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Unformatted text preview: TILTEK TILTEK Antenna Seminar This seminar was developed by Hector Boudreau with formatting assistance from Eileen Boudreau. Some diagrams were provided by Rene Duville and the International Wireless Packaging Consortium (IWPC). TILTEK Solutions that Work Affordable Quality ISO 9001:94 Reliability Service TILTEK Antenna Seminar TILTEK Frequency, Wavelength and Velocity Radio waves oscillate (alternate from plus to minus) This variation from plus to minus is called a cycle, since it repeats itself The number of cycles that the radio wave goes through in one second is called the frequency (f) 1 Wavelength Time TILTEK Frequency, Wavelength and Velocity Instead of saying “ cycles per second ”, we use the word Hertz (abbreviated Hz ) in honour of Heinrich Hertz who discovered radio waves. Also, since we are dealing with high frequencies, we use prefixes like kilo (1,000), Mega (1,000,000) and Giga (1,000,000,000) in front of Hertz, to further simplify the terminology. 5 cycles per second = 5 Hz 5,000 cycles per second = 5 kHz 5,000,000 cycles per second = 5 MHz 5,000,000,000 cycles per second = 5 GHz We know that radio waves travel at the speed of light (~186,000 miles per sec. Or 3 x 10 8 meters per sec.) and we can measure the frequency of the radio waves, therefore we can find out how far the wave travels in 1 cycle by dividing its’ speed by its’ frequency. We call this a wavelength (abbreviated ? ) Frequency Wavelength 150 MHz 2.0 m 900 MHz 33.3cm 2.4 GHz 12.5cm 5.8 GHz 52cm TILTEK The Decibel The decibel (dB) is a ratio, measured in logarithm, used to measure quantity. A dB has no dimensions. The decibel is used to compare one power (or voltage level) to another. Ratio in dB = 10log 10 (Power Ratio) = 20log 10 (Voltage Ratio) (Power is proportional to the voltage squared) 20 dB means a power ratio of 10 2 to 1 or 1,000:1 10 dB means a power ratio of 10 to 1 or 100:1 0 dB means a power ratio of 1 to 1 or 1:1 Because the dB is a ratio, it is dimensionless, however many times reference is made to the unit that is made as a ratio. e.g. dBm in the case of milliwatts 20 dBm means 100:1 over 1 milliwatt or 100mW e.g. converting 4W into dBm 10log 10 4000mW = 36 dBm 1mW Later on we will see that if an antenna has twice the power gain of a half wave dipole (an antenna used as a standard reference), that is a power ratio of 2 over the 1/2 wave dipole, then the antenna is said to have a gain of 3dBd. (3db over the1/2 wave dipole) 10log2=3 A +3dB gain represents a doubling of power while a 3dB loss represents 1/2 of the power What is an Antenna An antenna is a device which transforms electromagnetic signals from a transmission line, into electromagnetic waves radiating into free space, (transmit mode) and also collects electromagnetic waves, transforming them into electromagnetic signals and sends them to the transmission line. (receive mode) This is all the antenna is designed to do; it is a passive device. Antennas do not amplify, they simply focus radio energy.to do; it is a passive device....
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This note was uploaded on 08/08/2011 for the course CS 310 taught by Professor Aartisingh during the Spring '11 term at National Institute of Technology, Calicut.
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