Microstrip Coupled Lines

A pair of microstrip coupled transmission lines for directional couplers and filters.

using CircuitSim

circ = Circuit()

# Substrate definition
sub = Substrate("Sub1", er=4.5, h=1.6e-3, t=35e-6)
add_component!(circ, sub)

# Components
port1 = ACPowerSource("P1", port_num=1, impedance=50.0)
port2 = ACPowerSource("P2", port_num=2, impedance=50.0)
port3 = ACPowerSource("P3", port_num=3, impedance=50.0)
port4 = ACPowerSource("P4", port_num=4, impedance=50.0)
coupled = MicrostripCoupled("MCPL1", substrate=sub, w=1.0e-3, l=20e-3, s=0.2e-3)
gnd = Ground("GND")

add_component!(circ, port1)
add_component!(circ, port2)
add_component!(circ, port3)
add_component!(circ, port4)
add_component!(circ, coupled)
add_component!(circ, gnd)

# Connect 4-port device
@connect circ port1.nplus coupled.n1
@connect circ coupled.n2 port2.nplus
@connect circ port3.nplus coupled.n3
@connect circ coupled.n4 port4.nplus
@connect circ port1.nminus gnd
@connect circ port2.nminus gnd
@connect circ port3.nminus gnd
@connect circ port4.nminus gnd

# S-parameter analysis
sp_analysis = SParameterAnalysis(start=1e9, stop=10e9, points=50, z0=50.0)
result = simulate_qucsator(circ, sp_analysis)

freq = result.frequencies_Hz
s21 = result.s_matrix[(2,1)]
s31 = result.s_matrix[(3,1)]
println("Coupled lines S21 at ", freq[1]/1e9, " GHz: ", round(20*log10(abs(s21[1])), digits=2), " dB")
println("Coupled lines S31 at ", freq[1]/1e9, " GHz: ", round(20*log10(abs(s31[1])), digits=2), " dB")

Coupled lines S21 at 1.0 GHz: -0.92 dB
Coupled lines S31 at 1.0 GHz: -17.6 dB