Steve Foti

Indirect Holographic Techniques for Determining Antenna Radiation Characteristics and Imaging Aperture Fields

Indirect holographic techniques offer the potential of using simple and inexpensive near-field intensity-pattern measurements for the determination of the radiation characteristics of microwave antennas, and for the reconstruction of complex aperture fields. This work describes a practical method of applying indirect holographic techniques to microwave antennas. It describes how a technique originally developed at optical frequencies can be adapted to enable measurements to be taken on microwave antennas. The major difference is the replacement of a radiated reference signal by an electronically generated reference signal. This has enabled previous practical limitations to be overcome. Computer simulations and practical results are included for a large dish antenna at a sample spacing similar to those employed in direct holographic techniques. This work also describes how reducing the sample spacing significantly below a half wavelength enables the radiation characteristics of smaller antennas to be determined

A multiple switched beam Smart antenna with beam shaping for dynamic optimisation of capacity & coverage in mobile telecommunication networks

A four column Smart antenna array fed by a 4x4 Butler matrix augmented by a variable beam shaping network has been designed and simulated. It is demonstrated that using only three phase shifters within the beam shaping network provides dynamic beam flexibility including: four narrow switched beams, a right shaped beam, a left shaped beam and a broad broadcast channel beam. The shaped beams concentrate coverage at high capacity in either the right or left half of a sector while maintaining coverage at lower capacity over the reminder of the sector. The resultant antenna system represents an improvement in performance over a single multiple switched beam smart antenna without the cost and complexity of a fully adaptive smart antenna. Simulated radiation patterns over the full 3G frequency band show that useful dynamic coverage & capacity enhancement can be implemented with the proposed antenna system.

3D Microwave Imaging for Medical and Security Applications

The use of microwaves for imaging applications is currently of much research interest particularly in the areas of security imaging and medical imaging. Microwaves have been shown to be able to image objects concealed beneath clothing and recent research work has indicated that microwaves could offer a new low cost non-ionising technique for the detection and imaging of breast cancer tumours. Traditional intensity only measurements have only been able to provide 2D images of objects. This work describes how our indirect holographic approach can be used to reconstruct 3D images of objects from a single scalar 2D holographic intensity pattern

Early Stage Breast Cancer Detection using Indirect Microwave Holography

A novel microwave imaging approach for early stage breast cancer detection is described. The proposed technique involves the use of an Indirect Microwave Holographic technique employing a patented synthetic reference wave. This approach offers benefits in terms of simplicity, expense, comfort and safety when compared to current mammography techniques. Experimental results using a simulated phantom are included to demonstrate the validity of this technique

Imaging dielectric objects from scalar intensity patterns by means of indirect holography

An indirect microwave holographic technique for the reconstruction of complex scattered fields and the imaging of objects from a single holographic intensity pattern is described. The holographic intensity pattern is constructed by combining the signal scattered from the dielectric object with a synthesised reference signal. This dispenses with the need for expensive phase measuring equipment. Reconstructed magnitude and phase patterns of the original object have been determined using an adaptation of optical techniques. This work describes how dielectric objects of low contrast to the background when viewed using reconstructed magnitude patterns can be imaged from reconstructed phase patterns.

Imaging concealed objects from scalar microwave holograms

A new technique for the imaging of concealed objects using indirect holographic imaging principles is outlined. A brief examination of the underlying theory followed by a description of the novel experimental system that has been developed to overcome some of the previous issues regarding this technique, is presented along with some initial results obtained from the imaging of passive objects concealed by material and plastic.

Reduced height Luneburg lens antennas for satellite communications-on-the-move

The hemispherical (or half-Luneburg) lens antenna is a candidate type for satellite communications-on-the-move, either singly or as an element in a small array. It offers good aperture efficiency in a reduced height and excellent scanning performance. This work describes the development of half Luneburg lens antennas together with feeding arrangements to provide highly directive antennas with good scanning properties. The effects of the primary feed pattern and other loss mechanisms are investigated and reported. Measured gain for a 432mm diameter polymer lens at 30 GHz is 38.7 dBi.

The use of indirect holographic techniques for microwave imaging

The use of indirect holographic techniques for antenna testing has been shown to offer a simple, low cost scalar technique for the reconstruction of complex antenna aperture fields. This work extends the use of indirect holography to the imaging of objects. This work provides a brief outline of the basic theory of indirect microwave holography and how it can be used for the reconstruction of scattered complex fields at the measurement plane and how these results can be back propagated to provide images of the scattered fields at the position of the original object. The techniques described have been validated by experimental results on a range of objects including buried objects.