nsmission lines whistle will sound louder (addition of incident and transmission lines. For example, the dimensions of a typ- reflected signal); in other places the whistle will sound ical waveguide (Figure 2.2-3(a)) for use at frequencies weaker (subtraction of incident and reflected signal). between 10 GHz and 15 GHz are A = 19 mm, B = 9.5 Provided your friend maintains the whistle at a constant mm, C = 21.6 mm, D = 12.1 mm. amplitude and pitch, you will find that louder and weaker There are many types of transmission lines. 2 These sounds always occur at the same locations in the tunnel. range from the two wire lines which you find in your In other words, the pattern of louder and weaker sounds home for table lamps, and three wire lines used for your remains stationary and appears to be standing still. This electric kettle. Although these cables work efficiently at change in sound intensity levels therefore produces power frequencies (50-60 Hz), they become very in- a standing wave pattern along the length of the tunnel. efficient at high frequencies because their inherent con- The ratio of the maximum to minimum sound is known struction blocks high frequency signals and encourages as the standing wave ratio (SWR). It will be shown later radiation of energy. that the measurement of standing wave patterns is a very useful technique for describing the properties of trans- 2.2.3.1 Waveguides and coplanar mission line systems. In the above discussions, you have used knowledge waveguides gained from the university of life to understand the Other methods must be used and one method that definitions of many transmission line terms. These defi- nitions are not trivial because you will soon see that many comes readily to mind is the tunnel or waveguide de- of the above principles and terms also relate to electrical scribed in Section 2.2.2.2. This waveguide is shown in transmission lines. In fact, if you can spare the time, re- Figure 2.2-3(a). It works efficiently as a high frequency transmission line because of its l