Guide Wavelength Measurements

Only available on StudyMode
  • Download(s) : 373
  • Published : October 16, 2012
Open Document
Text Preview
|
Assignment 2|
Guide wavelength measurements|
|

|

Abstract
The purpose of this experiment is to demonstrate:
a) The techniques for measuring guide wavelength.
b) The relationship between the wavelength in free space and the guide wavelength. Furthermore, this experiment will be a way in which to gain experience in using different types of laboratory communications equipment.

Introduction
What is wavelength?
Wavelength of a sinusoidal wave is the distance between identical points in the adjacent cycles of a waveform signal. Wavelength is commonly designated by the Greek letter lambda (λ)Wavelength is inversely correlated to frequency (figure 1.1), therefore the higher the frequency of the signal, the shorter the wavelength. vp Is the phase velocity

f is the frequency

vp Is the phase velocity
f is the frequency

λ=vpf
Figure 1.1
What is a wave guide?

Figure 1.2
A waveguide is a special form of transmission line consisting of a rectangular (figure 1.2) or cylindrical metal tube or pipe, through which electromagnetic waves are propagated in microwave and RF communications. It is commonly used in microwave communications, broadcasting, and radar installations. A waveguide must have a certain minimum diameter relative to the wavelength of the signal and therefore are practical only for signals of extremely high frequency. Consequently below such frequencies, waveguides are useless as electrical transmission lines. “An electromagnetic field can propagate along a waveguide in various ways. Two common modes are known as transverse-magnetic (TM) and transverse-electric (TE). In TM mode, the magnetic lines of flux are perpendicular to the axis of the waveguide. In TE mode, the electric lines of flux are perpendicular to the axis of the waveguide. Either mode can provide low loss and high efficiency as long as the interior of the waveguide is kept clean and dry.” Some disadvantages are:

* The high cost, since the material used is special alloy (copper and silver). * It is not possible to pass DC currents along with your RF signal. * The volume and mass particularly are at lower frequencies. Although there is quite a few disadvantages the fact that you can transmit extremely high peak powers and very low loss outweighs it. Furthermore the Silver plating used on the inside walls of the waveguide decreases the resistance loss making the copper and aluminium waveguides even more efficient. Experimental notes

The experiment needs to be conducted to obtain the value of the guide wavelength and thereafter calculate the wave dimension and observe whether it matches the initial result that was measured. The initial result measured was the value a=22.860 whilst the given margin error of this experiment is +/- 0.046 mm. It may be shown that:

1λ2g =1λ2o- 1λ2c
Figure 1.1

λc = Cut-off wavelength for the wave guide mode being propagate λo = Wavelength in free space
λg = Guide wavelength, known as delta g
The equation to measure λo is already present as it is given by free-space. Although the cut-off wavelength can be calculated by rearranging the formula in figure 1.1, the experiment will be used to further confirm this mathematical formula. What we will acquire is a range of guide wavelengths throughout the experiment in order to find the Cut-off wavelength. Where is the cut-off wavelength for the waveguide mode being propagated? The dominant mode is being propagated in the rectangular waveguide (figure 1.2) which means where (a) is the internal broad dimension of the rectangular waveguide.

Block diagram

Microwave signal source
Isolator
Preset attenuator
Wave meter
Short circuit
Calibrated attenuator
Tuned SWR amplifier + meter
Standing wave detector
Microwave signal source
Isolator
Preset attenuator
Wave meter
Short circuit
Calibrated attenuator
Tuned SWR amplifier + meter
Standing wave detector

Microwave signal source
This device is the signal generator...
tracking img