2. Slide 1 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Antenna Fundamentals & UWB Antenna M.Sc. Eng. Mohamed El-Hadidy Duisburg-Essen Universität – Nachrichtentechniksystem UWB weekly

3. Slide 2 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

4. Slide 3 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 The head contains The eyes and the antennae grow from the head. The Antenna The Antennae

5. Slide 4 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

6. Slide 5 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

7. Slide 6 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

8. Slide 7 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Antenna Specifications Requirements of UWB antenna –2-Dimensional –Omni-directional field pattern –Small size –Low cost Possible candidates –Dipole antenna –Loop antenna –Microstrip antenna –…–…

9. Slide 8 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

10. Slide 9 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

11. Slide 10 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

12. Slide 11 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Things people care about – Directivity – Radiation efficiency – Radiation bandwidth – Polarization … Antenna Parameters

13. Slide 12 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

14. Slide 13 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

15. Slide 14 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

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29. Slide 28 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 UWB Antenna Requirements

30. Slide 29 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Transmission Line Basics

31. Slide 30 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 VSWR

32. Slide 31 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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.

33. Slide 32 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

34. Slide 33 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

35. Slide 34 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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)

36. Slide 35 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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.

37. Slide 36 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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.

38. Slide 37 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

39. Slide 38 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

40. Slide 39 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Curved Solid Diamond Dipole Curved Wire Diamond Dipole Sharp-Edged Wire Diamond Dipole Diamond Dipole Antenna

41. Slide 40 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Diamond Dipole Antenna VSWR

42. Slide 41 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Circular Disc Monopole Antenna

43. Slide 42 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Circular Disc Monopole Antenna

44. Slide 43 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 VSWR Characteristics

45. Slide 44 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Impulse Response

46. Slide 45 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Single Ended and Differential Elliptical Monopole Antennas (SEA and DEA) Elliptical Monopole Antennas

47. Slide 46 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Adjustment for ellipticity is achieved by defining L = 2*y radius (cm) & r = (x radius)/4 (cm). Elliptical Monopole Antennas

48. Slide 47 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 Elliptical Monopole Antennas

49. Slide 48 Mohamed El-Hadidy Duisburg/UWB weekly 14.12.2005 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

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