Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-05-30
2004-01-13
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06677902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circularly polarized antenna apparatus and a radio communication apparatus including the same.
2. Description of the Related Art
Recent radio communication apparatuses using circularly polarized waves, such as GPS (Global Positioning System) or DAB (Digital Audio Broadcast) systems, for use in mobile vehicles such as automobiles and ships, have incorporated a compact circularly polarized antenna apparatus, as described in Japanese Unexamined Patent Application Publication No. 2000-183637. This type of antenna apparatus is shown in FIG.
10
.
In the antenna apparatus shown in
FIG. 10
, a rectangular radiating electrode
4
having degeneracy-splitting elements
3
is provided on a first principal surface
2
of a solid rectangular substrate
1
, and a ground electrode (not shown) is provided on a second principal surface
5
of the substrate
1
. A strip feeding electrode
7
is provided on a side surface
6
of the substrate
1
so as to extend to the first principal surface
2
from the second principal surface
5
of the substrate
1
. Wide capacitor electrodes
8
, which are connected to the ground electrode, are provided at both sides of the feeding electrode
7
. These components define a more compact antenna apparatus.
In this antenna apparatus, the length of each edge of the radiating electrode
4
is equal to one half the effective wavelength &lgr;, that is, &lgr;/2, of an electromagnetic wave to be radiated. The leading edge of the feeding electrode
7
wraps around to the first principal surface
2
so as to face the center portion of one edge of the radiating electrode
4
with a gap therebetween, such that the feeding electrode
7
is capacitively coupled with the radiating electrode
4
. The degeneracy-splitting elements
3
are formed by cutting out the opposing corners of the radiating electrode
4
along a diagonal such that there is a difference between the diagonal electrical lengths of the radiating electrode
4
.
With this structure, when signal power is supplied to the feeding electrode
7
, two resonant currents which are out of phase by 90° are excited along the perpendicular diagonals of the radiating electrode
4
. The two resonant currents provide excitation sources from which two spatially perpendicular electromagnetic waves having different frequencies radiate in a direction that is perpendicular to the feeding electrode
7
.
In the aforementioned antenna apparatus, in order to reduce the dimensions, the capacitance of the capacitor electrode
8
is increased, while the area of the radiating electrode
4
provided on the first principal surface
2
is reduced. As a result, inevitably, the two resonant currents excited in the radiating electrode
4
flow in the radiating electrode
4
having a small area. Thus, even if the signal power supplied to the feeding electrode
7
increases to provide a high electric field strength for the electromagnetic waves to be radiated, the conductor loss of the radiating electrode
4
increases, which leads to a decrease in antenna gain.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a compact circularly polarized antenna apparatus which achieves high antenna gain, and a radio communication apparatus including the novel circularly polarized antenna apparatus.
One preferred embodiment of the present invention provides a circularly polarized antenna apparatus including a dielectric or magnetic substrate having a first principal surface, a second principal surface, and side surfaces, a radiating electrode provided on the substrate, a ground electrode provided on the second principal surface of the substrate, a feeding element for feeding excitation power to the radiating electrode, and a degeneracy-splitting element which causes two resonant currents to be excited in the radiating electrode, the two resonant current being split between degenerate modes. The radiating electrode is defined by a primary radiating electrode and secondary radiating electrodes, the primary radiating electrode is provided on the first principal surface of the substrate, and the secondary radiating electrodes are provided on the side surfaces of the substrate so as to connect to the primary radiating electrode, each secondary radiating electrode having substantially the same width as the primary radiating electrode.
The radiating electrode extends from the first principal surface to the side surfaces, and the area of the radiating electrode is increased at least by the area of the secondary radiating electrodes compared to the case where the radiating electrode is provided only on the first principal surface. This elongates the paths of the two resonant currents excited in the radiating electrode, thereby reducing the conductor loss of the primary radiating electrode. Moreover, since the area of the radiating electrode is increased, the size of the substrate is reduced, thus providing a compact antenna apparatus.
The degeneracy-splitting elements allow a difference between the electrical lengths along diagonals of the radiating electrode including the secondary radiating electrodes, thus causing two resonant currents to be excited along diagonals of the radiating electrode when signal power is supplied to the radiating electrode from the feeding element. The length of each edge of the radiating electrode preferably is substantially one half the effective wavelength of an electromagnetic wave to be radiated, although the secondary radiating electrodes are provided on the side surfaces of the substrate. This causes the two resonant currents which are out of phase with each other by 90° to flow in a substantially perpendicular manner.
Accordingly, the radiating electrode is provided on a first principal surface and on side surfaces of the substrate, thus achieving a compact circularly polarized antenna apparatus having a greatly reduced conductor loss of the primary radiating electrode with an increase in antenna gain.
The substrate preferably has a substantially rectangular shape with a first principal surface, a second principal surface, and four side surfaces. The primary radiating electrode of the radiating electrode is provided on the first principal surface of the substrate, and the secondary radiating electrodes of the radiating electrode are provided on two opposing side surfaces of the substrate.
The radiating electrode extends from the first principal surface to the two side surfaces, and the area of the radiating electrode is increased by the area of the secondary radiating electrodes provided on the two side surfaces in addition to the primary radiating electrode provided on the first principal surface. This elongates the diagonal electrical paths from the corners of one side surface to the corners of the other side surface, thereby reducing the conductor loss of the primary radiating electrode from which electromagnetic waves primarily radiate. Moreover, while the secondary radiating electrodes are provided on two side surfaces of the substrate, no secondary radiating electrode is provided on the other side surfaces of the substrate, such that there is no influence on the electric field strength of an electromagnetic wave to be radiated.
Accordingly, the radiating electrode is provided on a first principal surface and on two opposing side surfaces of the substrate, thus increasing the length of the paths of the two resonant currents excited in the radiating electrode. The secondary radiating electrodes are provided only on the two opposing side surfaces, thus achieving a compact circularly polarized antenna apparatus without interfering with the radiation of electromagnetic waves.
The degeneracy-splitting element preferably includes two capacitor electrodes having different lengths on the side surface of the substrate on which each of the secondary radiating electrodes is provided, each capacitor electrode having one end connected to the ground electrode, the capa
Akiyama Hisashi
Ito Shigehazu
Kawahata Kazunari
Keating & Bennett LLP
Le Hoang-anh
Murata Manufacturing Co. Ltd.
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