Radio wave emission source visualization apparatus and band expansion method

An apparatus includes antenna, selector, estimator, imager and creator. The antenna includes antenna elements of N rows by N columns (N is a natural number of 2 or more) arranged in an array and captures an incoming wave. The selector selects an antenna element group including antenna elements of M rows by M columns (M is a natural number less than N) from the antenna elements of N rows by N columns according to a band of the incoming wave. The estimator estimates an incoming direction of the incoming wave from an element signal of each of the antenna elements included in the selected antenna element group. The imager acquires image data by imaging an orientation direction of an aperture of the antenna. The creator creates a visualized image by visually synthesizing the estimated incoming direction with the image data.

FIELD

Embodiments described herein relate generally to a radio wave emission source visualization apparatus and a band expansion method.

BACKGROUND

A radio wave emission source visualization apparatus can specify a radiation position of a radio wave in a desired band and display it so as to be superimposed on a camera image. For example, since it can pinpoint illegal radio waves and their position can be displayed, it is operated in public service agencies, etc. Since the illegal radio waves are transmitted at various frequencies, it is required to expand a frequency band that can be captured.

In this type of apparatus, it is considered sufficient to cover at most 700 MHz to 1500 MHz; however, in recent years, in addition to this, the apparatus is required to be able to cover a band of 1400 MHz to 2700 MHz. That is, while a band of one octave has been sufficient conventionally, an apparatus capable of covering a band of two octaves at once is required.

However, as is well known, in an array antenna2, an arrangement at intervals of λ/2 with respect to a reception wavelength (λ) is ideal, and if an element interval is λ/2 or less, a peak of a visualization processing output becomes broad, and it becomes difficult to specify a radiation position. If λ becomes close to the element interval, the peak of the visualization processing output becomes sharp, but a virtual image also appears. As described above, in a target band of the radio wave emission source visualization apparatus, conditions related to an antenna design are strict, and it is difficult to widen the band.

DETAILED DESCRIPTION

In general, according to one embodiment, a radio wave emission source visualization apparatus includes an antenna, a selector, an estimator, an imager and a creator. The antenna includes antenna elements of N rows by N columns (N is a natural number of 2 or more) arranged in an array and captures an incoming wave. The selector selects an antenna element group including antenna elements of M rows by M columns (M is a natural number less than N) from the antenna elements of N rows by N columns according to a band of the incoming wave. The estimator estimates an incoming direction of the incoming wave from an element signal of each of the antenna elements included in the selected antenna element group. The imager acquires image data by imaging an orientation direction of an aperture of the antenna. The creator creates a visualized image by visually synthesizing the estimated incoming direction with the image data.

FIG.1is a functional block diagram showing an example of a radio wave emission source visualization apparatus according to an embodiment. The radio wave emission source visualization apparatus ofFIG.1includes an array antenna2, an antenna switcher3, a reference antenna4, a frequency converter5, an A/D (analog/digital) converter6, an incoming direction estimation processor7, a camera unit8, an image mixer9, a GPS receiver10, a direction sensor11, a map displaying processor12, a display13, and a memory14.

The array antenna2includes N (N is a natural number of 2 or more) antenna elements1-1to1-narranged in an array, and captures radio waves (incoming waves) from a radio wave emission source. The antenna switcher3is, for example, a switching element such as a diode switch, and selectively switches the antenna elements1-1to1-naccording to a band of an incoming wave to be captured. That is, the antenna switcher3selects an antenna element group including M (M is a natural number of N or less) antenna elements from the antenna elements1-1to1-naccording to the band of the incoming wave.

The antenna elements1-1to1-nand the reference antenna4all capture incoming waves in the same band and output element signals. The shape and type of the array antenna2, the total number of antenna elements, intervals between the antenna elements1-1to1-n, etc. are optimized according to a measurement target, a measurement purpose, etc.

If any one of the antenna elements1-1to1-nis used as the reference antenna4, a structure for separately attaching the reference antenna4can be omitted, which can contribute to reduction in size and weight.

The frequency converter5amplifies each element signal from the reference antenna4and the array antenna2, and performs frequency conversion to an intermediate frequency band in which sampling is possible. The A/D converter6converts an analog signal frequency-converted by the frequency converter5into a digital signal.

The incoming direction estimation processor7estimates an incoming direction of an incoming wave captured by the array antenna2. Specifically, the incoming direction estimation processor7detects a phase difference between an element signal of the reference antenna4and an element signal of each antenna element included in a selected antenna element group, and estimates the incoming direction of the incoming wave by, for example, a radio holography method. The incoming direction of the incoming wave estimated by the incoming direction estimation processor7indicates relative azimuth angle and elevation angle with respect to the direction of the array antenna2.

The camera unit8is installed in the vicinity of the array antenna2, and acquires image data by photographing an orientation direction of the aperture of the array antenna2. If a mounting position of the camera unit8is away from a phase center of the array antenna2, an accurate visualized image can be acquired by correcting a parallax.

The image mixer9generates a visualized image by visually synthesizing the incoming direction of the incoming wave estimated by the incoming direction estimation processor7with the image data acquired by the camera unit8. That is, the image mixer9creates a visualized image by synthesizing an electric field intensity distribution on a two-dimensional plane of the incoming wave with the image data.

The GPS receiver10acquires position information of the array antenna2. Specifically, the GPS receiver10receives a positioning signal from a GPS (Global Positioning System) satellite, and acquires position information such as latitude and longitude of the array antenna2. The direction sensor11is, for example, a magnetic direction sensor, and acquires direction information of the array antenna2using geomagnetism.

The map displaying processor12acquires map information around the array antenna2based on the position information acquired by the GPS receiver10. The map information can be acquired from map data14astored in advance in the memory14. Alternatively, the map information may be acquired from a network such as the Internet.

The display13is, for example, a liquid crystal display (LCD), and displays a map indicating the incoming direction of the incoming wave received by the array antenna2and the position of the array antenna2based on the map information output by the map displaying processor12. Further, the display13displays the visualized image generated by the image mixer9.

Various controls for the array antenna2, antenna switcher3, reference antenna4, frequency converter5, A/D (analog/digital) converter6, incoming direction estimation processor7, camera unit8, image mixer9, GPS receiver10, direction sensor11, map displaying processor12, and display13, or arithmetic processing by software is realized by a program14bstored in the memory14.

FIG.2is a diagram showing an example of display on the display13inFIG.1. The display13displays, for example, a camera window (a) and a map window (b).

The camera window (a) displays a superimposed image in which distribution of electric field intensity of an incoming wave on a two-dimensional plane is synthesized with an image captured by the camera unit8. In the camera window (a), the electric field intensity of the estimated incoming wave is drawn approximately on contour lines around an incoming direction estimated by the incoming direction estimation processor7. An image (color map) created with different display colors according to the electric field intensity may be displayed.

In the map window (b), a position (c) of the radio wave emission source visualization apparatus acquired by the GPS receiver10is displayed by being superimposed on the peripheral map acquired from the map data14a. Further, in the map window (b), an arrow is drawn from the position (c) of the radio wave emission source visualization apparatus to a position (d) of a radio wave emission source. According to the map window (b), this arrow indicates that the radio wave emission source is located slightly to the left of a person searching. This also corresponds to the visualization screen (a).

FIG.3is a diagram showing an example of the array antenna2viewed from the aperture face. The array antenna may have, for example, 25 antenna elements of 5 rows by 5 columns.

Here, consider capturing an incoming wave in a band ranging from 700 MHz to 2700 MHz, for example. In the existing technology, for example, it is necessary to divide the band as shown in the following (1) and (2) and to provide a dedicated array antenna for each band.(1) 700 MHz to 1500 MHz(2) 1400 MHz to 2700 MHz

Therefore, in the embodiment, a broadband antenna that covers the frequency bands (1) and (2) is used, and an antenna array is selected from a plurality of antenna arrays according to the reception frequency so that the element interval can be optimized.

As shown inFIG.4, when the band (1) is captured, a 3×3 array of antenna elements indicated by hatching (hatched lines) in the figure is selected, and an incoming radio wave direction is calculated from an element signal from each antenna element of this antenna element group. On the other hand, when the band (2) is captured, a 4×4 array of antenna elements indicated by hatching (hatched lines) inFIG.5is selected, and an incoming radio wave direction is calculated from an element signal from each antenna element of this antenna element group.

In this way, by selecting the antenna elements according to the band of the incoming wave to be captured and switching the antenna array, the intervals between the antenna elements can be adaptively set. As a result, two array antennas are integrated into one array antenna, and it is possible to observe an incoming broadband wave extending from 700 MHz to 2700 MHz, for example, using the common array antenna.

In the array antenna, an array arrangement at intervals of λ′/2 with respect to a reception wavelength (λ) is ideal. If the element interval is λ/2 or less, a peak of a visualization processing output becomes broad and it becomes difficult to specify a radiation position. Further, if λ, becomes close to the element interval, the peak of the visualization processing output becomes sharp, but a virtual image is also displayed. Thus, in the existing technology, an upper limit of a reception frequency range is a frequency twice that of a lower limit frequency, and the antenna elements are arranged in an array at intervals of λ/2 with respect to a wavelength at a center frequency. For this reason, the receivable band is naturally limited.

In contrast, in the embodiment, the antenna switcher3selects an antenna element group including antenna elements arranged at about half-wave intervals with respect to the wavelength of the incoming wave, so that the incoming wave can be captured by the antenna elements arranged in an array at the intervals of λ/2 with respect to the reception wavelength λ. For these reasons, according to the embodiment, it is possible to provide a radio wave emission source visualization apparatus and a band expansion method that achieve a wider band.

Note that the present invention is not limited to the embodiment described above. For example, the display13can be realized by a screen of a notebook personal computer separate from the radio wave emission source visualization apparatus. Alternatively, it may be a screen of a tablet. Further, the camera window (a) and the map window (b) do not need to be displayed together on the same screen, and the screen may be switched in response to a user's operation or the like.

The display method by the display13is not limited to the above-described method, and various modifications can be made. For example, the display13may display the incoming radio wave direction in the camera window (a) with a number, a symbol, a mark, or the like other than the color corresponding to the electric field intensity. Further, the display13may use a map in which various pieces of information other than buildings are described in the map window (b).

Further, it is also possible to take measures against multipath propagation.

FIG.6is a diagram for explaining that a plurality of antenna element groups can be formed. In the 5×5 array antenna, as shown inFIGS.6(a),6(b),6(c), and6(d), the 4×4 array antenna element group can be switched in four ways. The antenna switcher3selectively switches these plurality of antenna element groups, and switches and outputs the element signals from the antenna element groups. Then, the incoming direction estimation processor7averages the element signals from the antenna element groups to estimate an incoming direction of an incoming wave. In this way, it is possible to average and cancel an influence of multipath propagation generated in each antenna element group. As a result, it is possible to enhance resistance to an environment in which multipath propagation is likely to occur, such as an urban area.