TABLE OF CONTENTS Coaxial transmission line is popular for its wide bandwidth, high resistance to electromagnetic interference (EMI) and low cost. Figure 3.2 shows a coaxial transmission line with its dominant mode electric field configuration. The magnetic field is distributed in concentric circles about the center conductor. This electromagnetic field distribution is known as the transverse electromagnetic (TEM) mode since both electric and magnetic fields are transverse to the direction of propagation. This mode is also termed a differential mode, because the signal current flowing on the inner conductor is directed opposite to the ground current flowing on the outer conductor. The TEM mode has several unique characteristics: (1) at least two unconnected conductors and a single insulating material are required for it to exist; (2) its cutoff frequency is 0 Hz; (3) it has only two field components ( E ? and 
for the coaxial line) aligned with the transverse coordinates, no longitudinal ( z-directed) electric or magnetic field component ( E z or H z); and (4) its propagation constant is k = k 0 ? r 1/2, the wavenumber in vacuum multiplied with the square root of the relative dielectric constant of the insulator. Because the TEM mode cuts off at 0 Hz, we can solve for the electric and magnetic fields using static theory, and we can define the outer conductor as ground. We can define the characteristic impedance in terms of the static...
