Confidential ? ams AG 2013
Page 3
L = coil (antenna) inductance
l = loop radius
R = wire radius
NOTE: Value is an approximation !
A measurement of the antenna parameters using a Network Analyzer gives more accurate results. Source: Harold A. Wheeler, "Simple Inductance Formulas for Radio Coils," Proceedings of the .R.E.,
October 1928
Example: Circular Wire Loop
Confidential ? ams AG 2013
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For w << D
L = Loop inductance
D = size dimension
NOTE: Value is an approximation !
A measurement of the antenna parameters using a Network Analyzer gives more accurate results. Source: Harold A. Wheeler, "Simple Inductance Formulas for Radio Coils," Proceedings of the .R.E.,
October 1928
Example: Square Loop
Confidential ? ams AG 2013
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Index
R = Coil Mean Radius D/2 (mm)
tckCu = copper thickness (mm)
N = number of turns
NOTE: Value is an approximation !
A measurement of the antenna parameters using a Network Analyzer gives more accurate results. Source: Harold A. Wheeler, "Simple Inductance Formulas for Radio Coils," Proceedings of the .R.E.,
October 1928
Example: Planar Square Coil
Confidential ? ams AG 2013
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Index
Mlength = mean side length (mm)
tckCu = copper thickness (mm)
N = number of turns
K1= 2,34
K2 = 2,75
NOTE: Value is an approximation !
A measurement of the antenna parameters using a Network Analyzer gives more accurate results. Source: Harold A. Wheeler, "Simple Inductance Formulas for Radio Coils," Proceedings of the .R.E.,
October 1928
Example: Planar Square Coil
Confidential ? ams AG 2013
Page 7
Index
Mlength = mean side length (mm)
tckCu = copper thickness (mm)
N = number of turns
K1= 2,25
K2 = 3,55
NOTE: Value is an approximation !
A measurement of the antenna parameters using a Network Analyzer gives more accurate results. Source: Harold A. Wheeler, "Simple Inductance Formulas for Radio Coils," Proceedings of the .R.E.,
October 1928
Example: Planar Octagonal Coil
Confidential ? ams AG 2013
Page 8
The resonance frequency of antenna determined by inductance and parasitic capacitance.
The parasitic capacitance can be influence by gap, width and thickness.
Antenna Parameters VS Inductance
Confidential ? ams AG 2013
Page 9Influence of track width
Antenna Inductance Calculator
μ0 (H/m)
1.25664E-06 1.25664E-06 1.25664E-06Overall Dimension a o (mm)
606060Overall Dimension b o (mm)
606060Track thickness t (mm)
0.030.030.03Track width w (mm)
0.51 1.5Gap between tracks g (mm)
000Number of turns N a 2
22Equivalent Diameter of the track d (mm)0.34
0.660.97Average Dimension a avg (mm)59.00
58.0057.00Average Dimension b avg (mm)59.00
58.0057.00x1293.57
249.07221.22x2293.57
249.07221.22x369.12
67.9566.78x429.50
29.0028.50x488.14
76.7769.56Inductance L a (nH)
762.63639.58562.96
Confidential ? ams AG 2013
Page 10Influence of gap between tracks
Antenna Inductance Calculator
μ0 (H/m)
1.25664E-06 1.25664E-06 1.25664E-06Overall Dimension a o (mm)
606060Overall Dimension b o (mm)
606060Track thickness t (mm)
0.030.030.03Track width w (mm)
111Gap between tracks g (mm)
00.51Number of turns N a 2
22Equivalent Diameter of the track d (mm)0.66
0.660.66Average Dimension a avg (mm)58.00
57.0056.00Average Dimension b avg (mm)58.00
57.0056.00x1249.07
243.78238.51x2249.07
243.78238.51x367.95
66.7865.61x429.00
28.5028.00x476.77
75.2073.63Inductance L a (nH)
639.58625.80612.06
Confidential ? ams AG 2013
Page 11Influence of number of turns
Antenna Inductance Calculator
μ0 (H/m)
1.25664E-06 1.25664E-06 1.25664E-06Overall Dimension a o (mm)
606060Overall Dimension b o (mm)
606060Track thickness t (mm)
0.030.030.03Track width w (mm)
111Gap between tracks g (mm)
0.50.50.5Number of turns N a 1
23Equivalent Diameter of the track d (mm)0.66
0.660.66Average Dimension a avg (mm)58.50
57.0055.50Average Dimension b avg (mm)58.50
57.0055.50x1251.72
243.78235.89x2251.72
243.78235.89x368.54
66.7865.02x429.25
28.5027.75x477.55
75.2072.85Inductance L a (nH)
185.66625.801255.64
Confidential ? ams AG 2013
Page 12Influence of antenna size
Antenna Inductance Calculator
μ0 (H/m)
1.25664E-06 1.25664E-06 1.25664E-06Overall Dimension a o (mm)
506070Overall Dimension b o (mm)
506070Track thickness t (mm)
0.030.030.03Track width w (mm)
111Gap between tracks g (mm)
0.50.50.5Number of turns N a 2
22Equivalent Diameter of the track d (mm)0.66
0.660.66Average Dimension a avg (mm)47.00
57.0067.00Average Dimension b avg (mm)47.00
57.0067.00x1191.95
243.78297.38x2191.95
243.78297.38x355.06
66.7878.50x423.50
28.5033.50x459.74
75.2091.09Inductance L a (nH)
490.75625.80765.75
Confidential ? ams AG 2013
Page 13
1.The best case for an antenna placement would be far away from electronics or other
components like batteries, LCDs or large ground planes which harm the effective radiated RF field.
2.If the antenna is nearby the main board, the GND size on the PCB should be smaller because the GND can cause the field strength weaker particularly the small antenna design.
3.If design antenna for production, it’s better to design the coils of the antenna on the same layer, because the tolerance of the PCB may cause the antenna’s parameter changes if
designs the antenna on more than one layer.
4.
If the resonance frequency is lower the antenna is more sensitive because the metal or PICC can detune the antenna. The thickness of PCB can be thick which can get a higher resonance frequency.Antenna Layout Consideration
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Requirements La: 500nH~1000nH
Rs < 1Ohm (DC resistance)
Track width w: 0.5~1mm
Gap between tracks: 0.3~1mm
Number of turns: 2~3 turns
Resonance frequency of antenna: 60MHz~150MHz
Parameters preferred
AS3911 Antenna Design
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La = 100nH…2uH (antenna inductance, if the inductance is around 3500nH there is no need of
external capacitor)
Rs < 1Ohm (DC resistance)
Rp = 1kOhm …40kOhm (parallel resistance)
Ca = 1pF…20pF (parasitic capacitance)
fself = 13.56…200Mhz (self-resonance frequency of antenna)
Typical class 1 parameter: 50 Typical number of turns: 2 < t < 6 Gap between turns: 0.3mm < g < 0.8mm Track width: 0.4mm < w < 1mm Copper thickness: 35μm Parameters preferred AS3953 Antenna Design (https://www.doczj.com/doc/0815713436.html,/index.php?option=com_content&view=article&id=40&Itemid=36) miniVNA software (https://www.doczj.com/doc/0815713436.html,/zplots1.html#Download) Main window Confidential ? ams AG 2013 Page 17 Confidential ? ams AG 2013 Page 18 ? Any cable connected to the DUT port must be calibrated ? Set the measurement mode to reflection ? Open Calibration menu/Create ?Use the provided calibration kit and calibrate to open, short and load ? Save the measurement data for later use Calibration Confidential ? ams AG 2013 Page 19 Measure the frequency on 1MHz and resonance frequency point. Antenna matching measurement Confidential ? ams AG 2013 Page 20 1) Open the Smith diagram 2) Set start/stop frequency from 10-20MHz 3)Start measurement in free run mode (first hit the “Single” button and then click free run) Antenna matching measurement
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