antennas smart techniques

antennas

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Ericsson Internal | 2011-02-03 |

WHAT IS AN ANTENNA?

› Antennas are metallic structures designed for radiating or receiving electromagnetic/radio waves.

› It is just a passive conductor carrying RF current. It does not amplify RF energy.


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How an Antenna Radiates?

› All Charged particles produce an Electric field E

› Moving charged particles produce a changing electric field

› Changing electric field gives rise to magnetic field

› Hence, when a sinusoidal voltage is applied across the transmission line, Electric and Magnetic fields are created.


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› Due to the time varying electric and magnetic fields, electromagnetic waves are created and these travel between the conductors

› Inside the transmission line and the antenna, the electromagnetic waves are sustained due to the charges, but as soon as they enter the free space, they form closed loops and are radiated

Contd..


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TX RX

Width of banddenotes current

magnitude

Zero currentat each end

Maximum currentat the middle

Current induced inreceiving antennais vector sum of

contribution of everytiny “slice” of

radiating antenna

each tiny imaginary “slice”of the antennadoes its share

of radiating

Contd..

ANTENNA PERFORMANCE PARAMETERS


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Plot of signal strength radiated in each direction of an antenna.

The radiation pattern shows the strength of the antenna’s radiated field as a function of direction.

Main Lobe: The direction of maximum radiation.

Back Lobe: This is the minor lobe diametrically opposite the main lobe.

Side Lobes: These are the minor lobes adjacent to the main lobe

RADIATION PATTERN


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It is the angle between the half-power points ( 3DB Points) of the main lobe.

The 3DB Points are where the radiated power has reached half the amplitude of the main radiation direction.

The narrower the beamwidth the better is the concentration of the radiation.

beamwidth


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Antenna gain & directivity

ANTENNA GAIN: The Ratio of maximum radiation

intensity in a given direction to the maximum radiation intensity from a reference antenna in same direction with same power input.

Expressed in dBi

DIRECTIVITY: It is the ability of an antenna to

focus energy in a particular direction when transmitting, or to receive energy better from a particular direction when receiving.


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polarization

› Describes the orientation of the electric field vector.

› Maximum energy transfer between Tx and Rx antennas takes place when the antennas have the same polarization

› Mobile communications: vertical polarization

› Broadcast systems: horizontal polarization


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Effective Radiated Power (ERP and EIRP)

› It is defined as the apparent power in a particular direction.

› ERP is equal to actual transmitter power times antenna gain in that direction.

› ERP is expressed in comparison to a standard radiator

› ERP: compared with dipole antenna

› EIRP: compared with isotropic antenna


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FRONT TO BACK RATIO

› This is the ratio of the maximum directivity of an antenna to its directivity in the opposite direction. This is the ratio of the maximum directivity of an antenna to its directivity in the opposite direction.

› Front/Back = 10 log(FP/BP)

› Typically 18 to 30dB, the larger the better

Generic Categories of RF antennas…


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antenna types


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Omni directional

› Most common wireless LAN antenna is a dipole

› Radiates equally in all directions

› Omni-directional antennas are typically used in point-to-multipoint environments.


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Semi-directional

› Transmits energy significantly in one particular direction.

› Radiates in a hemispherical or cylindrical coverage pattern

› Low Gain, ranging between 7-15dBi

› Ideally suited for short and medium-range bridging

› Frequently used types:– Patch & Panel– flat, designed

for wall mounting– Yagi – elongated, ribbed, and

Common vertical & horizontal beamwidths of 90° or less


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Highly-directional

› High-gain antennas, typically concave, disk-shaped devices.

› Used for long distance, point-to-point wireless links

› High Gain, ranging between 18 to 28 dBi

› Have a very narrow beamwidth and must be accurately aimed at each other.

› Can transmit at distances up to 58 km

› Frequently used types: Parabolic dish and grid antennas

Antenna tuning


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Antenna Downtilt

Downtilt is used for

› Reducing interference• Reduce radiation toward a distant

co-channel cell

• Concentrate radiation within the serving cell

› Prevent overshoot


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Types of Antenna downtilt

Mainly of two types

› Mechanical Downtilt• Physically tilt the antenna

• front pattern goes down and behind goes up

› Electrical Downtilt• Phase shift to the elements is

applied in the feed network

• Pattern droops all around like an inverted saucer


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Reconfigurable beam antennas

[Tilting] [Tilting + Panning] [Tilting + Panning + Fanning]

Remote Electrical tilt

Remote Antenna Azimuth

Remote Antenna Beamwidth


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RET Framing

› Basic elements of RET system: controller and actuator

› RET devices connected to the controller using control cables.

› Daisy chaining or junction boxes used to join multiple actuators.

› Portable or rack mount controller used for managing RET devices.


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Ret system with bias tee

› AISG signals can be injected into existing RF cable

› Two options can be used at the top

• Use a second bias Tee at the top

• Use an AISG TMA


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RRH(remote radio head) aKa rru

› Transmit and receive electronics moved close to the antenna(s) in each sector

› Same as TRDU› RRH installed with minimal RF cabling


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Advantages of rrh

› For lowering capital and operating expenditure› Require little or no site footprint› Minimize feeder cable losses and thus improve the overall

base station power consumption.› Limited site space availability prevent the installation of

traditional BTS› Require fiber optic cables for transmit and receive signals


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Active antenna


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healing – active antenna


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Rrh --> active antenna

Smart antennas


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Analogy to smart antennas

› Close your eyes and converse with someone as they move about the room

› You hear the speaker's signals through your two ears, your acoustic sensors

› The voice arrives at each ear at a different time › Your brain, a specialized signal processor, does a large number of

calculations to correlate information and compute the location of the speaker

› Your brain also adds the strength of the signals from each ear together, so you perceive sound in one chosen direction as being twice as loud as everything else

Antennas are not smart….. Antenna systems are smart


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Smart antennas

› Smart Antenna system combines multiple antenna elements› Have signal processing capability› Automatically respond to the signal environment› Antenna array most often installed at a base station› Associated terms: intelligent antennas, phased array, SDMA, spatial

processing, digital beamforming, adaptive antenna systems.› SFIR uses beam directivity from Smart antennas to reduce interfernce


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Categories of smart antennas

› Switched beam : a finite number of fixed, predefined patterns or combining strategies

› adaptive array : an infinite number of patterns (scenario-based) that are adjusted in real time


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advantages

› Insures better range/coverage› Minimize interference› provides multipath rejection› Can easily meet the increased capacity

requirements› maximize intended signal reception


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Antenna naming conventions-EMS

RR65-17-00DP.DPARR33-20-00DPL4.DPA

Type

R = OptiRangeTM

F = OptiFillTM

D = Double Antenna

Polarization

V = Vertical

R = DualPol® Slant +/- 45°

S = DualPol® Simplex

TX – Verticle

RX – Dual Slant

Q = Quad

Horizontal Beamwidth

GainElectrical Downtilt

00 – 2 °

02 – 2 °

04 – 4 °

06 – 6 °

Connector Type

N = Type N Female

D = 7/16 DIN Female


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andrew

Thank you!!

antennas smart techniques

Technology

ericsson internal

reference antenna

isotropic antenna

direction of maximum

main radiation direction

directivity antenna

particular direction

dipole antenna eirp