HK1140265B - Apparatus for depicting test objects using electromagnetic waves - Google Patents

Description

Apparatus for imaging detection object using electromagnetic wave

Technical Field

The invention relates to a device for imaging a test object by means of electromagnetic waves, having the following features:

-an antenna (1) emitting electromagnetic waves, in particular millimeter waves,

-means for three-dimensional focusing of the transmitted waves, and

-means for suitable manipulation of the wave at the high focal point (5) so that this point (5) can act as a virtual moving antenna for SAR analysis,

the means for three-dimensional focusing comprise a rotationally mounted, focusing or defocusing quasi-optical element, and

-the means for steering the wave at the high focal point (5) comprise a reflector (4).

Background

German patent application 102005042463 describes such a device for checking whether a person or a piece of luggage (hereinafter referred to as an inspection object) is concealed with dangerous objects (weapons, explosives), which inspection object is scanned with millimeter waves in order to detect suspicious objects. The detection object is irradiated with millimeter waves continuously along its circumference, scattered waves are received and analyzed to image the detection object according to the SAR principle.

The device described in DE 102005042463 can be used with a two-dimensional SAR method, which allows a very high resolution both in the X direction and in the Y direction. The SAR method can be realized by adopting a movable virtual antenna without complex antenna control.

Disclosure of Invention

The object of the invention is to improve a device of this type in such a way that its resolution is increased with less expenditure on equipment, while distortion is reduced.

This task is solved by using quasi-optical focusing or defocusing elements and reflectors that can be rotated at the same angular speed around a common axis of rotation. This configuration makes it possible to enlarge the field angle of the electromagnetic radiation. This not only increases the scanning range of the detection object, but also makes the virtual antenna aperture for SAR analysis large. The distance between the axis of rotation of the focusing or defocusing element and the virtual antenna can be designed to be as large as possible in order to obtain a large scanning range on the examination object.

The way in which the quasi-optical focusing or defocusing element and the reflector are arranged in a common rotatable component has structural advantages.

By designing the reflector in a form that focuses or defocuses the electromagnetic wave, two focusing or defocusing elements like a telescope are obtained. This allows a virtual source of motion to be formed in a distortion-free manner.

Both as quasi-optical elements and as focusing reflectors, resulting in a compact construction of the telescope type.

The quasi-optical element and the reflector are preferably designed as mirrors. If the quasi-optical element and the reflector are designed and arranged such that the central ray incident on the quasi-optical element is parallel to the central ray leaving the reflector, the movement of the virtual antenna can be controlled and analyzed in as simple a manner as possible.

Drawings

The invention will be explained in detail below on the basis of two examples.

Figure 1 functional schematic diagram of the device according to the invention,

FIG. 2 is a rear view of

Figure 3 is a front view of the device with a Z-shaped ray path,

figure 4 is a cross-sectional view of a ray path,

figure 5 shows another arrangement with a U-shaped ray path,

fig. 6 is a cross-sectional view of the ray path of such a device.

Detailed Description

The devices shown in the figures are each part of a detection device for inspecting aircraft passengers at an airport. When checking in at an airport, a check-in device is used to check whether the aircraft passenger carries a suspicious item, such as a weapon or an explosive. The electromagnetic wave used to irradiate the detection object has a frequency between 1GHz and 10 THz. It is preferable to use millimeter waves having a frequency of 30GHz to 300 GHz. The reflected wave is received using the transmitting antenna itself or using a separate receiving antenna.

The inspection apparatus preferably includes a platform upon which the inspection object (e.g., an aircraft passenger) is positioned during the inspection process. According to one embodiment, the transmitting and receiving system rotates around a stationary test object, which is illuminated with millimeter waves along its periphery. Alternatively, the test object itself can be rotated on a platform in front of a fixedly mounted transmitting and receiving system.

The detection device also comprises an analysis system with corresponding operational capability, and the analysis system analyzes the waves scattered by the detection object according to the SAR principle so as to obtain an image display of the detection object. The formed image is displayed to the operator on the corresponding display device.

The embodiment shown in fig. 1 and 2 comprises an antenna 1, in particular a horn antenna, which emits millimeter waves 2. The millimeter waves 2 are directed to a rotationally mounted focusing or defocusing quasi-optical element 3, which reflects it and focuses it simultaneously. The element 3 is preferably a rotating focusing mirror which deflects the radiation 2 towards the reflector 4 and focuses it on the reflector such that the highest focus point 5 is on the reflector 4 and moves along a circle therewith. The reflector 4 is suitably shaped to interact with the rotating element 3 to scan the imaging surface 6 circularly, as shown in figure 1.

The highest focal point 5, i.e. the reflection point on the reflector 4, has a small extent so that it can be seen as a virtual antenna, forming a beam 7 with a large opening angle in the far field. Such a large field angle is required for good resolution when the analysis is performed by means of the SAR algorithm. The generated radiation beam 7 scans the object to be examined circularly.

The transmitting and receiving system is also caused to move horizontally (out of the plane of the drawing in fig. 1) or vertically (up and down in fig. 1) to scan the test object in two dimensions. Scanning from different viewing angles is also possible if the entire transmitting and receiving device is moved back and forth around the test object.

The key points of the invention are as follows: the quasi-optical element 3, which focuses or defocuses the waves from the antenna 1, and the reflector 4 can be rotated around a common axis of rotation at the same angular speed. These embodiments are preferred embodiments, and the quasi-optical element 3 and the reflector 4 are mirrors with focusing action. In order to achieve a construction which is as compact as possible and a simplified analysis, both the quasi-optical element 3 and the reflector 4 are designed and arranged such that the central ray which is directed from the antenna 1 to the quasi-optical element 3 is parallel to the central ray of the divergent ray bundle which leaves the reflector 4.

The quasi-optical element 3 and the reflector 4 of the two embodiments shown in the figures are arranged in a common part which can be rotated about an axis of rotation 8. The component is preferably connected to a rotary drive so that its axis of rotation 8 coincides approximately with the central ray of the radiation beam emerging from the antenna 1. The axis of rotation 8 passes through the element 3 approximately centrally and is oblique to its reflecting surface 9, as shown in figure 1. The components comprising the element 3 and the reflector 4 are made of a low inertia, light weight material. It comprises a reflection surface 9 of the quasi-optical element 3, by which the radiation incident from the antenna 1 is focused onto a reflection surface 10 of the reflector 4. The reflecting surface 10 of the reflector 4, which rotates about the axis of rotation, can thus serve as a virtual antenna required for the SAR analysis. The reflective surfaces 9, 10 of the quasi-optical element 3 and the reflector 4 in both embodiments are suitably designed and arranged such that the central ray incident on the quasi-optical element is parallel to the central ray leaving the reflector 4.

The components shown in figures 2 and 3 comprise quasi-optical elements 3 and reflectors 4 arranged in a Z-shape. The reflecting surfaces 9 of the elements 3 and the reflecting surfaces 10 of the reflector are arranged such that radiation incident from behind (arrow 11) is directed towards the reflecting surfaces 9, focused by them and directed towards the reflecting surfaces 10 of the reflector 4, then emitted in a radiation-emitting manner parallel to the incident radiation (arrow 11) and directed forwards from the component in the direction of the incident radiation (arrow 12).

Fig. 5 shows an alternative U-shaped arrangement, from which incident radiation 11 is directed towards the reflective surface 9 of the quasi-optical element 3 and then (as in the embodiment shown in fig. 2) is directed upwards towards the reflective surface 10 of the reflector 4. The reflecting surface 10 is suitably arranged such that the scattered ray bundle (arrow 12) reflected by it re-emerges from the component in a direction opposite to the direction of incidence (arrow 11) of the rays incident from the antenna 1. The central ray of the outgoing scattered ray beam (arrow 12) is also parallel to the central ray of the incoming ray beam (arrow 11) in this embodiment.

The above is the transmit case. Since the ray paths are reciprocal, the system can operate in a receive condition. The transmit and receive signals may be separated by suitable means, for example by means of a coupler, a circulator and/or by means of a polarization grating connecting the antenna 1 to a transmitting or receiving device.

It is likewise possible to use two antennas or antenna systems which are positioned in close spatial proximity instead of a single antenna 1 with a transmitting or receiving function. The antenna 1 will thus consist of at least one transmitting antenna and at least one spatially separated receiving antenna.

Claims (8)

1. An apparatus for imaging a test object using electromagnetic waves, having the following features:

-an antenna (1) emitting electromagnetic waves,

-means for three-dimensional focusing of the transmitted waves, and

-means for steering the wave at a high focal point (5) such that the high focal point (5) acts as a virtual moving antenna for SAR analysis, wherein

The means for three-dimensionally focusing the emitted wave comprise a rotatably mounted, focusing or defocusing quasi-optical element, and

-the means for steering the wave at the high focal point (5) such that the high focal point (5) acts as a virtual moving antenna for SAR analysis comprise a reflector (4),

characterized in that the quasi-optical element (3) and the reflector are rotatable around a common axis of rotation (8) at the same angular speed.

2. Device according to claim 1, characterized in that the quasi-optical element (3) and the reflector (4) are both arranged in one common part that can be rotated.

3. A device according to claim 1 or 2, characterized in that the reflector (4) is also designed to focus or defocus the electromagnetic waves.

4. A device according to claim 3, characterized in that not only the quasi-optical element (3) but also the reflector (4) are designed to be focused.

5. A device as claimed in claim 4, characterized in that the quasi-optical element (3) and the reflector (4) are designed as mirrors.

6. A device according to claim 1 or 2, characterized in that the quasi-optical element (3) and the reflector (4) are designed and arranged such that the central ray incident on the quasi-optical element (3) is parallel to the central ray leaving the reflector (4).

7. The device of claim 1, wherein the device is used to check whether a person carries a suspicious item.

8. The apparatus of claim 1, wherein the electromagnetic waves are millimeter waves.