# -*- coding: utf-8 -*-
"""
 Stripline to Microstrip Line Transition Tutorial

 Demonstrates a vertical transition from a stripline (port 1) to a microstrip
 line (port 2) connected by a conducting via through the shared substrate.

 Tested with
  - python 3.10
  - openEMS v0.0.35+

 (c) 2017-2026 Thorsten Liebig <thorsten.liebig@gmx.de>

"""

import os, tempfile
import numpy as np
import matplotlib.pyplot as plt

from CSXCAD  import ContinuousStructure
from openEMS import openEMS
from openEMS.physical_constants import *

### Setup the simulation
Sim_Path = os.path.join(tempfile.gettempdir(), 'StripLine2MSL')
post_proc_only = False

unit = 1e-6  # drawing unit in um

line_length              = 15000
substrate_width          = 10000
air_spacer               = 4000

msl_width                = 500
msl_substrate_thickness  = 254

strip_width              = 500
strip_substrate_thickness = 512

connect_via_rad  = 500/2
connect_via_gap  = 1250/2

substrate_epr   = 3.66
substrate_kappa = 1e-3 * 2*np.pi*2.45e9 * EPS0 * substrate_epr

f_max       = 10e9
resolution  = 250
edge_res    = 25
feed_shift  = 2500
meas_shift  = 5000

### Setup FDTD parameters & excitation
FDTD = openEMS(EndCriteria=1e-4)
FDTD.SetGaussExcite(f_max/2, f_max/2)
FDTD.SetBoundaryCond(['PML_8', 'PML_8', 'MUR', 'MUR', 'PEC', 'MUR'])

### Setup CSXCAD geometry & mesh
CSX = ContinuousStructure()
FDTD.SetCSX(CSX)
mesh = CSX.GetGrid()
mesh.SetDeltaUnit(unit)

edge_mesh = np.array([-1/3, 2/3]) * edge_res

mesh.AddLine('x', [-connect_via_gap, 0, connect_via_gap])
mesh.SmoothMeshLines('x', 2*edge_res, ratio=1.5)
mesh.AddLine('x', [-line_length, line_length])
mesh.SmoothMeshLines('x', resolution, ratio=1.5)

mesh.AddLine('y', [0])
mesh.AddLine('y', msl_width/2 + edge_mesh)
mesh.AddLine('y', substrate_width/2)
mesh.SmoothMeshLines('y', resolution/4, ratio=1.5)
y_pos = mesh.GetLines('y')
mesh.AddLine('y', -y_pos[y_pos > 0])

x_linex = mesh.GetLines('x', do_sort=True)
y_lines = mesh.GetLines('y', do_sort=True)

z_levels = np.concatenate([
    np.linspace(-strip_substrate_thickness, 0, 5),
    np.linspace(0, strip_substrate_thickness, 5),
    np.linspace(strip_substrate_thickness,
                strip_substrate_thickness + msl_substrate_thickness, 5),
    [2*strip_substrate_thickness + air_spacer],
])
mesh.AddLine('z', z_levels)
mesh.SmoothMeshLines('z', resolution)

### Substrate (lossy)
substrate = CSX.AddMaterial('RO4350B', epsilon=substrate_epr, kappa=substrate_kappa)
start = [x_linex[0], -substrate_width/2, -strip_substrate_thickness]
stop  = [x_linex[-1], substrate_width/2,  strip_substrate_thickness + msl_substrate_thickness]
substrate.AddBox(start, stop)

### Metal properties
gnd   = CSX.AddMetal('gnd')
metal = CSX.AddMetal('metal')

### Stripline port (port 1) with strip metal
portstart = [-line_length, -strip_width/2, 0]
portstop  = [0,             strip_width/2, 0]
port1 = FDTD.AddStripLinePort(1, metal, portstart, portstop, 'x', 'z',
                              strip_substrate_thickness,
                              excite=1, priority=100,
                              FeedShift=feed_shift, MeasPlaneShift=meas_shift)

### MSL port (port 2) on top surface
portstart = [line_length,  -strip_width/2, strip_substrate_thickness + msl_substrate_thickness]
portstop  = [0,             strip_width/2, strip_substrate_thickness]
port2 = FDTD.AddMSLPort(2, metal, portstart, portstop, 'x', 'z',
                        priority=100, MeasPlaneShift=meas_shift)

ports = [port1, port2]

### Transition via connecting strip to MSL pad
start = [0, 0, 0]
stop  = [0, 0, strip_substrate_thickness + msl_substrate_thickness]
metal.AddCylinder(start, stop, connect_via_rad, priority=100)

### Ground plane between strip and MSL with hole for via
# Ground plane with circular cutout for the via, split into left and right halves.
x0 = x_linex[0]
x1 = x_linex[-1]
y0 = y_lines[0]
y1 = y_lines[-1]

theta_l = np.linspace(-np.pi, 0, 11)
pts_x = np.concatenate([[x0, 0], connect_via_gap * np.sin(theta_l), [0, x0]])
pts_y = np.concatenate([[y0, y0], connect_via_gap * np.cos(theta_l), [y1, y1]])
gnd.AddPolygon([pts_x, pts_y], norm_dir=2, elevation=strip_substrate_thickness, priority=100)

theta_r = np.linspace(0, np.pi, 11)
pts_x = np.concatenate([[0, x1, x1, 0], connect_via_gap * np.sin(theta_r)])
pts_y = np.concatenate([[y0, y0, y1, y1], connect_via_gap * np.cos(theta_r)])
gnd.AddPolygon([pts_x, pts_y], norm_dir=2, elevation=strip_substrate_thickness, priority=100)

if 1:  # debugging only
    CSX_file = os.path.join(Sim_Path, 'simp_patch.xml')
    if not os.path.exists(Sim_Path):
        os.mkdir(Sim_Path)
    CSX.Write2XML(CSX_file)
    from CSXCAD import AppCSXCAD_BIN
    os.system(AppCSXCAD_BIN + ' "{}"'.format(CSX_file))

### Run the simulation
if not post_proc_only:
    FDTD.Run(Sim_Path, cleanup=True, debug_PEC=True)

### Post-processing
f = np.linspace(0, f_max, 1601)
for port in ports:
    port.CalcPort(Sim_Path, f, ref_impedance=50)

s11 = ports[0].uf_ref / ports[0].uf_inc
s21 = ports[1].uf_ref / ports[0].uf_inc

fig, axis = plt.subplots(num='S-Parameters', tight_layout=True)
axis.plot(f/1e9, 20*np.log10(abs(s11)), 'k-',  linewidth=2, label='$S_{11}$')
axis.plot(f/1e9, 20*np.log10(abs(s21)), 'r--', linewidth=2, label='$S_{21}$')
axis.grid()
axis.set_xmargin(0)
axis.set_ylim([-40, 2])
axis.set_xlabel('Frequency (GHz) $\\rightarrow$')
axis.set_ylabel('S-Parameter (dB)')
axis.legend()

plt.show()