RG302-70 QAXIAL

70.7Ω coaxial cable is often used to build power splitters and Wilkinson combiners, it is used also as λ/4 matching between 50 and 100Ω.

To demonstrate the operation of the λ/4 transormer we have verified the correct impedance transformation between 50 and 100Ω at the frequency of 142 MHz.

Z = √50 x 100 = 70.7Ω

λ/4C = λ/4 x V_F
λ/4C = Matching line 1/4 wavelength on cable
λ/4 = 1/4 wavelength at 142 MHz
V_F = Velocity factor 70% (for PTFE is 0.70)
λ/4 = 300/142 x 1/4 = 530mm
λ/4C = 530 x 0.70 = 370mm (this is the real length of the cable)

The graph below shows the return loss or impedance matching at the frequency of 142 MHz, as you can see the result is very good.

Example of very simple realization of a 2-way Wilkinson power divider at 950 MHz using only this cable, three SMA female connectors and a 100Ω balance resistor.

F = 950 MHz
V_F = 0.70
L = 300/950 x λ/4 x V_F = 55 mm (total cable length, 51 mm shield to shield)

The diagam shows the division of 3 dB per side and the return loss at -40 dB.