JPH09197042A - Millimeter wave camera device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a compact, light, and inexpensive millimeter wave camera device by planar antenna technology using a multilayer dielectric substrate. SOLUTION: A slot antenna and a detection element provided on a mutilayer dielectric substrate 1 are formed into one piece to form an imaging element 2. The imaging element structure solves such problems as a surface wave mode and a low gain which are peculiar to a planar antenna, eliminated the need for a semispherical lens which has been considered to be indispensable for an imaging element conventionally, and thereby, making compact, light, and less expensive a system. An image array where a number of imaging elements are arranged with a specific sampling interval is placed on the image surface of an objective lens 3 and a millimeter wave signal which is discharged or reflected from a target object is detected and processed, thus obtaining a two-dimensional or three-dimensional image of the target object even under poor conditions of rain and mist or even when the device is hidden under clothes, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to detection of metal / non-metal weapons and smuggled goods at airport safety gates, detection of handguns hidden under clothes, landing support for aircraft in bad weather, and eruption during eruptions. The present invention relates to a millimeter-wave band imaging sensor used for volcanic observation or on-vehicle radar for next-generation collision prevention.

[0002]

2. Description of the Related Art Millimeter-wave electromagnetic waves are significantly less attenuated by rain and fog than visible rays and infrared rays, and have higher spatial resolution than microwaves. Is effective as.
In particular, the imaging array, which is made by arranging a large number of receiving elements that integrate an antenna and a detection element, provides high-performance real-time imaging compared to the conventional method of performing mechanical or electrical scanning using a single element. Means can be provided.

FIG. 11 shows a conventional millimeter-wave band shown on page 472 of "Optimal Design of Yagi-Uda Antenna for Millimeter-wave Band Imaging Array" (Journal of the Institute of Electronics, Information and Communication Engineers, B-II, July 1992). It is a schematic block diagram of an imaging array. In the figure, 1 is a dielectric substrate, 2 is Yagi,
Uda Antenna type imaging element, 3 is an objective lens, 3
Reference numeral 0 is a hemispherical lens made of a material having the same dielectric constant as the substrate 1. Each imaging element is composed of a half-wavelength antenna 2a, a Yagi antenna element 2b, a detection element 2c, and an output extraction line 2d.

Next, the operation will be described. The millimeter wave signal incident from the target object is imaged by using the objective lens 3, the image signal is sampled by the imaging element placed on the image plane of the lens, and the image of the target object is reproduced through the signal function. Since the one-dimensional array is shown in FIG. 11, a two-dimensional image of the object can be obtained by scanning in the other direction by using, for example, a stepping motor.

Further, in the imaging array of FIG. 11, a hemispherical lens 30 made of the same material is attached to the back side of the dielectric substrate 1 to remove the surface wave due to the substrate mode. Further, the radiation effect can be narrowed to some extent by the lens effect, the antenna gain can be improved, and the beam matching with the objective lens can be improved. Note that FIG. 12 is a diagram showing the directional characteristics of this imaging element with a hemispherical lens.

[0006]

However, in the above imaging array with a hemispherical lens, the diameter of the lens must be set to be considerably larger than the size of the antenna itself in order to reduce the influence of aberration. In particular, when the number of arrays is large, the diameter of this hemispherical lens needs to be several tens of centimeters, which not only increases the manufacturing cost but also makes the volume extremely large, which makes it difficult to put into practical use. Therefore, this type of imaging sensor device has been used only in a very limited field such as pfuzuma measurement in nuclear fusion.

Further, as can be seen from the directional characteristics of the conventional imaging device shown in FIG. 12, the symmetry of the radiation patterns on the E and H planes is not always ideal, and the resulting image is adversely affected by distortion or the like. There is a possibility that the millimeter-wave camera will not be able to fully demonstrate its inherent performance.

The present invention has been made to solve the above problems, and realizes an imaging element which can be efficiently aligned with an objective lens without using a hemispherical lens having a large volume and high cost. It is an object of the present invention to realize a compact, lightweight and inexpensive millimeter wave camera device.

[0009]

According to a first aspect of the present invention, there is provided a millimeter wave camera device having an imaging element formed by integrating a slot antenna provided on a multilayer dielectric substrate and a detection element at a predetermined sampling interval. And an imaging array formed by arranging a plurality of the elements, a millimeter wave transmitter and a transmitting antenna for irradiating a target object, and an objective lens for forming an image of a signal reflected from the target object. A two-dimensional image of the target object is obtained by placing the array on the image plane of the objective lens and amplifying and processing the intensity of the signal independently detected by each imaging element.

According to a second aspect of the present invention, in a millimeter wave camera device, a large number of imaging elements formed by integrating a slot antenna provided on a multilayer dielectric substrate and a detection element are arrayed at a predetermined sampling interval. The imaging array, the imaging array including the objective lens for imaging the millimeter wave signal radiated from the target object, and the means for providing a local signal for heterodyne detection of the millimeter wave signal. Is placed on the image plane of the objective lens, and the intensity of the intermediate frequency signal independently detected by each imaging element is amplified and processed to obtain a two-dimensional image of the target object.

Further, according to a third aspect of the present invention, in a millimeter wave camera device, a large number of imaging elements formed by integrating a slot antenna provided on a multilayer dielectric substrate and a detection element are arrayed at a predetermined sampling interval. Imaging array formed by, a transmitter and a transmitting antenna for irradiating a frequency-modulated millimeter wave signal to a target object, a branching means for branching a part of the millimeter wave signal to the receiving side,
An objective lens for forming an image of a signal reflected from a target object and a branched signal is provided, the imaging array is placed on the image plane of the objective lens, and a beat signal independently detected by each imaging element is amplified. It is characterized in that a three-dimensional image of the target object is obtained by processing.

[0012]

1 is a schematic diagram of a millimeter wave camera device according to the present invention. The millimeter wave signal radiated or reflected from the target object 5 is imaged using the objective lens 3,
Each element 2 of the imaging array placed on the image plane of the lens independently receives and amplifies and processes the signal to reproduce the image 6 of the target object. The imaging element 2 in FIG. 1 includes a slot antenna and a detection element provided on a multilayer dielectric substrate 1 made by stacking substrates having different permittivities and thicknesses corresponding to ¼ wavelength in the dielectric. It is formed integrally. This imaging element is characterized in that the size of the antenna is half the wavelength or less in free space, the generation of surface waves due to the substrate mode can be suppressed, and the radiation pattern matches the aperture angle of the objective lens.

A millimeter wave camera device according to a first aspect of the present invention is an active imaging sensor having a transmitter and a transmission antenna for irradiating a target object with a millimeter wave signal. A two-dimensional image of the target object can be obtained by intensity-detecting the millimeter wave signal reflected from the target object by each element of the imaging array and amplifying and processing the obtained video signal.

A millimeter wave camera device according to a second aspect of the present invention is a passive imaging sensor that does not require irradiation of a target object with a millimeter wave signal. A weak millimeter wave signal radiated from the target object is mixed with a local signal prepared in advance, heterodyne detection is performed by each element of the imaging array, and the obtained intermediate frequency signal is amplified and processed to obtain the target object. A three-dimensional image can be obtained.

A millimeter wave camera device according to a third aspect of the present invention is a transmitter and a transmitting antenna for irradiating a target object with a frequency-modulated millimeter wave signal, and a part of the millimeter wave signal on the receiving side. And a branching means for branching to each element, and each element of the imaging array is used as an FM-CW radar. Furthermore, a three-dimensional image of the target object can be obtained by amplifying and processing the beat signal detected by each element.

[0016]

【Example】

(First Embodiment) FIG. 2 is a diagram showing a first embodiment of the present invention. In the figure, 1 to 5 are the same as in FIG. 7 is a millimeter wave oscillator, 8 is an amplitude modulator, 9
Is a signal generator for modulation, and 10 is a transmitting antenna. 11
Is a switch circuit for selecting the video signal detected by each imaging element, 12 is an amplifier for amplifying the selected video signal, 13 is an A / D converter, and 14 is an image display device.

Next, the operation will be described. A millimeter wave whose amplitude is modulated is radiated toward the target object 5, a reflected wave is imaged using the objective lens 3, and video detection is performed by each element 2 of the imaging array placed on the image plane of the lens. Switch circuit 1 for video signal of each imaging device
The data is sequentially taken out at 1, amplified by using a lock-in amplifier, for example, and then outputted through an A / D converter 13 and finally to an image display device such as a computer.

FIG. 3 is a perspective view showing the structure of the imaging array according to the first embodiment. In the figure, 1
Reference numerals a, 1c and 1e are alumina substrates having a relative dielectric constant of 10.0, and 1b1d are quartz substrates having a relative dielectric constant of 3.8. The thickness of each substrate is determined so as to have a quarter wavelength in the substrate. On the multilayer dielectric substrate 1 formed by stacking these substrates, two slots of one wavelength 2e are arranged in parallel to form a twin slot, which is integrated with the detection element 2c to form the imaging element 2. Further, 31 is a low-pass filter, 32 is a coplanar waveguide for extracting the output, and 33 is a ground conductor.

FIG. 4 is a diagram showing the results of measuring the directional characteristics of each imaging element in FIG. 3 at 60 GHz. It can be seen that the symmetry of the radiation patterns on the E-plane and the H-plane is improved compared to the directional characteristics of the Yagi-Uda antenna-type imaging element in FIG. In addition, 3 of E side and H side
The dB beam width is about 40 degrees and 30 degrees, respectively, and the F value is 1
It is possible to efficiently match with the aperture angle of the objective lens of about 2 or less. Further, the Yagi-Uda antenna type imaging array of FIG. 12 has a thickness of about 5 cm including the hemispherical lens, while the imaging array of FIG. The thickness can be reduced to about 1/20 of the conventional structure shown in FIG.

Further, when imaging elements are arranged side by side to form an array as shown in FIG. 3, mutual coupling between adjacent elements is an important problem. If the crosstalk between the elements is large, the obtained image will be adversely affected. On the other hand, in order to satisfy the Nyquist sampling condition, it is required that the element spacing be about half the wavelength in free space. FIG. 5 is a diagram showing a result of analyzing crosstalk between elements by using a finite difference time domain (FDTD) method when the element intervals are 0.5λ0 and 0.55λ0. As can be seen from the analysis result of FIG. 5, in the imaging array shown in FIG. 4, the crosstalk level is −2 at 60 GHz even if the element spacing is about half a wavelength.
It becomes 0 dB or less, and there is no concern that the reproduction of the image is adversely affected by the coupling between the elements.

FIG. 6 is a diagram showing a diffraction image for a point source of the millimeter wave camera system according to the first embodiment. In the figure, the dotted line is the calculation result by the Gaussian beam propagation theory, the solid line is the experimental result obtained by scanning any one imaging element in FIG. 3 in the horizontal direction, and the black circles are the six imaging elements in FIG. The experimental results obtained by sampling. From the result of FIG. 6, it is understood that the millimeter-wave camera device according to the first embodiment can realize the spatial resolution of diffraction limit. Of course, the wavelength of the millimeter wave of 60 GHz is 5
Since the wavelength is about 10,000 times the wavelength of visible light in millimeters, the optical camera has a spatial resolution of about 1 micron, while the millimeter wave camera has its own limit of about 1 cm.
However, on the other hand, it is possible to detect the target object by using the millimeter wave camera even in bad weather such as rain, snow, fog where the visible light sensor / infrared sensor cannot be used or when it is hidden by clothes. Therefore, it is possible to realize a sensor device that exceeds the limits of the conventional visible light sensor and infrared sensor.

FIG. 7 is a diagram showing an imaging result of an equilateral triangular metal plate having a side length of 12 cm by using the millimeter wave camera device according to the first embodiment. FIG. 7A is a photograph of the target, and FIG. 7B is a millimeter wave image obtained in the experiment. As can be seen from the experimental result of FIG. 7, by using the millimeter-wave camera device according to the first embodiment, it is possible to image a target having a size of about several centimeters.
Moreover, if the method of irradiating the target object is improved, the quality of the obtained image can be further improved.

In the case of the experiment of the six-element imaging array shown in FIG. 3, only six pixels can be obtained without scanning. Therefore, in order to identify the target by using the scanning with the stepping motor in combination. We decided to get the required number of pixels. However, in FIG.
If the required number of imaging elements are two-dimensionally arranged on the substrate, it is not necessary to perform mechanical scanning. Also,
Using a high-speed switch circuit makes it possible to obtain a two-dimensional image of the target object in real time.

(Second Embodiment) When it is inconvenient to irradiate a target object with millimeter waves, active imaging in which a weak millimeter wave signal emitted from the target object is detected by an imaging array is effective. FIG. 8 shows the second aspect of the present invention.
It is a figure showing an example. In FIG. 8, 1 to 14 are the same as in FIG. Reference numeral 15 is a quasi-optical diplexer for mixing a millimeter wave radiated from a target object and a local signal prepared in advance, and 16 is an intermediate frequency signal amplifier.

Next, the operation will be described. Although electromagnetic waves emitted from ordinary objects are extremely weak, if a local signal is prepared in advance, heterodyne detection is performed by each imaging element, and the detected intermediate frequency signal is amplified and processed, a two-dimensional image of the target object can be obtained. Can be obtained. The millimeter wave camera device according to the second embodiment basically has a spatial resolution equivalent to that of the millimeter wave camera device according to the first embodiment. Furthermore, in the second embodiment, since it is not necessary to irradiate the target object with the coherent millimeter wave signal, it is possible to obtain a good millimeter wave image even for an object having a complicated shape. The millimeter wave camera device according to the second embodiment is effective as a short-range sensor and also as a remote sensor for volcanic observation.

(Third Embodiment) FIG. 9 is a diagram showing a third embodiment of the present invention. In FIG. 9, 1 to 14 are the same as those in FIG. Reference numeral 17 is a voltage controlled oscillator (VCO) for obtaining a frequency-modulated millimeter wave signal, 1
8 is a beam splitter for branching a part of the millimeter wave signal from the transmitting antenna to the receiving side, and 19 is the analysis processing of the peat signal detected by each imaging element,
It is a signal processor for calculating a three-dimensional image of a target object.

Next, the operation will be described. The frequency-modulated millimeter wave is radiated to the target object using the transmission antenna 10, and at the same time, a part of the millimeter wave signal is branched to the imaging array side using the beam splitter 18. Since one imaging element receives only the signal reflected from some part of the target object, the beat frequency detected by that element corresponds to the range of this part of the target object. In this way, it is possible to obtain a three-dimensional image of the target object by operating each element of the imaging array as an FM-CW radar.

FIG. 10 is a diagram for explaining a method of calculating a three-dimensional image of a target object using the millimeter wave camera device of FIG. Since the frequency of the beat signal is proportional to the depth of the object, a three-dimensional distribution map as shown in FIG. 10 (b) is obtained for an object having a shape as shown in FIG. 10 (a). When the bandwidth of the modulation frequency is 500 MHz, the resolution in the distance direction is about 30 cm. The millimeter wave camera device according to the third embodiment is effective as a vehicle-mounted imaging radar for simultaneously detecting a plurality of vehicles or obstacles existing on a road ahead, for example.

[0029]

As described above in detail, according to the present invention,
A hemispherical lens, which was indispensable for conventional millimeter-wave imaging arrays, is no longer required, and the system can be made smaller and lighter and the cost can be reduced, and an inexpensive and high-performance millimeter-wave camera device can be provided in fields such as security. It is possible.

According to the first aspect of the present invention, a two-dimensional image of the target object can be obtained by irradiating the target object with millimeter waves and video-detecting the reflected signal with the imaging array. INDUSTRIAL APPLICABILITY The present invention is effective as a short-range sensor for detecting metal / non-metal weapons hidden under clothes and exceeds the limit of conventional sensor devices.

According to the second aspect of the present invention, even when it is inconvenient to irradiate the target object with millimeter waves,
A two-dimensional image of the target object can be obtained by heterodyne detection of a weak millimeter wave signal radiated from the target object with an imaging array. The present invention is effective as a short-range sensor and also as a remote sensor for volcanic observation and the like.

According to a third aspect of the present invention, a target object is irradiated with a frequency-modulated millimeter wave and each element of the imaging array is used as an FM-CW radar to obtain a three-dimensional image of the target object. Can be obtained. The present invention exceeds the limit of the conventional FM-CW radar and is extremely promising as a next-generation automobile collision prevention imaging radar.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a millimeter wave camera device according to the present invention.

FIG. 2 is a diagram showing a first embodiment of the present invention.

FIG. 3 is a perspective view showing the configuration of the imaging array according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an experimental result of directivity characteristics of each imaging element in FIG.

5 is a diagram showing an analysis result of inter-element coupling characteristics in the imaging array of FIG.

FIG. 6 is a diagram showing the imaging performance of the millimeter wave camera according to the first embodiment of the present invention.

7A is a photograph of a triangular metal plate target according to the first embodiment of the invention, and FIG. 7B is a millimeter wave image obtained in the experiment.

FIG. 8 is a diagram showing a second embodiment of the present invention.

FIG. 9 is a diagram showing a third embodiment of the present invention.

FIG. 10 is a diagram illustrating a method of calculating a three-dimensional image of an object according to the third embodiment of the present invention.

FIG. 11 is a diagram showing a schematic configuration of a conventional imaging array.

12 is a diagram showing the directional characteristics of each imaging element in FIG.

[Explanation of symbols]

 1, 1a to 1e Dielectric substrate 2 Imaging element 2a Half-wave antenna 2b Yagi antenna element 2c Detection element 2d Output extraction 2e Slot 3 Objective lens 4 Covering material such as clothes 5 Target object 6 Image of target object 7 Millimeter wave oscillator 8 Amplitude Modulator 9 Modulated signal generator 10 Transmission antenna 11 Switch circuit 12 Video signal amplifier 13 A / D converter 14 Image display device 15 Quasi-optical diplexer 16 Intermediate frequency signal amplifier 17 Voltage controlled oscillator 18 Beam splitter 19 Signal processor 30 Hemisphere Lens 31 low-pass filter 32 coplanar waveguide 33 ground conductor

Claims (3)

[Claims] 1. An imaging array formed by arranging a large number of imaging elements formed by integrating a slot antenna provided on a multilayer dielectric substrate and a detection element at a predetermined sampling interval, and for irradiating a target object. A millimeter wave transmitter and a transmitting antenna, and an objective lens for forming an image of a signal reflected from a target object are provided, the imaging array is placed on the image plane of the objective lens, and each imaging element detects independently. A millimeter-wave camera device characterized by obtaining a two-dimensional image of a target object by amplifying and processing the signal intensity 2. An imaging array formed by arranging a plurality of imaging elements, which are formed by integrating a slot antenna provided on a multilayer dielectric substrate and a detection element at a predetermined sampling interval, and a millimeter radiated from a target object. The imaging array is placed on the image plane of the objective lens, and the imaging elements are independent of each other, the objective lens for imaging the wave signal and means for providing a local signal for heterodyne detection of the millimeter wave signal. A millimeter-wave camera device characterized in that a two-dimensional image of a target object is obtained by amplifying and processing the intensity of the intermediate frequency signal detected in. 3. An imaging array, which is formed by arranging a large number of imaging elements formed by integrating a slot antenna provided on a multilayer dielectric substrate and a detection element at a predetermined sampling interval, and a frequency-modulated millimeter wave signal. And a transmitting antenna for irradiating a target object with a beam, branching means for branching a part of the millimeter wave signal to the receiving side, and an image of the signal reflected from the target object and the branched signal. An objective lens for controlling the imaging array, and placing the imaging array on the image plane of the objective lens to amplify and process the peat signal detected by each imaging element independently to obtain a three-dimensional image of the target object. Characteristic millimeter-wave camera device.