Skip to main content
9 votes
Accepted

Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true?

Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true? No, that is not true. I generally find that hams that ...
Glenn W9IQ's user avatar
  • 18.6k
7 votes

Dipole antenna radiation field equation

The antenna you describe is "omnidirectional" only in the xy-plane; it has zero radiation along the z-axis. Thus, your dipole is mounted vertically; i.e., x=0 and y=0 for all segments. According to ...
Brian K1LI's user avatar
  • 7,888
6 votes

Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true?

dBi is useful for comparing gains of real world antennas. For instance, an 80m mobile antenna may be -10 dbi, a 1/4WL vertical ground plane may be 0 dbi, a dipole may be 6 dbi, and a beam may be 10 ...
Cecil - W5DXP's user avatar
6 votes
Accepted

How to calculate/estimate the effect of having conductive material nearby an antenna

In your particular case, I'd note 2 things: The aluminium is directly above the whip, where the antenna's fields are the weakest. Aluminium is a good conductor, so unless there is something about it ...
Phil Frost - W8II's user avatar
5 votes

Antenna Patterns and Multipath Effect

On HF (1.5 to 30 MHz) amateur radio operators use antennas with the major directive lobe close to the horizon in order to maximize the distance the signal will travel. At these frequencies the signals ...
Glenn W9IQ's user avatar
  • 18.6k
5 votes

Antenna Q vs pattern shape

In general for a given antenna evaluated on a given frequency, if whatever is changing the Q occurs uniformly or universally and does not result in a change to the effective aperture, phasing, or ...
Glenn W9IQ's user avatar
  • 18.6k
5 votes

What are the effects of a ground plane under a horizontal dipole?

If the container is small relative to wavelength, then it won't have much effect at all. If it's very large (say, infinite) then it will reduce ground losses by providing a more conductive ground ...
Phil Frost - W8II's user avatar
5 votes
Accepted

What is the radiation pattern of a center fed dipole on the ground?

The best way to answer this is with a NEC simulation of a dipole on the ground. Using a "Pastoral, medium hills and forestation" ground, Conductivity 0.006 S/m Relative Permittivity 13. 18 ...
tomnexus's user avatar
  • 11.5k
4 votes

Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true?

Those that complain that dBi isn't useful because an isotropic antenna is only theoretical often advocate an alternate unit such as dBd, or decibels relative to a dipole. There are a couple arguments ...
Phil Frost - W8II's user avatar
4 votes
Accepted

How to derive antenna gain from radiation pattern

First a bit of context regarding terminology. In antenna engineering, we use the term "loss" to refer to RF energy that is lost as heat. This is typically an undesirable loss that creates ...
Glenn W9IQ's user avatar
  • 18.6k
4 votes

Directional antenna overlapping main lobes

Free space is (under normal conditions of frequency and power and atmosphere) a linear medium, so waves propagating in it follow the superposition principle, so they do not interact just because they ...
Kevin Reid AG6YO's user avatar
  • 24.7k
4 votes
Accepted

what is main reason for formation of side lobes in directional antennas?

Similar to optics or a water tank, waves passing through a finite aperture will produce a diffraction pattern. To over-simplify: In the far field, the difference between the distance to the left and ...
hotpaw2's user avatar
  • 13.5k
4 votes

450-ohm ladder line fact vs fiction

Here's some theory as to why this matters...keep this in mind and decide for yourself when you should worry. All transmission line (coax too, not just ladder line) works by forming opposing magnetic ...
user10489's user avatar
  • 6,543
3 votes

Do the Horizontal Conductors of a Ground Plane Antenna Adequately Decouple Its Feedline?

Below is a NEC4.2 comparison of the v-plane patterns of a 1/4-wave ground plane antenna mounted 5m above level Earth and using 4 x 1/4-wave, horizontal radials, with / without a coax transmission line ...
Richard Fry's user avatar
  • 2,932
3 votes

What Are Some of the Most Important Characteristics Applying to the Radiation of Monopole Antenna Systems?

VERTICAL MONOPOLE, EARTH, and BURIED RADIALS as FACTORS in ANTENNA SYSTEM RADIATION EFFICIENCY Considerations: The components shown in the ...
Richard Fry's user avatar
  • 2,932
3 votes
Accepted

How to plot transmitter coverage area?

The Longley-Rice model is a fairly common technique. However it's not a simple formula, and so requires some kind of software to implement. Unfortunately my favorite such tool, CRC CovWeb, has gone ...
Phil Frost - W8II's user avatar
3 votes

Phased Array Pattern

The hex grids can fit more transmitter/receivers into the same space, resulting in greater power output per square meter. But more importantly, the one you pictured also has independent ...
SDsolar's user avatar
  • 2,087
3 votes

What is the easiest way to eliminate a beam antenna's backward radiation (rear lobe)?

No real world antenna exhibits "zero" power in any particular direction. Careful design can minimize the power in the unwanted direction but not eliminate it. In a yagi antenna, the front to back ...
Glenn W9IQ's user avatar
  • 18.6k
3 votes
Accepted

450-ohm ladder line fact vs fiction

a repeated "consensus" is that the cable should be ... not on the ground or buried This is an accurate statement. Laying the cable on the ground, and especially burying it, is bad. The ...
Mike Waters's user avatar
  • 8,081
2 votes

How Might Nearby Re-Radiators Affect the Radiation Patterns of a Transmit Antenna?

The NEC4.2 study/graphic first below shows how a structure comprised of conductors to (roughly) emulate the a-c power lines in a wood-frame house might affect the radiation patterns of a 40m-band ...
Richard Fry's user avatar
  • 2,932
2 votes

What is the easiest way to eliminate a beam antenna's backward radiation (rear lobe)?

From the picture, it looks like you have a log-periodic antenna rather than a Yagi. In either case, optimizing some parameter like front-to-back ratio involves optimizing the spacing and length of ...
Phil Frost - W8II's user avatar
2 votes

How to calculate/estimate the effect of having conductive material nearby an antenna

There is modeling software you can use for this. EZNEC and 4nec2 are popular among hams, but they only do wires. You could try modeling the aluminium as a bunch of wires - spacing them, say, 0.05 wl ...
Jon Kåre Hellan LA4RT's user avatar
2 votes

How Does the Low-Angle Radiation of a Horizontal Dipole Compare to That of a Vertical Monopole?

The very small low-angle radiation noted above is the result of excluding the surface wave from the NEC calculations. Also the commonly-used "far-field only" patterns calculated by NEC are based on ...
Richard Fry's user avatar
  • 2,932
2 votes

How Does the Performance of an Inverted V Dipole Compare to a Linear Dipole?

NEC4.2 comparison of an inverted V, center-fed dipole with a linear center-fed dipole: AUTHOR EDITS: The apex angle in my plots here is mislabeled. The correct value is 120°. The graphic below ...
Richard Fry's user avatar
  • 2,932
2 votes

How Much Does the Radiation Pattern of an "EFHW" Antenna System Vary Across its Bands?

The analyses shown below provide one example of the difference in the radiation patterns of the EFHW system described there. ...
Richard Fry's user avatar
  • 2,932
2 votes

How to plot transmitter coverage area?

There is a web application already: https://www.ve2dbe.com/rmonline_s.asp 73, Brian, ZL1IE
user15101's user avatar
2 votes

Do Far-Field Radiation Patterns/Gains of NEC Software Accurately and Always Show the E-M Fields "Launched" by Vertical Monopoles?

The NEC4.2 analysis below compares the intrinsic fields/gains of the same monopole for the definitions and conditions shown in that graphic. Note that the monopole having a 10 Ω path connecting it to ...
Richard Fry's user avatar
  • 2,932
2 votes
Accepted

Total radiation pattern in antenna arrays

The first is still correct, and can be evaluated at any position. The second is true only at broadside, when $\theta=0$. In your attempts, do you find that $\vec{E}_{total}$ is the same in all ...
tomnexus's user avatar
  • 11.5k
2 votes
Accepted

Understand Radio Pattern of a WIFI antenna

The numbers arranged vertically are decibels. They tell you the relative radiant intensity in each direction. For example if in one particular direction you read 0 on that scale, and in another ...
Phil Frost - W8II's user avatar
2 votes

What is the radiation pattern of a center fed dipole on the ground?

Straight up and down. You create an earthworm sauna and a cloud burner. Half the power goes into the dirt, burned off as waste heat, and the other half goes straight up and will burn a hole in the ...
Dereck's user avatar
  • 694

Only top scored, non community-wiki answers of a minimum length are eligible