Slide 1 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Antenna Fundamentals & UWB Antenna...

Slide 1Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Antenna Fundamentals & UWB Antenna

M.Sc. Eng. Mohamed El-Hadidy

Duisburg-Essen Universität – Nachrichtentechniksystem

UWB weekly

Slide 2Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Contents

1 -General Introduction / Objective

2 -Directional Coupler Configurations

Delta Circuit Configuration

Discontinuities

Star Circuit Configuration

Potential Divider Configuration

3 -Comparison of Electromagnetic Properties

4 -Conclusion

5 -References

Antenna Fundamentals & UWB Antenna

Slide 3Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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The head containsThe eyes and the antennae grow from the head.

The Antenna

The Antennae

Slide 4Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Introduction

• UWB communication systems transmit pulses instead of modulated sine waves– Signal occupies a very broad BW (1Hz~2GHz)– Antenna can no longer be optimized at the carrier

frequency (no carrier in UWB!)– Frequency-independent antenna is needed

DSP

Slide 5Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Challenges in UWB Antenna Design

• EM aspects of UWB communication systems have not been studied adequately– Most of the conventional antenna analyses

assume harmonic time dependent (not the case in UWB)

– Time-domain EM analysis/simulation are needed• Issues in UWB antenna design

– Efficient pulse generation/reception– Pulse dispersion problem– Matching/Ringing problem

Slide 6Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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System Design Perspective

• UWB antenna is not likely to be a purely resistive load and may strongly influence the transmitter circuits– Antenna/circuit co-design is necessary

• Efficient pulse-shape design– Taking pulse-shape design into account adds one

more dimension to improve the performance of the antenna

Pulse Generator

BondingWire

TransmissionLine

Antenna

Slide 7Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Antenna Specifications

• Requirements of UWB antenna– 2-Dimensional– Omni-directional field pattern– Small size– Low cost

• Possible candidates– Dipole antenna– Loop antenna– Microstrip antenna– …

Slide 8Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Dipole Antenna

Feed point

• Consists of two straight wires

– Simple scheme, easy to analyze, mechanism is well-known

• Popular in narrow-band systems• “Humps” in frequency domain • Resistively loaded dipoles exhibit

very broad BW since reflection on the antenna is suppressed, but– Radiation efficiency is reduced– Termination is a problem

Slide 9Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Loop Antenna

• Circular turns of wire– To meet the 2D geometry spec

only 1 turn is used• Used for AM radio• Radiate normally/axially if the loop is

small/large relative to a wavelength • A modified version, Large Current

Radiator, is adopted by Aether Wire & Location, Inc., an UWB localizer company. Large radiation power can be delivered, but it’s shape is 3D

Input

Slide 10Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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• Metallic patches sit on a dielectric substrate• Usually made on PCB• Low profile, conformable to various surfaces,

inexpensive, durable, but narrow-band• Modify the shape to broaden the bandwidth, e.g.

bowtie antenna

Microstrip Antenna

Antenna Patch

Dielectric substrate

ground

Slide 11Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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• Things people care about– Directivity– Radiation efficiency– Radiation bandwidth– Polarization…

Antenna Parameters

Slide 12Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Antenna in Communication Systems

• At Receiver– E-field at the Rx is translated to a voltage source– By reciprocity theorem, Zant,rx=Zant,tx

• At Transmitter– Antenna is modeled as a passive circuit component;real part in it determines the radiated power (if s=¥)– Current distribution in the antenna determines Erad

Slide 13Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Traditional Antenna Design

• Designed for narrowband systems• Assume time-harmonic (steady-state sinusoidal)– Phasor is applied (d/dt=jw), Maxwell’s equations become more friendly.– Drive the antenna by cos(wt), radiate cos(wt+q1), and receive cos(wt+q2)– Matching is trivial à make it resonate

Slide 14Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Challenges in UWB Antenna Design

UWB means very broad bandwidth (DC~2GHz)• Phasor can no more be applied– Maxwell’s equations can’t be simplified• Waveform dispersion– Redefine directivity• Ultra-wideband matching– Ringing might happen– High radiation efficiency is hard to achieve• Flat frequency response

Slide 15Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Slide 16Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Slide 20Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Slide 21Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Slide 22Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Slide 23Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Slide 24Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Duisburg/UWB weekly14.12.2005

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Duisburg/UWB weekly14.12.2005

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Slide 27Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Duisburg/UWB weekly14.12.2005

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UWB Antenna Requirements

Slide 29Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Transmission Line Basics

Slide 30Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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VSWR

Slide 31Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Achieving Broader Bandwidths

For instance, it is well known that thickening a dipole leads to a broader bandwidth.

For example, an antenna with a ratio l/d =5000 has an acceptable bandwidth of about 3%, which is a small fraction of the center frequency.

An antenna of the same length but with a ratio l/d =260 has a bandwidth of about 30%. This would correspond to a bandwidth of approximately 2.0 GHz for a center frequency of 6.5 GHz, which is still not sufficient for the entire UWB bandwidth of 7.5 GHz.

Slide 32Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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There are also several known antenna topologies that are said to achieve broadband characteristics, such as the horn antenna, biconical antenna, helix antenna and bowtie antenna.

Achieving Broader Bandwidths

Slide 33Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Babinet’s Equivalence Principle

Z1Z2 = η2/4

This principle can be used to achieve impedance matching throughout frequency,

ZA = ZB= η/2

For all frequencies

Slide 34Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Rumsey’s Theory of frequency independent geometry

r=F(θ, φ)

r’ = KF(θ, φ)

KF(θ, φ) = F(θ, φ + C)

(dK/dC)F(θ,φ) = K∂F(θ,φ)/ ∂φ

1/K (dK/dC) = (1/r) ∂r/∂φ

The general solution for the surface r = F(θ,φ) of the antenna:

r = F(θ,φ) = eaφ f(θ) where a = 1/K (dK/dC)

Slide 35Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Equiangular Spiral Slot Patch Antenna

This spiral curve can be derived by letting f’(θ) = Aδ(π/2 – θ), where A is constant and δ is the three dimensional Dirac deltaFunction.

Letting θ = π/2, r = Aea(φ-φ0), where A= roe-aφ0. The representation of r in wavelengths,

rλ = Aea(φ-φ1), where φ1 = (lnλ)/a.

Slide 36Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Diamond Dipole Antenna

The diamond dipole antenna configuration follows from theory that thickening a dipoleincreases its impedance bandwidth.

Thickening a dipole spreads the energy throughout the dipole, therefore lowering its resonant Q value. Thin dipoles are analyzed theoretically under the assumption that all of the energy of the dipole is located within a few wire radii of the antenna.

Slide 37Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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If this assumption holds true (as it does for thin wire antennas), a TEM transmission line approximation can be applied to the analysis of these antennas.

However, this assumption breaks down as the antenna thickness is increased. Also, it becomes much harder theoretically to solve Maxwell’s equations for more complex shapes.

Simulation tools and empirical results attest to the claim that thickening a wire antenna increases its bandwidth.

Diamond Dipole Antenna

Slide 38Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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This theory mentioned that antennas in a loop configuration with sharp corners at the edges provide current nulls at the edges, which leads to lower standing wavelength ratios (SWR) at antiresonant frequencies.

This therefore leads to broader bandwidth.

Sharp Corners Theory

Slide 39Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Curved Solid Diamond Dipole

Curved Wire Diamond Dipole

Sharp-Edged Wire Diamond Dipole

Diamond Dipole Antenna

Slide 40Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Diamond Dipole Antenna VSWR

Slide 41Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Circular Disc Monopole Antenna

Slide 42Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Circular Disc Monopole Antenna

Slide 43Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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VSWR Characteristics

Slide 44Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Impulse Response

Slide 45Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Single Ended and Differential Elliptical Monopole Antennas (SEA and DEA)

Elliptical Monopole Antennas

Slide 46Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Adjustment for ellipticity is achieved by defining

L = 2*y radius (cm) & r = (x radius)/4 (cm).

Elliptical Monopole Antennas

Slide 47Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Elliptical Monopole Antennas

Slide 48Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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Commercial UWB Antennas

3.1—10 GHz Ultra-Wideband AntennaCommercial UWB Applications

FeaturesBased on Patent-pending Antenna ElementSmall and CompactDesigned for Low-cost Applications

Slide 49Mohamed El-Hadidy

Duisburg/UWB weekly14.12.2005

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