How do I calculate the J/S ratio at the victim radar receiver for a standoff jammer?

The J/S (jam-to-signal) ratio for a standoff jammer (SOJ) is different from a self-protection jammer because the jammer and the target are at different locations. The SOJ is positioned at a safe distance from the radar while jamming on behalf of the protected target: (1) J/S equation for standoff jammer: J/S = (P_j × G_j × R_t⁴ × 4π) / (P_t × G_t × sigma × R_j² × G_r(theta_j) / G_r_max × B_r/B_j). Where P_j = jammer power, G_j = jammer antenna gain toward the radar, R_t = range from radar to target, R_j = range from radar to jammer, sigma = target RCS, P_t = radar transmit power, G_t = radar transmit antenna gain, G_r(theta_j) = radar receive antenna gain in the direction of the jammer, G_r_max = radar maximum receive gain. (2) Key difference from SPJ: the standoff jammer is NOT co-located with the target. The radar can potentially reject the jammer by exploiting the angular separation between the jammer and the target. If the jammer is in the radar sidelobes: G_r(theta_j) / G_r_max = sidelobe level (e.g., -30 dB), and the J/S is degraded by 30 dB compared to a mainbeam jammer. If the jammer is in the radar mainbeam: G_r(theta_j) / G_r_max = 1 (0 dB), and the full jammer power is effective. (3) Example: radar: P_t = 1 MW, G_t = 35 dBi, G_r_max = 35 dBi. Target: sigma = 1 m², R_t = 100 km. Standoff jammer: P_j = 1 kW (60 dBm), G_j = 20 dBi, R_j = 200 km. Jammer in radar mainbeam (theta_j ≈ 0°): J/S = 60 + 20 + 4×50 - (90 + 35 + 0) - 2×53 - 11 = 60 + 20 + 200 - 125 - 106 - 11 = 38 dB. Jammer in radar sidelobe (-30 dB): J/S = 38 - 30 = 8 dB. In the sidelobes: J/S drops to only 8 dB, which may be marginal for effective jamming. (4) SOJ tactics: the standoff jammer should position itself in or near the radar mainbeam (along the radar-to-target line of sight) to maximize the J/S. Barrage mode: the SOJ jams continuously across the threat band, creating a noise corridor that masks all targets within the mainbeam. Support mode: the SOJ jams only when the radar beam scans past the protected target, conserving power.