Hello everyone, this is Chan Byoung Chae from Yonsei University. I'm really happy to take this opportunity to meet you through this online lecture. So if you have any questions about my lectures, you could drop me an email, or leave a message on Coursera website. I will try to get back as soon as possible, once I read your comments. Okay, let's get started. In the previous lectures, I believe you had to learn about the basics of cylinder networks, principles of wireless communications, and wireless radio management. In this module, I want to talk about the multiple antenna technologies. This is an agent of my lectures. After Basics of RF Antennas, we have some questions to understand the key concepts. The first question is, how can we achieve higher antenna gain? By the way, don't worry if you don't know some technical terms right now. If you already know the terms, you can skip my lectures. Second question is, how can we decrease error probability, especially in the high SNR regime? After that, we will try to have an answer to the question on how can we increase data rates? And we will conclude this lecture by answering the last question, which one is good, supporting just a single user or multiple users? Before introducing multiple antenna tactics, I'd first like to explain what the antenna is. I am pretty much sure that everyone taking this lecture has a cell phone or a smartphone. If you open the case of the phone, we should be able to see these kind of board, and you will see several antennas inside. Yes, we have already been using antennas. Then, what is the antenna? What's the role of an antenna? Are we not able to use smartphone without this antenna? An antenna is an electrical device that converts electric power into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies electrical current oscillating at a wave to the antenna's determiners. The antenna rated the energy from the cone as electromagnetic wave. And reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, and that is applied to our receiver to be amplified. Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field. The radio waves are electromagnetic waves that carry signals through the air at the speed of light with almost no transmission loss. The radio transmitters and receivers are used to convey signals, synchronize information here, and this system including broadcast radio, television, mobile telephones, WiFi, data matrix, many remote controlled devices, such as the wall remote sensors among many others. Radio waves are also used directly for the measurements in technologies, including radar and GPS. In each and every case, the transmitters and the receivers involved require antennas, although these are sometimes hidden, such as the antenna inside laptop computers, equipped with WiFi. In sum, the antenna is a bandpass filter, and it plays like our mouths and ears. Antenna can be classified in various ways. Monopole, the most common form is the quarter-wave monopole, which is one quarter of a wavelength long and has a gain of about 5.12 DVR when mounted over a ground plane. Monopoles have an only direction or wave patterns, so they are used for broad coverage of an area. Dipole, the most common type, a half way dipole consists of two regiment elements, just under a quarter wavelength long. This antenna radiates maximal in all direction, perpendicular to the antenna's axis, giving a small interactive gain of 2.15 DVR, practically, the lowest directive gain of any antenna. Although half way dipoles are used alone as only direction antennas, they are also a building block of many other more complicated, directional antennas. Microstrip is an example of dipole antennas. This consists of metal sheets mounted over a ground plane, which is similar to dipole with gain of 6.90 DVR. There is each fabrication a specific technique that have made them popular in modern wireless devices. Open using erase. In there, we use these kind of antennas for a smartphone. To achieve higher directivity gain, of course, I will explain later about this one. There are specialized antennas like feedhorn and cassegrain. Okay, then let's more focus on antennas for small devices like smartphones. As I explained, each type antennas are widely used, but even about 10 to 15 years ago, most cell phones have this kind of whip antennas. For small cell repeaters and Playstations, chip antennas have always been used. So far, we have learned how the antenna looks like, and here, I want to introduce a parameter that describes the electrical behavior of an antenna. S parameter is basically the return loss. Since we want to transmit a certain energy through the antenna, and we don't want to get any feedback see on the phone the antenna. Return loss is a loss of power And the signal return or reflected by discontinuity in a transmission line. This can be a mismatch with a terminating load or with a device inserted in the line. The return loss is a measure of how well antennas are matched. A match is good if the return loss is high. The high return loss is desired. Return loss with positive sign is identical to the magnitude of the red flashing coefficients. When expressed in decibels but are opposite sign, that is, return loss with negative sign is more properly called reflection coefficient. There's parameter S11 from 2 port, and that is frequently also called return loss, but it's actually equal to the reflection coefficient. Obviously, the smaller S11 and S21, the better performances. And let's have some S11 curves. Here, we plot the S11 versus frequency and that is for the communications, since it has relatively low return loss. And depending on the design requirements, we could have different curves. The lower S11 values like pink curve, the bandwidth becomes narrower. So, if your system issues a port wide band, then you might want to have a specially designed additional filter to guarantee the sufficiently low S11 values. Another important parameter we need to consider in this lecture is radiation pattern. The term radiation pattern refers to the direction or angular dependence of the strands of radio waves. Since electromagnetic radiation is dipole radiation, it is not possible to build an antenna that radiates coherently equally in all directions. Although, such a hypothetical isotropic antenna is used as a reference to calculate the antenna gain. The plot radius and pattern you might want to upload PCAAD which is a freeware for the point source for example, if we cut the sphere we always have a circle for electric field and magnetic field. However, the simplest antennas, monopole and dipole antennas consist of one or two straight metal rods along a common axis. These symmetry antennas have waves in patterns with a cylinder symmetric code, the omni-directional patterns. They radiates equal power in all directions perpendicular to the antenna with the power bearing only with the angle to the axis. Dropping of radiator at antenna's axis, this illustrates the general principle that if the shape of an antenna is symmetrical, its radiation pattern will have the same symmetry. An antenna's power gain will simply gain. It'll keep performance member that combines the antenna's directivity and also electrical efficiency. As a transmitter antenna, the gain describes how well the antenna converts input power into radio waves headed in specified directions. As a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electric power. When no direction is specify, the gain is understood. We refer to the peak value of the gain. A plot of the gain as a function of direction is called the radiation pattern. Antenna gain is usually defined as a ratio of power produced by the antenna from a far-field source on the antenna's beam axis, here at b. The power produced by hypothetical mostly are isotropic antenna, which equally sensitive to signal from all directions, here it's a. Usually this ratio is expressed in decibel, and these units are report as decibel isotropic, DBR. An alternative definition compares the antenna to the power received by lossless halfway dipole antenna in which case the units are written as DBD. To get the antenna gain, the same energy is assumed for the cases of with directivity and without directivity. Note that directive gain or directivity is a different measure that does not take an antenna's electrical efficiency into account. These terms is sometimes more relevant in the case of a receiving antenna where one is concerned mainly with the antenna to receive a singular from to one direction, while rejecting in a form coming from a deeper one direction. And then, there's a trade off between the antenna gain and the beam width. The higher the antenna gain, the narrower the beam width source, therefore, the copper with long range, you should have a passive beam. But if you try to mismatch the direction, you're going to lose huge mixed gain. This is a simple example. Suppose that he have transmits sudden dBm power and a passless between the transmitter and the receiver is 55 db. Then, without the antenna gain, the Rx would receive minus 25 dBm. However, with five dBr and 10 dBr the additional gain, we simply have -20dBm and -15 dBm, we see power. This is a simple link budget analysis Let's take a look at evolution of antennas. The first antenna were built in 888, 1888 by German Heinrich Hertz. He placed [INAUDIBLE] antennas at the focal point of parabolic reflectors for both transmitting and receiving. In 1926, approximately 40 years later from the first antenna, Uda and Yagi invented a directional antenna consisting of multiple parallel elements in a line. This kind of design achieved a very substantial increase in the antenna's directivity. Later Patch antenna also known as microstrip antenna was proposed. This is a narrow band and wide band antenna. By using the symbol entire elements, phase array are demonstrated in 1957 by Hughs Aircraft Company. They showed simultaneous electrical scanning in both azinous and elevation. Smart signal processing algorithms were used to identify the spatial signal's nature, such as the directional arrival of the signal for smart antenna systems. In 2000, PIFA has been widely used in mobile wireless devices for its space saving properties. As you can see from this slide, there has been very active research progress in the last 100 years. Mostly to achieve higher gain, wider bandwidth, better pattern, higher efficiency, lower cost and smaller size. Then let's take a different perspective. Evolution of antennas for link enhancement. In early 1900s we used non-adaptive static beamshaping. For this difference coppers together with fixed phase arrays and antenna arrays were used in forming networks. Such as partial matrix to create a radio beam in any criss-crossed direction. To increase the link reliability the receive diversity techniques were proposed and more sophisticated signal processing in spatial and temporal domains were developed. In 1990s the term MIMO, Multiple Input Multiple Output was first used for central propositions for single user scenarios and it was evolved into multi user scenarios. What is multiple antenna technique? What will we learn in this lecture? Let's have one more example. It might be quite ridiculous but suppose we have one more mouth and one more set of ears. If you're supposed to read a collection of fairy tales to your children you could say more. Or you could have clear message. This is the same for telecommunications. The antenna is like our mouth and ears. The more the antennas, the higher the transmission rate order, the better the link reliability. From now on, throughout this lecture, I will introduce some represented techniques to achieve this course. In the first part we have learned the basics of passive antenna device, antenna types, S parameters, antenna gain and so on. In the next part we will cover a way of increasing antenna gain through multiple antennas.
