RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 92
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 4.45. Layout of the Microstrip coupler.
To enhance the forward and reverse port isolation, two coupled lines are used and each
coupled line is terminated in a resistor, as shown in figures 4.44, 4.45 and 4.47. In figure
4.44, the blue variables for widths, length, coupling gap and capacitor values are the
parameters that are optimised to obtain the specified performance.
The resulting PCB layout is shown in figure 4.45. For a /4 long coupler and 20 dB
coupling, a 0.95 mm gap is required. For the shorter length coupler of figure 4.45, the
coupling gap is 0.2 mm, which is easy to achieve using current technology.
Figure 4.46. Simulated performance of the Microstrip coupler.
Figure 4.46 shows the simulated performance of such a 20 dB coupler. Comparing this
with figure 4.43 shows that the isolated port has a much better isolation and the coupled
port has a flatter and wider frequency response. This performance is obtained by using
the optimiser in AWR DE to vary the coupling gap, line widths, lengths and capacitance
values until a suitable performance is obtained.
RF Electronics: Design and Simulation
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