موهن قدرة

A 30 dB 5W RF-attenuator, DC-18GHz, with N-type coaxial connectors

100 Watt power attenuator

المهدئ في الإلكترونيات هوجهاز يعمل على تهدئة مطال أوقدرة الإشارة ، وهويماثل مجموعة من المقاومات موصلة على التوالي تعمل كمجزئ الجهد .

Attenuator circuits

π-type unbalanced attenuator circuit

π-type balanced attenuator circuit

T-type unbalanced attenuator circuit

T-type balanced attenuator circuit

Component values for resistive pads and attenuators

This section concerns pi-pads, T-pads and L-pads made entirely from resistors and terminated on each port with a purely real resistance.

All impedance, currents, voltages and two-port parameters will be assumed to be purely real. For practical applications, this assumption is often close enough.
The pad is designed for a particular load impedance, Z_Load, and a particular source impedance, Z_s.
- The impedance seen looking into the input port will be Z_S if the output port is terminated by Z_Load.
- The impedance seen looking into the output port will be Z_Load if the input port is terminated by Z_S.

Reference figures for attenuator component calculation

This circuit is used for the general case, all T-pads, all pi-pads and L-pads when the source impedance is greater than or equal to the load impedance.

The L-pad computation assumes that port 1 has the highest impedance. If the highest impedance happens to be the output port, then use this figure.

Unique resistor designations for Tee, Pi and L pads.

الرموز المستخدمة

Passive, resistive pads and attenuators are bidirectional two-ports, but in this section they will be treated as unidirectional.

Z_S = the output impedance of the source.
Z_Load = the input impedance of the load.
Z_in = the impedance seen looking into the input port when Z_Load is connected to the output port. Z_in is a function of the load impedance.
Z_out = the impedance seen looking into the output port when Z_s is connected to the input port. Z_out is a function of the source impedance.
V_s = source open circuit or unloaded voltage.
V_in = voltage applied to the input port by the source.
V_out = voltage applied to the load by the output port.
I_in = current entering the input port from the source.
I_out = current entering the load from the output port.
P_in = V_in I_in = power entering the input port from the source.
P_out = V_out I_out = power absorbed by the load from the output port.
P_direct = the power that would be absorbed by the load if the load were connected directly to the source.
L_pad = عشرة log₁₀ (P_in / P_out ) always. And if Z_s = Z_Load then L_pad = 20 log₁₀ (V_in / V_out ) also. Note, as defined, Loss ≥ 0 dB
L_insertion = عشرة log₁₀ (P_direct / P_out ). And if Z_s = Z_Load then L_insertion = L_pad.
Loss ≡ L_pad. Loss is defined to be L_pad.

Symmetric T pad resistor calculation

'"`UNIQ--postMath-00000001-QINU`"' see Valkenburg p 11-3

Symmetric pi pad resistor calculation

'"`UNIQ--postMath-00000002-QINU`"' see Valkenburg p 11-3

L-Pad for impedance matching resistor calculation

If a source and load are both resistive (i.e. Z₁ and Z₂ have zero or very small imaginary part) then a resistive L-pad can be used to match them to each other. As shown, either side of the L-pad can be the source or load, but the Z₁ side must be the side with the higher impedance.

'"`UNIQ--postMath-00000003-QINU`"'

'"`UNIQ--postMath-00000004-QINU`"' see Valkenburg p 11-3

Large positive numbers means loss is large. The loss is a monotonic function of the impedance ratio. Higher ratios require higher loss.

Converting T-pad to pi-pad

This is the Y-Δ transform

'"`UNIQ--postMath-00000005-QINU`"'

Converting pi-pad to T-pad

This is the Δ-Y transform

'"`UNIQ--postMath-00000006-QINU`"'

Conversion between two-ports and pads

T-pad to impedance parameters

The impedance parameters for a passive two-port are

'"`UNIQ--postMath-00000007-QINU`"'

It is always possible to represent a resistive t-pad as a two-port. The representation is particularly simple using impedance parameters as follows:

'"`UNIQ--postMath-00000008-QINU`"'

Impedance parameters to T-pad

The preceding equations are trivially invertible, but if the loss is not enough, some of the t-pad components will have negative resistances.

'"`UNIQ--postMath-00000009-QINU`"'

Impedance parameters to pi-pad

These preceding T-pad parameters can be algebraically converted to pi-pad parameters.

'"`UNIQ--postMath-0000000A-QINU`"'

Pi-pad to admittance parameters

The admittance parameters for a passive two port are

'"`UNIQ--postMath-0000000B-QINU`"'

It is always possible to represent a resistive pi pad as a two-port. The representation is particularly simple using admittance parameters as follows:

'"`UNIQ--postMath-0000000C-QINU`"'