Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2003-01-08
2004-08-24
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S033000, C333S109000, C333S185000, C333S212000, C333S219100
Reexamination Certificate
active
06781476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter having a directional coupler for use in microwave communication, and more particularly to a filter containing a directional coupler therein, a composite filter device and a communication device each including the same.
2. Description of the Related Art
Generally, a filter is disposed at the first stage in a communication device, and to check the operation of the communication device, a directional coupler is provided.
FIG. 1
is a block diagram of such a communication device such as a portable telephone or the like.
Referring to
FIG. 1
, a power amplifier power-amplifies a transmission signal, and a low-pass filter attenuates the higher harmonics of the signal. A directional coupler outputs a part of the transmission signal to the antenna transmission power monitor. The antenna transmission power monitor detects the input signal and adjusts the output of the power amplifier, which is transmitted to the antenna via the directional coupler. Thus, the output of the antenna to be radiated externally is continuously stabilized.
Such methods of designing filters for use in microwave communication as described above are known. For example, a low-pass filter using a coaxial line, a comb line filter, a waveguide filter, and so forth are described in: Matthaei and others, “Microwave Filters, Impedance-Matching and Networks, and Coupling Structure”, Artech House Co. Moreover, methods of designing a low-pass filter and a band-pass filter using microstrip lines are described in Konishi, “Design and Application of Filter Circuit for Communication”, Sougou-Denshi Shuppan (1994).
FIGS. 2 and 3
show typical low-pass filters produced by the above-mentioned methods.
FIG. 2
is an exploded perspective view of a low-pass filter using a coaxial line.
FIG. 3
is a perspective view of a microstrip type low-pass filter.
The low-pass filter shown in
FIG. 2
comprises an inner conductor
103
arranged in an outer conductor
104
. The inner conductor
103
comprises high impedance portions
101
and low impedance portions
102
alternately connected to each other. In each high impedance portion
101
, the size of a plane perpendicular to the signal propagation direction is small and the axial length is large. In each low impedance potion
102
, the size of a plane perpendicular to the signal propagation direction is large and the axial length is small.
The low-pass filter shown in
FIG. 3
contains a line electrode
107
formed on the front surface of a dielectric substrate
108
and a ground electrode
109
formed on the back surface of the dielectric substrate
108
. The line electrode
107
comprises high impedance portions
105
and low impedance portions
106
which are alternately arranged. For each high impedance portion
105
, the width with respect to the signal propagation direction is small, and the length is large. For each low impedance portion
106
, the width is large, and the length is small.
Since the high impedance portions and the low impedance portions are alternately arranged as described above, the high and low impedance portions function as inductors and capacitors, respectively.
FIG. 4
is an equivalent circuit diagram of the above-described low-pass filter. Thus, the low-pass filter comprising a multi-stage LC ladder circuit is formed.
Techniques for designing directional couplers are described in “Microwave Circuit for Communication”, The Institute of Electronics, Information, and Communication Engineers (1981).
FIGS. 5 and 6
show well-known typical structures of the couplers.
FIG. 5
is a schematic view of a hybrid circuit.
FIG. 6
is a schematic view of a transverse coupling type directional coupler.
In the hybrid circuit shown in
FIG. 5
, a main line
111
is formed on the front surface of a dielectric substrate
110
, and a ground electrode
112
is formed on the opposite surface of the substrate
110
. The lengths of the line portions
111
a
to
111
d
of the main line
111
are set to be equal to a quarter of the wavelength of a transmission signal, respectively, so that the characteristic impedances of the respective lines can be matched with each other.
Moreover, the transverse coupling type directional coupler shown in
FIG. 6
contains a distributed coupling line in which a main line
114
a
and a coupling line
114
b
adjacent to the main line
114
a
are formed on the front surface of a dielectric substrate
113
which has a ground electrode
115
formed on the back surface thereof. The smaller the line length of the coupling portion becomes, the more the directivity decreases. A superior directivity can be attained by setting the line length at a quarter of the wavelength of a transmission signal.
It is generally known that to increase the width of the frequency band in which the directivity can be attained, line conductors in a coupling portion have a multistage structure.
FIG. 7
shows a transverse coupling type directional coupler having the above-described multistage structure. In
FIG. 7
, a dielectric substrate
116
, a main line
117
a
, a coupling line
117
b
, and a ground electrode
118
are shown.
For the transverse coupling type directional coupler, the coupling degree has a limitation since the size is regulated. Thus, according to the structure shown in
FIGS. 8A and 8B
, coupling degree adjusting conductors
121
a
and
121
b
are arranged on a coupling portion so as to sandwich a dielectric. In
FIGS. 8A and 8B
, a dielectric substrate
119
, a main line
120
a
, a coupling line
120
b
, and a ground electrode
122
are shown. The first layer formed on the dielectric substrate
119
is the same as the circuit shown in FIG.
6
.
Communication devices provided with the above described filters and directional couplers still have the following problems.
In particular, a filter and a directional coupler are separately formed in the prior art communication devices. Thus, the size of the device is increased. Moreover, since a signal is transmitted via the two elements, the number of sites in which loss is generated when a signal passes the sites is increased. Thus, as a whole, the transmission loss is increased.
To solve the above-described problem, a method for forming a filter and a directional coupler on the same substrate or in the same case has been devised and disclosed.
Examples of such method are disclosed in Japanese Unexamined Patent Application Publication No. 6-120708, Japanese Unexamined Patent Application Publication No. 9-270732, Japanese Unexamined Patent Application Publication No. 11-220312, and Japanese Unexamined Patent Application Publication No. 2001-94315.
As described in Japanese Unexamined Patent Application Publication No. 6-120708, resonators constituting a filter and input-output terminals are connected to lines, respectively. A coupling line is formed adjacent to the 4 transmission lines to produce a directional coupler.
According to Japanese Unexamined Patent Application Publication No. 9-270732, a coupling line is arranged adjacent to a transmission line which constitutes a band-pass filter, formed on a dielectric substrate, as a demultiplexer, whereby a directional coupler is formed.
According to Japanese Unexamined Patent Application Publication No. 11-220312, a coupling line is arranged in the position where the line is to be coupled to the coil pattern portion of a low pass filter which is made of inner electrodes in a laminated multi-layer substrate, and is coupled to the coil pattern portion, whereby a directional coupler is formed.
According to Japanese Unexamined Patent Application Publication No. 2001-94315, a directional coupler comprises two coupling lines adjacent to each other. Lines which function as capacitors are arranged at both the ends of a main line of the coupling lines, so that the main line operates as an inductor. Thus, a low-pass filter is formed.
In the case of these integral devices comprising the directional couplers and the filters, a coupling line is arranged so as to be coupled to a transm
Ito Hiromitsu
Takei Yasunori
Tsunoda Kikuo
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
Pascal Robert
Takaoka Dean
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