T vs. Pi Attenuator Pads for RF Power Attenuation

This page compares the T attenuator pad and the Pi attenuator pad, outlining the differences between these two types of RF attenuator pads. These pads are highly useful in RF/Microwave circuit design, primarily providing RF power attenuation.

Essentially, pre-determined resistor values are selected and mounted to achieve the desired attenuation on the signal path. These pads are mainly used for adjusting the instantaneous power level at various points in the RF circuit. The frequency range and impedance value (typically 50 Ohm or 75 Ohm) are crucial in selecting the right chip resistors for the RF circuit design. Both Pi and T pads are commonly employed in the design of RF transceiver or power amplifier circuits.

For a deeper understanding of the application of these RF attenuator pads, refer to resources on RF frequency converter design.

Pi Attenuator Pad

Here’s a representation of a Pi attenuator pad:

R1=R2= Z ( K-1/K+1)

R3= 2 Z ( K / K^2 - 1)

Where:

• K is the impedance factor, equal to Antilog(dB/10) or 10^(dB/10)
• Source impedance Z_s = Load impedance Z_L = Z

T Attenuator Pad

Here’s a representation of a T attenuator pad:

R1=R3=Z ((K+1)/(K-1))

R2= Z ((K^2 -1 )/2K)

Manufacturers of Chip Resistors for RF Attenuator Pads

Here are some popular manufacturers of RF attenuators:

• Aeroflex: Offers PCB mountable attenuator pads and chip components.
  • Website: www.aeroflex.com
• RF Micro Devices: Provides various types of attenuators, including analog, digital, and temperature-controlled attenuators.
  • Website: www.rfmd.com
• Anaren: Specializes in chip attenuators/terminations and SMD attenuators/terminations.
  • Website: www.anaren.com
• JFW Industries: Offers connectorized RF attenuators of various types.
  • Website: www.jfwindustries.com
• EMC RF Labs: A good source for RF thermopads.
  • Website: www.emc-rflabs.com