RF Attenuators Includes:
Attenuator basics Attenuator specs Resistive attenuator design Attenuator resistor values table Balanced resistive attenuator pads Variable PIN diode attenuator Construction guidelines SMA attenuator
When designing, purchasing or using an RF attenuator it is necessary to be able to specify it to ensure that an attenuator with the correct performance is obtained. While some of the major specifications are detailed below, for some applications other parameters may need to be specified.
RF attenuator specifications
- Attenuation: This is the primary specification for an RF attenuator. It is the ratio between the output and the input power levels and is typically quoted in decibels (dB).
- Attenuation accuracy : It is often necessary to know the accuracy of the level of the attenuation of the attenuator. Particularly in applications where equipment is being tested, the attenuation accuracy is likely to be important. In these cases a tolerance on the nominal level of attenuation will be given.
- Frequency response: The level of attenuation of an attenuator will vary with frequency. This can result from the frequency dependence of the resistors or other components used in the RF attenuator, or where coupling between the input and output may exist as this will be frequency dependent. Some RF attenuators where the absolute level of attenuation is important may be provided with calibration charts measuring the absolute attenuation at different spot frequencies over a frequency band.
- Impedance : RF attenuators will be designed for use in systems with a given characteristic impedance. 50 ohms is the most common, although 75 ohms is also used, and it may be possible to obtain RF attenuators with other impedance values should the need arise.
- Power dissipation: In order to reduce the signal level, RF attenuators dissipate or absorb the unwanted power. For many small signal applications, power dissipation is not an issue, but for other applications where signal levels are higher, it is necessary to ensure that the RF attenuator will satisfactorily be able to handle the power levels anticipated. Power capabilities for RF attenuators may be quoted in Watts (or milliwatts) or as dBW - decibels relative one Watt (or dBm - decibels relative to a milliwatt)>
- Mechanical details of the attenuator: The mechanical details may include aspects such as the size and weight. The connectors may be included in this area of the attenuator specification.
- Environmental details: Many applications for attenuators are for use within benign conditions such as a laboratory environment. Environmental conditions would not be an issue. However for some applications it is possible that an environmental is required to detail factors such as vibration, temperature, humidity and the like.
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