On triplexers and their applications to harmonic load-pull

A revealing analysis of triplexer effects on harmonic load-pull measurements is conducted in the context of assessing the ability of the test system to maintain tuning independency between the fundamental and harmonic tuning ports. The type of triplexers studied consist of four port passive devices with one common port and 3 output ports; namely, fundamental, second harmonic and third harmonic tuning ports. It is shown in this work that very good isolation between the harmonic ports and very good rejection at unwanted frequencies between the common and each of the harmonic ports are of prime importance in establishing tuning independency. Influence of non-ideal isolation/rejection and lossiness of the triplexer on harmonic load pull applications will be presented, based on experimental results and analytical simulation of a commercially available load pull system and triplexer from Maury Microwave. For the analytical work, Agilent Technology's Advanced Design System-2002 was used along with a model for the triplexer, based on a signal flow graph analysis. Plots were generated to describe effects of non-ideal isolations, rejection, and loss on tuning independency and achievable max-reflection coefficient at the amplifier output plane. Discussions and simulation results are presented concerning compromise on isolations/rejections specifications for the triplexer to the extent that tuning independency is being maintained. As one example of the types of conclusions this model allows, it was determined that deviations in fundamental reflection coefficient with harmonic tuning are below measurement repeatability for a combined harmonic-to-common port rejection of 59 dB and harmonic-to-fundamental port isolation of 50dB. The experimentally examined triplexer provides performance exceeding these limits, with a margin. The authors believe that this is the first analysis of its kind providing a detailed consideration of non-ideal triplexers as used in harmonic load-pull measurement systems.