1. Field of the Invention
The present invention relates to a directional coupler, an antenna device, and a transmitting-receiving device which are useful for a radar or the like with which the distance to a detection object or a relative velocity of the object is measured by transmission-reception of an electromagnetic wave in the millimetric wave band.
2. Description of the Related Art
In recent years, a so called xe2x80x9cmillimetric wave radar for car-mountingxe2x80x9d has been developed, of which the purpose lies in that for example, the distance to a vehicle running ahead or after, and the relative velocity are measured from a running vehicle. In general, the transmitting-receiving device of the millimetric wave radar of the above type includes a module which comprises a millimetric wave oscillator, a circulator, a directional coupler, a mixer, an antenna, and so forth which are integrated together, and is attached to the front or rear of the vehicle.
For example, as shown in FIG. 25, at the vehicle on the right side in FIG. 25, the relative distance and relative velocity for the vehicle running ahead (shown on the left side in FIG. 25) are measured for example by transmission-reception of a millimetric wave according to the FM-CW system. FIG. 26 is a block diagram showing the overall configuration of the millimetric radar. In the case shown in FIG. 25, the transmitting-receiving device and the antenna shown in FIG. 26 are attached to the front of the vehicle, and ordinarily, the signal processing device is provided in an optional location. In the signal processing section of the signal processing device, the distance to and the relative velocity of the vehicle running ahead are extracted as numerical information by means of the transmitting-receiving device. In the control-alarm section, based on the velocity of the vehicle running after and the distance between both the vehicles, an alarm is provided when predetermined conditions are satisfied, or when the relative velocity of the vehicle running ahead exceeds a predetermined threshold.
In the conventional millimetric radar, the directivity of the antenna is fixed. Therefore, there occurs the case that the desired detection or measurement is not performed depending on conditions. More particularly, for example, if vehicles run in plural traffic lanes as shown in FIG. 27, it can not immediately be determined whether a vehicle running ahead is present in the lane where the vehicle is running after, based on only the received electromagnetic wave reflected from the vehicle running ahead. More particularly, as shown in FIG. 27, when an electromagnetic wave is sent from a vehicle Cm by use of a radiation beam designated by the reference character B2, a reflected wave from the vehicle Ca running ahead, together with a reflected wave from a vehicle Cb running in the opposite lane, is received. Accordingly, the determined relative velocity is unduly high, due to the reflected wave from the vehicle running in the opposite lane. As a result, inconveniently, an error alarm is given. Further, in an example shown in FIG. 28, even if an electromagnetic wave is sent forward from the vehicle Cm by use of the radiation beam designated by the reference character B1, the vehicle Ca running ahead in the lane where the vehicle is running after can not be detected. Further, as shown in FIG. 29, even if an electromagnetic wave is sent forward from the vehicle Cm by use of the radiation beam designated by B1, the vehicle Ca running ahead can not be detected.
Accordingly, it is proposed that the above-described problems can be solved by varying the direction of the radiation beam. For example, in the example of FIG. 27, by varying the radiation beam in the range of B1 to B3, operational processing, and comparing the measurement results obtained in the respective beam directions, the two detection objects running ahead and adjacent in the angular directions can be separately detected. Further, in the example shown in FIG. 28, by analyzing image information obtained by steering operation (steering by a steering wheel) or by means of a camera photographing the forward view with respect to the vehicle, the curve of the lane is judged, and the radiation beam is directed in the direction in dependence on the judgment, for example, the radiation beam is directed to the direction indicated by the reference character B2, and thereby, the vehicle Ca running ahead can be detected. Further, in an example shown by FIG. 29, by analyzing image information from a camera photographing the forward view, the hilly situation of the road is judged, and for example, the radiation beam is directed upwardly, namely, to the direction designated by the reference numeral B2, and thereby, the vehicle Ca running ahead can be detected.
However, referring to the method of changing the directivity of an electromagnetic wave in the conventional transmitting-receiving device operative in the microwave band or millimetric wave band, the whole of a casing containing the transmitting-receiving device including the antenna is rotated only with a motor or the like to change (tilt) the direction of the radiation beam. Accordingly, the whole of the device is large in size, and it is difficult to scan with the radiation beam while the direction of the radiation is changed at a high speed.
Accordingly, it is an object of the present invention to solve the above-described problems and to provide a directional coupler in which the relative positions of two transmission lines can be changed while the coupling of the two transmission lines is maintained, an antenna device, and a transmitting-receiving device which can be easily miniaturized due to the directional coupler and of which the directivity can be switched at a high speed.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a directional coupler comprising a first microstrip line and a second microstrip line adjacent to the first microstrip line, the relative positions of the first microstrip line and the second microstrip line being changeable.
According to a second aspect of the present invention, there is provided a directional coupler comprising a first strip line, a second strip line adjacent to the first strip line, the relative positions of the first strip line and the second strip line being changeable.
According to a third aspect of the present invention, there is provided a directional coupler comprising a first slot line and a second slot line adjacent to the first slot line, the relative positions of the first slot line and the second slot line being changeable.
According to a fourth aspect of the present invention, there is provided a directional coupler comprising a first coplanar line and a second coplanar line adjacent to the first coplanar line, the relative positions of the first coplanar line and the second coplanar line being changeable.
According to a fifth aspect of the present invention, there is provided a directional coupler comprising a first wave guide and a second wave guide adjacent to the first wave guide, the relative positions of the first coplanar line and the second coplanar line being changeable.
According to a sixth aspect of the present invention, there is provided a directional coupler comprising a first suspended line and a second suspended line adjacent to the first suspended line, the relative positions of the first suspended line and the second suspended line being changeable.
Thus, in a variety of applications, available is the directional coupler of which the relative positions of the two transmission lines can be changed while the coupling of the two transmission lines is maintained.
According to the present invention. preferably, there is provided an antenna device including the directional coupler according to any one of the first through sixth aspects of the present invention, a primary radiator coupled or connected to a part of the directional coupler, and a driving mechanism for driving the directional coupler and the primary radiator.
Further, according to the present invention, there is provided a transmitting-receiving device including the antenna device according to the seventh aspect of the present invention, and a transmitting-receiving circuit connected to the antenna device.
Thus, an antenna device and an transmitting-receiving device of which the sizes are relatively small, and with which scanning with a radiation beam can be performed while the radiation beam direction can be changed at a high speed, are provided.