Michael Elsdon

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

Microwave Holographic Imaging of Breast Cancer

Breast cancer is one of the most common forms of cancer in women. X-ray mammography is the most widely used technique for early detection but has limitations. In this paper, an alternative approach for breast cancer detection using microwave imaging is presented. This is based upon a microwave holographic approach, central to which is the use of a synthetic reference beam. This approach has benefits in terms of simplicity and expense. Experimental results using a breast phantom are included to demonstrate the potential of this approach.

Printed Slot Loaded Bow-Tie Antenna With Super Wideband Radiation Characteristics for Imaging Applications

A super wideband printed modified bow-tie antenna loaded with rounded-T shaped slots fed through a microstrip balun is proposed for microwave and millimeter-wave band imaging applications. The modified slot-loaded bow-tie pattern increases the electrical length of the bow-tie antenna reducing the lower band to 3.1 GHz. In addition, over the investigated frequency band up to 40 GHz, the proposed modified bow-tie pattern considerably flattens the input impedance response of the bow-tie resulting in a smooth impedance matching performance enhancing the reflection coefficient (S11) characteristics. The introduction of the modified ground plane printed underneath the bow-tie, on the other hand, yields to directional far-field radiation patterns with considerably enhanced gain performance. The S11 and E-plane/H-plane far-field radiation pattern measurements have been carried out and it is demonstrated that the fabricated bow-tie antenna operates across a measured frequency band of 3.1-40 GHz with an average broadband gain of 7.1 dBi.

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

Wideband metamaterial solar cell antenna for 5 GHZ Wi-Fi communication

In this paper, a novel design for a wideband integrated photovoltaic (PV) solar cell patch antenna for 5 GHz Wi-Fi communication is presented and discussed. The design consists of a slot loaded patch antenna with an array of complimentary split ring resonators (cSRR) etched in the ground plane. This is then integrated with a solar cell element placed above the patch, where the ground plane of the solar cell acts as a stacked antenna element from an RF perspective. The design is simulated on CST Microwave Studio and fabricated. The results indicate that an impedance bandwidth of 1 GHz is achieved to cover the 5 GHz Wi-Fi band with a gain of between 7.73 dBi and 8.18 dBi across this band. It is also demonstrated that size reduction of up to 25% can be achieved. Moreover, it is noted that using a metamaterial loaded ground plane acts as an impedance transformer, therefore the antenna can be fed directly with a 50 Ω microstrip feed line, hence further reducing the overall size.

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.

The development of indirect microwave holography for measurement and imaging applications

This work describes the development of indirect holographic techniques for microwave measurements and imaging. It outlines the basic theory of indirect holography and how it relates to optical holographic techniques. It starts with a description of the initial work using a single receiving antenna for the determination of antenna radiation patterns and the reconstruction of antenna aperture fields. This is followed by a description of how these techniques can be adapted for the imaging of passive objects. It also outlines the techniques for the imaging of objects using indirect holography. These techniques include simple back propagation for the reconstruction of objects in free space and inverse scattering techniques for objects in inhomogeneous media.

Microwave inverse scattering using scalar indirect holographic techniques

This paper describes the use of indirect microwave holographic together with inverse scattering techniques for the reconstruction of the dielectric properties of unknown objects. The use of indirect microwave holography enables the complex field scattered from the object under imaging to be recovered from intensity-only scalar microwave measurements and therefore removes the requirement of using expensive vector measurement equipment. This significantly reduces the cost of the imaging system and simplifies the hardware implementation. Following the successful implementation of indirect holography method for shape and position reconstruction, we have explored an algorithm which combines indirect holography method and CSI method to solve the phaseless data reconstruction problem. Results presented here indicate that the material properties of composite dielectric objects can be accurately reconstructed using scalar measurements from indirect holography.

A Novel Simplified Mathematical Model for Antennas used in Medical Imaging Applications

In this paper a new technique is proposed to model the current across a monopole antenna and thereby the radiation fields of the antenna can be calculated. Generally, the Method of Moments (MOM) technique is used for this purpose whereby the integral equations are discretised to find the fields of an antenna. The proposed model requires only the knowledge of three parameters (Initial Current I0, Damping coefficient a and the radial parameter τ) and hence considerably reduces the computational time and space as its results do not depend on the number of functions involved. The new technique is also developed to take account of the conductivity property of the surrounding medium. Hence this technique can be used in field prediction for antennas employed in medical imaging applications. Initial results obtained from the new technique show good correlation in comparison with the MOM technique.