Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2001-10-22
2003-07-22
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S785000, C343S772000, C333S02100R
Reexamination Certificate
active
06597323
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dielectric leaky-wave antenna. More particularly, in a dielectric leaky-wave antenna for leaking an electromagnetic wave formed by a ground plane and a dielectric from a transmission guide, the present invention relates to a dielectric leaky-wave antenna having a single-layer structure which adopts a technique for enabling radiation of various kinds of polarized electromagnetic waves by a simple structure.
BACKGROUND ART
In recent years, demands for a planar antenna which can be used in a millimeter wave region for an automotive radar or a wireless LAN have been increasing.
As such an antenna for a millimeter wave region, there have been proposed various kinds of antenna, e.g., one for leaking an electromagnetic wave from slots provided to a wave guide, a so-called triplate antenna for feeding power through a triplate line by providing a coupling slot on a board and others.
However, among these antennas, an antenna using a wave guide is disadvantageously difficult to be manufactured since it has a three-dimensional structure partitioned by a metal wall.
Further, the triplate antenna has a large line loss although it is not as large as that of a micro-strip line, and unnecessary waves caused due to reflections of radiating elements are transmitted in the triplate line, which prevents the efficiency of the antenna to increase.
Therefore, there is proposed a parallel-plate slot array antenna in which a transmission guide which is equivalent to a wave guide is constituted by upper and lower metal surfaces of a printed board and through-holes formed so as to pieces the metal surfaces (TECHNICAL REPORT OF IEICE. A.P 99-114, RCS99-11 (199-10)).
However, the parallel-plate slot array antenna constituting the transmission guide equivalent to the wave guide by using the through-holes to the printed board as mentioned above is structurally complicated as compared with the dielectric leaky-wave antenna, and its manufacturing cost involved by processing of the through-holes is increased.
Further, in the case of this antenna, since a uniform electromagnetic field mode, i.e., a TEM mode is used in a cross section which is vertical to the transmission direction, the same strong electric current flows to the upper and lower metal plates, and the conductor loss is generated, which is a factor of occurrence of the large loss.
Furthermore, since a dielectric plate is actually inserted to the parallel plates in order to shorten the guide wavelength and suppress the grating lobe, the dielectric loss is also generated, and there is a limit in reducing the loss.
Moreover, as another type of antenna, there is proposed a leaky-wave antenna in which a dielectric rod for radiation which has a narrow width is arranged on a dielectric slab having a double-layer structure to provide a transmission line, the height of the transmission line is partially changed and metal strips are cyclically provided to lower parts (U.S. Pat. No. 4,835,543, “Dielectric slab antenna”).
This is a one-dimensional array antenna. In order to obtain a two-dimensional antenna which is practically important, however, since a plurality of dielectric rods for radiation must be arranged, the mass production property is poor, and a power feeding system to these rods in phase becomes complicated.
Besides, there is proposed a method by which a dielectric slab having a projection portion in a direction vertical to the plate is manufactured, the surface of the slab is metalized in order to form a continuous transverse slub and the obtained slub is utilized for an antenna (U.S. Pat. No. 5,266,961 “Continuous transverse slub element devices and method of making same”).
This is a slot array antenna which is uniform in the transverse direction and uses a parallel-plate wave guide in which a dielectric is inserted. However, a dielectric material such as alumina is generally difficult to be processed at a high frequency of, e.g., a millimeter wave and with low loss. Manufacturing the complicated dielectric slab having many protrusions leads to the problems in cost.
Thus, there has been expected realization of a planar antenna which has a simple structure and the high efficiency and can emit various kinds of polarized electromagnetic waves respectively suitable for an automotive radar or a wireless LAN.
Therefore, the present international patent applicant (inventor) filed a patent application “dielectric leaky-wave antenna (double-layer structure)” to Japan (JPA2000-54487, JPA2000-22471), United States (dielectric leaky-wave antenna filed on Dec. 19, 2000) and Europe (EPA00127989. 2).
This “dielectric leaky-wave antenna (double-layer structure)” greatly reduces the electric currents flowing to a ground plane and the conductor loss and realizes the high efficiency by providing a small air layer between the ground plane and a dielectric slab (plate) and obtaining the double-layer structure.
Moreover, by providing such a double-layer structure, since a metal strip can be also printed on a back surface of the dielectric slab, reflection in the line can be suppressed.
In an antenna for the 76 GHz band manufactured by way of trial based on these techniques, the antenna efficiency of 76% which is far greater than the conventional antenna efficiency of approximately 50% is realized.
Meanwhile, when trying to apply the “dielectric leaky-wave antenna (double-layer structure)” to a low-frequency domain of a quasi-millimeter wave or a millimeter wave for wireless access (for example, FWA: Fixed Wireless Access) and the like in the 20 GHz band, the wavelength becomes approximately two fold to three fold. Therefore, the necessary thickness of the dielectric slab becomes as thick as approximately 2 mm, whereas the conventional thickness is approximately 0.6 to 0.8 mm.
Thus, such a thickness (approximately 2 mm) can not be realized easily by using alumina which is generally used for such a dielectric slab because of technical problems in manufacture. In addition, since the board having a special thickness which can not be observed in the standard size is necessary, the cost for materials is disadvantageously increased.
Therefore, the inventor of this international patent application has obtained the following knowledge by eagerly adding examination in order to apply the above-described “dielectric leaky-wave antenna (double-layer structure)” to communication in a quasi-millimeter wave region such as a 20 GHz band, e.g., wireless access, an indoor wireless LAN and the like, or a low-frequency domain of a millimeter wave.
At first, the important knowledge is that, by providing a “dielectric leaky-wave antenna having a single-layer structure” of a so-called image guide type in which a dielectric slab is laid on a ground plane, the thickness of the dielectric slab can be ½ of the thickness in case of applying the above-described “dielectric leaky-wave antenna (double-layer structure)” to the quasi-millimeter wave region (not more than approximately 1 mm). Therefore, the board having the thickness of approximately 0.6 to 0.8 mm in the standard size can be used.
Another knowledge is that, by providing such a “dielectric leaky-wave antenna having a single-layer structure”, although the entire conductor loss is increased as compared with the case when providing an air layer as in the above-mentioned “dielectric leaky-wave antenna (double-layer structure)”, the conductor loss itself is in proportion to a square-root of a frequency. Therefore, the influence of the conductor loss is relatively small in the quasi-millimeter wave region.
Still another knowledge is that, in such a “dielectric leaky-wave antenna having a single-layer structure”, the antenna structure in which uniform metal strip rows are provided in the transverse direction on the dielectric slab surface or a reflection suppression strip is provided on the same surface is also common to the above-described “dielectric leaky-wave antenna (double-layer structure)”.
DISCLOSURE OF INVENTION
In view of the above-described prior art problems and the knowledg
Hidai Takashi
Kawahara Yuki
Teshirogi Tasuku
Yamamoto Aya
Anritsu Corporation
Frishauf Holtz Goodman & Chick P.C.
Ho Tan
LandOfFree
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