Understanding Programmable RF Attenuators as Variable Attenuators

This page discusses programmable RF attenuators, which serve as variable attenuators for adjusting signal attenuation.

Fixed RF attenuator chips are readily available for various frequency ranges. These components provide a fixed amount of attenuation in the RF signal path. Based on the 1dB compression points of devices like mixers and amplifiers in the RF signal chain, appropriate attenuator values (e.g., 3dB, 6dB) are selected. However, situations often require variable attenuation, making variable attenuators necessary. Typical applications include Automated Test Equipment (ATE), manual testing, and more.

Variable attenuators mainly come in two types: digital and analog. Furthermore, depending on the application, either connectorized or connectorless attenuators are used.

Fig-1 shows a digital programmable RF attenuator. As illustrated, the device is digitally controlled, either via RS232 or TTL. This allows easy control using a microcontroller or processor. Writing different bit patterns to the digital control lines sets different attenuation values. The RUDAT-6000-110 from Minicircuits offers attenuation up to 110 dB across a frequency range extending to 6 GHz. This programmable RF attenuator has a step size of 0.25dB and can be controlled via USB or RS232. The attenuation accuracy varies with frequency, ranging from +/-0.15 to +/-0.80 dB. VSWR performance also varies across different frequency ranges. Typically, for the 4000 to 6000 MHz range, VSWR is 1.30:1 for attenuation settings from 0 to 20 dB, and 1.15:1 for attenuation in the range from 20.25 dB to 110.00 dB.

Fig-2 illustrates an analog variable attenuator. As depicted, the device’s attenuation is varied by changing the analog voltage applied to its control pin. This principle is utilized in rotary-type RF variable attenuators.

For example, the HMC346MS8G from Hittite Microwave is a voltage variable attenuator with the following features:

• Frequency range: DC to 8 GHz
• Attenuation Range: 0 to 32 dB
• IIP3: 10 dBm
• Control voltage: 0 to -3V
• Loss: 1.5 dB

RF Variable Attenuator Manufacturers

Here’s a list of popular variable attenuator manufacturers:

• Hittite Microwave
• Minicircuits
• JFW Industries
• Maxim Integrated
• Analog Devices
• API technologies corp.