MULTIPLEXING CIRCUIT AND DESIGNING METHOD THEREFOR

• US 20090147805A1
• Filed: 08/31/2006
• Published: 06/11/2009
• Est. Priority Date: 09/05/2005
• Status: Active Grant

• Current Assignee: National Universit Corporation The University of Electro-Communications
• Original Assignee: National Universit Corporation The University of Electro-Communications
• Inventors: Wada, Kouji
• Granted Patent: US 8,494,008 B2
• Time in Patent Office: Days
• US Class Current: 370/497
• CPC Class Codes: H01P 1/2135 using strip line filters H01P1/2131 takes precedence

Abstract

The present invention includes two or more bandpass filters, for passing signals of mutually different frequency bands therethrough, including one or more stages of units having coupling devices and resonance circuits coupled, in a tap type, to the coupling device, one end of each bandpass filter is directly connected to a common port, the coupling device and the resonance circuit of the first stage nearest to the port of each bandpass filter has a function of impedance matching means for each bandpass filter, in addition to a function of resonance means, respectively.

Claims

1. A multiplexing circuit comprising:

two or more bandpass filters, for passing signals of mutually different frequency bands therethrough, comprising one or more stages of units having coupling devices and resonance circuits coupled, in a tap type, to the coupling devices, wherein;

one end of each bandpass filter is directly connected to a common port; and

the coupling device and the resonance circuit of the first stage nearest to said port of each bandpass filter has a function of impedance matching means for each bandpass filter, in addition to a function of resonance means, respectively.

2. The multiplexing circuit as claimed in claim 1, wherein:

a value of each coupling device in the first stage and an impendence, a coupling position, and a phase constant of each resonance circuit of the first stage are selected in such a manner that a signal passing band of each bandpass filter is desired frequencies, and, as a result, each coupling device of the first stage and each resonance circuit of the first stage have the function of the impedance matching means for each bandpass filter, in addition to the function of the resonance means.

3. The multiplexing circuit as claimed in claim 1 or 2, wherein:

each bandpass filter is designed in such a manner that, at each center frequency,

when a signal is made to pass through a required bandpass filter, a contact point of the resonance circuit in another bandpass filter is in a short-circuit state so that admittance viewed from the side of the port of the required bandpass filter has a desired value,

in the short-circuit state, taking a first virtual coupling device corresponding to the coupling device into consideration, admittance viewed from the side of said port of the coupling device of the required bandpass filter, the coupling device of the another bandpass filter which influences the required bandpass filter and the first virtual coupling device has a desired value, for the required bandpass filter,

taking a second virtual coupling device which is a counterpart of the first virtual coupling device into consideration, a circuit system including the resonance circuit and the second coupling device meets a resonance condition at a desired center frequency, and,

a susceptance slope parameter of a part including the resonance circuit and the second virtual coupling device agrees with a susceptance slope parameter of a lumped constant device type resonance circuit corresponding to the resonance circuit.

4. The multiplexing circuit as claimed in any one of claims 1-3, wherein:

the plurality of bandpass filters include a transmitting side bandpass filter for passing a transmission signal therethrough, and a reception side bandpass filter for passing a reception signal therethrough, and

said port is connected to an antenna.

5. The multiplexing circuit as claimed in any one of claims 2-4, wherein:

a length of a stub of one side of the resonance circuit of one bandpass filter is designed in such a manner as to generate an attenuation pole corresponding to a passing band frequency of another bandpass filter.

6. A designing method for a multiplexing circuit, comprising:

directly connecting one ends of two or more bandpass filters to a common port, which bandpass filters are for passing signals of mutually different frequency bands therethrough, and comprise one or more stages of units each having a coupling device and a resonance circuit coupled, in a tap type, to the coupling device, wherein;

each bandpass filter is designed in such a manner that, at each center frequency,

when a signal is made to pass through a required bandpass filter, a contact point of the resonance circuit in another bandpass filter is in a short-circuit state so that admittance viewed from the side of the port of the required bandpass filter has a desired value,

in the short-circuit state, taking a first virtual coupling device corresponding to the coupling device into consideration, admittance viewed from the side of said port of the coupling device of the required bandpass filter, the coupling device of the another bandpass filter which influences the required bandpass filter and the first virtual coupling device has a desired value, for the required bandpass filter,

taking a second virtual coupling device which is a counterpart of the first virtual coupling device into consideration, a circuit system including the resonance circuit and the second coupling device meets a resonance condition at a desired center frequency, and,

a susceptance slope parameter of a part including the resonance circuit and the second virtual coupling device agrees with a susceptance slope parameter of a lumped constant device type resonance circuit corresponding to the resonance circuit.