Hybrid RF-Digital Feed-Forward Filter for High-Order Frequency Agile Filtering

Wireless network operators, spectrum managers and wireless infrastructure vendors have generated demand for frequency agile RF filters. The current state of the art frequency agile RF filters are limited to low filter order.;The digital subsystem is placed in one of the feed-forward paths, and includes a digital filter. The digital filter permits the system to have a high filter order. The digital system is bookended with frequency down and up conversion stages to permit the digital filter to be used at any RF frequency. The second feed-forward path consists of an RF system, and in the simplest case is just a transmission line. This path provides a high dynamic range route through the filter, specifically for passband signals.;Noise and attenuation analyses are performed that incorporate the non-linear effects of the digital components into conventional RF performance metrics. The noise analysis demonstrates the potential for the filter to exhibit less than 1 dB of noise figure. RF measurements are used to demonstrate proper operation of a hardware prototype. The prototype is targeted towards the RF front-end of a receiver with a dynamic interference environment at its input. Measurements demonstrate interferer suppression for operation at several bands between 800 and 1800 MHz. The group delay mismatch between the feed-forward paths is reduced with a delay line to achieve between 32 to 24 dB of attenuation for interferers with bandwidths from 1 to 8 MHz. The largest digital filter used within the prototype has 64 complex taps, thereby providing the hybrid RF-DSP FF filter with 64 tunable transfer function zeros.;The hybrid RF-DSP feed-forward filter represents a fundamental change to frequency agile RF' filter design. This fundamental change is based on harnessing the ever increasing processing power of DSP instead of the more traditional approach of incrementally improving the quality factor of tunable resonators.;This thesis introduces a frequency agile RF filter that is fundamentally different from the current state of the art. Digital and RF systems are combined in a feed-forward architecture. This architecture provides a frequency response with multiple tunable transfer function zeros. This feed-forward architecture is called the hybrid RF-DSP feed-forward filter.