Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
1999-12-23
2001-06-12
Phan, Tho G. (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S753000, C343S909000, C343S91100R
Reexamination Certificate
active
06246375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna device for millimeter wave band or the like comprising a dielectric lens and a primary radiator, and also relates to a transmit-receive unit using the antenna device.
2. Description of the Related Art
Radar for a vehicle, using the millimeter wave band, for example, radiates a highly directed radar beam forward or rearward of the vehicle, receives waves reflected from a target such as another vehicle traveling in front of or behind the vehicle, and determines the distance to the target and its speed relative to the vehicle itself based on time delay, frequency difference, and the like, between the radiated and received signals. In a millimeter wave radar of this type, when a scan is to be conducted across a small angular range, the radar need only to radiate the transceiver beam in a fixed direction. In contrast, when scanning is to be conducted across a large angular range, the radar must change the direction of the beam while maintaining a high directivity so as to maintain high gain without reducing the resolution.
Accordingly, in a conventional millimeter wave antenna device, such as that shown in
FIG. 7
, a dielectric lens
2
and a primary radiator
1
constitute a single antenna device, and the direction of the beam is changed by changing the relative position of the primary radiator
1
with respect to the dielectric lens
2
. In
FIG. 7
, reference numerals
1
a,
1
b,
and
1
c
simultaneously represent three positions during the beam scanning of a single primary radiator. When the primary radiator
1
is at position
1
a,
the beam is formed as shown by Ba; when the primary radiator
1
is at position
1
b,
the beam is formed as indicated by Bb; and when the primary radiator
1
is at position
1
c,
the beam is formed as indicated by Bc.
FIG. 8
shows an example of changes in the beam depending on the position of the primary radiator
1
.
Since the above-mentioned dielectric lens is a rotationally symmetric body having its central axis as its center, a focal point is normally created on this central axis (hereinafter termed the “optical axis”), and the resulting beam is most focused when the phase center of the primary radiator is at the focal position. In the example shown in
FIG. 7
, the beam Bb, formed when the primary radiator is at the position indicated by
1
b,
is focused and is obtained with high gain. The further the phase center of the primary radiator deviates from the focal point, the wider the beam (half-value angle), and the weaker the emission, with a consequent reduction in the gain. Accordingly, in general, the phase center of the primary radiator is moved along the plane (hereinafter termed the “focal plane”) perpendicular to the optical axis passing through the focal point, and tracking is performed keeping the beam as focused as possible, thereby preventing a reduction in gain.
However, when there is a need to widen the angle of the beam scanning, the displacement of the primary radiator increases, and is inclined greatly with respect to the optical axis of the dielectric lens. As a result, the open efficiency of the dielectric lens decreases. In addition, the effects of aberration increase, greatly changing the gain of the antenna. Furthermore, even when the angular range of the beam scanning is relatively small, when a more uniform gain is required, there is still the problem of changes in gain due to the displacement of the primary radiator.
SUMMARY OF THE INVENTION
The present invention provides an antenna device wherein changes in gain during beam scanning, resulting from displacement of a primary radiator with respect to a dielectric lens, are reduced, and a transmit-receive unit which can scan over a large angular range with uniform gain.
The antenna device of the present invention comprises a dielectric lens, a primary radiator and a primary radiator displacement device to relatively displace the primary radiator with respect to the dielectric lens and change the directivity direction of a beam in accordance with the displacement of the relative positions of the phase center of the primary radiator and the dielectric lens. The primary radiator displacement device displaces the primary radiator so that the path of movement of the phase center of the primary radiator is not parallel to the focal plane of the dielectric lens. As a consequence, unlike the case where the primary radiator is only displaced on the focal plane, fluctuation in the open efficiency and aberration of the dielectric lens due to the displacement of the primary radiator, can be controlled.
The primary radiator displacement device displaces the primary radiator so that the phase center of the primary radiator moves farther away from the focal plane as it moves closer to the optical axis of the dielectric lens. Furthermore, a focal point is created substantially on the path of motion of the phase center of the primary radiator, and in addition, at a position removed from the center axis of the dielectric lens. As a consequence, it is possible to control fluctuation in the antenna gain arising as a result of fluctuation in the open efficiency and aberration of the dielectric lens due to the displacement of the primary radiator.
Moreover, a transmit-receive unit of the present invention comprises the antenna device described above, an oscillator for generating a transmission signal to the antenna device, and a mixer for mixing a received signal from the antenna device with a local signal. As a consequence, it is possible to scan for a target, with stable gain, irrespective of the search direction.
REFERENCES:
patent: 3775769 (1973-11-01), Heeren et al.
patent: 3881178 (1975-04-01), Hannan
patent: 4062018 (1977-12-01), Yokoi et al.
patent: 4338607 (1982-07-01), Drabowitch
patent: 19642810 (1998-04-01), None
patent: 0852409 (1998-07-01), None
patent: 0867972 (1998-09-01), None
patent: 0920068 (1999-06-01), None
patent: 0971436 (2000-01-01), None
Nakamura Fuminori
Nishiyama Taiyo
Tanizaki Toru
Yamada Hideaki
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Phan Tho G.
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