How do you test microwave filters for wireless communication?

2 Measuring the insertion loss

The second step to test microwave filters is to measure the insertion loss, which is the ratio of the output power to the input power of the filter. The insertion loss indicates how much the filter attenuates the signal in the passband, which is the frequency range that the filter allows to pass through. To measure the insertion loss, you need to set the signal generator to sweep the frequency range of interest, and observe the output spectrum on the spectrum analyzer. You should record the minimum and maximum insertion loss values in the passband, and compare them with the specifications of the filter.

3 Measuring the return loss

The third step to test microwave filters is to measure the return loss, which is the ratio of the reflected power to the incident power of the filter. The return loss indicates how well the filter matches the impedance of the system, and how much the signal is reflected back to the source. To measure the return loss, you need to disconnect the spectrum analyzer from the output port of the filter, and connect a directional coupler instead. The directional coupler splits the signal into two paths: one that goes to the filter, and one that goes to the spectrum analyzer. You should set the signal generator to sweep the frequency range of interest, and observe the reflected spectrum on the spectrum analyzer. You should record the minimum and maximum return loss values in the passband, and compare them with the specifications of the filter.

4 Measuring the rejection

The fourth and final step to test microwave filters is to measure the rejection, which is the ratio of the output power to the input power of the filter in the stopband, which is the frequency range that the filter blocks or rejects. The rejection indicates how well the filter isolates the desired signal from unwanted signals or noise. To measure the rejection, you need to reconnect the spectrum analyzer to the output port of the filter, and set the signal generator to sweep the frequency range of interest. You should record the minimum and maximum rejection values in the stopband, and compare them with the specifications of the filter.

5 Here’s what else to consider

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