PCB天线设计指南.pdf
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2009-10-20
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Nordic VLSI ASA - Vestre Rosten 81, N-7075 Tiller, Norway - Phone +4772898900 - Fax +4772898989
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February 2003
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/4 printed monopole antenna for 2.45GHz
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Taking the demand for small size, easy fabrication and low cost into account in the
development of low-power radio devices for short-range 2.4GHz applications, a
quarter wavelength monopole antenna implemented on the same printed circuit board
as the radio module is a good solution. A printed quarter wavelength monopole
antenna is very easy to design and can be tuned simply by slight changes in length.
This article presents basic guidelines on how to design such an antenna for use
together with the nRF2401 Single chip Transceiver and the nRF2402 Single chip
2.4GHz Transmitter.
The described antenna should be fabricated on standard 1.6mm, low cost FR4 printed
circuit board (PCB).
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A quarterwave monopole is a ground plane dependent antenna that must be fed single-
ended. The antenna must have a ground plane to be efficient. The length of the
monopole PCB trace mainly determines the resonant frequency of the antenna.
Because of the very wide gain bandwidth of the quarterwave monopole, the length of
the monopole PCB trace is not too critical. But like any other antenna types, the gain
of a quarterwave monopole antenna will vary if parameters in the surroundings like
case/box materials, distance to the ground plane, the size of the ground plane, width
and thickness of the PCB trace are varied. If any of these parameters are changed, a
retuning of the monopole PCB trace length may be necessary for optimum
performance in each application.
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The antenna is fabricated on a standard 1.6mm FR4 substrate material with an
estimated dielectric constant ε
r
of 4.4 at 2.45GHz. The width of the monopole trace is
W = 1.5mm. With these parameters given, it can be shown that the effective dielectric
constant ε
eff
for the substrate surrounding the monopole trace is ε
eff
= 3.16, which
gives a guided wavelength on the substrate of λ
g
= 6.89cm.
The theoretical, physical length of a printed quarterwave monopole antenna on this
substrate is L = 1.72cm.
When implementing the monopole as a trace on the PCB, the length of the trace
should be extended somewhat (e.g. 5mm) to allow for some fine-tuning of the antenna
to resonance at 2.45GHz, see Figure 1.
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