Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-09-18
2002-11-19
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06483465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circularly polarized wave antenna, and particularly, to a circularly polarized wave antenna excited in a higher order mode such as in a DAB (Digital Audio Broadcast) system, and to a manufacturing method therefor.
2. Description of the Related Art
As an antenna excited in a higher order mode, one which is disclosed in Japanese Examined Patent Application Publication No. 07-46762 is known. As shown in
FIGS. 10 and 11
, this antenna has a two-layer structure wherein a microstrip antenna
2
for use in the major mode excitation is placed on a microstrip antenna
1
for use in the higher order mode excitation.
Specifically, in the microstrip antenna
1
for use in the higher order mode excitation, a dielectric substrate
3
having a square shape in a plan view is used, a plan-view circular radiation electrode
4
for use in the higher order mode excitation is formed on the front surface of the substrate, and a ground electrode
5
is provided over the entire back surface of the substrate
3
. On the other hand, in the microstrip antenna
2
for use in the major mode excitation, a disk shaped substrate
6
is used, and a radiation electrode
7
for use in the major mode excitation is formed over the entire circular surface of the substrate
6
, as well as a center pin
8
is disposed along the center axis of the radiation electrode
4
for use in the higher order mode excitation and the radiation electrode
7
for use in the major mode excitation, thereby ensuring the symmetry between the major mode and the higher order mode.
In the microstrip antenna
2
for use in the major mode excitation, probes F
1
and F
2
for use in the major mode excitation are disposed at the angular positions of 90° with respect to the center pin
8
, on the surface of the radiation electrode
7
. These probes are provided so as to pass through the substrates
3
and
6
without contacting the radiation electrode
4
for use in the higher order mode excitation and the ground electrode
5
.
Also, in the microstrip antenna
1
for use in the higher order mode excitation, probes G
10
, G
11
, G
20
, and G
21
for use in the higher order mode excitation are disposed on the 0° and 45° lines passing through the center pin
8
, on the surface of the radiation electrode
4
. Specifically, a pair of probes G
10
and G
11
for use in the first order mode excitation are disposed at the positions symmetrical with each other around the center pin
8
on the line connecting the center pin
8
and the probe F
1
, and a pair of probes G
20
and G
21
are disposed at the positions on the 45° line which divides the angle formed by the probes F
1
and F
2
into equal halves. The probes G
10
, G
11
, G
20
, and G
21
are provided so as to pass through the substrate
3
without contacting the ground electrode
5
.
In the above-described features, when signal powers for the major mode excitation are supplied to the probes F
1
and F
2
for use in the major mode excitation, with a phase difference of 90° provided therebetween using a 90° hybrid or the like, a circularly polarized wave is generated. On the other hand, when in-phase signal powers for the higher order mode excitation are each supplied to the probes G
10
and G
11
, and the probes G
20
and G
21
for use in the higher order mode excitation, and signal powers which have a mutual phase difference of 90° are supplied to the probes G
10
and G
11
, and the probes G
20
and G
21
for use in the higher order mode excitation, a circularly polarized wave in the second order mode (TM
21
mode) is generated.
In the microstrip antenna
1
for use in the higher order mode excitation which has the above-described features, since four probes G
10
, Gil, G
20
, and G
21
for use in the higher order mode excitation are disposed so as to pass through the dielectric substrate
3
, the interference (intercoupling) between the radiation electrode
4
for use in the higher order mode excitation and each of the probes G
10
, G
11
, G
20
, and G
21
easily occurs, so that there may be a case where the matching between resonant frequencies cannot be achieved.
Also, since the dielectric substrate
3
has a square shape in a plan view, the distances between the periphery of the plan-view circular radiation electrode
4
and the edge line of the substrate
3
are mutually different between the two directions of higher order mode excitation, so that the mutual difference in edge effect, in other words, the mutual difference in the capacitance between the periphery of the radiation electrode
4
and the ground electrode occurs between the two directions. Particularly when the dielectric constant of the substrate
3
is high, this difference becomes significant. The difference in the edge effect would cause a difference in the frequency characteristic of linearly polarized waves between the two directions of the higher order mode excitation. This causes a problem in that circularly polarized waves in a higher order mode reduce the bandwidth in the axial ratio-frequency characteristic.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above-described problems, and an object thereof is to provide a circularly polarized wave antenna which allows a superior higher order mode excitation to be achieved, and to provide a manufacturing method for the same which allows various electrodes to be easily formed.
In order to achieve the above-described object, the present invention uses the following configurations to solve the above-described problems. The circularly polarized wave antenna in accordance with the present invention comprises a substantially cylindrical substrate comprising a dielectric body; a radiation electrode having a circular shape in a plan view, the radiation electrode being formed on one main surface of the substrate; a ground electrode formed on the other main surface of the substrate; a flat portion formed by flattening a portion of the peripheral side surface of the substrate; and at least two strip shaped feeding electrodes which are formed on the flat portion so as to extend from the ground electrode side to the radiation electrode side.
In the circularly polarized wave antenna with the above-described features, the main surface of the substrate comprises a perfect circle, and the radiation electrode is formed so as to have a diameter smaller than that of the main surface of the substrate so as to be effective diameter to excite the TMn1 (n≧2, n: natural number) mode which is a higher order mode. The radiation electrode is disposed coaxially with the main surface of the substrate, and the flat portion provided on the substrate is formed as a flat plane parallel to an imaginary plane (hereinafter, referred to the “axial plane”) passing the center axis of the substrate.
The two feeding electrodes are disposed so as to form an angle of 90
° (n≧2, n: natural number) with respect to the center axis of the substrate, and disposed at the positions which form a plane-symmetry with another axial plane perpendicular to the flat plane. When a signal power is supplied to each of the feeding electrodes, two linearly polarized waves which spatially form 90
°, are excited, and by making a phase difference of 90° between the two signal powers, a circularly polarized wave in a higher order mode is radiated.
In the circularly polarized wave antenna in accordance with the present invention, it is preferable that the flat portion be provided with a second electrode in conjunction with the feeding electrodes.
In the present invention, since the two feeding electrodes are disposed at angular positions forming 90
° with respect to the center axis of the substrate, the space between the two feeding electrodes remains blank. A second electrode, therefore, is provided making use of the blank between the two feeding electrodes.
The manufacturing method for a circularly polarized wave antenna in accordance with the present invention comprises the steps of forming a radiation elect
Akiyama Hisashi
Itoh Shigekazu
Kawahata Kazunari
Yuasa Atsuyuki
Ho Tan
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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