The need for RF design services has become quite extensive today. From aeronautical engineering service providers and cell phone manufacturers, all of them need RF designs for their products. Development of wi-fi and blue tooth technologies did away with hardwire usage. In avionics as well as in commercial use bandpass filters are required. There is so much traffic in the ether that you don’t want frequency distortion. There are some specialist companies that provide RF design services, and if they specialize in avionic instrumentation designs, then they have to be familiar with DO-178B / DO-254. These are software standards for airborne systems and hardware and their required certification.
There are not many companies that have the necessary qualifications to qualify for these stringent standards. But defense departments do know where to find the people who know these standards and can provide RF designs. Today with the amount of frequencies and bandwidths being used, anyone who is designing a new aircraft or a piece of new RF technology will require specialist companies to do the RF design for them. If you remember seeing the famous popular cultural expression ‘Killroy was here’ well a band pass designer may have thought of it while studying a bandpass filter that resembles it.