RF Attenuator basics
This page covers rf attenuator basics, specifications, types, design using PIN diodes and also provide manufacturers of rf attenuator.
There are very rarely any communication system where you can not find RF attenuator. It is used in all the RF communication systems to reduce the power level of the signal by means of attenuating the signal. It provides opposite functionality to amplifier which usually increases or boosts power level.
Figure shows connectorised rf attenuator of 30dB from Agilent technologies.
Types of attenuator
RF attenuators are of two main types, viz. fixed and variable. Fixed attanuator will provide fixed attenuation and usually designed with the use of discrete or chip resistors.Variable attenuator will provide variable level of attenuation. This Variable attenuator also has two categories, first one changes attenuation based on fixed steps and the other one changes attenuation continuouly. The variable type of attenuator is usually designed with the help of PIN diode or FET. All variable attenuators require control voltage as input to change the attenuation value. One such PIN diode design of the variable RF attenuator is depicted below.
As mentioned in the figure in this rf circuit, resistance across diode is function of applied voltage(bias). Here resistor R2 acts as potentiometer and changes voltage applied to the diode terminals which in tern provides attenuation to the Power Input. Variation of this circuit using four pin diodes arranged in a bridge shape is most popular for variable RF attenuator design.
There are rf attenuators available which changes attenuation based on temperature. This type of rf attenuators are often called as thermopad or temperature variable attenuators. This thermopad is very useful to take of drastic changes in gain due to atmospheric conditions where the device/equipment is going to be used.Temperature versus attenuation curves are available from thermopad manufacturers which helps in design of thermal resistant rf units.
• Frequency range over which it should work
• Impedance value whether 50 Ohm or 75 Ohm
• Attenuation value in fixed value or variable steps or continuously variable in unit of dB.
• Type of connector for connectorized version such as SMA,N type,BNC,TNC and more.
Designing fixed attenuator using rf chip resistors
One can use T and Pi based formule or equations to arrive at values of individual chip components. One such calculation for 3dB and 6dB rf attenuators as per pi type which we have used in our designs and provided satisfactory results are mentioned in fig.3 below.
RF Attenuator Manufacturers
The following are few of the popular manufacturers of RF attenuator.
Aeroflex- PCB mountable attenuator pads and chip components are available.
Hittite Microwave- Digital control variable attenuator for various frequency ranges up to 30 GHz are available.
Voltage variable attenuators are also available.
Narda Microwave- Connectorised attenuators of all types fixed,variable and step are available.
Minicircuits-ideal for connectorised rf attenuators of SMA/N-type/BNC type/TNC type and more.
RF Micro Devices-various types of attenuators viz. analog,digital and temperature controlled are available.
Skyworks-Digital RF attenuators ideal for rf transceiver design is available.
Anaren- Chip attenuators/terminations and SMD attenuators/terminations are available.
Website : www.anaren.com
JFW Industries, Connectorised RF attenuators of various types available.
EMC RF Labs , Ideal for RF thermopad purchase.
Microlab USA,UK - Ideal for coaxial rf attenuators.