Wave transmission lines and networks – Long lines – Strip type
Reexamination Certificate
2002-01-29
2004-09-28
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Long lines
Strip type
C333S219000, C333S204000
Reexamination Certificate
active
06798320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microstrip line, a resonator element, a filter, and a high-frequency circuit that utilize the microstrip line, and to an electronic circuit, circuit module, and communications device that utilize the resonator device, filter, and high-frequency circuit.
2. Description of the Related Art
In small electronic devices having microwave or milliwave circuitry, a microstrip line, as shown in
FIG. 23
, is generally used as a transmission line for transmitting signals having frequencies in the microwave or milliwave band.
FIG. 23
shows a portion of a microstrip line
1
that includes a dielectric substrate
2
, a ground electrode
4
provided on the back
3
of the dielectric substrate
2
, and a flat line electrode
6
provided on the front
5
of the dielectric substrate
2
.
It is well-known that most of the line transmission loss in the microstrip line
1
is conductor loss attributable to the concentration of current at the edges
7
and
8
of the line electrode
6
, and that an “edge effect” exists (R. A. Pucel, “Losses in Microstrip,” IEEE Trans. on MTT, Vol. MTT-16, June 1968, pp. 342-350). Conductor loss is greater when the line electrode
6
is narrow. Consequently, it is difficult to produce an electronic circuit having highly integrated microstrip lines
1
and very narrow line electrodes
6
.
An effective way to improve this situation is to increase the thickness of the line electrode
6
and to reduce the current density at the edges
7
and
8
of the line electrode
6
.
FIGS. 24A and 24B
are graphs of the transmission characteristics (calculated) for the microstrip line
1
when the thickness of the line electrode
6
is varied. In
FIG. 24A
, Qo is the resonance when the microstrip line
1
is cut to a specific length and made into a resonator. The value of Qo increases as the conductor loss of the line electrode
6
decreases. In
FIG. 24B
, Zo is the characteristic impedance of the microstrip line
1
, and K
off
is the effective dielectric constant of the dielectric substrate
2
.
The microstrip line
1
used in the calculation of transmission characteristics for
FIGS. 24A and 24B
was configured such that the dielectric constant of the dielectric substrate
2
was
38
, the thickness of the dielectric substrate
2
was 300 &mgr;m, and the width of the line electrode
6
was 20 &mgr;m. As is clear from
FIGS. 24A and 24B
, when the thickness of the line electrode
6
is varied over a range of 1 &mgr;m to 25 &mgr;m, the characteristic impedance Zo and the effective dielectric constant Keff changes very little. In contrast, the Qo value increases in proportion to the thickness of the line electrode
6
, which indicates that the conductor loss decreases.
A problem, however, is that when the thickness of the line electrode
6
is increased, the precision of the electrode pattern of the electronic circuit decreases. Consequently, there have been attempts at decreasing the edge-effect without increasing the thickness of the line electrode
6
. The following is a conventional example of such attempts.
The microstrip line shown in
FIG. 25
is discussed in “Multilayered MMIC, V-Groove Microstrip Line Characteristics,” by Hasegawa et al., 1990 Electronic Information Communications Society, National Fall Conference, lecture C-55. A microstrip line
10
has a V-shaped groove
13
provided on the front
12
of a dielectric substrate
11
, and a V-shaped line electrode
14
having a crease
15
is provided in the middle of this groove
13
. As a result, the electric field is concentrated between the V-shaped lower end portion of the line electrode
14
and a ground electrode
16
provided on the back of the dielectric substrate
11
, thereby reducing the concentration of current at the edges
17
and
18
of the line electrode
14
.
Japanese Laid-Open Patent Application 10-313203 discloses a microstrip line in which a groove is provided in a dielectric substrate to reduce the transmission loss of high-frequency signals. As shown in
FIG. 26
, this microstrip line
20
is designed such that a flat line electrode
23
is provided on the front
22
of a dielectric substrate
21
, a V-shaped groove
25
is provided on the back
24
of the dielectric substrate
21
at a location across from the line electrode
23
, and a ground electrode
26
is provided to include the groove
25
. With this configuration, an electric field is concentrated between the line electrode
23
and the ground electrode
26
in the V-shaped portion
27
of the ground electrode
26
, which reduces the concentration of current at the edges
28
and
29
of the line electrode
23
.
Furthermore, Japanese Laid-Open Patent Application 8-288463 discloses a microstrip line in which the transmission loss of the line is decreased by utilizing a skin effect. As shown in
FIG. 27
, this microstrip line
30
includes a ground electrode
33
provided on the back
32
of a dielectric substrate
31
, and a line electrode
38
provided on the front
34
of the dielectric substrate
31
, on the sides
35
and
36
of the line electrode
38
a plurality of grooves
37
are provided. This expands the surface area of the sides
35
and
36
of the line electrode
38
, thereby increasing surface current at the sides
35
and
36
and reducing transmission loss.
Nevertheless, with the microstrip line
10
in
FIG. 25
, it is difficult to form the V-shaped groove
13
with high precision in the dielectric substrate
11
, and with the microstrip line
20
in
FIG. 26
, it is difficult to machine the V-shaped groove
25
with high precision in the dielectric substrate
21
. Moreover, the configurations of these microstrip lines
10
and
20
do not provide the benefit of greatly increasing the Qo value of the microstrip line. With the microstrip line
30
in
FIG. 27
, the method of forming the line electrode
38
is complicated and the manufacturing costs are high.
SUMMARY OF THE INVENTION
To overcome the above-described problems, preferred embodiments of the present invention provide a microstrip line that reduces the edge effect of the line electrode, a high frequency circuit and a resonator device including the microstrip line that reduces the edge effect of the line electrode, a filter including the resonator device, an electronic circuit constituted including this filter, a circuit module including this electronic circuit, and a communications device including these devices.
A microstrip line according to a second preferred embodiment includes a dielectric substrate, a ground electrode provided on the back of the dielectric substrate, and a line electrode provided on the front of the dielectric substrate, and edge electrodes provided at the edges on both sides of the line electrode. The edge electrodes extend in a direction that is substantially perpendicular to the front of the dielectric substrate.
With the microstrip line according to the second preferred embodiment, the reduction in transmission loss in the microstrip line is proportional to the height of the edge electrodes. However, when short edge electrodes are provided on the line electrode, the line electrode and edge electrodes can be provided with high precision using thin film forming methods.
A microstrip line according to a third preferred embodiment includes a dielectric substrate, a ground electrode provided on the back of the dielectric substrate, and a line electrode provided on the front of the dielectric substrate, and edge electrodes provided at the edges on both sides of the line electrode. The edge electrodes are preferably arranged at an angle with respect to the front of the dielectric substrate.
With the microstrip line according to the third preferred embodiment, even though the edge electrodes are arranged at an angle to the front of the dielectric substrate over their entire length, there is a reduction in the conductor loss of the microstrip line, corresponding to the length from the front of the dielectric substrate to the tops of the edge electrodes,
Chikagawa Osamu
Ida Yutaka
Ieki Tsutomu
Tanaka Hiroaki
Yagi Yoshikazu
Keating & Bennett LLP
Lee Benny
Murata Manufacturing Co. Ltd.
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