TWO-WAY RADAR EQUATION
(BISTATIC)

Summary of Two-Way Bistatic Radar Equations Developed In This Section Peak power at the radar receiver input is: or in simplified log terms: 10log Pr = 10log Pt + 10log Gt + 10log Gr + G - Tx - Rx (in dB) Note: Losses due to antenna polarization and atmospheric absorption are not included in these equations.
Target gain factor; G = 10log + 20log f1 + K2 (in dB)	One-way free space loss; Tx or Rx = 20log (f1 RTx or Rx) + K1 (in dB)
K2 Values (dB) RCS () (units) m 2 ft 2 f1 in MHz K2 = -38.54 -48.86 f1 in GHz K2 = 21.46 11.14	K1 Values (dB) Range (units) NM Km m yd ft f1 in MHz K1 = 37.8 32.45 -27.55 -28.33 -37.87 f1 in GHz K1 = 97.8 92.45 32.45 31.67 22.13

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 :

* Keep or c, , 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 - 20log f + 20log c - 30log 4 - 20log R_Tx - 20log R_Rx [2]

or in simplified terms:

10log P_r = 10log P_t + 10log G_t + 10log G_r + G - _Tx - _Rx (in dB) [3]

Where _Tx corresponds to transmitter to target loss and _Rx corresponds to target to receiver loss, or:

_Tx = 20log (f₁ T_Tx) + K₁ (in dB) and _Rx = 20log (f₁T_Rx) + K₁ (in dB)

with K₁ values provided in the summary equation box at the beginning of this section and with f₁ being the MHz or GHz value of frequency.

Therefore, the difference between monostatic and bistatic calculations is that two '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).