Narrowband Planar Filter Design with NI AWR Design Environment Software

Presented by: Daniel G. Swanson Jr., General Partner, SW Filter Design
Sponsored by: National Instruments

Planar microwave filters can be found in low cost PCB environments as well as higher performance thin-film technologies. The number of potential topologies to consider and the design trades to be made can be intimidating for the non-expert. Fortunately, there is a straightforward design flow that can efficiently address this design challenge.

This design flow starts with narrowband filter design concepts pioneered by Dishal. On top of that we layer modern cross-coupled filter concepts developed by Atia, Williams, Cameron and others. Once we have a circuit theory based prototype, we can turn it into an EM model using NI AWR Design Environment (EMSight/AXIEM). Next we apply port tuning concepts developed by Swanson and Wenzel to bring the EM model into perfect equal ripple tune. The resulting circuit theory based tunings are a direct indication of the direction and relative magnitude of every resonator and coupling error in the filter. The physical dimensions of the filter can then be adjusted with relatively few EM simulations of the complete filter. The outlined procedure is much more efficient and intuitive than a brute force optimization of filter dimensions in an EM simulator.

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