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Hybrid Active Load Pull

Achieve high VSWR at the DUT reference plane with Hybrid Active Load Pull. Navigate complex test systems to optimize performance using feedback amplifiers, synchronized sources, and in-situ vector power wave measurement.

FOCUS-A6-HYBRIDACTIVELOADPULL
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Features

A hybrid load-pull system combines the features of both active and passive tuning techniques to offer a versatile and efficient solution for impedance tuning in RF testing setups. By integrating an active loop with passive tuners, hybrid load-pull systems can leverage the benefits of both approaches.

Passive tuners, while effective in many cases, may struggle to synthesize complex impedance conditions, especially near the edge of the Smith chart for devices with very low impedance. Additionally, the presence of any loss between the tuner and the Device Under Test (DUT) reference plane, as seen in setups like On-wafer vector load-pull configurations, can further limit impedance synthesis capabilities.

In a hybrid load-pull system, the passive wideband tuner is used to create a reflection factor close to the optimal load impedance that may be challenging to achieve solely with passive tuning. The active power injection component then supplements this by generating additional reflection factors necessary to push the impedance conditions to the border of the Smith chart (Γ=1). This combined approach allows for enhanced mismatch conditions, which can result in lower power requirements compared to full active load-pull systems.

By merging the speed and tuning range advantages of active systems with the power handling capabilities of passive systems, hybrid load-pull setups offer a comprehensive solution for optimizing impedance matching in RF testing scenarios.

Setup

Parameters

Setup

To increase the reflection factor at the probe tip (DUT) and minimize the power loss we must maximize S21 and minimize S11. Any mismatch loss must be compensated by additional injected power in a hybrid (active/passive) tuner. 

Parameters

Hybrid tuning is not a panacea. Whereas it allows high VSWR at DUT reference plane, it still remains a rather complex test system with feedback power amplifiers and, often, a second, synchronized, signal source, plus the requirement for in-situ vector power wave measurement, possible through directional couplers inserted between the DUT and the tuner; this on the other hand reduces the tuning range and increases the need for even higher power amplifiers. Passive pre-matching tuning in hybrid systems reduces the requirement for high power from the feedback amplifiers, but only to some extent: passive tuners are not lossless. Tuner loss increases rapidly with reflection factor and so does the power requirement. The critical quantity in tuner loss calculations is “mismatch loss”. Mismatch loss is S212/(1-S112).

For high S11 values, as needed to pre-match for enhancing the passive reflection factor with active injection in a hybrid configuration, it happens that any increase in insertion loss S21 (due to cables, adapters etc. between tuner and DUT) is multiplied by a factor M=1/(1-S112).

Typical values of the multiplication factor:

S11=0.9 (VSWR=19:1) -> M=5.3

S11=0.96 (VSWR=50:1) -> M=13

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