Communications: radio wave antennas – Antennas – With lumped reactance for loading antenna
Reexamination Certificate
2002-10-23
2004-09-07
Chen, Shih-Chao (Department: 2821)
Communications: radio wave antennas
Antennas
With lumped reactance for loading antenna
C343S7000MS
Reexamination Certificate
active
06788265
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a top-loading monopole antenna element and, more particularly, to the configuration of a monopole antenna element being low in price and usable in a wide band, for which fine adjustment of input impedance and resonance frequency is easily carried out.
BACKGROUND OF THE INVENTION
Computer networking has been advancing rapidly along with the widespread use of computers such as PCs. Based on this, attention is currently focused on wireless LAN systems that are capable of establishing computer networks without links between computers by a network cable or the like.
Such wireless LAN system includes an antenna element (hereinafter simply referred to as antenna) for sending/receiving data exchanged between computers via radio waves. The antenna is mainly comprised of a circular plate made of conductors such as metals, a printed board including a dielectric board, and a conductive monopole that is joined with the center of the circular plate at one end and with the printed board at the other end.
In the following, a description will be given of the configuration of a conventional antenna element.
FIG. 1
is a perspective view showing the configuration of a conventional antenna element which, for example, sends/receives data using a 2.4 GHz or 5 GHz band.
The antenna shown in
FIG. 1
comprises a circular plate
901
made of conductors such as metals, a monopole
902
that is also made of conductors such as metals, and a printed board
903
. The top of the monopole
902
is joined with the center of the circular plate
901
.
The printed board
903
includes a conductive ground board
904
as an upper layer and a dielectric board
905
as a lower layer. Further, there is arranged a microstrip line
906
made of a conductor under the dielectric board
905
. The ground board
904
is provided with a pattern clearance hole
907
. The lower end of the monopole
902
extends through the pattern clearance hole
907
without touching the ground board
904
, and is joined with the microstrip line
906
by soldering or the like at a power supply point
908
.
Next, a description will be given of the principle of electrical operation of the conventional antenna. FIGS.
2
(
a
) and
2
(
b
) are diagrams showing the current distribution of the conventional antenna. Referring to FIG.
2
(
a
), a current i
0
runs through the monopole
902
. Meanwhile, there are currents i
1
to i
4
flowing in the circular plate
901
. As can be seen in FIG.
2
(
a
), by the use of the circular plate
901
, the original current i
0
is distributed over the circular plate
901
. Accordingly, the antenna can be shortened or lowered.
The currents in the circular plate
901
, which are represented by the four currents i
1
to i
4
as a pattern in FIG.
2
(
a
), flow in all directions from the center of the circular plate
901
. Considering field emissions from these currents, it is readily understood that the current i
0
generates vertical polarized waves being parallel to the current i
0
, which are uniformly radiated in a horizontal plane. Meanwhile, electromagnetic radiations generated from the currents i
1
to i
4
vectorially counteract each other. Thus, it turns out that there is no field radiation having horizontal components.
On the other hand, considering the range of frequencies, the antenna almost invariably resonates at a wavelength resulting from the current running through the length of l
0
and l
1
since the radius of the circular plate
901
, where the currents i
1
to i
4
flow, is invariant. Thus, the conventional antenna exhibits a bandwidth capability equal to or lower than that of monopole antennas having no plate.
FIG. 3
is a graph showing the return loss of the conventional antenna by actual measurement. The antenna has the configuration illustrated in FIG.
1
. The diameter of the circular plate is approximately 6 mm. The distance between the circular plate and the upper surface of the printed board, that is, the length of the monopole except for the part inserted in the printed board is 5.5 mm. In addition, the microstrip line is arbitrarily provided with stubs thereon to carry out adjustment of return loss characteristics. As can be seen in
FIG. 3
, the conventional antenna is operational in a bandwidth of 280 MHz, which constitutes about 5.1% of the frequency spectrum.
In the communication facilities of various nations, frequency assignments for the wireless LAN system are tend to expand because of the convenience or usability of the system. Accordingly, there is need for techniques to produce wideband antennas used in the wireless LAN system.
Additionally, with the popularization of the wireless LAN system, it becomes an important issue for manufacturers to reduce the cost of hardware. Therefore, considerable importance is attached to ideas on the antenna structure for realizing inexpensive antennas.
Besides, adjustments of analog RF characteristics are carried out by necessity at the production inspection section of each manufacturer. Should the adjustments be accomplished in antennas, the direct first run rate (yield ratio) can be improved. As a result, the total cost of the antennas can be reduced.
However, in the configuration of the above-mentioned conventional antenna, a current flows the uniform length of the monopole and the radius of the circular plate. Therefore, the antenna does not resonate at a number of wavelengths.
In addition, while the combination of the monopole and circular plate is created by cutting off them from single piece of substance, by molding, or by soldering after manufacturing them separately, any of the methods entails relatively high manufacturing cost. Moreover, since it is difficult to carry out fine adjustment for antenna part after manufacturing, the direct first run rate (yield ratio) cannot be improved effectively, which precludes the supplies of low cost antennas.
For example, there is described a top-loading antenna in Yasuto Mushiake,“Antennas and Radio Propagation,” pp. 69-70 (Corona Inc.). This type of antenna has a load such as a circular ring at its top. Although the antenna was originally devised for the purpose of keeping an elevation angle of radiation small or reducing high-angle radiation, it also had the effect of shortening or lowering the antenna itself Since the antenna had been used in medium waves with low frequency, the antenna was chiefly aimed at improving the elevation angle of radiation and shortening or lowering its height. Consequently, the uniformity of directivity in a horizontal plane (rotational symmetry), cross-polarized wave characteristics, wideband applicability, and easy adjustment were not taken into consideration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an antenna element being usable in a wider band as compared to the conventional antennas.
It is another object of the present invention to provide an antenna element which is simple in structure and low in price.
It is yet another object of the present invention to provide an antenna element, for which fine adjustment of input impedance and resonance frequency is easily carried out.
In accordance with the first aspect of the present invention, to achieve the above objects, there is provided an antenna element comprising: a top plate; a printed board; and a monopole that is joined with the top plate at one end and with the printed board at the other end in such a manner as to hold the top plate in a fixed posture toward the printed board; wherein, the top plate is symmetrical with respect to two orthogonal axes which are perpendicular to the thickness of the top plate and passing through the center of the area of the top plate; and the lengths of the axes are different from each other.
In accordance with the second aspect of the present invention, in the first aspect, the top plate has an elliptical shape.
In accordance with the third aspect of the present invention, in the first aspect, the top plate has a shape selected from polygons including rectangle, rhombus
Chen Shih-Chao
Foley & Lardner LLP
NEC Corporation
LandOfFree
Antenna element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Antenna element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Antenna element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3262066