CWNP CWNA – RF Signal and Antenna Concepts Part1
RF Signal and Antenna Concepts Part1 So in this module, we’re going to talk about the radio frequency signal as it relates to the antennas and the concepts about these antennas. So we’re going to look at a lot of what we can design with antennas to affect the actual signal. That means we’re going to look at azimuth and elevation charts and talk about how they should be read. And then we’re going to talk about some of the different types of antennas, whether they’re omnidirectional, semi directional, highly…
So in this module, we’re going to talk about the radio frequency signal as it relates to the antennas and the concepts about these antennas. So we’re going to look at a lot of what we can design with antennas to affect the actual signal. That means we’re going to look at azimuth and elevation charts and talk about how they should be read. And then we’re going to talk about some of the different types of antennas, whether they’re omnidirectional, semi directional, highly directional, a sector antenna, or an antenna array. And with each of those, we’re going to be talking about the beams. So we’re going to talk about static beam forming, dynamic beam forming, and transmit beam forming.
So when we look at these azimuth and elevation charts, what we’re doing is looking at side-by-side comparisons of the antennas. Now, for you to manually make one of these, you would normally get your antenna, start transmitting, walk around the antenna with an RF meter, and take a bunch of different signal measurements.
So you can then plot the measurements, perhaps on the ground or on a piece of paper that represents the environments, and say, “Okay, based on my survey, I know what area the Santana will cover.” And of course, when I talk about being covered, we have to look at it from more than just a horizontal perspective. Right. This is what happens when we look from the side, but also when we look horizontally. That is, am I transmitting a beam to the people in the office above or below me, as well as how far out in the office coverage is required?
So that’s really the hardest way to do that. Most of your manufacturers will already have these charts made for you, but you also have to remember they’re making them in a perfect environment where there’s nothing but free pathloss to cause a problem with the RF. They’re not going to do it in an area where you go through walls, desks, and all that other sort of stuff.
Now, as I said, the manufacturers will create the azimuth charts for you and the elevation charts; these are often called “radiation patterns,” and they do them for all of the different antennas that they make. Now, a lot of times they call them polar charts. And whatever word you want to use, it’s just basically a way for us to be able to see the signal strength relative to where the antenna is. Did you hear me say relative to where the antenna is? That’s an important aspect because you look at some of these charts and you might say, “Wow, look at that coverage,” when really what the chart is showing you is how the signal attenuates going by the DB rating.
So you might see one that looks like it’s going to conquer the world when it might only have a distance of 20 ft. It’s relative. It’s kind of like if I were to shine a flashlight at my hand, and you would see the shadow of my hand on the wall. The further I move the flashlight from my hand, the smaller it’s going to look. The closer I get it to my hand, the bigger it’s going to look. But these charts are just a representation of the antenna and my fingers, right? It doesn’t actually represent the area of coverage, but it’s just representing my hand. Whether it’s a tiny chart or a big chart, it’s still in my hand. So that’s why it’s a relative type of measurement.
Now, in these charts, the antenna is basically designed to be placed at the center. We look at it in two different ways. We have the H plane, which is the H plane. Over here, I’ll put an H in case it’s not as easy to see, which is looking down at the top of the antenna. And what you aren’t really seeing very well is that there is a little line here that’s showing me the strength of that signal from that relative location looking straight down. Then there’s the elevation and the east view. .
We’re looking at it from the side. It’s as though the antenna were right here. And you’re looking at it straight on from the side to see what the areas of coverage are. As previously stated, the H is top-down. So when you look at it and you start seeing these numbers, these numbers are representing the strength of the signal that we would expect and, of course, in which direction. Because if we had a highly focused or directional antenna, you would see something completely different.
This, as an example, looks, from the top view, like it’s an omnidirectional antenna because we see this coverage going all the way around. And when we look at it from the side, what we’re seeing from the side is the coverage. If this was your office, So maybe in your office, the roof and the ceiling are right here, and here are your walls, and you’re getting an idea of the coverage.
The problem is when I drew something like this rectangle to represent your office, you might actually think by looking at this chart, that you’re going to be able toxoid the entire building with one access point, when in reality well, and I don’t want to mess up everything, the office might actually be much bigger. Because, as I previously stated, these charts show you the relative right. How close is the flashlight to my hand? And most of our coverage is designed to be from side to side. But some of that signal could, depending on where you place it, be found or seen by the people on the floor above you. Or it could be the people at the floor below you.
It’s just a matter of showing you the relative signal strengths. And remember, this chart is going to be the same whether I say I’m using 50 milliwatts or 100 milliwatts. And we just went through a bunch of math in a different location of this course. If it’s 200 milliwatts, what am I saying? that as we increase our power, we will effectively gain more physical distance.
But the shape and pattern of the signal are still going to be the same. So these numbers don’t represent how many feetor meters away or anything like that. It doesn’t represent the actual strength of the RF signal. It is just showing you the pattern of coverage that you would have at whatever intensityor signal strength that you’re using.
So I guess what you’re hearing me say is that these charts can often be misinterpreted and misread. And the reason that the charts are misinterpreted is that they represent the decibel mapping of the antenna coverage. And that becomes confusing when we start talking about what’s happening. So what was it we learned about decimals? That you enjoy using log rhythms to perform their calculations. And so when we’re looking at a chart, let’s say that this first chart up here is representing an area of coverage, and it’s not really being expressed logarithmically.
It is expressed in a linear manner by stating that we may have one room that is one foot by one foot or a box that is one foot by one foot. The next box is 2 feet by 2ft.The next box is 4 feet by 4 feet. Right. So it doesn’t really show me the actual logarithmic part of that concept. Whereas if I actually made a one by one, a two by two, a four by four, and an eight by eight, the same representation, but in a logarithmic way, it looks, well, almost too big or too scaled. But it’s harder to make this kind of map because of how difficult it would be to chart it. Imagine if you had boxes that went all the way up to 512, right.just wouldn’t fit on the screen.
All right, so let’s take another look at a logarithmic chart versus a linear chart. So, again, when we start looking at the sections, we notice, right, that the numbers are representing a minus ten DB in the signal strength as we’re going through, but we can see logarithmically that somebody would say, “Hey, look at this coverage.” I’ll give it to the floor above me; I’ll give it to the floor behind me. Again, we could look at it and say that this antenna has great coverage.
Well, again, it’s just a representation of the signal. If we put it into a linear model, it’s still the same data. It just doesn’t look like it’s covering things the same way as you would have thought by looking at the logarithmic chart. When we look at this chart, each of these rings that are coming around represents a minus ten DB. And, of course, if you did, the math would show a 70% decrease in coverage. Let’s see if I can spell “decrease” properly here. And so, again, looking at this, it is just showing you the relay of the radio frequency to where that particular capability or that particular antenna is in the middle. And so that’s, and perhaps this is demonstrating it to you, where we’re seeing that loss as we go with each ring. And that’s a little more difficult to read on the logarithmic chart, where it might be a little easier to read when we look at it from the linear scale.
Now look what happens when we get into directional antennas again. The directional antenna is not showing me how far away I am. It’s just a relative reading of what the strength of that signal is going to be and in which direction. By the way, even if you have the best of these directional antennas, there’s always going to be a little coverage over to the side. In reality, this looks like I’m getting a lot of side coverage instead of what I wanted, which was for my beam to go in a certain direction, where the linear scale, I think, makes it a little bit easier to read.
Another concept we consider, particularly with our semidirectional directional, is beam width. So it’s basically a measurement of how broad or narrow the focus of an antenna is. And we do measure it horizontally and vertically to get an idea of what that width is. And the measurements will help us actually get the angle right. I mean, if you would. This is an angle.
At some point, as we get further away, the beam width is going to get bigger. Maybe not as strong, but it’s going to get bigger. So we’re pointing it from the centre of what we do anyway, which is to look at the centre of the strongest point of that antenna signal, and then we try to find the points along that horizontal and vertical axis where the power decreases by half. And once we get to that half again, remember the laws of threes and tens. Then we’ll basically say that is the beam width. And when we get the actual physical distances, both from the centre to the top axis and the bottom axis, if you will, the diameter of the circle, then you will be able to figure out what the angle is of that beam width.
All right, so let’s take a look at how we would figure out the beam width. If you will, of this specific antenna. Now, remember that this circle represents 360 degrees. So you don’t have to take any actual measurements. You simply look at where it is plotted on the circle and then calculate how many degrees are between. After that, you’ll notice that the solid circles represent the change in DBS, the minus ten, the 20s and 30s, and the 30 DB line. Let me take a look at how they’ve set up this chart. All Right. So what we want to do is figure out where the strongest point of this particular setup is, and the dotted lines that you see here are actually going to represent the angle of the beam’s width. or what the beam width actually is. So you’d take the strongest part of the signal and divide it by zero.
So that’s where we’d start, and then we’d proceed to move along that pattern from the peak signal. Step two, we’ll move in both directions until we reach what’s known as a minus three DB loss, which means we’re at half the power. And when we get to those points, and I’ll put a little extra line there when we get to those points, then what we have, or at least now know, is what the actual angle of the beam width is between those two points. So when we get to half power, we go back to the centre of where that axis or that antenna is, and then we can determine from there what the actual angle is of that beam width.
Now let’s take a look at the different types of antennas—the things that are causing this really frustrating view of charts and beam with. Hopefully it’s not too frustrating, but it is certainly something we need to know, as I said before, when we’re doing our site surveys and trying to decide where to put the coverage and the types of antennas we might want. So there are three main categories of an antenna. The Omnidirectional wireless device, which most of you have in your home, It’s radiating in a way that if you turned on a light bulb in the house, your light bulb is going to radiate light out in every direction. And that’s easy, right, for a home user to put in their house?
The problem is that it’s going to COVID areas like your neighbor’s house, and if they try to use your cable Internet, you might not be happy with that, but it’s designed to give you general coverage in all directions. Now, in an office environment, I might say to myself, “Omnidirectional” doesn’t sound good because I’m going to be giving WiFi access potentially to people in their cars, in the parking lot, or walking by. You know, there was a time—I don’t think it’s as popular now as it used to be—when people would do what’s called “war driving” or “war walking.” When people were “war driving,” they were driving down roads in major cities looking for a signal and examining how it was encrypted, if it was encrypted at all, and what the SSID was called.
And they would draw maps so people could go into a city. One of the more well-known ones was Las Vegas. To go into that city and say, “Hey, if you park over here, you can use the Internet for free because they’re not doing anything to secure it and it’s open and blah, blah, blah.” That is sometimes inconvenient. So that brings us to the next type of antenna, which is the semi directional there. It will emit RF in a manner similar to that of a street lamp.
You know what I mean by “street lamp”? In many subdivisions or out on the freeway, you’ll see these big poles that then stick out at a right angle with a light that’s shining straight down. And the purpose there is to clean the road. So it’s not omnidirectional, but it’s not very confined, right? It’s trying to light up the roads so you can see where you’re driving, rather than just using your headlights alone. And then a highly directional transmitter is going to radiate that RF in a fashion that would be a lot like a spotlight. Perhaps you’ve noticed that when there’s a new sale or the grand opening of a store, they sometimes put these big spotlights out there and you can see that beam going back and forth in the hope that it’ll help you drive in that direction.
I guess they think we’re moths and we’re going to drive to the lights, but it’s more like that. Or sometimes we use that to light up a floor flag or a sign. Those are highly directional. They would not be good for driving down the motorway and trying to see where I’m going because they would only show me a small area, maybe a section of a lane, rather than the whole area.
So again, omnidirectional antennas are designed to radiate that radio frequency in all directions. But this is a side view that we’re looking at, because when you hear this term, “all directions,” you think, “If I had that antenna, wouldn’t that encompass height, right, and all that area?” But really, it’s not. We’re focusing on this coverage from one lobe to the other, which, by the way, has height, which just simply means that we’re going to be able to get all the laptops and other machines while people are at their desks, standing up, or walking around.
However, it does not go very high vertically. And that’s another good thing to have because that way you know that it’s going to be per, let’s say, floor of an office or per floor of a hotel or things like that. Typically, these used to be called, well, you know, I think we call them rubber duckies, but they were rubber-coated antennas. I don’t know how well I can draw one, but usually you saw this little antenna with the connector, and then it had another connector that fit into the side of your access point.
Well, that was the most common type of antenna. And then many of them started getting coated in plastic. And today, when you buy an access point, you don’t even see an antenna because those antennas are hidden inside that actual access point. And the direction of this coverage literally depends on the orientation of that access, at this point. So where they used to be very common, when they would call them the default, they’re not as common anymore.
SY0-501 Section 1.1- Implement security configuration parameters on network devices and other technologies.