SE-IT Joint M-AESA Program: Overview and Status

A. Ouacha#, A. Fredlund+, J. Andersson+, H. Hindsefelt+, V. Rinaldi* and C. Scattoni*

#FOI, Swedish Defence Research Agency, Division of Information Systems, P.O. Box1165, SE-581 11 Linkoping, Sweden aziz.ouacha@foi.se

+FMV, Swedish Defence Materiel Administration, Air and Space Procurement Command, SE-115 88 Stockholm, Sweden. anders.fredlund@fmv.se

*SGD, General Secretariat of Defence, 5th Dept. R&T 2st Office, Via XX settembre 123/A-00187 Rome, Italy. (V. Rinaldi) r5u2s2@sgd.difesa.it

Abstract—The Multi-function Phased Array (M-AESA) program is a joint SE-IT initiative for the development of a capability driven multifunction phased array system concept. This paper will present the progress the M-AESA research and development program has made over the last three years and it follows the paper “New concepts for MRFS evolutionary trends. The M-AESA program: A joint IT-SE capability driven approach” by V. Carulli et al. presented at the Radar Conference 2008 in Rome [1]. The program, based on a number of different national initiatives, benefits from different cultural approaches and perspectives, and aims to lead an initiative in Europe for such a new family of RF systems. An overview and status of this unique R&D partnership will be discussed with a mission of evaluating new technology and system architecture for developing the next generation phased array antenna system capable of exploiting the most relevant operational functions (Radar, EW, Comm) according to the operational scenarios. However, a number of technical, operational and cost issues are still remaining to be addressed before M-AESA can become a reality. 1. INTRODUCTION There is no doubt that the changes in the defence environment that we will experience in the future dictate commonality across our services. Moreover, the limited research and development funds drives defence organizations to seek joint projects with the aim of finding common solutions. Today’s radar, communication and electronic warfare functions will be enhanced using the M-AESA concept. Compared to existing federated systems, the M-AESA concept will, due to the multi-task capabilities and the ability to automatically adapt to dynamic battlefield conditions, allow future systems to provide decision makers with better overall situational awareness at significantly lower operational and maintenance costs. Using a scalable and open architecture this will ensure compatibility with Navy, Air and Ground command and control systems and allow upgradeability of the system via the insertion of future technologies. An example of similar ongoing programs are the advanced multifunction RF concept (AMRFC) [2], which is mainly aimed at naval applications,

wherein multiple simultaneous signals will be transmitted/received from a common aperture, and the advanced shared aperture program (ASAP) [3] array design which is mainly focused on fighter applications. In this paper we will present an overview and status of this unique R&D partnership that was initiated in 2005 with a mission of evaluating new technology and system architecture for developing the next generation phased array antenna system M-AESA. An industrial consortium formed of ELETTRONICA, SAAB and SELEX-SI was awarded the contract to conduct this program.

2. AIM AND BENEFITS OF M-AESA PROGRAM

Figure 1 - Illustration of the operational concept of M-AESA performing multiple tasks.

Some of the important aims of this joint SE-IT program are: (1) to explore the possibility of integrating Radar, EW and Communication (data links), using wideband shared aperture and (2) M-AESA program will represent the majority of the development cost for the next generation microwave system regardless of platform.

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The advantages and benefits of M-AESA are significant. The M-AESA concept will, due to the ultra wideband frequency range compared to now existing federated system, give the ability for multi-mission performance and the capability to automatically adapt to the dynamic battlefield conditions allowing future decision makers a better overall situational awareness at significantly lower operational and maintenance costs. Figure 1 depicts the operational concept of simultaneous beams performing multiple missions. The aim of the Swedish and Italian MoD’s is to insert this multifunction system into their future ground, air and sea platforms with an approach of a system that will have common technology applicable to all platforms. It is expected that M-AESA concept will provide several pay-offs despite the high initial development cost.

3. PROGRAM STATUS Figure 2 shows a diagram of the M-AESA program activities. The proposed work includes critical technology development, building M-AESA test bed, and performing life cycle cost analysis of a future defence acquisition program. This program is organized into three phases as illustrated in Figure2. Phase 1 (2005-2006): Technology concept and/or application formulated.

• Purpose: Analysis of current system and related technological base to jointly outline possible applications for future systems

• Output: Joint Statement Of Work (SOW) and Work Breakdown Structure (WBS) for phase 2. An industry joint final planning and costing for phase 2 and 3.

Phase 2 (2007-2010): Concept Refinement

• Purpose: Select an applicable architecture for the M-AESA system concept, system studies, identify critical enabling technologies, select an applicable architecture for the emulator and develop a Technology Development Strategy for phase 3.

• Output : TRL 4 (Breadboard validation in laboratory environment).

Phase 3 (2011-2014): Technology development

• Purpose: To reduce technology risks and determine appropriate sets of technologies to be inserted into a full system.

• Output: A M-AESA Field system demonstration TRL 6 (System demonstration in a relevant environment)

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Figure 2 - Diagram showing M-AESA program activities

The M-AESA program activities often run in parallel to allow feasibility considerations of design decisions. The critical line for the program is indicated in red.

4. SYSTEM CONCEPT AND TECHNOLOGY DEVELOPMENT

The purpose of this paragraph is to provide the AESA community with the technical approaches that are used to demonstrate the feasibility of the M-AESA concept. Figure 3 shows a simplified overall design process of the M-AESA concept where the interaction between the different Work Packages (WP) is illustrated.

Level one WBS

WP A: Emulator• Performs Experiments on apertures and a “representative”

demonstrator• Anticipates integration issues• Simulates some critical aspects of the future System• Collect results from all the packages and integrates them in a

single vision• Carries out feedback to System Studies and Technology Studies

WP B: Basic Technology• Produces studies on technology issues• Produces samples of critical items• Carries out feedback to System architecture

and solutions

WP C: System Studies• Performs modeling and simulation• Proposes candidate System architectures• Produces performances estimations• Carries out feedback to Technology studies

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Figure 3 - M-AESA design iteration approach

To manage the interrelationships among work packages and to ensure their convergence to the appropriate and common goal, an iterative approach has been adopted. Iterations are successive refinements of the whole work and address the totality of the topics right from the start. During Phase 2 three iterations have been adopted for system specification, architecture definition and technology development. Since systems studies WP is the driver for the whole Phase 2 work, the complete work cycle is performed three times which in turn resulted into three iterations in the other work packages.

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Figure 4 - Illustration of antenna concepts

A—System Concept

Phase 1 has pointed out some directions for the architecture of the “New System Concept”. Some of the main identified issues are: • The top level architecture envisioning a common RF

subsystem (EXR + BF + Antenna + TRM) performing all receive and transmit functions for all system functions.

• The antenna configurations (A1, A1’, A2 and A3), as shown in Figure 4, giving constraints on the front-end part of the RF-subsystem.

• One set of EXR-building blocks and two types of TRMs to support all antenna concepts.

• Many problems and risks especially connected to the A1 and A1’ antenna concept which resulted in specific studies in some areas.

In this paragraph, we describe and compare the two main antenna concepts A1 and A3 defined within the M-AESA program and their differences are shortly discussed. The A1’ and A2, shown in Figure 4, are considered as intermediate between A1 and A3 and will not be discussed here. 1—Description of Concept A1: This is a shared aperture concept where a single common aperture is used to perform multiple functions (Radar, ECM, ESM, COM) simultaneously. The approach, although potentially the most advantageous, is also the most challenging since significant issues arise such as the one related to isolation. This concept is motivated by what can be called the “ultimate” vision. Here a single common RF-frond-end is used for all the defined RF-functions over an extremely wide bandwidth. The aperture which is built with identical elements and TRM performing transmitting functions in the band (4.5 – 18 GHz) and receiving functions in the band (2 – 18 GHz). Due to its modular design, the aperture is dynamically reconfigurable so that different functions can use the appropriate part of the whole aperture at the appropriate time. In other words, the aperture is used by the different functions by area sharing and/or time sharing. A practical constraint that affects an A1 antenna architecture – as well as other array architectures – is that the TRM’s can be

allocated to different activities in a small group – subarray – with fixed dimensions (n by k modules), e.g. the radar search uses K sub-arrays, the high accuracy ESM uses L sub-arrays, and so on. The constraint derives from the need to have a reduced complexity of the components downstream the active array. An ideal array controlled at single TRM level would need an entire Rx/Tx chain down to the A/D converters for each single TRM. An important hypothesis which the A1 architecture depends on is the assumption that the coupling among elements (or subarrays) can be “controlled”, i.e. that it is possible to perform reception activities simultaneously with transmission activities, although this might result in reduced performance. During analysis, a realistic approach to this matter shall be taken.

2—Description of Concept A3: The system uses different apertures for all the main RF functions of M-AESA. The concept is motivated by: • The idea of solving the coupling issue among the main

functions (one transmitting, the other receiving) by allocating them into separate apertures.

• The use of optimized TRM’s specialized for the main RF functions. For example, the radar functions are performed by modules allocated in C or/and X-band (motivated by the type system), the EW (ESM, ECM) functions are performed by wideband modules, the COM functions are performed by modules in some band (likewise the radar functions) or by wideband modules (likewise the EW functions).

3—Differences between A1 and A3: A main difference between concept A3 and concept A1 is that the maximum dimensions of the arrays allocated to different functions is fixed: • In A1 the whole aperture could be used for radar

activities, as well as for ECM, ESM and COM activities; the minimum aperture is dictated by the subarray dimensions.

• In A3 the maximum antenna dimension usable by a function is dictated by the aperture dedicated to that function. Generally speaking the single A3 apertures (dedicated to the single RF function) can also be reconfigured according to the specific need and the minimum aperture is still dictated by the subarray dimension.

It can be observed that the main difference between A1 and A3 resides in the reconfigurability of the whole antenna in A1 than in the use of equal or different kinds of TRM. As an example if we consider separate apertures for different functions, but with the same kind of wideband TRM’s, this architecture has to be considered as A3. Another example is a unique aperture (assumed without strong coupling problems) with unique TRM, where the sub-arrays (or elements) are allocated to a specific function in a fixed manner. In this case the architecture can once again be

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considered as an A3. Similar issues has been discussed in the frame of scalable multifunction RF (SMRF) program and a trade-off analysis has been performed between a wideband and a multiband SMRF architecture by Albert G. Huizing [4].

B—Technology Development

During Phase 2 of the M-AESA program the objective of the work package Basic Technology was: • To develop generic and multi-application RF building

blocks for future M-AESA products. • To develop necessary technology for future M-AESA

products according to Phase 1 roadmap. • Select the technology needed for Phase 3 system

demonstrator. A thorough work has been performed in this WP by the consortium to support the architecture design decisions and developing the building blocks for Phase 3 demonstrator. This has been done by taking into account some of the important system characteristics such as scalability, maintainability, supportability and other characteristics needed to accomplish the operational requirements as required by the IT and SE MoD’s. Several building blocks are still under development and some have been developed. This includes:

Figure 5 - M-AESA Core Chip 2-18 GHz.

Chip size: 4.57 x 5.35 mm2

Figure 6 - M-AESA 4.5-18GHz HPA using Lg=0,25µm EBL p-HEMT GaAs technology. Chip size: 5.2 × 2.9 mm2

• Various wideband antenna arrays. • Two types of TRM’s supporting the different system

concepts discussed above. • Core chip in different technologies using both TTD’s

and phase shifters. • Exciter Receiver (EXR) with the properties of high

dynamic range, wideband digital receiver function and ultra wideband receiver function.

• Beamformer architectures supporting the recommendations from system design guideline for both analog and digital beamforming and different subarray arrangements.

• Highly integrated Multipack solutions The photographs in Figures 5-11 show some examples of the building blocks that have been developed within M-AESA program.

Figure 7 - M-AESA 5-12GHz HPA using Lg=0,25µm EBL p-HEMT GaAs technology. Chip size: 5 × 3.5 mm2

Figure 8 - Wideband Digital Receiver with 1 GHz instantaneous bandwidth providing one feet resolution in SAR and HRR applications, wide instantaneous spectrum coverage in EW applications and high data rate for communication applications.

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Figure 9 - Example of a multipack assembly suitable for small arrays

Figure 10 - Example of a multipack assembly suitable for large arrays

4. PHASE 3 - CONCEPT DEMONSTRATION

The consortium together with the SE and IT MoD’s has developed a preliminary program plan with the aim to design, manufacture and evaluate a Phase 3 Demonstrator. This demonstrator, when completed, will provide a valuable tool for investigating the technological issues and risks associated with shared aperture(s) and particularly with common system manager (CSM). Some of the aspects that the CSM should provide are: scheduling and allocation of shared resources, interconnection of resources into the required configuration, prioritising of functions in case of conflict, and maintenance of the shared resource pool. The development of the demonstrator is scheduled to start in the last quarter of 2010 and hopefully four years later will be able to prove the possibility of integrating Radar, EW and Communication (data links), using wideband shared aperture(s).

Figure 11 - Two examples of antenna arrays that have been developed and evaluated. Above is a 37x64 elements single polarized array. Below is a 25x25 elements double polarized array.

5. SUMMARY Although the studies that have been performed in this program, and other international programs, show the benefits that would be achieved from a multifunction phased array system compared to dedicated systems, one should realise that a number of technical, operational and cost issues are still remaining to be addressed before M-AESA can become a reality. The technical challenge resides in realising an affordable architecture, including its associated subsystems and components, that allows combining the functionality of several antennas into one shared aperture and at the same time supporting future decision makers with a better overall situational awareness at significantly lower operational and maintenance costs

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compared to the case with existing federated systems. Moreover, the limited research and development funds drives defence organizations to seek joint projects, bilateral or multinational, with the aim of finding common and beneficial solutions. This requires a tremendous effort from the program management team to find a strategy to bridge the different nations interests and not the least the cultural aspect of each nation.

ACKNOWLEDGMENT The authors would like to express their thanks to SELEX-SI, ELETTRONICA and SAAB for their contributions to this article.

REFERENCES [1] V. Carulli, R. Nordenberg, A. Fredlund and A. Ouacha, ”New concepts for MRFS evolutionary trends. The M-AESA program: A joint IT-SE capability driven approach”, Proc IEEE Radar Conference 2008, (2008). [2] BAA on Advanced Multifunction RF Systems (AMRFS), Office of Naval Research (ONR) Guide to Programs dated January 1996. [3] Hemmi, Dover, Vespa, Fenton, Advanced Shared Aperture Program (ASAP) Array Design. 1996 IEEE International Symposium on Phased Array Systems and Technology. [4] Albert G. Huizing “Wideband vs. Multiband Trade-offs for a Scalable Multifunction RF system” Proc IEEE Radar Conference 2005, (2005).

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