Attenuator in microwave's primary function is to reduce the signal strength before it reaches sensitive circuit components. Today, we will learn how to select an attenuator suitable for its application.
Attenuator in microwaves reduce the required or unnecessary signal intensity along the signal path. They can be used to reduce the output signal of the Device Under Test (DUT) before sensitivity testing and measuring receivers to ensure more consistent impedance matching or to ensure precise control of the signal amplitude at the transmitter output. The attenuation level of the device-the signal power/voltage amount lost through the device-is typically measured in decibels (dB) or in terms of voltage ratio.
Attenuator in microwaves can be based on passive resistors, absorptive materials/technologies, PIN diodes, or field-effect transistor (FET) technologies. Additionally, attenuators can be developed using coaxial transmission lines, stripline, surface-mount, or even waveguide interconnect technologies. The performance and physical characteristics of these technologies vary considerably. The quality and cost of the construction can affect the range of performance, thermal performance, and physical characteristics.
Attenuator in microwaves can also be classified as fixed or adjustable attenuators. Adjustable attenuators include switch attenuators with discrete attenuation levels and continuously variable attenuators with analog adjustment capabilities. Both types of attenuators can be designed for electrical or mechanical control. Some attenuators can be programmatically controlled through digital signals or even software.
Depending on the design purpose, the input and output impedance of attenuator in microwaves may vary. It could be the common 50 ohms, 75 ohms, or custom impedance values. Moreover, some attenuators are designed to allow DC bias to pass through, known as DC bias pass-through attenuators.
Additionally, attenuators can be categorized based on attenuator technology as reflective or non-reflective. Reflective attenuators will reflect the attenuated signal energy rather than absorb it. The reflected signal energy is a function of the attenuation level.
When selecting an appropriate attenuator in microwave for a specific application, system engineers usually need to balance multiple factors. One application might require the attenuator to have higher electrical, physical, or environmental characteristics, which ultimately determine the design constraints when selecting an attenuator.
In selecting an attenuator in microwave, it is essential to deeply understand its various indicators. Besides the attenuation function and some basic parameters (such as insertion and reflection loss), several other characteristics can describe attenuator components, including:
IC maintains its specified characteristics frequency.
The amount of suppression beyond the insertion loss.
The variation of the attenuation level (dB) across the entire frequency range (Hz).
The total attenuation value provided by the component.
Usually represented by the 3rd-order intermodulation point (IP3), which defines the hypothetical input power level at which the power of the respective spurious component would reach the same level as the fundamental components.
Typically represented by the input 1 dB compression point, which defines the input power level when the insertion loss of the attenuator decreases by 1 dB.
Power handling characteristics are generally determined for average and peak input power levels in steady-state and hot-switching modes.
The phase shift introduced in the signal by the attenuator component.
In addition to these common parameters, switch characteristics are used to describe variable attenuators, typically in terms of rise time and fall time, turn-on and turn-off time, and the amplitude and phase settling time of the RF output signal.