Transmitter

Receiver

Introduction The antenna is the interface between the transmission line

and space

Antennas are passive devices; the power radiated cannot be greater than the power entering from the transmitter

When speaking of gain in an antenna, gain refers to the idea that certain directions are radiated better than others

Antennas are reciprocal - the same design works for receiving systems as for transmitting systems

What is an ‘antenna’?

An antenna is a device that is made to efficiently radiate and receive radiated electromagnetic waves.

An antenna is an electrical conductor or system of conductors.

Transmission - radiates electromagnetic energy into space

Reception - collects electromagnetic energy from space.

In two-way communication, the same antenna can be used for transmission and reception.

Transmitter

Receiver

RADIO WAVES

Electromagnetic radiation comprises both an Electric and a Magnetic Field.

The two fields are at right-angles to each other and the direction of propagation is at right-angles to both fields.

The Plane of the Electric Field defines the Polarisation of the wave.

z

x

y

Electric

Field, E

Magnetic

Field, H

Direction of

Propagation

FOR A SHIELD TO BE EFFECTIVE,

WE MUST BLOCK

BOTH

ELECTRIC AND MAGNETIC

FIELDS …IN ANY COMBINATION

THEY MAY APPEAR.

10

Antenna types Antennas come in a wide variety of sizes and shapes

Horn antenna Parabolic reflector antenna Helical antenna

Horn Antenna Horn antennas are very popular at UHF (300 MHz-3

GHz) and higher frequencies.

Horn antennas often have a directional radiation pattern with a high antenna gain, which can range up to 25 dB in some cases, with 10-20 dB being typical.

Horn antennas have a wide impedance bandwidth, implying that the input impedance is slowly varying over a wide frequency range.

Horn Antenna The gain of horn antennas often increases as the frequency

of operation is increased.

This is because the size of the horn aperture is always measured in wavelengths, a higher frequency has a smaller wavelength.

Since the horn antenna has a fixed physical size, the

aperture is more wavelengths across at higher frequencies. Horn antennas have very little loss, so the directivity of a

horn is roughly equal to its gain.

Types of horn antenna

Figure 1. E-plane horn antenna. Figure 2. H-Plane horn antenna.

Figure 3. Pyramidal horn antenna

14

The Yagi-Uda antenna or Yagi Antenna is one of the most brilliant

antenna designs.

It is simple to construct and has a high gain, typically greater than 10

dB.

The Yagi-Uda antennas typically operate in the HF to UHF bands

(about 3 MHz to 3 GHz),

although their bandwidth is typically small, on the order of a few

percent of the center frequency.

You are probably familiar with this antenna, as they sit on top of

roofs everywhere. TV antennas are still a major application of the

Yagi antenna.

An example of a Yagi-Uda antenna is shown below.

Yagi - Uda

15

Yagi - Uda The Yagi was first widely used during World War II for

airborne radar sets, because of its simplicity and

directionality.[14][15] Despite its being invented in Japan, many Japanese

radar engineers were unaware of the design until very late in the war.

Yagi arrays of the German FuG 220

radar on the nose of the late-

WWII Messerschmitt 110 fighter aircraft.

A Nakajima J1N1-S night fighter with

quadruple Yagi radar transceiver antennas

Yagi - Uda Driven element induces

currents in parasitic elements

When a parasitic element is slightly longer than /2, the element acts inductively and thus as a reflector -- current phased to reinforce radiation in the maximum direction and cancel in the opposite direction

The director element is slightly shorter than/2, the element acts inductively and thus as a director -- current phased to reinforce radiation in the maximum direction and cancel in the opposite direction

The elements are separated by ≈ 0.25

3 Element Yagi Antenna Pattern

2.4 GHz Yagi with 15dBi Gain

G ≈ 1.66 * N (not dB)

N = number of elements

G ≈ 1.66 *3 = 5 = 7 dB

G ≈ 1.66 * 16 = 27 = 16 dB

A log periodic is an extension of the Yagi idea to a broad-band, perhaps 4 x in wavelength, antenna with a gain of ≈ 8 dB

Log periodics are typically used in the HF to UHF bands

Log-Periodic Antennas

Parabolic Reflectors A parabolic reflector

operates much the same way a reflecting telescope does

Reflections of rays from the feed point all contribute in phase to a plane wave leaving the antenna along the antenna bore sight (axis)

Typically used at UHF and higher frequencies

Stanford’s Big Dish 150 ft diameter dish on

alt-azimuth mount made from parts of naval gun turrets

Gain ≈ 4 A/2 ≈ 2 x 105 ≈ 53 dB for S-band (l ≈15 cm)

Parabolic Antenna The most well-known reflector antenna is the parabolic

reflector antenna, commonly known as a satellite dish antenna.

Examples of this dish antenna are shown in the following Figures.

Figure 2. A random direcTV dish

antenna on a roof.

Figure 1. The "big dish" antenna of

Stanford University.

Parabolic Antenna Parabolic reflectors typically have a very high gain (30-40

dB is common) and low cross polarization. They also have a reasonable bandwidth, with the fractional

bandwidth being at least 5% on commercially available models, and can be very wideband in the case of huge dishes.

The smaller dish antennas typically operate somewhere between 2 and 28 GHz.

The large dishes can operate in the VHF region (30-300 MHz), but typically need to be extremely large at this operating band.

The largest radio telescopes • Max Plank Institüt für Radioastronomie radio

telescope, Effelsberg (Germany), 100-m paraboloidal reflector

The Green Bank Telescope (the National Radio Astronomy Observatory) – paraboloid of aperture 100 m

Source: adapted from N Gregorieva

Source: adapted from N Gregorieva

The New Mexico Very Large Array

27 antennas along 3 railroad tracks provide baselines up to 35 km. Radio images are formed by correlating the signals garnered by each antenna.

[Sky & Telescope

Feb 1997 p. 30]

Owens Valley Radio Observatory The Earth’s atmosphere is transparent in the narrow visible-light window (4000-7000 angstroms) and the radio band between 1 mm and 10 m. [Sky & Telescope Feb 1997 p.26]

The Arecibo Observatory Antenna System

The world’s

largest single

radio telescope

304.8-m

spherical

reflector

National

Astronomy and

Ionosphere

Center (USA),

Arecibo,

Puerto Rico

The Arecibo Radio Telescope

[Sky & Telescope Feb 1997 p. 29]

Slot Antenna A slot antenna consists of a metal surface, usually a

flat plate, with a hole or slot cut out.

When the plate is driven as an antenna by a driving frequency, the slot radiates electromagnetic waves in similar way to a dipole antenna.

Often the radio waves are provided by a waveguide, and the antenna consists of slots in the waveguide.

Slot antennas are used typically at frequencies between 300 MHz and 24 GHz.

Slot Antenna Slot antennas are often used

at UHF and microwave frequencies instead of line antennas when greater control of the radiation pattern is required.

Widely used in radar antennas, for the sector antennas used for cell phone base stations.

Often found in standard desktop microwave sources used for research purposes.

Slot Antenna

Planar Microstrip Antenna

Planar antenna technology used for wireless system

Planar antenna application are:

- Arrays for low or medium directivity

- Efficient radiators

- Printed antenna

Planar Antenna Originated from the use of printed microwave technologies.

The begin antenna printed in the mid 1970.

The layered structure with 2 parallel conductors separated by a thin dielectric substrate and the lower conductor acting as a ground plane.

Printed belongs to the resonant antennas. Printed antennas have found use in most classical microwave applications.

Operates typically from 1- 100 GHz.

Planar Antenna

Antenna Characteristics It should be apparent that antennas radiate in

various directions

The terms applied to isotropic and half-wave dipole antennas are also applied to other antenna designs

The Half-Wave Dipole A more practical antenna is the half-wave

dipole

Dipole simply means it is in two parts

A dipole does not have to be one-half wavelength, but that length is handy for impedance matching

A half-wave dipole is sometimes referred to as a Hertz antenna

Dipole antenna basics Dipole antenna consists of two terminals or "poles" into which

radio frequency current flows.

This current and the associated voltage causes and electromagnetic or radio signal to be radiated.

Dipole is generally taken to be an antenna that consists of a resonant length of conductor cut to enable it to be connected to the feeder.

The basic half wave dipole antenna

The current distribution along a dipole is roughly sinusoidal.

falls to zero at the end and is at a maximum in the middle.

voltage is low at the middle and rises to a maximum at the ends.

It is generally fed at the centre, at the point where the current is at a maximum and the voltage a minimum.

This provides a low impedance feed point which is convenient to handle.

High voltage feed points are far less convenient and more difficult to use.

Dipole polar diagram The polar diagram of a half wave dipole antenna that the

direction of maximum sensitivity or radiation is at right angles to the axis of the RF antenna.

The radiation falls to zero along the axis of the RF antenna as might be expected.

Polar diagram of a half wave dipole in free space

If the length of the dipole antenna is changed then the radiation pattern is altered.

As the length of the antenna is extended it can be seen that the familiar figure of eight pattern changes to give main lobes and a few side lobes.

The main lobes move progressively towards the axis of the antenna as the length increases.

The dipole antenna is a particularly important form of RF antenna which is very widely used for radio transmitting and receiving applications.

The dipole is often used on its own as an RF antenna, but it also forms the essential element in many other types of RF antenna.

As such it is the possibly the most important form of RF antenna.

Radiation pattern and gain Dipoles have a radiation pattern, shaped like a toroid (doughnut)

symmetrical about the axis of the dipole.

The radiation is maximum at right angles to the dipole, dropping off to zero on the antenna's axis.

The theoretical maximum gain of a Hertzian dipole is 10 log 1.5 or 1.76 dBi.

The maximum theoretical gain of a λ/2-dipole is 10 log 1.64 or 2.15 dBi.

Monopole (dipole over plane)

If there is an inhomogeneity (obstacle) a reflected wave, standing wave, & higher field modes appear

With pure standing wave the energy is stored and oscillates from entirely electric to entirely magnetic and back

Model: a resonator with high Q = (energy stored) / (energy lost) per cycle, as in LC circuits

Low-Q

Broadband

High-Q

Narrowband Smooth

transition

region

Uniform wave

traveling

along the line

Basics of the Half-Wave Dipole Typically, the length of a half-wave dipole is 95% of

one-half the wavelength measured in free space:

c

f

Radiation Resistance

The half-wave dipole does not dissipate power, assuming lossless material

It will radiate power into space

The effect on the feedpoint resistance is the same as if a loss had taken place

The half-wave dipole looks like a resistance of 70 ohms at its feedpoint

The portion of an antenna’s input impedance that is due to power radiated into space is known as radiation resistance

Radiation Patterns

Antenna coordinates are shown in three-dimensional diagrams

The angle f is measured from the x axis in the direction of the y axis

The z axis is vertical, and angle q is usually measured from the horizontal plane to the zenith

Plotting Radiation Patterns Typical radiation patters are displayed in a polar plot

Gain and Directivity

In antennas, power gain in one direction is at the expense of losses in others

Directivity is the gain calculated assuming a lossless antenna

Beamwidth A directional antenna can be said to direct a beam

of radiation in one or more directions

The width of this beam is defined as the angle between its half-power points

A half-wave dipole has a beamwidth of about 79º in one plane and 360º in the other

Many antennas are far more directional than this

Front-to-Back Ratio

The direction of maximum radiation is in the horizontal plane is considered to be the front of the antenna, and the back is the direction 180º from the front

For a dipole, the front and back have the same radiation, but this is not always the case

Major and Minor Lobes

In the previous diagram, the antenna has one major lobe and a number of minor ones

Each of these lobes has a gain and a beamwidth which can be found using the diagram

Effective Isotropic Radiated Power and Effective Radiated Power

In practical situations, we are more interested in the power emitted in a particular direction than in total radiated power

Effective Radiated Power represents the power input multiplied by the antenna gain measured with respect to a half-wave dipole

An Ideal dipole has a gain of 2.14 dBi; EIRP is 2.14 dB greater than the ERP for the same antenna combination

Impedance

The radiation resistance of a half-wave dipole situated in free space and fed at the center is approximately 70 ohms

The impedance is completely resistive at resonance, which occurs when the length of the antenna is about 95% of the calculated free-space, half-wavelength value

If the frequency is above resonance, the feedpoint impedance has an inductive component; if the frequency is below resonance, the component is capacitive

Ground Effects

When an antenna is installed within a few wavelengths of the ground, the earth acts as a reflector and has a considerable influence on the radiation pattern of the antenna

Ground effects are important up through the HF range. At VHF and above, the antenna is usually far enough above the earth that reflections are not significant

Ground effects are complex because the characteristics of the ground are variable

Other Simple Antennas

Other types of simple antennas are: The folded dipole

The monopole antenna

Loop antennas

The five-eighths wavelength antenna

The Discone antenna

The helical antenna

Antenna Arrays Simple antenna elements can be combined to form

arrays resulting in reinforcement in some directions and cancellations in others to give better gain and directional characteristics

Arrays can be classified as broadside or end-fire Examples of arrays are:

The Yagi Array

The Log-Periodic Dipole Array

The Monopole Phased Array

Other Phased Arrays

Antenna arrays Consist of multiple (usually identical) antennas (elements)

‘collaborating’ to synthesize radiation characteristics not available with a single antenna. They are able to match the radiation pattern to the desired coverage area to change the radiation pattern electronically (electronic scanning)

through the control of the phase and the amplitude of the signal fed to each element

to adapt to changing signal conditions to increase transmission capacity by better use of the radio

resources and reducing interference

Complex & costly Intensive research related to military, space, etc. activities

Smart antennas, signal-processing antennas, tracking antennas, phased arrays, etc.

Source: adapted from N Gregorieva

Variable phase Shifter

SMA

Rotary Step Attenuator

Shielded power

divider

Microstrip array antenna

Microstrip array antenna

Ground Plane

Superstrate

Satellite antennas (TV) Not an array!

Reflectors It is possible to construct a conductive surface

that reflects antenna power in the desired direction

The surface may consist of one or more planes or may be parabolic

Typical reflectors are: Plane and corner Reflectors

The Parabolic Reflector

Cell-Site Antenna

For cellular radio systems, there is a need for omnidirectional antennas and for antennas with beamwidths of 120º, and less for sectorized cells

Cellular and PCS base-station receiving antennas are usually mounted in such a way as to obtain space diversity

For an omnidirectional pattern, typically three antennas are mounted on a tower with a triangular cross section and the antennas are mounted at 120º intervals

In its most basic form, a planar Microstrip patch antenna consists of a radiating patch on one side of a dielectric substrate which has a ground plane on the other side

Structure of a Microstrip Patch Antenna

For good antenna performance, a thick dielectric substrate having a low dielectric constant is desirable since this provides better efficiency, larger bandwidth and better radiation .

In general Micro strip antennas are also

known as

“ PRINTED ANTENNAS ”.

These are mostly used at microwave

frequencies.

Because the size of the antenna is directly

tied the wavelength at the resonant

frequency.

Micro strip patch antenna or patch antenna

is a narrowband wide-beam antenna.

Planar Micro-Strip Antennas

Micro strip antennas are easy to

fabricate and comfortable on curved

surface .

The directivity is fairly insensitive to

the substrate thickness.

Micro strip patch antennas patches

are in variety of shapes ,

such as rectangular , square ,

triangular and circulator …etc.

The patch usually fed along the

centerline to symmetry and thus

minimize excitation of undesirable

modes.

Patch Shapes are: (a) Single radiating patches

(b) Single slot radiator

(d) Microstrip antenna arrays

Substrates are:

The most commonly used substrates are,

1) Honey comb(dielectric constant=1.07)

2)Duroid(dielectric constant=2.32)

3)Quartz(dielectric constant=3.8)

4)Alumina(dielectric constant=10)

A thicker substrate will increase the radiation power , reduce conductor loss and improve Band width.

Comparison of various types of flat profile printed antennas:

Characteristics Microstrip patch antenna

Microstrip slot antenna

Printed dipole antenna

Profile Thin Thin Thin

Fabrication Very easy Easy Easy

Polarization Both linear& circular

Both linear& circular

Linear

Dual freq operation

Possible Possible Possible

Shape Any shape Rec &circle Rec &tiangular

Spurious radiation Exists Exists exists

Advantages:

Low fabrication cost, hence can be manufactured in large quantities.

Easily integrated with microwave integrated circuits (MICs).

Capable of dual and triple frequency operations.

Supports both, linear as well as circular polarization.

Low cost , Less size , Low Mass .

Mechanically robust when mounted on rigid surfaces.

High Performance

Light weight and low volume.

Disadvantages:

Narrow bandwidth associated with tolerence problem

Lower Gain(Nearly 6db) .

Large ohmic losses in feed structure of arrays.

Excitation of surface waves .

Most microstrip antennas radiate into half-space . Relatively low efficiency (due to dielectric and conductor losses) . relatively high level of cross polarization radiation Spurious feed radiation (surface waves, strips, etc.) Inherently low impedance bandwidth. Low efficiency . Extraneous radiation from feeds and junctions . Low power handling capacity.

Remedies:

Low power and low gain can overcome by arrays configuration.

Surface wave associated limitations such as poor efficiency,increased mutual coupling , reduced gain and radiation pattern can overcome.

The band width can increase up to 60% by using some special techniques.

Applications:

Used in mobile satellite communication system.

Direct broad cast telivision(DBS).

Wire less LAN’S.

Feed elements in coaxial system

GPS system.

Missiles and telementry

UHF Patch Antennas for Space

Planar Microstrip Patch Antennas Design

Used for some reasons:

Flat surface makes them ideal for mounting on airplane

Impedance matching fairly simple

Microstrip patch antennas have a very high antenna quality factor(Q).

Q represents the losses associated with the antenna and a large Q leads to narrow bandwidth and low efficiency.

Q can be reduced by increasing the thickness of the dielectric substrate. But as the thickness increases, an increasing fraction of the total power delivered by the source goes into a surface wave

UHF Patch antenna

UHF Patch Antennas for Space Antenna Development Corporation, Inc.(AntDevCo) employees have designed and manufactured spacecraft microstrip patch antennas for many small spacecraft programs.

These antennas are capable of supporting high data rates to at least 10 Watts of transmitted power. Applications include GPS,, radar transponder.

The antennas can be supplied with LHCP, RHCP, or linear polarization .

Radiation patterns of a rectangular microstrip patch antenna

The directivity of a microstrip antenna as a function of dielectric constant computed :-

Figure shows that :A microstrip patch that uses a thicker substrate is more efficient. In addition, as the substrate thickness increases, the radiation Q of the antenna decreases. Thus, impedance bandwidth increases with increasing substrate thickness.

Radiation efficiency, h, and unloaded radiation Q, Q o, as a function of substrate thickness .

Optimizing the Substrate Properties for Increased Bandwidth

The easiest way to increase the bandwidth of an MSA is to : 1) Print the antenna on a thicker substrate. However, thick substrates tend to trap surface wave modes , especially if the dielectric constant of the substrate is high .

Finally if the substrate is very thick, radiating modes higher than the fundamental will be excited.

2) Decrease the dielectric constant of the substrate.

However, this has detrimental effects on antenna size reduction since the resonant length of an MSA is shorter for higher substrate dielectric constant..

In addition, the directivity of the MSA depends on the dielectric constant of the substrate.

3) Stack two patches on top of each other separated by a dielectric substrate or spacers.

The application involved two identical circular patches stacked on top of each other. The lower patch was fed using a coaxial probe feed, and the top patch was electromagnetically coupled to the lower one .

A stacked circular patch EMC-MSA fed using a coaxial probe.

Comparing the different feed techniques :-

Feeding Techniques: Coaxial feed

Microstrip feed

Proximity coupled microstrip feed

Aperture coupled microstrip feed

Coplanar wave guide

Line Feed 1-Microstrip Line Feed :

In this type of feed technique, a conducting strip is connected directly to the edge of the microstrip patch.

This kind of feed arrangement has the advantage that the feed can be etched on the same substrate to provide a planar structure.

2-Coaxial Feed :-

The Coaxial feed or probe feed is a very common technique used for feeding Microstrip patch antennas.

Probe fed Rectangular Microstrip Patch Antenna from top

Probe fed Rectangular Microstrip Patch Antenna from side view

The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance.

This feed method is easy to fabricate and has low spurious radiation.

However, its major disadvantage is that it Coaxial Ground Plane Connector Substrate Patch provides narrow bandwidth and is difficult to model since a hole has to be drilled in the substrate . and the connector protrudes outside the ground plane, thus not making it completely planar for thick substrates .

3-Aperture Coupled Feed

In this type of feed technique, the radiating patch and the microstrip feed line are separated by the ground plane .

Coupling between the patch and the feed line is made through a slot or an aperture in the ground plane.

Aperture-coupled feed

The coupling aperture is usually centered under the patch, leading to lower cross polarization due to symmetry of the configuration.

The amount of coupling from the feed line to the patch is determined by the shape, size and location of the aperture.

Two dielectric substrates are used such that the feed line is between the two substrates and the radiating patch is on top of the upper substrate.

4-Proximity Coupled Feed

This type of feed technique is also called as “the electromagnetic coupling scheme” .

Proximity-coupled Feed

The main advantage of this feed technique is that it eliminates spurious feed radiation and provides very high bandwidth due to overall increase in the thickness of the microstrip patch antenna.

This scheme also provides choices between two different dielectric media, one for the patch and one for the feed line to optimize the individual performances.

Matching can be achieved by controlling the length of the feed line and the width-to-line ratio of the patch. The major disadvantage of this feed scheme is that it is difficult to fabricate because of the two dielectric layers which need proper alignment. Also, there is an increase in the overall thickness of the antenna.

c 2 f r

W 2

εr +1

For design the patch antenna using the approximate equations developed by

the transmission

line model and then verify the design using the FEM method. You will notice a

slight change in

performance characteristics of the antenna from the full-wave analysis to the

transmission line

calculations. The FEM analysis is much more accurate. The following is a step-

by-step guide to

calculate the dimensions of the patch.

Step 1: Specify the relative dielectric constant of the substrate, εr, the resonant

frequency of the patch, fr, and the height of the substrate, h.

Step 2: Calculate the width, W, of the patch using the following equation:

Planar Antenna Design

Step 4: Determine the extension of the length, ΔL, using:

Step 5: Determine the actual length of the patch.

c L − 2ΔL

2 f r eff

Patch Antenna Design (con’t)

Step 3: Determine the effective constant of the

Microstrip antenna using:

Design a rectangular Microstrip antenna using Rogers

RT/Duroid 5880™ with a

dielectric constant of 2.2 with a height of 3.2 mm so as to resonate at 2.97 GHz.

Design Example

Full-wave CEM techniques

Approximations of Maxwell’s equations may be classified into several categories, e.g., low-frequency, quasi-static, full-wave, lumped element equivalent, etc. This tutorial deals with the finite element method a full-wave technique. Full-wave techniques have the potential to be the most accurate of all numerical approximations because they incorporate all higher order interactions and do not make any initial physical approximations Examples include:

– – – – – –

Finite difference time domain (FDTD) Method -- SEMCAD X Method of Moments (MoM) Method ---CST, IE3D, FEKO Finite Element (FEM) Method ---HFSS, ADS Transmission Line Matrix (TLM) Method The Method of Lines (MoL) The Generalized Multipole Technique (GMT)

The FDTD, MoM and FEM are the most popular today!

– – – – – – – – – – –

Draw a geometric model Modify a model’s design parameters Assign variables to a model’s design parameters Specify solution settings for a design Validate a design’s setup Run a HFSS simulation Create a 2-D plot of the antenna radiation pattern Create a 3-D plot of the antenna radiation pattern Create a field overlay plot of the results Study the mesh created by HFSS for the solution Create a phase animation of the results

Simulation Setup (HFSS)

Step-by-step through the design of a Probe Feed CP Patch Antenna by following the steps :

Simulation Setup (HFSS)

Example Microstrip Patch Antenna

Antenna Patch

Infinite Ground Plane

Substrate Material

Artificial absorbing region (box surrounding the antenna)

Step-by-step through the design of a Probe Feed CP Patch Antenna by following the steps :

Draw a geometric model Modify a model’s design parameters Assign variables to a model’s design parameters Specify solution settings for a design Validate a design’s setup Run a HFSS simulation Create a 2-D plot of the antenna radiation pattern Create a 3-D plot of the antenna radiation pattern Create a field overlay plot of the results Study the mesh created by HFSS for the solution Create a phase animation of the results

Create Reports Create a report that plots the input return loss vs. frequency 1. To create this report, select the menu item HFSS>Results>Create Report 2. In the Create Report Window, select: Report Type: Terminal Solution Data Display Type: Rectangular Plot

3. 4.

5.

6.

7. 8.

Click the OK button In the Traces window, select the following: Solution: Setup1: Sweep 1 Domain: Sweep

Click the Y tab and select: Category: Terminal S Parameter

Quantity: St(p1,p1)

Function: dB

Click the Add trace button Click the Done button Use the Data Marker to find the resonant frequency of the structure.

50

Create Reports (con’t)

Create a 2-D plot of the far field pattern 1. To create a 2-D polar far field plot, select the menu item HFSS>Results>Create Report

2. In the Create Report Window, select: Report Type: Far Fields

Display Type: Radiation Pattern

3. Click the OK button

4. In the Traces window, set the following: Solution: Setup1:Sweep1

Geometry: ff_2d 5. In the Sweeps tab, select Phi under the Name column, and on the drop list, select Theta.

This changes the primary sweep to Theta. 6. In the Sweeps tab, select the row labeled Freq and select the resonant frequency 2.3375

from the list 7. In the Mag tab,select:

Category: Gain

Quantity: Gain Total

Function: dB

8. Click the Add Trace button 9. Click the Done button

Create Reports (con’t) Create a 3-D plot of the far field pattern 1. To create a 3-D polar far field plot, select the menu item HFSS>Results>Create Report 2. In the Create Report Window, select: Report Type: Far Fields Display Type: 3D Polar Plot

3. Click the OK button

4.

5.

6.

7.

8.

In the Traces window, set the following: Solution: Setup1:Sweep1 Geometry: ff_3d

In the Sweeps tab, select the row labeled Freq and select the resonant frequency 2.3375 from the list In the Mag tab,select: Category: rE Quantity: rE Total Function: <none>

Click the Add Trace button Click the Done button

Create a Field Plot Create a Magnitude Magnetic Field Plot on the substrate

1.

2.

3. 4.

5.

6.

To create a Magnetic Field Plot, return to the 3-D Modeler Window by selecting HFSS>3D Model Editor. Note: This step is only necessary if you have a Plot window open.

Switch to face selection mode by clicking Edit>Select>Faces

Select the top face of the substrate. You may need to use the B button to select the face

behind the current selection.

To open the Create Field Plot window, click HFSS>Fields>Fields>H>Mag_H

Select Setup1:LastAdaptive as the solution to plot in Solution pull-down list

Accept the default settings by clicking Done

Far-Field, Near-Field Near-field region:

Angular distribution of energy depends on distance from the antenna;

Reactive field components dominate (L, C)

Far-field region: Angular distribution of energy is independent

on distance;

Radiating field component dominates (R)

The resultant EM field can locally be treated as uniform (TEM)

Radiation pattern The radiation pattern of antenna is a representation

(pictorial or mathematical) of the distribution of the power out-flowing (radiated) from the antenna (in the case of transmitting antenna), or inflowing (received) to the antenna (in the case of receiving antenna) as a function of direction angles from the antenna

Antenna radiation pattern (antenna pattern): is defined for large distances from the antenna, where the spatial (angular)

distribution of the radiated power does not depend on the distance from the radiation source

is independent on the power flow direction: it is the same when the antenna is used to transmit and when it is used to receive radio waves

is usually different for different frequencies and different polarizations of radio wave radiated/ received

Normalized 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 when plotted in dB.

3-D pattern Antenna radiation pattern

is 3-dimensional

The 3-D plot of antenna pattern assumes both angles θ and ϕ varying, which is difficult to produce and to interpret

3-D pattern Source: NK Nikolova

2-D pattern Usually the antenna pattern

is presented as a 2-D plot, with only one of the direction angles, θ or ϕ varies

It is an intersection of the 3-D one with a given plane usually it is a θ = const plane

or a ϕ= const plane that contains the pattern’s maximum

Two 2-D patterns

Source: NK Nikolova

Example: a short dipole on z-axis

Source: NK Nikolova

Principal patterns Principal patterns are the 2-D patterns of linearly

polarized antennas, measured in 2 planes

1. the E-plane: a plane parallel to the E vector and containing the direction of maximum radiation, and

2. the H-plane: a plane parallel to the H vector, orthogonal to the E-plane, and containing the direction of maximum radiation

Source: NK Nikolova

Example

Source: NK Nikolova

Isotropic antenna Isotropic antenna or

isotropic radiator is a hypothetical (not physically realizable) concept, used as a useful reference to describe real antennas.

Isotropic antenna radiates equally in all directions. Its radiation pattern is

represented by a sphere whose center coincides with the location of the isotropic radiator.

Source: NK Nikolova

Directional antenna Directional antenna is an antenna, which radiates

(or receives) much more power in (or from) some directions than in (or from) others.

Note: Usually, this term is applied to antennas whose directivity is much higher than that of a half-wavelength dipole.

Source: NK Nikolova

Omnidirectional antenna An antenna, which has a

non-directional pattern in a plane

It is usually directional in other planes

Source: NK Nikolova

Selected References Nikolova N K: Modern Antennas in Wireless Telecommunications EE753

(lecture notes) talia@mcmaster.ca Griffiths H & Smith BL (ed.): Modern antennas; Chapman & Hall, 1998 Johnson RC: Antenna Engineering Handbook McGraw-Hill Book Co. 1993 Kraus JD: Antennas, McGraw-Hill Book Co. 1998 Scoughton TE: Antenna Basics Tutorial; Microwave Journal Jan. 1998, p. 186-

191 Stutzman WL, Thiele GA: Antenna Theory and Design JWiley &Sons, 1981 http://amanogawa.com Software

http://www.feko.co.za/apl_ant_pla.htm Li et al., “Microcomputer Tools for Communication Engineering” Pozar D. “Antenna Design Using Personal Computers” NEC Archives www.gsl.net/wb6tpu /swindex.html ()

Test Equipment: The Anechoic Chamber

The anechoic chamber is used to set up antennas in a location that is free from reflections in order to evaluate them

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