KYAMBOGO
UNIVERSITY
FACULTY OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
COURSE UNIT: PRINCIPLES OF COMMUNICATIONS SYSTEMS
COURSE CODE: 2102
LECTURER: MR.MAITEKI BENJAMIN
GROUP ONE MEMBERS
NAME
KASOZI DAVID PAUL
ATENIA JOEL
SSEGAWA MARK RAYMOND
SUUBI MARIA
KAGIRI MOHAMMED MPIIMA
REGISTRATION NUMBER
20/U/ODT/8377/PE
20/U/ODT/8369/PE
20/U/ODT/8379/PE
20/U/ODT/8385/PE
20/U/ODT/8381/PE
SIGNATURE
Questions
1. Describe the different basic antenna parameters?
2. Briefly describe the different types of antenna arrays, stating the advantages, disadvantages
and application of each type?
3. Briefly describe what is meant by the term resonators in relation to wave propagation and give
the different types of resonators?
SOLUTIONS
1.ANTENNA PARAMETERS
In order to describe the performance of an antenna, we use various, sometimes
Interrelated, parameters. These include;
1)
2)
3)
4)
5)
6)
7)
8)
Radiation Pattern
Beam width
Antenna Efficiency and Gain
Effective Area
Polarization
Radiation Intensity
Directivity
Radiation Power Density
1. Radiation Pattern
Antenna Radiation Pattern: An antenna radiation pattern or antenna pattern is defined as a mathematical
function or a graphical representation of the radiation properties of the antenna as a function of space
coordinates.
• Defined for the far-field.
• As a function of directional coordinates.
• There can be field patterns (magnitude of the electric or magnetic field) or power patterns (square of the
magnitude of the electric or magnetic field).
• Often normalized with respect to their maximum value
The power pattern is usually plotted on a logarithmic scale or more commonly in decibels (dB).
Radiation patterns are conveniently represented in spherical coordinates. Pattern:
E(µ,Á).
All three patterns yield the same angular separation between the two half power
points, 38.64±, on their respective patterns, referred to as HPBW.
Radiation Pattern Lobes
A radiation lobe is a portion of the radiation pattern bounded by regions of relatively weak radiation
intensity.
• Main lobe
• Minor lobes
• Side lobes
• Back lobes
Minor lobes usually represent radiation in undesired directions, and they should be minimized. Side lobes
are normally the largest of the minor lobes.
The level of minor lobes is usually expressed as a ratio of the power density, often termed the side lobe
ratio or side lobe level.
In most radar systems, low side lobe ratios are very important to minimize false target indications
through the side lobes (e.g., -30 dB).
Components in the Amplitude Pattern
• There would be, in general, three electric-field components (Er ,Eµ,EÁ) at each observation point on the
surface of a sphere of constant radius.
• In the far field, the radial Er component for all antennas is zero or vanishingly small.
• Some antennas, depending on their geometry and also observation distance ,may have only one, two, or
all three components.
• In general, the magnitude of the total electric field would be
Isotropic, Directional, and Omnidirectional Patterns
1. (Isotropic Radiator). A hypothetical lossless antenna having equal
radiation in all directions.
2.(Omnidirectional Radiator). An antenna having an essentially non directional
pattern in a given plane (e.g., in azimuth) and a directional pattern in
any orthogonal plane.
3.(Directional Radiator). An antenna having the property of radiating
or receiving more effectively in some directions than in others. Usually the
maximum directivity is significantly greater than that of a half-wave dipole.
2 Beam width
The beam width of an antenna is a very important figure of merit and often is used as a trade-off between
it and the side lobe level; that is, as the beam width decreases, the side lobe increases and vice versa.
• The beam width of the antenna is also used to describe the resolution capabilities of the antenna to
distinguish between two adjacent radiating sources or radar targets.
 (Half-Power Beam Width (HPBW)). In a plane containing the direction of the maximum of a
beam, the angle between the two directions in
which the radiation intensity is one-half value of the beam.
 (First-Null Beam width (FNBW)). Angular separation between the first nulls of the pattern.
Resolution
• The most common resolution criterion states that the resolution capability of an antenna to distinguish
between two sources is equal to half the first-null beam width (FNBW/2),which is usually used to
approximate the HPBW.
• That is, two sources separated by angular distances equal or greater than
FNBW/2 ¼ HPBW of an antenna with a uniform distribution can be resolved.
• If the separation is smaller, then the antenna will tend to smooth the angular
separation distance.
3.Efficiency and Gain
Antennas are subject to physical losses, just like any other electrical device. These can take the form
of leakage current through dielectrics and resistance losses in imperfect conductors. The efficiency of
an antenna is defined as the radiated power divided by the power delivered to the antenna:
Thus, if the antenna has 95% efficiency and 100W is being delivered to the antenna, then 95W will
be converted into electromagnetic radiation.
The gain of an antenna is a measure of how much of its input power is converted into a directed
beam. The gain is calculated as the product of the efficiency and the directivity
Since the efficiency of an antenna can take on any value between 0 and 1, and the directivity can take
on any value greater than or equal to one, the gain can be any positive value.
4.Effective Area
The effective area of an antenna (also known as the aperture) is an important parameter for a
receiving antenna. It is a measure of how effectively the antenna converts from electromagnetic
radiation (measured by SAV) to electrical power available at its output terminals (P L). It is defined
mathematically as:
The effective area can be calculated from the directivity and wavelength as:
Allowing for imperfect conductors and insulators in the antenna, we can rewrite the above
equation to use gain (which includes efficiency) rather than
directivity
5.Polarization
Polarization is the curve traced by the end point of the arrow (vector) representing the instantaneous
electric field. The field must be observed along the direction of propagation.
• Polarization is classified as linear, circular, or elliptical.
• If the vector that describes the electric field at a point in space as a function of time is always directed
along a line, the field is said to be linearly polarized.
• In general, the figure that the electric field traces is an ellipse, and the field is said to be elliptically
polarized
Polarization Types
• Linear polarization and circular polarization are special cases of elliptic polarization
.
• Polarization can be clockwise (CW, right-hand polarization), or counter clockwise (CCW, left-hand
polarization).
2. ANTEENA ARRAYS
An antenna array is group of antennas connected and arranged in a regular structure to form a single
antenna that is able to produce radiation patterns not produced by individual antennas. Antenna arrays
are groups of isotropic radiators of electromagnetic frequency and energy.
Furthermore; An antenna array can be defined as is a set of multiple connected antennas which work
together as a single antenna, to transmit or receive radio waves. The individual antennas are usually
connected to a single receiver or transmitter by feed lines that feed the power to the elements in a
specific phase relationship.
PHASED ANTENNA ARRAYS
Phased array antennas are a type of antenna array that comes with the feature of electronic
steering to change the direction and shape of radiated signals, without any physical movement of
the antenna. The phase difference between the radiated signals from each antenna in the array is
responsible for this electronic steering.
The fundamental principle of the phased array antenna is the phase-dependent superposition of
two or more radiated signals. When the signals are in-phase, they combine together to form a
signal of additive amplitude. When the signals are counter phase, they cancel each other.
Phased array antennas, these include multiple emitters and are used for beam forming in high frequency
applications
The three types of phased array antennas are
1) Linear array
2) Planar array
3) Frequency scanning array.
1. Linear Array: The array elements are placed in a straight line with a single-phase shifter.
Even though the antenna arrangement is simple, the beam steering is limited to a single
plane. The vertical arrangement of several linear arrays forms the flat antenna.
2. Planar Array: For each antenna in a planar array, there is a phase shifter. The matrix
arrangement of the individual antennas form the planar arrangement. The beam can be
deflected in two planes. The disadvantage of planar array antennas is the large number of
phase shifters required.
3. Frequency Scanning Array: If the beam steering control is a function of the frequency of
the transmitter, then phased array antennas utilizing such technology are called frequency
scanning array antennas. No phase shifters are present in frequency scanning array
antennas, and the beam steering is controlled by the transmitter’s frequency.
Advantages of Phased Array Technology
Beam forming with phased array antennas is necessary at high frequencies (approximately WiFi
frequencies and higher) to overcome losses during transmission. With an appropriately sized
phased array antenna, radiation from high gain emitters can be directed over a broad solid angle.
Phased array technology has helped enhance the characteristics of the collective signal or
radiation pattern. Features of individual signals from the radiator and the collective signal from
phased array antennas are like separated poles. The enhancement in various parameters and
quantities upon arraying can be summarized as follows:
a. Power—the power of the collective signal is the summation of the individual signal
powers, therefore, the strength is increased.
b. Beam forming—the shape of the beam can be controlled by the phase difference of the
individual signals and the radiation pattern of the phased array antenna is narrow
compared to single antennas.
c. Beam Steering—the elimination of mechanical repositioning makes the beam steering or
beam positioning flexible. The beam steering is established using electronically variable
phase shifters.
d. Multi-Beams—with the help of phase shifters, hundreds of beams can be synthesized in
phased array antennas.
e. Digital or Mixer Option—phase shifting can be achieved either in an analog or digital
way. The analog phase shifters rely on down-conversion and time-shifting of signals. The
digital approach is to shift the phase of the Intermediate Frequency (IF) mixer or Local
Oscillator (LO) signal.
f. Weight—the weight of phased array antennas is less than the mechanically-steered single
antenna.
g. Cost—a mechanically-steered antenna can be replaced by a less expensive phased array
antenna, keeping the resolution the same.
h. Reliability—the reliability of phased array antennas is much greater than single antennas.
If one array antenna becomes impaired, the remaining antennas in the array will continue
to function with a slight modification of the radiation pattern.
Disadvantages of phased antenna arrays
1.
2.
3.
4.
5.
6.
Limited scanning range (up to max. 120° in azimuth and elevation)
Deformation of the antenna pattern during beam steering
Low frequency agility
Very complex structure (computer, phase shifter, data bus to each radiator)
High costs (still)
Note: the limitation of the scanning range can be overcome with a three-dimensional radiator
distribution.
The other basic types of arrays are −
1.
2.
3.
4.
5.
6.
7.
8.
Collinear array
Broad side array
End fire array
Parasitic array
Yagi-Uda array
Log-peroidic array
Turnstile array
Super-turnstile array
1.Collinear array consists of two or more half-wave dipoles, which are placed end
to end. These antennas are placed on a common line or axis, being parallel or collinear.
The maximum radiation in these arrays is broad side and perpendicular to the line of
array. These arrays are also called as broad cast or Omni-directional arrays.
Frequency range
The frequency range in which the collinear array antennas operate is around 30 MHz to
3GHz which belong to the VHF and UHF bands.
Construction of Array
These collinear arrays are uni-directional antennas having high gain. The main purpose
of this array is to increase the power radiated and to provide high directional beam, by
avoiding power loss in other directions.
The above images show the pictures of collinear arrays. In figure 1, it is seen that collinear array
is formed using folded dipoles, while in figure 2, the collinear array is formed by normal dipoles.
Both types are half-wave dipoles used commonly.
Radiation Pattern for Collinear arrays
The radiation pattern of these collinear arrays is similar to that of a single dipole, but the array
pattern of increasing number of dipoles, makes the difference.
The radiation pattern of collinear array when made using two elements, three elements and four
elements respectively are shown in the figure given above.
Advantages of collinear antenna array
The following are the advantages of collinear array antennas −
1) Use of array reduces the broad ends and increases the directivity
2) Minor lobes are minimised
3) Wastage of power is reduced
Disadvantages of collinear antenna array
The following are the disadvantages of collinear array antennas −
1) Displacement of these antennas is a difficult task
2) Used only in outdoor areas
Applications of collinear antenna array
The following are the applications of collinear array antennas −
1) Used for VHF and UHF bands
2) Used in two-way communications
3) Used also for broadcasting purposes
Broad-side Array
The antenna array in its simplest form, having a number of elements of equal size, equally
spaced along a straight line or axis, forming collinear points, with all dipoles in the same phase,
from the same source together form the broad side array.
Frequency range
The frequency range, in which the collinear array antennas operate is around 30 MHz to 3GHz
which belong to the VHF and UHF bands.
Construction & Working of Broad-side Array
According to the standard definition, “An arrangement in which the principal direction of
radiation is perpendicular to the array axis and also to the plane containing the array element” is
termed as the broad side array. Hence, the radiation pattern of the antenna is perpendicular to
the axis on which the array exists.
The following diagram shows the broad side array, in front view and side view, respectively.
The broad side array is strongly directional at right angles to the plane of the array. However, the
radiation in the plane will be very less because of the cancellation in the direction joining the
center.
The figure of broad side array with λ/4 spacing is shown below.
Typical antenna lengths in the broad side array are from 2 to 10 wavelengths. Typical spacings
are λ/2 or λ. The feed points of the dipoles are joined as shown in the figure.
Radiation Pattern
The radiation pattern of this antenna is bi-directional and right angles to the plane. The beam is
very narrow with high gain.
The above figure shows the radiation pattern of the broad side array. The beam is a bit wider and
minor lobes are much reduced in this.
RESONATORS
A resonator is a device or a system that exhibits resonance or resonant behavior that is naturally
oscillates with greater amplitude at some frequencies called resonant frequencies than at other
frequencies. The oscillations in a resonator can either be electromagnetic or mechanical
Types of Resonators Used Across the RF/Microwave Universe
Resonators are key to the performance of a range of RF/microwave components, such as oscillators and
filters.
The types of available resonators include
1.
2.
3.
4.
5.
6.
Coaxial
Dielectric
Crystal
Ceramic
Surface acoustic wave (SAW)
Yttrium iron garnet (YIG)
Given this variety, it is essential for designers to understand the characteristics of the various
resonators.
A. Coaxial Resonators
Coaxial resonators are commonly used to design components like voltage-controlled oscillators (VCOs),
coaxial-resonator oscillators (CROs), and filters. This form of resonator is essentially a ceramic coaxial
line. Often, coaxial resonators are implemented in oscillators as high-quality-factor (high-Q) inductors,
thereby creating a resonant circuit when paired with a capacitor or varactor diode. A coaxial resonator
has an outer conductor with an approximately square-shaped cross-section and a cylindrical center
conductor.
Coaxial resonators have two different forms:
a) Quarter-wavelength (λ/4) resonator with one end shorted and the opposite end open;
b) Half-wavelength (λ/2) resonator with both ends open.
A coaxial resonator’s material has a high dielectric constant (εr) value, components designed with them
can be reduced in size. Typical εr values range from 10 to 100.
Ceramic coaxial resonators are offered by companies like Integrated Microwave Corp.
These resonators are intended for a range of applications, including oscillators, bandpass/bandstop
filters, and electromagnetic-interference (EMI) filtering. They can be used to satisfy frequency
requirements ranging from 200 MHz to 10 GHz. Customers can select from nine different sizes, which
range from 2 to 18 mm. In addition, IMC offers the resonators in five different materials.
For its part, Trans-Tech offers a line of coaxial resonators that are intended to serve as ceramic coaxial
line elements. They are available in seven sizes and four εr values. The company offers these resonators
for applications that span from ultra-high frequency (UHF) to 6 GHz.
Ceramic coaxial resonators are also offered by Tusonix. The company offers these products in four sizes
and four εr values. They cover 800 MHz to 5.9 GHz. Their intended applications include oscillators,
filters, and duplexers.
Temex Ceramics offers a product line of coaxial resonators intended for telecommunications, military
and space, industrial, and wireless applications. The resonators are offered for applications from 300
MHz to 6 GHz. In addition, selections can be made from different sizes along with several εr values.
B. Dielectric Resonators
A dielectric resonator can be used to replace resonant cavities in components, such as filters and
oscillators. It is typically a disc-shaped material with a high εr value. This high εr value provides a
significant advantage, enabling the size of a circuit designed with a dielectric resonator to be
significantly smaller than when an air-filled cavity resonator is employed. Electromagnetic fields are
largely confined within a dielectric resonator, allowing radiation losses to be extremely small and a high
quality-factor (Q) to be achieved
Although a dielectric resonator will resonate in several modes, the TE01δ (transverse-electric) mode is
most commonly used in many applications. When operating in this mode, a dielectric resonator may be
magnetically coupled to a circuit by several different methods. One method is to couple the resonator to
a microstrip line. This approach can be used to create components like dielectric-resonator oscillators
(DROs).
One company offering dielectric resonators is MCV Microwave. These components are typically used in
oscillators, satellite-based communication equipment, microwave filters, and combiners. They can be
selected for applications spanning 260 MHz to 26 GHz.
In addition to their line of coaxial resonators, Temex Ceramics offers a selection of dielectric resonators.
They are intended to be used for applications like telecommunication infrastructures, alarms/detection,
military and space, and automotive. The resonators cover 800 MHz to 50 GHz. They are available in six
different materials.
Dielectric resonators are also offered by Trans-Tech for both commercial and military applications.
Among their applications are cellular base station filters and combiners, direct broadcast satellite (DBS)
receivers, and motion detectors. They are intended for applications ranging from below 850 MHz to
above 32 GHz.
C. Crystal Resonators
Quartz crystals can be used as high-quality electromechanical resonators. Their piezoelectric properties
allow them to be used as frequency-control elements in crystal oscillators. Quartz crystals offer high Q
and superior frequency stability. In fact, their high Q is the main reason why crystal oscillators are often
employed instead of LC oscillators.
Piezoelectric materials have the capability to convert mechanical energy into electrical energy and vice
versa. When a mechanical stress is applied, an electric charge is generated. This electric charge is
proportional to the applied mechanical stress. The same material becomes strained when an electric
field is applied.
In a quartz crystal resonator, a thin slice of quartz is placed between two electrodes. This quartz slice is
obtained by cutting the original material at specific angles in regard to the various axes, which
determines the resonator’s physical and electrical parameters. Thus, a quartz crystal can be classified by
the manner it was cut from the original material. Resonators can be generated from a variety of cuts,
such as the widely used AT- and SC-cuts.
According to IQD Frequency Products, when the frequency of an applied voltage approaches one of the
mechanical resonance frequencies of the quartz slice, the amplitude of the vibrations becomes very
large. The accompanying displacement current also increases, which decreases the magnitude of the
device’s effective impedance. Thanks to the impedance’s rapid change as the frequency varies near
resonance, quartz crystal resonators can be used as frequency-control elements in crystal oscillators.
As an example, IQD Frequency Products offers a range of quartz crystals spanning 10 kHz to 250 MHz
with frequency stability as low as ±5 ppm. High-specification AT-cut quartz crystals are also offered,
providing a fundamental mode frequency from 10 to 42 MHz. In addition, the company offers crystals
for automotive applications.
D. Ceramic Resonators
Ceramic resonators are a viable alternative to quartz crystals. Although they are less accurate than
quartz crystals, ceramic resonators do offer other benefits. For instance, they can be manufactured in
smaller packages and at lower costs. In addition, they provide a lower start-up time than quartz crystals.
Ceramic resonators utilize the mechanical resonance of piezoelectric ceramics, such as lead zirconium
titanate (PZT). Two metal electrodes are evenly placed on both the top and bottom of the ceramic
substrate. When a voltage is applied, the substrate vibrates between the electrodes. The resonant
frequency is determined by the substrate’s thickness. A ceramic resonator’s equivalent electric circuit is
identical to a quartz crystal. Because its operation is similar to a crystal, it can be used in the same
oscillator configurations.
For example, Murata offers the CERALOCK Series ceramic resonators. These products are intended for
arrange of applications including automotive electronics, communications, personal computing, and
medical/healthcare equipment.
Other suppliers of ceramic resonators include


Oscilent
Abracon.
E. Saw Resonators
A surface acoustic wave (SAW) that is propagating at the surface of a piezoelectric crystal can be used to
carry information. A basic SAW resonator consists of an interdigital transducer and two grating
reflectors, which are fabricated on a piezoelectric material by a photolithographic process. The
reflectors form a resonant cavity, which the transducer couples to the external circuit. Like crystal
resonators, SAW resonators can be used to build oscillators—often in higher-frequency applications.
They can also be used to build bandpass filters, such as those offered by Qorvo, Phonon, and Vectron, to
name a few. The crystal resonator’s equivalent LC circuit takes the same form. Automotive remotekeyless-entry (RKE) devices, security systems, and garage door openers are some examples of consumer
commandproducts that commonly use SAW resonators.
As an example, ECS Inc. International offers a variety of SAW resonators. They are available in both
surface-mount and through-hole packages. The company offers these SAW resonators for wireless
security and remote control applications.
A portfolio of SAW resonators from Murata spans 300 MHz to 1 GHz while achieving center frequency
tolerances as low as ±50 kHz. The resonators are available in a variety of packages. In addition, Abracon
offers a line of SAW resonators covering 117.2 to 916.5 MHz. These products are intended for
applications like wireless remote controllers and mobile communications. They are available in both
surface-mount and through-hole packages. Lastly, a range of SAW resonators covering 100 MHz to 1.1
GHz is offered by Golledge Electronics.
F.YIG Resonators
Yttrium iron garnet (YIG) resonators can be used to design oscillators and filters. A YIG is a crystal that
has a very high Q, enabling oscillators to be designed with very low phase noise. Multi-octave
bandwidths are another benefit than can be achieved by using YIG resonators.
YIGs are most often used in a sphere configuration. However, other shapes have also been used over the
years. A YIG will resonate at microwave frequencies when it is immersed in a direct-current (DC)
magnetic field. This resonance is directly proportional to the strength of the applied magnetic field,
which is generated using an electromagnet, a permanent magnet, or a combination of both.
A number of YIG-based products are offered by Micro Lambda Wireless. That company’s YIG-tuned
oscillators cover 500 MHz to 44 GHz with output power levels that range from 0 to +23 dBm. The
company also offers a line of YIG-tuned filters that span 500 MHz to 50 GHz.
In summary, a wide range of resonators is available from a plethora of suppliers. With many potential
applications, it is important to have an understanding of the different varieties and how they can be
implemented in a design. Each type of resonator is well suited for different applications, which prompts
the need to understand the performance characteristics offered by each resonator type.