Scalar Holographic Artificial Impedance Surface

Ramsha BukhariReg # 140218060Scalar Holographic Artificial Impedance Surface

IntroductionA method for controlling electromagnetic surface wave propagation and radiations from complex metallic shapes.

An artificial impedance surface is implemented as sub-wavelength metallic patches on a grounded dielectric substrate.The effective impedance is pattern over the surface by varying the size of metallic patches.

Using holographic technique, a surface is designed to scatter a known input wave into a desired output wave.Problems AddressedTwo grey areas in the domain of antennas are

Integration of antennas on complex shaped structures. Radiating the regions otherwise shadowed.

ApplicationsElectrically controllable conformal antennas.High-impedance ground planes.Phase shifters for electronic beam steering. Leaky-wave antennas for efficient radiation beam steering. Reflector-type antennas for efficient radiation beam steering. Antenna arrays for suppressing the mutual coupling of antenna elements. Leaky Waves on Modulated Impedance surface Mathematical foundation for this work is Oliners comprehensive analysis of leaky waves on modulated impedance surface. He describes how the propagation and radiation of leaky waves are controlled by the magnitude, modulation depth and period of the surface impedance.Mathematical BasisI implemented Oliners impedance boundary conditions using an artificial impedance surface and extended the modulation concept using a 2D holographic patterning method.

Xs -value of surface reactance constant over all the surface. M-amplitude of modulation. a-phase of modulation.guided-wave are of two types, the surface waves who propagate along the direction parallel to the surface and decays exponentially with depth, while leaky surface waves are attenuated in the surface direction and radiate energy into space.When the modulation spacing a is small, the guided wave is a (trapped) surface wave; when this spacing exceeds a critical value, a leaky wave is created and radiation occur.

Holographic leaky wave antenna concept

Surface waves (undulating arrows) are excited on an artificial impedance surface, and are scattered by variations in the surface impedance to produce the desired radiation (straight arrows).

Microwave HolographyThe basic principle of optical holography was introduced by Dennis Gabor in 1948.Holo meaning whole or full and Graphe meaning writing.It is called so because the method works on the complete information of a wave i.e. phase and amplitude rather than just intensity values.

According to Gabor, holography was a two-step process.Writing involving the recording of complete information of a wave(phase and amplitude) on a photographic film.Reading the hologram done by illuminating the photographic film by the same reference wave that has been used in the writing.

The same principle of optical holography is implemented for microwave holography.

In Microwave holography a surface wave produced by a source antenna is the reference wave and the wave with desired radiation characteristics is the object.

And when the hologram (interference pattern) is illuminated by the same reference wave , we can retrieve the copy of original wave.

Scalar impedance pattern formed from holographic interference

light areas corresponding to high impedanceThe interference pattern produced by these two is replaced by scatters which scatter the reference wave to produce the desired radiation characteristics.

Holographic pattern implemented using square metallic patches

High impedance regions have small gaps (and are darker).

Summer Project PlanThe summer period will start on June 15, 2015.

Three main tasks areCoding and SimulationFabrication and MeasurementDissertation writing ,poster and presentation

Coding and SimulationSub tasks for coding and simulation are

Implementation of hologram in Matlab using C language.

Implementation of geometry in CST design studio.

Modification of the design of second part for a plane wave .

Modification of the design of second part for a monopole antenna.

Fabrication and Measurementsartificial impedance surface would be implemented using the hologram obtained in first phase and testing part would be performed at Communication Research group at the University of SheffieldGantt Chart

Risk Assessment

Milestones & DeliverablesMilestones

Deliverables

Interim report with all literature review and project plan.

CST model for artificial impedance surface with metallic patches on grounded dielectric substrate.

Presentation for the second marker.

Fabricated artificial impedance surface.

Matlab code for microwave holography.

Final dissertation and project poster.