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Switched filter banks (SFBs) are traditionally found in RF front ends or intermediate stages of sensitive receivers for military and defense applications, as they help reduce harmonic and spurious content which is critical to communications systems. Until recently, high-power SFBs (Fig. 1) have been limited to fixed locations or on larger mobile platforms due to their inherent large size.
Gallium-nitride (GaN) power amplifiers (PAs) have reduced the size and weight of high-power transmitters in the hundreds of watts range. The demand for SFB assemblies has thus followed suit. However, the leap from traditional SFBs to high-power equivalents is not straightforward, and many tradeoffs and design considerations must be made in order to develop a suitable high-power SFB.
One application that has driven the early development of high-power SFBs is communications band signal jamming at VHF and UHF frequencies. These devices have predominantly been used to prevent communications band signals to remotely triggered explosives and to deny cellular service near secure governmental and military facilities. Ironically, technology that has initially been leveraged to mitigate communications may be a solution that enhances communications in modern and future trending applications.
Practical Justifications for High-Power SFBs
As communications band usage increases with the explosion of the Internet of Things (IoT) and machine-to-machine (M2M) devices, there may be greater commercial and industrial sector demand for high-power amplification and switching technology that limits the spurious content in these bands. A reason for this is that any additional harmonics or spurious content could dramatically increase the interference and noise to nearby low-power IoT/M2M systems.
For example, the latest autonomous (or connected) car may heavily rely on a constant communication channel to a common base station and between other vehicles for safe operation. In a world with a densely packed web of critical systems, cranking up the transmitter power won't be an option to preserve reliable communications. Thus, the high-power systems in heterogeneous networks may require more stringent operational specifications.
Another future application of high-power SFBs could be enabling high-speed communications channels for commercial and industrial drones. The adoption of unmanned aerial systems (UAS) technology is accelerating and may play a larger role in commercial and industrial applications. The reliable control and communication with these systems will require more agile and small...