Article: Selecting Filter Response Type for Specific Applications

By Mike Ball / 20 Feb 2020
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NuWaves Engineering RF filter

NuWaves’ C-Band Cavity Filter, which allows signals in the 5.8 GHz frequency band to pass through, reducing out-of-band interference received by a receiver, or radiated by a transmitter.

NuWaves Engineering, a leading developer of radio frequency and microwave solutions for unmanned aerial systems (UAS), has released the following article detailing the correct selection of filter reponse type for applications such as UAS communication systems.

RF filtering is important, as filters reduce the interference in the environment that affects the performance of the communication system, as well as reducing the interference caused by the system itself. Once you have identified the system-level need for a filter, the next step is to determine which filter response type will accommodate your other system-level requirements.

At NuWaves, the most commonly utilized response types are the Chebyshev, Bessel-Thomson and Butterworth. These are carefully chosen after a thorough review of the customers’ specifications and requirements. Below is a quick overview of these filter response types and their implications on the overall system performance.

The Chebyshev filter is the most common filter response used to fill customer requirements. For applications that require high out-of-band rejections, or for those that require stopband rejections close in to the passband corner, the Chebyshev filter is the right choice. This response type provides steeper roll-off (attenuation) to stopband frequencies, with the drawback being that it can create large variation in group delay flatness.

The Bessel-Thomson filter type provides the maximum group and phase delay flatness, allowing the filter to preserve the input waveform shape. For a given percentage bandwidth and order, this type delivers the lowest attenuation in the stopband. The drawback to the Bessel-Thomson filter type is that is does not preserve amplitude flatness.

The Butterworth response type is another approach commonly taken to ensure that the filter will integrate properly into the higher-level system requirements. This filter type produces better group delay flatness, overshoot, and lower (or absent) passband ripple when compared to the Chebyshev filter type. The drawback to a Butterworth filter is that it has a much slower roll-off to the stopband and can require a higher order filter to achieve a desired attenuation at the stopband frequency.

Selecting the correct filter type is important to the overall system performance. Taking the time to understand the impacts to the overall system requirements, including the requirements of a given waveform, are important when choosing which filter response type will result in a successful integration.

If your UAS communication system is not meeting the expected performance, NuWaves can help with adding filters to your design. Filters are easy additions to the system – they can be small and lightweight, do not require electrical power to function, and are generally low-cost items. Filtering can make a significant difference in the performance of your UAS.

NuWaves Engineering has developed a wide variety of off-the-shelf RF amplifiers with rich features to support mission-critical CONOPS in telemetry, ISR, and tactical communication systems applications. Frequency ranges are available from UHF through C-band with output power levels ranging from 5 to 50 W.

Learn more about NuWaves’ RF and microwave filters for UAVs and unmanned systems here>

Posted by Mike Ball Mike Ball is our resident technical editor here at Unmanned Systems Technology. Combining his passion for teaching, advanced engineering and all things unmanned, Mike keeps a watchful eye over everything related to the unmanned technical sector. With over 10 years’ experience in the unmanned field and a degree in engineering, Mike’s been heading up our technical team here for the last 8 years. Connect & Contact
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