Non-linear RF devices will generate harmonic power when they are driven into compression. By re-injecting this power back to their device, designers can greatly affect key parameters in an RF design. The harmonic tuner plays a different role in a load pull system than the fundamental tuner as we are not trying to match the device impedance, but in fact we are simply reflecting as much harmonic power back to the device at a given phase. Ultimately this re-injected power will change the device’s non-linear behavior and allow the designers to optimize efficiency and linearity.
Programmable harmonic tuners (MPT)
MPT-3620 Harmonic tuner covers from 2-36GHz
There are many different technologies for harmonic tuners but cascading wideband tuners are the most popular technique of tuning harmonic impedances. Programmable harmonic tuners with open stub resonators (US patent 6,297,649) were the first commercially available solutions on the market in the early 2000s. Wideband tuners combined with a triplexer then came along, but this solution was not well adopted by the market due to its limited tuning range and bulky setup.
MPT-807 Harmonic tuner covers 700MHz-8GHz
Cascading wideband tuners is not a trivial task, and having three tuners in one self-contained instrument is a significant technical challenge. The main advantage of having the three tuners in one instrument is simply to reduce the loss between the tuner and the DUT, therefore increasing the tuning range. Another key advantage is usability; designers want to perform these measurements on-wafer where space is limited.
The graph on the right shows the frequency response of a fundamental tuner. As we can see the frequency response is very linear and predictable. Once we cascade a second tuner the frequency response changes significantly and provides additional control at given harmonics, but some blind spots might appear. The third plot shows that when cascading three tuners you get full control of all harmonic frequencies.
Electro Rent offers a wide range of Focus Microwaves automated, multi-harmonic and manual tuners, test fixtures and calibration kits for purchase or rental. These automated tuners are used in applications including Load Pull, Pulsed IV and Noise Measurements.
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