Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2001-11-29
2003-03-18
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S771000
Reexamination Certificate
active
06535173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a slot array antenna and more particularly to the arrangement of a feed port formed in a slot array antenna.
2. Description of the Background Art
Generally, an array antenna has a plurality of antenna elements or segments arranged in a certain pattern for acquiring characteristics impractical with a single antenna. Further, by regulating the respective antenna elements in phase, it is possible to control the directivity of the entire array antenna.
Today, frequency bands allocated to a variety of communication apparatuses are becoming short due to the remarkable development of radio transmission technologies. To make up for short frequency bands, it is necessary to more effectively use frequencies and to further shift frequencies to a higher range. Technologies meeting such requisites are therefore an urgent issue. Recently, a millimeter wave, for example, that has not been taken into consideration except for fundamental studies is planned for the application to ITS (Intelligent Transport System). In motorized societies, millimeter-wave transmission apparatuses are expected to be used as popularly as household appliances in the near future.
Under the above circumstances, the application of various parts and devices to the millimeter-wave range is, of course, necessary in the millimeter-wave transmission field. An antenna is one of the most important devices for millimeter-wave transmission systems. Millimeter transmission systems are not practicable without an antenna capable of transmitting and receiving millimeter-wave signals. Today, research institutions and manufacturers joining in the worldwide study and development of millimeter-wave transmission systems are competing with each other for high performance millimeter-wave antennas. While some different millimeter-wave antennas have already been proposed, one of them featuring high performance is a slot array antenna.
The slot array antenna is made up of a plurality of conventional slot antennas or antenna elements arranged in a certain pattern. The slot antennas are sized and arranged in a particular pattern implementing a desired electric field distribution in a certain region. For example, the type of slot antennas arranged bidimensionally in a rectangular region can have an electric field which distributes uniformly in direction, phase and amplitude. Theoretically, the slot array antenna is substantially the same in radiation characteristics as the aperture antenna having a uniform electric field distribution. However, the slot array antenna is superior to the aperture antenna when it comes to the freedom of configuration and the uniformity of the electric field distribution.
FIG. 1
shows the basic configuration of a conventional, bidimensional array antenna. As shown, the array antenna includes feed port or signal generator
20
and antenna elements or segments
21
. Transfer paths
22
connect the feed port
20
with antenna elements
21
. At the same time, the transfer paths
22
play the role of phase shifters. More specifically, each of the transfer paths
22
determines the phase of an electromagnetic wave to be radiated from one of the antenna elements
21
associated therewith, and has critical influence on the radiation characteristics of the entire array antenna. To further adjust the phases, additional phase shifters may serially be arranged on respective transfer paths, as the case may be.
FIG. 2
shows a specific configuration of a slot array antenna using a single, rectangular waveguide tube. As shown, the slot array antenna includes a waveguide
31
formed with slots
32
in one of the walls thereof. Usually, each slot
32
has its length that is equal to about one-half of the wavelength &lgr; of an electromagnetic wave input to the waveguide
31
, and its width that is equal to about one-twentieth of the wavelength &lgr;. In the specific configuration, when the waveguide
31
is driven in the dominant mode TE
10
, the magnetic and electric fields are distributed in the directions of the length and the width of the slots
32
, respectively.
The electromagnetic wave mode referred to in the present specification is the dominant mode TE
10
unless otherwise stated explicitly. Generally, as shown in
FIG. 2
, the pitch between the slots
32
spaced in the longitudinal direction of the waveguide
31
is equal to about one-half of the guide wavelength &lgr;g. The pitch between the nearby slots
32
aligned in each of the longitudinal lines, or slot arrays, is substantially equal to the guide wavelength &lgr;g.
A desired distribution of electromagnetic fields can be set up to some extent on the outer wall
33
of the waveguide if the dimensions and position of the slots
32
cut in the wall
33
are appropriately adjusted. Such a slot array antenna is monodimensional. By arranging a plurality of slot array antennas in parallel, each of which has the configuration shown in
FIG. 2
, there can be implemented a bidimensional slot array antenna. Today, a bidimensional slot array antenna is recognized as one of high-gain antennas theoretically and experimentally, as discussed in a Japanese document, “Fundamentals and Applications of Millimeter-Wave Technologies”, REALIZE INC., Tokyo, Japan, pp. 140-184, Jul. 31, 1998.
FIG. 3
shows a conventional, bidimensional slot array antenna in an exploded view. A bidimensional, slot array antenna will be simply referred to as a slot array antenna hereinafter unless stated otherwise. As shown, the slot array antenna is generally made up of a slot plate
411
and a waveguide plate
412
forming waveguides. Generally, the slot plate
411
is implemented by a thin, electro-conductive plate and formed with a plurality of slots
421
, see FIG.
4
. The plate
412
is a relatively thicker, electro-conductive plate having rectangular-cross-sectional grooves formed therein. The grooves are configured such that an input electromagnetic wave can be fed from a single feed port to all of the slots
421
of the slot plate
411
. More specifically, when the slot plate
411
is laid on and adhered to the plate
412
into an assembly, the arrays of slots are positioned right above the grooves associated therewith with parts of the plate
411
forming the walls of waveguides established by those grooves. In this arrangement, the entire assembly operates as a slot array antenna. The higher the conductivity of the conductors constituting the slot plate
411
and the plate
412
, the smaller the ohmic loss of the entire antenna. Further, the accuracy in assembly and adhesion of the slot plate
411
with the plate
412
noticeably influences on the radiation characteristics of the resultant antenna.
As shown in
FIG. 4
, while each slot
421
formed in the slot plate
411
is basically rectangular, its opposite ends are sometimes rounded for manufacturing reasons. Each slot
421
has its length that is equal to about one-half of the wavelength of an electromagnetic wave to be radiated, and its width that is equal to about one-twentieth of the same, as stated earlier. The pitch between the nearby slots
421
on the same array is substantially equal to the guide wavelength &lgr;g.
As seen in
FIG. 5
, the plate
412
has a feed port
431
cut therein. When the slot plate
411
and plate
412
are adhered together into assembly, a portion
432
indicated by a dashed ellipse in
FIG. 5
constitutes an H plane tee junction as referred to in the art of microwave circuit devices. An electromagnetic wave input via the feed port
431
is split into two at the H plane tee junction
432
in the opposite directions perpendicular to each other. The resulting two electromagnetic waves are of the same phase as to power.
A matching lug or post
433
plays the role of a matching stub included in a conventional H plane tee junction. The lug or post
433
protrudes toward the feed port
431
, as seen in
FIG. 5. A
groove extending in the opposite directions from the H plane tee junction
432
constitutes a waveguide when the slo
Kim John H.
Le Hoang-anh
Oki Electric Industry Co. Ltd.
Sartori Michael A.
Venable
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