Wave Guides Flashcards

Question

What can we deduce about the speed of waves through a waveguide?

Answer 1

Waves travel slower through a waveguide than through free space. Higher frequency waves travel faster than lower frequency waves for a given mode.

Answer 2

How fast the wave changes phase parallel to the propagation path.

Answer 3

The phase velocity can travel faster in a waveguide than through free space. This is not in violation of relativity since no energy is being transmitted. At higher frequencies, the phase velocity decreases.

Answer 4

Reflections due to disconinuities Currents in waveguide walls Dielectric filling of waveguide

Answer 5

Plate the inside with a layer of highly conductive metal such as gold or platinum.

Answer 6

The physical size and the dielectric.

Answer 7

Increasing the air pressure increases the dielectric strength, increasing the power rating.

Answer 8

Reducing moisture will increase the dielectric strength, increasing the power rating.

Answer 9

Higher dielectric strength - increased losses but higher power rating

Answer 10

Dielectrics are poor conductors of current but support electric fields which in turn allow propagation of EM waves. Good dielectrics have high permittivity, the ability of a material to store energy in an electric field. Permittivity represents the ability for the medium to be polarized. A medium which is not easily polarized will not support an electric field well. High permittivity: High power rating. High permittivity will result in dielectric heating loss, conversion into heat. When an alternating electric field is applied to the dielectric, the dipoles change direction continuously to orient themselves with the field, which abosrbs energy and produces heat. You do not need a medium to support an EM. You dont want it to conduct easily or you would get dielectric breakdown.

Answer 11

Better bandwidth: Increases the effective width, lowering the cutoff frequency Worse power rating: Can introduce reflections and uneven field distributions, affecting power dielectric losses

Answer 12

Bends in plane of the electric field.

Answer 13

Bends in plane of magnetic field.

Answer 14

The bend radius should be at least 2 wavelengths, but by making at integral number of wavelengths, reflections will cancel.

Answer 15

For large wavelengths, a simple miter bend may reduce the distance between walls, risking dielectric breakdown.

Answer 16

A 90 degree twist should be undertaken over a distance greater than 2 wavelengths.

Answer 17

The ratio of the forward power to the reverse power measured by the detector

Answer 18

The fraction of power from the main waveguide that makes it into the axiliary waveguide.

Answer 19

EM waves will bounce back and forth between the walls of the cavity and construct until they reach the resonant frequency, at which point they will form a standing wave. The resonant frequency is determined by the physical dimensions.

Answer 20

Smaller waveguide -> Higher cutoff frequency -> more losses

Answer 21

Larger waveguide -> More possible modes and lower cutoff frequency -> Greater bandwidth

Answer 22

Higher power rating Lower losses Expensive Difficult to install

Answer 23

Reflections from obstacles, discontinuities, or misaligned sections Currents in the waveguide walls Dielectric losses =

Answer 24

Geater BW Lower Power Handling Greater Attenutation