Basic concepts of wave guides
- In figure a region of non conducting space is bounded by an infinitely long perfectly conducting tube.
- The shape of this tube is arbitrary and it also has a uniform cross sectional area throughout the tube.
- We consider that the bounded region is lossless.
- In this way a structure, which guides the transmission of E.M. energy in the direction of the axis is called a waveguide.
- A wave guide is a cylindrical pipe bound by a conductor of high conductivity filled with a dielectric having very small loss of energy and having arbitrary cross section.
- When E.M. wave enters into the wave guide it undergoes multiple reflection from its wall and then it propagates along its axis (z-axis).
At a point on bound region E and H satisfy the Maxwell’s equation
- For non-conducting medium σ = 0
- Here E and H are the functions of position and time.
- The time dependence of E and H are generally described in terms of e-jωt
- Vector identity
- Since E and H both are the functions of position and time, so if
- If we resolve E and H into the component parallel to z (Ez or Hz) and transverse to z-axis (Et or Ht), then
- Above equation shows that the transverse component of field can be easily determined by axial components of field.
- So it is sufficient to determine the axial component of field as appropriate solution of equations of E and H.
Since ∇t2 E + k’2 E = 0
∴ ∇t2 Ez + k’2 Ez = 0
and ∇t2 Hz + k’2 Hz = 0
- At boundary, the tangential component of E and normal component of H are continuous.
- Since the boundary condition for E and H are different so they can not be satisfied simultaneously.
- Therefore the electromagnetic fields are divided into two categories.
- It depends on either Ez is present or Hz or both.
Transverse electric (TE ) mode
- In this case Hz is present and Ez = 0 everywhere.
Transverse magnetic (TM ) mode
- In this case Ez is present and Hz = 0 everywhere.
Transverse electromagnetic (TEM ) mode
- In this mode Ez = 0 and Hz = 0
- It is found that either TE wave or TM wave propagate through the wave guide but no TEM wave.
- To know in detail about Basic concepts of waveguide click here.
Our other websites
https://vacancy.sacademy.co.in
Our YouTube channels