sensors Review Multifunction RF Systems for Naval Platforms Peter W. Moo 1,* and David J. DiFilippo 2 1 Defence Research and Development Canada–Ottawa Research Centre, Ottawa, ON K1A 0Z4, Canada 2 Dannaven Inc., Ottawa, ON K1A 0Z4 Canada; djjdifi[email protected] * Correspondence: [email protected]; Tel.: +1-613-998-2879 Received: 7 May 2018; Accepted: 26 June 2018; Published: 28 June 2018 Abstract: The evolving role of modern navies has required increasingly higher levels of capability in the Radio Frequency (RF) shipboard systems that provide radar, communications, Electronic Attack (EA) and Electronic Support (ES) functions. The result has been a proliferation of topside antennas and associated hardware on naval vessels. The notion of MultiFunction RF (MFRF) systems has drawn considerable interest as an approach to reversing this trend. In a MFRF system, RF functions are consolidated within a shared set of electronics and antenna apertures that utilize Active Electronically Scanned Array (AESA) technology. This paper highlights a number of issues to be considered in the design and implementation of a naval MFRF system. Specifically, the key requirements of the RF functions of interest are first reviewed, and MFRF system design trade-offs resulting from costs and/or performance limitations in existing hardware technology are then discussed. It is found that limitations in hardware technology constrain the implementation of practical MFRF systems. MFRF system prototype development programs that have been conducted in other countries are described. MFRF resource allocation management is identified as an important future research topic. Keywords: naval systems; multifunction RF systems; active electronically steered arrays; radar; electronic support; electronic attack; communications 1. Introduction The evolving role of modern navies has required increasingly higher levels of capability in the Radio Frequency (RF) shipboard systems that provide radar, communications and Electronic Warfare (EW) functions, including in the latter case both Electronic Attack (EA) and Electronic Support (ES). The result has been a proliferation of topside antennas on naval vessels. It has been estimated that the number of topside antennas has roughly doubled on ships launched in the 1990s relative to those launched in the 1980s, with the antenna count on a typical 1990s-era destroyer for example being on the order of 80 [1]. This has led to a number of problems, including increased mutual electromagnetic interference, larger ship Radar Cross Section (RCS), and higher life-cycle costs associated with the operation of multiple unique RF systems. Since the late 1990s, the idea of MultiFunction RF (MFRF) systems has drawn considerable interest as an approach to addressing this issue. In a MFRF system, several RF functions are consolidated within a shared set of electronics and antenna apertures. Active Electronically Scanned Array (AESA) technology is a key enabler for these systems. A modern AESA employs a separate transmit (Tx) and/or receive (Rx) channel for each of its radiating elements, with a high-power amplifier (HPA) and low-noise amplifier (LNA) in each of the transmit and receive channels respectively. Often, there is also some type of beamforming element in each channel, such as a phase shifter or true time-delay (TTD) circuit. The HPAs, LNAs and beamforming elements are typically packaged into Monolithic Microwave Integrated Circuit (MMIC) modules that are incorporated in the array structure to be as close as possible to the radiating elements, thereby minimizing system losses. In general, the Sensors 2018, 18, 2076; doi:10.3390/s18072076 www.mdpi.com/journal/sensors Sensors 2018,, 18,, 2076x 2 of 3736 architecture allows dynamic reconfiguration of the antenna aperture, including partitioning of the array AESAelements architecture into subarrays, allows to dynamicform multiple reconfiguration simultaneous of transmit the antenna and/or aperture, receive including beams in independent partitioning ofdirections the array with elements different into beam subarrays, patterns to formand waveforms. multiple simultaneous This provides transmit the level and/or of flexibility receive beamsthat is inrequired independent to support directions multiple with RF functions different beamwith the patterns same antenna and waveforms. aperture. 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Figure 1.1. Conceptual diagram for MFRF system.system. MFRF systems can potentially provide the following benefits: Sensors 2018, 18, 2076 3 of 37 MFRF systems can potentially provide the following benefits: • Reduction