Wave transmission lines and networks – Miscellaneous – Multipactor applications
Reexamination Certificate
2000-03-10
2004-05-25
Lee, Benny T. (Department: 2817)
Wave transmission lines and networks
Miscellaneous
Multipactor applications
C333S204000, C333S246000
Reexamination Certificate
active
06741142
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-frequency circuit element, such as a filter, etc., used for a high-frequency signal processor in communication systems, etc.
BACKGROUND OF THE INVENTION
In high-frequency communication systems, a high-frequency circuit element such as a filter, a branching filter, or the like, is an essential component. Many of conventional high-frequency circuit elements, such as resonator filters, etc. have a structure that is electromagnetically shielded by enclosing a resonator in a metal box in order to prevent the radiation of electromagnetic field energy and the entrance of electromagnetic noise from the outside.
FIGS. 7 and 8
respectively show one example of a conventional high-frequency circuit element using a transmission line structure. In
FIG. 7
, a box lid
81
shown in
FIG. 8
is omitted so that the internal structure of the box of the high-frequency circuit element can be seen.
As shown in
FIG. 8
, in the conventional high-frequency circuit element, &lgr;/2 resonators
86
a
,
86
b
,
86
c
,
86
d
of a strip conductor pattern and input/output lines
87
a
,
87
b
are formed on the surface of the subtrate
85
made of dielectric monocrystal, or the like. The high-frequency circuit having a microstrip structure is fabricated from &lgr;/2 resonators
86
a
,
86
b
,
86
c
,
86
d
, input/output lines
87
a
,
87
b
and a ground plane
88
. This high-frequency circuit includes four coupled &lgr;/2 resonators and functions as a four-stage band pass filter.
The box of the high-frequency circuit element is formed of a conductor material and includes, as shown in
FIG. 8
, a box frame
82
(also see
FIG. 7
) and a box bottom
83
(also see FIG.
7
). A substrate
85
(see
FIG. 7
) is fixed to the box bottom
83
with, for example, conductive adhesives so that the box is electrically connected to the ground plane
88
.
On the side face of the box frame
82
, input/output terminals
84
a
,
84
b
(also see
FIG. 7
) having a coaxial connector are placed. Inner conductors of the input/output terminals
84
a
,
84
b
are electrically connected to the input/output lines
87
a
,
87
b
and outer conductors of the input/output terminals
84
a
,
84
b
are electrically connected to the box, respectively.
FIGS. 9 and 10
respectively show another example of a conventional high-frequency circuit element using a strip conductor pattern. Also in
FIG. 97
, a box lid
81
shown in
FIG. 10
is omitted so that the internal structure of the box of the high-frequency circuit element can be seen. In the configuration shown in
FIG. 10
, eight hairpin resonators
89
a
,
89
b
,
89
c
,
89
d
,
89
e
,
89
f
,
98
g
,
86
h
are used so as to form an eigth-stage band pass filter. The structure of the other parts is the same as the conventional high-frequency circuit element shown in
FIGS. 7 and 8
and will not be further described.
When inputting a high-frequency signal from, for example, the input/output terminal
84
a
in the conventional high-frequency circuit elements having the structure mentioned above, as shown in
FIG. 11
, electromagnetic waves in a quasi-TEM mode, i.e. a fundamental mode propagate through the input/output line
87
a
that is a microstrip conductor transmission line.
FIG. 11
is a cross-sectional view showing the box, which is cut along the plane perpendicular to the input/output line
87
a
.
FIG. 11
schematically shows the directions of the electric fields based on the analysis results of a three-dimensional electromagnetic field simulation (HFSS manufactured by Hewlett Packard Company).
The electromagnetic waves in the quasi-TEM mode propagating though the input/output line
87
a
cause resonance phenomena in each resonator
86
a
-
86
d
or
89
a
-
89
h
, thus functioning as a band pass filter. Therefore, only an in-band signal of the filter passes through between the input/output lines
87
a
and
87
b
and is output therefrom.
However, in the conventional high-frequency circuit element mentioned above, not only the quasi-TEM mode in which electromagnetic waves propagate through the strip conductor transmission line is excited, but also a waveguide mode is excited due to discontinuity in the converting part from the input/output terminals
84
a
,
84
b
to the input/output lines
87
a
,
87
b
, as well as due to the component of the radiation electric field caused by the quasi-TEM mode, as shown in FIG.
12
. The wave guide mode is an unwanted higher-order mode, in which electromagnetic waves propagate through the space between the box lid
81
and the substrate
85
. As a result, the frequency characteristic of the high-frequency circuit element is adversely affected. Similarly to
FIG. 11
,
FIG. 12
is a cross-sectional view showing the box, which is cut along the plane perpendicular to the input/output line
87
a
, and illustrating the analysis result of the three-dimensional electromagnetic field simulation.
Unlike the quasi-TEM mode, since such a waveguide mode is not under the influence of the filter function, electromagnetic waves propagate in regardless of the passband of the filter, thus deteriorating the characteristic of the high-frequency circuit element as a filter. Particularly, there arise some problems, for example, the decrease in attenuation in a rejection band, i.e., the increase in the background level, the deterioration of capability of rejecting out-of-band signals of the filter.
In order to reduce the influence of the waveguide mode (unwanted higher-order mode), the box may be designed so that the cutoff frequency in the space between the box lid
81
and the substrate
85
is set to be sufficiently higher than the center frequency of the filter. However, great attenuation, for example, −80 dB or less is required in the rejection band and so the propagation of only a few high-frequency signals may cause a problem. Consequently, a solution only by designing the box taking into account the cutoff frequency is not sufficient.
Such a problem becomes further significant when it is necessary to miniaturize a high-frequency circuit element, to increase an operation frequency or to use a material such as a superconductive conductor having a large conductivity, in order to reduce a loss.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems of the prior art mentioned above. That is, the object of the present invention is to provide a high performance high-frequency circuit element capable of suppressing the generation of an unwanted higher-order mode in the space inside the metal box of the high-frequency circuit element and having an excellent frequency characteristic.
In a basic configuration, a high-frequency circuit element according to the present invention includes a substrate, a high-frequency circuit formed on the substrate, a metal box electromagnetically shielding the high-frequency circuit by enclosing the substrate, an input/output terminal placed on the metal box and inputting/outputting a high-frequency signal to/from the high-frequency circuit, and at least one shielding element for interrupting an unwanted higher-order mode by suppressing the propagation of high frequency waves between the input-output terminals.
In a first specific configuration, a high-frequency circuit element according to the present invention includes a substrate, a high-frequency circuit formed on the substrate, a metal box electromagnetically shielding the high-frequency circuit by enclosing the substrate, an input/output terminal placed on the metal box and inputting/outputting a high-frequency signal to/from the high-frequency circuit, and at least one plate for interrupting an unwanted higher-order mode substantially dividing an internal space of the metal box and cutting off the propagation path for the high-frequency waves in the internal space of the metal box.
According to such a configuration, having the plate for interrupting an unwanted higher-order mode, it is made possible to suppress the propagation of the electromagnetic waves in a waveguide mode gene
Enokihara Akira
Okazaki Yasunao
Setsune Kentaro
Lee Benny T.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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