detect this switch in frequency quickly enough or predict the next hop frequency, and switch their own jamming frequency accordingly during the receiving time window. The most advanced jamming techniques have a very wide and fast frequency range, and might possibly jam out an antijammer. This method is also useful against barrage jamming in that it forces the jammer to spread its jamming power across multiple frequencies in the jammed system's frequency range, reducing its power in the actual frequency used by the equipment at any one time. The use of spread-spectrum techniques allow signals to be spread over a wide enough spectrum to make jamming of such a wideband signal difficult. Sidelobe blanking Radar jamming can be effective from directions other than the direction the radar antenna is currently aimed. When jamming is strong enough, the radar receiver can detect it from a relatively low gain sidelobe. The radar, however, will process signals as if they were received in the main lobe. Therefore, jamming can be seen in directions other than where the jammer is located. To combat this, an omnidirectional antenna is used for a comparison signal. By comparing the signal strength as received by both the omnidirectional and the (directional) main antenna, signals can be identified that are not from the direction of interest. These signals are then ignored. Polarization Polarization can be used to filter out unwanted signals, such as jamming. If a jammer and receiver do not have the same polarization, the jamming signal will incur a loss that reduces its effectiveness. The four basic polarizations are linear horizontal, linear vertical, right-hand circular, and left-hand circular. The signal loss inherent in a cross polarized (transmitter different from receiver) pair is 3 dB for dissimilar types, and 17 dB for opposites. Aside from power loss to the jammer, radar receivers can also benefit from using two or more antennas of differing polarization and comparing the signals received on each. This effect can effectively eliminate all jamming of the wrong polarization, although enough jamming may still obscure the actual signal. Radiation homing Another practice of ECCM is to program sensors or seekers to detect attempts at ECM and possibly even to take advantage of them. For example, some modern fire-and-forget missiles like the Vympel R-77 and the AMRAAM are able to home in directly on sources of radar jamming if the jamming is too powerful to allow