RF Attenuator Resistor Values Table

The resistor values for Pi, T & bridged T attenuator pads are easy to calculate, but here is a ready calculated table of values.

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

Bridged T resistor attenuator pad — Bridged T attenuator pad

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
1	2.9	433	870	5.8	6.1	410
2	5.7	215	436	11.6	12.9	193
3	8.5	142	292	17.6	20.6	121
4	11.3	105	221	23.8	29.3	85.4
5	14.0	82.2	179	30.4	38.9	64.3
6	16.6	66.9	151	37.3	48.9	50.3
7	19.1	55.8	131	44.8	61.9	40.4
8	21.5	47.3	116	52.8	75.6	33.0
9	23.8	40.6	105	61.6	90.9	27.5
10	26.0	35.1	96.2	71.2	108	23.2
11	28.0	30.6	89.2	81.7	128	19.6
12	29.9	26.8	83.5	93.2	149	16.8
13	31.7	23.6	78.8	106	173	14.4
14	33.4	20.8	74.9	120	201	12.4
15	34.9	18.4	71.6	136	231	10.8
16	36.3	16.3	68.8	154	265	9.4
17	37.6	14.4	66.5	173	304	8.2
18	38.8	12.8	64.4	195	347	7.2
19	39.9	11.4	62.6	220	396	6.3
20	40.9	10.1	61.1	248	450	5.6

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.