Waveguides are classified into four types
- Rectangular waveguides
- Circular waveguides
- Elliptical waveguides
- Ridge waveguides
- Single – Ridge waveguides
- Double – Ridge waveguides
Among those four waveguides, Elliptical waveguides are made from Circular waveguides and Ridge waveguides are made from Rectangular waveguides in which Ridge waveguides are again classified into Single Ridge waveguides and Double Ridge waveguides. For practical purposes Elliptical and Ridge waveguides are not used , only Rectangular and Circular waveguides are used.
Rectangular Waveguides :
Rectangular waveguide is the most commonly used waveguide than any other waveguide.Rectangular waveguides support TE and TM modes but not TEM waves because we cannot define a unique voltage since there is only one conductor in a rectangular waveguide. Rectangular waveguide cannot propagate below certain frequency that frequency is called cut off frequency.
Circular Waveguides :
In Circular waveguides, twisting of wave will be there because of its physical dimensions. We are using it in rotating antenna as in Radar. Circular waveguides are those that maintain a uniform circular cross section along their length . Method of solution of electromagnetic field equation for circular waveguide is similar to that for rectangular waveguides.
Types of modes in waveguide propagation :
Different types of wave propagation modes can exit on waveguides. The propagating modes along the waveguide may be classified on the basis of the field components present in the wave. The field component in the direction of wave propagation are defined as longitudinal components and those which are perpendicular to the direction of propagation are defined as transverse components.
Assume the waveguide is oriented along the z-axis, the modes may be classified as follows :
- Transverse electromagnetic (TEM) modes :
The electric and magnetic fields are transverse to the direction of wave propagation with no longitudinal components(Ez=Hz=0). TEM modes cannot exit on single conductor during structure.
- Transverse electric (TE) modes :
The electric and magnetic field is transverse to the direction of propagation , whereas the magnetic field has both transverse and longitudinal components ( Ez = 0, Hz ǂ 0).
- Transverse magnetic (TM) modes :
The magnetic field is transverse to the direction of propagation (no longitudinal magnetic field component ), whereas the electric field has both transverse and longitudinal components ( Hz = 0 , Ez ǂ 0).
TE and TM modes are commonly reffered to as waveguide modes since they are the only modes which can exit in an enclosed guiding structure. TEM modes cannot exist on single conductor guiding structures , such as rectangular waveguide and circular waveguides.