# Multifunction RF Systems for Naval Platforms
## 6 Conclusions  
This paper discusses the key issues that must be considered in the design and development of an AESA-based MFRF system that replaces a number of single-purpose RF systems and associated topside antennas on a modern naval vessel. The RF functions that are candidates for consolidation within a MFRF system are radar, EA, ES and communications. Radar subfunctions comprise Volume Search, Horizon Search, and Terminal Illumination. Communication services that are suitable for inclusion in an AESA-based MFRF system are X-band, \(\mathrm{K_{u}}\)-band and \(\mathrm{K_{a}}\)-band SATCOM, as well as \(\mathrm{K_{u}}\)-band TCDL. The key transmit and receive requirements of the candidate RF functions were reviewed, namely, frequencies of operation, signal bandwidth, dynamic range, EIRP, one-way beamwidth, duty cycle, and signal polarization. These particular requirements pose the greatest challenges to development of a system that allows sharing of AESA radiating elements and RF components between multiple RF functions. Factors that drive these requirements for each RF function were also discussed. An ideal MFRF system design architecture was presented that would accommodate the requirements of the individual RF functions, minimize the number of required AESAs and provide the maximum flexibility to facilitate dynamic assignment of system resources to these functions by a resource allocation manager. The key features of this ideal architecture are: (1) each radiating element in an AESA is shared by a transmit and receive channel, where generally each of the two channels can be used by a different RF function at the same time; (2) the AESA radiating elements are dual orthogonally polarized to allow reception/transmission at all signal polarizations; (3) all components have sufficient bandwidth to support the full operating range of frequencies for the RF functions of interest; and (4) each transmit channel and receive channel has its own digital waveform generator and digital receiver respectively to fully capture the benefits of element-level digitization and waveform generation. Currently, costs and/or performance limitations in existing hardware technology result in design trade-offs and compromises that prevent achievement of this ideal architecture. The trade-offs fall into three categories (1) combined vs. separate transmit/receive arrays; (2) wideband vs. multiband operation; and (3) element-level vs. subarray-level digitization/waveform generation. The considerations involved in these trade-offs were discussed in detail. The consequences of departure from the ideal MFRF system architecture are generally a larger number of required AESAs, and less flexibility in assigning AESA resources to the different RF functions. A description was provided of MFRF system prototype development programs that have been conducted in other countries. The AMRFC program, which was carried out from 1998-2009 under the sponsorship of the US ONR, demonstrated for the first time the concept of a MFRF system covering 6-18 GHz, with real-time radar, EW, EA and communications functions sharing usage of waveform generators, receivers and a single pair of separated receive and transmit AESAs. The InTop program was initiated by ONR in 2009 as a follow-on to AMRFC and is still ongoing. It has the goal of further advancing wideband array and RF component technology for use in MFRF systems through the development of five RF system prototypes, each with less MFRF capability than the AMRFC testbed, but with higher TRL to facilitate spin-off into acquisition programs. The M-AESA program was a joint Sweden-Italy effort conducted from 2005-2014. Its aim was to develop and implement new hardware technology and system concepts in a next generation AESA-based MFRF system prototype that integrated radar, EA, ES and communication functions over a 2-18 GHz operating range. The primary RF building blocks that emerged from the M-AESA program were wideband antenna arrays and wideband T/R modules incorporating analog TTD beamforming elements.