Active and Passive Matching in RFPAs: A Quirky Partnership

Microwave designers have been slow to embrace the many possibilities offered by active, as opposed to the traditional passive, matching techniques. For example, well-known physical limitations of passive matching, such as the famous Fano limit, can be “defeated” using active techniques. But active matching incurs an obvious cost; extra power is consumed. This power can in some cases be fully retrieved, but not always. In particular, the Doherty PA, in its ideal form, “recycles” the power from the auxiliary device, but this desirable property erodes as the impedances become reactive. In many cases a combination of active and passive matching is used in order to restrict the “auxiliary” power to manageable limits. This results in the unfamiliar situation where passive networks have variable terminations, something that classical network theory does not fully address. This talk will discuss some of the potential benefits, but also the possible hazards, of this approach in PA design.

Presented by: Dr. Steve C. Cripps, Cardiff University