User Manual

Antenna integration: Antenna requirements
Integrator’s Guide – RIM 801D OEM Radio Modem
26
radiator with a spherical radiation pattern. That is, the field energy density is
identical in any direction from the radiator at each fixed distance from the
radiator.
Antennas produce gain by concentrating radiated energy in certain areas,
and radiating less energy in other directions.
Antenna match
Antenna match is related to the Voltage Standing Wave Ratio (VSWR), a
ratio of incident and reflected power due to impedance mismatch and
antenna efficiency. Impedance mismatches can be due to cable connections,
cable lengths, and imperfections in the cables and connectors. The mismatch
causes some of the radio frequency energy to be reflected back from the
location of the mismatch, which interferes with the signal and reduces its
amplitude, resulting in a power loss.
VSWR =
+1
P
P
1-
P
P
reflected
output
reflected
output
Equation 1: VSWR
Antenna mismatch can be expressed as a Return Loss (RL): a 10 x log
10
of
the ratio of reflected power to the incident power.
RL =×








10
10
log
P
P
reflected
output
Equation 2: Return Loss
The antenna match for “best performance” is a VSWR ≤ 1.5 or a RL < -14
dB.
The antenna match which is the minimum acceptable for the RIM 801D is a
VSWR ≤ 2.0 or a RL < -10 dB.