequency band radiometer systems.)

1. A new design method for a scanning antenna mainly comprises the following steps: determining the working frequency, the imaging resolution and the imaging distance (the distance between the satellite and the ground) according to the system requirements; calculating the width of an emergent beam according to the imaging resolution and the imaging distance; according to system requirements, determining the approximate focal length of the reflector antenna and the offset angle of the system; calculating the width of an incident beam according to the width of an emergent beam; designing a feed source based on the Gaussian beam theory according to the width of an incident beam; determining the size of a reflecting surface according to the number of feed sources, and verifying the effectiveness (physical dimension effectiveness and electromagnetic performance effectiveness) of the design by using a quasi-optical formula (Gaussian beam transformation formula); if the precision needs to be further improved, the third step can be returned to carry out iterative processing; and solving the shape surface of the reflecting surface according to the final parameters.

2. A scanning antenna system as claimed in claim 1, characterized in that the system has two key components, a main reflector and an array of feeds.

3. The method of claim 2, wherein the conventional design of the main reflecting surface is based on physical optics or geometric optics, and the design of the present invention is based on quasi-optics theory of gaussian beam.

4. The feed antenna of claim 2, wherein the design of the feed antenna is strictly related to the design of the main reflector and requires the horn to produce a gaussian beam.

5. The apparatus of claim 2, wherein the primary reflector is not a standard paraboloid, nor a standard ellipsoid or sphere, but rather a special quadric surface obtained by one revolution of a conic about the axis of rotation.

6. As stated in claim 5, the quadratic curve can be a part of a parabola, ellipse, circle or hyperbola, or other curve with a focus.

7. As described in claim 6, the reflecting surface is formed by rotating a part of a quadratic curve, the length of which is required to satisfy the size requirement in the quasi-optical theory.

8. As described in claim 3, the gaussian beam collimation method can predict the beam width of the emergent beam, which is advantageous in that accuracy and efficiency are well balanced.

Technical Field

The invention relates to an antenna system design technology for the fields of remote sensing and detection imaging by using millimeter wave and terahertz wave bands, in particular to a novel method for designing a remote sensing scanning antenna based on a quasi-optical technology.

Background

At present, millimeter wave and terahertz systems are widely applied to the fields of atmospheric remote sensing, imaging detection, maritime satellites and radio astronomy. In various fields, a detection scanning system of millimeter waves and terahertz is required to scan and image a target region in a short time to obtain electromagnetic characteristics and other target characteristics of the target region. The speed of the scanning speed and the imaging quality are mainly determined by the scanning antenna system. The design of the scanning antenna is therefore critical.

In millimeter wave and terahertz wave bands, common scanning mechanisms include cone scanning, left-right pendulum scanning, synthetic aperture radar and broom scanning. The conical scanning and the left-right pendulum scanning both need the integral rotation of the antenna system, and the rotational inertia can be increased, so that the mechanical difficulty is increased; the synthetic aperture radar has complex algorithm and is easy to form a virtual image; broom scanning is imaging through a one-dimensional array, forming a two-dimensional image while the satellite is moving.

However, the one-dimensional array of the broom antenna has a plurality of feed sources, and the feed sources are difficult to be placed at the focus, so that the reflecting surface is required to form a local focus for each feed source, and the far field error of a beam formed by each feed source is ensured to be within an index range. In addition, too many feed source arrays easily cause too long design process and calculation time.

Disclosure of Invention

In view of the above, the main object of the present invention is to provide a new method for designing a scanning antenna, which reduces the design difficulty and the computation time. The method has the advantages that the design result can be directly calculated through a formula, the design flow and the calculation process are greatly simplified, and the design and calculation method is greatly different from the traditional physical optics and geometric optics method.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

the invention discloses a novel method for designing a scanning antenna based on quasi-optical technology, which is characterized in that a scanning antenna system consists of two devices, one is a main reflecting surface and one is a feed source array system. The algorithm mainly comprises the following steps.

A. According to the system requirements, the working frequency, the imaging resolution and the imaging distance (the distance between the satellite and the ground) are determined.

B. And calculating the width of the emergent beam according to the imaging resolution and the imaging distance.

C. According to system requirements, the size of the approximate focal length of the reflector antenna and the offset angle of the system are determined. And calculating the equivalent focal length of the reflecting surface according to the quasi-optical theory.

D. And calculating the width of the incident beam according to the width of the emergent beam.

E. And designing a feed source based on the Gaussian beam theory according to the incident beam width.

F. The size of the reflecting surface is determined according to the number of the feed sources, and the effectiveness (physical size and electromagnetic performance effectiveness) of the design is verified by using a quasi-optical formula (Gaussian beam transformation formula).

G. If the precision needs to be further improved, the iterative processing can be carried out by returning to the step C.

H. And determining the shape surface of the reflecting surface according to the final result.

The reflecting surface is a special quadric surface obtained by rotating a part of a parabola, an ellipse, a circle or a hyperbola around a rotating shaft for one circle.

The horn antenna can be a corrugated horn antenna, can also be a smooth inner wall circular caliber antenna, can also be in other horn feed source forms, but needs to be in a feed source form capable of generating Gaussian beams.

The iterative method may be any custom error function.

It can be seen from the above technical solutions that the main technical means of the present invention is to design a scanning antenna by using a quasi-optical method (especially based on a gaussian beam method). The traditional scanning antenna is designed by adopting a physical optics method or a geometric optics method, and the main defects are that the physical optics method is low in calculation efficiency and the geometric optics method is low in calculation accuracy. In the invention, the quasi-optical design technology is introduced into the scanning antenna measurement, and the incident and emergent and input-output conversion of the scanning antenna are described by using the Gaussian beams, so that the effect of directly obtaining system parameters from index parameters is achieved, and the design efficiency is greatly improved.

Drawings

Fig. 1 is a flow chart for designing a scanning antenna using gaussian beams.

Fig. 2 shows a scanning antenna using gaussian beam design.

Fig. 3 is a relationship diagram of outgoing beam parameters of a scanning antenna.

Fig. 4 a schematic view of a scanning antenna.

Figure 5 is a graph of the results of scanning the antenna exit beam.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples, wherein a specific flow chart is shown in fig. 1.

The system consists of two parts, as shown in fig. 2, a feed array antenna and a main reflecting surface. Wherein, each unit of the feed source array antenna should adopt the same horn antenna in the best scheme; the main reflecting surface should be a curved surface (in this example, a parabola is taken as an example) that conforms to a quadratic equation. The purpose of this design is to achieve symmetry in performance while reducing the complexity of the tooling.

The method comprises the following steps: determining operating frequencyfResolution of imagingd _gDistance of imagingh. In addition, the angle between the outgoing beam of the antenna system and the plumb line needs to be determinedα. The specific parameter diagram is shown in fig. 3. Taking meteorological satellite as an example, the height of polar orbith836km, the angle between the outgoing beam of the antenna system and the plumb lineαIs 43 degrees. One of the operating frequencies is 150 GHz. The imaging resolution is required to be 15km-50 km.

Step two: calculating the outgoing beam width according toβ

(1)

Wherein the content of the first and second substances,d _gin order to achieve the resolution of the image,his the imaging distance.

Step three: determining approximate focal length of reflector antenna based on system requirementsFSize of (2), offset angle of the systemθ _fAnd is combined withBy usingCalculating the equivalent focal length of the reflecting surfaceρ. The specific parameter diagram is shown in fig. 4.

Step four: and calculating the width of the incident beam according to the width of the emergent beam. The width of the emergent beam isβThe beam waist radius of the input beamw _0inCan be expressed asw _0in=ρθ _0out=ρβAnd width of incident beam. Specific parameters are schematically shown in fig. 2-4.

Step five: and designing a feed source based on the Gaussian beam theory according to the incident beam width. According to the Gaussian beam theoryw ₀= ka, for a corrugated horn,k=0.644, andarepresenting the radius of the inner wall of the feed.

Step six: the size of the reflecting surface is determined according to the number of the feed sources, and the effectiveness (the effectiveness of physical dimension and the effectiveness of electromagnetic performance) of the design is verified by using a quasi-optical formula (Gaussian beam transformation formula). Assuming the number of feed sources isNThe thickness of the feed source wall istThen the diameter of the feed placement dimension D1=2 ×(s) is requiredN×a+t) And the other dimension is D2. In general, D2 is required>D1 additionally, according to the Gaussian beam propagation formula, the beam radius at the main reflecting surface is

(2)

Must satisfyD ₂>2.5w _ρThe requirement of-10 dB to-14 dB coning degree of the Gaussian beam boundary feed source can be met.

Step seven: if the design does not meet the requirement, the parameters can be adjusted in the third step until the conditions in the sixth step meet the requirement.

Step eight: and determining the shape surface of the reflecting surface according to the final result. As shown in fig. 4, in a coordinate systemExpressed in polar coordinate form, can be obtained(ii) a Is expressed in the form of rectangular coordinates and can be obtained,. Thus, the relationship of the two coordinate systems

（3）

Wherein the content of the first and second substances,θ _sis the opening angle of the reflecting surface. In thatxozCoordinate system and coordinate systemCoordinate relationship of

（4）

Thus, any point on the parabola is

（5）

Rotating the parabola about the axis has

（6）

The expression defines each point of the entire reflecting surface.

To further illustrate the effectiveness of the algorithm, we illustrate the effectiveness of the algorithm and system by an example. The parameters of this example are shown in table 1:

TABLE 1 example parameter Table

The above example design process was implemented using computer within 1 minute, much less than the time of physical optics. In addition, a three-dimensional view of the outgoing beam is shown in fig. 5. It can be seen from the results that the normalized gain at the very edge (relative to the center beam) is-0.264 dB, satisfying the requirement that the beam gain variation is typically less than 0.5 dB.

This example demonstrates the effectiveness and efficiency of the present algorithm.