To understand the characteristics of waveguide, we have to do some maths...
General Equations MaxwellHelmholz - we therefore have a 3-variable differential equation that needs to be solved.
General Equations A wave travelling in the z-direction according to cos(wt- βz) can be represented as e -jβz, with β called the propagation constant - once we have solved e z and h z we can calculate all the other fields
Parallel Plate Waveguide the most basic of transmission lines is simply two parallel plates separated by an isolating medium
Parallel Plate Waveguide Solution 1 [kc=0] Boundary condition is that electric field tangential to the conductor must be zero. - this solution is called the TEM solution, as e z and h z are both zero
Parallel Plate Waveguide Why is the possibility of different modes in a waveguide a problem?
Parallel Plate Waveguide Normally, we use waveguide in a single propagating mode configuration. The useful frequency range is then limited by: low side: the exponentially increasing loss close to cut-off high side: the cut-off frequency of the next mode
Let’s Play... Once we understand how waveguides work, we can use their peculiar characteristics to our advantage, by using them as natural high-pass filters using overmoded guides to build more than one device in the same physical space add modes to create aperture distributions of our choice, and thus specified radiation patterns [Madelé van der Walt] build wideband transitions from coaxial line to waveguide tot antenna [Dirk de Villiers] Thank you