When designing an RF or microwave application, you will always need some level of filtering to attenuate or remove unwanted signals from the desired channel. Since the end goal of what a filter must accomplish is quite broad, it may seem daunting to know what qualities to look for in a filter to get there.
To simplify, let’s think about the search for the perfect filter like we were looking to hire our next great RF engineer. If we went out to LinkedIN or Indeed.com in search of the ideal filter to “hire,” our job post would look a lot like the following:
Basic Job Requirements
- Low insertion loss over a defined frequency range (passband)
- Good return loss over the passband
- High insertion loss outside of the defined frequency range (rejection band)
- Establish channel bandwidth (passband)
- Lower noise floor by reducing channel bandwidth to the passband frequency range
- Remove out-of-band signals from the receiver chain to minimize/eliminate undesired signal contamination
- Minimize high-level out-of-band signals to help prevent channel component saturation
- Remove signals above passband frequency range to prevent aliasing in analog-to-digital conversions (ADCs)
- Eliminate/minimize out-of-band signals to aid in regulatory compliance
- Set IF frequency bandwidth of up/down converter stages
- Reduce/eliminate LO signals, spurious products, harmonics, and sidebands in the IF bandwidths and provide flatter channel responses, lower noise floors, and increase channel saturation levels in the IF stages by reducing power from unwanted signals
In general, all filters have the same basic job to do, and a generic job description like the one above can help you get started. However, the specific job requirements, such as rejection levels and bandwidth, needed for each filter will vary depending on the application – and that’s where our experts come in.