Dra Report Mithlesh Final

7/29/2019 Dra Report Mithlesh Final

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Overview

Introduction of an antenna Types of antenna. Basic parameters of DRA antenna. working of DRA. Advantage of DRA antenna. Mathematical analysis of DRA.

Resonant frequency selection factors ofDRA.


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Design steps of DRA antennaPcb layout designing.Etching of pcb.Probe connection on pcb. Dielectric insertion in cylindrical pipe.

Coupling techniques for DRA antennaTesting of DRATesting instruments.Testing purpose and results. Application of DRA antenna


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What is an Antenna?

Antennas are metallic structures designed for radiating and receiving

electromagnetic energy. An antenna acts as a transitional structure

between the guiding device like waveguide, transmission line etc. and

the free space. Antennas are frequency dependent devices. Each antennais designed for a certain frequency band beyond which it rejects the

signal. So we can look at them as band pass filter and transducer.

Antennas are therefore very essential components of all or mostly any

equipment that uses radio.

How an Antenna Radiates?

Antennas basically consists of arrangement of metallic conductors,electrically connected (mostly through a transmission line) to the

receiver or the transmitter. One oscillating current of electrons will

create an oscillating magnetic field around the antenna elements while

the charge of the electrons (e-s) also creates an oscillating electric field

along the elements. The entire time-varying field radiates away from the

antenna into space as a moving EM field wave. During the reception,

conversely, the oscillating electric (E-field) and magnetic fields (H-Fields) of an incoming radio-wave exert force onto the electrons (e-s) in

antenna elements, causing them to move, creating radiation.

Parameters affecting Antenna: Some basic parameters are there whichaffect an antennas performance. The designer must consider these while

designing and should be able to adjust, as needed. Some criticalparameters are as follows:

Antenna radiation patterns

Power Gain

Directivity

Polarization


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Impedance

Radiation efficiency

RADIATION PATTERN:The radiation pattern of an antenna is a plot of the relative field strength

of the radio waves emitted by the antenna at different angles. It is

typically represented by a three dimensional graph, or polar plots of the

horizontal and vertical cross sections. The pattern of an ideal isotropic

antenna, which radiates equally in all directions, the radiation of many

antennas shows a pattern of maxima or "lobes" at various angles,

separated by "nulls", angles where the radiation falls to zero. This is

because the radio waves emitted by different parts of the antenna

typically interfere, causing maxima at angles where the radio wavesarrive at distant points in phase, and zero radiation at other angles where

the radio waves arrive out of phase. In a directional antenna designed to

project radio waves in a particular direction, the lobe in that direction is

designed larger than the others and is called the "main lobe". The other

lobes usually represent unwanted radiation and are called "sidelobes".

The axis through the main lobe is called the "principal axis" or

"boresight axis".

Gain:Gain is a parameter which measures the degree of directivity of the

antenna's radiation pattern. A high-gain antenna will preferentially

radiate in a particular direction. Specifically, the antenna gain, or power

gain of an antenna is defined as the ratio of the intensity (power per unit

surface) radiated by the antenna in the direction of its maximum output,

at an arbitrary distance, divided by the intensity radiated at the same

distance by a hypothetical isotropic antenna.

The gain of an antenna is a passive phenomenon - power is not added by

the antenna, but simply redistributed to provide more radiated power in a

certain direction than would be transmitted by an isotropic antenna. An

antenna designer must take into account the application for the antenna

when determining the gain. High-gain antennas have the advantage of


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longer range and better signal quality, but must be aimed carefully in a

particular direction. Low-gain antennas have shorter range, but the

orientation of the antenna is relatively inconsequential. For example, a

dish antenna on a spacecraft is a high-gain device that must be pointed at

the planet to be effective, whereas a typical Wi-Fi antenna in a laptopcomputer is low-gain, and as long as the base station is within range, the

antenna can be in any orientation in space. It makes sense to improve

horizontal range at the expense of reception above or below the antenna.

Polarization:The polarization of an antenna is the orientation of the electric field (E-

plane) of the radio wave with respect to the Earth's surface and is

determined by the physical structure of the antenna and by itsorientation. It has nothing in common with antenna directionality terms:

"horizontal", "vertical", and "circular". Thus, a simple straight wire

antenna will have one polarization when mounted vertically, and a

different polarization when mounted horizontally. "Electromagnetic

wave polarization filters"[citation needed] are structures which can be

employed to act directly on the electromagnetic wave to filter out wave

energy of an undesired polarization and to pass wave energy of a desired

polarization.

Reflections generally affect polarization. For radio waves the most

important reflector is the ionosphere - signals which reflect from it will

have their polarization changed unpredictably. For signals which are

reflected by the ionosphere, polarization cannot be relied upon. For line-

of-sight communications for which polarization can be relied upon, it

can make a large difference in signal quality to have the transmitter and

receiver using the same polarization; many tens of dB difference are

commonly seen and this is more than enough to make the differencebetween reasonable communication and a broken link.


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EfficiencyEfficiency of a transmitting antenna is the ratio of power actually

radiated (in all directions) to the power absorbed by the antenna

terminals. The power supplied to the antenna terminals which is not

radiated is converted into heat. This is usually through loss resistance inthe antenna's conductors, but can also be due to dielectric or magnetic

core losses in antennas (or antenna systems) using such components.

Such loss effectively robs power from the transmitter, requiring a

stronger transmitter in order to transmit a signal of a given strength.

ImpedanceAs an electro-magnetic wave travels through the different parts of the

antenna system (radio, feed line, antenna, free space) it may encounterdifferences in impedance (E/H, V/I, etc.). At each interface, depending

on the impedance match, some fraction of the wave's energy will reflect

back to the source, forming a standing wave in the feed line. The ratio of

maximum power to minimum power in the wave can be measured and is

called the standing wave ratio (SWR).Complex impedance of an antenna

is related to the electrical length of the antenna at the wavelength in use.

The impedance of an antenna can be matched to the feed line and radio

by adjusting the impedance of the feed line, using the feed line as an

impedance transformer. More commonly, the impedance is adjusted at

the load (see below) with an antenna tuner, a balun , a matching

transformer, matching networks composed of inductors and capacitors,

or matching sections such as the gamma match.

radiation efficiencyThe radiation efficiency rad describes the losses within the antenna

structure. It is defined by the ratio of the radiated power Prad over the

power Pin going into the antenna terminal.

Radiation Efficiency= Prad/ Pin= Prad/ Prad+ Ploss


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rad= Radiation Efficiency =Rrad/Rrad+Rlos

Where Prad= power radiated

Pin = power fed to antenna (W)Ploss = power lost by the antenna (W)

Rrad= radiation resistance of the antenna ()

Rloss=loss resistance of the antenna ()

For physically small antennas, the Wheeler cap method [48] is highly

preferred for measuring the radiation efficiency. According to this

method, if a radiation shield is placed around the antenna so as to

enclose the near fields of the antenna, the radiation resistance of the

antenna is reduced to zero while the loss resistance and the stored energyremain the same as for the unshielded antenna [49]. When covering the

antenna with a metal cap, the radiation is suppressed and the input power

(proportional to the input resistance) is equal to the power loss

(proportional to the loss resistance). Without the cap, the input power is

equal to the radiated power plus the power loss(input resistance +loss

resistance). The radiation efficiency of the antenna can be obtained from

these two parameters.

Meaning of dielectric resonator:Dielectric resonators (DRs) emerged as a substitute to resonant metallic

cavities and waveguides in microwave devices like filters, oscillators,

and phase shifters. As for metallic cavities, the resonant frequency of a

DR is determined by its dimensions and also exhibits high Q-factors.

But the main difference between the two is that the wavelength in

dielectric materials (non-magnetic) is reduced by a factor of one over

square root of the dielectric constant, at which is much higher than unity

for most materials. Hence the resonator can be made smaller byChoosing a high dielectric constant material. However, the reactive

power stored in a DR during resonance is not strictly confined inside the

resonator.The leakage fields from the resonator can be used for energy

coupling, frequency tuning or radiation purpose. To be useful in

practical applications, a DR basically requires a high dielectric constant


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(er > 20) for promising size reduction, high Q-factor to store more

energy.

Working of DRAIn this antenna, only ionised currents contribute to radiate

Energy in conducting fluid. Radiating resistance and resonant

Frequency shall depend on shape of fluid inside the tube and Nano

particles of the fluid.

A dielectric resonator antenna is a radio antenna mostly used at

microwave frequencies and higher, that consists of a block of ceramic

material of various shapes, the dielectric resonator, mounted on a metal

surface, a ground plane. When RF signal applied to DRA, Radio wavesare introduced into the inside of the resonator material from the

transmitter circuit and bounce back and forth between the resonator

walls, forming standing waves. The walls of the resonator are partially

transparent to radio waves, allowing the radio power to radiate into

space. An advantage of dielectric resonator antennas is they lack metal

parts, which become lossy at high frequencies, dissipating energy. So

these antennas can have lower losses and be more efficient than metal

antennas at high microwave and millimeter wave.

DRA characteristics There is no inherent conductor loss in dielectric resonators. This

leads to high radiation efficiency of the antenna. This feature is

especially attractive for millimeter (mm)-wave antennas, where the

loss in metal fabricated antennas can be high.

DRAs offer simple coupling schemes to nearly all transmissionlines used at microwave and mm-wave frequencies. This makes

them suitable for integration into different planar technologies.

The coupling between a DRA and the planar transmission line canbe easily controlled by varying the position of the DRA with


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respect to the line. The performance of DRA can therefore be

easily optimized experimentally.

The operating bandwidth of a DRA can be varied over a widerange by suitably choosing resonator parameters. For example, thebandwidth of the lower order modes of a DRA can be easily varied

from a fraction of a percent to about 10% or more by the suitable

choice of the dielectric constant of the resonator material.

Each mode of a DRA has a unique internal and associated externalfield distribution. Therefore, different radiation characteristics can

be obtained by exciting different modes of a DRA.

DRA advantages The DRA is an antenna that makes use of a radiating mode of a

dielectric resonator (DR).

It is a 3-dimensional device of any shape, e.g., hemispherical,cylindrical, rectangular, triangular, etc.

Resonance frequency determined by the its dimensions and dielectric

constant .

Low loss (no conductor loss)

Small size and light weight

Reasonable bandwidth (~10% for r ~10)

Easy of excitation


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High radiation efficiency ( generally) > 95%)

Compared with the micro strip antenna, DRA has a muchwider impedance bandwidth. This is because the micro strip

antenna radiates only through two narrow radiation slots, whereasthe DRA radiates through the whole antenna surface except the

grounded part. Moreover the operating bandwidth of a DRA can

be varied by suitably choosing the dielectric constant .

Many of the existing feeding schemes can be used (slots, probes,micro strip, coplanar waveguides, dielectric image guide, etc.).

This makes them easy to integrate with existing technology

DRAs have been designed to operate over a wide frequency range(1 GHz to 44 GHz) compared with other antennas existing in the

literature.

DRAs have a high dielectric strength and hence power handling

capacity. Moreover the temperature-stable ceramics enable the antenna

to operate in a wide temperature range.

The antenna offers good radiation and reflection properties as well.

Fundamental Modes and Their Radiation Mechanism in DRA:

A microwave resonator has an infinite number of resonant modes, each

corresponding to a particular resonant frequency at which the stored

electric energy is equal to the magnetic energy. The excited modes for

circular DRA can be classified into three distinct types: TE, TM,and hybrid. The fields for TE and TM modes are axis symmetric,


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whereas hybrid modes are azimuthally dependent. The TE, TM, and

hybrid modes are classified as TEmnp+d, TMmnp+d and HEmnp+d

respectively.

The index m denotes the number of full-period field variations inazimuthally direction.

The index n (n = 1, 2, 3) denotes the order of variation of the field

along the radial direction.

The index p + d (p = 0, 1, 2) denotes the order of variation of the

fields along the Z-direction.

The third index denotes the fact that the dielectric resonator is shorter

than integer multiples of half the dielectric wavelength.The actual value of d depends on the relative dielectric constant of the

resonator and the substrate

and on the proximity to the top and bottom conductor planes. An

interesting feature of DR is the variation in field distribution of different

modes, because the modes behave like electric and

magnetic multipoles such as dipole, quadrupole, octupole, etc. The

mode nomenclature makes possible the accurate prediction of far-field

radiation of dielectric resonators in their application as antenna

Resonant frequency selection factors of DRAQuality factor

Quality or Q-factor is a measure of the ability of the DR to store

microwave energy with minimal signal loss. The inherent Q-factor of a

DR solely

depends on the loss factor of the dielectric material. But in practicalapplications,the resonator is always associated with metallic parts, in the

form of shields or ground planes. In general, the loaded Q-factor of a

resonant cavity can be defined

as the ratio of the stored energy to the dissipated power The denominator

term, which is the total power dissipation, can occur in many Ways such


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as conductor losses (PC), dielectric losses (Pd), radiation losses(Pr) and/

or losses in the external circuits (Pm).

Q= stored energy/ dissipated energy

Q= 2 W Es/ Pdis(9)

.i Pd = PC + Pd + Pr + Pm

The impedance bandwidth (BW) of the DRA can be estimated from the

radiation Qfactor

using:

BW=(s-1/Q*s^0.5)..(10)

where Sis the maximum acceptable voltage standing-wave ratio

(VSWR). The above equations can be used to generate the graphs which

plot the normalized Q-factor (Qe) as a function of the DRA dimensions

d/b for various values of dielectric constant and various values ofa/b.:

Analysis on the dielectric material choice:To supply satisfactory answers about the effects of dielectric material

properties, this section will present a careful and extensive investigation

into relevant cases. Indeed, properties of

the dielectric material have an influence on antenna characteristics, i.e.

impedance bandwidth, Q factor, resonant frequency and radiation

efficiency

BW=1/Q*s^0.5)=f/f0(11)

Where f is the absolute bandwidth, f0 is the resonant frequency and s

the maximum acceptable voltage standing wave ratio (VSWR).The Q

factor equation is deriving from the cylindrical dielectric resonator

model approach by assuming perfect magnetic and/or electric walls on


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resonator faces. These equations are not absolutely accurate but they

offer a good starting point for the design of cylindrical design.

the resonant frequency decreases when the dielectricpermittivityincreases. Moreover, bandwidth is the widest forr=10.

Fields are less confined for a low dielectric permittivity DRA, it isthus more difficult to couple the mode inside the resonator.

Indeed, for higher dielectric values (r>10), strong coupling is

achieved, however, the maximum amount of coupling is

significantly reduced if the dielectric permittivity of the DRA is

lowered.

That is why the bandwidth is low for r under 10. For a dielectricpermittivity over 10, the Q factor is increasing and therefore the

impedance bandwidth is decreasing(bw)

DIFFERENT DR GEOMETRIES:

One of the attractive features of a DRA is that it can assume a number of

shapes. Moreover the mode of operation and performance of a DRA can

be varied by selecting a DR with desired structure . Hence a number of

DRA geometries have already been tried experimentally. The first

systematic, theoretical, and experimental study was made

on cylindrical disk DRA geometry. Later geometries such as split

cylinder, , cylindrical rings, metalized DRAs, triangular,

rectangular,notchedrectangularDRA,chamferedDRA,conical,elliptical,spherical,hemispherical,spherical cap, tetrahedral, perforated DRA,

stepped DRAs, and hybrid DRAs, have been


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Cylindrical DRA

reported. It was found that DRAs operating at their fundamental modesradiate like an electric or magnetic dipole, which depends on the mode

of excitation and geometry of the bulk dielectric material. Geometries

like conical, stair stacked triangular etc emerged for dual band or

wideband applications while those like , hexagonal, cylindrical-comb etc

emerged for circular Rectangular waveguide

.

Cylindrical

Rectangular ring


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Different DR geometries used

Coupling techniques for DRA antennaThe selection of the feed and that of its location both play an important

role in determining which modes are excited. This, in turn, will

determine the input impedance and radiation characteristics of the

DRAs. The coupling mechanism can also have a significant impact on

the resonant frequency and Q-fact ,A knowledge of the internal field

configuration is essential for understanding howthe various feeds can excite different modes within the DRA.


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COUPLING COEFFICIENTSFor most practical applications, power must be coupled into or out of the

DRAthrough one or more ports.

The type of port used and the location of the port with respect to the

DRA will determine which mode will be excited and how much powerwill be coupled between the port and the antenna. The mode or modes

generated, the amount of coupling, and the frequency response of the

impedance are all important in determining the performance of the DRA.

Although these quantities are difficult to determine without using

numerical methods, a great deal of insight can be obtained by knowing

the approximate field distributions of the modes of the isolated DRA and

by making use of the Lorentz Reciprocity Theorem and some coupling

theory borrowed from resonator circuits .When coupling to a DRA, thesource can typically be modeled as either an electric or magnetic current,

and the amount of coupling, between the source and the fields within the

DRA can be determined by applying the reciprocity theorem with the

appropriate boundary conditions.

more common coupling methods to DRAs APERTURE COUPLINGIn slot-fed DRA, a narrow slot is formed on the ground plane of the

structure through which energy is coupled to the DR. The slot acts as a

magnetic current element perpendicular to the micro strip. The magnetic

coupling through the slot avoids the drawbacks of the probe coupling.

This also has the advantage of isolating the radiator from

the feed as well as blocking the spurious radiations from the strip . Also

slot coupling provides low cross-polarization level since both the slot

and the DR radiate like horizontal magnetic dipoles .Length of themicrostrip stub that extends beyond the slot can be used to cancel the

reactance of the slot, thus allowing good impedance matching. Also this

feed is well-suited in monolithic microwave integrated circuits

(MMICs). But at lower frequencies, the size of the slot becomes large so

that such coupling is advised at higher frequencies


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Coaxial ProbeThis is the simplest means for coupling energy to a DR. , the DR is

placed on a conducting ground plane and the central conductor of a

coaxial connector extends from the bottom to the top plane to make

contact with the DR. The outer conductor of the connector makes

contact with the ground plane. The probe can be placed either touching

the periphery of the DR or inside a hole drilled on the bottom face of the

DR . Amount of coupling can be controlled by varying the probe

position and/ or length with When the probe is at or near the periphery

of the cylinder, the broadside Hem11 m ode is excited while when the

probe is inserted at the centre, the monopole -mode TM01s is excited.However this kind of coupling requires drilling

a hole through the DR especially when its dielectric constant is low,

which is very difficult in practice. Any direct radiation from the probe

can increase the cross polarization in the H-plane of the DRA . Also the

probe introduces ohmic loss and self-reactance at higher frequencies . In

addition, the air gap between the probe and the DR can prominently

affect the DRA performance.

Co-planar FeedHere, both the feed and the ground plane are etched on the same side of

a Substrate. This kind of feed has been found the most suitable for

MMICs, arrays, circularly polarized antennas, dual-frequency structures,

wide-band structures, and active Antennas. Impedance matching is set

by the geometry and the dimensions of the slot.

Waveguide FeedThe primary advantage of a waveguide is that it is extremely less lossy

inthe millimeter wave and higher frequencies. Since the wave is


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completely guided within the metallic structure, there is no threat of

radiation loss when used as a

feed line. As both the waveguide and DR are very low-loss, they form an

excellent combination for low-loss millimeter wave communication

systems Coupling to the DR can be achieved through a probe or a slot.

Hardware design steps of DRAPcb layout designing.

Etching of pcb.

Probe connection on pcb.

Dielectric insertion in cylindrical pipe.

Pcb layout designing:

After getting the proper dimension according to the mathematical

analysis of DRA ,with shape and size of DR, and the feding technique

next step to design the pcb layout with that dimension.

Etching

There are many alternatives for etching liquids, and you can use the one

that suits your taste. I use ferric chloride (the brown stuff): its cheap,

can be reused many times, and doesnt require heating. Actually,

moderate heating can speed up etching, but I find it reasonably fast also

at room temperature (1015 minutes). The down side of this stuff is

that its incredibly messy. It permanently stains everything it gets in

contact with: not only clothes or skin (never wear your best clothes

when working with it!), but also furniture, floor tiles, tools, everything.

It is concentrated enough to corrode any metalincluding your chrome-

plated sink accessories. Even Vapours are highly corrosive: dont forgetthe container open or it will turn any tool or metallic shelf nearby into

rust.

For etching, I place the container on the floor (some scrap cardboard or

newspaper to protect the floor from drops). I fit the board on the hanger,

and submerge the PCB. Stir occasionally by waving the hanger


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Etching

Probe connection on pcb

Once the cooper material is removed from the undesired place of thepcb , by the etching process next step to connect the SMA connector

according to feed techniques used to give RF signal to the DR.

Sma connector can be connected with help of soldering machine.

Dielectric insertion in cylindrical pipe:Once all the work related to designing of DRA hardware is Completed,

next step to insert some dielectric solution in to the cylindrical pipe ,the

dielectric solution may vary for different DRA ,choose dielectric withparticular application of that antenna ,because change in dielectric

,material will directly affects the resonant frequency of DRA, hence the

working bandwidth also gets change.


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Testing of DRATesting Measurements of the characteristics of the DR and the radiation

properties of the DRAS are carried out in the microwave research lab in

Ambedkar institute of advance communication technology and research,

The basic measurement setup comprises of:

Network Analyzer Unit DeviceUnder-Test (DUT)

When measuring DUTs like cavities, only the network analyser unit is

used,but for antenna measurement, all the above four units are used.

Network analyser unitNetwork analyzer is a sophisticated instrument, generally used tomeasure

the reflection and transmission of signals associated with an electrical

network,

especially at higher frequencies., a fully integrated vector network

analyzer (V NA) system, is used in the present study. It measures the

magnitude and phase characteristics of electronic networks and

components such as filters, amplifiers, attenuators and antennas. The

instrument has four inputs, two independent measurement channels, andan internal microcomputer to automate measurements, conduct data

processing, display results, and manage data input output operations.

The dedicated system bus provides fast digital communication between

individual system instruments, allowing the network analyzer to fully

use the source and test set capabilities

Antenna under TestThe AUT is the antenna designed using the fabricated method . in our

DRA dielectric constant is 51',diameter 2a and height d are used.

The DRA is fed by a 5O Q micro -strip transmission line of radius( a) 17

mm

and height 50 mm, the characteristic impedance (Z0 = 50 The


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merits of using micro -strip feed are well-known, where fine adjustment

of impedance matching between the feed and the DR can be easily

achieved by

adjusting the DR position relative to the feed.

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