AWR eBooks

RF Electronics Chapter4: Transmission Line Transformers and Hybrids Page 79 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. line TL3 can thus be disconnected at port 4 and line TL4 can be disconnected at port 2, without any effect, as shown in figure 4.23. Figure 4.23. 1.5 Rat-Race hybrid for analysis. The resulting circuit is thus just like a Wilkinson hybrid, without the terminating resistor. The line impedances should thus be 70.71 , just like the Wilkinson hybrid. The same analysis can be repeated by looking into each port in turn. A three-quarter wavelength transmission line has exactly the same impedance transformation ratio as a quarter- wavelength line. All the line impedances will thus be 2Z 0 . The 1.5 Rat-Race hybrid has an advantage over the Wilkinson hybrid that for a 50 system, a 50 load resistor to ground is required for the termination, rather than a 100 load resistor between two active inputs. High power 50 loads are readily available from several manufacturers [6, 7]. 100 floating high power loads are however more difficult to obtain. For TV transmitters, the hybrid is normally made using high power coaxial cables, to combine the outputs from two transmitters into one antenna. If one transmitter fails, the radiated output drops 6 dB and the resistive load then dissipates the same power as is radiated, without any switching being required. If both transmitters are working, no power is dissipated in the resistive load and the sum of the transmitter power is radiated. Figure 4.24. PCB layout of a 1.5 Rat-race hybrid. TLIN ID=TL1 Z0=70.7 Ohm EL=90 Deg F0=1000 MHz TLIN ID=TL2 Z0=70.7 Ohm EL=90 Deg F0=1000 MHz TLIN ID=TL3 Z0=70.7 Ohm EL=270 Deg F0=1000 MHz TLIN ID=TL4 Z0=70.7 Ohm EL=90 Deg F0=1000 MHz PORT P=1 Z=50 Ohm PORT P=3 Z=50 Ohm PORT P=2 Z=50 Ohm PORT P=4 Z=50 Ohm RF Electronics: Design and Simulation 79 www.cadence.com/go/awr

• Cover