Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-02-28
2002-04-23
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C257S728000
Reexamination Certificate
active
06377141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter device used mainly in a microwave or millimeter wave band and, more particularly, to a distributed constant filter in which various wiring patterns are formed as circuit devices, a method of manufacturing the distributed constant filter, and a distributed constant filter circuit module.
2. Description of the Related Art
In a cellular telephone system such as a portable telephone or car telephone, or a communication system such as a wireless LAN (Local Area Network) using high frequency radio waves in the microwave band or millimeter wave band as carriers, a filter device such as a low pass filter (LPF), high pass filter (HPF), or band pass filter (BPF) is usually designed not as a lumped parameter line or a concentrated constant circuit but as a distributed constant circuit (or a distributed parameter circuit). The lumped parameter line is a circuit in which the physical size of a device as a component of the circuit is sufficiently smaller than the wavelength of an electric signal and which uses chips such as an inductance L and a capacitor C as circuit devices. The distributed constant circuit is constructed by using microstrip lines which will be described hereinlater and uses various wiring patterns each having the length that is about the same as the wavelength of an electric signal as circuit devices.
FIG. 15
shows a plan view of a BPF having microstrip line patterns formed in one plane on a dielectric substrate. The BPF shown in the diagram has a structure such that a plurality of narrow microstrip lines
102
(
1
) to
102
(
5
) made of a conductor such as copper are disposed in parallel so as to be apart from each other at predetermined intervals on a dielectric substrate
101
made of a material such as ceramic. The neighboring microstrip lines are disposed so as to be staggered each other in the longitudinal direction in such a manner that a part of a length, which is about the quarter of a pass wavelength &lgr;, of one of the neighboring microstrip lines overlaps with that of the neighboring microstrip line. The microstrip lines
102
(
1
) to
102
(
5
) can be simultaneously formed in a process of forming a wiring pattern on a wiring board performed by printing or lithography.
In the BPF of the configuration of using such microstrip lines, for example, an RF signal RF
1
supplied from an end of the microstrip line
102
(
1
) passes through the microstrip lines
102
(
1
) to
102
(
4
), during which high frequency components except for a component of the wavelength &lgr; in the RF signal RF
1
are eliminated. Only an RF signal RF
2
of the wavelength of &lgr; is outputted from an end of the microstrip line
102
(
5
). When it is assumed that the wavelength of a radio wave in a space is &lgr;
0
and the effective dielectric constant of the substrate is &egr;w, the pass wavelength &lgr; is given by the following equation (1). By optimizing the pattern of the microstrip lines
102
(
1
) to
102
(
4
), therefore, RF signals in a desired frequency band can be selectively allowed to pass.
&lgr;=&lgr;0/(&egr;
w
)
½
(1)
In recent years, also in the uses of high frequencies, a demand of reducing the size of a device and a substrate has been becoming stronger. In the BPF of the configuration using the microstrip lines shown in
FIG. 15
, however, the length of the pattern of the microstrip line is almost determined by the pass wavelength. Consequently, the reduction in the pattern occupying area is naturally limited and it is difficult to reduce the size of the device and substrate.
For example, as shown in
FIGS. 16 and 17
, what is called a triplate structure filter in which a conductor pattern is not formed in the surface layer of the substrate but a pair of conductor patterns are formed in an inner layer of a substrate having ground conductive layers on both sides has been proposed.
FIG. 16
is a perspective view of the triplate structure filter.
FIG. 17
is a plan view of the filter. As shown in the diagrams, the filter comprises a first substrate
111
a
made of a dielectric, a pair of conductor patterns
115
(
1
) and
115
(
2
) formed on the first substrate, and a second substrate
111
b
made of a dielectric stacked on the first substrate
111
a
so as to sandwich the conductor patterns
115
(
1
) and
115
(
2
). A stacked substrate
111
comprised of the first and second substrates
111
a
and
111
b
is covered with a ground conductive layer
117
connected to the ground except for a pair of side end face areas
113
(
1
) and
113
(
2
).
The conductor pattern
115
(
1
) functions as an input side conductor pattern and has a form in which a relatively wide conductor pattern
115
(
1
)
a
as a low impedance line (hereinbelow, also referred to as a low impedance pattern for short) and a relatively narrow conductor pattern
115
(
1
)
b
as a high impedance line (hereinbelow, also simply referred to as a high impedance pattern for short) are cascade connected. On the other hand, the conductor pattern
115
(
2
) functions as an output side conductor pattern and has a form in which a relatively wide conductor pattern
115
(
2
)
a
and a relatively narrow conductor pattern
115
(
2
)
b
are cascade connected. The conductor patterns
115
(
1
) and
115
(
2
) are disposed at a predetermined interval so as to be in parallel to each other in the longitudinal direction. The narrow conductor patterns
115
(
1
)
b
and
115
(
2
)
b
are respectively connected in their inter mediate parts in the longitudinal direction to an input part pattern
116
(
1
) to which the RF signal RF
1
is supplied and an output part pattern
116
(
2
) from which the RF signal RF
2
filtered in a band is outputted. One end of each of the narrow conductor patterns
115
(
1
)
b
and
115
(
2
)
b
is connected to the ground conductive layer
117
covering one end face of the stacked substrate
111
.
As illustrated in
FIG. 18
, the filter is equivalently expressed in a form in which a parallel resonance circuit PR
1
comprising a capacitor C
1
and an inductance L
1
connected between the input part pattern
116
(
1
) and the ground and a parallel resonance circuit PR
2
comprising a capacitor C
2
and an inductance L
2
connected between the output part pattern
116
(
2
) and the ground are capacitive coupled to each other via a capacitor C
3
.
In the filter, the RF components except for the wavelength &lgr; of the RF signal RF
1
supplied from the end of the input part pattern
116
(
1
) are eliminated through the conductor patterns
115
(
1
) and
115
(
2
) functioning as the parallel resonance circuits PR
1
and PR
2
. Only the RF signal RF
2
of the wavelength &lgr; is outputted from the end of the output part pattern
116
(
2
). According to the filter of the triplate structure, the area occupied by the conductor patterns can be reduced more than the microstrip filter shown in
FIG. 15
, so that the miniaturization of the BPF can be realized.
When the triplate structure filter is allowed to function as an equivalent circuit shown in
FIG. 18
, a filter of a combine type in which a pair of lines (conductor patterns) each having a length of the quarter of the pass wavelength &lgr; are capacitively coupled is usually employed. In the patterns shown in
FIGS. 16 and 17
, by cascade connecting the lines of different impedances, the line overall length La is made shorter than &lgr;/4, thereby realizing the miniaturization. In the following description, a BPF of such a type will be called a shortened combine type distributed constant BPF.
As described above, the BPF using the microstrip lines shown in
FIG. 15
can be formed by one operation as a part of a pattern of the surface layer of a substrate in a wiring process of forming a wiring pattern on the surface layer of a wiring board by printing or lithography. For instance, as shown in
FIG. 19
, line connection between the BPF comprising the microstrip lines
102
(
1
) to
102
(
5
) and circuit chips such as an MMIC (Microwave Mon
Jones Stephen E.
Pascal Robert
Sonnenschein Nath & Rosenthal
Sony Corporation
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