Recent efforts by several researchers around the world to combine fractal geometry with electromagnetic theory have led to a plethora of new and innovative antenna designs. In this report, we provide a comprehensive overview of recent developments in the rapidly growing field of fractal antenna engineering. Fractal antenna engineering research has been primarily focused in two areas: the first deals with the analysis and design of fractal antenna elements, and the second concerns the application of fractal concepts to the design of antenna arrays. Fractals have no characteristic size, and are generally composed of many copies of themselves at different scales. These unique properties of fractals have been exploited in order to develop a new class of antenna-element designs that are multi-band and/or compact in size. On the other hand, fractal arrays are a subset of thinned arrays, and have been shown to possess several highly desirable properties, including multi-band performance, low sidelobe levels, and the ability to develop rapid beamforming algorithms based on the recursive nature of fractals. Fractal elements and arrays are also ideal candidates for use in reconfigurable systems. Finally, we provide a brief summary of recent work in the related area of fractal frequency-selective surfaces.

An overview of fractal antenna engineering research

Soil Moisture and Ocean Salinity, European Space Agency, is the first satellite mission addressing the challenge of measuring sea surface salinity from space It uses an L-band microwave interferometric radiometer with aperture synthesis (MIRAS) that generates brightness temperature images, from which both geophysical variables are computed The retrieval of salinity requires very demanding performances of the instrument in terms of calibration and stability This paper highlights the importance of ocean salinity for the Earth's water cycle and climate; provides a detailed description of the MIRAS instrument, its principles of operation, calibration, and image-reconstruction techniques; and presents the algorithmic approach implemented for the retrieval of salinity from MIRAS observations, as well as the expected accuracy of the obtained results

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SMOS: The Challenging Sea Surface Salinity Measurement From Space

A prototype microwave breast imaging system is used to scan a small group of patients. The prototype implements a monostatic radar-based approach to microwave imaging and utilizes ultra-wideband signals. Eight patients were successfully scanned, and several of the resulting images show responses consistent with the clinical patient histories. These encouraging results motivate further studies of microwave imaging for breast health assessment.

Microwave Breast Imaging With a Monostatic Radar-Based System: A Study of Application to Patients

This invention is in the field of base station antennas for wireless communications. The present invention refers to a slim multi-band antenna array for cellular base stations, which provides a reduced width of the base station antenna and minimizes the environmental and visual impact of a network of cellular base station antennas, in particular in mobile telephony and wireless service networks. A multiband antenna array comprises a first set of radiating elements operating at a first frequency band and a second set of radiating elements operating at a second frequency band, said radiating elements being smaller than λ/2 or smaller than λ/3, being (λ) the longest operating wavelength. The ratio between the largest and the smaller of said frequency bands is smaller than 2.

Slim Multi-Band Antenna Array For Cellular Base Stations

The present invention consists of an antenna comprising at least two radiating structures, said radiating structures taking the form of two arms, said arms being made of or limited by a conductor, superconductor or semiconductor material, said two arms being coupled to each other through a region on first and second superconducting arms such that the combined structure of the coupled two-arms forms a small antenna with a broadband behavior, a multiband behavior or a combination of both effects. According to the present invention, the coupling between the two radiating arms is obtained by means of the shape and spatial arrangement of said two arms, in which at least one portion on each arm is placed in close proximity to each other (for instance, at a distance smaller than a tenth of the longest free-space operating wavelength) to allow electromagnetic fields in one arm being transferred to the other through said specific close proximity regions. Said proximity regions are located at a distance from the feeding port of the antenna (for instance a distance larger than 1/40 of the free-space longest operating wavelength) and specifically exclude said feeding port of the antenna.

Coupled multiband antennas

A simple model that explains the behavior of the Sierpinski fractal antenna is presented. This model shows that the multiband behavior of the Sierpinski fractal antenna is a consequence of its fractal nature. The model is applied to predict the behavior of the Sierpinski fractal antenna when the flare angle is modified and its validity is assessed by comparing its predictions with measured data.

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An iterative model for fractal antennas: application to the Sierpinski gasket antenna

Antenna arrays which can work simultaneously in various frequency bands thanks to the physical disposition of the elements which constitute them, and also the multiband behaviour of some elements situated strategically in the array. The configuration of the array is described based on the juxtaposition or interleaving of various conventional mono-band arrays working in the different bands of interest. In those positions in which elements of different multiband arrays come together, a multiband antenna is employed which covers the different working frequency bands. The advantages with respect to the classic configuration of using one array for each frequency band are: saving in cost of the global radiating system and its installation (one array replaces several), and its size and visual and environmental impact are reduced in the case of base stations and repeater stations for communication systems.

Interlaced multiband antenna arrays

A classification of system errors in aperture synthesis radiometry applied to Earth obervation is presented. A general procedure to quantify th eimpact of antenna errors on the radiometric accuracy is developed and is then particularized to an L-band Y-shaped interferometer called MIRAS (microwave imaging radiometer by aperture synthesis) currently under study at the European Space Agency. This work analyze in detail the impact of antenna errors on the radiometric accuracy of the instrument. These antenna errors are grouped into amplitude and phase antenna pattern errors, antenna position errors and antenna cros polarization errors. Special attention is paid to antenna coupling effects because of their importance in the selection of a suitable inversion algorithm for large aperture synthesis interferometers: the G-matrix techniques or the Fourier techniques proposed for MIRAS.

Impact of antenna errors on the radiometric accuracy of large aperture synthesis radiometers. Study applied to MIRAS

Fractal-shaped antennas and their application to GSM 900/1800

The dual multitriangular antennas (AMD) of the present invention can be applied mainly to base stations of both cellular telephone systems (GSM and DCS). They provide radioelectric covering to any user of a cell operating in any of the two bands or in both simultaneously. The object of the invention is to provide an antenna of which the radiant element is comprised basically of various triangles joined exclusively by their apex. The function of the antenna is to operate simultaneously in the bands of the radioelectric spectrum corresponding to the cellular telephone systems GSM 890 MHz - 960 MHz and DCS 1710 MHz - 1880 MHz.

Jordi Romeu Robert

Papers

An iterative model for fractal antennas: application to the Sierpinski gasket antenna

Interlaced multiband antenna arrays

Impact of antenna errors on the radiometric accuracy of large aperture synthesis radiometers. Study applied to MIRAS

Fractal-shaped antennas and their application to GSM 900/1800

Dual multitriangular antennas for gsm and dcs cellular telephony