Advanced Communications: Wireless Comms

-Point-Contact diode -Schottky barrier (or Hot-carrier) diode -Varactor Diode -Gunn Diode -IMPATT and TRAPATT -Tunnel Diode

Types of Semiconductor Diodes

Cellular Telephone Systems Data Communications and Networking Microwave Radio Communications Satellite Communications

Types of Wireless Communications

Two-cavity klystron amplifier reflex klystron

Types of klystron amplifier

20 to 60 degrees.

Typical flare angles vary from ___________

Vacuum tubes

devices used for controlling a large signal with a smaller signal to produce amplification, oscillation, switching, and other operations.

Pyramidal Horn

flaring both dimensions of the horn

Sectoral Horn

flaring the waveguide in only one direction.

Schottky diode semiconductor metal

has a metal semiconductor junction, mostly of them are made with N-type silicon on which has been deposited a thin metal layer. It is ideal for mixing, signal detection, and other low level signal operations. Widely used in balanced modulators and mixers. The ______________ forms the cathode, and the _________forms the anode

Traveling Wave Tube

has extremely wide bandwidth of operation and not resonant in single frequency. consists of a cathode and filament heater plus an anode that is positively biased to accelerate electron beam forward into a narrow beam, applied by very high DC voltage

Microwave signals 1 cm and 60 cm

has relatively short wavelength, and ranges between __cm and __cm

terminal stations

in microwave radio link diagram, the Information originates and terminates at the _____________

Repeaters

in microwave radio link diagram, the _________ simply relay the information to the next downlink microwave station.

interaction chamber

in the center if magnetron circular anode is ___________ which is a circular cathode that emits electrons when heated.

electrons

in two-cavity klystron amplifier, at very high temperature the cathode emits ___________

no energy is propagated

in waveguides, at the cut-off frequency and below _________________

Step-recovery diode or Snap-off varactor

is a PN junction diode made with gallium arsenide or silicon.

Tunnel Diode

is a negative resistance diode. It produces a narrow range of negative resistance when forward-biased.

Teflon

is used as the base for some PCBs in microwave applications.

RADAR

it is a method of detecting the presence of distant object and determining its distance and direction.

gunn diodes

klystrons are replaced by __________ because they are smaller, lower in cost and doesnt require high dc voltage

electromagnetic focusing

makes use of coils around the tube through which current is passed to produce magnetic field

Long-Haul

microwave systems used to carry information for relatively long distances such as interstate and backbone route applications

Klystron Magnetron Traveling-wave tubes (TWT)

microwave tubes still widely used today

Klystron

microwave vacuum tube using cavity resonators to produce velocity modulation of the electron beam and produce amplification.

density modulation

modulation produced in TWT and causes bunch if electrins to group together one wavelength apart

Satellite transponders

most common application of TWTs is as power amplifier in _______________

operating mode

pattern of the electromagnetic fields within a waveguide takes many forms and called as

Conical Horn

produced when a circular waveguide is flared

permanent magnet or electromagnet

surrounds the tube within TWT that keeps electrons tightly focused in narrow beam

Cathode repeller plate

the _________ of a reflex klystron emits electrons which accelerates forward by accelerating grid with a positive voltage on it and focused into narrow beam and undergoes velocity modulation and creates bunches of electrons. the bunches of electrons then move toward the _______ which is made negative.

frequency of operation

the _____________ of a klystron is set by sizes of the input and output cavities

fast switches

Because of their very high frequency response, Schottky diodes are also used as _____________ at microwave frequencies.

oscillation

the bunches of electrons are repelled rather than attracted to the repeller plate since they are both negative and it bounces back to the cavity (which is positive). this repeated process causes ________ at cavity frequency. the __________ between the repeller plate and cavity plays a crucial part for proper time of synchronization.

helix

the electron beam of TWT passes through the center or axis of the ________

electrostatic and electromagnetic focusing techniques

the electrons emitted by a two-cavity klystron amplifier are focused into a very narrow stream by ___________________

lower cavity loop

the microwave signal amplified in two-cavity klystron amplifier is applied to the _____________ through a coupling ____________

velocity modulation

the speeding and slowing down of the electron beam is known as

Sectoral Horn Pyramidal Horn

Different horn antenna flaring

1. Difficult to analyze and design circuits at microwave frequencies. 2.Measuring techniques are more difficult to perfect and implement at microwave frequencies. 3. It is difficult to implement conventional circuit components (resistors, capacitors, inductors, etc) at microwave frequencies. 4. Transient time / Transit time is more critical at microwave frequencies. 5 It is often necessary to use specialized components for microwave frequencies 6. Microwave frequencies propagate in a straight line, which limits their use to line-of-sight applications.

Disadvantages of Microwave Radio

Microwaves

Electromagnetic waves with frequencies that range from approximately 500 MHz to 300 GHz.

10 to 60 degree

Horn antennas typically have a beam angle somewhere in the__________degrees range.

cathode anode

In Point-contact Diode the current flows easily from the fine wire or the ____________ to the semiconductor material or the ______________

Transverse electric

In ___________ mode, the E field exists across the guide and no E lines extend lengthwise along the guide

transverse magnetic

In _____________- mode, the H lines form loops in planes perpendicular to the walls of the guide, and no part of H line is lengthwise along the guide.

power measurements

In microwave circuits, ___________are more common than voltage and current measurements.

Point-Contact Diode

It is a piece of semiconductor material and a fine wire which makes contact with the semiconductor material. The capacitance is very low.

Gunn Diodes microwave oscillator

It is a thin piece of N-type Gallium Arsenide or Indium Phosphite which forms a special resistor when voltage is applied to it. It is primarily used as a _______________.

True

True or False Klystrons are used at frequencies as low as UHF and as high as 1 GHz in microwave region

True

True or False At low frequencies, the transit times are totally negligible, but at very high (microwave) frequencies, transit time becomes a high percentage of the actual signal period.

True

True or False Coupling losses must be high to prevent the transmit signal from one antenna interfering with a receive signal of another antenna.

False microwave signals are not deflected or absorbed in the ionosphere

True or False In Space Comms, microwave signals are deflected or absorbed by the ionosphere as are many lower frequency signals.

False, it decreases

True or False The beamwidth increases with increases in antenna gain.

True

True or False The gain of a parabolic antenna is directly proportional to the aperture of the parabola.

True

True or False The longer and more gradual the flare of a horn antenna, the better the impedance match and the lower the loss and the greater its gain and directivity.

False the higher the aperture area*

True or False The lower the aperture area, the higher the gain and directivity.

True

True or False the higher the frequencies, the higher the radiation in microwave frequencies

True

True or False the purpose of the helix inside TWT us to provide path for the RF signal that will slow down propagation

True

True or False: For a given size of aperture area, decreasing the length increases the flare angle.

aperture ratio or aperture of the parabola.

The ratio of the focal length to the diameter of the mouth of the parabola (FX / WZ) is called the

center focal point

The waveguide feeds through the ____________ of the parabolic dish and is curved around so that the horn is positioned exactly at the ___________

aperture

The___________ is the area of the outer circle of the parabola. A=3.14R^2

Gallium arsenide

This element is used instead of silicon because it has lower transit time.

1. front-to-back ratio 2. side-to-side coupling 3. back-to-back coupling

Three important characteristics of microwave antennas:

radio telescopes

Through the use of _________________ astronomers can study the stars and other bodies in this galaxy and beyond.

4-8 Ghz

A microwave frequency band "C" denotes how much frequency?

18-27GHz

A microwave frequency band "K" denotes how much frequency?

27-40Ghz

A microwave frequency band "Ka" denotes how much frequency?

12-18 GHz

A microwave frequency band "Ku" denotes how much frequency?

1-2 GHz

A microwave frequency band "L" denotes how much frequency?

2-4 GHz

A microwave frequency band "S" denotes how much frequency?

8-12 GHz

A microwave frequency band "X" denotes how much frequency?

1. parabolic reflector 2. feed mechanism

A parabolic antenna consists of two main parts:

reciprocity

A parabolic antenna exhibits the principle of ____________________

Space Communications

Communications with satellites, deep-space probes, and other space crafts is usually done by microwave transmissions

Radio Detection and Ranging

Complete name for RADAR

transferred-electron device (TED)

Gunn diode is also called a _____________________. It is not a diode since it has no junction.

Helical Antenna

-A center insulating support is used to hold a heavy wire or tubing formed into a circular coil or helix. -Most use 6 to 8 turns. -A circular or square ground plane reflector is used behind the helix. -Gain: 12 to 20 dB. -Beam width: 12 to 45 degrees.

Bicone

-Omnidirectional microwave antenna -The upper cone acts as a reflector and causes the signal to be radiated equally in all directions with very narrow beam width.

-Microstrip -Stripline -Waveguides

3 Major Transmission Lines

parabola

A ___________ is a locus of point that moves so that its distance from a point to a straight line is constant.

horn antenna

A ________________ is nothing more than a flared waveguide.

cavity resonator

A __________________ is a short segment of waveguide that acts as a high-Q parallel resonant circuit. It is said to resonate and act like a parallel resonant circuit.

loop

A _______________can also be used to introduce electromagnetic radiation into the waveguide. It is is mounted in the closed end of the waveguide.

probe

A common method of applying a microwave signal to a waveguide is done using a _________________. It is a quarter-wavelength vertical antenna at the signal frequency which is inserted in the waveguide one-quarter wavelength from the closed end.

Cassegrain feed

A horn antenna is positioned at the center of the parabolic reflector. At the focal point is another small reflector either parabolic or hyperbolic shape.

waveguide

A___________ is a hollow metal tube designed to carry microwave energy from one place to another

waveguide transmission line is shorter, and eliminated radical bends. less signal attenuation

Advantage of Cassegrain feed

- simplicity and low cost. -It radiates circularly polarized (emf is caused to rotate) -Circular polarization: -Either right-hand (clockwise) or left-hand (counter clockwise) depending upon the direction of winding. -Right-hand circularly polarized (RHCP) signal cannot be picked up by a left-hand circularly polarized (LHCP) antenna and vice versa.

Advantage of Helical Antenna

1. Radio systems do not require right-of-way acquisitions between stations 2. Each station only requires purchase or lease of small area of land 3. microwave radio systems can carry large quantities of information (due to high-op freq) 4. High frequencies mean short wavelengths, = smaller antennas 5. Radio signals are more ez to propagate around physical obstacles such as water and high mountains.

Advantages of Microwave Radio

C.) the higher the frequency, the higher the bandwidth

An advantage of Microwave Radio is that the ________ the frequency, the __________ the bandwidth available for transmission of information. a.) the higher the frequency, the lower the bandwidth b.) the lower the frequency, the higher the bandwidth c.) the higher the frequency, the higher the bandwidth d.) the lower the frequency, the lower the bandwidth

gain

An antenna has an apparent_________because it concentrates the radiated power in a narrow beam rather than sending it uniformly in all directions

highly directive

Antennas used for microwave must be

•Long-distance Telephone Systems •Radar •Television Stations and Networks •Space Communications •Microwave Heating

Applications of Microwave Signlas

high-pass filter

At frequencies above the cut-off frequency, the waveguide will propagate electromagnetic energy. Therefore, waveguide is a _________________with a cut-off frequency.

electric and magnetic fields

At microwave frequencies, most components and circuits are analysed in terms of

all the energy is radiated

At microwave frequencies, virtually ___________________; therefore, little energy ever reaches the end of the transmission line.

IMPATT and TRAPATT

Both are PN junctions made of silicon, GaAs, or InP. They are designed to operate with a high reverse bias that causes them to avalanche or breakdown.

tuned circuits microwave integrated circuits (MIC)

Both stripline and microstrip are widely used to form the__________ used in microwave receiver front ends and in low-power amplifier sections of transmitters. When combined with diodes, transistors, and other components, _______________ are formed.

- Smoke Signals - Torch Signals - Flashing lights - Signal Flares - Waving Flags

Examples of wireless communication during Pre-Industrial Age

long-distance telephone

Many __________________ systems use microwave relay links for carrying telephone calls

straight line

Microwave frequencies propagate in a _______________, which limits their use to line-of-sight applications.

1GHz

Microwave has signals with a frequency greater than

geographically

Microwave stations must be ____________ placed in such a way that the terrain do not interfere with transmissions between stations.

Short-Haul

Microwave systems used to carry information for relatively short distances, such as between cities within the same state

germanium P-type silicon tungsten

Most early point-contact diodes used ____________ as the semiconductor material. But today point-contact diodes are made of _____________ with a fine _________ wire (whisker) as cathode.

waveguides

Most microwave energy transmission is handled by

microstrip and stripline.

PCB technique is used to create special microwave transmission lines called

beam width

Recall that the _______________ is the angle formed by extending lines from the center of the antenna response curve to the 3-dB-down points.

printed circuit boards (PCBs)

Special transmission lines are constructed by using ______________________________

klystrons magnetrons, and traveling wave tubes

Special vacuum tubes known as ______________, _________________, and ________________________are the primary components for power amplification.

strip lines, microstrips, waveguides, and cavity resonators

Special versions of transmission lines known as _____________, _____________, _______________ and ________________ are widely used to implement tuned circuits and reactances.

2 to 15 wavelengths 0.03 m or 1.18 in.

The length of a typical horn is usually _______________ at the operating frequency. Assume an operating frequency of 10 GHz. The length of one wavelength at this frequency is ____________

circular anode

The magnetron consists of a _______, made with copper in which has been machined an even number of resonant cavities, the diameter of each cavity should be 1/2 wavelength of desired operating freq.

parabolic reflector.

The most common type of antenna used for microwave transmission and reception is the ____________________

forward biased reverse-bias

Step-recovery diode or Snap-off varactor When it is _____________it conducts as any diode, but a charge is stored in the depletion layer. When _________________ is applied, the charge keeps the diode on momentarily. Then suddenly the diode turns off abruptly.

2-to-1

TWT frequency range is approximately _______ in the desired segment of microwave region to be amplified

transverse electric (TE) or transverse magnetic (TM).

The operating modes are classified as either______________

size width height

The ________ of the waveguide that determines its operating frequency. The _________ of the waveguide is designated "a", and the ____________ is designated "b".

side-to-side back-to-back

The _____________ and _______________ coupling express in decibels the coupling loss between antennas carrying transmitter output signals and nearby antennas carrying receiver input signals.

front-to-back ratio

The _____________ of an antenna is defined as the ratio (20dB or more) of its maximum gain in the forward direction to its maximum gain in its backward direction.

stripline

The ________________ is a flat conductor sandwiched between two ground planes. It is a transmission line that does not let electric energy radiate. The length is also one-quarter or one-half wave.

aperture area

The ____________is the area of the rectangle formed by the opening of the horn and is simply the product of the height and width of the horn.

feed mechanism

The active element of a parabolic antenna is

current - voltage relationships

The analysis of electronic circuits at lower frequencies, (below 30 MHz) is based upon

paraboloid

The curved surface dish is called a ____________

Pre-Industrial Age

The first wireless networks were developed in ?

fco=300/2a

The frequency of operation which is known as the waveguide cut-off frequency is computed as:

horn length, aperture area, and flare angle.

The gain and directivity of a horn is a direct function of its various dimensions, that includes:

gallium arsenide

Varactor Diodes are made of

frequency multipliers

Varactor Diodes main application is

electric and magnetic fields

We regularly measure voltages and currents, but in microwave circuits, the measurements are those of

Varactor Diodes

When reverse is applied to the diode, it acts like a capacitor. Its capacitance depends upon the value of the reverse bias.

buncher cavity catcher cavity RF

_________ is the input cavity in klystron amplifier which produces bunches of electrons, then they pass through the center of the second cavity which is called ____________ and excites the cavity into oscillation at resonant freq. The DC energy is then converted into _______ energy. the output is extracted from this cavity into the loop and produce amplified signals.

Transit time

_________ refers to the amount of time it takes for the current carrier (holes or electrons) to move through a device.

Distributed circuit elements

_____________ are used at microwave frequencies like transmission lines which constitute inductance and capacitance.

Point-contact diodes

______________ are delicate; ideal for low-signal applications and are widely used in microwave mixers and detectors, though it cannot withstand high power

Waveguides aluminum, brass and copper silver

____________________ may be used to carry energy between pieces of equipment or over longer distances to carry transmitter power to an antenna, it is made from________________. Often the insides of these are plated with ___________ to reduce their resistance to a very low level

printed circuit board (PCB)

_____________________ is a flat insulating base made of phenolic or fiberglass to which is bonded copper on one or both sides and sometimes in several layers.

Microstrip , one quarter or one-half , ground plane

______________is a flat conductor separated from a large conducting ground plane by an insulating dielectric. The length is usually ____________________ wavelength. The _____________ is the circuit common

Wireless Communications

any transmission that occurs without the use of a cable or wire

Transmission lines

are the means for carrying electromagnetic energy from one place to another

center

beam of electrons inside a two-cavity klystron amplifier passes through the _________ of two cavity resonators

Magnetron

combination of simple diode vacuum tube with built-in cavity resonators and powerful permanent magnet

Reflex Klystron

commonly used as microwave oscillator and uses a single(parang ikaw) cavity

common resistor, inductive reactance, capacitance, LCR Physical limits

the____________ component may show pure resistance at lower frequencies but exhibits other characteristics in microwave frequencies; the short leads of it , even less than an inch, may show a significant amount of ________________ at very high freq. and a small amount of __________ may also exist, so this component looks like a complex ____________ circuit in Microwave frequencies. _______________ become a problem. Even half inch piece of wire represents a significant amount of inductance at microwave frequencies.

cathode filament

two-cavity klystron amplifier vacuum tube contains a ___________ which is heated by _____________

electrostatic focusing

uses focusing plates which had been applied high voltages to force the electrons into a narrow beam

Television stations and networks

uses microwave relay links to transmit TV signals over long distances.

Cable TV networks

uses satellite communications to transmit programs from one location to another

10 wavelengths

•Most parabolic reflectors are designed so that the diameter is no less than ______________at the lowest operating frequency.

mixers mixer

•The most important use of microwave diodes is as____________. The__________ is usually the input circuit in a microwave receiver to convert microwave signal to a lower frequency level.