Matched antenna for near-field, pulsed radar

Focused and matched antenna for pulsed radar in different matter


The use of radar technology as sensors has emerged lately because miniaturized radar solutions operational at short range have become available. The sensing capability of radar is based on backscattering (reflection) of radiowaves (RF) from object, a phenomena happening with radiowaves are travelling in air/vacuum and hit some surface with different dielectric properties. New technology has enabled small and accurate radar systems suitable for short-range operation. Such miniaturization opens for new and interesting applications of radar exploring RF penetration abilities for inspecting solid or opaque objects. However, penetration of heavy materials is prevented due to reflections (scattering) from the air/material dielectric differences. In order to avoid such reflections, dedicated antennas matched for the material to expose are required. Then air/material reflections are removed and RF energy is released into the material provided minimal air is present in the signal path (coupled antenna).

The Iris research Institute in Stavanger (http://www.iris.no/home) is exploring radar inspection of sandstone to determine salt-water saturation. Even detection of water-front in the porous stone during the saturation process is interesting as well as saturation profile. The M.Sc. project will model, design a directional antenna matched for sandstone water saturation using microwave RF signals. Both conductance as well as permittivity may provide indications. A suitable antenna will be fabricated either in aluminum or on a 3D printer coated with conductive paint. The measurements will be analyzed with researchers from the IRIS institute.

Background

Traditional radar is made for far-field usage. Obstacles are visible from boats and aircrafts and required resolution is in the order of meters. As ultra wideband (UWB) radio transmission for microwaves (2000/2002) new generation of radar sensing technologies has emerged. One of them came from IFI and is now commercially available from Novelda AS. Unlike traditional radar, these systems are small and suited for short-range sensing and imaging. In order to detect object, these reflection are desirable and useful. However, radiowaves also have interesting penetration properties. We know even weak GPS signals in mobile devices are detectable even inside concrete buildings. However, some materials like metals are highly conductive and absorb radiated energy converting it to currents. Other materials like concrete and stone may also be good RF shields. Normally the relative dielectric constant is used as describing RF properties of materials (vacuum=1). Provided the observed material does not have too high relative dielectric constant, ensuring proper coupling using matched antennas, surface reflections are removed and significant energy is penetrating the material. In general, antennas close to the material (< quarter wavelength) provide coupling, but such RF radiators tend to have wide beams giving wide exposure and minimal gain. Focused antenna are “growing” in depth and are often called horn antennas. The exposing material must be “extended” into the horn (hard to do with a stone or the human body). However, suitable foam may be used ensuring proper antenna match. Such antennas are rarely found in the literature and are a good topic for a M.SC. project with significant potential for good science (publishable).

The project will be carried out in the MilliLab facilities at IFI in collaboration with antenna manufacturing at the ROBIN group. The “users” at IRIS will be involved in antenna assessment. The project is suitable for students with background in electromagnetics and with interest in real world used involving modeling and measurements with advanced RF equipment.

Workplan

periode

task

Results

Month 1-3

Study for literature and understand requirements for matched antenna. Learn to use instruments in MilliLab.

Potential antenna shapes and sizes.

Months 3-6

Modeling and simulation of antennas in 3D EM tools.

Written report/ essay

Months 7-9

Detailed model for 3D fabrication

First fabricated antenna

Months 10-12

Assessment and characterization of fabb-ed antenna(s). Comparison with models

Priliminary results

Months 13-16

Redesign and fab of “best” antenna based on previous assessment

Measured results

Months 17-18

Final writeup

M.Sc. thesis/publication

 

Veiledere:

Tor Sverre Lande, IFI

Kristian Kjelgård, IFI

Mats Høvin, IFI

Publisert 11. nov. 2014 09:51

Omfang (studiepoeng)

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