"""Hecken taper for microstrip impedance matching.
Adapted from PHIDL https://github.com/amccaugh/phidl/ by Adam McCaughan
"""
from __future__ import annotations
import numpy as np
from numpy import log
import gdsfactory as gf
from gdsfactory.component import Component
from gdsfactory.components.analog.microstrip import (
_G,
_find_microstrip_wire_width,
_microstrip_v_with_Lk,
_microstrip_Z_with_Lk,
)
from gdsfactory.typings import LayerSpec
[docs]
@gf.cell_with_module_name
def taper_hecken(
length: float = 200,
B: float = 4.0091,
dielectric_thickness: float = 0.25,
eps_r: float = 2,
Lk_per_sq: float = 250e-12,
Z1: float | None = 50,
Z2: float | None = 100,
width1: float | None = None,
width2: float | None = None,
num_pts: int = 100,
layer: LayerSpec = "WG",
) -> Component:
"""Creates a Hecken-tapered microstrip.
Args:
length: Length of the microstrip.
B: Controls the intensity of the taper.
dielectric_thickness: Thickness of the substrate.
eps_r: Dielectric constant of the substrate.
Lk_per_sq: Kinetic inductance per square of the microstrip.
Z1: Impedance of the left side region of the microstrip.
Z2: Impedance of the right side region of the microstrip.
width1: Width of the left side of the microstrip.
width2: Width of the right side of the microstrip.
num_pts: Number of points comprising the curve of the entire microstrip.
layer: Specific layer(s) to put polygon geometry on.
Returns:
Component containing a Hecken-tapered microstrip.
"""
if width1 is not None:
Z1 = _microstrip_Z_with_Lk(
width1 * 1e-6, dielectric_thickness * 1e-6, eps_r, Lk_per_sq
)
if width2 is not None:
Z2 = _microstrip_Z_with_Lk(
width2 * 1e-6, dielectric_thickness * 1e-6, eps_r, Lk_per_sq
)
# Normalized length of the wire [-1 to +1]
xi_list = np.linspace(-1, 1, num_pts)
if Z1 is None or Z2 is None:
raise ValueError(
"Z1 and Z2 must be specified either directly or via width1/width2"
)
Z = [np.exp(0.5 * log(Z1 * Z2) + 0.5 * log(Z2 / Z1) * _G(xi, B)) for xi in xi_list]
widths = np.array(
[
_find_microstrip_wire_width(
z, dielectric_thickness * 1e-6, eps_r, Lk_per_sq
)
* 1e6
for z in Z
]
)
x = (xi_list / 2) * length
# Compensate for varying speed of light in the microstrip by shortening
# and lengthening sections according to the speed of light in that section
v = np.array(
[
_microstrip_v_with_Lk(
w * 1e-6, dielectric_thickness * 1e-6, eps_r, Lk_per_sq
)
for w in widths
]
)
dx = np.diff(x)
dx_compensated = dx * v[:-1]
x_compensated = np.cumsum(dx_compensated)
x = np.hstack([0, x_compensated]) / max(x_compensated) * length
# Create blank device and add taper polygon
c = gf.Component()
xpts = np.concatenate([x, x[::-1]])
ypts = np.concatenate([widths / 2, -widths[::-1] / 2])
points = np.column_stack((xpts, ypts))
c.add_polygon(points, layer=layer)
# Snap port widths to even multiples of 0.002 um (2 dbu)
width1_snapped = round(widths[0] / 0.002) * 0.002
width2_snapped = round(widths[-1] / 0.002) * 0.002
c.add_port(
name="o1", center=(0, 0), width=width1_snapped, orientation=180, layer=layer
)
c.add_port(
name="o2", center=(length, 0), width=width2_snapped, orientation=0, layer=layer
)
# Add meta information about the taper
c.info["num_squares"] = float(np.sum(np.diff(x) / widths[:-1]))
c.info["width1"] = float(widths[0])
c.info["width2"] = float(widths[-1])
c.info["Z1"] = float(Z[0])
c.info["Z2"] = float(Z[-1])
# Note there are two values for v/c (and f_cutoff) because the speed of
# light is different at the beginning and end of the taper
# c.info["w"] = widths.tolist()
# c.info["x"] = x.tolist()
# c.info["Z"] = Z if isinstance(Z, list) else list(Z)
# c.info["v/c"] = (v / 3e8).tolist()
time_length = float(np.sum(np.diff(x * 1e-6) / (v[:-1])))
c.info["time_length"] = time_length
c.info["f_cutoff"] = 1 / (2 * time_length)
c.info["length"] = float(length)
return c
if __name__ == "__main__":
c = taper_hecken(Z1=50, Z2=100)
c.show()
