# Multifunction RF Systems for Naval Platforms
## 2 Requirements for Naval RF Functions
### EA Function Requirements  
In general, a naval EA suite may utilize both onboard and off-board active devices, as well as off-board passive decoys, to provide platform self-protection by executing soft-kill countermeasures against threat RF systems. Since a MFRF system would be an onboard implementation, only the portion of the EA suite functionality represented by the onboard active device is considered for inclusion in such a system. The EA function transmits a RF signal to jam a threat electronic system, which is usually a radar. The following generic categories of jamming techniques are typically employed:  
* Noise jamming
* Multiple false targets
* Range gate pull-off (RGPO)
* Angle gate pull-off (AGPO)Noise jamming of a threat radar is intended to prevent the hostile platform from detecting the ship or at least denying it range information until it gets much closer, making it more susceptible to a counterattack. Generation of multiple false targets within the coverage area of the threat radar makes it more difficult for the threat platform to identify or lock on to the ship, or can result in a threat missile being launched with less accurate targeting information. The goal of RGPO and AGPO is to lure the tracking gates of a threat radar off the ship's signature in range and angle respectively. This leads to a break-lock situation in the case of a fire control radar, preventing the launch of a threat missile, while for the scenario of an active missile seeker being jammed, a successful AGPO causes the threat missile to miss the target. In modern EA systems, these techniques are executed coherently, meaning that the jammer transmits a replica of the threat radar waveform based on digital samples of that waveform which have been captured and stored internally in a high-speed _d_igital _r_adio _f_requency _m_emory (DRFM) [10]. Consequently, the jamming waveform enjoys the same pulse compression gain in the threat radar as the original radar signal, thereby reducing the amount of jamming power needed to be effective. The jammer may also modify the replica before re-transmitting, such as adding a time delay to effectively impart a range offset to a false target. In the case of noise jamming, so-called \"spot\" noise can be generated with a bandwidth matched to that of the captured waveform in the DRFM, to ensure that the full jammer power is injected into the instantaneous bandwidth of the threat radar. The frequency range of operation for the EA function, as shown in Table 1, corresponds to the frequencies of a wide variety of threat systems that the EA function may be required to jam. The largest threats of concern are represented by active missile seekers, as well as surveillance and fire control radars that may be used to target the ship. It is seen that the frequencies of operation for the ES and EA functions are the same. The instantaneous bandwidth requirement also mirrors that of the ES function, and refers in this case to the maximum bandwidth of the threat signal that it may need to replicate and transmit as part of a coherent jamming technique. As a point of clarification, a conventional active EA system has its own receive channels and digitizers to capture and store threat system waveforms in DRFMs for implementation of coherent jamming, as mentioned above. However, as part of a MFRF system, the receive portion of the EA function would likely be provided by the ES function, since the frequencies of operation, instantaneous bandwidths and polarization requirements of the ES function are compatible with those of an EA receive subsystem. Consequently, the EA function is considered to operate in a transmit-only mode within a MFRF system, and therefore, has no dynamic range requirement. The EIRP requirement specified for the EA function assumes the use of previously mentioned coherent jamming techniques, which maximize the effect of the available jamming power on threat radar systems.