15/07/10
Antenna Design Guide
By Nigel Gaylard
This guide is intended to provide a brief overview of the key considerations when selecting an antenna or looking to implement a custom antenna design. Unfortunately despite the enormous progress made on simplifying radio transmitter and receiver design to the point where simply following the guidelines laid down by the manufacturer can result in a working design, antenna design still requires a grasp of the underlying theory.
TERMINOLOGY
Bandwidth: The range of frequencies on either side of the centre frequency where the antenna characteristics (such as input impedance, polarization, gain and efficiency) are within an acceptable value of those at the centre frequency.
Directivity: The ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions.
Efficiency: The amount of energy radiated, compared to the amount of energy at the input terminals of the antenna.
Gain: Closely related to directivity but takes into account the antenna efficiency.
Impedance: The impedance presented by an antenna at its input terminals.
Polarisation: The vector traced by the electric field as viewed along the direction of propagation.
Radiation Resistance: The equivalent resistance that would dissipate the amount of power lost through radiation.
Radio Frequency Identification (RFID)
Radio Frequency IDentification abbreviated, as RFID is a Dedicated Short Range Communication (DSRC) technology.
RFID technologies are grouped under the more generic Automatic Identification (Auto ID) technologies.
RFID TECHNOLOGY AND ARCHITECTURE
In an RFID system, the RFID tag, which contains the tagged data of the object, generates a signal containing the respective information, which is read by the RFID reader, which then may pass this information to a processor for processing the obtained information for that particular application.
RFID tag or transponder
RFID reader or transceiver
Data processing subsystem
The transponder, or RF tag tags can be either active or passive. While the active tags have on-chip power, passive tags use the power induced by the magnetic field of the RFID reader. Thus passive tags are cheaper but it got a limitation that, it work in a limited range (RFID Frequencies: RFID systems are differentiated based on the frequency range it works. The different ranges are Low-Frequency (LF: 125 - 134.2 kHz and 140 - 148.5 kHz), High-Frequency (HF: 13.56 MHz) and Ultra-High-Frequency (UHF: 850 MHz - 950 MHz and 2.4 GHz - 2.5 GH).
RFID, Tag, transponder, Radio, Frequency, Identification
Ultra-High-Frequency RFID systems offer transmission ranges of more than 90 feet. The standards used in RFID: RFID standards mainly stressed in the following areas
Data Content - Organizing of data in the Tags
RFID technologies are grouped under the more generic Automatic Identification (Auto ID) technologies.
RFID TECHNOLOGY AND ARCHITECTURE
In an RFID system, the RFID tag, which contains the tagged data of the object, generates a signal containing the respective information, which is read by the RFID reader, which then may pass this information to a processor for processing the obtained information for that particular application.
RFID tag or transponder
RFID reader or transceiver
Data processing subsystem
The transponder, or RF tag tags can be either active or passive. While the active tags have on-chip power, passive tags use the power induced by the magnetic field of the RFID reader. Thus passive tags are cheaper but it got a limitation that, it work in a limited range (RFID Frequencies: RFID systems are differentiated based on the frequency range it works. The different ranges are Low-Frequency (LF: 125 - 134.2 kHz and 140 - 148.5 kHz), High-Frequency (HF: 13.56 MHz) and Ultra-High-Frequency (UHF: 850 MHz - 950 MHz and 2.4 GHz - 2.5 GH).
RFID, Tag, transponder, Radio, Frequency, Identification
Ultra-High-Frequency RFID systems offer transmission ranges of more than 90 feet. The standards used in RFID: RFID standards mainly stressed in the following areas
Data Content - Organizing of data in the Tags
Digital Television Broadcasting and Single Frequency Networks
When we talk about digital broadcasting we usually talk about better picture and sound, high definition television, MPEG compression and more choice. The roots of transition to digital television broadcasting lie in more effective use of radio-frequency spectrum. In analog television world we have radio-frequency channels (frequencies) where each frequency transmits one TV channel (program) and in order to avoid interference the same frequency can be used again only far away. Digital technology enables us to use advanced compression algorithms to compress audio and video signals, consequently we can use one frequency channel to transmit more than one service (usually three to ten and even more TV channels), and we can build a network of transmitters operating on the same frequency thus significantly lower the number of frequencies (channels) needed to cover a territory.
There are a few standards for digital television broadcasting. Frequency plans for DVB-T are based on allotments - areas where all transmitters transmit on the same frequency. It helps in demodulating the signal. During the guard interval the same symbols with varying arrival times can be received without any inter-symbol interference. This is the basic principle of Single Frequency Networks (SFN).
There are a few standards for digital television broadcasting. Frequency plans for DVB-T are based on allotments - areas where all transmitters transmit on the same frequency. It helps in demodulating the signal. During the guard interval the same symbols with varying arrival times can be received without any inter-symbol interference. This is the basic principle of Single Frequency Networks (SFN).
14/07/10
Radio Frequencies - What Do They Mean and Why Are They Important?
Radio frequency spectrum is a natural and limited resource. One of the most important properties of any waves is their wavelength or frequency. Radio frequency determines the position in Radio frequency spectrum and hence all the properties of radio wave propagation and potential use.
Because radio waves travel across country borders and may interfere with other radio waves there are many rules, frequency plans and procedures that define how to use radio frequency spectrum to avoid interferences. Because different frequencies have different properties there are some general harmonized frequency bands that define main purpose of the band and basic technical parameters of transmitters using these frequencies. The so called allocations are accepted on international levels and provide basic rules for frequency usage. One of the most popular services using radio frequencies is terrestrial or satellite broadcasting. Large coverage areas also mean coverage across the border.
Of course, there are special cases like digital broadcasting and single frequency networks where nearby transmitters operate on the same frequency without causing interference, but for analog broadcasting careful frequency planning is a must.
When we would like to listen to a particular radio we need to know the frequency on which this radio broadcasts.
Because radio waves travel across country borders and may interfere with other radio waves there are many rules, frequency plans and procedures that define how to use radio frequency spectrum to avoid interferences. Because different frequencies have different properties there are some general harmonized frequency bands that define main purpose of the band and basic technical parameters of transmitters using these frequencies. The so called allocations are accepted on international levels and provide basic rules for frequency usage. One of the most popular services using radio frequencies is terrestrial or satellite broadcasting. Large coverage areas also mean coverage across the border.
Of course, there are special cases like digital broadcasting and single frequency networks where nearby transmitters operate on the same frequency without causing interference, but for analog broadcasting careful frequency planning is a must.
When we would like to listen to a particular radio we need to know the frequency on which this radio broadcasts.
History of the Radio
The radio, as we know it today, owes its existence to two previous inventions, the telegraph and the telephone. In 1895, Italian inventor Guglielmo Marconi transmitted and received the first radio signal, proving the possibility of radio communication. This event marked the first time a transatlantic radiotelegraph was successful.
When radio was first used, it did not transmit audio as it does today, but signals of dots and dashes similar to Morse code. There are two accounts of the human voice first being transmitted by radio, and it is unclear which is authentic. Natan B. Stubblefield transmitted the phrase "Hello Rainey" in 1892 in Murray, Kentucky. The first daily radio programs began in 1920 with the broadcasted return of the Harding-Cox election. Today, radio has become such a commonplace form of technology, most people hardly even notice it. However, the forefathers of radio technology surely had no idea that one day a radio would be standard in every car or that we would even listen to radio stations over the Internet.
When radio was first used, it did not transmit audio as it does today, but signals of dots and dashes similar to Morse code. There are two accounts of the human voice first being transmitted by radio, and it is unclear which is authentic. Natan B. Stubblefield transmitted the phrase "Hello Rainey" in 1892 in Murray, Kentucky. The first daily radio programs began in 1920 with the broadcasted return of the Harding-Cox election. Today, radio has become such a commonplace form of technology, most people hardly even notice it. However, the forefathers of radio technology surely had no idea that one day a radio would be standard in every car or that we would even listen to radio stations over the Internet.
About Radio Signals, Frequency and Wavelength?
Firstly radio was invented as a method of sending and receiving bits of information. At one end of a radio signal there is a transmitter. Effectively this uses magnetic fields and electric fields to create electrons which are changed into the radio waves and set out into the ether. The fields of a radio wave oscillate through different strengths and the length of time taken for a wave to get back to where it started is a cycle. Now remember that radio waves move at a constant speed and when it oscillates differently, it will take a different time to complete a cycle. The distance that a wave travels in one cycle is the wavelength.
The lower the frequency, the slower to complete so it will travel further in each cycle so you can see that waves of low frequency have long wavelengths and vice versa.
The frequencies of radio waves vary between a couple of hundred KHz (KHz = kilohertz = 1,000 hertz) right up to around 1,000 GHz (GHz = gigaHertz = 1 billion Hertz). When you are tuning your radio in to pick up a signal, that is in fact a frequency. These signals are put into groups and are called bands.
The lower the frequency, the slower to complete so it will travel further in each cycle so you can see that waves of low frequency have long wavelengths and vice versa.
The frequencies of radio waves vary between a couple of hundred KHz (KHz = kilohertz = 1,000 hertz) right up to around 1,000 GHz (GHz = gigaHertz = 1 billion Hertz). When you are tuning your radio in to pick up a signal, that is in fact a frequency. These signals are put into groups and are called bands.
What is Radio?
Radio waves are used for a wide range of applications, including AM and FM radio broadcasts, satellite communications, cordless phones, baby monitors, television broadcasts, wireless networks, cell phones, GPS receivers, ham radios, police radios, garage door openers, radio-controlled toys, and wireless clocks.
To transmit audio, video, or data, all of today's radios use continuous sine waves. Each sine-wave uses a different frequency to distinguish between the types of devices using the radio waves.
First, the transmitter converts the information into a sine wave and then transmits it along with a radio signal. Then, the receiver obtains the signal and decodes the information from the sine-wave. A battery provides a good working example of a radio transmitter. Messages are encoded into sine waves through modulation. There are three types of modulation: pulse modulation, amplitude modulation, and frequency modulation. In pulse modulation, the sine wave is turned on and off to transmit information. Using frequency modulation, the frequency of the wave is changed slightly to transmit information.
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