higher-order modes will occur in coaxial line whenever the wavelength of operation is close to the physical dimensions of the coaxial line. under these conditions, higher-order modes will be able to propagate through the coaxial line. in addition to the TEM wave, the TE or TM higher-order modes can exist. for the transverse electric wave TE, the component of the magnetic field is in the direction of propagation. for the transverse magnetic wave TM, the component of the electric field is in the direction of propagation. both the TE and TM waves are shown in fig.4-1b and c. higher-order modes also are generated in the coaxial line at points of discontinuity and will be discussed later in this chapter in the section entitled ''higher mdes possible in waveguides.''
the liwest wavelength that will propagate within the coaxial line is called the cutoff wave-length. for each TE higher mode, the cutoff wavelength may be approximated by using half