|
The technical indicators of attenuators include: operating frequency band, attenuation, power capacity, return loss, etc.
(1) Operating frequency band
The operating frequency band of an attenuator refers to the attenuation that can reach the indicator when the attenuator is used within a given frequency range. Since the RF/microwave structure is related to the frequency, components of different frequency bands have different structures and cannot be used interchangeably. The operating frequency band of modern coaxial attenuators is quite wide.
(2) Attenuation
The attenuator is a two-port network, which can be represented by the following figure.
The power at the signal input end is P1, and the power at the output end is P2. The power attenuation of the attenuator is A (dB). If P1 and P2 are expressed in decibel milliwatts (dBm), the relationship between the powers at both ends is
P2 (dBm) = P1 (dBm) - A (dB), that is:
It can be seen that attenuation describes the degree to which the power decreases after passing through the attenuator. The magnitude of the attenuation is determined by the material and structure of the attenuator. The attenuation is measured in decibels. The figure below is a 70dB attenuator, which means that the power of the signal will decrease by 70dB when it enters from port one and exits from port two.
For example, if I connect the attenuator to the signal source, I will use 0dBm power as the transmission standard.
The signal received on the spectrum analyzer is around -70dBm.
The attenuation can also be measured through the network, which is still very flat.
(3) Power capacity
The attenuator is an energy-consuming component, and the power is converted into heat after consumption. It can be imagined that once the material structure is determined, the power capacity of the attenuator is determined. If the power that the attenuator is subjected to exceeds this limit, the attenuator will be burned. For example, because the coaxial attenuator is a passive power device, the temperature coefficient must be considered, which indicates the change in attenuation with temperature. Usually, as the temperature rises, the attenuation decreases.
(4) Return loss
The return loss is the standing wave ratio of the attenuator, which requires that the input and output standing wave ratios at both ends of the attenuator should be as small as possible. The attenuator we want is a power-consuming component that cannot affect the circuits at both ends, that is, it matches the circuits at both ends.
The standing wave of the attenuator in the above picture is already very low. The basic composition of the attenuator The basic material of the RF/microwave power attenuator is resistive material. The usual resistor is a basic form of attenuator, and the resistive attenuation network formed by this is a lumped parameter attenuator. By placing the resistive material into the RF/microwave circuit structure of different bands through a certain process, an attenuator of the corresponding frequency is formed. If it is a high-power attenuator, the volume must be increased, and the key is the heat dissipation design. The one at hand is an electrically adjustable attenuator, and the interface in the figure below is the interface for controlling the current. Since there is no screwdriver to disassemble it, you can't see what it looks like inside.
Application of attenuator
(1) Control power level: In microwave superheterodyne receiver, the output power of the local oscillator is controlled to obtain the best noise figure and frequency conversion loss, and achieve the best reception effect. In microwave receiver, automatic gain control is implemented to improve the dynamic range. In addition, when using a spectrum analyzer, the amplitude gear is adjusted, which means that the pre-attenuator of the spectrum analyzer is adjusting the gear.
(2) Improve impedance matching: If some circuits require a relatively stable load impedance, an attenuator can be inserted between the circuit and the actual load.
(3) Relative standard: used as a relative standard for comparing power levels.
(4) Jump attenuator used in radar anti-interference: a variable attenuator with a sudden change in attenuation. It does not introduce attenuation at ordinary times, but suddenly increases attenuation when encountering external interference.
(5) Improve the insertion loss measurement accuracy of network analyzers: when using a network analyzer to measure the insertion loss of passive devices (especially low-loss devices such as cable assemblies, air lines, etc.), since the reflected power will decrease after passing through the attenuator, connecting an attenuator to the port can improve matching, reduce standing waves, and improve measurement accuracy.
| 
提升卡
变色卡
千斤顶
