EducationAttenuator definition - How attenuators works

Attenuator definition – How attenuators works

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Attenuator definition

Attenuator is a kind of passive component that is part of the fiber optic pathway. The attenuators are designed to reduce the energy produced by the signal transmitted. This way, we are able to completely control the entire process as it takes place. We can differentiate between adjustable and fixed attenuators.

The attenuator is located in the optical fiber system just in the front of the sensor. As the power of the light passes through the attenuator it’s value starts to be within the operating range for the device. This entire process happens through optical fibers that are located inside the corresponding connector (male-female type). The importance of signal attenuation in connectors is precisely specified. On the market, you are able to find attenuators for the SC, FC ST, LC, and the MU connector.

In the various kinds that are fiber optic attenuators it is important to identify the kind that is an adapter attenuator. Similar to their predecessors, the function of such devices is to reduce the optical strength of the signal being transmitted. In general it is not different in any way from an connector attenuator with the exception of one aspect. In this instance the element that is attenuating signals can be described as a fiber optic adapter and not appropriate fibers. The attenuation process is clearly specified. The adapter comes in three variations: SC, ST and FC.

The final kind of fiber fixed attenuators can be described as “In-line” devices. The signal attenuation is accomplished by using specially designed splices. Naturally, the effectiveness of this method is clearly established.

Principle of operation

The basic principle behind attenuators employed to reduce radio frequencies follows: Voltage divisors in capacitors or resistors. Input signal split into the resistors in proportion of their resistance. The most straightforward solution is a divider composed of two resistors. This type of attenuator is referred to as”L-shaped” attenuator (in technical literature from outside the country the term is L-shaped). The output and input can be on the opposite side of this asymmetrical device. L-shaped attenuators are distinguished by their the low loss of matching between input and output.


L-A type

Types of attenuators

In the real world the real world, L-type attenuators are less often used mostly to match the output and input impedances. The most commonly used devices in order to standardize the signal’s attenuation are the P-type (Pi in the literature of foreign countries derived is derived from Pi in literature from the Latin word”p” in foreign literature)) as well as T-type. This is because it allows to develop devices with identical output and input imperceptibility (but different impedances may be employed if required).

T-type and π-Type attenuator

T-type and π-Type

The image illustrates devices that are symmetrical. The source and the load should be connected on both sides using unbalanced cables – coaxial cables etc.

For symmetrical lines (twisted-pair, etc. ) Symmetrical circuits are utilized. These are also known as HO-type attenuators however, they are simply variations on the earlier devices.

attenuator type

Adding one (two) resistors makes the T-type (H) attenuator a bridge attenuator.

attenuator type

Attenuators can be found on the market for industrial use as complete units with connectors to connect, however they can also be constructed using an electronic circuit board part of a larger circuit. Capacitive and resistive attenuators have a major benefit – they don’t contain nonlinear elements. This doesn’t distort the signal or create new harmonics in the spectrum , or cause existing ones to fade away.

Apart from resistive attenuators There are various kinds of attenuators. Most commonly used in industrial applications are:

  • Limiting and the polarizing attenuators based on the physical properties of waveguides
  • absorption attenuators reduce signal intensity due to the absorption of energy by certain materials
  • optic attenuators.

These devices are utilized in microwave technology as well as light frequencies. For radio and low ranges, attenuators based on resistors and capacitors are employed.

Paremeters of the attenuator

The coefficient of attenuation is the principal parameter that determines the characteristics of attenuators. The measurement is in decibels. To determine how often the signal’s amplitude decreases following going through an attenuation circuit change the coefficient in decibels into times. Its output capacity of the device that decreases the signal’s amplitude to N decibels is M times less:

M=10^(N/20) (for the power that is M=10^(N/10))

Inverse conversion:

N=20log10(M) (for the power N=10log10(M))

Thus, for an attenuator that has Kosl = -3 decibels (always negative because the value is always decreasing) the output signal will have an amplitude of equal or greater than 0.708 that of its original. If the output amplifies is the same as half of the original value Kosl is approximately -6dB.

These formulas can be quite difficult to figure out within your head, which is why it is recommended to make use of online calculators of which you can find many available on the Internet.

In the case of devices that can be adjusted (step or smooth) the limitations of the settings are set.

Another vital aspect is the impedance between the output and the input (they may be identical). The impedance that is related to this is a feature known as the standing-wave ratio (SWR) that is usually found on commercially produced products. If it is only active loads the calculation is made by formula:

VSW = r/R

when r>R with R being the resistance of the load and the line’s impedance.

VSW= R/r, if r

VSW will always be greater than or equal to 1. If R=r, all power will be passed to load. The more the values diverge from each other, the more power is lost. For instance when VSW=1.2, 95 percent of the power gets to the load, while at VSW=3 75 percent. If you connect a 75-o attenuator to 50 O line (or reverse) the result is VSW=1.5 and the loss would be 4percent.

Other significant features worth mentioning include:

  • Operating frequency range
  • maximum power.

It is also important to ensure the accuracy, i.e., the acceptable variation of attenuation in relation to the nominal attenuation. For industrial attenuators the specifications are displayed onto the enclosure.

In some instances the strength of the device is vital. The energy that doesn’t get to the attenuator is absorbed by the attenuator components, therefore it is essential not to overburden the attenuator.

There are formulas to calculate the fundamental characteristics of resistive attenuators with various designs however, they are difficult to use and require logarithms. So, you’ll need at least a calculator utilize these. It is therefore more practical to use specific software (including online) to calculate your own calculations.

Adjustable attenuators

The attenuation coefficient and the VSW are affected by the ratings of the components that are part of the attenuator Therefore, creating devices that have resistors that are variable parameters that can be adjusted continuously is difficult to design. When you alter the attenuation or attenuation coefficient, the VSWR factor has to be adjusted as well, and in reverse. This can be accomplished through amplifiers with gains that are less than one.

The amplifiers are constructed with transistors or OPAMPSale. The problem is linearity. It’s not simple to design an amplifier that doesn’t alter the waveform across the entire frequency range. The most common type of amplifier is the step control. attenuators connect in series and the attenuation combined. Circuits that require to be attenuated are left out (relay contacts, etc.). This means that the needed attenuation coefficient can be obtained without changing the impedance of the wave.

step attenuator

There are plans that can be infinitely adjusted attenuators that are based in broadband transformers (BFTs). They are utilized in communications for amateurs in which the requirements for matching input and output are minimal.

The smooth tune of waveguide attenuators can be achieved by altering the dimensions of the geometric. optical attenuators with an adjustable attenuation can also be found however they come with a quite a complex design because they comprise a set of optical filters, lenses and other components.


If an attenuator is equipped with different output and input impedances, it may be used as a matching device in addition to the attenuation function. For instance, if a 75-ohm and 50-ohm cables are to be joined an appropriate cable with the right rating could be used between them, and the degree of matching can be altered in conjunction by the standardized amount of attenuation.

In reception application, attenuators are used to ensure that input circuits are not overloaded with high-frequency interfering signals. In some instances the attenuation of an interference signal, even in conjunction with an unimportant signal could enhance reception quality by lessening intermodulation noise.

In the field of measurement, attenuators can be used as decoupling elements to reduce the impact upon the source of reference. Optic attenuators are often used in the evaluation of both receiving and transmitting optic devices. They are utilized to mimic attenuation on an actual line, and also to assess the conditions and limitations of a steady link.

For audio engineers, attenuators can be used to control power. As opposed to potentiometers, attenuators accomplish this without causing power loss. In this scenario it is easier to offer seamless control since their impedance wave isn’t important as it’s the attenuation that is the most important factor. In cable TV network, attenuators eliminate congestion of TV inputs, allowing the transmission quality to be preserved regardless of reception conditions.

Attenuators, while not the most complicated devices, are widely employed for radio frequency systems. They can be utilized for various applications. In the microwave and optical frequency they are constructed differently, and are complicated industrial assemblies.


Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.