Linx Technologies EVM-868-EUR - Manual (Page 10)

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Common Antenna Styles
There are hundreds of antenna styles and variations that can be employed
with Linx RF modules. Following is a brief discussion of the styles most
commonly utilized. Additional antenna information can be found in Linx
Application Notes AN-00100, AN-00140, AN-00500 and AN-00501 (Figure
14).
Whip Style
A whip style antenna (Figure 8) provides
outstanding overall performance and stability.
A low-cost whip is can be easily fabricated from
a wire or rod, but most designers opt for the
consistent performance and cosmetic appeal of a
professionally-made model. To meet this need, Linx
offers a wide variety of straight and reduced height
whip style antennas in permanent and
connectorized mounting styles.
The wavelength of the operational frequency
determines an antenna’s overall length. Since a
full wavelength is often quite long, a partial half or
quarter-wave antenna is normally employed. Its size and
natural radiation resistance make it well matched to
Linx modules. The proper length for a straight
quarter-wave can be easily determined using the formula
in Figure 9. It is also possible to reduce the overall height of the antenna by
using a helical winding. This reduces the antenna’s bandwidth but is a great
way to minimize the antenna’s physical size for compact applications. This
also means that the physical appearance is not always an indicator of the
antenna’s frequency.
Specialty Styles
Linx offers a wide variety of specialized antenna
styles (Figure 10). Many of these styles utilize
helical elements to reduce the overall antenna size
while maintaining reasonable performance.
A helical antenna’s bandwidth is often quite
narrow and the antenna can detune in
proximity to other objects, so care must be
exercised in layout and placement.
Figure 8: Whip Style Antennas
L =
234
F
MHz
Figure 9:
L = length in feet of
quarter-wave length
F = operating frequency
in megahertz
Figure 10: Specialty Style Antennas