Course #21

Advanced Array Antennas: Conformal Arrays and Digital Beamforming

October 25-28, 2010. Barcelona, Spain

INSTRUCTORS
Professor Lars Josefsson, Lars Microwave, Gothenburg, Sweden
Dr Patrik Persson, Ericsson AB, Gothenburg, Sweden
Dr Hans Steyskal, S4 Inc, Hanscom AFB, MA, USA

TECHNOLOGY FOCUS 
The demand for evermore-sophisticated information from communication and radar systems leads to concomitant requirements on antenna performance. Conformal array antennas and digital beamforming are emerging technologies that can meet these demands. 

Conformal arrays, i.e. array antennas on curved surfaces, are suitable for integration on various vehicles: cars, aircraft, satellite bodies, etc. They can provide wide angular coverage, which makes them attractive for several communication and surveillance applications. With modern high-density packaging of microelectronic components a complete antenna system can be made as a thin multilayer design, a “smart skin”. 

Digital beamforming is a powerful technique to enhance antenna performance. DBF arrays digitize the received signals at the element level, thus preserving the total information available at the aperture, and then process these signals in the digital domain to form the desired beams. Microwave ICs, high-speed digital electronics and signal processors are now making DBF practical in many applications such as fast adaptive interference rejection, high resolution direction finding, ultra-low sidelobes, and various forms of adaptive space-time processing, both for communication and radar (incl. MIMO systems). 

COURSE CONTENT 
This course spans a range of technologies significant for the development of advanced antenna systems. Arrays on curved surfaces are compared with traditional planar arrays. Practical conformal array configurations are presented taking examples from base stations, radar, and satellite communication applications. Basic DBF systems are contrasted with analog beamforming systems. Typical DBF applications, their components and system architectures, are reviewed. We discuss applications where both DBF and conformal antenna technology are likely to be combined in future antenna systems. 

Monday – JOSEFSSON/PERSSON 

Conformal Array Antennas 
Basic concepts are reviewed to establish a common understanding of important characteristics and definitions. Array antennas in general are discussed, starting with linear and planar arrays. 

• Radiation Mechanisms, Antenna Impedance
• Mutual Coupling Effects, Bandwidth, Beam Steering Performance 
• Applications 

Circular Array Antennas 
The circular array can be seen as a building block of many conformal antennas, e.g. arrays on cones and cylinders. We give examples of typical performance and discuss design rules, phase mode theory, omni-directional patterns, pattern bandwidth, and suppression of spectral harmonics.

• Design Rules
• Phase Modes and Pattern Characteristics
• Suppression of Harmonic Radiation 

Computational Methods for Conformal Antennas 
We discuss commonly used methods for analyzing conformal antennas to get a physical understanding rather than specific details of the different methods. Canonical examples are given.

• Modal Solutions, MoM, FEM, and FDTD
• Asymptotic and Hybrid Methods
• Geodesics 

Tuesday – PERSSON /JOSEFSSON 

Conformal Array Characteristics 
General characteristics of conformal array antennas are reviewed. Canonical array designs and expected performances are discussed. 

• Mechanical Aspects, Active Surface Definition
• Phase Scanning, Commutating 
• Grating Lobes, Tapering, Element Impedance Variations 

Singly Curved Array Antennas 
Their characteristics are discussed, using wave-guide-fed apertures and microstrip-patches as examples. The focus is on mutual coupling and its effect on radiation characteristics. 

• Mutual Coupling vs. Surface Shape 
• Embedded Element Patterns
• Dielectric Radome Effects 

Doubly Curved Array Antennas 

• Polarization and Element Distribution 
• Mutual Coupling and Radiation Properties 

Polarization 

• Cross Polarization Effects, Definitions 
• Sources of Cross Polarization in Curved Arrays 
• Controlling Cross Polarization 

Analog Beamforming (ABF) 
ABF and beam scanning principles for conformal array antennas are presented. Solutions for commutating the active sector as well as beam steering and multiple beam generation for circular and cylindrical arrays are discussed.

• Feed Networks, Matrix Feed Systems
• Quasi-Optical Feeds 

Wednesday – PERSSON /JOSEFSSON/STEYSKAL 

Conformal Array Synthesis and Design 
Pattern synthesis is just the starting point in a design problem. We also treat mechanical design aspects and mutual coupling effects. 

• Conformal Array Shape Optimization 
• Pattern Synthesis: Linear vs. circular arrays 
• Accounting for Mutual Coupling 

Conformal Array Antenna Scattering 
Radar Cross Section (RCS) characteristics of conformal antennas are presented, incl. scattering vs. radiation performance trade-off. 

• Scattering Cross Section 
• Impedance Load Effects and Curvature Effects 

Demonstration of Analysis and Design 

• Theoretical Design Using Software Tools 
• Practical Design Examples 

Digital Beamforming (DBF): System and Components 
A generic DBF receiver system and the effects of the subsystems on overall system performance are discussed. Basic system parameters are defined and present commercial component performance indicated.

• Review of Sampling Theory and Channel Capacity 
• Receivers, A/D Converters, Digital Beam Former, Beam Controller, Calibration Network 
• DBF in the Transmit Mode, Direct Digital Synthesis (DDS) 

Typical DBF Applications 
DBF offers several unique capabilities.

• Review of Matrix Algebra.
• Open- Loop Adaptive Interference Suppression: Various adaptive criteria, array 
  tolerance effects

Thursday – STEYSKAL 

Typical DBF Applications (cont´d) 

• Spatial Multiplexing: Simultaneous transmission of independent signals in different directions on the same frequency 
• Multiple Input, Multiple Output (MIMO) Systems for Communication 
  and Radar
• Array Element Decoupling
• Array Calibration 

Partial DBF and Sub-arraying Architectures, DBF Systems 
Trade-offs between DBF system performance and cost. 

• Periodic and Random Sub-Arrays, Thinned and Wideband Arrays 
• Experimental DBF Systems with Planar and Conformal Arrays 

Regular Course Fee: EUR 2490

Early Registration Course Fee: EUR 2240
This applies to firm registrations received 2 months before course start. 

University Student and Faculty Rate:
Two university participants are welcome to attend for one course fee if payment is to be made from university funds.

Deliverables:
The course fee covers tuition, course material, and the day conference packages (morning/afternoon refreshments, lunches etc.) paid on your behalf to the course venue. Accommodation is not included.