Page 443 - Complete Wireless Design

Wireless Issues

442 Chapter Ten

Figure 10.24 A helical circularly polarized antenna.

Special null-fill antennas are designed to abate the transmitted signal’s
nulls that naturally exist within a coverage area. This is accomplished by the
selective tweaking of certain antenna parameters. However, wideband anten-
nas for high-bit-rate applications are less successful at obtaining true null-fill
performance.
There is a 2.15-dB difference in gain between an antenna that is rated in dB
instead of dBi. As mentioned, the dBi rating is comparing the increase in gain
over the antenna under consideration to that of an isotropic source, while the
dB rating is a comparison to the gain of a dipole antenna, with its superior
gain of 2.15 dB. In other words, a dipole starts out with an initial gain of 2.15
dBi. Thus, an antenna manufacturer that states that its product’s gain is 6 dB
could also state a gain of 8.15 dBi.

10.9 RF Connectors
10.9.1 Introduction
An RF connector is a part that is adopted to obtain a permanent or temporary
connection for the transferring of RF energy from one circuit or cable to the
next, preferably at a constant impedance.
All connectors will have a finite lifetime. Indeed, some high-frequency, high-
precision units must be discarded after as little as 100 connects/disconnects.
This limitation is due to wear between the two mating surfaces causing a
change in the connector’s geometry, thus increasing the insertion loss and
decreasing the return loss.
Any connector that must function reliably out of doors in the wind, rain, ice,
and snow should be specifically made for this type of abuse, and must be prop-
erly shielded. If not, corrosion will cause damage, sometimes quite rapidly,
decreasing the connector’s rated specifications.

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