What are the practical uses of Cylindrical circular and elliptical metallic waveguides?

Question

In a microwave book i found that cylindrical waveguides are not used for practical purposes. If so, why the authors of many micro. books have given the analysis of circular metallic waveguide ? what is the mystery behind this. Please say something....

Answer 1

Hello dear,

Every Microwave Component has its use, it could be rare application, however, important.

The Circular Waveguides are usually used when you have a 360deg rotating element connected with fixed base. A good example for this is 360deg scanning radars used on ships or in small bases

The Elleptical Waveguides are the widely commonly used waveguides due to ease of manufacturing it in flixible form that could be bent in shape of "cable drum" and could be installed on telecom towers (freq 6GHz and above). These types of cables are also made with corregated outer surface to avoid damage during bending

Answer 2

Basically, waveguides work by allowing standing waves to have nodes that terminate at edges of the waveguide. Since the circular waveguide only has one radius, it only allows one type of wave (give or take a few Hz) to propagate.

For rectangular waveguides, not only are you able to have two different lengths for the base and width (allowing for two signals to propagate), but you can also position it to best align with the incoming signal.

As far as why give an analysis of it, it's because circular waveguides are a very good theoretical study, but more importantly, when coupled with another center core conductor become one of the best no-loss waveguides around: Coaxial cables. These not only have very high fidelity, but also have a fixed impedance REGARDLESS OF LENGTH. You could have a 4 foot coax with the same resistance as a 20 footer.

Answer 3

Hi. Someone will have a better answer I'm sure but in UHF amateur radio rectangular cross section wave guides keep the microwaves in more or less the same orientation. This increases the efficiency for communication. A microwave oven, on the other hand, wants to have the waves scattered (reduces "hot spots").

Answer 4

i can't explain your "microwave book," but i can tell you, having taken courses in radar and maxwell equations, circular wave guides have (or a least had when i took the courses) big applications in radar. by the way, maxwell equations are four equations that link electrical and magnetic forces, and that form the mathematical bases for radar, radio, TV, and most other electrical/electronic goodies.