1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
|
# -*- coding: utf-8 -*-
"""
Created on Fri Dec 18 20:56:53 2015
@author: thorsten
"""
### Import Libraries
import os, tempfile
from pylab import *
from CSXCAD import ContinuousStructure
from openEMS import openEMS
from openEMS.physical_constants import *
### General parameter setup
Sim_Path = os.path.join(tempfile.gettempdir(), 'Simp_Patch')
post_proc_only = False
# patch width (resonant length) in x-direction
patch_width = 32 #
# patch length in y-direction
patch_length = 40
#substrate setup
substrate_epsR = 3.38
substrate_kappa = 1e-3 * 2*pi*2.45e9 * EPS0*substrate_epsR
substrate_width = 60
substrate_length = 60
substrate_thickness = 1.524
substrate_cells = 4
#setup feeding
feed_pos = -6 #feeding position in x-direction
feed_R = 50 #feed resistance
# size of the simulation box
SimBox = np.array([200, 200, 150])
# setup FDTD parameter & excitation function
f0 = 2e9 # center frequency
fc = 1e9 # 20 dB corner frequency
### FDTD setup
## * Limit the simulation to 30k timesteps
## * Define a reduced end criteria of -40dB
FDTD = openEMS(NrTS=30000, EndCriteria=1e-4)
FDTD.SetGaussExcite( f0, fc )
FDTD.SetBoundaryCond( ['MUR', 'MUR', 'MUR', 'MUR', 'MUR', 'MUR'] )
CSX = ContinuousStructure()
FDTD.SetCSX(CSX)
mesh = CSX.GetGrid()
mesh.SetDeltaUnit(1e-3)
mesh_res = C0/(f0+fc)/1e-3/20
### Generate properties, primitives and mesh-grid
#initialize the mesh with the "air-box" dimensions
mesh.AddLine('x', [-SimBox[0]/2, SimBox[0]/2])
mesh.AddLine('y', [-SimBox[1]/2, SimBox[1]/2] )
mesh.AddLine('z', [-SimBox[2]/3, SimBox[2]*2/3] )
# create patch
patch = CSX.AddMetal( 'patch' ) # create a perfect electric conductor (PEC)
start = [-patch_width/2, -patch_length/2, substrate_thickness]
stop = [ patch_width/2 , patch_length/2, substrate_thickness]
patch.AddBox(priority=10, start=start, stop=stop) # add a box-primitive to the metal property 'patch'
FDTD.AddEdges2Grid(dirs='xy', properties=patch, metal_edge_res=mesh_res/2)
# create substrate
substrate = CSX.AddMaterial( 'substrate', epsilon=substrate_epsR, kappa=substrate_kappa)
start = [-substrate_width/2, -substrate_length/2, 0]
stop = [ substrate_width/2, substrate_length/2, substrate_thickness]
substrate.AddBox( priority=0, start=start, stop=stop )
# add extra cells to discretize the substrate thickness
mesh.AddLine('z', linspace(0,substrate_thickness,substrate_cells+1))
# create ground (same size as substrate)
gnd = CSX.AddMetal( 'gnd' ) # create a perfect electric conductor (PEC)
start[2]=0
stop[2] =0
gnd.AddBox(start, stop, priority=10)
FDTD.AddEdges2Grid(dirs='xy', properties=gnd)
# apply the excitation & resist as a current source
start = [feed_pos, 0, 0]
stop = [feed_pos, 0, substrate_thickness]
port = FDTD.AddLumpedPort(1, feed_R, start, stop, 'z', 1.0, priority=5, edges2grid='xy')
mesh.SmoothMeshLines('all', mesh_res, 1.4)
# Add the nf2ff recording box
nf2ff = FDTD.CreateNF2FFBox()
### Run the simulation
if 0: # 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)
os.system(r'AppCSXCAD "{}"'.format(CSX_file))
if not post_proc_only:
FDTD.Run(Sim_Path, verbose=3, cleanup=True)
### Post-processing and plotting
f = np.linspace(max(1e9,f0-fc),f0+fc,401)
port.CalcPort(Sim_Path, f)
s11 = port.uf_ref/port.uf_inc
s11_dB = 20.0*np.log10(np.abs(s11))
figure()
plot(f/1e9, s11_dB, 'k-', linewidth=2, label='$S_{11}$')
grid()
legend()
ylabel('S-Parameter (dB)')
xlabel('Frequency (GHz)')
idx = np.where((s11_dB<-10) & (s11_dB==np.min(s11_dB)))[0]
if not len(idx)==1:
print('No resonance frequency found for far-field calulation')
else:
f_res = f[idx[0]]
theta = np.arange(-180.0, 180.0, 2.0)
phi = [0., 90.]
nf2ff_res = nf2ff.CalcNF2FF(Sim_Path, f_res, theta, phi, center=[0,0,1e-3])
figure()
E_norm = 20.0*np.log10(nf2ff_res.E_norm[0]/np.max(nf2ff_res.E_norm[0])) + nf2ff_res.Dmax[0]
plot(theta, np.squeeze(E_norm[:,0]), 'k-', linewidth=2, label='xz-plane')
plot(theta, np.squeeze(E_norm[:,1]), 'r--', linewidth=2, label='yz-plane')
grid()
ylabel('Directivity (dBi)')
xlabel('Theta (deg)')
title('Frequency: {} GHz'.format(f_res/1e9))
legend()
Zin = port.uf_tot/port.if_tot
figure()
plot(f/1e9, np.real(Zin), 'k-', linewidth=2, label='$\Re\{Z_{in}\}$')
plot(f/1e9, np.imag(Zin), 'r--', linewidth=2, label='$\Im\{Z_{in}\}$')
grid()
legend()
ylabel('Zin (Ohm)')
xlabel('Frequency (GHz)')
show()
|
