Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-01-20
2002-08-06
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S177000, C333S185000, C333S202000
Reexamination Certificate
active
06429753
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high-frequency filters, complex electronic components using the filters, portable radio apparatuses using the filters or the components, and a frequency adjustment method for a high frequency filter and more particularly, to a high-frequency filter formed of a plurality of transmission lines side-coupled in a plurality of stages, a complex electronic component using the filter, a portable radio apparatus using the filter or the electronic component, and a frequency adjustment method for a high frequency filter.
2. Description of the Related Art
In recent years, compact, high-performance portable radio apparatuses have been increasingly developed in the mobile communication field. To this end, a high-frequency circuit needs to have higher performance. Among high-frequency circuits, a high-frequency filter, which has a great effect on the performance of a portable radio apparatus, is strongly required to be made compact and to have higher performance. A conventional side-coupled high-frequency filter using a transmission line will be described below.
FIG. 12
is a block diagram of a conventional side-coupled high-frequency filter. A high-frequency filter
50
serving as a bandpass filter has three transmission lines SL
51
to SL
53
which are side-coupled in three stages. The transmission lines SL
51
to SL
53
are connected in parallel to capacitors C
51
to C
53
for parallel resonance, respectively. One end of the transmission line SL
51
is connected to an input terminal Pi through an input capacitor C
54
. One end of the transmission line SL
53
is connected to an output terminal Po through an output capacitor C
55
. The other ends of the transmission lines SL
51
and SL
53
and one end of the transmission line SL
52
are connected to the ground.
In the above conventional high-frequency filter, however, as shown in
FIG. 13
, the frequency characteristic is gentle at both sides of the center frequency, no pole exists at both sides of the center frequency, and attenuation is insufficient in the vicinity of the center frequency.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems. Accordingly, it is an object of the present invention to provide a high-frequency filter having a pole at either the higher-frequency or lower-frequency side of the center frequency and sufficient attenuation in its frequency characteristic, a complex electronic component using the filter, a portable radio apparatus using the filter or the electronic component, and a frequency adjustment method for a high frequency filter.
To solve the foregoing problems, the present invention provides a high-frequency filter including: a plurality of transmission lines side-coupled in a plurality of stages; capacitors for parallel resonance respectively connected in parallel to the plurality of transmission lines, an input terminal connected through an input capacitor to one end of an input transmission line among the plurality of transmission lines; an output terminal connected through an output capacitor to one end of an output transmission line among the plurality of transmission lines; and an inductor for forming a pole provided between the ground and the connection point where the other end of the input transmission line is connected to the other end of the output transmission line.
According to the above high-frequency filter, since the other end of the input transmission line is connected to the other end of the output transmission line and the inductor for forming a pole is provided between the connection point and the ground, a pole is formed at the higher-frequency or lower-frequency side of the center frequency and sufficient attenuation is ensured.
The present invention also provides a high-frequency filter including: a plurality of transmission lines side-coupled in a plurality of stages; an input terminal connected to one end of an input transmission line among the plurality of transmission lines; and an output terminal connected to one end of an output transmission line among the plurality of transmission lines, wherein the other end of the input transmission line is connected to the other end of the output transmission line to form a closed circuit including the plurality of transmission lines between the input transmission line and the output transmission line; and the connection point between the other end of the input transmission line and the other end of the output transmission line is connected to the ground through an inductor for forming a pole.
According to the above high-frequency filter, since the other end of the input transmission line is connected to the other end of the output transmission line to form the closed circuit between the input transmission line and the output transmission line, and the connection point between the other end of the input transmission line and the other end of the output transmission line is connected to the ground through the inductor for forming a pole, due to a current flowing through the closed circuit, a pole is formed at the higher-frequency or lower-frequency side of the center frequency and sufficient attenuation is ensured.
The magnitude of the current flowing through the closed circuit can be changed by changing the inductance of the inductor for forming a pole. Therefore, since the frequency at the pole can be adjusted by the magnitude of the current flowing through the closed circuit, the attenuation at the pole at the higher-frequency or lower-frequency side of the center frequency and the position where the pole is formed can be easily changed.
The above high-frequency filter may be configured such that it includes a dielectric substrate formed of a plurality of dielectric layers; the transmission lines, the capacitors for parallel resonance, the input capacitor, the output capacitor, and the inductor for forming a pole are formed inside the dielectric substrate; and the input terminal and the output terminal are formed on a surface of the dielectric substrate.
According to this structure, since the high-frequency filter is formed of the dielectric substrate, the transmission lines, the capacitors for parallel resonance, the input capacitor, the output capacitor, and the inductor for forming a pole of the high-frequency filter can be built in the dielectric substrate. Therefore, the high-frequency filter can be made compact.
The above high-frequency filter may be configured such that the inductor for forming a pole is formed of a via-hole electrode connecting a connection electrode, which connects the other end of the input transmission line to the other end of the output transmission line formed inside the dielectric substrate, to the ground electrode formed inside the dielectric substrate.
According to this structure, since the inductor for forming a pole is formed of the via-hole electrode connecting the connection electrode, which connects the end of the input transmission line to the end of the output transmission line formed inside the dielectric substrate, to the ground electrode formed inside the dielectric substrate, the inductance of the inductor for forming a pole can be easily specified in the design stage by adjusting the length or the diameter of the via-hole electrode. Therefore, the attenuation at the pole at the higher-frequency or lower-frequency side of the center frequency and the position where the pole is formed can be easily changed in the design stage.
The above high-frequency filter may be configured such that the dielectric substrate includes first to fifth dielectric layers; the transmission lines are formed of the ground electrode formed on the upper surface of the first dielectric layer and coil electrodes formed on the upper surface of the second dielectric layer; the inductor for forming a pole is formed of a via-hole electrode passing through the second dielectric layer; the input capacitor and the output capacitor are formed of first capacitor electrodes provided for the upper surface
Bando Tomoya
Mandai Harufumi
Shimada Norihiro
Tonegawa Ken
Tsuru Teruhisa
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
Summons Barbara
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