Antenna Basics: An Introduction to Key Concepts and Parameters

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Antenna Basics
MD MUSTAFIZUR RAHMAN
RNPO Engineer
LinkedIn: Mustafizur

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Antenna Basic
• Introduction
• Antenna Parameters
• Polarization
• Polarization Loss & Isolation
• Antenna Types
• Antenna Gain
• Radiation Pattern
• Antenna Tilt
• Working Frequency of the Antenna
• The input impedance of antennas
• Reflection Loss and VSWR
• PIM/IM
• Antenna Spectification
• Split Antenna
• Different Antenna Types
• Tilt vs Cell Redius
• Clutter Wise Antenna Selection
Accessories
Feeder Cable
Grounding Kit
Jumper
Lightning
Protection
Jumper
RF Antenna
TMA/TMB
Md Mustafizur Rahman, Grameenphone Ltd

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What is an antenna?
At its most basic level, an antenna is the portion of a radio system that can:
1. Take radio energy from a transmission line and radiate it into space in a predictable pattern, and
2. Receive radio energy from open space and feed it back down the transmission line.
Antennas are surprisingly efficient in this line-to-space and space-to-line energy conversion process. In fact, when
properly configured with the right components, antennas can yield 80 percent efficiency or greater – a remarkably high
figure in engineering terms. By way of comparison, consider the common incandescent light bulb, which yields only
20% efficiency – this means that, of the amount of energy put into a bulb as electricity, only 20% of that energy is put
out as light. An important consideration to maintain an antenna’s extraordinary efficiency lies in the transmission cable
that connects it to the transmitter.
What does antenna DO?
It converts the energy of one medium into the energy of a free-space medium (or vice versa) as efficiently
as possible, while in the same time the radiated power has a certain desired pattern of distribution in space.
An antenna is the converter between two kinds of electromagnetic waves :
cable bounded waves ⇔ free space waves
Basics of Antenna: Introduction

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How does antenna radiate energy?
Antenna principle shown by bending a coax cable open
• the pulsing electrical field, created by the transmitter‘s high
frequency power, cannot leave the cable
• the field lines become longer and are orthogonal to the
wires
• the field lines have reached the maximum length and allow
a wave to free itself from the cable
• ⇒ basic radiating element : λ/2 dipole

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Electrical and magnetic field on a dipole
• maximum voltage is between the ends of the dipole
• the electrical field lines occur between these two charge
Centers
• the current on the dipole causes a magnetical field with an
opposite amplitude distribution (max. at the feeding point,
min. at the dipole ends
Wave propagation :
• Permanent conversion from electrical into magnetical energy
and vice versa

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Antenna parameters
• Gain
• Vertical opening angle
• Horizontal opening angle
• Front to Back ratio
• Tilt
• Upper side lobe suppression
• Null fill
• Polarization
• CPR(Cross Polar Ratio)
• VSWR/Return Loss
Basics of Antenna: Antenna Parameters

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Polarization of radio waves
The direction of the electric field of radio waves is defined as the
direction of polarization.
If this electrical field is perpendicular to the ground, the radio wave is defined as
vertical polarized.
If this electrical field is parallel to the ground, the radio wave is said to be
horizontal polarized.
Vertical polarized Horizontal polarized
Basics of Antenna: Polarization

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Polarization loss and isolation
To receive the greatest possible energy, transmitting and receiving antennas must be of the same
polarization, namely, V-polarized waves must be received by V-polarized receiver antennas, and the
same goes for other types. If the polarization direction of the radio wave is different from that of the
receiver antenna, polarization loss results.
Isolation is defined as the proportion of the signal fed to one polarization to that appearing in
another polarization.
Basics of Antenna: Polarization Loss & Isolation

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(1)Isotropic Antenna
It is just a point radiation source which radiates uniform energy in all 3 dimension.
Unfortunately, an isotropic antenna cannot be made in the real world, but it is useful for comparison with other practical antennas.
Basics of Antenna: Antenna Types
A dipole is the smallest, least gain practical antenna that can be made.
(2)Dipole antenna
1/2
matelinje

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Formation of Dipole Antenna
A conducting line radiates radio waves when AC circuit flows through it. The efficiency of the radiation depends on the length and the
shape of the conducting line. If two conducting lines are closely positioned, the induced electromotive forces will be neutralized, hence
radiation little energy. If the two lines are positioned apart with the currents in the same direction, the induced electromotive forces will
strengthen each other, hence radiating more energy. When the length of the conductor is far less than the wavelength and the current is
small, the resulting radiation will be very weak.
Radiators with two arms of the same size are called dipoles. The length of each arm is a quarter of the wavelength. Dipoles with their
length equal to the wavelength is called full-wavelength dipoles. When the hands of the antenna are folded then it is called folded dipole as
it is shown below:

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(3)Omni directional Antenna:
This antenna radiates energy in all 360 degree direction of horizontal plane but limited radiation in vertical
plane (like a pancake)

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Formation of Omni Directional Antenna from Dipole radiation
A single element creates the pattern like a bread ring
In order to direct the signal to the receivers close to the surface of the earth, the bread ring can be pressed flat. An array
of symmetrical dipole elements radiates energy like a “flat bread ring”:
Basics of GSM Antenna : Antenna Types

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(4)Directional antenna
This types of antenna radiate energy in certain direction controlling radiation both in horizontal plane and vertical plane(just like a
balloon)
Basics of Antenna : Antenna Types

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Formation of Directional Antenna or Panel antennas
Consists of dipoles placed in front of a reflector wall (grounded metal reflector).
Many different radiation patterns can be achieved by variation of the distance between the dipoles to the reflector and number of dipoles in width and
height. Mostly used in mobile communication as sector coverage antenna.
Basics of Antenna : Antenna Types
More
Reflecting boards are intended to focus the radiated energy in a certain
direction. An antenna with a reflecting board on one side of the element
array is defined as a sector coverage antenna or panel antenna. In such an
antenna, the reflecting board focuses the energy in one direction, hence
enhancing the gain. In this case, the gain of a sector antenna is greater
than an omni-directional antenna by 9dBd.
10log(8mW/1mW)=9dBd

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Antenna Gain
Basics of Antenna: Antenna Gain
Gain is defined as the ratio of the square of the point in space effected by a certain antenna and that effected by an ideal radiating unit. Gain
generally has to do with the radiation pattern of the antenna, namely, the narrower the main beam and the smaller the back beam and side beam,
the higher the gain.
In general, the narrower the beam-width, the higher the gain
and the more directive is the antenna.

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Radiation Pattern
Radiation Pattern gives us a pictorial shape of how the energy radiation of an antenna looks like in the free space
The radiation pattern (RP) (or antenna pattern) is the representation of the radiation properties of the antenna as a function of space coordinates. The trace of the spatial
variation of the received/radiated power at a constant radius from the antenna is called the power pattern.
The trace of the spatial variation of the electric (magnetic) field at a constant radius from the antenna is called the amplitude field pattern.
Usually, the pattern describes the normalized field (power) values with respect to the maximum value.
Note: The power pattern and the amplitude field pattern are the same when computed and plotted in dB.
Basics of Antenna: Radiation Pattern
Horizontal Beam (top view) Vertical Radiation Pattern (side view)
In radiation patterns, there are two or more beams/lobes. The biggest of these beams/lobes is called the main beam/lobe, the rest, side beam/lobe. Antenna gain is defined
along the main beam/lobe.

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Half power/effective angel: The angel where the
gain has dropped 3 dB from maxima
Opening angle: The angle between the first
minima
Opening angle and Half Power/effective angle
The angle between the two half-power points of the main beam is defined as the beam width, or half-power angle. The
narrower the beam width, the better the directionality and the resistance to interference.

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Beam width and Gain
Horizontal Pattern
Vertical Pattern

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Side beam and Null
Upper Side Lobe Suppression and Null Fill: Suppressing the upper side lobe, redirecting the power to
lower side in order to fill the first lower null is known as null fill.
Upper and Lower NULL

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Front to back ratio
Front-to-back ratio is the ratio of the maximum power of the front beam to that of the back beam. The higher the
front-to-back ratio,the better the performance of the antenna in directional reception.
The front-to-back ratio of an omni-directional antenna is 1, receiving signals from all direction with the same
sensitivity.
The front-to-back ratio is an important specification in directional antennas.
(B is short for back; F for front)
The typical value of front-to-back ratio of a sector antenna
=10log(front power/back power)
=25dB,
so that the back radiated power is minimum. Md Mustafizur Rahman, Grameenphone Ltd

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Some concepts related to the pattern terminology
a) Isotropic pattern is the pattern of an antenna having equal radiation in all directions. This is an ideal
(not physically achievable) concept. However, it is used to define other antenna parameters. It is
represented simply by a sphere whose center coincides with the location of the isotropic radiator.
b) Omni directional antenna is an antenna, which has a non-directional pattern in a given plane, and a
directional pattern in any orthogonal plane (e.g. single-wire antennas). Normal dipole antenna creates omni
directional radiation.
c) Directional antenna is an antenna, which radiates (receives) much more efficiently in some directions
than in others. Usually, this term is applied to antennas whose directivity is much higher than that of a half
wavelength dipole. Here dipole with reflector is used create directivity.

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dB
-3
0
dB
-3
0
dB
-3
0
3dB
-3dB BW
Azimuth (or Horizontal) beam width sets the “footprint” of the antenna coverage
Basics of Antenna: Gain / Beam Width / Efficiency

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Peak: 0dB point
3dB
-3dB BW
-10dB BW
10dB
-10dB
point
3 dB BW just one way to describe antenna’s ability to focus

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12dBi 16dBi 18dBi 21dBi
If HBW keep unchanged(eg. 65 ), the antenna gain improved only by changing
VBW. The smaller the VBW, The higher the gain. the VBW is wider, the gain is
lower.
Major trade-off is between vertical beam width and gain

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Basics of Antenna: Antenna Tilt
Vertical Downtilt
The down-tilt design is intended for the beam to tilt toward the ground
• As a standard the vertical beam is pointing to the horizon
• Downtilting of the pattern provides the following benefits :
- the majority of the radiated power is concentrated within the sector
- the reduction of the power towards the horizon avoids interference problems with the next sector
• Good results when fieldstrength in the horizon is reduced by about 6 dB

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Mechanical and Electrical Tilt
The down-tilt design is intended for the beam to tilt toward the ground

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Mechanical Tilt
• A mechanical downtilt kit increases the upper distance to the mast and
makes the antenna pointing down
• The requested downtilt angle is achieved only in main direction
• At +/- 90° from the main direction the downtilt angle is always zero (rotation
axis)
• Effective downtilt varies across the azimuth
• Effect on the horizontal pattern at the horizon :
• Reduction of the fieldstrength in main direction without any change +/-
90° to it results in deformation of the horizontal pattern
• this effect of changing half power beam width can hardly be considered
in the network planning and reduces the prediction accuracy

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Electrical Tilt
• More elegant is the electrical downtilt with the antenna remaining upright;
instead of equal phases on the dipoles, particular phase distributions are
selected by varying the cable lengths to the dipoles
• The fixed phase distribution applies to all azimuth directions
⇒ electrical downtilt angle is constant
• The shape of the horizontal pattern remains constant
• Accurate network planning is assured

Basics of Antenna:Antenna Tilt

Basics of Antenna: Diversity / Principle
• Unsymmetrical situation of downlink and uplink :
✓ uplink (mobile) : limited power, small antenna
✓ downlink (BTS) : high power, high antenna gain
• Consequence : Diversity
• The diversity concept bases on the idea to have two independent signals available at the base station (two Rx antennas)
• Considering both signals results in avoiding nulls and improving the average signal level (diversity gain)

Basics of Antenna: Working Frequency of the Antenna
Working Frequency of the Antenna (bandwidth)
Antennas, receiving or transmitting, work within a certain range of frequencies (or within
a certain bandwidth).
To bandwidth, different definitions are given below:
Def.1 Bandwidth refers to the bandwidth when the gain of the
antenna drops by 3 dBi;
Def.2 Bandwidth refers to the working bandwidth of the antenna when the VSWR is
decided.
In mobile communication, Def.2 is adopted, namely, bandwidth refers to the working
bandwidth when VSWR≤1.5.
If the input/received working wavelength is different from the designed value, the
performance of the antenna suffers. In some cases, the input or received frequency is a
little mismatching, the antenna works somehow acceptably.

Basics of Antenna: The input impedance of antennas
The input impedance of antennas
The ratio of the induced signal voltage to the induced signal current at the point where the antenna is connected to the feeding cable is
called input impedance.
The input impedance consists of the electric resistor and electric reactive components.
The electric impedance component reduces the power of the effective signal fed by the antenna into the cable.
So, efforts are made to make the electric reactive component to be zero, so that the input impedance will be pure electric resistor.
Impedance and matching
Such case that the load impedance Z equals the characteristic impedance of the cable Z0 is called matching. If the load is an
antenna, which has a thick oscillator, the input impedance changes less with frequency and the matching between the cable and the antenna is easier to
achieve and the working frequency range of the antenna can be very wide, vise versa.
In reality, the input impedance of the antenna is subject to surroundings and stray capacity effects. To secure matching
between the feeder cable and the antenna, measurement, adjustment in the structure or application of some matching gadgets is wholly necessary in
antenna installation.
Matching is a must to get
satisfactory electrical
performance.

Basics of Antenna: Impedance & VSWR
• For an optimized system performance, all components have to be
matched
• Professional applications use a nominal impedance of 50 Ohms
• Exact value only for one frequency; over the operating band deviations
from 50 Ohms are specified by the VSWR
• A generator will generate a frequency and send it to a termination.
• The termination may not accept the entire input power (green line), and therefore will
reflect some of the input power (red line) back to the generator.

Basics of Antenna: Impedance & VSWR

Basics of Antenna: Reflection Loss and VSWR
Reflection Loss and VSWR
In the case of matching between the feeder cable and the antenna, the high-frequency energy will be completely absorbed by the load (the
antenna), when in the cable there exists only input wave. In this case, the amplitude of the voltage in the cable is the same at every point and
impedance at every point equals its characteristic impedance.
In the case of mismatching, that is, when the impedance of the antenna is not the same as the characteristic impedance of the cable, the fed
signal can not be absorbed by the load completely. Part of the input wave will be reflected as reflected wave.
VSWR (Voltage Standing/Static Wave Ratio): The ratio of the wave loop voltage to the wave node voltage is called static wave ratio, or
voltage static wave ratio. VSWR is another representation of reflection loss.
In the case of mismatching, input wave and reflected wave co-exists in the cable. The two waves combine to affect wave loops where the
magnitude is increased and wave node where the magnitude is decreased and other points where the magnitude remains between the loop
and the node, called static wave. The ratio between the magnitude of the reflected wave to the input wave is called reflection ratio.
Reflection ratio Γ = mag of reflected wave /mag of input wave
= (Z-Z0)/(Z+Z0)
Here, the reflection loss is 10log(10/0.5) = 13dB
The closer the load impedance value to that of the characteristic, the lesser the reflection loss and VSWR and the better is the performance.

Basics of Antenna: PIM/IM
Origin of Intermodulation Products
• PIM is a form of intermodulation distortion that occurs in components normally thought of as linear, such as cables, connectors and antennas.
However, when subject to the high RF powers found in cellular systems, these devices can generate intermodulation signals at –80 dBm or higher.
• If two frequencies f1 and f2 pass through a non linear element (semi conductor effect), harmonics of the original frequencies are created (2f1,3f2,...)
• Combinations of these harmonics result in a frequency spectrum called intermodulation products
• IM products occur in even and odd orders
• IM product of even order (e.g. f1 + f2 or 2f2 - 2f1) : uncritical because
of
1. the big distance to original frequencies
2. signals used in mobile communication show no static
component. Products of even orders will not occur.
• IM products of odd orders (e.g. 2f2 - f1 or 4f1 - 3f2) dangerous
due to their closeness to the original frequencies
• IM products falling into the Rx band, cannot be suppressed by
filters and may cause interferences with operating frequencies
Even Orders PIM: Less Dangerous Odd Orders PIM: High Impact

Basics of Antenna: PIM/IM
Effects of intermodulation
- blocking of Rx frequencies
- overloading the system by creating non-existing
subscribers
- higher amount of drop calls, higher bit failure rate
PIM Sources

Basics of Antenna: Antenna Spectification
Specification of a Typical GSM Antenna
Frequency range MHz: 820 – 960
Band width MHz: 130
Gain dBi: 18
Polarization: Cross(+45/-45)
Impedance Ω: 50
Reflection loss dB: >18
Front-to-back ratio dB: >30
Tilt(adjustable): 0 - 7 °
HPBW(-3dB) beamwidth: H: 63 V: 7
10dB beamwidth H: 120 ° V: 30 °
Suppression of upper beam dB: < -12
Null Fill of lower beam: 2%

Basics of Antenna: Capacity Expansion by Split Antenna
More capacity with fewer antennas
Cellular antennas are directional, often covering 120 degrees, or one-third of a complete circle. Mounted together on a triangular tower,
three sets of these antennas can cover all directions. But in densely urban areas that require more capacity, narrower focus-antennas
(called a six-sector scheme) can handle additional traffic – along with the cost of adding more antennas. Having so many antennas in a
single location makes it more likely to run afoul of local zoning codes.

Basics of Antenna: Capacity Expansion by Split Antenna
Another type of antenna addresses growing capacity needs by intelligently steering
themselves for maximum efficiency.
In addition to electronic downtilt, these multiple degree-of-freedom antennas incorporate
azimuth beam steering plus or minus 30 degrees and azimuth beam adjustment from 35 to
105 degrees (figure 3.23).

Basics of Antenna: Different Antenna Types

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Evolution of Antenna Deployment
Naked Antenna.
Cluttered,
Offensive
Beautifying with
Add-on Radome.
Less Visual Impact
Comprehensive
Camouflage Solution
with Cables & RF
Equipment
Fully immersed to
Environment
Integrated Camouflage
Antenna.
Design as a whole,
Guaranteed Performance
Relieve Public Concern & Resistance
Reduce Visual Impact
Help to Acquire Sites
Evolution of Antenna Deployment : Camouflage Antenna

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Road Lamp Lawn Lamp Spotlight Billboard Mushroom Lawn Board
5）Camouflage Antennas for Community Coverage
a) Wide selections of radomes to fit different scenes
b) Ground deploy., upward cover lower floor users
c) Rooftop/sidewall deploy., downward cover high floor users
d) 800-2700MHz, 2G/3G/LTE coverage
Evolution of Antenna Deployment : Camouflage Antenna

Basics of Antenna: Tilt vs Cell Redius
Required tilt from required coverage distance
Required Tilt is calculated from required cell boundary which we get from area of Best server
calculation of a particular cell:
VO
R
h
VO
d
h
VOquiredtilt
2
1
2
tan
2
1
tan
2
1
Re
1
1
+=
+=
+=
−
−

here, d = cell radial range or distance
= 2R;
( /2.6)AreaR =
d
tilt
ө
ө
d
h

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Antenna selection
Pure Rural Area: Coverage is main target. As we are densely populated, we are using sectorized sites which are built with 3
sectors 120 degree apart. High gain antenna with low vertical opening angle(6/7) and moderate H/O angle(65-90 degree
depending on situation) is preferable. In case of scattered traffic, higher horizontal beam width and even omni antenna
can be used. This will increase trunking efficiency. Splitters and repeaters can also be used for the same reason.
Suburban area: District town is considered suburban area where we can follow same as rural area except using
omni/repeater/splitter.
Here site position is important which should keep in mind the future traffic trend and major traffic source. Most of our
district areas have one big umbrella site with small capacity sites where we should use mid gain antenna.
Urban areas: Grid structure and orientation should be strictly maintained. Antenna with low gain(dense urban) or mid
gain(urban) and 65 H/O angle.V/O angle will depend on consistency of building height. If the building height is more or less
same then low V/O is preferable otherwise high vertical opening can be a choice which also ensure high-rise building
coverage.
Highway/Railway coverage: 2-sector(back to back) site along the direction of road. High gain low v/o and h/o antenna is
preferable. Other strategies depend on position of site and direction of road ( using high H/O angle to cover length of
road)
Basics of Antenna: Clutter Wise Antenna Selection

Basics of Antenna: Anatenna & Cable System for Celluler Network
Antenna & Cable System of Base Station

MD MUSTAFIZUR RAHMAN
Principal Engineer, Radio
Network Planning & Optimization
Grameenphone Ltd.

Antenna Basics: An Introduction to Key Concepts and Parameters

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Antenna Basics: An Introduction to Key Concepts and Parameters