Signal Strength and Antennas - USALearning Strength and Antennas. ... one that's the least strong on the . signal; and then makes the replies to . the traffic inbound off the one that's

Signal Strength and Antennas

Table of Contents

Antennas ......................................................................................................................................... 2

Antennas Concerning Gain/Loss ..................................................................................................... 3

The Reference Antennas ................................................................................................................. 4

Antenna Coverage Patterns ............................................................................................................ 5

Antenna Patterns and Uses -1 ........................................................................................................ 6


Antenna Patterns and Uses -1 ........................................................................................................ 8


Antenna Patterns and Uses -1 ...................................................................................................... 10



Diversity Antenna Systems ........................................................................................................... 14

Notices .......................................................................................................................................... 16

Page 1 of 16

Antennas

30

Antennas

**030 So then we're going to talk about antennas.

Page 2 of 16

Antennas Concerning Gain/Loss

31

Antennas Concerning Gain/Loss

Gain is an increase in signal strength.

Loss is a decrease in signal strength.

Gain can be active (as in an amplifier).

Passive gain occurs when existing RF energy is refocused into a smaller area, increasing signal strength in that area.

• Using antennas to focus signal strength will create passive gain. — Can enhance security by decreasing signal strength in unwanted areas)

**031 Gain being an increase in signal strength; loss being a decrease. Gain can be active. Active gain is known as an amplifier; because it's actually going to put more power into the system. And passive gain occurs when the existing energy is refocused into a smaller area, like this.

Page 3 of 16

The Reference Antennas

32

The Reference Antennas

The isotropic antenna (the theoretical point in space emitting a signal) is a 0dB gain antenna.

A half-wave dipole antenna is the practical reference, with a spherical-shaped radiation.

**032 So there's your isotropic reference antenna.

Page 4 of 16

Antenna Coverage Patterns

33


Antennas can be• Omnidirectional – a 360° pattern on one axis• Semi-directional – directional pattern down to 30°• Highly directional – patterns below 30° on an axis

Antenna beamwidth can be diagrammed on two planes• Azimuth (top-down view) (the “H” or horiz. plane)• Elevation (side view) (the “E” or elevation plane)

**033 And antennas can be omnidirectional, semi-directional or highly directional. And we already said this one is omni. Right? This one is-- Student: Semi-directional. Joe Mayes: Semi. And this one is? Student: Highly directional. Joe Mayes: Right. You know how you can tell this one's highly and this one's semi? You don't feel threatened when I point this one at you. You do feel threatened when I point this one at you. It looks like the ray gun. Right?

Page 5 of 16

Student: Hum. Joe Mayes: Antenna beamwidth is diagrammed on two planes: Azimuth and Elevation; otherwise known as the H plane or the E plane.

Antenna Patterns and Uses -1

34


Dipole omnidirectional• Good for general area coverage: doughnut pattern extends

horizontal distance in 360° radius.

**034 There's that donut I was talking about. So just for fun, this is an omnidirectional antenna on which azimuth? Oh they forgot already. Student: Yes.

Page 6 of 16


33




**033 Horizontal or Elevation? Student: Horizontal. Student: I see both. Student: Horizontal. Joe Mayes: Right. If I looked at this from the top down, what would I see?

Page 7 of 16


34




**034 A perfect circle. Right? So it's 360 degrees from looking the top down.

Page 8 of 16


33




**033 So from the top down or the H plane it's a omnidirectional antenna.

Page 9 of 16


34




**034 From the E plane it's not omnidirectional; is it? From the E plane it's going to look like a figure 8 on its side. Because I'm looking at the side of the donut. If I cut the donut in half, what do I see? I see two circles here. Correct? You can see it on the screen. Right? So from the side view it's not omnidirectional; it's not even across the whole 360 degrees. If it were, looking at it from the side view I'd just see another circle. But I don't see a circle, I see a donut; I see a donut sliced in half.

Page 10 of 16


35


Patch antennas and Panel antennas• Mount flat against walls• Pattern extends horizontal distance in

approx. 180° radius• Used to focus signal within a building by

mounting inward-facing on interior of building shell walls

**035 So a patch antenna and panel antennas; they're going to generally speaking extend out in some 120, 180 degree radius. Basically they're trying to cover somewhere between a third and a half of the environment. They're not highly directional, they're just moderately directional. With a patch antenna it's not about where it goes as much as it is about where it didn't go. Generally speaking, when you want to use a patch antenna you're not as concerned about where the signal's going as you are about where you don't want it to go.

Page 11 of 16

If you put this on an outside wall, your primary concern is not where the signal is going, it's where the signal is not going; like not into the parking lot. If I'm doing this one here, my primary concern is where it's going. Do I want to pick up off of Tracy or do I want to pick up off of John? If I'm using this antenna, I'm more concerned that I'm not picking up from behind me; I don't care where I pick up out here. Does that make sense? Student: Mm-hm.

Page 12 of 16


36


Yagi antennas and parabolic dish antennas

• Highly directional antennas for focused or point-to-point coverage

• Used either to achieve distance or to deny signal in unwanted areas

**036 Joe Mayes: And then there's always the highly directional antennas: Yagis and parabolic dish antennas. When you go to look at these things, they actually will give you antenna patterns.

Page 13 of 16

Diversity Antenna Systems

37

Diversity Antenna Systems

Usually use 2 dipole antennas

Use electronics to search for best signal between 2 antenna elements

• Elements are separated by a distance that can compensate for multipath fading.

Only one antenna transmits/receives at a time.

**037 So you can see exactly what you're going to get. Now what's diversity antenna systems? Diversity antenna means I've got two elements or two antennas coming off the same box. Now if you think about all the things we talked about, especially Rayleigh Fadings and stuff like that, why would you put two antennas on a box? Student: Pick up more- more of the same spectrum.

Page 14 of 16

Joe Mayes: Mm-hm. How many of them are active at one time? Only one of the two. What happens is-- remember Rayleigh Fading said if it bounces off it's going to cancel the signal out; but if I move over just a little bit it won't be cancelled out? Well one way to move over a little bit is to have two antennas. And by the way, when you see two antennas on the side of a box, the distance apart they are is determined by the frequency-- I'm sorry, determined by the wavelength. Because what they're trying to do is move over exactly half a wavelength away. So that if it's cancelling out on this one, it can't also be cancelling out on this one at the same time. And what happens is it looks for relative signal strength coming in off of both of them and shuts down the one that's the least strong on the signal; and then makes the replies to the traffic inbound off the one that's up. And it can do that thousands of times a second too. We're not talking about turning it off and changing it for half an hour. It can change dynamically thousands of times a second. Because if you have 20 different users in 20 different locations, this antenna may be best for six of them and this antenna may be best for the other 14.

Page 15 of 16

So it dynamically runs that; and that's why they're built in; and that's why it's cool; and that's why it costs more money to get a fancy machine with two antennas than this cheap machine with only one. Because a cheap machine with only one doesn't have a diversity antenna system.

Notices

2

Notices© 2014 Carnegie Mellon University

This material is distributed by the Software Engineering Institute (SEI) only to course attendees for their own individual study.

Except for the U.S. government purposes described below, this material SHALL NOT be reproduced or used in any other manner without requesting formal permission from the Software Engineering Institute at [email protected].

This material was created in the performance of Federal Government Contract Number FA8721-05-C-0003 with Carnegie Mellon University for the operation of the Software Engineering Institute, a federally funded research and development center. The U.S. government's rights to use, modify, reproduce, release, perform, display, or disclose this material are restricted by the Rights in Technical Data-Noncommercial Items clauses (DFAR 252-227.7013 and DFAR 252-227.7013 Alternate I) contained in the above identified contract. Any reproduction of this material or portions thereof marked with this legend must also reproduce the disclaimers contained on this slide.

Although the rights granted by contract do not require course attendance to use this material for U.S. government purposes, the SEI recommends attendance to ensure proper understanding.

THE MATERIAL IS PROVIDED ON AN “AS IS” BASIS, AND CARNEGIE MELLON DISCLAIMS ANY AND ALL WARRANTIES, IMPLIED OR OTHERWISE (INCLUDING, BUT NOT LIMITED TO, WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE, RESULTS OBTAINED FROM USE OF THE MATERIAL, MERCHANTABILITY, AND/OR NON-INFRINGEMENT).

CERT ® is a registered mark owned by Carnegie Mellon University.

Page 16 of 16

Documents

Signal Strength and Antennas - USALearning Strength and Antennas. ... one that's the least strong on the . signal; and then makes the replies to . the traffic inbound off the one that's