Antenna Theory and Design

Transcription

1 Antenna Theory and Design Antenna Theory and Design Associate Professor: WANG Junjun 王珺珺 School of Electronic and Information Engineering Beihang University New Main Building F1025

2 General Information Scopes: Antenna theory and Design. Review from electromagnetics, microwave technology, the antenna family, fundamental parameters of antennas, point source, wire antennas, microstrip antennas, broadband antennas, some special antennas, antenna design software, antenna measurement, laboratory experiments. Pre-request Courses: Electromagnetics Theory, Microwave technology Textbook: John D. Kraus, Antennas: For All Applications 3rd edition, Constantine A. Balanis, ANTENNA THEORY- ANALYSIS AND DESIGN, 3 rd edition, Grading policy: final: 70%, homework+experiment: 20%, attendance: 10% Class/Laboratory Schedule: 26 lectures+6 experiments 8-9 weeks, every Wednesday, 4 classes/week

3 What is an antenna? A usually metallic device (as a rod or wire) for radiating or receiving radio waves.

4 4 What is an antenna? In science and engineering: A usually metallic device for radiating or receiving radio waves. In layman s opinion: magic! In electric engineer s opinion: it s a simple piece of metal with a highly complex task. In my opinion: it s an artwork!

5 A typical microwave communication system Analog Baseband and RF Circuits Communication Algorithms Protocols

6 Types of transmission lines TEM (quasi-tem) wave transmission lines Fig 1 TEM (quasi-tem) wave transmission line (a)parallel lines (b) Coaxial line (c) Stripe line (d) Microstrip line Wide bandwidth, high loss at high frequencies

7 Types of transmission lines TE & TM wave transmission lines Fig 2 Wave-guide transmission lines (a)rectangular waveguide (b) Circular waveguide (c) Ridged wave-guide (d) Elliptic waveguide Narrow bandwidth, low loss, high power, big volume

8 Types of transmission lines Surface wave transmission lines Fig 3 Surface wave transmission line (i) Dielectric waveguide (j) Mirror image transmission line (k) Single surface wave transmission line Simple structure, high power, small volume

9 Types of transmission lines Coax Connectors

10 Types of transmission lines Striplines Microstrip Embedded stripline Coplanar stripline

11 Chapter 1 Introduction

12 Chapter 1 Introduction General description of antennas Related history The EM spectrum and RF bands Types of antennas Radiation mechanism Future challenges Applications

13 1. Related history The history of antennas dates back to James Clerk Maxwell (a Scottish scientist) who unified the theories of electricity and magnetism, and eloquently represented their relations through a set of profound equations best known as Maxwell s Equations. His work was first published in He also showed that light was electromagnetic and that both light and electromagnetic waves travel by wave disturbances of the same speed.

14 1. Related history In 1886, Professor Heinrich Rudolph Hertz (a German physicist) demonstrated the first wireless electromagnetic system. It was not until 1901 that Guglielmo Marconi was able to send signals over large distances. From Marconi s inception through the 1940s, antenna technology was primarily centered on wire related radiating elements and frequencies up to about UHF. It was not until World War II that modern antenna technology was launched and new elements (such as waveguide apertures, horns, reflectors) were primarily introduced.

15 1. Related history While World War II launched a new era in antennas, advances made in computer architecture and technology during the 1960s through the 1990s have had a major impact on the advance of modern antenna technology, and they are expected to have an even greater influence on antenna engineering into the twenty-first century. Beginning primarily in the early 1960s, numerical methods were introduced that allowed previously intractable complex antenna system configurations to be analyzed and designed very accurately. With the advent of radar, centimeter wavelengths became popular and the entire radio spectrum opened up to wide usage. GPS, cellular phone, planets of the solar system, aircraft and ships, all types of wireless devices

16 2. Frequency bands Commercial broadcasting RF Band

17 2. Frequency bands Microwave band

18 3. Types of antennas 1 Wire antennas Wire antennas are familiar to the layman because they are seen virtually everywhere on automobiles, buildings, ships, aircraft, spacecraft, and so on.

19 1 Wire antennas Dipole

20 2 Aperture antennas Aperture antennas may be more familiar to the layman today than in the past because of the increasing demand for more sophisticated forms of antennas and the utilization of higher frequencies.

21 2 Aperture antennas Pyramidal horn Conical horn Rectangular waveguide

22 3 Microstrip antennas Microstrip antennas became very popular in the 1970s primarily for spaceborne applications. Today they are used for government and commercial applications. These antennas consist of a metallic patch on a grounded substrate.

23 3 Microstrip antennas Rectangular patch Circular patch

24 4 Array antennas Many applications require radiation characteristics that may not be achievable by a single element.

25 4 Array antennas Yagi-uda array Microstrip patch array Aperture array

26 5 Reflector antennas Because of the need to communicate over great distances, sophisticated forms of antennas had to be used in order to transmit and receive signals that had to travel millions of miles.

27 5 Reflector antennas Parabolic reflector Cassegrain reflector Corner reflector

28 6 Lens antennas Lenses are primarily used to collimate incident divergent energy to prevent it from spreading in undesired directions. By properly shaping the geometrical configuration and choosing the appropriate material of the lenses, they can transform various forms of divergent energy into plane waves.

29 6 Lens antennas

30 4. Radiation mechanism 1. Single Wire Charge uniformly distributed in a circular cross section cylinder wire Basic radiation equation: Charges (q) for transients and pulses Currents (I) for time harmonic variations I z : current over the cross section of the thin wire q l : charge per unit length in the thin wire v z : uniform velocity when total charge Q with volume V is moving in the z direction

31 4. Radiation mechanism Radiation condition: or a time-varying current an acceleration (or deceleration) of charge No moving charges no current no radiation (necessary) No variation in velocity of charges no acceleration (or deceleration) no radiation (enough) Question If charge is oscillating in a time-motion, radiation? Yes, it radiates.

32 4. Radiation mechanism 2. Two Wires Source Transmission line Antenna When the EM waves are within the transmission line and antenna, their existence is associated with the presence of the charges inside the conductors. However, when the waves are radiated, they form closed loops and there are no charges to sustain their existence.

33 4. Radiation mechanism Source Transmission line Antenna Electric charges are required to excite the fields but are not needed to sustain them and may exist in their absence.

34 4. Radiation mechanism If the electric disturbance is of a continuous nature, EM waves exist continuously and follow in their travel behind the others.

35 5. Radiation pattern

36 6. Antenna applications

37 Applications of an antenna Communication Basic operation of transmit and receive antennas in a communication system

38 Applications of an antenna Communication Radar Basic operation of transmit and receive antennas in a radar system

39 Applications of an antenna Communication Radar Wireless power transfer RFID Wireless charging Energy harvesting Collect energy from the environment Store the energy like a battery Drive low-power modules like sensors Virtue battery

40 Applications of an antenna Communication Radar Wireless power transfer RFID Wireless charging Energy harvesting Collect energy from the environment Antenna Store the energy Rectifier Storage module Communication Send signal of the sensor

41 Conclusions 1.What s the antenna basic radiation equation? 2.What s the microwave bands? 3.The introduction of the antenna family. 4.The radiation mechanism of the antenna? Question: 1. The current distribution on a linear dipole antenna of length and?