Antennas and Microwaves
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Matlab RFutilities
Stepped and Tapered Line Impedance Transformers
One of the commonest problems facing the Rf/Microwave engineer is matching, whether for maximum power transfer, minimum noise figure or optimum bandwidth, matching usually crops up somewhere in the design. Lumped element and stub type matching is the most common and very well documented, less well documented is stepped and tapered line matching.
Lumped element and stub type matching can provide very effective and compact matching solutions. The price paid for this compactness is that relatively** high currents and voltages must exist in the matching components. High current densities in the conductors result in ohmic losses, while high voltages across the capacitors result in dielectric losses. Bandwidth can be improved by using more complex networks with increased the component count, but accounting for ‘strays’ can make a practical design increasingly difficult.
Stepped and tapered line matching solutions are unlikely to be the most compact but are well suited to applications requiring wide bandwidth, low loss or high power operation. Typical applications include receiver front ends, transmitter outputs and general test and measurement.
The Rfutils_M section of the Rfutils toolbox allows a variety of stepped and tapered line impedance transformer designs to been explored.
Note ** Relative to those on the matched line carrying the same power.
The return loss plot (left) shows the response for Exponential, Triangular and Klopfenstein
tapers implemented as half-
The impedance curves (right) show the impedance profiles for each taper design.
The tapers are modelled using 50 lambda/100 transmission line sections, hence the
x-