Nonreciprocal transmission line apparatus whose propagation constants in forward and backward directions are different from each other

1. A nonreciprocal transmission line apparatus configured by connecting in cascade at least one unit cell, each unit cell including:

(a) a microwave transmission line section;

(b) a series branch circuit equivalently including a capacitance element; and

(c) first and second parallel branch circuits provided branched from the transmission line section, each of the first and second parallel branch circuit equivalently including an inductive element between first and second ports,

wherein a propagation constant in a forward direction and a propagation constant in a backward direction of the nonreciprocal transmission line apparatus are different from each other,

wherein the transmission line section of each unit cell has spontaneous magnetization so as to have gyro anisotropy by being magnetized in a direction different from a propagation direction of microwaves or by being externally magnetized by an external magnetic field,

wherein the first parallel branch circuit is a first stub conductor having a first electrical length,

wherein the second parallel branch circuit is a second stub conductor having a second electrical length shorter than the first electrical length, and

wherein, when a phase constant in a first mode of propagation in the forward direction is β p , and a phase constant in a second mode of propagation in the backward direction is β m , the first and second electrical lengths are set so that a function of nonreciprocal phase shift amount β NR =(β p −β m )/2 with respect to the operating angular frequency comes close to a function of nonreciprocal phase shift amount β NRZ with respect to an operating angular frequency, when beam squint of such a phenomenon that a radiation direction of electromagnetic waves radiated from the nonreciprocal transmission line apparatus changes in accordance with frequency does not occur in the vicinity of an intersection of a dispersion curve representing a relation between the phase constant β p and the operating angular frequency and a dispersion curve representing a relation between the phase constant β m and the operating angular frequency.

2. The nonreciprocal transmission line apparatus as claimed in claim 1 ,

wherein the function is a function proportional to the operating angular frequency.

3. The nonreciprocal transmission line apparatus as claimed in claim 2 ,

wherein the first stub conductor has a first admittance,

wherein the second stub conductor has a second admittance, and

wherein the first and second electrical lengths are set such that:

(a) the first admittance substantially coincides with the second admittance at a predetermined operating angular frequency lower than the operating angular frequency at the intersection, and

(b) respective imaginary parts of the first and second admittances are negative at the predetermined operating angular frequency.

4. The nonreciprocal transmission line apparatus as claimed in claim 3 ,

wherein the first stub conductor is a short-circuit stub, and the first electrical length is set to be longer than one-half of a guide wavelength, and

wherein the second stub conductor is a short-circuit stub, and the second electrical length is set to be shorter than one-fourth of the guide wavelength.

5. The nonreciprocal transmission line apparatus as claimed in claim 3 ,

wherein the first stub conductor is an open stub, and the first electrical length is set to be longer than one-fourth of a guide wavelength, and

wherein the second stub conductor is a short-circuit stub, and the second electrical length is set to be shorter than one-fourth of the guide wavelength.

6. The nonreciprocal transmission line apparatus as claimed in claim 1 , further comprising a grounding conductor provided between the first stub conductors, the grounding conductor providing a shield between the first stub conductors.

7. An antenna apparatus comprising a nonreciprocal transmission line apparatus configured by connecting in cascade at least one unit cell, each unit cell including:

(a) a microwave transmission line section;

(b) a series branch circuit equivalently including a capacitance element; and

(c) first and second parallel branch circuits provided branched from the transmission line section, each of the first and second parallel branch circuit equivalently including an inductive element between first and second ports,

wherein a propagation constant in a forward direction and a propagation constant in a backward direction of the nonreciprocal transmission line apparatus are different from each other,

wherein the transmission line section of each unit cell has spontaneous magnetization so as to have gyro anisotropy by being magnetized in a direction different from a propagation direction of microwaves or by being externally magnetized by an external magnetic field,

wherein the first parallel branch circuit is a first stub conductor having a first electrical length,

wherein the second parallel branch circuit is a second stub conductor having a second electrical length shorter than the first electrical length, and

wherein, when a phase constant in a first mode of propagation in the forward direction is β p , and a phase constant in a second mode of propagation in the backward direction is β m , the first and second electrical lengths are set so that a function of nonreciprocal phase shift amount β NR =(β p −β m )/2 with respect to the operating angular frequency comes close to a function of nonreciprocal phase shift amount β NRZ with respect to an operating angular frequency, when beam squint of such a phenomenon that a radiation direction of electromagnetic waves radiated from the nonreciprocal transmission line apparatus changes in accordance with frequency does not occur in the vicinity of an intersection of a dispersion curve representing a relation between the phase constant β p and the operating angular frequency and a dispersion curve representing a relation between the phase constant β m and the operating angular frequency.