Slide 1 Mohamed El-Hadidy Duisburg/UWB weekly Antenna Fundamentals & UWB Antenna M.Sc. Eng. Mohamed El-Hadidy Duisburg-Essen Universität – Nachrichtentechniksystem UWB weekly

Slide 2 Mohamed El-Hadidy Duisburg/UWB weekly 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 3 Mohamed El-Hadidy Duisburg/UWB weekly The head contains The eyes and the antennae grow from the head. The Antenna The Antennae

Slide 4 Mohamed El-Hadidy Duisburg/UWB weekly 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 5 Mohamed El-Hadidy Duisburg/UWB weekly 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 6 Mohamed El-Hadidy Duisburg/UWB weekly 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 Bonding Wire Transmission Line Antenna

Slide 7 Mohamed El-Hadidy Duisburg/UWB weekly 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 8 Mohamed El-Hadidy Duisburg/UWB weekly 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 9 Mohamed El-Hadidy Duisburg/UWB weekly 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 10 Mohamed El-Hadidy Duisburg/UWB weekly 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 11 Mohamed El-Hadidy Duisburg/UWB weekly Things people care about – Directivity – Radiation efficiency – Radiation bandwidth – Polarization … Antenna Parameters

Slide 12 Mohamed El-Hadidy Duisburg/UWB weekly 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 13 Mohamed El-Hadidy Duisburg/UWB weekly 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 14 Mohamed El-Hadidy Duisburg/UWB weekly 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 15 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 16 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 17 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 18 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 19 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 20 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 21 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 22 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 23 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 24 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 25 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 26 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 27 Mohamed El-Hadidy Duisburg/UWB weekly

Slide 28 Mohamed El-Hadidy Duisburg/UWB weekly UWB Antenna Requirements

Slide 29 Mohamed El-Hadidy Duisburg/UWB weekly Transmission Line Basics

Slide 30 Mohamed El-Hadidy Duisburg/UWB weekly VSWR

Slide 31 Mohamed El-Hadidy Duisburg/UWB weekly 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 32 Mohamed El-Hadidy Duisburg/UWB weekly 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 33 Mohamed El-Hadidy Duisburg/UWB weekly Babinet’s Equivalence Principle Z 1 Z 2 = η 2 /4 This principle can be used to achieve impedance matching throughout frequency, Z A = Z B = η/2 For all frequencies

Slide 34 Mohamed El-Hadidy Duisburg/UWB weekly 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) = e aφ f(θ) where a = 1/K (dK/dC)

Slide 35 Mohamed El-Hadidy Duisburg/UWB weekly 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 delta Function. Letting θ = π/2, r = Ae a(φ-φ0), where A= r o e -aφ0. The representation of r in wavelengths, r λ = Ae a(φ-φ1), where φ1 = (lnλ)/a.

Slide 36 Mohamed El-Hadidy Duisburg/UWB weekly Diamond Dipole Antenna The diamond dipole antenna configuration follows from theory that thickening a dipole increases 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 37 Mohamed El-Hadidy Duisburg/UWB weekly 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 38 Mohamed El-Hadidy Duisburg/UWB weekly 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 39 Mohamed El-Hadidy Duisburg/UWB weekly Curved Solid Diamond Dipole Curved Wire Diamond Dipole Sharp-Edged Wire Diamond Dipole Diamond Dipole Antenna

Slide 40 Mohamed El-Hadidy Duisburg/UWB weekly Diamond Dipole Antenna VSWR

Slide 41 Mohamed El-Hadidy Duisburg/UWB weekly Circular Disc Monopole Antenna

Slide 42 Mohamed El-Hadidy Duisburg/UWB weekly Circular Disc Monopole Antenna

Slide 43 Mohamed El-Hadidy Duisburg/UWB weekly VSWR Characteristics

Slide 44 Mohamed El-Hadidy Duisburg/UWB weekly Impulse Response

Slide 45 Mohamed El-Hadidy Duisburg/UWB weekly Single Ended and Differential Elliptical Monopole Antennas (SEA and DEA) Elliptical Monopole Antennas

Slide 46 Mohamed El-Hadidy Duisburg/UWB weekly Adjustment for ellipticity is achieved by defining L = 2*y radius (cm) & r = (x radius)/4 (cm). Elliptical Monopole Antennas

Slide 47 Mohamed El-Hadidy Duisburg/UWB weekly Elliptical Monopole Antennas

Slide 48 Mohamed El-Hadidy Duisburg/UWB weekly Commercial UWB Antennas 3.1—10 GHz Ultra-Wideband Antenna Commercial UWB Applications Features Based on Patent-pending Antenna Element Small and Compact Designed for Low-cost Applications

Slide 49 Mohamed El-Hadidy Duisburg/UWB weekly