RF Attenuators Includes:
Attenuator basics Attenuator specs Resistive attenuator design Attenuator resistor values table Balanced resistive attenuator pads Variable PIN diode attenuator SMA attenuator
When designing resistive attenuator pads it is often useful to have a table or chart of ready calculated values available. This makes for easy selection of values and determination or which format to use in terms of the usage of convenient values.
The table below provides a summary at 1 dB intervals for Pi section, T section and Bridged T resistive attenuators for attenuation levels between 1 and 20 dB. Attenuation levels above 20 dB per section are not advised as leakage and other issues mean that the performance is unlikely to be as good. If higher values of attenuation are required then it is suggested that several sections of 20 dB or less are used - typically the level of attenuation I averaged over each section.
Resistive attenuator component numbers
The circuits below details the different components used within the attenuator pads. The component numbers given in these diagrams relate to the resistor values provided in the table below.
T section attenuator pad resistors
Pi section attenuator pad resistors
Bridged T section attenuator pad resistors
RF attenuator resistor values chart
The table or chart given below provides the resistor values for Pi and T pad RF resistor attenuator circuits. The values in this table have been calculated for a characteristic impedance of 50Ω.
|RF Attenuator Pad Resistor Values Table
for 50Ω Characteristic Impedance
|Loss in dB||R1||R2||R3||R4||R5||R6|
Attenuator resistor values for other impedance systems
The attenuator resistor values in the table are given for a 50 ohm system as this is the most likely impedance system required. However it is recognised that other impedance systems may also be used.
To convert the values in the table to another value of impedance, they should be multiplied by the factor Z / 50, where Z is the characteristic impedance of the required system.
The values given in the table above for the resistive attenuator resistor values provides an easy look-up table. It provides an ‘at a glance’ view of the resistor values needed for Pi, T and Bridged T resistive attenuator pads, enabling an easy selection of the values as well as the most appropriate type of pad according the resistor values that may be available.
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