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# Electronic Warfare and Radar Systems Engineering Handbook- Two-Way Radar Equation (Bistatic) -

The following table contains a summary of the equations developed in this section.

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.

[1]

* Keep λ or c, σ, and R in the same units.

On reducing the above equation to log form we have:

10log Pr = 10log Pt + 10log Gt + 10log Gr + 10log σ - 20log f + 20log c - 30log 4π - 20log RTx - 20log RRx   [2]

or in simplified terms:

10log Pr = 10log Pt + 10log Gt + 10log Gr + Gσ - αTx - αRx (in dB)   [3]

Where "Tx corresponds to transmitter to target loss and "Rx corresponds to target to receiver loss, or:

αTx = 20log(f1TTx) + K1 (in dB) and αRx = 20log(f1TRx) + K1 (in dB)

with K1 values provided on page 4-6.1 and with f1 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