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New for March 2025. This network was derived from the Schiffman 90 degree phase shifter. It came about by accident, playing with different coupling and unleashing the infinite monkeys contained in Keysight's Advanced Design System optimizer.
Let's start with a look at the Schiffman Type A network, shown below. The phase shift is produced by comparing a 3/4 wavelength transmission line to a 90 degree shorted coupler. Bernard Schiffman suggested using rho =2.28 (coupling factor -4.1 dB). Rho is the ratio of even-mode impedance to odd-mode impedance.
This produces a flat phase shift over a narrow band, as shown below.
In the Microwaves101 180 degree phase shifter, the coupled/shorted line is extended to 180 degrees, and it is compared to a 180 degree straight line. Rho is 6.6, which means the coupling factor is a sporty -1.3 dB. You could realize that coupling in a broadside stripline circuit.
Here is the M101 phase shift. We tweaked the coupling factor to result in +/-5 degrees phase shift over as much bandwidth as possible. It ended up with 64% BW.
Why did we call this effort "Type A"? That's because we think there might be some alternative networks that could extend the bandwidth, like Schiffman did with his Type B, C and F circuits. Maybe someone out there can synthesize a better 180-degree bit using shorted couplers. Send us your solution and if we like it, we will post it and send you a check for $100!