Recent Improvements in Real-Time Load-Pull Systems

In this paper, some recent advances in real-time load-pull technologies are described. Directional couplers losses, limiting the reflection coefficient at the device under test reference plane, are reduced, exploiting a novel coupling device designed by the authors. This device is formed by two double directional couplers and called "double head". The "double head" is implied in real-time load-pull test-benches and measurements give evidence that it can be used up to 15 GHz, where it is nearly "transparent77. Furthermore, some advices to bypass the remaining unavoidable losses due to probes and cables are given. We will show with some measurements that the combined use of double head, passive tuner and active loop, not only boosts the available Gamma_L, but also decreases the output power requested from the loop amplifier, with a sensible reduction of the overall cost of the system