And they are 180 degrees out of phase due to the half-wavelength that the CCW signal travels that the CW signal doesn't. The recombining signals at port 3 end up equal in amplitude (half power or the CW signal is lost in resistor R1, while half of the CCW signal is output port 1. Part of it goes clockwise through the resistor and part goes counterclockwise through the upper arm, then splits at the input port, then continues counterclockwise through the lower arm toward port 3. Why is port 2 isolated from port 3 and vice-versa?Ĭonsider that the signal splits when it enters port 2. Note that for a signal input at either port 2 or 3, half the power is dissipated in the resistor and half is delivered to port 1. The resistor thus serves the important function of decoupling ports 2 and 3. In this case, it splits equally between port 1 and the resistor R with none appearing at port 3. Okay, what about as a power combiner? Consider a signal input at port 2. The characteristic impedance of the quarter-wave lines must be equal to 1.414xZ 0 so that the input is matched when ports 2 and 3 are terminated in Z 0. The quarter-wave transformers in each leg accomplish this without the quarter-wave transformers, the combined impedance of the two outputs at port 1 would be Z 0/2. The two output port terminations will add in parallel at the input, so they must be transformed to 2xZ 0 each at the input port to combine to Z 0. Since each end of the isolation resistor between ports 2 and 3 is at the same potential, no current flows through it and therefore the resistor is decoupled from the input.
Here is how the Wilkinson splitter works as a power divider: when a signal enters port 1, it splits into equal-amplitude, equal-phase output signals at ports 2 and 3. The arms are quarter-wave transformers of impedance 1.414xZ 0 (thanks for the correction, Rod!) Here we show a three-port circuit (the most common in practice by far, but Wilkinson described an N-way divider). In its simplest form, an equal-amplitude, two-way split, single-stage Wilkinson is shown the figure below. Check out Baltic Lab (formerly Jaunty Electronics) for more videos by Sebastian on designing electronics.Ĭheck out another video of Sebastian explaining lumped element Wilkinson design. Here's a video by Sebastian that explains the basics of Wilkinson design. N-way Wilkinsons with unequal split (separate page) How many sections do you need in a Multi-stage Wilkinson?Ĭompact Wilkinsons (separate page, multiple examples!) Multistage Wilkinsons (separate page, multiple examples!) Lumped-element Wilkinson example by Sebastian (video page, new for January 2022) Two-port single-stage equal-split Wilkinsons (this page) Here's a clickable index to our treasure-trove of material on Wilkinson power splitters:
328-333Ĭlick here to go to our main page on couplers and splitters Pozar, Microwave Engineering, 4th Edition, John Wiley & Sons: New York, 1998, pp. Wilkinson, "An N-way Power Divider", IRE Trans. The resistor adds no resistive loss to the power split from port 1, so an ideal Wilkinson splitter is 100% efficient.Ī veteran of WWII, Mr. The resistor does a lot more than allow all three ports to be matched, it fully isolates port 2 from port 3 at the center frequency: if you put power into port 2 or port 3, all of it goes up in heat in the ideal case. Wilkinson relied on quarter-wave transformers to match the split ports to the common port.īecause a loss-less reciprocal three-port network cannot have all ports simultaneously matched, Wilkinson knew he had to cheat so he added one resistor and the rest is history. It splits an input signal into two equal phase output signals, or combines two equal-phase signal into one in the opposite direction.
The Wilkinson power splitter was invented around 1960 by an engineer named Ernest Wilkinson.
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