Antenna device and radio-wave radiating method

An antenna device according to an embodiment includes a main line, radiating elements, and feed lines. The radiating elements are arranged along the main line and radiate radio waves. The feed lines connect the main line and the respective radiating elements. Moreover, the feed lines are inserted into the respective radiating elements by inserted lengths so that an electrical coupling degree between one of the feed lines and corresponding one of the radiating elements is larger as the one feed line is located closer to a leading end than a base end of the main line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2017-163781, filed on Aug. 28, 2017, the entire contents of which are incorporated herein by reference.

FIELD

The embodiment discussed herein is directed to an antenna device and a radio-wave radiating method.

BACKGROUND

Conventionally, there has been known an antenna device that is formed on a board as a surface pattern, such as a microstrip antenna. The antenna device includes, for example: radiating elements that radiate radio waves; and a main line that supplies electric power, which is supplied from a controller of a radar apparatus etc., to the radiating elements (see, e.g., Japanese Laid-open Patent Publication No. 2016-086432).

In such an antenna device, for example, shapes and/or element widths of the radiating elements are changed for each of the radiating elements so as to adjust a distribution ratio of electric-power to be supplied to the radiating elements, and thus the directivity of radio waves is designed to be low side lobe.

However, when matching elements are used for the radiating elements in order to realize a desired electric-power distribution ratio, for example, an impedance adjusting circuit is to be additionally provided to each of the elements, and thus the configuration becomes complicated. Moreover, when the element widths of the radiating elements are changed, there exists possibility that the robustness is reduced due to effects of manufacturing tolerance. As described above, conventionally, there exists possibility that an antenna shape becomes complicated in order to achieve the desired electric-power distribution ratio.

SUMMARY

An antenna device according to an embodiment includes a main line, radiating elements, and feed lines. The radiating elements are arranged along the main line and radiate radio waves. The feed lines connect the main line and the respective radiating elements. Moreover, the feed lines are inserted into the respective radiating elements by inserted lengths so that an electrical coupling degree between one of the feed lines and corresponding one of the radiating elements is larger as the one feed line is located closer to a leading end than a base end of the main line.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an antenna device and a radio-wave radiating method disclosed in the present application will be described in detail with reference to the accompanying drawings. Moreover, the embodiment described below is merely one example, and not intended to limit the present disclosure.

First, a radar apparatus in which antenna device according to an embodiment is provided will be explained with reference toFIG. 1.FIG. 1is a diagram illustrating a radar apparatus1according to the embodiment. The radar apparatus1is an apparatus that radiates radio waves having, for example, a Frequency Modulated Continuous Wave type (FM-CW type), a Fast-Chirp Modulation type (FCM type), or the like.

As illustrated inFIG. 1, the radar apparatus1according to the embodiment includes an antenna device2and a controller3. The controller3transmits a frequency-modulated signal to the antenna device2, for example. The antenna device2is an antenna device for transmitting that radiates the signal transmitted from the controller3.

Furthermore, the radar apparatus1further includes an antenna device (not illustrated) for receiving in addition to the antenna device2for transmitting. Moreover, inFIG. 1, the number of the antenna devices2is one; however, the number of the antenna devices2provided in the radar apparatus1may be equal to or more than two.

As illustrated inFIG. 1, the antenna device2according to the embodiment includes: a main line10, a plurality of radiating elements20ato20f; and a plurality of feed lines30ato30fso as to perform the radio-wave radiating method according to the embodiment. Furthermore, hereinafter, the plurality of radiating elements20ato20fmay be referred to as “radiating elements20”, and the plurality of feed lines30ato30fmay be referred to as “feed lines30”.

The main line10is a line through which electric power supplied from the controller3flows at a predetermined wavelength from a base end (negative side of Z-axis) toward a leading end (positive side of Z-axis). Hereinafter, the wavelength of the electric power in the main line10, namely, a guide wavelength may be referred to as “λg”.

The radiating elements20resonate with electric power supplied from the main line10and are in a resonant state so as to radiate radio waves toward the outside. The radiating elements20as well as the feed lines30are arranged to be tilted from the main line10by an angle of 45 degrees. The feed lines30are inserted into the respective radiating elements20so as to connect the main line10and the radiating elements20. Specifically, the feed lines30are arranged at intervals of “λg” that is a guide wavelength of the main line10.

In the radio-wave radiating method according to the embodiment, the feed lines30of the antenna device2are inserted into the respective radiating elements20by inserted lengths so that an electrical coupling degree between one of the feed lines30and corresponding one of the radiating elements20is larger as the one feed line30is located closer to the leading end (positive side of Z-axis) than the base end (negative side of Z-axis) of the main line10.

The coupling degree is a value indicating what rate of electric power flows, from the electric power flowing in the main line10, into the feed line30. In other words, when input electric power in the main line10is constant, the electric power flowing from the main line10to the feed line30is larger as the coupling degree is larger.

Here, a conventional antenna device will be explained. Conventionally, an antenna device has been desirably designed so that the directivity of a radiated radio wave has a lower side lobe. Thus, in the conventional antenna device, in order to realize the low side lobe, it was preferable that, when the electric power flowing in the main line was defined as 100%, the radiant power was the highest at a center radiating element (inFIG. 1, radiating element20d) and the radiant power was smaller as a position of a radiating element was closer to any of ends (base end and leading end). The magnitude of the radiant power was able to be changed by changing the distribution ratio of the electric power flowing in the main line.

Moreover, electric-power amount of the electric power flowing in the main line was smaller as a position was closer to the leading end, and thus the coupling degree was to be increased as the position is closer to the leading end. In the conventional antenna device, shapes of the radiating elements, element widths of the radiating elements, and feed-line lengths among other things were changed to achieve a desired electric-power distribution ratio.

When matching elements are used for the radiating elements, for example, impedance adjusting circuits are to be additionally provided to the respective elements, and thus the configuration becomes complicated. Moreover, when element widths of the radiating elements are changed, the manufacturing tolerance is inclined to increase, and thus there exists possibility that the robustness is reduced as a result. As described above, conventionally, there existed possibility that an antenna shape became complicated in order to achieve a desired electric-power distribution ratio.

Thus, in the antenna device2according to the embodiment, the inserted lengths of the feed lines30into the respective radiating elements20are adjusted to more increase a coupling degree as a position is closer to the leading end of the main line10. In other words, only adjusting the inserted lengths is sufficient, and thus it is possible to achieve a desired electric-power distribution ratio along with a simple antenna shape without changing shapes of the radiating elements20and the feed lines30. Here, the antenna device2according to the embodiment will be specifically explained with reference toFIG. 2.

FIG. 2is a diagram illustrating the antenna device2according to the embodiment. As illustrated inFIG. 2, the feed line30is inserted into the radiating element20so as to form a slit21of the antenna device2. A length of the slit21corresponds to an inserted length I. Moreover, inFIG. 2, an element length L and a feed-line length D of the radiating element20are further depicted.

The element length L of the radiating element20is set to be “λg/2”, which is half of the guide wavelength of the main line10, in order to turn the radiating element20into a resonant state, for example. Moreover, the feed-line length D is set to be any one of “¼λg×(2n+1)” and “¼λg×(2n)” (“¼λg” is one fourth of guide wavelength and “n” is integer).

Specifically, in the feed line30, there presents a standing wave of the electric power supplied from the main line10. In a distribution of this standing wave, the voltage is the maximum value at “0λg”, and subsequently and alternately becomes the maximum and minimum values at intervals of “¼λg”.

In other words, the voltage in the standing wave is the minimum value when the feed-line length D is “¼λg×(2n+1)”, and the voltage in the standing wave is the maximum value when the feed-line length D is “¼λg×(2n)”. The voltage is a voltage that occurs in a connector between the main line10and the feed line30.

Thus, a method for setting the inserted length I is changed depending on whether the feed-line length D is “¼λg×(2n+1)” or the feed-line length D is “¼λg×(2n)”. The setting method of the inserted length I will be specifically explained with reference toFIGS. 3 to 5.

First, a setting method of the inserted length I when the feed-line length D is “¼λg×(2n+1)” will be explained with reference toFIGS. 3 to 5, and a setting method of the inserted length I when the feed-line length D is “¼λg×(2n)” will be subsequently explained with reference toFIGS. 6 to 8.

FIG. 3is a diagram illustrating relationship between the inserted length I and the impedance. In a graph depicted inFIG. 3, the lateral axis indicates the inserted length I and the vertical axis indicates the impedance. Furthermore, each numeric value on the lateral axis indicates a ratio of the inserted length I to the element length L.

In other words, when the inserted length I is “0.2”, the length of the inserted length I is 20% of the element length L. Moreover, the impedance mentioned here indicates input impedance on the radiating elements20side viewed from a connection point of the main line10and the feed line30(seeFIG. 2).

As illustrated inFIG. 3, when the feed-line length D is “¼λg×(2n+1)”, the impedance is larger as the inserted length I is longer. To be more specific, within a range of the ratio of the inserted length I from “0” to “0.4”, the impedance transitions between “0Ω” to “50Ω”, on the other hand, when the ratio is “0.5”, the impedance rapidly increase to approximately “1400Ω”.

In other words, when the feed-line length D is “¼λg×(2n+1)”, electric power easily flows from the main line10to the radiating element20within the range of the inserted length I from “0” to “0.4”, on the other hand, when the inserted length I is “0.5”, the electric power does not easily flow from the main line10to the radiating element20. In other words, the coupling degree reduces more as the inserted length I is longer.

Furthermore, although not illustrated in the graph depicted inFIG. 3, when the ratio of the inserted length I is equal to or more than “0.5”, the impedance reduces again. In other words, in a case where the feed-line length D is “¼λg×(2n+1)”, when the ratio of the inserted length I is approximately “0.5”, the impedance becomes the highest, in other words, the coupling degree becomes the lowest.

An arrangement example of the radiating elements20using such impedance characteristics is illustrated inFIG. 4.FIG. 4is a diagram illustrating the arrangement example of the antenna device2according to the embodiment. InFIG. 4, a case is exemplified in which the seven radiating elements20ato20gare individually connected to the main line10. Moreover, assume that the feed-line length D is “¼λg×(2n+1)”.

As illustrated inFIG. 4, the inserted lengths I of the six radiating elements20ato20fobtained by excepting the leading-end radiating element20gfrom the seven radiating elements20ato20gare set so as to be gradually shorter as the radiating element20is located closer to the leading-end radiating element20fthan the base-end radiating element20a. In other words, the coupling degree is gradually larger as the radiating element20is located closer to the leading-end radiating element20fthan the base-end radiating element20a. Furthermore, a matching element whose coupling degree is “100%” is arranged at the radiating element20gdisposed on the leading end.

Moreover, as illustrated inFIG. 4, matching circuits40ato40fare disposed at the respective connection parts of the main line10and the feed lines30ato30f. Each of the matching circuits40ato40fis a circuit for matching with respect to the impedance for the inserted length I of corresponding one of the radiating elements20ato20f, and the performance according to this impedance is set.

Next, a simulation result indicating relationship between the inserted length I and the coupling degree when the feed-line length D is “¼λg×(2n+1)” will be explained with reference toFIG. 5.FIG. 5is a diagram illustrating relationship between the inserted length I and the coupling degree. As illustrated inFIG. 5, within a range of the inserted length I from “0” to approximately “0.5”, the maximum value of the coupling degree was approximately “0.7 (70%)”, and the minimum value of the coupling degree was approximately “0.15 (15%)”. In other words, the coupling degree was able to be adjusted within a range from “15%” to “70%” by adjusting the inserted length I.

In other words, the coupling degree is able to be adjusted without changing shapes of the radiating elements20and the feed lines30, and thus it is possible to achieve a desired electric-power distribution ratio along with a simple antenna shape. Moreover, when the ratio of the inserted length I to the element length L is set to be equal to or less than “50%”, it is possible to easily adjust the coupling degree.

Next, a method for setting the inserted length I when the feed-line length D is “¼λg×(2n)” will be explained with reference toFIGS. 6 to 8.

FIG. 6is a diagram illustrating relationship between the inserted length I and the impedance. In a graph depicted inFIG. 6, the lateral axis indicates the inserted length I, and the vertical axis indicates the impedance. Furthermore, the definition of the inserted length I indicated by the lateral axis and the impedance are similar to that depicted inFIG. 3, and thus the description thereof is omitted.

As illustrated inFIG. 6, when the feed-line length D is “¼λg×(2n)”, the impedance is smaller as the inserted length I is longer. To be more specific, the impedance transitions between “0Ω” to “370Ω” within a range of the ratio of the inserted length I from “0” to “0.5”. In other words, when the feed-line length D is “¼λg×(2n)”, the coupling degree increases more as the inserted length I is longer, and thus the electric power easily flows to the radiating element20.

Furthermore, although not illustrated in the graph depicted inFIG. 6, when the ratio of the inserted length I is equal to or more than “0.5”, the impedance increases again. In other words, in a case where the feed-line length D is “¼λg×(2n)”, when the ratio of the inserted length I is approximately “0.5”, the impedance becomes the lowest, in other words, the coupling degree becomes the highest.

An arrangement example of the radiating elements20using such impedance characteristics is illustrated inFIG. 7.FIG. 7is a diagram illustrating an arrangement example of the antenna device2according to the embodiment. InFIG. 7, a case is exemplified in which the seven radiating elements20ato20gare individually connected to the main line10. Moreover, assume that the feed-line length D is “¼λg×(2n)”.

As illustrated inFIG. 7, the inserted lengths I of the six radiating elements20ato20fobtained by excepting the leading-end radiating element20gfrom the seven radiating elements20ato20gare set so as to be gradually longer as the radiating element20is located closer to the leading-end radiating element20fthan the base-end radiating element20a. In other words, the coupling degree is gradually smaller as the radiating element20is located closer to the leading-end radiating element20fthan the base-end radiating element20a. Furthermore, a matching element whose coupling degree is “100%” is arranged at the radiating element20gdisposed on the leading end.

Moreover, as illustrated inFIG. 7, matching circuits40ato40f, which have performances according to the respective impedances, are disposed at the respective connection parts of the main line10and the feed lines30ato30f.

Next, a simulation result indicating relationship between the inserted length I and the coupling degree when the feed-line length D is “¼λg×(2n)” will be explained with reference toFIG. 8.FIG. 8is a diagram illustrating relationship between the inserted length I and the coupling degree. As illustrated inFIG. 8, within a range of the inserted length I from “0” to “0.5”, the maximum value of the coupling degree was approximately “0.65 (65%)”, and the minimum value of the coupling degree was approximately “0.25 (25%)”. In other words, the coupling degree was able to be adjusted within a range from “25%” to “65%” by adjusting the inserted length I.

In other words, the coupling degree is able to be adjusted without changing shapes of the radiating elements20and the feed lines30, and thus it is possible to achieve a desired electric-power distribution ratio along with a simple antenna shape.

Moreover, in both case where the feed-line length D is “¼λg×(2n+1)” and the feed-line length D is “¼λg×(2n)”, adjusting the inserted length I within a range equal to or less than “50%” of the element length L is able to reduce variation of the inserted length I, so that it is possible to avoid complexity in manufacturing processes.

As described above, the antenna device2according to the embodiment includes: the main line10; the radiating elements20; and the feed lines30. The radiating elements20are arranged along the main line10and radiate radio waves. The feed lines30connect the main line10and the respective radiating elements20. Moreover, the feed lines30are inserted into the respective radiating elements20by inserted lengths I so that an electrical coupling degree between one of the feed lines30and corresponding one of the radiating elements20is larger as the one feed line30is located closer to a leading end than a base end of the main line10. Thus, it is possible to achieve a desired electric-power distribution ratio along with a simple antenna shape.

Furthermore, in the above-mentioned embodiment, the inserted length I of the feed line30is described to be a length (length of slit21) along the insertion direction into the radiating element20; however, not limited thereto. Another example of the inserted length I will be explained with reference toFIG. 9.

FIG. 9is a diagram illustrating the antenna device2according to a modification. InFIG. 9, the element length L is defined as a length of the radiating elements20along a direction perpendicular to the insertion direction of the feed line30. The inserted length I is defined by an inserted position of the feed line30with respect to the perpendicular direction.

Moreover, the feed-line length D is set to be any one of “¼λg×(2n+1)” and “¼λg×(2n)”. The setting method of the inserted length I differs depending on whether the feed-line length D is “¼λg×(2n+1)” or “¼λg×(2n)”.

In other words, when the feed-line length D is “¼λg×(2n+1)”, the impedance gradually increases in a range of the ratio of the inserted length I from “0” to “0.5”. In other words, the impedance value presents a tendency similar to that of the graph depicted inFIG. 3, furthermore, the values themselves are also similar to those of the graph depicted inFIG. 3.

Moreover, when the feed-line length D is “¼λg×(2n)”, the impedance gradually decreases within a range of the ratio of the inserted length I from “0” to “0.5”. In other words, the impedance value presents a tendency similar to that of the graph depicted inFIG. 6, furthermore, the values themselves are also similar to those of the graph depicted inFIG. 6.