Installation Instructions

Hardware Installation
RVP8 User’s Manual
September 2005
2–11
2.2.8 IF Gain and System Performance
The previous discussion was concerned with measuring the dynamic range of a stand-alone IFD.
We will now examine how the unit performs in the context of a complete radar receiver. We
assume that an LNA/Mixer has already been selected that offers an appropriate balance between
price and noise figure. Having chosen these front-end components, the only parameter that
remains to be determined is the total RF/IF gain between the antenna waveguide and the IFD.
Assume that the thermal noise (kT) of the system is –114dBm/MHz, and that the noise figure of
the LNA/Mixer is 2dB. We wish to bring this –112dBm/MHz noise level up into the working
range of the IFD so that the received echoes can be optimally processed. However, in trying to
select the required gain, we realize that we must make a tradeoff between preserving the receiver
sensitivity that has been established by the LNA, and preserving the overall dynamic range of
the IFD. This is the exact same tradeoff that is made in traditional multi-stage analog receiver
systems that include a wide dynamic range LOG receiver.
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Reduction of Receiver Sensitivity (dB)
Reduction of IFD Dynamic Range (dB)
Figure 2–2: Tradeoff Between Dynamic Range and Sensitivity
Recommended
Operating Region
Power Ratio R = 10log
10
( N
LNA
/ N
IFD
)
The solid red curve in Figure 2–2 shows that these two variables interact in a symmetric manner,
so that any operating point (x,y) is always matched by a dual operating point at (y,x). To
understand the construction of this plot, let N
IFD
represent the stand-alone (terminated input)