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IFA
Design Curves for an Inverted F Antenna (IFA)
Description of Antenna:
The geometry of an IFA is shown
in the diagram below, with relevant parameters.
Geometry
of an IFA
* H is the height of the horizontal
element above the ground plane
* LF is the horizontal length from the feed point to the open
end of the antenna
* LB is the horizontal length from the feed point to the closed
end of the antenna
Design Curves:
The following three design
curves enable the design of an IFA in relation to H, LF and
LB, at a centre frequency of 500Mhz and for standard input
impedances of 50 ohm and 75ohm.
| Figure
1 shows the ranges of height (H) possible at real
input impedances of 50 ohm and 75 ohm. |
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Figure
1: Impedance(?) vs Height(?) at resonance.
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| This curve
may be used to find a specific height which can then be
related to a length for LF using Figure 2, which
shows the length LF as a function of height(H) at resonance
for two standard input impedances. |
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Figure
2: Length (LF) vs Height at resonance
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| The stub length
(LB) can be determined using Figure 3, which shows
LB as a function of Height for two standard impedances.. |
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Figure
3: Stub Length (LB) vs Height at resonance
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These three curves fully specify
the antenna's geometry, the following curves will illustrate
some electrical charateristics of the antenna.
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Figure
4: Return Loss of resonant IFA at 500 MHz
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Figure
4: Bandwidth of an IFA
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Example:
A 500MHz Inverted F antenna
of input impedance 50 ohm is required. The height of the antenna
cannot exceed 70mm (0.1167 lambda).
The antenna can be designed
with a height of 66mm (0.11 lambda), and according to figure
2 the length of LF will be approximately 0.156 lambda, or
94mm. The stub length, LB, will be approximately 0.04 lambda,
or 24mm according to figure 3. The electrical characteristics
of the antenna will be approximately 8.4% as shown in figures
4 and 5
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Note: these
design curves provide only a rough estimate of a particular
antenna's dimensions and performance. In order to fully specify
the antenna it should be simulated, using the values obtained
from the curves if so desired.
Reference:
Fourth Year Design Report, "Design Curves for an Inverted
F Antenna" prepared by L.F.V. Neves Leal for the School
of Electrical and Information Engineering, University of the
Witwatersrand, August 2003.
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