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TWO-WAY RADAR EQUATION (BISTATIC)
The following table contains a summary of the equations developed in this section.
BISTATIC RADAR
There are also true bistatic radars - radars where the transmitter and receiver are in different locations as is depicted in Figure
1. The most commonly encountered bistatic radar application is the semi-active missile. The transmitter is located on, or near, the launch platform
(surface or airborne), and the receiver is in the missile which is somewhere between the launch platform and the target.
The transmitting
and receiving antennas are not the same and are not in the same location. Because the target-to-radar range is different from the target-to-missile
range, the target-to-radar and target-to-missile space losses are different.
The peak power at the radar receiver input
is :
[1]
* Keep λ or c, σ, and R in the same units.
On reducing the above equation to log form we have:
10log P_{r} = 10log P_{t} + 10log
G_{t} + 10log G_{r} + 10log σ - 20log f + 20log c - 30log 4π - 20log R_{Tx} - 20log R_{Rx}
[2]or in simplified terms:
10log P
_{r} = 10log P
_{t }+ 10log G
_{t} + 10log
G
_{r} + G
_{σ} -
α_{Tx} -
α_{Rx} (in dB)
[3]
Where "Tx corresponds to transmitter to target loss and "Rx corresponds to target to receiver loss, or:
α_{Tx} = 20log(f
_{1}T
_{Tx}) + K1 (in dB) and
α_{Rx}
= 20log(f
_{1}T
_{Rx}) + K1 (in dB)
with K1 values provided on page 4-6.1 and with f
_{1} being the MHz or GHz value
of frequency.
Therefore, the difference between monostatic and bistatic calculations is that two
α's are calculated
for two different ranges and different gains may be required for transmit and receive antennas.
To avoid having to include additional
terms for these calculations, always combine any transmission line loss with antenna gain.
As shown in Figure 2, it should also be noted
that the bistatic RCS received by the missile is not always the same as the monostatic RCS. In general, the target's RCS varies with angle.
Therefore, the bistatic RCS and monostatic RCS will be equal for receive and transmit antennas at the same angle to the target (but only if
all three are in a line, as RCS also varies with elevation angle).
Figure 2. Bistatic RCS Varies
Table of Contents for Electronics Warfare and Radar Engineering Handbook
Introduction |
Abbreviations | Decibel | Duty
Cycle | Doppler Shift | Radar Horizon / Line
of Sight | Propagation Time / Resolution | Modulation
| Transforms / Wavelets | Antenna Introduction
/ Basics | Polarization | Radiation Patterns |
Frequency / Phase Effects of Antennas |
Antenna Near Field | Radiation Hazards |
Power Density | One-Way Radar Equation / RF Propagation
| Two-Way Radar Equation (Monostatic) |
Alternate Two-Way Radar Equation |
Two-Way Radar Equation (Bistatic) |
Jamming to Signal (J/S) Ratio - Constant Power [Saturated] Jamming
| Support Jamming | Radar Cross Section (RCS) |
Emission Control (EMCON) | RF Atmospheric
Absorption / Ducting | Receiver Sensitivity / Noise |
Receiver Types and Characteristics |
General Radar Display Types |
IFF - Identification - Friend or Foe | Receiver
Tests | Signal Sorting Methods and Direction Finding |
Voltage Standing Wave Ratio (VSWR) / Reflection Coefficient / Return
Loss / Mismatch Loss | Microwave Coaxial Connectors |
Power Dividers/Combiner and Directional Couplers |
Attenuators / Filters / DC Blocks |
Terminations / Dummy Loads | Circulators
and Diplexers | Mixers and Frequency Discriminators |
Detectors | Microwave Measurements |
Microwave Waveguides and Coaxial Cable |
Electro-Optics | Laser Safety |
Mach Number and Airspeed vs. Altitude Mach Number |
EMP/ Aircraft Dimensions | Data Busses | RS-232 Interface
| RS-422 Balanced Voltage Interface | RS-485 Interface |
IEEE-488 Interface Bus (HP-IB/GP-IB) | MIL-STD-1553 &
1773 Data Bus |
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