Very-Wide-Band Impedance-Matching Network

A method is described for combining two transformers and supplementary network elements in a class of wideband impedance-matching networks whose over-all bandwidth in octaves is essentially the sum of those of the two component transformers. One transformer transmits the high-frequency portion of the required operating range and is relieved of the low-frequency requirements, while the other transformer transmits the complementary low-frequency range. Thus the composite network characteristic is all-pass over a very large frequency band. The basic network has a group-delay characteristic which is non fiat over the band-pass region; it is shown how additional all-pass sections may improve this characteristic. An experimental coupling network exhibits an extension in frequency response by about a factor of 40 over that obtainable with the low-frequency transformer alone.