RECIPROCITY THEOREM
If voltage is applied to terminals of an antenna A and the current is measured at another antenna B, then an equal current (bot amplitude and phase) will appear at terminals of antenna A if same voltage is applied to antenna B.
Application of reciprocity theorem
Equality of Directional Patterns
Statement: 'The directional pattern of an antenna as a receiving antenna is identical to that when used as a transmitting antenna."
Proof: The above mentioned antenna theorem is the outcome of the application of the reciprocity theorem used in the linear and bilateral networks. Basically a directional pattern of a transmitting antenna is represented as a polar characteristic because it indicates the strength (amplitude) of the
radiated
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This current is the measure of the electric field at different positions of the dipole antenna. Now using the concept of the reciprocity theorem, the positions of the voltage excitation and the current measurement are interchanged. Now the same voltage V is applied to the terminals of the small dipole antenna which is moved along the surface of the sphere and the current I is measured in the test antenna located at the centre. Thus the receiving pattern for the test antenna can be obtained. But according to the reciprocity theorem, for every location of the dipole antenna, the ratio of V to I is same as before obtained for the test antenna as a transmitting antenna. Thus the radiation pattern i.e. directional pattern of a receiving antenna is identical to that of the transmitting antenna. Instead of the circular polarization, if the linear polarization is considered, then under such condition, the small dipole exploring antenna is oriented in such a way that direction is perpendicular to the radius vector and parallel to the electric …show more content…
Hence from equation (4) it is clear that the receiving antenna impedance is equal to the transmitting antenna impedance.
In the discussion of the impedance measurement of an antenna, we consider two antennas which are widely separated. But we can use the same concept for several antennas assuming all are widely separated from the antenna whose impedance is to be measured. Now assume that the other antennas are placed very close to the antenna being considered for impedance measurement. Under such condition, the mutual impedance cannot be ignored as it is comparable with the self impedance. Thus the receiving impedance will be the addition of the antenna self impedance and the impedance due to the presence of other antennas. But even under such condition, the transmitting impedance is equal to the receiving impedance if for the transmitting condition, other antennas are connected to the impedances equal to the impedances of the generators that used to excite
Usually a vertical antenna is located on the right, which controls the pitch. The closer the players hand is, the higher the pitch. A horizontal loop antenna is located on the left and controls the volume. The closer the hand is, the louder the volume. Patented in 1928 by Leon Theremin, the theremin has not escaped its original status as a novelty instrument.
1. D. Halliday, R. Resnik & K. Krane, Physics, vol. 2, 4th ed. John Wiley & Sons Inc., 1992.
"Radar during World War II." - GHN: IEEE Global History Network. N.p., n.d. Web. 16 Feb. 2014. .
Wire time (or panghantar such as an antenna) conducts alternating current, electromagnetic radiation is propagated at the same frequency as the electric current. Depending on the situation, electromagnetic waves can be waves or like particles. As a wave, characterized by speed (speed of light), wavelength, and frequency. When considered as particles, they are known as photons, and each has an energy associated with the frequency of the waveform shown by the Planck relationship E = Hν, where E is the photon energy, h is the Planck constant - 6.626 × 10 -34 J · s - and ν is the frequency of the
Radio systems must have transmitter to modulate some property of the energy produced to impress a signal on it. To using amplitude modulation or angle modulation ,which can be frequency modulation or phase modulation. Radio systems have antenna to convert
"The Future of the Wireless Art," Wireless Telegraphy and Telephony, 1908, pg. 67–71, Nikola Tesla
All the issues, raised by the author, are due to the fact, that the author decided not to use α', but α as an angle, that is equal to π/2, in order to define transverse Doppler effect. It is obvious, that α is the angle b...
Radio Detection And Ranging (RADAR) “is a method of using radio waves to detect the existence of an object and then to find its position in relation to a known point, usually the site of the radar installation.” Radar technology can be used to detect the position, speed, and direction of the moving or stationary objects (“Pulse-modulated”). Radars, often used for “electromagnetic surveillance,” has various hardware and software parts that work together to produce an effective reading of the position and motion of the objects. The transmitter of the radar is used to initiate the process by amplifying the pulse signals. It has three parts: “a high powered amplifier (HPA) with a high-stability electron gun, waveform generator and timing, and an antenna” (Kolawole, 37). “The low energy signal, collected by the antenna, is brought through the circulator and the transmit...
The level of RF a person receives is related to many factors, not only the placement of the antenna. Factors that can increase the level of RF are the number of “cells”, the distance to the “base station”, or the obstacles between the caller and the station. The number of cell zones depends on the user population. Heavily populated areas have more cells allowing for more telecommunication traffic. Being close to a cell site lowers the power needed to sustain a call, hence reduces the exposure to RF.
Radar can be traced back as far as 1832 when British physicist Michael Faraday suggested the existence of an electromagnetic field between certain objects from his scientific observations. Working from these ideas, British physicist James Clerk Maxwell predicted mathematically the existence and behavior of radio waves in 1873. In 1886, physicist Heinrich Hertz from Germany and Elihu Thomson from America confirmed the existence of radio waves with demonstrations showing examples of reflection, refraction, and direction finding of radio waves. By 1904, Christian Hulsmeyer, a German inventor, applied for a patent for a device that used radio waves in a collision-avoidance device for ships.
In an electromagnetic wave, the constantly changing electric and magnetic fields affect each other so they both oscillate in different axis while the wave moves in a direction perpendicular to the oscillation of the fields as shown in Figure 1.
increases in the opposite or negative direction until it attains maximum negative value at 270 degrees, and finally decreases to zero value again at 360 degrees. It follows, then, that the induced emf can be completely described by the relation.
Often the antenna is packaged with the transceiver and decoder to become a reader (a.k.a. interrogator), which can be configured either as a handheld or a fixed-mount device. The reader emits radio waves in ranges of anywhere from one inch to 100 feet or more, depending upon its power output and the radio frequency used. When an RFID tag passes through the electromagnetic zone, it detects the reader's activation signal. The reader decodes the data encoded in the tag's integrated circuit (silicon chip) and the data is passed to the host computer for processing.
If a radiowave of constant amplitude is incident on the irregularity slab of thickness L (Fig 2.2) where the layer is assumed to be a phase changing screen, the wave changes its phase when propagates through it. The emergent wave is represented as,
The waves can be absorbed and reflected by surrounding objects before they reach the nearest cell tower. For example when you put your phone next to your head, during a...