Gain Flatness test | Gain Flatness Measurement Formula

This page covers gain flatness test or gain response measurement testing. It mentions Gain Flatness Measurement Formula. This can be used for gain flatness measurement of RF Upconverter, downconverter, RF amplifier etc.

The gain flatness has been usually given in the technical specifications of RF systems as mentioned below:
RF Up converter: Gain response should be +/- 1 dB for all the transponders in the range from 5925 to 6425 MHz. For example, +/-1dB for 6175+/-18 MHz as transponder bandwidth is about 36 MHz.
Similarly for C band RF down donverter from 3700 to 4200 MHz band.
RF Power Amplifier: +/- 1 dB for C band Frequency from 5925 to 6425 MHz for all the transponders.

Gain flatness measurement formula

gain flatness measurement
Figure-1 : Gain flatness response

As mentioned, gain flatness is the difference between maximum gain (GMax) and minimum gain (GMin) measured over frequency range of interest. The flatness measurement formula can be expressed as follows.

flatness measurement formula

Gain Flatness Test Setup

gain flatness test setup
Figure-2 : Gain flatness test setup

The figure-2 depicts typical gain flatness measurement test setup. As mentioned tools such as Sweep Oscillator, Scalar Network Analyzer (SNA), RF detectors, RF power splitter, attenuator pads and DUT(Device Under Test) are used. Following steps are usually performed for gain flatness measurement.

➨First calibrate SNA for through measurement with all the required RF components needed in the set up such as power splitter, detectors and attenuator pads.

➨Do the settings of input frequency range of DUT as needed in the sweep oscillator before calibration. Also take care of desired input power level needed for the Device Under test e.g. RF amplifier or RF Up converter module of RF Transceiver.

➨Now insert DUT in the setup. One can observe the gain response as shown in the figure-1 above. Use two markers on the SNA.Keep one on maximum and the other on minimum points. The difference between these two points is known as gain flatness or gain response.

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