Branching filter having specific impedance and admittance characteristics
First Claim
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1. A branching filter comprising:
- an input/output (I/O) port;
a transmitter filter and a receiver filter, each said filter having a respective port, each said filter being a dielectric filter; and
a branching filter circuit coupling said filters together, the branching filter circuit including;
a first conductive strip line having a first line length l12 coupling said I/O port with said receiver filter port;
a second conductive strip line having a second line length l23 coupled between said receiver filter port and said transmitter filter port; and
a third conductive strip line having a third line length l20 coupled between said receiver filter port and ground,said branching filter being configured so that for ZL12 =∞
, ZL12 being the impedance corresponding to l12, an input admittance Yin looking toward said transmitter filter and said receiver filter from the I/O port is expressed by the following equation;
space="preserve" listing-type="equation">Y.sub.in =Y.sub.T +Y.sub.RF +Y.sub.20whereinYT is a synthetic admittance of the input admittance of the second conductive strip line having the line length l23,YRF is the input admittance of said receiver filter, andY20 is the input admittance of the third line having line length l20,YT being expressed by the following equation, ##EQU14## wherein YTF is the input admittance of said transmitter filter,θ
23 is the phase constant of the second line having line length l23, andY20 being expressed by the following equation, ##EQU15## where θ
20 is a phase constant of the third line having line length l20 ;
wherein said input admittance YRF of said receiver filter at a pass band of said transmitter filter is expressed by YRF ≈
Y20, and wherein the synthetic admittance YT at a pass band of said receiver filter is expressed by YT ≈
Y20, the third line length l20 of the third line being such that a selected one of YRF ≈
Y20 and YT ≈
Y20 is satisfied; and
wherein the input impedance Zin looking toward said transmitter filter and said receiver filter from the I/O port is expressed by the following equation, ##EQU16## wherein θ
12 is a phase constant of the first line having line length l12,the input admittance YTF contained in the admittance Yin being such that the input impedance Zin is increased at a receiving frequency band, and the input admittance YRF contained in the admittance Yin being such that the input impedance Zin is increased at a transmitting frequency band.
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Abstract
A branching filter in which an input/output port, a first dielectric filter for use in transmission and a second dielectric filter for use in reception are coupled with each other through a branching filter circuit. The branching filter circuit includes a first line provided between the input/output port and an input port of the second dielectric filter, a second line provided between the input/output port and an output port of the first dielectric filter, and a third line provided between the input/output port and the ground. In the filter, conductor lines for use in connection between ports are used for the first and second lines.
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Citations
7 Claims
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1. A branching filter comprising:
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an input/output (I/O) port; a transmitter filter and a receiver filter, each said filter having a respective port, each said filter being a dielectric filter; and a branching filter circuit coupling said filters together, the branching filter circuit including; a first conductive strip line having a first line length l12 coupling said I/O port with said receiver filter port; a second conductive strip line having a second line length l23 coupled between said receiver filter port and said transmitter filter port; and a third conductive strip line having a third line length l20 coupled between said receiver filter port and ground, said branching filter being configured so that for ZL12 =∞
, ZL12 being the impedance corresponding to l12, an input admittance Yin looking toward said transmitter filter and said receiver filter from the I/O port is expressed by the following equation;
space="preserve" listing-type="equation">Y.sub.in =Y.sub.T +Y.sub.RF +Y.sub.20wherein YT is a synthetic admittance of the input admittance of the second conductive strip line having the line length l23, YRF is the input admittance of said receiver filter, and Y20 is the input admittance of the third line having line length l20, YT being expressed by the following equation, ##EQU14## wherein YTF is the input admittance of said transmitter filter, θ
23 is the phase constant of the second line having line length l23, andY20 being expressed by the following equation, ##EQU15## where θ
20 is a phase constant of the third line having line length l20 ;wherein said input admittance YRF of said receiver filter at a pass band of said transmitter filter is expressed by YRF ≈
Y20, and wherein the synthetic admittance YT at a pass band of said receiver filter is expressed by YT ≈
Y20, the third line length l20 of the third line being such that a selected one of YRF ≈
Y20 and YT ≈
Y20 is satisfied; andwherein the input impedance Zin looking toward said transmitter filter and said receiver filter from the I/O port is expressed by the following equation, ##EQU16## wherein θ
12 is a phase constant of the first line having line length l12,the input admittance YTF contained in the admittance Yin being such that the input impedance Zin is increased at a receiving frequency band, and the input admittance YRF contained in the admittance Yin being such that the input impedance Zin is increased at a transmitting frequency band. - View Dependent Claims (2, 3)
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4. A branching filter comprising:
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an input/output port coupled through a branching filter circuit to a transmitter filter and a receiver filter, respectively for use in transmitting and receiving, each said filter having an input port and an output port;
said branching filter circuit comprising;a first conductive strip having a first line length l12 and connecting said input/output port and said input port of said receiver filter; a second conductive strip having a second line length l23 and connecting said input port of said receiver filter and said output port of said transmitter filter; and a third conductive strip having a third line length l20 provided between said input port of said receiver filter and a first potential, wherein for ZL12 =∞
, ZL12 being the impedance corresponding to l12, an input admittance Yin at the input port is expressed by the following equation;
space="preserve" listing-type="equation">Y.sub.in =Y.sub.T +Y.sub.RD +Y.sub.20where YRF is an input admittance of said receiver filter, Y20 is an input admittance of the third line having line length l20, and expressed by the equation;
##EQU17## where θ
20 is a phase constant of said third conductive strip having line length l20, and YT is a synthetic admittance, including an input admittance of the second conductive strip having line length l23 and an input admittance of said transmitter filter, and is expressed by the equation;
##EQU18## where YTF is an input admittance of said transmitter filter and θ
23 is a phase constant of the second conductive strip having line length l23,said input admittance YRF of said receiver filter at a pass band of said transmitter filter and said synthetic admittance YT at a pass band of said receiver filter are expressed by YRF ≈
Y20 and YT ≈
Y20, respectively, said third line length l20 of the third conductive strip satisfying a selected one of equation YRF ≈
Y20 and equation YT ≈
Y20, andwherein an input impedance Zin at the input/output port is expressed by the equation ##EQU19## where θ
12 is a phase constant of the first conductive strip having line length l12,said input impedance Zin having at least a selected one of the components of said input admittances YTF and YRF contained in said admittance Yin to achieve an increased return loss at said input/output port. - View Dependent Claims (5, 6)
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7. A method of constructing a branching filter comprising a transmitter filter having input and output ports, a receiver filter having input and output ports, an input/output (I/O) port, and a ground, said method comprising the steps of:
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coupling a first conductive strip line having a first line length l12 between said input/output port and said input port of said receiver filter; coupling a second conductive strip line having a second line length l23 between said input port of said receiver filter and said output port of said transmitter filter; coupling a third conductive strip line having a third line length l20 between said I/O port and said ground; configuring the filters and first, second, and third conductive strip lines so that for ZL12 =∞
, ZL12 being the impedance corresponding to l12, an input admittance Yin looking toward said transmitter filter and said receiver filter from the input port is expressed by the following equation;
space="preserve" listing-type="equation">Y.sub.in =Y.sub.T +Y.sub.RF +Y.sub.20where YT is a synthetic admittance of an input admittance of the second line having line length l23 and an input admittance of said transmitter filter, and is expressed by the following equation;
##EQU20## wherein;
YTF is the input admittance of said transmitter filter,θ
23 is the phase constant of the second line having line length l23,YRF is the input admittance of said receiver filter, and Y20 is the input admittance of the third conductive strip line having line length l20, and is expressed by the following equation;
##EQU21## wherein θ
20 is a phase constant of the third conductive strip line having line length l20,wherein, assuming that the synthetic admittance YT at a pass band of said receiver filter is YT1, the third line length l20 of the third conductive strip line is such that the equation YT1 ≈
Y20 is satisfied; andwherein an input impedance Zin looking toward said transmitter filter and said receiver filter from the input/output port is expressed by the following equation;
##EQU22## wherein θ
12 is phase constant of the first line having line length l12 ;adjusting the input admittance YTF contained in the admittance Yin in such a manner that the input impedance Zin is increased at a receiving frequency band; and adjusting the input admittance YRF contained in the admittance Yin in such a manner that the input impedance Zin is increased at a transmitting frequency band.
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Specification