Microwave mixing circuit

Claim 2

A microwave mixing circuit constructed of a microwave integrated circuit, comprising: (a) a main transmission line having an input port at one end thereof for receiving an input high frequency, and an output port at an opposite end thereof; (b) a band pass filter responsive to a local oscillation frequency, said band pass filter having a parallel-coupled strip line filter which is electromagnetically coupled to said main transmission line at a point between said input and output ports; (c) a mixing diode having an input terminal connected to said output port for producing an intermediate frequency by mixing said local oscillation frequency, supplied to said diode in one direction along a portion of said main transmission line, with said input high frequency, supplied to said diode in the same direction along said main transmission line including said main line portion; and (d) a band stop filter for simultaneously blocking said local oscillation frequency and an image frequency, produced by said diode in response to said input high frequency and to said local oscillation frequency, said band stop filter being electromagnetically coupled to said main transmission line between said input port and said point in such a manner the the impedance at said local oscillation frequency viewed from said point toward said input port is infinite and that the impedance at said image frequency viewed from the input terminal of said mixing diode toward said point is either zero or infinite.

Claim 3

A microwave mixing circuit as claimed in claim 1, wherein the distance between a zero impedance point in a coupling area of said band stop filter and said point corresponds to: ##EQU8## and wherein the distance between the zero impedance point and the input of said mixing diode corresponds to: ##EQU9## wherein "n" is a positive integer; λ L is the effective wavelength of said local oscillation on said main transmission line; and λ I is the effective wavelength of said image frequency on said main transmission line.

Claim 4

A microwave mixing circuit as claimed in claim 2 or 1, wherein said band stop filter comprises two L-shaped striplines which are arranged symmetrically with respect to the longitudinal direction of said main transmission line.

Claim 5

A microwave mixing circuit constructed of a microwave integrated circuit, comprising: (a) a main transmission line having an input port at one end thereof for receiving an input high frequency, and an output port at an opposite end thereof; (b) a band pass filter responsive to a local oscillation frequency, said band pass filter having a parallel-coupled strip line filter which is electromagnetically coupled to said main transmission line at a point between said input and output ports; (c) a mixing diode having an input terminal connected to said output port for producing an intermediate frequency by mixing said local oscillation frequency, supplied to said diode in one direction along a portion of said main transmission line, with said input high frequency, supplied to said diode in the same direction along said main transmission line including said main line portion; and (d) first means for blocking said local oscillation frequency, said first means being electromagnetically coupled to said main transmission line in such a manner that the impedance at said local oscillation frequency viewed from said point toward said input port is infinite; and (e) second means for blocking an image frequency produced by said diode in response to said input high frequency and to said local oscillation frequency, said second means being electromagnetically coupled to said main transmission line in such a manner that the impedance at said image frequency viewed from the input terminal of said mixing diode toward said point is either zero or infinite.

Claim 6

A microwave mixing circuit constructed of a microwave integrated circuit, comprising: (a) a main transmission line having an input port at one end thereof for receiving an input high frequency, and an output port at an opposite end thereof; (b) a band pass filter responsive to a local oscillation frequency, said band pass filter having a parallel-coupled strip line filter which is electromagnetically coupled to said main transmission line at a point between said input and output ports; (c) a mixing diode having an input terminal connected to said output port for producing an intermediate frequency by mixing said local oscillation frequency, supplied to said diode in one direction along a portion of said main transmission line, with said input high frequency, supplied to said diode in the same direction along said main transmission line including said main line portion; and (d) first means for blocking said local oscillation frequency, said first means being electromagnetically coupled to said main transmission line in such a manner that the impedance at said local oscillation frequency viewed from said point toward said input port is infinite; and (e) second means for blocking an image frequency produced by said diode in response to said input high frequency and to said local oscillation frequency, said second means being electromagnetically coupled to said main transmission line in such a manner that the impedance at said image frequency viewed from the input terminal of said mixing diode toward said point is either zero or infinite.

Claim 7

A microwave mixing circuit as claimed in claim 4, wherein said first and second means respectively comprise first and second band stop filters, said first band stop filter being coupled to said main transmission line between said input port and said point, said second band stop filter being coupled to said main transmission line between said point and said output port.

Claim 8

A microwave mixing circuit as claimed in claim 2, wherein the distance between a zero impedance point in a coupling area of said first band stop filter, and said first point corresponds to: ##EQU10## wherein "n" is a positive integer and λ L is the effective wavelength of said local oscillation frequency on said main transmission line.

Claim 9

A microwave mixing circuit as claimed in claim 2, wherein the distance between a zero impedance point in a coupling area of said second band stop filter, and the input of said mixing diode corresponds to: ##EQU11## wherein "n" is a positive integer and I is the effective wavelength of said image frequency on said main transmission line.

Claim 10

A microwave mixing circuit as claimed in claim 4, further comprising a low pass filter connected to said mixing diode.

Claim 11

A microwave mixing circuit as claimed in claim 4, further comprising a stub filter interposed between said output port and ground.

Claim 12

A microwave mixing circuit as claimed in claim 5 or 1, wherein said band stop filter comprises a parallelcoupled stripline filter.

Claim 13

A microwave mixing circuit as claimed in claim 5 or 1, wherein said band stop filter comprises an L-shaped stripline arranged in the vicinity of said main transmission line.

Claim 14

A microwave mixing circuit as claimed in claim 5 or 1, wherein said band stop filter comprises a stub physically connected to said main transmission line.