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What is a Frequency Extender?

What is a freq extender

In the Test & Measurement field a frequency extender is defined as an electronic device that allows for extending the frequency coverage of the equipment that it is intended to work with. A frequency extender performs frequency conversion, either by multiplication or by heterodyne mixing, or by a combination of both.



Frequency multiplication is realised by a device in which its output frequency is the harmonic (multiple) of the input frequency i.e. FOUT = N x FIN. A frequency multiplier typically uses nonlinear semiconductor circuits to generate harmonics of the input signal. Typically, we see such devices with multiplier factors of 2, 3, 4 and 5, however 6 and beyond are also possible in a multistage or cascaded circuit configurations.

A conceptual diagram of a multiplier.
figure 1. a conceptual diagram of a multiplier.

Heterodyne mixing is achieved in a device called a mixer, which operates on a principle of mixing one of the two signals, either radio frequency (RF) or intermediate frequency (IF), with a local oscillator (LO) frequency to produce new frequencies. In its most common application, the mixer produces a sum and a difference of the two signals applied to its inputs i.e.  IF = RF ± LO for a mixer operating as a down-converter, or RF = LO ± IF in case of an up-converter. Other more complex scenarios, in which mixing of signals’ harmonics is considered, are also possible.


A conceptual diagram of a mixer.
figure 2. a conceptual diagram of a mixer.

In principle, a relatively simple device such as a mixer or a multiplier, can be considered a frequency extender. In practice however, extending the range of a modern electronic equipment requires more complex solutions. In such cases, frequency extension is achieved by a combination of both frequency multiplication and heterodyne mixing, and aims to extend the frequency coverage of the equipment without deteriorating its other key parameters – for example output power, stability and/or dynamic range.


There are various types of test & measurement equipment for which frequency extenders are designed and manufactured, with vector network analysers, spectrum & signal analysers, noise figure analysers, signal generators to name just a few. Such frequency extension systems are used in applications that require high frequency operation such as radar testing, antenna measurements, on-wafer measurements, wireless communication and material characterisation.

Antenna range measurement setup.
figure 3. antenna range measurement setup.

Click here to learn more about how frequency extenders work

Click here to learn more about the different types of frequency extenders

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