Sources and Ports

rfx distinguishes between sources (field injection without impedance loading) and ports (sources with a matched load for S-parameter extraction).

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Waveforms

All sources accept a waveform object that defines the time-domain excitation envelope.

GaussianPulse

A Gaussian-modulated sinusoid (default excitation for ports):

from rfx import GaussianPulse

pulse = GaussianPulse(
    f0=2.4e9,       # centre frequency (Hz)
    bandwidth=0.8,  # fractional bandwidth (default 0.8 -> wideband)
    amplitude=1.0,  # peak amplitude
)

The pulse energy is concentrated in [f0*(1-bw/2), f0*(1+bw/2)]. Set bandwidth below 0.5 for narrowband excitation near f0.

ModulatedGaussian

Like GaussianPulse but with zero DC content. This is often the better choice for resonance-focused add_source() runs because it prevents static charge accumulation on PEC surfaces:

from rfx import ModulatedGaussian

waveform = ModulatedGaussian(f0=3e9, bandwidth=0.6)

If waveform is omitted, the current high-level API uses GaussianPulse. Pass ModulatedGaussian(...) explicitly when you want zero-DC excitation.

CWSource

Continuous-wave sinusoid, useful for steady-state field visualisation:

from rfx import CWSource

cw = CWSource(
    f0=5.8e9,       # frequency (Hz)
    ramp_steps=200, # linear ramp-up steps to avoid impulse at t=0
)

CustomWaveform

Arbitrary time-domain waveform via a JAX-compatible callable:

from rfx import CustomWaveform
import jax.numpy as jnp

def chirp(t):
    f_start, f_end = 1e9, 4e9
    rate = (f_end - f_start) / 10e-9
    return jnp.sin(2 * jnp.pi * (f_start * t + 0.5 * rate * t**2))

sim.add_source((0.02, 0.02, 0.01), "ez", waveform=CustomWaveform(func=chirp))

---

Point source (add_source)

A soft current source injected at a single Yee cell. No resistive load — cavity Q is not affected.

sim.add_source(
    position=(0.025, 0.025, 0.010),  # (x, y, z) in metres
    component="ez",                   # "ex", "ey", or "ez"
    waveform=GaussianPulse(f0=3e9),
)

Use add_source for resonance characterisation (Harminv) where port loading would suppress the ring-down signal.

---

Polarised source (add_polarized_source)

Injects a source with a specified Jones-vector polarisation:

# Linear
sim.add_polarized_source((0.025, 0.025, 0.01), polarization="ez")

# 45-degree slant linear
sim.add_polarized_source((0.025, 0.025, 0.01), polarization="slant45")

# Right-hand circular
sim.add_polarized_source(
    (0.025, 0.025, 0.01),
    polarization="rhcp",
    waveform=GaussianPulse(f0=3e9),
)

# Arbitrary Jones vector (complex)
sim.add_polarized_source(
    (0.025, 0.025, 0.01),
    polarization=(1.0, 1j),   # (Ex, Ey) — normalised internally
    waveform=GaussianPulse(f0=3e9),
)

Supported string shortcuts: "ex", "ey", "ez", "circular" / "rhcp", "lhcp", "slant45".

---

Lumped port (add_port)

A single-cell port with a resistive load equal to impedance. Enables S-parameter extraction referenced to that impedance.

sim.add_port(
    position=(0.01, 0.025, 0.010),
    component="ez",
    impedance=50.0,                      # ohms
    waveform=GaussianPulse(f0=5e9),
)

Run with compute_s_params=True to extract the S-matrix:

result = sim.run(n_steps=2000, compute_s_params=True)
s11 = result.s_params[0, 0, :]   # (n_freqs,) complex

!!! tip Multiple add_port() calls create a multi-port structure. rfx drives one port at a time and assembles the full N×N S-matrix automatically.

---

Wire port (add_port with extent)

A wire port spans multiple Yee cells along the port axis, connecting conductor to conductor across a gap. This is the standard model for coaxial probe feeds and SMA connectors:

# Port spans 1.5 mm in z, from substrate bottom to patch surface
sim.add_port(
    position=(0.029, 0.030, 0.0),    # start of wire
    component="ez",
    impedance=50.0,
    extent=0.0016,                    # wire length in metres
    waveform=GaussianPulse(f0=2.4e9),
)

The extent parameter turns the lumped port into a WirePort. S-parameters are extracted using JIT-DFT voltage/current integrals over the wire span. Wire ports are more accurate for feed structures that are several cells long.

!!! warning extent must be aligned with the component direction. For component="ez", extent spans in the z-direction from position[2] to position[2] + extent.

---

Waveguide port (add_waveguide_port)

Modal waveguide excitation for rectangular waveguide S-matrix extraction. Injects a specific TE/TM mode and decomposes the reflected/transmitted fields into the same modal basis.

sim.add_waveguide_port(
    x_position=0.01,              # physical x-coordinate of port face
    y_range=(0.0, 0.023),         # aperture y-extent
    z_range=(0.0, 0.010),         # aperture z-extent
    mode=(1, 0),                   # TE10 mode
    mode_type="TE",
    direction="+x",                # propagation direction
    f0=10e9,
    bandwidth=0.5,
    name="port1",
)

After running, access calibrated S-parameters:

result = sim.run(n_steps=3000)
sp = result.waveguide_sparams["port1"]
# sp.freqs, sp.s11, sp.s21

---

TFSF plane-wave source (add_tfsf_source)

Total-field/scattered-field plane wave for scattering and RCS simulations:

sim.add_tfsf_source(
    f0=5e9,
    bandwidth=0.4,
    polarization="ez",
    direction="+x",    # propagation direction
    angle_deg=0.0,     # oblique incidence angle (degrees from normal)
)

!!! warning add_tfsf_source cannot be combined with lumped ports or waveguide ports.

---

Summary table

Method	Use case	S-params
add_source()	Resonance, visualisation	No
add_polarized_source()	Antenna radiation, polarimetry	No
add_port(extent=None)	Lumped-port S-params	Yes
add_port(extent=...)	Wire / probe-feed S-params	Yes
add_waveguide_port()	Modal waveguide S-matrix	Yes
add_tfsf_source()	RCS, scattering, plane-wave	No