Gain & Directivity

You have to first understand an isotropic antenna. The isotropic antenna does not actually exist. It is a theoretical construct of an antenna for the sake of comparing real antenna. An isotropic antenna is a point source antenna with absolutely no orientation or alignment concerns. It has no peak orientation or blind spot. The closest thing to an isotropic antenna would be a star thousands of light years away with nothing between the star and observer to alter the spherical radiation field.

So that's the ideal, I see. So in designing antenna, an engineer would have to always approach to design such ideal condition right?

I just don't understand why is Gain unit is on dB? For an isotropic antenna it follows that η=1?

how is gain related to Power radiated? I am messed up, really.

Messed up? Yes!

Read up on antennas. Why do you insist on asking the forum to spoon feed you an education.

Here's two pictures of gain:

dB stands for deciBel. When you talk about gain in general, say of an amplifier, the signal is multiplied by a certain factor. If you connect two amplifiers together in tandem, the first feeding into the second, if their gains are G1 and G2 then the resultant gain would be G1 x G2. In analyzing systems, it's easier to add and subtract than to multiply and divide, so engineers use logarithms, which is where dB comes in.

A factor of 10 (in voltage) is 1 Bel, a term almost never used. Instead we use decibel, where 10 decibel is a factor of 10. Power is equivalent to voltage squared, so if the signal is increased by a factor of 10, the power is 20 dB higher. If power is increased by a factor of 100, it's 40 dB higher, and so on.

Gain in an antenna is not an amplification of power but a concentration in a certain direction. It works like a flashlight, which directs the light from a bulb into a beam in a certain direction. More power from the bulb is directed to where the beam is shining.

No, you design an antenna to meet a specific requirement. An isotropic antenna radiates equally in all directions. Seldom does an engineer want that capability. For example if you're designing cell phone towers, you don't want the signal going up, you may or may not want distant horizon coverage, you might just want close in saturated coverage. How else would you choose to measure the difference between an isotropic antenna and the one you designed? dB has worked well for decades, why change it. Radiated power is like the horsepower at the drive wheels. It makes no difference how much the transmitter generates if the wrong medium is used to get the power to the antenna.

Study both of these, THEN USE THEM:

How to Search the Internet - 9 Easy Steps (with Pictures)

Electronics for beginners: A simple introduction

Allso: ANTENNA DESIGN AND CHARACTERIZATION BASED

ARRL Antenna Handbook can be found using How to Search the Internet - 9 Easy Steps (with Pictures) This is a test. Let's see if you know how to search the internet!

Not really. By going away and reading-up the topic elsewhere, the average quality of CR4's original posts will rise.

How do you define Gain in laymans term?
Getting more out than you put in.

It's a laundry detergent.

No, its a dessert topping.

Or it could be Rogaine^TM, which I could use if I really cared.

Maybe an analogy might help to get a feel of the equation. Imagine light source like a car headlight bulb, roughly the light intensity from say a given distance (1 meter say) would be spread evenly over the surface of a sphere area 4 pi squared meters. This is a bit like an isotropic antenna, now imagine we have a parabolic mirror where we take this spherical energy and squeeze into a smaller conical energy volume you will now have a much greater intensity of light depending on the geometrical properties of your reflecting mirror (antenna), the ratio can be likened to gain if the ratio is 2 a convention is used which takes the log of 2 to base 10 and then multiplies this result by 10 which gives 3 decibels or we say 3 db. Its just an historic way of expressing gain every 3 db is doubling the gain so 6 db is 4 times, 9 db is 8 times . Light is very much like radio waves, its just the wavelength is so much smaller and "light antennas" can be much smaller for the same gain as radio antennas.

Hope this helps

A time-varying current flowing in ANY conductor radiates an EM wave; how much depends on its size (expressed in wavelengths), the amount of current, and how much of the field is cancelled by return currents flowing close to it, either by design or by accident.

Those of us who work in EMC or SI spend a lot of time (we get paid, too, sometimes more, sometimes less) PREVENTING this radiated wave from affecting nearby circuits or devices, exceeding regulatory interference limits or causing harmful interference to reception, and, because reciprocity means a wave impinging on our own designs induces current too, that our equipment doesn't shut down if a strong enough RF field is present.

Thank you for all the contributor, I certainly learn the approach. Not all that I read, I can absorbed-though some purely madly deeply advised or recommended to use search engine-google. Expert's perspective is way better than any other. A simplified and practical version is easy to grasp.There are points in learning not mentioned in books, where it all needed to be searched. Experts who have been through almost all angles, could tell the difference. I really appreciate it.

Bonus point, Kulas, for replying to the posts and thanking folks. A rare event, especially on the short questions from "beginners" in a subject

I guess you have learnt that if a posted question on CR4 looks dead to effort and initiative, eagles arrive to eat the carcass. Folk who expect us to answer their "homework" questions are annoying.

Did your formula quote the units of measurement? Not doing that is a fault with some engineers who should know better when writing reports etc. I have also seen many drawings, which are fine pictures, where just the dimension or unit one needs is omitted.

I found this most annoying with vibration where mean, average, root mean square [rms], peak and "peak to peak" are all used and the frequency range of the filters is essential. These terms can also apply to a measured voltage, current or power.

67model

Power Signal In x Gain Factor - Losses = Power Out

Therefore a voltage amplifier circuit with a gain of 2 and zero losses would yield:

5V Input x Gain of 2 - 0 = 10V out

Or more simply put: Gain (factor) is the input signal multiplier in an amplification circuit.

When dealing with antennae gain consideration of the square of signal wave length is critical in allowing the antenna to resonate at maximum transmission efficiency usually measured in Watts.

Motorola published many excellent instruction books specific to circuit analyses and antenna design which can be found on the internet and/or purchased cheaply.

The OP does not want to be bothered reading anything.

That's why he uses this forum.

Don't look back, something could be gaining on you!