![]() Modern noise jamming systems generate noise jamming signals by frequency modulating a carrier wave at the frequency of the victim radar. This method of generating radar noise jamming was used extensively during WW II. Employing any other form of power amplification would alter the Gaussian distribution of the jamming signal. The maximum power available from linear wideband power amplification is extremely limited. The DINA method of noise generation has a serious limitation. This method is called direct noise amplification (DINA). This signal is filtered and directly amplified to the maximum power that can be generated by the transmitter. The simplest method of generating a high-power Gaussian noise jamming signal is to employ a highly amplified diode to generate a noise signal at the frequency of the victim radar. Noise jamming takes advantage of this radar characteristic to delay or deny target detection. To detect these pulses, a radar receiver must be very sensitive and be able to amplify the weak target returns. Reflected radar pulses from target aircraft are extremely weak. Since noise from numerous sources is always present and displayed on a radar scope, noise jamming adds to the problem of target detection. Noise jamming is produced by modulating an RF carrier wave with random amplitude or frequency changes, called noise, and retransmitting that wave at the victim radar's frequency. The polarization of the noise jamming signal impacts the J/S ratio and the power density. A more serious power loss, nearly 100%, in ERP occurs when the jamming antenna is orthogonally polarized with the victim antenna. ![]() This results in a 50% reduction in effective radiated power (ERP) for most threat systems. Most threat systems are horizontally or vertically polarized. Noise jamming systems designed to counter multiple threat radars, with various polarizations, generally use a transmitting antenna with a 45° slant or use circular polarization. As discussed in Chapter 2, if the polarization of the jamming signal does not match the antenna polarization of the victim radar, there is a significant power loss in the jamming signal. Polarization of the noise jamming signal is another significant factor that impacts its effectiveness. In order to be effective, the jamming signal should exactly match the characteristics of the thermal noise signal of the victim radar receiver. A Gaussian distribution is simply a bell-shaped distribution of amplitudes. All of the frequencies in the bandwidth of the receiver have the same spectrum and amplitude that varies based on Gaussian distribution. Thermal noise is referred to as white noise and has a uniform spectrum. This ensures that the radar operator or automatic detection circuit cannot distinguish between the noise jamming and normal thermal noise. To effectively jam a radar receiver with noise, the jamming signal must emulate the thermal noise generated by the receiver. The quality of the noise jamming also determines its effectiveness. ![]() Radar systems that are frequency agile or that employ a wide bandwidth can reduce, or negate, the effectiveness of noise jamming by reducing the power density of the jamming signal. If the generated noise jamming signal has to cover a wide bandwidth or frequency range, the power density at any one frequency is reduced. The ability of a noise jammer to concentrate the jamming signal depends on the ability of the jammer to identify the exact frequency and bandwidth of the victim radar. If the noise jamming signal is centered on the frequency and bandwidth of the victim radar, the jamming signal has a high power density. The power density of the noise jamming signal has a direct relation to the J/S ratio. These high-power jamming signals can be introduced into the victim radar's main beam to deny range information and into the victim radar's sidelobes to deny azimuth information.Īnother factor which impacts the effectiveness of radar noise jamming is the power density. To achieve this level of jamming power, radar noise jammers usually generate high-power jamming signals. The power output of the noise jammer must be greater than the power in the target return, as measured at the output of the radar receiver. One of the most important factors that impacts the effectiveness of radar noise jamming is the J/S ratio. These factors include the jamming-to-signaI (J/S) ratio, power density, the quality of the noise signal, and the polarization of the transmitted jamming signal. The effectiveness of radar noise jamming depends on numerous factors.
0 Comments
Leave a Reply. |