Session 4: Diffraction Prof. Katsuyuki Haneda, Clemens Icheln Dept. - PowerPoint PPT Presentation

Aalto University School of Electrical Engineering ELEC-E4750 Radiowave Propagation and Scattering Session 4: Diffraction Prof. Katsuyuki Haneda, Clemens Icheln Dept. of Electronics and Nanoengineering 1 ELEC-E4750 03.10.2018

Course books, current topics and exercises  Course books  Main books used in this course:  S. Saunders, Antennas and Propagation for Wireless Communication Systems , Chapters 3, 5, 6-8, 10, 12 15, Wiley.  H. L. Bertoni, Radio propagation for modern wireless systems , Chapters 2-6, Prentice Hall.  A. F. Molisch, Wireless Communications , Chapters 1, 5 and 8, Wiley.  R. Vaughan and J. B. Andersen, Channels, propagation and antennas for mobile communications, Chapter 3.2.1, IEE Press.  Supplemental book (for prerequisites)  D. M. Pozar, Microwave Engineering, Chapters 1 and 14, Wiley.  Topic 3: Reflection, transmission and diffraction (Ch. 3, Ch. 5)  Exercise 1: Frequency dependency of reflection and transmission  Exercise 2: Diffraction due to an absorbing knife edge  Topic 4: Diffraction (Ch. 3, Ch. 5)  Exercise 1: Modeling human-body blockage  Exercise 2: Diffraction losses due to multiple screens  Exercise 3 (bonus): Diffraction due to building corner Aalto University School of Electrical 2 Engineering

Schedule Wk Date Location New topics, lectures and deadlines Mon. 10 Sep. R032/A116 seminar Introduction room 37 Wed. 12 Sep. R032/A113 simlab Lecture 1: prerequisite Mon. 17 Sep. R032/A116 Exercise return session 1 38 Wed. 19 Sep. R032/A113 Lecture 2: reflection and transmission Mon. 24 Sep. R032/A116 Exercise return session 2 39 Wed. 26 Sep. R032/A113 Lecture 3: reflection, transmission and diffraction Exercise return session 3 (a) Mon. 01 Oct. R032/A116 40 Lecture 4: diffraction (b) Wed. 03 Oct. R032/A113 Mon. 08 Oct. R032/A116 Exercise return session 4 41 Wed. 10 Oct. R032/A113 Lecture 5: scattering a: Pasi and Usman are present. Aalto University Aalto University b: Lecturer: Clemens Icheln School of Electrical School of Electrical 3 Engineering Engineering

Human Blockage Loss • An absorbing knife-edge diffraction model (with multiple edges) reproduces the measurement well Tx Seen from top: antenna Rx antenna Aalto University Aalto University School of Electrical School of Electrical 4 Engineering Engineering

Q1: Which statement is incorrect? A. Curve “a” fluctuates the most because of the shortest wavelength. B. Curve “c” is for the lowest frequency as the loss is smallest in LOS. C. Human blockage is more significant as the frequency is higher. D. With increasing frequency, absorption becomes more and more ✓ significant than scattering. Additional loss vs. free-space Link geometry at three different frequencies c b a Aalto University School of Electrical Engineering

Validation of human blockage loss model • Diffraction model AKE (absorbing rectangle with four knife edges) vs. measurements (with real human) RX TX f Azimuth orientation of human body blocking the link: y Tx Rx Aalto University Aalto University f School of Electrical School of Electrical 6 x Engineering Engineering

Multi-Screen Link Blockage • Examples: terrestrial links over several hills and cellular links over several rooftops. Aalto University Aalto University School of Electrical School of Electrical 7 Engineering Engineering

Divergence Factor • … describes how much the energy is spread after some propagation distance        2 A r sin d d R 1 = r 1 : Small R1 1 z area Δ A R        2 R 2 = r 2 : A r sin d d R2 2 2    Spherical wave A r   Divergence  R1 1 from a point θ    source (at origin) factor   A r R R2 2 O Power spectral density φ  A   R1 S S    y R R 2 R R 1 A x R2 2   P G P G r      tx tx 1 tx tx   Aalto University Aalto University   School of Electrical School of Electrical 2 2   r 4 r 4 r Engineering Engineering 2 1 2

Diffraction of Spherical Waves side view Point source d θ d φ r 0 θ top view ~sin( d  )·( r + r 0 ) ρ ~sin( d  )· r Δ A ρ r Δ A r Absorbing screen Aalto University Aalto University School of Electrical School of Electrical 9 Engineering Engineering

Q2: Which equations are         A. A r ( 0 r ) d d correct? Choose two!  0 ✓          B. answer. A ( 0 r ) d d  Point source      d   C. A r ( 0 r r ) d d θ ✓ d φ      d   D. ( 0 ) d A r r r r r 0 θ ρ Δ A ρ r Δ A r Absorbing screen Aalto University School of Electrical Engineering

Diffraction behind a screen • Diffracted field for ρ << r 0 Divergence factor:     j kr  j k A e e 0 r          j /4 0 E ( , ) e D ( )   D  A r r r r r 0 0 Point source  Diffracted field in general d θ d φ   j k ( r r ) e r 0 θ 0      j /4 ( , ) ( ) E r e D ρ D  r r ( r r ) Δ A ρ 0 0 r where 1 + cos q Δ A r Absorbing 1 D ( q ) = - diffraction coefficient for GTD 2sin q screen 2 p k solution of an absorbing screen (see slides of lecture #3) Aalto University Aalto University School of Electrical School of Electrical 11 Engineering Engineering

Diffraction behind a second screen side view Point source d φ d θ r 0 top view θ r 1 ρ Absorbing screen #1 Δ A ρ r Δ A r Absorbing screen #2 Aalto University Aalto University School of Electrical School of Electrical 12 Engineering Engineering

Q3: Which is the correct Divergence Factor valid behind the second diffraction from two half-plane absorbing screens?   A r   A. First choice is not a 1 Point source   A r r r d φ right answer. r 1  d θ     A ✓ r r r 0   0 1 B. Second choice is a    θ r 1 A r r r r right answer. r 0 1     A ρ r r r Absorbing   C. Third choice is not a 0 1 screen #1 Δ A ρ r      A r r r r r r right answer. Δ A r r 0 1 0 1 Absorbing screen #2 D. None of above. Aalto University School of Electrical Engineering

Diffraction behind a second screen • Diffracted field for ρ << r 1     j k ( r r ) j k e e 0 1           j /4 j /4 E ( , ) e D ( ) e D ( ) D 1  2  r r ( r r ) 0 1 0 1      A r r   • Divergence factor 0 1    A r r r r r 0 1  Diffracted field in general    j ( ) k r r r e 0 1       j /2 E ( r , ) e D ( ) D ( )   D 1 2 r r r ( r r r ) 0 1 0 1 Aalto University Aalto University School of Electrical School of Electrical 14 Engineering Engineering

Deygout Method for multiple knife edges Main edge  ˆ ˆ      E D ( ) D ( ) D ( )     1 2 3 4 ( d d d d ) 1 2 3 4 ෡ ෡ 𝐸 1 is the diffraction coefficient when Rx ( : Tx) is replaced by 𝐸 3 ෡ 𝐸 3 the main edge as a virtual secondary receiver ( : secondary source). Aalto University Aalto University School of Electrical School of Electrical 15 Engineering Engineering

Q4: Which statement is incorrect when calculating the pathloss for the illustrated hilly terrain using the Deygout method? A. The main edge is hill #2. B. The diffraction coefficient of hill #3 is calculated with a virtual source located at the tip of hill #2. C. The diffraction coefficient of hill #4 may be inaccurate when using the GTD. ✓ D. The diffraction coefficient of hill #4 is calculated using d 3 , d 4 and d 5 . Aalto University School of Electrical Engineering

Diffraction from a Right-Angle Wedge • … is applicable to determine field attenuation due to a building corner Diffraction coefficient from GTD for a Reflected wave wedge of perfect electric conductor shadow boundary 𝐸 𝜒, 𝜒 ′ = 𝐸 1 + 𝐸 2 + Υ 𝐹,𝐼 (𝐸 3 + 𝐸 4 ) Incident wave shadow 𝜒 cot 𝜌 ± (𝜒 − 𝜒 ′ ) boundary −1 𝐸 1,2 = 𝑃 3 Rx 3 2𝜌𝑙 Tx cot 𝜌 ± (𝜒 + 𝜒 ′ ) −1 𝜒 ′ 𝐸 3,4 = 3 3 2𝜌𝑙 Υ 𝐹 = −1 for perpendicular polarization Right-angle wedge Υ 𝐼 = 1 for parallel polarization Disclaimer: The formulas are from Section 5.3c of Bertoni’s book. However, prof. Haneda was not able to track exact derivations of these formulas after reading the books of Bertoni Aalto University Aalto University and McNamara. For now we therefore take these formulas as granted for the practical School of Electrical School of Electrical study of building-corner loss in exercise problem 5.3 (bonus exercise). Engineering Engineering