What is Antennas: Definition and 96 Discussions

In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment.
An antenna is an array of conductors (elements), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional, or high-gain, or “beam” antennas). An antenna may include components not connected to the transmitter, parabolic reflectors, horns, or parasitic elements, which serve to direct the radio waves into a beam or other desired radiation pattern.
The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of waves predicted by the electromagnetic theory of James Clerk Maxwell. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving. Starting in 1895, Guglielmo Marconi began development of antennas practical for long-distance, wireless telegraphy, for which he received a Nobel Prize.

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  1. M

    Blocking electro-magnetic waves between two near field antennas

    Its been a while since I studied physics, so pardon my ignorance. I have two near field antennas (NFC). The range of the antennas is about 2-3 cm. I am looking for a way where I can block and unblock the communication between them. One of the way that I tried is to place a flat tightly...
  2. E

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    Seems to me in that an antenna is carrying microamps at most that slightly higher resistance of steel Vs copper wouldn't matter. What's the fault of this logic??
  3. dexterdev

    Current flows only when circuit is closed, right? but for antennas

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  4. U

    Anyone familiar with Blaw-Knox Antennas?

    I grew up not far from WLW and it's giant diamond antenna mast. picture These Blaw-Knox antennas were extremely popular in the 1930s. I always wondered why the diamond shape. I found the original patent here, but it really doesn't say specifically why the diamond shape was chosen. It looks like...
  5. A

    How Do Antenna Size and Frequency Affect Power Density Calculations?

    Antenna is in size of 0.5[m] X 0.5[m], with transmit frequency of 10GHz. In a distance of 100m the electric field is 250 [V/m]. I calculated the density of power with the formula: 0.5*(E^2)/(120*pi) and got: 82.891 [W/m^2]. the question is: can I calculate the density of power again but un...
  6. P

    Conceptual doubts about capacitors and dipole antennas

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  7. J

    Hey guise, Question about how antennas detect electromagnetic waves?

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  8. W

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  9. B

    Why is copper tubing used to make high q antennas?

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  10. W

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  11. T

    How EMR interacts with matter and how antennas differ to other rods

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  12. P

    Antennas causing destructive interference

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  13. berkeman

    Why Choose a Parabolic Wire Antenna over a Solid Parabolic Antenna?

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  14. M

    Orientation of Receiver Antennas given orientation of transmitter

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  15. O

    Dipole antennas & Conductivity

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  16. A

    Understanding Antennas based on GPS

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  17. G

    Impedance matching in antennas

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  18. Y

    Any other forum more into antennas?

    Anyone have suggestion on other forums that are more into antenna theory and design?
  19. Y

    Optical Antennas: Experiencing Light Differenly?

    Hi everyone, Light has a dual nature ; wave and particle. Particle part can be explained using Quantum approaches while the wave nature is described by Maxwell Equations. I am interested in light - matter interactions from wave approach which is also my thesis subject. (also I would like to...
  20. D

    Receiver antennas, performance metrics

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  21. D

    Are There Better Antennas for Tx433/RX433 RF Modules?

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  22. C

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  23. P

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  24. F

    Questions about superposition of two antennas

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  25. S

    Near field from cell phone antennas?

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  26. B

    What is the formula for calculating G_T in line-of-sight antennas?

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  27. T

    Can TV Antennas Pick Up CMB Radiation?

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  28. T

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  29. S

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  30. R

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  31. Z

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  32. U

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  33. T

    Designing RF Antennas: From Intuition to Simulation Tools

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  34. A

    Why is it that very low frequency signals cannot be transmitted by antennas?

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  35. P

    Testing VHF Radio Wave Performance with Different Antennas

    Hi. I am designing an experiment focused on radio waves for my experiment and this is the basis of it: Three antenna's will be tested for point to point transmission (VHF): [ 144 MHz ] >>3/4 Wave antenna >>1/4 Wave antenna >>5/8 Antenna (Best Angle of Radiation Usually) These...
  36. J

    Active Antennas: How Do They Work?

    Hello All, I have a question related to the understanding of how an active antenna works. From my *extremely limited* knowledge of the subject, I hear that an active antenna is able to receive a stronger signal from a transmitting source by transmitting a wave of the same frequency such that...
  37. R

    Directivity of array of antennas

    Homework Statement I am trying to understand how the total directivity of an array of antennas is calculated. Homework Equations 1. A_e = (D * lambda^2)/(4 * pi) where: A_e = effective aperature (or area of antenna) D = Directivity of one antenna lambda = wavelength 2. D_t =...
  38. A

    Boost Your Antenna Design Skills: Essential Resources for Microwave Antennas

    Dear PF members , I need you help. I am offered to work on a project at a University. The offered project is microwave antenna design. I asked for some topics to study to keep me updated and ready to work on the project from day one and the professor gave me these : small antennas, planar...
  39. B

    Analyzing Electromagnetic Radiation Intensity: N Antennas with Random Phases

    1. Consider N similar antennas emitting linearly polarized electromagnetic radiation of wavelength \lambda and velocity c. The antennas are located along the x-axis at a separation \lambda form each other. An observer is located on the x-axis at a great distance from the antennas. When a single...
  40. K

    MATLAB Simulating Dipole Antennas in MATLAB with PDETOOL

    Hello people: Have you ever simulated a dipole antenna in MATLAB, for example, using PDETOOL? I am trying to achieve this, but I reach to non-accurate solutions when I set non-canonical phantoms in the environment of the dipole, comparing the results with comercial softwares. This is...
  41. D

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    Hi to everyone. I have heard that we usually prefer to modulate signals at high frequencies so the wave length is small compared to the length of the antenna. Is there any rule or equation that implies this requirement?
  42. D

    .Understanding DBI & DBD: Antennas & Gain

    Hi i need information about th dbi and dbd... I know what db is but i am trying to understand dbi and dbd... Also i want to know what if the antennas or the tvs antennas has some gain.. I know that the gain refers to the antennas surface... that's why the satellite antennas have a big surface...
  43. D

    What Are the Limitations and Risks of Using Squared Pulses in Antennas?

    Hi. Yesterday i have had a strange question.. why can't we use squared pulses in antennas? What kind of pulse can we use in antennas? Thx a lot
  44. Loren Booda

    Reciprocity applied to complementary antennas

    Does reciprocity, the rule that electrical specifications of an antenna are essentially the same for receiving and transmitting [Wikipedia], apply to the following situation: Antenna Y transmits with power PY which antenna Z receives as power PZ. Does this mean if that antenna Z...
  45. E

    Electromagnetic waves - antennas

    I just need a little direction to get started on this problem. A magnetic dipole is uded to detect an electromagnetic wave. The antenna is a coil of 50 turns with radius 5.0 cm. The EM wave has frequency 870 kHz, electric field amplitude 0.50 V/m, and magnetic field amplitude 1.7 x 10^-9...
  46. T

    RFID Antennas with ferrite Rod

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