Introduction to Radar Systems – Lecture 1 – Introduction; Part 1

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Summary

This lecture, part of MIT Lincoln Laboratory's course on radar systems, introduces the historical and technical context of radar technology's development, with a focus on its impact during World War II, particularly in the Battle of Britain. Radar's role in military and civilian contexts is emphasized, from enhancing air defenses to aiding in complex military strategies and operations. The lecture also outlines the fundamental principles of radar, such as wave frequency, polarization, and how radar waves are used to detect objects.

Highlights

Radar tech has been crucial for MIT Lincoln Laboratory since 1951, focusing on air defense. 📡
Few US universities offer radar courses, so the lab educates both staff and external partners. 🎓
The Chain Home radar system was key in the British defense during the Battle of Britain. 🛡️
Radar helps eliminate the 'fog of war' by providing critical early warnings and object detection. 🌫️
The lecture covers basic radar concepts like wave frequency and polarization for object detection. 📏
Radar is used in various fields, from military to civilian, including air traffic control. ✈️

Key Takeaways

Radar has been integral to MIT Lincoln Laboratory's mission since 1951, particularly in air defense technologies. 📡
Educational initiatives at the laboratory aim to fill the gap in radar education within US universities. 🎓
Radar technology was a game-changer in WWII, notably in the Battle of Britain with the Chain Home system. 🛡️
The foundational principles of radar, such as wavelength and polarization, are crucial for detecting objects. 📏
Radar applications range from military to civilian uses, including air traffic control and automotive safety. 🚗

Overview

Radar technology has been a cornerstone of MIT Lincoln Laboratory's mission since its inception in 1951. The lab has played a crucial role in the development of radar systems, initially for air defense against potential threats like Russian bombers. Given the scarcity of radar courses in American universities, MIT Lincoln Laboratory has also been a hub for educating both its staff and external stakeholders on radar technology.

The lecture highlights radar's historical significance in military operations, particularly during World War II. The British Chain Home radar system was pivotal in the Battle of Britain, allowing for advanced warning and successful strategic deployment against German forces. This technology fundamentally changed the dynamics of military operations by offering early detection and helping to mitigate the 'fog of war.'

Radar extends beyond military applications, finding usage in civilian sectors such as aviation and automotive industries. Its ability to detect objects through diverse conditions, including adverse weather, makes it invaluable. Fundamental radar concepts, including wave frequency and polarization, are explored in this lecture, laying the groundwork for understanding radar's technical and practical applications.

Chapters

00:00 - 05:30: Course Introduction and Overview The chapter provides an introduction to the course on radar systems, highlighting the historical context of radar development at Lincoln Laboratory. Formed in 1951, the Laboratory's mission included creating an air defense system to counter potential attacks, particularly against Russian bombers in the early 1950s. The chapter sets the stage for understanding the integral role radar systems play in defense and technology development.
05:30 - 10:30: Educational Programs and Course Development The chapter discusses the involvement of the laboratory in educational programs and course development, particularly in the field of radar technology. The laboratory has been a significant player in creating programs to keep their staff updated with the latest advances in radar, due to the scarcity of radar courses available in US universities. This effort has been ongoing for many years, highlighting the laboratory's commitment to education and staying ahead in technological advancements.
10:30 - 16:30: Radar in Different Fields The chapter discusses the role of radar systems in various fields and the educational efforts to train new staff members at different educational levels such as bachelors, masters, or PhD. It emphasizes the introduction of radar technology and systems to new staff members.
16:30 - 19:30: Military Application of Radar This chapter discusses the origin of the lectures as a derivative of an intense three-day course designed for military officers and government civilians. The focus is on those involved in the procurement, technical evaluation, and operation of radar systems. The course is not only relevant to the Department of Defense but also to other government agencies like the FAA and NOAA.
19:30 - 23:30: Battle of Britain Radar Impact The chapter 'Battle of Britain Radar Impact' discusses the creation of a specialized course designed for individuals like lieutenant-colonels, who typically have advanced degrees such as a master's in business administration, as well as backgrounds in various engineering fields like chemical or mechanical. These individuals may also have an educational background from a service academy.
23:30 - 31:00: Modern Radar Systems The chapter begins with an introduction to the educational background of individuals involved in radar systems, noting that while many had college degrees, advanced degrees weren't as common among them. The text mentions the creation of a new course designed to educate these individuals in the fundamental concepts, technology, and vocabulary associated with radar systems. The course aims to bridge the knowledge gap and modernize their understanding to align with the expertise found at institutions like Lincoln Laboratory.
31:00 - 39:00: Basics of Radar Functionality The chapter, 'Basics of Radar Functionality,' discusses various aspects of radar technology, specifically focusing on techniques that are more effective in rejecting clutter and detecting targets. It highlights the importance of understanding important radar terms such as beam width and bandwidth. The content is part of an intensive three-day course designed to enhance comprehension of radar's fundamental concepts and terminologies.
39:00 - 45:30: Electromagnetic Spectrum and Radar Wavelength In this chapter, the lecture series on radar technology begins with an introduction to what is not included in the session. It highlights the absence of laboratory experiences, demonstrations, and facility tours that are usually part of a comprehensive course. Additionally, it mentions that discussions on operational military radar systems are restricted due to confidentiality agreements. Despite these exclusions, the series aims to cover the fundamental principles of radar technology for the audience, which is eager for this knowledge.
45:30 - 56:30: Wave Properties and Phase The chapter introduces a course on radar technology, particularly focusing on its availability to military contractors and their support and administrative staff. It highlights the potential audience for the course, emphasizing its usefulness across diverse fields in America. The chapter suggests that a basic understanding of how radar works could benefit not just experts in radar, but also individuals in various professional domains, underlining the broad applicability and importance of radar knowledge.
56:30 - 59:30: Polarization and Electromagnetic Waves The chapter discusses the basics of radar technology, possibly from a legal or governmental perspective. It highlights the relevance of radar in various fields such as patent law, government arms control and development, and automotive industries, particularly in collision-avoidance systems.

Introduction to Radar Systems – Lecture 1 – Introduction; Part 1 Transcription

00:00 - 00:30 well welcome to this course introduction to radar systems since Lincoln Laboratory was formed in 1951 the development of radar systems has been an integral part of our initial mission developing an air defense system to protect against a polar attack from Russian bombers in the early 50s but it's also been the development of radar
00:30 - 01:00 systems has been a major part of many of our programs at the laboratory given that and given that very few courses in radar are available at US universities and have been for decades and decades the laboratory has been involved in a significant educational program for our staff members to not only keep them abreast of the latest radar technology
01:00 - 01:30 developments but to educate new staff members as they come into the laboratory at that different educational levels of the bachelors masters or PhD to introduce them to radar systems and technology in 2001 I believe we realized that a lot of our sponsors could use some of this education to to help them to do their work and we developed a
01:30 - 02:00 course that this set of lectures is derivative from that particular course was an intense three-day course for our sponsors military officers and government civilians those involved in the procurement of radar systems and there are technical evaluation and their operation and not only with the Department of Defense but also with other government agencies that we do work for like the FAA and NOAA
02:00 - 02:30 and so what we did was we put together a course for their level of knowledge that they'd come into the course with a typical person coming into the course might be a lieutenant-colonel a very smart person and he or she would have maybe have a master's in business administration they might have some engineering background but it might be in chemical or mechanical engineering they might come from a service academy
02:30 - 03:00 where they had a diverse background in education but many of them would not have they would have had a college degree certainly but they wouldn't be as involved in the the formalism and have the advanced degrees that many of us at Lincoln Laboratory have so we put this course together to teach them the basic concepts of radar and the technology and the vocabulary of radar so that when we
03:00 - 03:30 briefed them and explained to them different areas of radar technology why one technique was better than another for rejecting clutter and seeing targets and in that sort of thing are all sorts of things they'd understand the vocabulary they know the difference between the beam width and bandwidth words you'll get to know and so we put together this course and this course is again three days very intense
03:30 - 04:00 now there's some things that this set of ten lectures certainly doesn't have it doesn't have the laboratories it doesn't have the demonstrations the tours of facilities at the laboratory and it certainly doesn't have certain lectures on operational military radar systems that are covenants don't allow me to present to this public audience but this is the core of the basics of what radar is all about and there are many people outside of the government who asked us
04:00 - 04:30 to make this course available to them particularly military contractors they have many people in their organizations that they thought this would be a useful course for not their engineers who are experts in radar but people who work in support and administrative area and likewise as I look at the potential audience for this course there are many in diverse fields in America where a very basic course in how radar works would be very useful you might be a
04:30 - 05:00 patent attorney who has come across a patent that involves radar and you'd like to understand the basics of the nomenclature of what's going on there it might be you work in the government in the arms control and development agency and your background is in the law you might be in the automotive industry and radars are being looked at if a Kalitta collision-avoidance small compact and
05:00 - 05:30 expensive radars you might want to get an understanding of what this technology can and can't do in a general sense so they and that's just the beginning a plethora of people you might be a civilian air traffic controller a civilian pilot wants to know how the radars work that's C and keep them safe so there are lots of different people that this course will be useful for and this is a first basic cut we of course at the laboratory have a series of courses which Dolf higher and higher
05:30 - 06:00 into the technology efforts and if this course is successful I hope to put together the next level up where this would be the introduction and then there'd be an intermediate and etc which would be of use to people with need of a deeper intellect a deeper knowledge excuse me of the formalism and the mathematics that goes with this ok first I'm going to introduce the whole subject of radar in the first lecture in other
06:00 - 06:30 words in the first hour we're going to do the whole courses very quickly and very lightly first I'd like to acknowledge that let's see about 2,000 early six seven years ago like katatak or similar to this for our entering bachelors of science graduates who would come to the laboratory did the whole thing myself certainly when one would put together a three-day intensive course you don't
06:30 - 07:00 want to see 1015 hours of Bob O'Donnell in a row or even interspersed with labs and lectures so we had a whole series of best lecturers at the laboratory and experts in these different fields work on my set of lectures to modify them and make them optimum for this new audience and here I acknowledge Eric Evans and Andy ghurabaa who provided the manage support and guidance and overall helped
07:00 - 07:30 in putting this to not help with guidance in putting this whole course together along with a dozen or so of the key people who took my course and we all work together as a team and and got the visualizations the view graphs to be the best way to help augment the words that the lecture would say to communicate just how radar works and these people are just been marvelous and I'll probably acknowledge through
07:30 - 08:00 the different lectures an individual person or two as they as their lecture when it's clear that you know they've been just a major contributor and in all of this it's something you don't like blame me give them the kudos okay so as I mentioned before and this is just to recapitulate it's one of the many courses we have at the radar this one this look lecture you'll see set of lectures is relatively short ten lectures originally dr. Evans and I have
08:00 - 08:30 given this set of view graphs to as a six hour tutorial Electrical Engineering symposia and I'm going to be taking more time to go over things that was compressed where the certain lectures would be a half an hour a certain 45 minutes it was a time constraint of putting as much as we could in the three days that material is put is going to
08:30 - 09:00 take longer because I have the the freedom to go over and add more texture to make the course I hope a little more a little less like a marathon and more like a walk in the park easier to digest intellectually but it will be ten lectures we're going to divide the lectures the introduction lecture will
09:00 - 09:30 are probably broken into two pieces one half an hour or maybe the other half an hour which I'm just going to let the flow go to say the material take the time but not make the lectures each individual piece of a lecture each quantum so to speak more than a half an hour so that you can watch a half of a half of the introduction and a half an hour than the other half and another half an hour in terms of the scope as I said basic concepts and terminology is
09:30 - 10:00 what you'll have we're going to have a minimum of mathematical formalism and as with all good courses you tell people what the prerequisite is and really it's a college degree because if you have a college degree if probably in all probability of taking a basic course in the physical sciences which talks about the very basics of electromagnetism and also you're going to have taken at least a course in mathematics as part of your
10:00 - 10:30 general education requirement which you'll have a solid understanding of the algebra and that's about what we're going to start at the ground at the ground floor and the first lecture to some people may seem is quite pendentive but we'll move on I'd rather start a little lower and go over certain very elementary concepts and build them up rather than miss a bunch of the audience I already mentioned to the course was four and that we have other more
10:30 - 11:00 advanced courses at the laboratory that we'll be working about so this is really the the outline of the three big things we want to go over it's really two big things because the course agendas at the very end and that's just one view graph going over the outline of the agenda we're going to spend a chunk of time on why people build radars and therefore in very simple terms and I'm going to use you and use an illustrative example from World War two when radar was first developed to show you the
11:00 - 11:30 impact that radar had in a very major way in the strategic outcome of the Battle of Britain Wow you know and we'll go over the basic concepts of the very basics of the flow of a radar and what the basic vocabulary is and then we're going to take apart each piece of the radar later in a lecture and go over it in detail okay what radar is able to do
11:30 - 12:00 is so to speak lift the fog of war what am i mean by the fog of war war is utterly chaotic Eisenhower said that and I'm paraphrasing him that all planning plans in war are useless but planning is indispensable and when he said that first part that plans are useless it's because you just don't know what's going
12:00 - 12:30 to happen all of you of probably are watching this have seen either Saving Private Ryan or the HBO series the end of brothers the airborne troops landing god knows we're far away from where they're supposed to the utter chaos on Omaha Beach supposedly intelligence said it was going to be defended by conscripts from Eastern Europe and at the last minute the Germans had brought in a Panzer Division a lot of things
12:30 - 13:00 that was supposed to work didn't going ashore was supposed to be amphibious tanks the waves were high and they all just about sunk it was just an awful lot of unexpected happened and so the ability of not only generals who will run a whole army during that dynamic essence of a war but the Colonel's who run their big chunk of it
13:00 - 13:30 a brigade or a regiment the lieutenant's that run a company they want to see what's in front of them know what's there and radar is able to to wipe away that fog of war and certainly you can see on the left-hand side in that view graph that smoke is on the the banks and the the the cliffs of of Normandy is metaphorical and and very vivid of what
13:30 - 14:00 the fog of war that those brave soldiers were facing when they went ashore at d-day and if you go to the Pacific just the the banging together of the the the general that was in charge of Iwo Jima had 21,000 troops on Iwo Jima and he said a million troops in a thousand years would not be able to take it the alive said we're going to shore with the
14:00 - 14:30 usual number three and a half times that number and we're going to take it in five days well it took him 25 days in innumerable deaths and heroism and it was utterly chaotic you could see you could mention a time and time again the unexpected and so often you'd like something to tell you what's ahead of you okay so we have military means of sensing that is to say what's out there electronic systems and and and they can
14:30 - 15:00 be divided up into electrical optical infrared systems radar acoustic and other and I'm not going to focus on the electro-optics or the acoustic or other sensors but just on radar and what their functions are what is it that they can do they can give you surveillance to tell you are there targets out there that we should worry about and you can track them follow the targets and see where they are direct the
15:00 - 15:30 interceptors to those targets to knock them down use radar to identify the targets identified from airborne radars targets on the ground where you can do surveillance reconnaissance map where troops are detect Morrow moving targets both in the air and on the ground and in space do air traffic control to keep track of your aircraft whether you're in a certainly in this military environment
15:30 - 16:00 but your traffic control radars in the civilian environment very important you can also put small radars on missiles to help the missiles seek and find targets now what are the attributes that radar has if you had your list it can see long distances if I get up on a mountain and I look out in the clearest of days I can see an aircraft 10 15 miles away maybe a big jet you can see hundreds of miles for the radar and also you can see in
16:00 - 16:30 day and night and you can see in all weather you can see through weather you can locate here we say in 3-space that means in both height angle and just to know exactly in space XY and Z you know where the target is and radar is reasonably robust to people trying to countermeasure it that is with put adding noise jamming the radar as it's
16:30 - 17:00 called or dropping so-called chaff to give false targets it's reasonably robust to handle that okay now I want to go into an example and this is really history to show how radar made such a big difference in 1936 Great Britain new war was impending and it built a series of radars at these 21 locations where you see the dots and this was called the
17:00 - 17:30 chain home radar system okay and it was all operational in the summer of 1940 when the Battle of Britain started and Germany started trying to bomb Great Britain into submission here we see on the right a picture of three of the towers which supported the antennas this picture was taken about a year ago by a tourist to Robert Cromwell and these still stand
17:30 - 18:00 over on this by Dover that's the radar site at Dover now the antennas that were part of this radar none of them exist and this is a visualization from technical documents that describe the radars on what this radar system was like it had redundant antennas one on the right and one on the left and the end the frequencies of the
18:00 - 18:30 radar were the frequency range that the radar operated and was 20 to 30 million cycles per second that it emitted the pulsed radiation that's a wavelength that corresponds to 10 to 15 meters 30 to 45 feet the the antennas are quite simple they were wires dipole arrays 8hi and if you look at this particular configuration of antenna it reminds one
18:30 - 19:00 it was built at this high frequency because that was the frequency that they could build transmitters in those days they couldn't build transmitters well they were just starting to when the war began build transmitters of smaller wavelengths which you'll see later implies smaller antennas than these large structures the asmath beam was with us about a hundred degrees and it had a peak power of the pulse of energy of about 350 kilowatts was later raised
19:00 - 19:30 to 750 kilowatts and pulses of energy was sent out about 20 times a second excuse me I think was about 15 times a second and the pulse width was about 20 microseconds and that radar had the ability to detect a German bomber at about 125 to 150 and on one of the pages that said 160 miles okay and it used one set of antennas to transmit and another set of antennas
19:30 - 20:00 over here to receive if we go to the next view graph here's what those antennas look like in detail the of steel tau is 360 feet high and this string of dipoles eight high and this particular these wavelengths the beam that went out had a big null the beam went out and had another called a side law but there was a big empty space and have had another antenna
20:00 - 20:30 whoa-ohh which was a set of four dipoles which filled in that null when we deal with propagation you'll understand more about this effect of the multipath that had lower frequencies and what it looks like and why it gives you detection issues well also going to study in detail antenna structures the receive antennas were sets of crossed dipoles so this system was able to see way out 160
20:30 - 21:00 miles that the germans were coming with one of the arrays and remember they were coming at night now the British had about 1,400 fighters and they were dispersed at many airfields and with little warning time if they didn't have this radar system which gave them great warning the British would wouldn't be able to concentrate the eliminate forces to attack the concentrated German forces coming at them and so there'd be an unevenness to the defending German
21:00 - 21:30 fighters protecting the abhorrent bombers and the British interceptors that wanted to knock them down the Bombers would have got in and dropped their bombs and got back before the British were able to do much but with this extra warning time it allowed the British to get their fighters the Spitfires and their hurricanes off the ground and that timely warning allowed them to focus their interceptors and achieve numerical parity with the
21:30 - 22:00 attacking Germans why was us all just important the Germans at this time wanted to invade Great Britain they knew they couldn't invade Great Britain without air superiority they didn't have such a great Navy relative to the British and the British had kept theirs in their harbors up in the fjords and Scotland and if an invasion started to come they'd bring down their Navy and sink though the invasion barges so what the British of the adjournments had to
22:00 - 22:30 do was get air superiority and it turned out in the Battle of Britain they could not achieve air superiority and the reason was is because the chain home system allowed them to concentrate their fighters and wear down the Germans to the point where they said we just can't do it it's an interesting innit note that even though once the Germans attacked the chain home antennas they never really understood what that these
22:30 - 23:00 were in a crucial radar system that provided that extra warning for the British and this really allowed the Germans to well excuse me it didn't allow them it denied them if superiority and consequently the invasion of Great Britain was postponed indefinitely one can just imagine if the Allies did not have Great Britain as a staging area the
23:00 - 23:30 the great difficulty that it would have been invading Europe later on in the war so that's a great example of how radar really made a difference in world war two since then we have built and the world has built all kinds of different radars that do many many different things here is a collage of photographs of a great number of different radars that do surveillance and fire control and I'll just a spotlight one or two of
23:30 - 24:00 them this is a photograph of a phased array radar that's a radar that electronically scans this particular one is down in Cape Cod and it gives warning during it particularly during the Cold War of Soviet there was an attack from Soviet submarine launched ballistic missiles here's the Patriot radar from the Patriot air defense missile system this is actually the first phased array
24:00 - 24:30 electronically scanned fitly phased array that was ever built in the in in the world it was in it's down in Florida at Eglin Air Force Base still operates and does the majority of the measurement and cataloguing of satellites that are rotating around the earth now here's a missile defense radar system and and here is these faces right here and here are the phased array radars with about a
24:30 - 25:00 10 centimeter wavelength the thousands of elements in each one of these two faces they're similar faces in the aft portion of the ship and they provide the they're the eyes of the carrier from the battle group and pretend do air defense for the fleet now when we look at airborne and air traffic control radars now here we see a picture of an air traffic control radar an FAA air traffic control radar there's one of these in
25:00 - 25:30 each one of the hundreds of couple hundred biggest airports in the United States and they keep track of all the aircraft within 60 miles of the terminal here we see an airborne radar on a kc-135 and the antenna is located in this rotating it rip radome here's a photograph of that antenna this particular radar mechanically rotates
25:30 - 26:00 and asmath and electronically scans also the fleet have airborne radars that give them warning these planes could get up high and give the fleet warning if there's an attack to the fleet and fighter planes have in their noses radars that will tell the fighter pilots when there are many many many many miles away if there are aircraft heading their
26:00 - 26:30 way there's also radars in the Global Hawk unmanned air vehicle and then there is a class of radar called instrumentation radars that very accurately and precisely measure the characteristics of targets a number of these are located on in Kwajalein and the Marshall Islands of the ones I've shown you this particular radar as I think oh seven or eight
26:30 - 27:00 hundred thousand pounds it is it's a it's just huge it's so big that it has railroad tracks that it rotates on and here is the facility of millstone Hill haystack radar and the haystack auxiliary radar out on millstone Hill and there's a hundred and twenty foot dish antenna similar to this under the
27:00 - 27:30 radome and the eye admits radiation at just three centimeters and building an antenna that precisely is just is a quite a feed one hundred and twenty feet across and you have to keep it to be a parabola to a tenth of a wavelength or a tenth of three centimeters so an engineering marvel to build that radars way back when it was built okay so now go down to the basics what is radar and how does it work well here
27:30 - 28:00 we see a visualization of an antenna and behind it of course is a transmitter and a receiver and building a shed or whatever and that antenna will take the emissions the microwave emissions from the transmitter and a pulse of energy will be transmitted it will go out it will propagate through the atmosphere and then it will impinge on a target here we
28:00 - 28:30 see visualized an aircraft and that target will then scatter some of the energy back to the radar where a switch will turn off the the transmitter and earlier it did after the pulse and listen for echoes and that echo the reflected pulse will be sensed by the radar and from the delay time of going out and back one can measure the range from where the antenna is pointing you
28:30 - 29:00 can measure the azimuth and elevation of the targets angles from the size of the echo its amplitude you can measure the target size it's so-called radar cross-section we'll get to what that is in a bit and also from looking at the frequency of the radiation the shift in the frequency of the radiation that comes back you can measure the speed of the target and also other features with processing such as imaging now the words radar come from radio detection in
29:00 - 29:30 ranging the acronym these words were used initially when radars would developed when people were dealing more with radio frequencies and they didn't really want to say microwave detection microwave electromagnetic wave detection and ranging now what part of you I've been alluding to the fact that these are electromagnetic waves that were transmitted and I want to I want to let
29:30 - 30:00 you know what part of the electromagnetic spectrum that we're dealing with and here we have a table with some visualizations there's courtesy of Berkeley National Laboratory which break up in it's a logarithmic scale it breaks up into each one of these units is a factor of and in wavelength and there's something that tells you how big it is like ten to the minus one and this is in meters that size of a baseball and radio waves are
30:00 - 30:30 very long ways say that they're the size of houses and soccer fields and then when we get down to very very short waves we are dealing with like a water molecule size waves x-rays gamma rays and in here of visible waves and the wavelengths are a millionth of a meter so called you know 10,000 angstroms so very very sure
30:30 - 31:00 microwaves are right here in the middle and and radio radar frequencies operate in the microwave region and some radars a little bit down in what's known as the very high frequency ultra high frequency and high frequency region but pretty much in this region here where we're dealing with wavelengths that typically are about an inch to maybe as tall as a human being that's generally ballpark
31:00 - 31:30 what the radiation that today's radars there are some radars that operate in the millimeter wave region and there are some radars that operate up and 10 meters 10 me too wavelength region but most of them the sizes are down in here and these correspond to certain frequencies I'm going to show you how the frequency and the wavelength are related in a minute through the speed of light but these frequencies correspond to 10 million up
31:30 - 32:00 to 10 billion cycles per second waves per second periods per second and you'll hear the words gigahertz and megahertz and I'm going to show tell you what those acronyms mean in a minute if you're not familiar okay so what are the properties of waves every wave has a wavelength and what does that mean here we have a simple periodic wave it's a sign
32:00 - 32:30 and it's if you were looking at a wave rippling along and a brook you know if you drop the pebble in and see that wave go out there's a peak in a trough and the distance between the two peaks is the wavelength that's called the period the distance is a wavelength the time it takes if we to watch that peak go to the next peak is the period of the wave and one over that period is the frequency the number of Peaks per second that you that go by and they are related through
32:30 - 33:00 this formula that the frequency of the wave is equal to its speed and since we're talking about electromagnetic waves which travel at the speed of light it's the speed of light divided by the wavelength and meters now the speed of light is very fast that's three times ten to the eighth or one and eight zeros meters per second that's 300 million
33:00 - 33:30 meters in a second and in our normal units its own width you deal with feet and miles it's a 186,000 miles per second okay now for the wavelengths that we're talking about these are frequencies that this corresponds o so a three gigahertz radar which that air traffic control rate I would have the one I showed you the wavelength is 10 centimeters and these
33:30 - 34:00 these show you the correspondence and they're just related through this formula okay the next concept I want to bring about is phase you can see that there was that up-and-down periodicity and you can measure the phase of one wave relative to another by looking at where one peak is relative to the other in this case we have two waves that are offset by 90
34:00 - 34:30 degrees so we call that a 90 degree phase offset and the algebraic expression for this wave is its height or amplitude time's the sign of the phase angle the phase angle over a period goes from 0 to 360 degrees 0 to 2pi ok for engineers there think I'm going to slow lawyers of barely remembering this from the trigonometry probably anyway and we see
34:30 - 35:00 down here this would be the algebraic expression this is going to be very important that difference in phase because sometimes if I add the two waves together it's important what the phase is one relative to the other whether they add constructively and reinforce or destructively now this talks about that constructive or destructive addition of
35:00 - 35:30 two waves in the upper left we have the constructive addition of two waves the peak matches the time of the peaks here and we come out with a wave which is twice the height than the same frequency if the waves are out of phase by a hundred and eighty degrees the peak of one will correspond to the the trough of the other if this is plus a that's minus
35:30 - 36:00 say add them together you get zero you come here at the zero point the zero allowed with a zero so in two waves out of phase by 180 degrees and you add them you get zero output if they're partially in phase we have partially constructive we'll get an answer for the addition in between now what we have if we have just random noise that's coming out they'll add together and there'll be a partial
36:00 - 36:30 because they're not in phase because the Cova the noncoherent noise just doesn't have coherence at all to it it's the sort of the addition of a whole bunch of random coherent signals and but the randomness is in the phase and when you add them together you'll get some addition and it will be in between but it isn't as much as you can't get the full Co
36:30 - 37:00 here in addition from knowing coherent signals what this tells you now here we have an example of want to go back there of the concept of polarization to describe polarization I have to describe to you what an electromagnetic wave is and how its generated and that takes a minute and right after that we're going to take a break an electromagnetic wave is generated in the simplest form by taking
37:00 - 37:30 an electric charge and accelerating it up and down if you have celery to charge you get an electric field that varies with time and that an accelerating charge is a current that's changing and that current that's changing generates a magnetic field and Maxwell in the late 1800s figured out how this all ties together mathematically with a set of equations which really describe
37:30 - 38:00 electromagnetism ok these are called Maxwell's equations and with Maxwell's equations that's the mathematical description and what that says basically is that when you have an accelerating charge you generate an electromagnetic wave and the energy that's transmitted in that electromagnetic wave comes from the charge the moving charge going up and down and in the simplest terms that's how you generate electromagnetic
38:00 - 38:30 waves now the polarization is the orientation of the electric field vector ok I want to go back and here you see an electromagnetic wave propagating out in this Z direction and you see that the B field the electromagnetic field up here is vertical it's going up and down and that's referred to as vertical
38:30 - 39:00 polarization when the electric field is up and down if it was an electromagnetic field that came from accelerating and charged horizontally the electric field to be moving back and forth horizontally and that's called horizontal polarization and you can make will go Lane when we talk about antennas we'll talk about other kinds of polarization here's an example of the electric field for when it's vertically polarized the wave is and here the horizontal polarization
39:00 - 39:30 example now I'm going to take a break and we'll take a cut to the tape a break and then we'll come back and continue the introduction