Another important and useful network that is used extensively is the pi type symmetric attenuator. It has equal I/O impedances and presents its terminal impedances in shunt. Please visit the Signal Processing Group Inc., website for more information on this very useful network and its design equations.
The T – type attenuator can also be used with unequal I/O impedances to match the input line impedance with the output line impedance, as well as, providing attenuation of the signal. This can be done if proper values of the resistors are chosen . A brief paper on this is available on the SPG website under the “complementary” menu item.
The t type attenuator is a very useful circuit and is used quite extensively to not only attenuate signals but also to match inputs and outputs. This post presents the derivation of the design equations for this type of attenuator. The equations have been derived for a symmetric t type attenuator with equal I/O impedances. Please visit the SPG website and select the relevant post from the complementary menu items.
A javascript script is available to calculate the resistors needed for the t type attenuator in the case of equal input/output impedances. Given the required attenuation and “characteristic impedance” the script will calculate the resistors required. Please visit the SPG website and select the “complementary” menu item and then select the javascript from the list of items.
The T type attenuator can also be made using L and C ( “lossless” components. In this case the defining equations are slightly modified. Please find the equation and info on the SPG website under “complementary” items.
The T type attenuator is a very useful circuit block that has the capability to simultaneously match two transmission lines and attenuate the signals traveling on them. It is a symmetric circuit and when its impedances are chosen correctly the I/O can be exchanged without affecting the signals. Unequal impedances can also be used with appropriate modifications. These and other characteristics are explained in the “T pad” post on the Signal Processing Group Inc, website. Please visit for more info.