Fed Corner Truncated Microstrip Patch Antenna

Ultra-Wide band communications attracted great interest of researchers as it has become one of the most promising technologies for short range mobile systems, Personal Area Networks (PAN) and high speed indoor data communication applications. FCC mentioned parameters for the complete functioning of UWB antennas and they have to cover the bandwidth specified by FCC to attain adequate performance.

UWB has the advantage of high data rates with extremely low interference to other narrow band systems. The ultra short pulses provide extremely good spatial resolution, as the range provided by UWB is enough to seize down the major applications of daily life like in ground penetrating radars, parking radars, biomedical imaging, precision tracking and location finding. Various types of UWB antennas have been proposed and implemented with different feeding techniques, such as transmission line, probe feed, dual feed and coplanar waveguides (CPW).

A compact antenna design fed by coplanar waveguide (CPW) is proposed. Overall dimensions of antenna are 28Ã-24 mm2. The design is fabricated and further analyzed to confirm its proper working in UWB range. The design of antenna is quite flexible as fiddling with the patch of microstrip antenna has been done in order to enhance the bandwidth which is the most valued obsession in the current environment. On the other hand, CPW has many advantages such as low radiation leakage, less dispersion at higher frequency, small mutual coupling between two adjacent lines which is helpful to place circuit elements close together without adding an additional layer of substrate and coplanar capability. Using CPW as feeding structure to excite a patch antenna has become very popular recently.

The proposed antenna offers an excellent performance for UWB systems by providing bandwidth ranging up to 15.65GHz. Critical design parameters return loss and radiation patterns are investigated in detail. Proposed antenna provides good impedance matching, stable gain characteristics and consistent radiation patterns over its almost whole frequency band of interest.

Chapter 1

Introduction

Project Overview

IEEE defines antenna as “a device for radiating and receiving electromagnetic waves”. They are used both as transmitter and receiver. This is era of wireless communication. Antennas are an important means of wireless communications now days. The need of time is compact small size antennas with enhanced bandwidth and gain. Amongst all antenna types microstrip patch antennas are most common. They are light in weight and consume low power. But patch antennas have disadvantage that they have narrow bandwidth. Many techniques are used to enhance bandwidth.

Ultrawide band antennas have many applications and for many years they have been used for broadband and spread spectrum features in radar systems. The UWB performances of antennas result from excitation by non-sinusoidal signals with quickly time-varying performances [1]. UWB are low power consumption antennas and are for unlicensed applications. As name suggests, they have broad spectrum.

Problem Statement

Ultra wideband technology is used in low power, short range and high bandwidth communication. In UWB; through spreading information can be transmitted over a larger bandwidth and spectrum is also shared with the other users at the same time.

Federal Communication Commission (FCC) allocated the license free band of 3.1GHz-10.6GHz for use in UWB applications. Since then there is a growing demand of UWB antennas for high data rate applications i.e. wireless personal area network (WPAN).

UWB has had a important effect on antenna design. The major challenge in UWB antenna design is to achieve wide impedance bandwidth and stable gain while maintaining high radiation efficiency.

Project Objective

The purpose of this project is to design, stimulate, analyze and fabricate ultra wide band antenna using co-planer waveguide.

Design and analysis of a compact antenna fed by CPW for UWB Applications is proposed

Bandwidth of the proposed antenna is 15.65 GHz.

Antenna offers an excellent performance for ultra-wide band systems by providing an ultra-wide bandwidth ranging from 3.1 – 18.75 GHz.

Gain of the proposed antenna is 4.91dBi over its almost whole frequency band of interest

Small size of antenna makes it suitable for applications which demand miniaturization of antenna structure and input impedance of 50 Ω.

Methodology

We have simulated the designed antenna using Ansoft HFSS. Then the simulated antenna is fabricated and tested on the network analyzer. The simulated and measured results are also explained.

Organization of the thesis

This report is divided into 6 chapters.

Chapter 2 presents the fundamental parameters of antenna. This includes an explanation of various parameters related to antenna performance including radiation intensity ,radiation pattern, power density , gain, directivity and polarization etc.

Chapter 3 discusses the Microstrip Patch Antenna and Feeding techniques.

Chapter 4 includes Ultra wide band microstrip patch antenna, history of UWB antennas, their features and advantages.

Chapter 5 describes antenna design, simulated results, 2D and 3D radiation patterns for different frequencies and fabricated results.

Chapter 6 concludes the entire work done throughout the designing of proposed antenna. Conclusion and future work helps to explore enormity of the subject.

Chapter 2

Fundamental Parameters of Antenna

2.1 Radiation Pattern

The radiation pattern describes the strength of the radiated field in different directions from the antenna, at a constant distance. The radiation pattern is also reception pattern, as it describes the receiving properties of the antenna. It is defined as “a mathematical function or a graphical representation of the radiation properties of antenna as a function of space coordinates. In most cases the radiation pattern is determined in far field regions and is defined as a function of the directional coordinates. Radiation properties include power flux density, radiation intensity, field strength, directivity phase or polarization” [2].

The radiation pattern is three-dimensional, but measured patterns are usually two dimensional in vertical or horizontal plane view. These measured patterns are presented in either rectangular or polar format. Following figure shows radiation pattern of an antenna in polar plane and Cartesian coordinate systems.

http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/images/0900aecd806a1a3e_null_null_null_08_07_07-03.jpg

Figure-2.1: Radiation Pattern of an antenna in Cartesian and polar coordinates

Radiation patterns are further categorized as relative and absolute radiation patterns. Absolute radiation patterns have absolute units of power or field strength. Relative radiation patterns are presented in relative units of power or field strength. The radiation measurement patterns are mostly relative to isotropic antennas, absolute gain of the antenna is established by antenna gain transfer method.

The radiation pattern varies with the distance i.e. the patterns in near filed and far filed are different. The field pattern that exists close to the antenna is known as near filed, and far-field refers to the field pattern that exists at large distances. The far-field is called radiation field. Radiation field and power are what is commonly of interest, so antenna patterns are generally measured in the far-field region. For antenna pattern measurement the distance should be chose large enough not to be in near-field or in far field. The minimum allowed distance depends on the dimensions of the antenna relative to the wavelength. The formula for this distance is:

rmin = 2d2/λ (2.1)

Where, rmin is the minimum distance from the antenna

d is the largest dimension of the antenna

λ is the wavelength.

2.1.1 Radiation Pattern Lobes

Radiation lobes are defines as “portion of radiation pattern bounded by regions of relatively weak radiation intensity” [3]. These lobes are categorized as follow

Major Lobes

Minor Lobes

Side Lobes

Back Lobes

2.1.2 Major Lobe

A major lobe is defined as “the radiation lobe containing the direction of maximum radiation” [2]. Normally an antenna has one major lobe.

2.1.3 Minor Lobe

Any lobe except major lobe is called minor lobe. It usually represents the radiation pattern which is not desirable.

2.1.4 Side Lobe

A side lobe is “a radiation lobe in any direction other than the main lobe” [2]. Usually a side lobe is next to the main lobe and is in direction to the main lobe.

2.1.5 Back Lobe

A back lobe is “a radiation lobe whose axis makes an angle of approximately 180° with respect to the beam of an antenna” or that is directed away from the main lobe [2].

File:Typical Antenna Pattern.jpg

Figure 2.2: An illustration of major and minor lobes of radiation pattern

2.2 Field Regions

The antenna fields are divided into three regions

Reactive near field

Radiating near field (Fresnel)

Far field (Fraunhofer)

http://www.nearfield.com/images/theory-ffdist.jpg

Figure 2.3: Figure of Near Field and Far Field Regions

2.2.1 Reactive Near Filed

It is the region immediately around the antenna. In this region the reactive filed predominates. The distance of this filed with antenna is usually R< 0.62, where λ is the wavelength and D is the largest dimension of antenna.

2.2.2 Radiating Near Field (Fresnel)

Radiating near filed is defines as “that region of the field of an antenna between the reactive near-filed and the far-filed region wherein radiation fields predominate and wherein the angular field distribution is dependent upon the distance from the antenna” [2]. The distance of inner boundary is R< 0.62, and the distance of outer boundary R< 2D2/ λ.

2.2.3 Far Field Region (Fraunhofer)

Far Field region is defined as “that region of the field of an antenna where the angular filed distribution is essentially independent of the distance from the antenna” [2].

2.3 Radiation Intensity

Radiation Intensity is the power radiated from an antenna per unit solid angle. It is the parameter of far field radiation.

2.4 Directivity

Directivity is figure of merit for antennas. It is the power density an antenna radiates in direction of maximum radiation to the average power density radiated by an isotropic antenna. Directivity for an isotropic antenna is always unity. It is expressed as

D= (2.2a)

(2.2b)

Where, D is directivity and U is radiation intensity, Uo is Intensity if an isotropic source and Prad is total radiation power.

2.5 Gain

The gain and directivity of an antenna are closely related to each other. However for gain in denominator it is total power accepted by an antenna rather than total power radiated by an antenna.

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G= (2.3)

Gain is dimensionless. According to IEEE standards, gain doesn’t include losses arising from impedance mismatching or polarization mismatches.

2.6 Bandwidth

The bandwidth is basically the difference or range between highest and lowest frequencies on which an antenna is operated. It is advantageous to have an antenna with high bandwidth. The bandwidth is expressed in term of ratio of upper cut off to the lower cutoff for broadband antennas.

2.7 Beamwidth

Beamwidth is the angle usually measured in degrees; between the -3dB power radiated in the main lobe of radiation pattern.

img383

Figure 2.4: Illustration of Beamwidth

2.8 Return Loss

It is the amount of power that is reflected back in to the transmission line due to mismatching or any other error. It is the efficiency of power delivered to the load from the transmission line. Mathematical representation of Return loss is

RL = 10log (2.4)

Return loss is measured in dB.

http://www.mwrf.com/Files/30/11240/Figure_05.gif

Figure 2.5: Return Loss

2.9 Polarization

Polarization is defined as point of reference of the electric field of the wave radiated by the antenna. It is categorized in three types:

Linear

Circular

Elliptical

2.9.1 Linear Polarization

When there is zero phase difference between x and y component of a wave then polarization is called linear polarization. Linear polarization is further divided into

Horizontal polarization

Vertical polarization

http://www.ccrs.nrcan.gc.ca/glossary/images/3104.gif

Figure 2.6: Linear Polarization

2.9.1.1 Horizontal Polarization

Horizontal polarization is the one in which wave propagates in x-direction and there is no propagation along y direction. A horizontally polarized wave is explained as a function of time T and E-field position

Ex = E1 sin ( É·t – ᵝz) (2.5)

http://www.cfht.hawaii.edu/~manset/PolHoriz.gif

Figure 2.7: Horizontal Polarization

2.9.1.2 Vertical Polarization

Vertical polarization is the one in which wave propagates in y-direction and there is no propagation along x direction. It can be written in mathematical form as

Ey = E2 sin ( É·t – ᵝz) (2.6)

http://www.cfht.hawaii.edu/~manset/PolVert.gif

Figure 2.8: Vertical Polarization

2.9.2 Circular Polarization

If there is equal phase difference between two waves then there is circular polarization, either clockwise or anticlockwise. Wave moving in clockwise rotation is said to be left circularly polarized and the one propagating in counterclockwise rotation is right circularly polarized. Mathematically it is defined as

Ex = E1 sin (É·t – ᵝz) (2.7)

Ey = E2 sin (É·t – ᵝz + δ) (2.8)

E1 is the amplitude of wave linearly polarized in x direction.

E2 is the amplitude of wave linearly polarized in y direction.

δ is the phase difference.

http://www.cfht.hawaii.edu/~manset/PolCirc.gif

Figure 2.9: Circular Polarization

2.9.3 Elliptical Polarization

If two waves have unequal amplitude or phase then there is elliptical polarization.

graphic 1

Figure 2.10 (a): Graphical Representation of Elliptical Polarization

http://www.nsm.buffalo.edu/~jochena/images/elliptic2.gif

Figure 2.10 (b): 3-D view of Elliptical Polarization

2.10 Voltage Standing Ratio

VSWR is the ratio between maximum voltage and the minimum voltage. If there is a difference between load impedance and input impedance then there occurs reflection which causes instructive interference and destructive interference. Instructive and destructive interference produces maximum and minimum amplitudes respectively. Mathematical Expression for VSWR is

VSWR= (2.9)

http://www.microwaves101.com/encyclopedia/images/VSWR/waves5.jpg

Figure 2.11: Different Voltage amplitudes at different distances

2.11 Types of antennas

There are six different types of antennas [2].

Microstrip Patch Antenna

Lens Antenna

Wire Antenna

Array Antenna

Reflector Antenna

Aperture Antenna

2.11.1 Microstrip Patch Antenna

Microstrip patch antennas fall into the category of printed antennas [4]. A radiating patch is printed on a grounded substrate which is usually feed via a transmission line or coaxial cable. Patch can be of any shape and size i.e. circular, square, triangular or rectangular. Amongst all printed antennas i.e. Dipole, Slots, Tapered Slots antennas; Microstrip Patch Antennas are most famous. They are small in size, light in weight and low power consuming. But their bandwidths are smaller and have low gain. They are easy to integrate, good radiation control and cost of production is low. To increase bandwidth many techniques are used that is introducing slots and slits etc. They are used commercially in radars, wireless communications, satellites and mobiles etc.

Figure 2.12: Microstrip patch Antenna

http://images.books24x7.com/bookimages/id_22121/fig188_01.jpg

Figure 2.13 (a): Rectangular Patch Antenna (b): Circular Patch Antenna

Microstrip Patch antennas are used in Microwave frequency range. They are used in arrays to increase the bandwidth and gain and for other purposes.

http://www.antennamagus.com/database/antennas/99/Stacked_microstrip_patch_array-antenna_design.png

Figure 2.14: Array of rectangular patch antennas

2.11.2 Lens Antenna

Lens antennas are used to convert spherical radiated waves into plane waves in specific direction by using a source with microwave lens. It actually stops the divergent radiated energy to spread in undesired directions. These are mostly used for the high frequencies. A lens antenna may be of concave or convex shape. They are directional antennas and can scan wider angles. In comparison to reflectors; their gain is 1 or 2 dB less. Lens antennas may be constructed of non-metallic dielectrics or of metallic (artificial) dielectrics [5].

http://www.xibao-electronictech.com/images/product/2/210Lens-Antenna.gifhttp://telecom.esa.int/telecom/media/img/largeimage/WaveguideLensAntennaPrjObj_404.jpg

Figure 2.15 (a): Lens Antenna Figure 2.15 (b): Wave guide Lens Antenna

2.11.3 Wire Antenna

Wire antennas consist of a simple wire that is used to radiate electromagnetic energy. These wire antennas can be of different shapes. Most commonly used are straight wire antennas i.e. dipoles, loops and helix. Beside half-wave dipoles and quarter wave monopoles, wires of arbitrary lengths are often used to form antennas. Wire antennas can be vertical, horizontal or sloppy with respect to the ground. They may be fed from centre, at end or anywhere in between. The wires can be thick or thin, the radiation of antenna depends upon the thickness of the wire. Antennas with length larger than λ/2 are called Long-wire antennas.

Figure 2.16 (a): Wire Antennas (a) Figure 2.16 (b): Dipole Circular loop

2.11.4 Array Antenna

Array antennas are made up of more than one element basic of which is a dipole. Array antennas are the combination of radiating elements in such way that the radiation from these add up giving maximum or minimum radiation in a specific direction. They are used for higher directivity. They are made up of helices, dishes and other antennas. These elements are arranged to form broadside, end fire, collinear, driven and patristic arrays [5]. They are used in applications in which radiation cannot be achieved from single radiating element. They are low weight and low cost antennas. Examples of array antennas are Yagi-Uda,

http://www.tennadyne.com/images/tennlpdanavy.JPG

Figure 2.17: Log Periodic Dipole Array Antenna

2.11.5 Reflector Antenna

They are widely used to modify the radiation pattern of radiating elements. They are classified as active and passive reflectors. The active reflectors have corners made up of plane surfaces and they include periscopic antennas, flat-sheet reflectors and corner-reflector antennas. An active reflector may have corner elliptical, parabolic or spherical shape. Active reflectors include parabolic dish, truncated parabola, pill box etc. Reflectors are simple in design, involve only one surface and obey simple laws of optics. The applications of reflector antennas are radars and other point to point communication systems [5].

http://www.sameercal.org/images/reflector_antenna.jpg

Figure 2.18: A co-secant Reflector Antenna

2.11.6 Aperture Antenna

Aperture antenna is an important antenna for space communication. As the name suggests they consist of some cavity through which electromagnetic waves are transmitted or received. Apertures may be of any shape i.e. rectangular, circular or spherical. Larger the size of antenna larger will be the gain. Aperture antennas have to be placed carefully because they have narrow beam widths. Examples of aperture antennas include waveguides, reflectors horns, slots and lenses. Aperture antennas are commonly used in aircraft and spacecraft applications.

http://www.analyzemath.com/antenna_tutorials/introduction_3.gif

Figure 2.18: Horn Aperture Antenna

Chapter 3

Microstrip Patch Antenna and Feeding techniques

3.1 Introduction

Spaceships, aircrafts and other military applications such as missiles where important constraints to consider are performance, manufacturing expenditures, smooth profile and ease of installation and now a day’s other systems such as wireless communication requires similar type of specifications to consider . And the basic component which is required by these listed applications for transmission of instructions or data and to receive these instructions on the receiver end is “antenna”. Hence to meet the requirements listed above e.g. smooth profile, cost and performance etc Microstrip antennas are used.

Microstrip antennas are diminutive profile, conformable to planar and non-planar surfaces, easy and cheap to construct using the up to date printed circuit technology. Microstrip antennas have very flexible behavior to polarization, resonant-frequency, and impedance and radiation pattern. They are also used to increase the bandwidth. They consist of a ground plane over which a substrate is mounted and the radiating patch is mounted on the substrate. Generally the ground plane and the dielectric substrate have equal length and width. The Microstrip antennas are illustrated by the width, length and the height of the dielectric substrate which is sandwiched in between the ground plane and the radiating patch

3.2 Structural Configuration

The structural configuration of micro strip patch antenna is shown in figure

Figure 3.1: Structural Configuration of Patch Antenna

It consist of a thin (t<< λ) metallic radiating patch on one side of the dielectric material (substrate) and a ground plane on the other side of it as shown in above figure, the metallic radiating patch can be made from different materials like copper, silver or gold etc. it can be designed in different shapes like rectangle, square, triangle, elliptical etc. Patch antennas are characterized by the length width and height of the dielectric substrate as shown in figure

Figure 3.2: Side View of Patch Antenna

The length of the patch is usually λ/3 <L< λ/ 2 and the height is 0.003 ≤ h ≤ 0.05 above the ground plane. The range of dielectric constant is 2.2 ≤ ɛr≤12.

3.3 Formula for Rectangular Patch Antenna

To draw the width of the patch we use the formula

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(3.1)

And the length of the patch can be drawn as:

(3.2)

To reduce the fringing effects we use the following formula

∆L= 0.412h (3.3)

Here ∆L is the trimmed length from antenna.

(3.4)

3.4 Feeding Methods

Following feeding methods are most popular and are used with microstrip antennas

1. Microstrip line feed

2. Coaxial probe feed

3. Aperture coupled feed

4. Proximity coupled feed

5. Coplanar waveguide feed

These methods are either contacting or non-contacting. Contacting methods are those in which there is a direct contact between the transmission line and the radiating surface whereas in non-contacting methods, electromagnetic field coupling method is used to transfer the power.

3.4.1 Microstrip Line Feed

In this feeding method, the line feed is conducting strip of small width as compared to the patch. It is the easiest feeding method; easy to fabricate and simple to model. The radiating strip is placed at radiating patch’s edge and it is of the same material that is used for patch. If length of the strip is greater than the wavelength, losses will be generated. It can be reduced if the strip line has a substrate with high dielectric constant and low weight, so that the fields are confined to the strip line. A line feed of dimensions 17x3mm is used to obtain 50Ω input resistance.

Figure 3.1: Patch with Microstrip Line Feed

3.4.2 Coaxial probe feed

In coaxial probe feeds, coax inner conductor is attached to the radiating patch while the other conductor is connected to the ground plane. It is used widely. Its fabrication is easy and has low spurious radiation that is radiation outside the band frequency. It is has narrow bandwidth and it is hard to model for thick substrate. Matching also becomes difficult for thicker substrate because of increase length of probe make it more inductive, its inductance effect can be reduced by using a series of capacitors.

Figure 3.2: Patch with coaxial probe feed

3.4.3 Aperture coupling feed

It is the non-contacting feed. The two substrates are separated by ground plane in it. The microstrip feed line is on the bottom side of the lower substrate there is a; whose energy is coupled to the patch through a slot on the ground plane which separates the two substrates. A material with higher dielectricity is used for bottom substrate therefore, by this arrangement independent optimization of the feed mechanism and the radiating element can be carried out.

For top substrate a thick, low dielectric constant material is used. The ground plane between the two substrates isolates the feed from the radiating element and minimizes the interference. The configuration is shown in the figure

Figure 3.3: Patch with aperture coupling feed

Matching is performed by controlling the width of the feed line and the length of the slot. Amongst all four techniques this is the hardest to fabricate and has narrow bandwidth. It is somehow easy to model and has moderate spurious radiation.

3.4.4 Proximity coupling feed

In this feeding method, microstrip line is placed between two substrates and the radiating patch is placed on the upper substrate. This coupling is capacitive in nature. This coupling has the largest bandwidth as high as 13%. It is easy to model and has low spurious radiation. Its fabrication is somehow difficult. However, length of the stub help in improving the bandwidth, and width-to-line ratio of the patch can be used to control the match. The coupling feed is shown

Figure 3.4: Patch with Proximity Coupling Feed

3.4.5 Coplanar Waveguide Feed

This feeding technique is used when patch antenna is used in microwave monolithic integrated circuits (MMIC). The coplanar feed is fabricated on a ground plane and coupling is achieved through a slot. This feeding method reduces the radiation from feed structure because of its unusual method of coupled slot. Since CPW (coplanar waveguide) has many advantages such as low radiation leakage, less dispersion and small mutual coupling between two adjacent lines, which is helpful to place circuit elements close together without adding an additional layer of substrate, using CPW as the feeding structure to excite the patch antenna through a slot has become very popular recently. In addition, CPW structure can maintain constant characteristic impedance while varying its geometry, which provides a better impedance matching possibility

Figure 3.5: Patch with Coplanar Waveguide Feed

3.3 Categorization on the basis of bandwidth:-

On the basis of range of frequency bands, microstrip patch antennas can be categorized into three main classes which are:

antenna for narrow band applications

antenna for wide band applications

antenna for ultra wideband applications

Chapter 4

ULTRA WIDEBAND

4.1 Introduction

A series of very short baseband pulses with time duration in nano-seconds that exist on ALL frequencies simultaneously. Pulse repetition frequency (PRF) can range from hundreds of thousands to billions of pulses/second. Very low power: 41dbm/MHz (FCC) and wide bandwidth: 3.110.6 GHz

Modulation techniques include

pulse-position modulation

binary phase-shift keying

And

others

Radio technology that modulates impulse based waveforms instead of continuous carrier waves

4.1.1 Narrow band vs. Wide band signals

UWB could be used to Indoor, short-range communications for high data rates, OR Outdoor, long-range, but for very low data rates

4.1.2 Large Relative Bandwidth

UWB is a form of extremely wide spread spectrum where RF energy is spread over gigahertz of spectrum. Wider than any narrowband system by orders of magnitude. Power seen by a narrowband system is a fraction of the total.UWB signals can be designed to look like imperceptible random noise to conventional radios

4.1.3 Large Fractional Bandwidth

Large fractional bandwidth leads to High processing gain and Multipath resolution and low signal fading. Fractional Bandwidth is the ratio of signal bandwidth (10 dB) to center frequency: Bf = B / FC = 2(Fh-Fl) / (Fh+Fl)

4.1.4 Scalable Technology with Low Power

UWB benefits from basic information theory results when: Signal Bandwidth >> Data Rate .Power efficient low-order modulation can be used even for relatively high data rates.Data rates can scale independent of PRF by integrating bit intervals over multiple pulse intervals

4.1.5 Multipath Performance

Ultra-wide bandwidth provides robust performance in multipath environments .

4.1.6 UWB Data Rates

4.2 UWB channels

Indoor

Within a room (LOS & NLOS)

Investigates the impact of

Distance

Rx/Tx antenna heights

Antenna polarization

C:mat_dirsuwblimitsindoor5.tif

UWB Emission Limit for Indoor Systems

Outdoor

Campus environment

Low altitude

Mobility

C:mat_dirsuwblimitsoutdoor5.tif

UWB Emission Limit for Outdoor Hand-held Systems

4.3 Emission limits for UWB

UWB Emission Limits for GPRs, Wall Imaging, & Medical Imaging Systems.

Operation is limited to law enforcement, fire and rescue organizations, scientific research institutions, commercial mining companies, and construction companies.

UWB Emission Limits for Thru-wall Imaging & Surveillance Systems

4.4 Features of UWB :-

Ultra-short pulses

Baseband transmission

Low duty cycle operation

Low complexity of UWB transceiver

Precise ranging capability

Have very good time domain resolution allowing for location and tracking applications. Precise timing required to receive sub-nanosecond pulses presents the opportunity to precisely determine range between Tx. And Rx. In order of several centimeters

Capacity: a channel is linearly proportional to its bandwidth. UWB can go up to 2 Giga-Hz in bandwidth.

Simplicity: it’s essentially a base-band system (Carrier free), for which the analog front-end complexity is far less than that for a traditional sinusoidal radio.

Extremely low transmission energy ( less than 1mW)

Very high bandwidth within short range (200Mbps within 10m)

Extremely difficult to intercept

– Short pulse excitation generates wideband spectra – low energy densities

– Low energy density also minimizes interference to other services

Multipath immunity

Commonality of signal generation and processing architectures

Radar

– Inherent high precision – sub-centimeter ranging

– Wideband excitation for detection of complex, low RCS targets

Geolocation/Positioning

– Sub-centimeter resolution using pulse leading edge detection

– passes through building blocks, walls, etc. (LOS not required)

Low Cost

– Nearly “all-digital” architecture

– ideal for microminiaturization into a chipset

Frequency diversity with minimal hardware modifications

4.5 merits of UWB

Resilient to distortions and fading (Great for indoor usage)

High information redundancy and frequency diversity provides protection against multi-path distortion

Low power

Transmitting at microwatts (one tenth thousandth power of cell phone) results in very low harmful interference to other radio systems. Usually below the noise floor and undetectable

Longer battery life for mobile devices

Simplicity translate to lower hardware cost

Security

UWB is inherently secure: Only a receiver that knows the schedule of the transmitter can assemble the apparently random pulses into a coherent message

High data capacity

Multiple Access provided by time hopping scheme. Can support close to 30,000 users at 19.2kbps

4.6 Demerits of UWB

Interference with GPS

Global positioning satellite currently have more than 10 million users and it’s primarily applications are used for the safety of public. (I.e. aircraft flight and approach guidance.) UWB presents a problem to GPS because their frequency overlaps, and GPS signal is particular sensitive to interference

Limited on range

Output power is limited due to its overlapping frequency bandwidth with other radio systems

One kilometer with high gain antenna

Ten to twenty meter with regular antenna

Affects on economy and current businesses

Speculations on UWB making current billion dollar FCC licensed frequencies worthless

Increased competition for local cable or phone company. Making their existent investments on cable and equipments obsolete

4.7 Challenges for UWB

Wide RF Bandwidth Implementation

In-Band Interference

Signal Processing Beyond Current DSP (today requires analog processing)

Global Standardization

Broadband Non-resonant Antennas

4.8 UWB applications

Wireless Communication Systems

LAN & PAN

Roadside info-station

Short-range radios

Military communications

defense tracking and vehicle speed detection for law enforcement

Radar & Sensing

Vehicular radar

Medical imaging

Surveillance

High data rate (HDR) is the most basic application provided by this band.

weather monitoring

air traffic control.

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maritime vessel traffic control

4.9 Related standards

UWB is complementary to other radio technologies in existing 802 standards

IEEE 802.15 : Wireless Personal Area Network (WPAN)

IEEE 802.15.1 : Bluetooth, 1Mbps

IEEE 802.15.3 : WPAN/high rate, 50Mbps

IEEE 802.15.3a: WPAN/Higher rate, 200Mbps, UWB

IEEE 802.15.4 : WPAN/low-rate, low-power, mW level, 200kbps

4.10 UWB Advocators

Intel

Time Domain Corp

Siemens invested 5 million in Time Domain

Qwest bought 5% of time domain

Motorola

Siemens

IBM

Sony

Æther Wire & Location (USA)

Pulse-Link (USA)

MultiSpectral Solutions, Inc (MSSI) (USA)

XtremeSpectrum (USA)

McEwan Techologies

Wisair (Israel

4.10.1 UWB Contesters

Sprint PCS (PCS )

US Department of Defense and the airline industry

4.11 Future of UWB

Manny engineers’ and researchers are attracted towards UWB technology due to its advantages, high transmitting data rate and low power consumption. But the premature developments in UWB lacked performance, cost too much and had compatibility issues with worldwide standards which have been topic to much debate and clash. In addition to them, representative companies leading towards the UWB technology run out of funding and shut the doors because of the economic drawbacks which lead UWB industry go downhill. However, all the new technologies suffer the growing pains. UWB communications are the probable candidates for WPAN as they are five times faster than Wi-Fi, 10 times more power efficient and superior user density plus there is no superior technology to transfer media content wirelessly, at high-speed and low-power. Thus, In the future, UWB technology will be applied to several fields such as stealth, LAN, position location, security and vehicular radar system and wireless USB’s.

CHAPTER 5

CPW Feedline Background and Theory

Basic concept and theory for CPW-Fed microstrip patch antennas is described in this chapter. In addition advantages of coplanar waveguide are discussed along with important literature review.

5.1 CPW-Fed Microstrip Patch Antennas

Microstrip antennas have found extensive applications for microwave as well as millimeter wave systems. On the other hand coplanar line is gaining an increasing interest for components including active devices, especially Monolithic Microwave Integrated Circuits (MMICs). Coplanar line helps avoiding via hole connections by allowing the apprehension of series as well as shunt connections. Moreover, the substrate can be relatively thick. This fact, on the other hand, matches well with good efficiency and improved bandwidth of microstrip antennas integrated on the same substrate.

5.2 Advantages of Coplanar Waveguide Feedline

Some of the advantages of CPW Feedline are as follow

Active devices can be mounted on top of the circuit, like on microstrip.

It can provide extremely high frequency response (60GHz or more).

It simplifies fabrication

Connecting to CPW does not entail any parasitic discontinuities in the ground plane.

Immediate access to adjacent power planes provides shorter power delivery

CPW gives lower conductor losses and dispersion

5.3 Innovational shapes of UWB Antennas

Various types of UWB antennas have been suggested and implemented via transmission line [4] and coplanar waveguide [8]. Some of the innovational designs of CPW-Fed microstrip patch antennas for UWB applications have been presented in different research papers which are given in the figure given below.

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Figure 2.17: The CPW-Fed UWB Antennas

Miniaturization is the major issue in all of the above mentioned antennas. As we know that the need for compact antennas has greatly increased with the recent advances in telecommunication industry. Due to the development of integrated circuits electronic equipment has rapidly reduced in physical size, especially in mobile communications; the demand for the miniaturize antennas is quite strong. However, small equipment requires severe antenna performance, since the antenna performance should not be significantly despoiled as the size become compact.

CHAPTER 6

Design and Simulation Analysis

6.1 Introduction

This chapter describes the Design of the proposed antenna presented in this project, followed by its results and analysis. Several corner truncation schemes were simulated before achieving the designed shape of microstrip patch antenna. The basic antenna structure consists of a rectangular patch. The corners of the rectangular patch are truncated to reduce the size and to enhance the bandwidth of the proposed antenna. After achieving the best possible results by truncating all four corners from the patch two slits each have been added in the square truncated corners to further widens the bandwidth suitable for UWB applications. Simulated return loss of the proposed antenna clearly indicates that the impedance bandwidth of the antenna is 15.65 GHz (3.1 GHz – 18.75 GHz) for a return loss less than -10 dB.

6.2 Steps Sequence

Design methodology is shown by steps sequence. Proposed antenna is achieved after truncating all corners from the patch. Each step along with their simulated return loss is as follow.

6.2.1 Step1

The first step is to simulate conventional shape of rectangular Microstrip patch antenna as shown in Fig 3. Finite coplanar ground plane is adjusted accordingly to achieve the best possible results for UWB applications.

Figure 4: Circular Corner Truncation

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Figure 4: Circular Corner Truncation

Simulated return loss achieved by simulating the above rectangular patch indicates that the bandwidth of antenna is 6.75GHz (3.1GHz – 9.85GHz). In order to achieve the band defined by FCC we further have to apply some techniques which in our case is the corner truncation.

6.2.2 Step 2

Circular truncation of the corners is the second step. A circle of radius 1.8mm is subtracted from the upper right and lower left corner of the patch as shown in the Fig 4 along with the simulated return loss in Fig 4a.

Figure 4: Circular Corner Truncation

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Figure 4a: Simulated Return Loss

In this step each corner was truncated one by one and along with different combinations at all four corners at the same instant. Optimized shape is achieved after the comparison of all the circular corner truncations. It is clear from the above plot that circular truncation of corners clearly widens the band ranging from 3.1GHz – 11.02GHz

6.2.3 Step 3

Square truncation of the corners is the third step. A square with the dimensions of 1.8mm x1.8mm is subtracted from the upper left and lower right corner of the patch as shown in the Fig 5 along with the simulated return loss in Fig 5a

Figure 5: Square Corner Truncation

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Figure 5a: Simulated Return Loss

Different dimensions of the square truncation were simulated before achieving the optimized shape. Considerable enhancement in the bandwidth is realized after the truncation of corners via square i.e. 3.1GHz – 14.90GHz.

6.2.4 Step 4

After implementing the circular and corner truncation schemes, pair of slits has been introduced in the square truncated corners which further widen the bandwidth up to 15.65GHz ranging from 3.1GHz – 18.75GHz.

Figure 6: Introducing Slits

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Figure 6a: Simulated Return Loss

The simulated return loss of the proposed antenna with final optimized dimensions by truncating all four corners from the patch is shown in Figure 6a. The return loss characteristic of the corner truncated patch antenna shows that impedance bandwidth extends up to 15.65GHz (3.1GHz – 18.75 GHz) which is more than the ultra wide bandwidth as defined by FCC [1].

6.3 Radiation Patterns

The simulated far field radiation pattern of the designed antenna in xy, xz and yz plane at five different frequencies 3.11GHz, 5.20GHz, 5.80GHz, 9.46GHz and 15.40GHz are given below. It is noticed that the radiation pattern is omni-directional in H plane and bi-directional in E-plane.

6.3.1 At 3.11GHz

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6.3.2 At 5.20GHz

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6.3.3 At 5.80GHz

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6.3.4 At 9.46GHz

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6.3.5 At 15.40GHz

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CHAPTER 7

Fabrication and Measured Results

In this chapter we will discuss the fabrication procedure that we adopted to manually fabricate our proposed antenna design. Later measured results taken with the help of Network Analyzer will be presented along in comparison with the simulated results.

CHAPTER 8

Conclusion and Future Work

8.1 Conclusion

Wideband microstrip patch antennas are very important for modern applications, but their large size is a major issue. The problem was solved by proposing a miniaturize microstrip patch antenna designed on Rogers RT/duroid 5880 substrate with corner truncation schemes to provide 15.65GHz of bandwidth suitable for UWB applications. The proposed antenna was first simulated using HFSS 11 and the results were later verified using Network Analyzer. The simulated and measured results prove that the designed antenna has compact structure, wide impedance bandwidth and appropriate gain characteristics within UWB frequency range. The Ultra Wide Band microstrip patch antenna designed is applicable in 802.16 standards, MAVCAS, Amateur Radio, Radar SART, Bluetooth etc.

8.2 Future Work

The antenna mentioned in this thesis can be further modified and improved by using several techniques such as.

FCC defined band for UWB lies in the frequency range 0f 3.1-10.6 GHz. Whereas the WLAN IEEE 802.11 operates at 5.1-5.825 GHz. Moreoverb3.5 GHz band is operational for some other networks such as fixed broad wideband access. This can cause interference between the two operating bands. In order to overcome this issue, the frequency range which causes interference should be rejected. For this purpose a band reject filter can be designed. Several band notched filters can be implemented using techniques such as parasitic patches, slot ring resonators, inserting inverted L and C shaped slots in the patch [13-16].

Another modification can be made in this design to overcome the fading effect by using the antenna diversity. It can be achieved by integrating multiple antennas in mobile terminals and then combining the received signal. This results in high data rate transmissions over wireless communication systems [17, 18].

UWB antennas can be designed on PIFA materials which are used in electronic devices.

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