Fixed Attenuators/Terminations
Fixed attenuators are found in a wide variety of electronic equipment for extending the dynamic
range of measuring equipment, for preventing signal overload in transmitters and receivers, and
for impedance matching to reduce the effects of improper input/output terminations of
oscillators, amplifiers and test setups.
The important parameters associated with fixed attenuators include the amount of attenuation,
the flatness over a specified frequency, range, VSWR, average and peak power-handling
capability, size and height, and performance over a given temperature range. Average power
limit decreases linearly as temperature increases and burnout will result (or calibration will be
altered) if average power limit is exceeded.
Mini-Circuits' fixed attenuators, packaged in rugged plug-in and connector models, are available
in both 50- and 75-ohm models ranging from 1 to 40 dB spanning DC to 1500 MHz.
Definition of Terms
fixed attenuator
A device used to reduce power levels of a signal by a fixed amount with little or no reflections.
The output signal is attenuated relative to the input signal while the input and output impedance
is maintained close to 50 ohms (or 75 ohms) over the specified bandwidth. Hence, this device is
often used to improve interstage matching in a circuit.
flatness
The total variation in attenuation over the specified frequency range. Flatness generally becomes
worse at higher frequencies where attenuation starts to increase with increasing frequency.
vswr
Voltage-standing-wave ratio is a measure of the deviation from 50 ohms or 75 ohms of the input
and output impedance. A VSWR of 1.0:1 represents a perfect 50-ohm or 75-ohm match. A
VSWR slightly greater than 1.0:1 represents a slight impedance mismatch, implying a small
amount of signal reflection.
termination
An ideal load of impedance Z0, when connected to the end of a transmission line whose
characteristic impedance is also Z0 will absorb all power in the transmission line traveling toward
the load.
maximum rf power
The amount of power that can be applied to an attenuator or load which does not result in
excessive heating of the attenuator or load.
return loss
The minium return loss the termination exhibits when used for terminating a transmission line it
is designed to match. For an attenuator, return loss is measured at one port when the other port is
terminated in 50- or 75-ohms for which it is designed.
Most Often Asked Questions
Q. Many of MCL's fixed attenuators are specified up to 1500 MHz. How will they perform at
higher frequencies?
A.
With the exception of the 75-ohm models, most fixed attenuators perform reasonably well
above 2000 MHz. Please refer to data pages for actual performance characteristics.
Q. What internal design configuration is used in the fixed attenuators and are they
symmetrical?
A. Both 
and T type configurations are used and both are symmetrical. Hence, the input and
output are interchangeable.
Q. Are surface-mount packages available?
A.
Yes. Consult the factory to discuss your application and the parameters of surface-mount
packages.
Q. What is the difference between the flatness spec and the deviation on the nominal
attenuation spec?
A.
The nominal or average value of attenuation of a particular attenuator is guaranteed to be
within the nominal spec window, and is measured at the low frequency end of the band. The
flatness spec only refers to variation of attenuation across the specified bandwidth.
Q. Can Mini-Circuits' provide terminations at different impedances upon request?
A.
The impedance of Mini-Circuits' terminations are either 50- or 75-ohms. Other impedances
are not available.
Last Updated: 09/08/1999