ABSTRACT
At the end of this chapter you should be able to:
• understand the function of an attenuator
• understand characteristic impedance and calculate for given values
• appreciate and calculate logarithmic ratios
• design symmetrical T and symmetrical π attenuators given required attenuation and characteristic impedance
• appreciate and
• determine iterative T and π networks
• appreciate and
• calculate attenuation
• understand and apply
An attenuator is a device for introducing a specified loss between a signal source and a matched load without upsetting the impedance relationship necessary for matching. The loss introduced is constant irrespective of frequency; since reactive elements (L orC) vary with frequency, it follows that ideal attenuators are networks containing pure resistances. A fixed attenuator section is usually known as a ‘pad’. Attenuation is a reduction in themagnitude of a volt-
age or current due to its transmission over a line or through an attenuator. Any degree of attenuation may be achieved with an attenuator by suitable choice of resistance values, but the input and output impedances of the pad must be such that the impedance conditions existing in the circuit into which it is connected are not disturbed. Thus an attenuator must provide the correct input and output impedances as well as providing the required attenuation. Attenuation sections are made up of resistances
connected as T or π arrangements (as introduced in Chapter 37).
