Specifications

4
Parameter Equation Definition
Gain V
trans
The ratio of the amplifier’s output power (delivered to a Z
O
load) to the input power
(delivered from a τ = ______ Z
O
source). Z
O
is the characteristic impedance, in this
case, 50 Ω.
V
inc
Gain (dB) = –20log
10
|τ| For small signal levels, the output power of the amplifier is proportional to the input
power. Small signal gain is the gain in this linear region.
Gain (dB) = P
out
(dBm) – P
in
(dBm) As the input power level increases and the amplifier approaches saturation, the output
power reaches a limit and the gain drops. Large signal gain is the gain in this nonlinear
region.
Gain flatness The variation of the gain over the frequency range of the amplifier.
Reverse isolation The measure of transmission from output to input. Similar to the gain measurement
except the signal stimulus is applied to the output of the amplifier.
Deviation from linear phase The amount of variation from a linear phase shift. Ideally, the phase shift through an
amplifier is a linear function of frequency.
Group delay The measure of the transit time through the amplifier as a function of frequency. A per-
fectly linear phase shift would have a constant rate of change with respect to frequency,
yielding a constant group delay.
Return loss (SWR, ρ) The measure of the reflection mismatch at the input or output of the amplifier relative to
the system Z
O
characteristic impedance.
Reflection coefficient = ρ
Return loss (dB) = –20log
10ρ
Complex impedance The amount of reflected energy from an amplifier is directly related to its impedance.
Complex impedance consists of both a resistive and a reactive component. It is derived
from the characteristic impedance of the system and the reflection coefficient.
Gain compression An amplifier has a region of linear gain where the gain is independent of input power
level (small signal gain). As the power is increased to a level that causes the amplifier
to saturate, the gain decreases.
Gain compression is determined by measuring the amplifier’s 1 dB gain compression
point (P
1dB
) which is the output power at which the gain drops 1 dB relative to the small
signal gain. This is a common measure of an amplifier’s power output capability.
Amplifier parameters
tg(sec) = – = –
∆θ
∆ϖ
∆θ
∆f
1
360
*
Γ = = ρ∠θ
V
refl
V
inc
SWR =
1 + ρ
1 – ρ
Z = Z
O
= R + jX
*
1 + Γ
1 – Γ