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).
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