1. Waveguides An Introduction P Meyer Department of Electrical and Electronic Engineering University of Stellenbosch December 2008

2. Outline  Introduction  Parallel Plate Guide  Rectangular Guide  Circular Guide  Ridge Guide

3. Introduction - these days, most people are used to electronic circuits looking like this:

4. Introduction - or this:

5. Introduction - at microwave frequencies, things look quite different, though...

6. Introduction Waveguide Coaxial Line

7. Introduction Even for electronic engineers, waveguide remains a strange medium to work with.

8. Introduction Dual Ridged Waveguide Quad Ridged Waveguide

9. Introduction

10. To understand the characteristics of waveguide, we have to do some maths...

11. General Equations MaxwellHelmholz - we therefore have a 3-variable differential equation that needs to be solved.

12. 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

13. Parallel Plate Waveguide the most basic of transmission lines is simply two parallel plates separated by an isolating medium

14. 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

15. Parallel Plate Waveguide Ideal Practical

16. Parallel Plate Waveguide

17. However, we have other solutions as well... Each value of n is a separate solution, with a different field pattern, and is known as a mode Modes are denoted TEM, TM (h z =0) and TE (e z =0)

18. Parallel Plate Waveguide

19. Cut-off in Waveguide

20. Losses in Parallel Plate Waveguide

21. Parallel Plate Waveguide Why is the possibility of different modes in a waveguide a problem?

22. 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

23. Rectangular Waveguide

24. Each m,n combination form a specific waveguide mode. ie the TM10, or TE10 There is no TEM mode

25. Cut-off in Rectangular Waveguide

26. Mode Patterns in Rectangular Waveguide

27. Losses in Rectangular Waveguide

28. Circular Waveguide

29. Modal Patterns in Circular Waveguide

30. Losses in Circular Waveguide

31. Ridged Waveguide It is clear that the possibility of higher order modes limits the useful frequency range of waveguide systems severely. Ridged guide can be used to extend this range significantly

32. Ridged Waveguide

34. 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