Antenna Definition and 406 Threads

How do I go about building a simple antenna to measure 25MHz to 100 MHz radiated emissions? I have an oscillator in my ckt that's radiating at 75MHz. Just want to make sure it's the 3rd harmonic of fundamental frequency (25MHz).

If I'm not mistaken, an antenna transmits radio waves when electrical current runs up and down the antenna. The frequency at which these electrons travel up and down the antenna, in other words the frequency at which they oscillate is proportional to the frequency of electromagnetic waves...

Hello, I'm trying to improve the gain of my antenna using superstrate. I read a few journals regarding this topic but i could not determine the thickness of the superstrate needed. Any help would be greatly appreciated. Thanks..

Is the current direction shown correct ?

Hey, So I want to make an antenna which emits powerful waves in the frequency range of 1-50 MHz. Yet I don't know exactly how powerful those waves should be, but a normal solenoid is not enough... :P It should be really powerful... :D Any help is welcome :)

Im trying to expand the range of my wifi network, and I am not sure exactly what to expect from a +27 dbi antenna. As I understand it, this will cause the power density to increase by a factor of 2^9. Does that mean the range will increase by a factor of 2^9? or would it be more like...

We all know that current can't flow in open circuit. Then why does current flow in the wires of half wave dipole antenna ? I am confused , can't visualize.

I am trying to calculate the voltage induced onto a shielded cable by a 200 V/m external electric field. I found an antenna equation that relates the power received to the incident electric field, but I need to define an antenna gain (G) for the cable. I am not sure how to get that. Am I on...

Hi I am trying to build a satellite tracker for fun, to get information out of the cube sat projects or any satellite I can track. I was wondering if there was any open source java scripts for an arduino controller that would take and input for azimuth and elevation and output for two stepper...

Suppose we have an antenna which has large directional gain. Suppose the antenna broadcasts linearly polarized radiation in a narrow beam and at constant frequency. Sketch the electric field in the plane which contains both the electric field and the beam axis. Does the attached come close?

From my understand, electrical current is required to generate RF. In the picture below, only one end of the antenna is connected L1. If only one end of the antenna is connected, how can electrical current travel up the antenna to generate RF?

Does it draw the frequencies it's made for, or just stand in their way and gather them as they hit it? What is the difference between a round antenna rather than one with straight lines?

This is not a homework, too old for that! I just have a question that I create myself. All the books only show the pattern that is more obvious...they show either the E or the H pattern. I took an exercise that asked for the H pattern, in turn, using the pattern multiplication to try to find the...

Dear All I want to design a Full motion Antenna. But I want to start from the scratch. Suppose I have a 1m parabolic Antenna and I want to install two motors (Elevation and Azimuth) The motors should be DC. And I want to know how to calculate all the parameters required to move the...

In the middle picture, since the current is directed downward (I think), by the right hand rule shouldn't the magnetic field lines be clockwise? Thanks!

Dear all, Let's assume that I have just bought the perfect omnidirectional antenna and I try to understand how the wavelengths are transmitted. If I got it right, there are wavelengths getting 'out' towards the 360 degrees directions. Now let's assume that I have a perfect receiver antenna...

The definition of Beam solid angle: For an antenna with single main lobe, the Beam solid angle defines as: The solid angle \; \Omega_A\; where all the radiated power would flow with radiation intensity equal to maximum and constant inside the Beam solid angle \; \Omega_A\;. The book gave...

I have been looking into how antennas work, and I have found that antennas of half wave-length are apparently optimal, but I don't understand why. If anybody could explain why this is, I would appreciate it. Thanks! (I do have an understanding of electromagnetic waves)

I am sorry please delete this post if it has been already asked Light is an electromagnetic wave right? i haven't have ever heard of light distorting or causing disturbances in antenna signal,why is it so isn't it also an electromagnetic wave?

Why isn't the antenna impedance (usually 50 ohms) matched with free space impedance (377 ohms)? Won't the mismatch result in some loss.

Homework Statement An electromagnetic wave from a wire antenna travels (from the reader) toward the plane of the paper. At time t = 0.0 s it strikes the paper at normal incidence. At point O and t = 0.0 s, the magnetic field vector has its maximum value, 5.01E-8 T, pointing in the negative...

Hello friends... I have an small antenna( irregular shape) , mass about 1.5 Kg (about CG), the moment of ineria about spinning axes(Iyy) is 0.0255kg.m^2. product of inertia also known (Ixy, Iyz, Ixz). Required angular velocity (w) = 50 deg/sec angular acceleration (a) = 400 deg/sec^2 The...

Homework Statement i just have a few questions about the radiation pattern of a half wave dipole antenna. firstly i know the for the half wave dipole we can dervie and expression for the electric field in the zenith angle and the magnetic field in the azimutal angle by using the far field...

any body know where to get some high quality gsm antenna ?

Greetings, How far apart should the wires be on a 2.4 GHz parabolic grid antenna? Is it determined by the frequency? Thanks

Hi, all I want to control the power ratio of my series array antenna. I heard there is some relation between width of rectangular patch antenna and power to control the power ratio. I want to know.. Do you know some relation?

Hi :) I am designing 6x1 series fed microstrip rectangular patch antenna by using HFSS. The schematic of the my design is below. This figure is the half of my design for the past analysis. My goal is below. SLL(side lobe level <-25dB) S11(<-20dB) After I design the patch...

How do I make a Yagi-Uda antenna smaller? I am trying to build a Yagi antenna for 900mhz and I am using this formula: http://www.skyscan.ca/Antennas.htm Length: Reflector length = 0.495 x wavelength Dipole radiator = 0.473 x wavelength Director D1 = 0.440...

I am building a 125kHz Near-Field Magnetic Induction Communication system and so will be using ferrite cored inductors for the transmitter and receiver. I am worried about RF radiation as it pertains to the conformance of FCC part 15. I haven't been able to get any good info on how an...

I'm wrestling with the notion that a small coil of wire in a planar flat spiral can be a real tuned antenna. The fact that the coil is only three turns and about the diameter of a quarter further irritates my ability to understand how such a simple thing can be viewed as a real antenna. The...

Hello, I have a question related to coordinate transform. If this is not the right section please feel free to move this thread. My problem is the following: I have a positioning system to move an antenna, that allows me to perform scans according to a great circle coordinate system. Check...

I would like to ask a few questions. Does a table of refractive indices of materials at rf frequencies (say for TV) exists? Is there a way for me to estimate it for some materials? Are the refractive indices of these materials higher? Will those materials have low absorption losses at these...

Bad news: http://blogs.discovermagazine.com/cosmicvariance/2011/04/06/nasa-gives-up-on-lisa/

Hello Experts, I am a novice trying to make a small atenna for GSM signals. I tried using insulated iron wire. Its my 1st time experimenting with antennas. My question is how does the type of metal used affect an antenna? For example, some use copper wire. Will it have a better...

Homework Statement An antenna in RECEIVING mode is a device that (a) convert electric field to magnetic field (b) convert high freq current to electromagnetic waves (c) convert magnetic field to electric field (d) convert electromagnetic waves to high freq current (MARK OUT ALL THAT...

Homework Statement The Effective Isotropic Radiated Power of an antenna is 60dBm. If the gain of the antenna is 30dB what is the input power to the antenna? (a) 3W (b) 2W (c) 4W (d) 5W Homework Equations EIRP = Power x Gain (in watts) EIRP = Power + gain (in dbm) The...

We have no longer have cable TV but receive free local broadcast via a homemade coat-hanger TV antenna, see...

hi this is vebi , i want to design rfid tag antenna with moisture sensor can anybody suggest me how to design

I have an Antenna system using two patch antennas, and I'm trying to determine the SNRin and SNRout of the system. I'm trying to determine the noise figure - is there a way to do it using scattering parameters? Thanks!

Homework Statement Your automobile antenna is 1m in length and is fixed at one end, free at the other. When you drive on an uneven road, waves can be excited on the antenna. Compute the wavelengths of the four longest wavelength standing waves that your antenna will allow. Homework Equations...

Antenna theory is quite new to me and I found in constantine Balanis's book that there's a relationship between maximum directivity and effective area of an antenna-if we increase effective area, directivity will also increase. The picture of antenna author used to derive the equation was a horn...

I am trying to get an understanding of how to create an electrically shielded loop antenna. Is it possible to have a multi-turn electrically shielded antenna? Also how does an electric field create interference with the loop antenna? Is it because the electric field is not constant throughout...

We know to make antenna dimension reasonably small, we modulate baseband signal with a high frequency carrier. Antenna size as far as I know is in the order of one tenth of carrier signal wavelength. For example, for a 3 GHz carrier signal, receiver antanna size is 1 cm. But, in frequency...

Does the length of an antenna feed affect the length of the antenna one should use? Intuitively I'm thinking 'NO' since in some applications the user supplies (variable length) antenna feed cables, but the antenna is still made to be resonant to the application frequency. BUT in the RF...

Hi, We're trying to build a simple antenna that's able to pick up a frequency of 457 KHz from a maximum distance of 20 metres. I'm totally new to this stuff, so I looked up the yagi antenna and some formulas used to determine the length of the antenna, but the results I got were huge...

Why is it that an antenna length must be somehow proportional to the wavelength of the frequency

I am building a resonant RLC network in which the inductor is actually a loop antenna that will pick up changes in magentic fields and represent them as a voltage. Is this configuration actually feasible where the loop antenna is both the voltage source and the inductor? Also slightly related...

I found in many sources describing microstrip antennas are 'low profile'. Well, I know several antenna parameters like radiation pattern, antenna gain, intensity, directivity etc. But what is this 'low profile'?? Can anyone tell me what sort of property of an antenna does the term 'low profile'...

Hello community Sorry if this is a repost, but I don't find what i am looking for. I am reading the book "anntenas", by Kraus and Marhefka In page 30, says the antenna impedances are complex. Z{\tau} = + R{\tau} + jX{\tau} .. Could anyone please tell me what does the complex part imply in...

If electric energy is supplied in the form of high voltage & low current & if the same energy is supplied in the form low voltage & high current will there be in difference in the photons emitted by the antenna?the frequency is same for both the cases.One electron can interact with just one atom...