Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-04-28
2002-04-16
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S202000, C333S206000
Reexamination Certificate
active
06373352
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a duplexer using a dielectric block and, more particularly, to a duplexer with stepped impedance resonators.
BACKGROUND ART
Recently, in radio communication systems, transmitting frequency and receiving frequency have been used in a similar band for improving usefulness of frequency. For high frequency circuits of these communication systems, transmit-receive branching filters have been widely used.
A duplexer, which is one of these transmit-receive branching filters, must have the excellent attenuation characteristics at receiving and transmitting terminals. The transmitting filter needs the excellent attenuation characteristics in the frequency band (receiving frequency band) higher than the pass band, but the receiving filter needs the excellent attenuation characteristic in the frequency band (transmitting frequency band) lower than the pass band. Further, with the miniaturization of the communication systems, small-sized and light dudlexers are required.
A conventional duplexer using a dielectric block is shown in
FIG. 1
, wherein the conventional duplexer is formed by an integrated structure having a dielectric block
100
and a plurality of resonators
111
to
120
formed therein. In
FIG. 1
, the duplexer has four resonators
111
to
114
for transmitting filters, five resonators
115
to
119
for receiving filters, and one resonator
120
for a branch circuit separating transmission signals from receiving signals.
The dielectric block
100
includes apertures corresponding to the resonators
111
to
120
and the apertures extending from one surface, that is, a top surface, to an opposite (bottom) surface, are arranged in a line in parallel with each other. All the surfaces of the dielectric block
100
, except the top surface thereof, and inner surfaces of the apertures are coated with a conductive film. Then, the bottom surface of the dielectric block
100
acts as a shorted portion connected to a ground voltage level and the top surface thereof forms an open ended portion and then the aperture acts as a resonator of ¼ wavelength. Also, This resonator is the UIR (uniform impedance resonator) having the same impedance in the open ended portion and the shorted portion.
Conductive rods
131
and
141
for input and output terminals are inserted into the apertures of the first and last resonators
111
and
119
, respectively, and dielectric materials
132
and
142
for a capacitive coupling are formed between the conductive film formed on the inner surfaces of the apertures and the conductive rods
131
and
141
. At an antenna terminal
121
, the resonator
120
is used as a branch circuit for the impedance matching in the transmitting terminal and the receiving terminal. Accordingly, an input signal, which is input into the filter of the transmitting terminal, is not transmitted to the receiving terminal but the antenna terminal
121
and an input signal from the antenna terminal
121
is not transmitted to the transmitting terminal but the receiving terminal.
In the above duplexer, the coupling between the resonators is accomplished by a single coupling line in which admittance in the odd and even modes of the open ended portion and the shorted portion is constant and, except the top surface of the dielectric block, all the surfaces thereof are coated with a conductive film.
Shown in
FIG. 3
is an insertion loss characteristic graph at transmitting and receiving terminals using the duplexer of FIG.
1
. As shown in
FIG. 3
, there is scarcely any attenuation characteristic at frequency higher or lower than its pass band.
However, in the mobile communication, the transmitting frequency band is near to the receiving frequency band for effectively using the frequency band and it is required that the band-pass filter at the transmitting terminal has the attenuation characteristics at frequency higher than the pass band width to increase the attenuation at frequency next to it. Also, the receiving terminal requires the band-pass filter to have the high attenuation characteristics at frequency lower than the pass band width.
If the number of resonators increases to improve the attenuation characteristics at this band-pass filter, the insertion loss and the size of the filter may increase. Accordingly, a filter having a pole, which cuts off signals at a specified frequency without increasing the number of resonators, has be needed.
FIG. 2
is a perspective view illustrating another conventional duplexer having shorted resonators of ¼ wavelength and massive elements such as inductor and capacitor.
Referring to
FIG. 2
, a filter at a transmitting terminal uses three separate resonators and a chip capacitor
211
is formed between a resonator
251
and an input terminal
231
. At the transmitting terminal, the coupling between the resonators is obtained through external chip capacitors
212
and
213
which are formed on the printed circuit board (PCB)
210
and electrically connected to each other by electrical patterns formed thereon. To cut off signals at a specified frequency, a chip inductor
232
is formed at an open ended resonator
252
. That is, by connecting the inductor
232
to the open ended resonator
252
, the frequency, at which the impedance of the resonance circuit is “0”, exists at frequency higher than the resonance frequency. At this time, since the signal from an input side flows into a ground voltage level through the resonance circuit, the pole frequency to cut off an output signal is produced. Since this pole frequency is generated at higher frequency than the pass band width of the transmitting filter, the attenuation of the receiving frequency signal may be increased.
A filter at a receiving terminal employs four separate resonators
254
to
257
and a chip capacitor
217
is formed between a resonator
257
and an output terminal
241
. At the receiving terminal, the coupling between the resonators is obtained through external chip capacitors
214
to
216
which are formed on the printed circuit board (PCB)
210
and electrically connected to each other by electrical patterns formed thereon. To cut off signals at a specified frequency, a chip capacitor
242
is formed at an open ended resonator
255
. Accordingly, the frequency, at which the impedance of the resonance circuit is “0”, exists at frequency lower than the resonance frequency. At this time, since the signal from an input side flows into the ground voltage level through the resonance circuit, the pole frequency to cut off an output signal is produced. Since this pole frequency is generated at higher frequency than the pass band width of the received signal, the attenuation of the transmitting frequency signal may be increased.
Further, a chip inductor
222
and a chip capacitor
223
are used for matching the impedances of the antenna terminal
221
and the filters at the transmitting and receiving terminals. Accordingly, the signal which is input into an input port at the transmitting terminal is not transmitted to the filter at the receiving terminal but propagated via the antenna terminal. Also, the signal received by the antenna is transmitted to the filter at the receiving terminal so that an external energy is transferred to the receiving terminal.
FIG. 6
shows an insertion loss characteristic graph at the filter at the receiving terminal of the duplexer according to the prior art and the present invention. As shown in
FIG. 6
, in the duplexer according to the prior art, the attenuation characteristics are improved at the frequency band lower than the pass band width.
Although the above-mentioned duplexer improves the attenuation characteristics with the small number of resonators and the filter to have a pole, its size is large and a method for fabricating thereof is complicate because of the external elements, such as a chip capacitor and a chip inductor.
With the miniaturization of communication systems, it is required that the duplexer should be miniaturized and also that the duplexer have excellent atte
Choy Tae Goo
Jun Dong Suk
Kim Meyng Soo
Koo Bon Hee
Lee Chang Hwa
Antonelli Terry Stout & Kraus LLP
Electronics and Telecommunications Research Institute
Glenn Kimberly E.
Pascal Robert
LandOfFree
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