ICTP School on Applicaons of Open Spectrum and White Spaces Technologies ICTP, Trieste-Miramare, 3 - 14 March 2014

Antenna Fundamentals

Prof. Ryszard Struzak • Beware of misprints! These materials are preliminary notes intended for my lectures only and may contain misprints. • Feedback is welcome: if you noce faults, or you have improvement suggesons, please let me know. • This work is licensed under the Creave Commons Aribuon License (hp://creavecommons.org/ licenbses/by/1.0) and may be used freely for individual study, research, and educaon in not- for-profit applicaons. Any other use requires the wrien author’s permission. • These materials and any part of them may not be published, copied to or issued from another Web server without the author's wrien permission. • If you cite these materials, please credit the author and ICTP. • Copyright © 2012 Ryszard Struzak.

(CC) R Struzak 2 • Objecve: • Topics for discussion: to refresh basic 1. Antenna funcons concepts related to the 2. Antenna matching antenna physics 3. Antenna polarizaon – needed to understand beer the operaon of 4. Antenna direcvity wireless (radio) links/ 5. Antenna arrays networks

(CC) R Struzak 3 Antennas for laptop applicaons

Linksys

Source: D. Liu et al.: Developing integrated antenna subsystems for laptop computers; IBM J. RES. & DEV. VOL. 47 NO. 2/3 MARCH/MAY 2003 p. 355-367 (CC) R Struzak 4

Antenna funcons

• Transformaon of a guided EM wave into an unguided wave Space wave freely propagang in space (or the opposite) – a me-funcon in 1-D space à a me-funcon in 3-D space – The specific form of the radiated wave is defined by the antenna structure and the environment

Guided wave

(CC) R Struzak 9 TEM - simplest EM wave

Linearly-polarized plane wave traveling in vacuum with the speed of light: (x, t) = A sin[ω(t - x/c) + ϕ]; ω = 2πF; c ~3.108m At large distances spherical wave-front ~ plane Java applet plane wave: hp://www.amanogawa.com/archive/wavesA.html

R. Struzak 10 Power Flow

• In free space, the radiated energy streams from the antenna in radial lines, i.e. the Poynng vector has only the radial component • A source that radiates uniformly in all direcons is an isotropic source (radiator, antenna). For such a source the radial component of the Poynng vector is independent of θ and ϕ.

(CC) R Struzak 11 Topics for discussion

1. Antenna funcons 2. Antenna matching 3. Antenna polarizaon 4. Antenna direcvity 5. Antenna arrays

(CC) R Struzak 12 Basic transmier/ receiver parts

• The transmission line • The juncon • The antenna radiator (size comparable with λ/2) • The EM wave

• Notes: – Possible power reflecons (impedance matching) – Possible resonaces (for broadband applicaons must be aenuated)

13 Transming antenna equivalent circuit

Antenna

Transmier Transm. line Radio wave

The transmier with the transmission line is represented by an (Thevenin) equivalent generator jX jXA G The antenna is represented by its input impedance (which is frequency-dependent and is influenced by objects nearby) as seem from RG the generator R r jXA represents energy stored in electric (Ee) and magnec (Em) near-field components; if | Ee| = |Em| then XA = 0 (antenna resonance) Generator Generator Can be approximated by the impedance of a transmission line

R Rr represents energy radiated into space (far- VG l field components) Rl represents energy lost, i.e. transformed into heat in the antenna structure

(CC) R Struzak 14 Power transfer

1 • The maximum power is delivered to (or from) the 0.5 antenna when the PA / PAmax antenna impedance and the impedance

0 of the equivalent 0.1 1 10 RA / RG; (XA+XG = 0) generator (or load) are matched

(CC) R Struzak 15 • When the antenna impedance is not matched to the transmier output impedance (or to the receiver input impedance) or to the transmission line between them, impedance-matching devices must be used for maximum power transfer • Inexpensive impedance-matching devices are usually narrow-band • Transmission lines oen have significant losses

(CC) R Struzak 16 • When the impedances are matched – Half of the source power is delivered to the load and half is dissipated within the (equivalent) generator (as heat)

– In the case of receiving antenna, a part (Pl) of the power captured is lost as heat in the antenna elements, the other part being re-radiated (scaered) back into space • Even when the antenna losses tend to zero, sll only half of the power captured is delivered to the load (in the case of conjugate matching), the other half being scaered back into space

(CC) R Struzak 17 Receiving antenna equivalent circuit

Antenna

Radio wave Transm.line Receiver

The antenna with the transmission line is represented by an (Thevenin) equivalent generator jXA The receiver is represented by its input impedance as seen from the antenna jXL terminals (i.e. transformed by the Rr transmission line)

V is the (induced by the incident wave) voltage at the antenna terminals A R Antenna R l L determined when the antenna is open circuited

V Note: The antenna impedance is the same when the A antenna is used to radiate and when it is used to receive energy

Thevenin equivalent

(CC) R Struzak 18 Radiaon efficiency

• The radiaon efficiency e indicates how efficiently the antenna uses the RF power • It is the rao of the power radiated by the antenna into the space and the total power delivered to the antenna terminals (in transming mode). In terms of equivalent circuit parameters: R e = r Rr + Rl

(CC) R Struzak 19 Topics for discussion

1. Antenna funcons 2. Antenna matching 3. Antenna polarizaon 4. Antenna direcvity 5. Antenna arrays

(CC) R Struzak 20 Antenna polarizaon

• The polarizaon of an antenna in a specific direcon is defined to be the polarizaon of the wave produced by the antenna at this direcon at a great distance • By convenon the "polarizaon" of an EM wave refers to the polarizaon (direcon) of oscillaons of the electric field vector. • The oscillaon may be in a single direcon (linear polarizaon), or the field may rotate (circular or ellipcal polarizaon).

(CC) R Struzak 21 Polarizaon filters/ reflectors

Wall of thin parallel wires (conductors)

|E |>0 1 |E | = 0 |E1|>0 2 |E2| ~ |E2|

Vector E || wires Vector E ⊥ wires

Wire distance ~ 0.1λ • At the surface of ideal conductor the tangenal electrical field component = 0

(CC) R Struzak 22 Polarizaon states

LHC (Poincaré sphere) UPPER HEMISPHERE: ELLIPTIC POLARIZATION LEFT_HANDED SENSE LATTITUDE: REPRESENTS AXIAL RATIO EQUATOR: LINEAR POLARIZATION

LOWER HEMISPHERE: 450 LINEAR ELLIPTIC POLARIZATION RIGHT_HANDED SENSE LONGITUDE: REPRESENTS TILT ANGLE RHC POLES REPRESENT CIRCULAR POLARIZATIONS

(CC) R Struzak 23 Topics for discussion

1. Antenna funcons 2. Antenna matching 3. Antenna polarizaon 4. Antenna direcvity 5. Antenna arrays

(CC) R Struzak 24 Point Source

• For many purposes, it is sufficient to know the direcon (angle) variaon of the power radiated by antenna at large distances. • For that purpose, any praccal antenna, regardless of its size and complexity, can be represented as a (distant) point-source. • The actual field near the antenna is then disregarded.

(CC) R Struzak 25 • The EM field at large distances from an antenna can be treated as originated at a point source - ficous volume-less emier. • The EM field in a homogenous unlimited medium at large distances from an antenna can be approximated by an uniform plane TEM wave

(CC) R Struzak 26 PFD: Isotropic Radiator Power Flux Density (PFD) P PFD = T r 4πr 2

• Loss-less propagaon medium assumed • Isotropic radiator cannot be physically realized • PFD does not depend on frequency/ wavelength

15 Feb 2001 Property of R. Struzak 27 PFD: Example 1

• What is the PFD from 1.8•102 •103 PFD = TV broadcast GEO 4•! •(38•106 )2 satellite at ICTP? 5 1.8•10 -2 • EIRP = 180 kW ! 16 ![Wm ] 1.8•10 (52.5 dB(W)) =1•10"11 [Wm-2 ] • Distance: ~38'000 km = "100 [dB(Wm"2 )] • Free space

15 Feb 2001 Property of R. Struzak 28 PFD: Example 2

• What is the PFD 1.8 from a hand-held PFD = 4•! •(3.8•10!2 )2 phone at the head? 1.8 " ![Wm-2 ] • EIRP = 1.8 W 1.8•10!2 3 -2 100•10 -2 =100 [Wm ] = [mWcm ] • Distance = ~3.8 cm 104 -2 • Free space =10![mWcm ]

15 Feb 2001 Property of R. Struzak 29 Short dipole antenna: summary

• Eθ & Hθ are maximal in the equatorial plane, zero along the antenna axis

• Er is maximal along the antenna axis dz, zero in the equatorial plane • All show axial symmetry • All are proporonal to the current moment Idz • Have 3 components that decrease with the distance- to-wavelength rao as – (r/λ)-2 & (r/λ)-3: near-field, or inducon field. The energy oscillates from enrely electric to enrely magnec and back, twice per cycle. Modeled as a resonant LC circuit or a transmission-line resonator; – (r/λ)-1: far-field or radiaon field – These 3 component are all equal at (r/λ) = 1/(2π) (CC) R Struzak 30 Field components

1000 C C, Q: Induction fields 100 Q

10 FF 1

FF 0.1 FF: Radiation field

Q Relative fieldstrength 0.01

C 0.001 0.1 1 10 Relative distance, Br

(CC) R Struzak 31 EM field intrinsic impedance

100 Field Short dipole impedance 10 Z = E/H depends 1 Z / 377 on the 0.1 antenna Small loop type and 0.01 0.01 0.1 1 10 100 on Distance / (lambda/ 2Pi) distance

(CC) R Struzak 32 Far-Field, Near-Field

• Near-field region: – Reacve field components dominate (L, C) – The resultant EM field highly non-uniform – Angular distribuon of energy depends on distance from the antenna; • Far-field region: – Radiang field component dominates (R) – The resultant EM field can locally be treated as uniform (TEM) – Angular distribuon of energy is independent on distance;

(CC) R Struzak 33 • For a 60 cm diameter satellite TV antenna operang at a frequency of 12GHz, (a wavelength of 25mm), R1 = 0.85m and R2 = 29m. Example A Solar Power Satellite beams RF energy from a geostaonary satellite down to a receiving site on the ground of 10 km diameter. • The power density in the beam exceeds that from isotropic antenna by the rao of the area of a sphere of radius equal to the antenna to spot distance to the area of the spot. This is the ‘Gain’ of the antenna system: = 4(r/ra)2. • With the satellite altude r = 35786 km, earth radius R = 6371 km and the rectenna radius ra = 5 km, the gain is ~2.84 million or 84dB. • This would require antenna about 5000 wavelengths across (600m at 2.4GHz), or in wavelength terms about the same as the human eyeball! Source: A. Marvin: Introducon to Electromagnec Fields and Waves (slides) Short antenna radiaon paern

(CC) R Struzak 36 Linear Antennas

• Summaon of all vector components E (or H) produced by each antenna element " ! ! ! E = E1 + E2 + E3 +... ! ! ! ! H = H1 + H 2 + H3 +... O • In the far-field region, the vector components are parallel to each other • Phase difference due to – Excitaon phase difference – Path distance difference • Method of moments - NEC

(CC) R Struzak 37 Reference Antennas

• Isotropic radiator

– isolated in space (Gi, absolute gain, or isotropic gain) • Half-wave dipole

– isolated in space, (Gd, gain relave to λ/2 dipole)

15 Feb 2001 Property of R. Struzak 38 Satellite antenna mask (example)

0 0dB Phi0/2 RR/1998 APS30 Fig.9

-10 Phi COPOLAR -3dB -20

-30 Relative gain (dB)

-40 CROSSPOLAR

-50 0.1 1 10 100 Phi/Phi0

Reference paern for co-polar and cross-polar components for satellite transming antennas in Regions 1 and 3 (Broadcasng ~12 GHz)

15 Feb 2001 Property of R. Struzak 39 Typical Gain and Beamwidth

Type of antenna Gi [dB] BeamW. Isotropic 0 3600x3600 Half-wave Dipole 2 3600x1200 Helix (10 turn) 14 350x350 Small dish 16 300x300 Large dish 45 10x10

(CC) R Struzak 40 Topics for discussion

1. Antenna funcons 2. Antenna matching 3. Antenna polarizaon 4. Antenna gain 5. Antenna arrays

(CC) R Struzak 41 Antenna arrays

• Mulple antennas collaborang’ to synthesize radiaon characteriscs not available with a single antenna, able – to match the radiaon paern to the desired coverage area – to change the radiaon paern electronically (scanning) through the control of the phase & amplitude of the signals in each element – to dynamically adapt to changing signal condions – to increase transmission capacity by beer use of the radio resources and reducing interference • Complex & costly – Intensive research related to military, space, etc. acvies » Smart antennas, signal-processing antennas, tracking antennas, phased arrays, MIMO anternnas, etc. • Passive & unintenonal antennas

Source: adapted from N Gregorieva (CC) R Struzak 42 Antenna Arrays: posibilies

• Possibilies to control electronically – Direcon of maximum radiaon – Direcons (posions) of nulls – Beam-width – Direcvity – Levels of sidelobes using standard antennas (or antenna collecons) independently of their radiaon paerns • Antenna elements can be distributed along straight lines, arcs, surfaces, squares, circles, etc.

(CC) R Struzak 43 Switched arrays

• Switched beam antennas – Based on switching funcon between separate direcve antennas or predefined beams of an array • Space Division Mulple Access (SDMA) = allocang an angle direcon sector to each user – In a TDMA system, two users will be allocated to the same me slot and the same carrier frequency – They will be differenated by different direcon angles

(CC) R Struzak 44 Phased Arrays

• Array of N antennas in a linear or two-dimensional configuraon + beam-forming & control device • The amplitude and phase excitaon of each individual antenna controlled electronically (“soware-defined”) – Diode phase shiers – Ferrite phase shiers • Inera-less beam-forming and scanning (µsec) with fixed physical structure

(CC) R Struzak 45 2 GHz adapve antenna

An array of 48 2.4 GHz antennas The Square Kilometre Array (SKA). Source: Arraycomm A radio telescope in development in Australia/New Zealand/Africa. Radius: 3000 km; Budget: €1.5 billion

(CC) R Struzak 46 Adapve (“Intelligent”)Antennas

• Array of N antennas in a linear 1 or spaal configuraon w1 • Used for receiving signals from desired sources and suppress incident signals from undesired Σ sources • The amplitude and phase excitaon of each individual antenna controlled wN electronically (“soware- N defined”) • The weight-determining algorithm uses a-priori and/ or Weight-determining measured informaon algorithm • The weight and summing circuits can operate at the RF or at an intermediate frequency

15 Feb 2001 Property of R. Struzak 47 2 omnidireconal antennas

1 1 1

0.5 0.5 0.5

0 0 0 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1

-0.5 -0.5 -0.5

-1 -1 -1 D = 0.5λ, θ= 00 D = 0.5λ, θ= 900 D = 0.5λ, θ= 1800

Run simulaon program: Array2ant_Demo1.xlsm

(CC) R Struzak 48 What we have learned

• Symmetrical role of transming and receiving antennas • Crical elements of transmission chain – Power matching between transmission-line and antenna – Polarizaon matching between antennas – Direcon matching of transming and receiving antennas – Unintenonal antennas Antenna simulators

• Polarizaon: – hp://www.amanogawa.com/archive/wavesA.html • Linear dipole antennas: – hp://www.amanogawa.com/archive/DipoleAnt/DipoleAnt-2.html – hp://www.amanogawa.com/archive/Antenna1/Antenna1-2.html • 2 antennas: – hp://www.amanogawa.com/archive/TwoDipole/Antenna2-2.html • Antenna design using MiniNEC – hp://www.sopedia.com/get/Science-CAD/Expert-MININEC- Classic.shtml

(CC) R Struzak 50

Thank you for your aenon

(CC) R Struzak 51