Transmission lines and microwave circuits

A transmission line is called uniform when its parameters do not vary in the direction of propagation. If we assign the z coordinate to the propagation direction then the propagation of a sinusoidal wave can be described by a function exp(jωt — γz) which is common to all field components. The constant y is called the propagation exponent and is in general a complex quantity. Its real part (α) is called the damping coefficient and its imaginary part (k) the propagation coefficient or wave number. For lossless lines the t-z dependence simplifies to exp[j (ωt — kz)]. Another important quantity that characterizes a transmission line is the characteristic impedance Zo, in principle also a complex quantity.