What is Antennas: Definition and 95 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. bob012345

    Simulation of two Small Interacting Antennas

    I would like to simulate two small interacting antenna's with fields and forces in 3D. They can be simple wire antenna. I am asking if there is a recommendation for software that can reasonably accurately handle that which is free? Thanks.
  2. DC2

    A Calculation of EM fields induced by an antenna in the near field

    The title pretty much covers it. I'm having to calculate the field induced inside the human body by an antenna in the near field (essentially, a phone placed close to a user's head), and I'm drawing a blank on how to relate the field generated by the antenna to the field induced inside the...
  3. B

    I Estimation of E-field strength at a distance from dipole antenna

    Hello everyone, I was asking myself about electric field strength estimation at a distance d from - in my case - a half wave dipole antenna. There are pretty much a lot of information about this on internet or in books but still, there are a few things that are confusing to me that I would...
  4. A

    Dish Antennas C/N Problem

    Summary:: I am stuck on a problem on dish antenna C/N and it's relation to frequency. Please see below for thought process. Problem Statement: , Link budget formula in dB form: Pr = Pt + Gt + Gr + 20*log10(lambda/(4*pi*distance)) - Losses [dB] C/N = Pr - Pn [dB], where Pn = 10*log10(k*T*B)...
  5. Johan L

    EM re-radiation from a metal object (antennas)

    Consider the following situation. Two identical monopole antennas are placed in a field with distance d. One of them is used to receive signals and the other is disconnected and can therefor be considered to be just a metal rod (my guess). A plane wave of a single frequency is coming from a...
  6. P

    Calculating Radiation Pattern for a grid of two rows of dipole antennas

    Although problem says sketch, what I really want is the formulae by θ for the radiation. After trying this for a while I cheated and looked at the solution. I still can't figure out the steps on how to get to the solution. the answer is: What I tried: I'll assume that the intensity from a...
  7. tworitdash

    A Maximum reception/transmission criteria for Conical Horn Antennas

    I have written a solver for my thesis which determines various parameters of a conical horn antenna for astronomy application. It is done with Mode Matching Technique (MMT) and some Rumsey's integrals for the aperture free space transitions. I have made some goal functions with the solver which...
  8. P

    Maximizing radiation southward, minimizing it northward, antennas

    Homework Statement: More of a conceptual question than a homework question. Maximizing radiation southward and minimizing it northward. Homework Equations: (See picture in attempt at solution) For two antennas separated along the north-south direction, operating with the same amplitude...
  9. shushi

    Beginner's question about antennas

    Hello! This may be an obvious idea and I feel silly for asking this, but just out of curiosity, if I have a large dish satellite where I could fit three antenna transmitters in the center that send different types of signals (a broad-band radio antenna, an ultrasonic antenna/sensor, and a...
  10. M

    Questions about Antennas

    For RF devices that charge/take in energy through RF waves, does it only take in electricity from a frequency it's wired/set to pickup/receive or does it get electricity from all RF waves? Can an antenna fold in (collapse but still connect like tent poles) and still remain operational like it...
  11. M

    A couple of questions about antennas, bandwidths and power

    Does it take more electrical energy to transmit HF and lower frequencies than it takes to transmit VHF and above? Are there any wavelengths beyond radio waves and gamma rays? Is it true that the lower the frequency, the lower the amount of data that's being sent? I read on this wiki that...
  12. M

    KiwiSDR and recommendations for antennas and cables

    I recently bought a KiwiSDR and it's my first SDR so far. I was wondering, what antennas you guys recommendation for it and whether this recommended antenna is truly good for it (it was listed on the KiwiSDR site as a recommended antenna, but it's a bit pricey for me). I'm trying to find signals...
  13. P

    THz Radiation, Antennas: Need background knowledge

    I want to use small molecular - preferably CNT - "antennas" to produce THz signals to monitor activity in biological systems. After some googling, I've been reading things like "absorption spectra", "energy bands", "spectroscopy", as well as a bunch of antenna-science related jargon... I need...
  14. V

    A Material for Antennas: Can Slow Velocity Dipoles be Used?

    Would it be possible in theory to develop a material with very slow velocity factor to build dipoles immersed in a slow velocity factor gas in order to make much smaller HF antennas?
  15. alan123hk

    Why can't antennas be made smaller and smaller?

    Why can't antennas be made smaller and smaller? Assuming we implement the following measures : - 1. use room temperature superconductor to eliminate the ohmic loss of antenna 2. reduce the thermal noise of antenna by lowering its temperature 3. Perfect impedance matching network by means of...
  16. T

    Half Wave Helical Antennas

    I'm extremely interested in the self resonant frequency of an inductor. This is to be used as a half wave helical antenna on our ham bands. The usual helical is operated as a ground plane but I have not seen a complete set of design equations for the former. The initial problem with this is...
  17. S

    Co-located pair of Phased Array Antennas

    I have been debating with a friend about a thought experiment that evolved out of an entirely unrelated discussion, but which has now become a subject of argument. Consider a "dual" phased array antenna that has every odd-numbered radiating element driven from input port 1 and every...
  18. D

    *Very* Small Low Freq Antennas with directivity?

    I'm curious about anyone that has concrete hands on experience tinkering with very small low frequency antennas. My band of interest is 6, 13 or 27 MHz. I wonder if it is possible to design a very small physical antenna that will radiate with some directivity even if the efficiency is not so...
  19. davenn

    One of those WOW moments -- Airliner Antennas

    just stumbled across this article I am sure other tech types like me will appreciate this article ... http://www.mro-network.com/engineering-design/understanding-today-s-antenna-complexitiesenjoy cheers Dave
  20. T

    Using two connected Yagi antennas to "bend" a mobile signal

    I have a typical problem. I have two bars mobile signal in my attic - none at ground floor level. The reason is a roadside pole transmitter less than 500m away installed down in a dip behind houses (duh!) An electrically powered signal booster is illegal in the UK which atracts a £5000 fine...
  21. M

    B-Probes and loop antenna

    Hi the difference between a loop antenna and a magnetic probe (B-Probe) is only that the loop antenna works in far field and B-Probe works in near field? The standard features of magnetic antenna (antenna factor, impedance matching, radiation patterns, efficiency, ecc) have the same definition...
  22. J

    Conservation of momentum in antennas

    When an RF antenna absorbs a signal, the momentum is transferred in quantized photon-electron interactions. The electrons in the metal will be given both perpendicular momentum (the actual signal information) and momentum in the direction of propagation (shown below): The momentum in the...
  23. M

    Difference between DC/AC coupling (Antennas)

    Good evening everyone! Given that I have no experience in antenna physics or related areas, I'm studying a paper for a project I will be involved. It is an image sensor for THz e.m. waves and exploits micro-bowtie antennas to "capture" the signal and convert it through a standard CMOS imager...
  24. qnach

    Why do these antennas have different radiation patterns?

    In Kraus book on antenna (3ed page 203) example 7-4.1 the difference between those antenna is (to my understanding) only the wave length. How could they have different radiation pattern?
  25. P

    Permittivity of a Lossy Medium using Antennas

    First of all I will being with I'm not an electric engineer so I might be out of my wits, but I will give it a try. So I have an instrument which reads relative permittivity using a transmitter and two receiver placed at different distances. The instrument is calibrated to read either in a...
  26. M

    Determining the Poynting Vector for Loop Antennas

    So I came across the following image (from Wikipedia) where the electric and magnetic field lines are depicted for a dipole antenna. From the field lines, it is possible to determine the direction of the poynting vector, using the right-hand rule. If all possible combinations of poynting...
  27. P

    Antennas and electromagnetic radiation

    Antennas work with variable current that leads to accelerations and deceleration ofor the electrons, the frequency of the photon or the electromagnetic radiation I want to generate depends on the change in kinetic energy of the electron E= hf= change of kinetic energy of the electron, according...
  28. Newtons Apple

    A few Questions on Antennas

    Antenna Size So I was reading the above thread, and loved the explanation at the end. But my remaining question on Antenna Size is that..Okay I get why for low frequencies we *need* to have bigger antenna, so how it is that people like Hams transmit on lower frequency, long wavelength channels...
  29. qnach

    Analytic solution for these two antennas

    I am trying to solve the following two antenna. Perhaps they have already solved in some textbooks. Could anyone advice me where can I find them?
  30. berkeman

    Stealthy Antenna Spotted in Santa Clara - Share Your Story!

    I spotted this "palm tree" in Santa Clara a few days ago. It's in a church parking lot, near some other real palm trees. Pretty clever way for the church to make some extra money on the side from a cell phone provider. My girlfriend spotted a much stealthier cell antenna tower disguised as a...
  31. Anton Alice

    Understanding the Resonance of Dipol Antennas

    Alright. I have also a few questions concerning dipol-antennas: first: It has often been said, that the dipol antenna, in order to receive a certain frequency, needs to have a length of λ/2. I don't see a clear reason for that. If one would not know that, one had to calculate the Capacity...
  32. R

    How RF Antennas Work: A Beginner's Guide

    Okay, sorry for my frustration at this fundamental subject, but I am going completely insane not understanding it! All this near-field / far-field stuff is messing with my head. I simply want to know how RF works. Let's start simple. HOW IN THE WORLD IS AN RF SINGAL MADE!? Let's say I have some...
  33. Tyatyra

    Wifi Antennas' Danger....?

    berkeman, I read a post of yours stating that "the house next door a wifi cell tower was more dangerous than the one with the antenna on top" Would you please elaborate? Is this because of the umbrella effect? I am considering buying a home which is next door to a house that installed a wifi...
  34. A

    Electromagnetics radars and antennas

    What are the best universities in the world offering ms programs in applied electromagnetics, radars and Antennas.
  35. U

    What's different between a receiver & transmitter antennas?

    Hello, I'm currently working on satellite model for high-school compatition, and I'm not sure if there's a visual difference between a reciver & transmiter antenas (on satellites)... Also, is it possible to satellite to recive a radio wave information from another satellite Thank you
  36. P

    An Explanation of the Effective Area of Isotropic Antenna

    Hey all, I realize a question on this topic has been asked elsewhere, but the links to references they use seem to be dead, so I'll press on! I'm reading some introduction to antenna theory and I've often puzzled on the equation: A_{eff} = \frac{\lambda^2}{4\pi} which relates the effective...
  37. R

    Are all antennas traveling wave antennas?

    Hi, I've been reading a lot about traveling and standing waves, and i am right now reading about traveling wave antennas, to my understanding ALL antennas should be traveling wave antennas, but this is not the case of what i read online, and there is also not too much information about it. For...
  38. L

    Young's double slit and radio antennas

    Homework Statement antennas can both receive and emit electromagnetic radiation depending on wetter their connecting cicuit is monitored for, or driven by a current. the pattern of emitted radiation is identical to the pattern for absorbed incident radiation. As shown in the notes, far-field...
  39. Averagesupernova

    Anyone amateur radio ops here have experience with end fed HF antennas?

    Having not been set up with a station for quite a few years I am thinking of setting up an end fed antenna for HF. It seems the only way I will enjoy a little 'hamming' again is to start out simple and quick. Trying to avoid clutter in the middle of the yard. I have enough tower sections get...
  40. S

    Infinite wavelength resonant antennas

    Could somebody explain what does mean "infinite wavelength antenna" and what advantages does it have? What is resonant antenna and advantages...
  41. J

    Coupled Antennas: Literature on Small Separation Distances

    Can anyone provide some literature on antennas spaced apart such that the spacing distance is much less than the wavelength? I am specifically interested in the mutually coupling behaviour as a function of small separation distances.
  42. R

    Simulation of antennas in Low Frequency

    Hey everybody! I wanted to simulate an antenna in Low Frequency, but I don't know any suitable software for this purpose. I'll appreciate if anybody could help me out... Thanks
  43. U

    Two interfering antennas with single photon radiation

    Consider this: Two antennas are set up in a vacuum. They both radiate electromagnetic waves of the exact same frequency, and an interference pattern can be observed on a screen placed some distance away. Now suppose the emission density was reduced (in both antennas) to one photon at a...
  44. S

    Radio Antennas and Young's Double slit

    Homework Statement Two radio antennas separated by d = 294 m as shown in the figure below simultaneously broadcast identical signals at the same wavelength. A car travels due north along a straight line at position x = 1 290 m from the center point between the antennas, and its radio...
  45. I

    Radio Wave Interference between Two Antennas

    Homework Statement Two antennas located at points A and B are broadcasting radio waves of frequency 99.0 MHz, perfectly in phase with each other. The two antennas are separated by a distance d= 12.40 m. An observer, P, is located on the x axis, a distance x= 58.0 m from antenna A, so that APB...
  46. N

    Smaller Antennas, Higher Frequencies: The Need for Size Reductions

    Why antenna needs to be smaller in size with higher frequencies (EM waves)? please
  47. D

    Why is a 1/4 wavelength antenna limited to 1/4 wavelength length?

    Why does a 1/4 wavelength antenna have to be 1/4 wavelength? What property of the wave is responsible for this restriction? I've been trying to understand how a 1/4 wavelength antenna works and the best explanation, relatively speaking, was on the following website...
  48. harts

    Understanding the physics of antennas

    I'm currently preparing for a challenge exam, and I'm having trouble understanding antennas. My physics book is good, but it is very brief in its section on antennas. I know there are more complicated types of antennas, but let's just stick with the "simple" half-wave antenna (or dipole antenna...
  49. 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...