NuWaves Engineering, a developer of radio frequency (RF) and microwave solutions for unmanned aerial systems (UAS) and robotics, has released the following article outlining the benefits of using a tunable filter for covering multiple frequencies.
Filters are a staple of RF designers everywhere, especially in applications where the integrity of the signal cannot be compromised. When you’re only concerned about a single frequency, it is relatively easy to add in a fixed-tuned filter. However, it becomes slightly more difficult when you need to cover multiple frequencies and cannot simply utilize a roofing filter. To avoid having to use multiple individual filters, thus in effect creating a complex switched filter bank module, a tunable filter may be the solution.
One of the most common applications for a tunable filter is as a pre-selector in a receive path, where there is a need to filter out adjacent channel (cosite) interference. It is very common, especially in modern communication systems, for the receiver to need to operate over a wide frequency range. To make things worse, the interference often comes from co-located transmitters at the same location. Due to the minimal antenna isolation, especially on smaller command/control vehicles, filtering is needed to protect the receiver front end.
A tunable filter can also be used in the transmit path, as a post-selector on the output of an exciter or low power transmitter. This is especially useful if the transmitter is not spectrally clean. These lower level transmitters are often used to drive higher power amplifiers, so filtering is needed before further amplification, in order to clean up the signal and avoid sending out ‘splatter’ across the spectrum.
There are a variety of choices available for frequency-agile tunable filter modules, so it all comes down to the desired specifications for a given application. One example is the NuWaves HiPerTuner, which provides filtering across the 200 MHz to 2.5 GHz frequency range. With 1 MHz channel spacing, the HiPerTuner is the equivalent of 2,301 bandpass filters in a single ruggedized chassis.