Oct. 16, 2006 Midterm Next Class Assignment #4 is Marked Problem session in lab today – review for midterm More Antennas

Midterm Overview Midterm Info: Sample questions: http://people.okanagan.bc.ca/dwilliams/courses/nten216/nten216_Quiz1.htm Sample questions: http://people.okanagan.bc.ca/dwilliams/courses/nten216/Tests/NTEN216_Midterm1SampleQuestions.pdf

Antenna Characteristics Gain and Directivity Radiation Pattern Polarization Input Impedance Antenna Efficiency Bandwidth Reciprocity

Bandwidth Range of frequencies over which antenna can transmit or receive signals effectively Can apply to a certain antenna Measurement is (Upper Frequency-Lower Frequency)/(Upper Frequency) e.g. 2.4GHz Dipole antenna may be able to transmit signals from 2.28 to 2.52GHz without significant loss of signal power. BW = (2.52-2.28)/2.4 = 10% Can apply to a certain type of antenna E.g. Half-wave dipole antennas in general have a bandwidth of 6GHz (0-6GHz) as long as the specific dipole size is set to the half-wave length

Antenna Input Impedance Want input impedance to match impedance of incoming cable Minimize reflections Maximize signal in to antenna Eliminate VSWR Impedance mismatch will reduce the antenna efficiency

Reciprocity An antenna can be used for transmitting and receiving If you know the transmit properties of an antenna, you know the receive properties of an antenna…they are the same Applies to: Gain, Radiation Pattern, Polarization, Input Impedance, Efficiency, and Bandwidth

Cutoff for Midterm Topics

Types of Antennas Omnidirectional Directional Half-wave dipole Quarter-wave monopole Directional Yagi-Uda antenna Patch antenna Parabolic Dish Phased Array Sector Antennas

Omnidirectional Antennas Ideally, radiates energy equally in all directions Isotropic antenna In reality, radiates energy equally in one plane, but not in other plane Omnidirectional in one plane

Half-Wave Dipole Dipole antenna consists of two conductors which stretch out in opposite directions Best dipole is when length is equal to half the wavelength of EM being radiated

Half Wave Dipole Characteristics Gain: 2dBi Typical Beamwidth: 80° x 360° Omnidirectional in horizontal plane Beamwidth in vertical plane can vary Polarization: linear, and perpendicular to antenna Bandwidth: 10%. Effective from 0-6GHz

Half Wave Dipole Radiation Pattern

Quarter Wave Monopole One conductor carrying the signal referenced to a ground plane Virtual mirror image of conductor created on opposite side of plane 2 x λ/4 = λ/2. This is effectively a half-wave dipole

λ/4 Monopole Characteristics Gain: 2-6dBi Typical Beamwidth: 45° x 360° Omnidirectional in horizontal plane Beamwidth in vertical plane can vary Polarization: linear, and perpendicular to antenna Bandwidth: 10%. Effective from 0 to very high

λ/4 Monopole Radiation pattern

Directional Antennas Focus coverage more in one direction than others Refers to all antennas that are not omnidirectional. Wide range of degrees of directionality Semidirectional: smaller gain, wider coverage region Highly directional: high gain, focused strongly in one direction, long distance range

Yagi Antenna One radiating dipole, one reflector to reflect signal in opposite direction, several directors to focus energy Size and number of directors determines directivity and gain

Yagi Antenna Characteristics Gain: 5-15dBi Typical Beamwidth: 50° x50° Polarization: Horizontal Bandwidth: 5% Effective from 50MHz to 2.5GHz

Yagi Antenna Radiation Pattern

Patch or Panel Antenna Consists of metallic plate and base sandwiching an insulating material Easy to manufacture Easy to mount Similar to Yagi Antennas in terms of performance Better than Yagis for cost, ease of use and aesthetics

Patch/Panel Antenna Characteristics Gain: 5-18dBi Typical Beamwidth: 50° x50° Polarization: Bandwidth: Effective from XXXHz to XXX Hz

Patch/Panel Antenna Radiation Pattern

Parabolic Dish or Grid Antenna Highly directional antennas, beamwidth can be as small as a couple of degrees Used for fixed location, long distance communications E.g. satellite, microwave towers Parabolic dish or grid focuses energy in one direction.

Dish Antenna Characteristics Gain: 20-30dBi Beamwidth: 1-10 degrees Polarization: can be linear or circular Bandwidth: 30% Effective from 400MHz to 13GHz

Parabolic Dish Radiation Pattern

Phased Array Antennas Group of independently fed active elements Input signals can be controlled to cause required constructive/deconstructive waveforms Result: antenna can be aimed without any moving parts

Phased Array Antenna Characteristics Gain: Varies widely Beamwidth: Varies Widely Polarization: depends on array. Bandwidth: depends on array. Effective from 10MHz to 10GHz Radiation Pattern: depends on array

Sector Antennas Generate “Pie Slice” radiation patterns “Pie Slice” width depends on particular antenna Because of predictability of slice, multiple antennas may be mounted together to give larger coverage area E.g. want 270° of coverage, but have only 90° sector antennas, what do you do.

Sector Antenna Characteristics Gain: 10-21dBi. A 90° sector antenna can still have variable gain by changing the vertical pattern Beamwidth: Depends on Pie Slice size Polarization: linear Bandwidth: Effective from

Sector Antenna Radiation Pattern

Increase coverage area by joining three 120° antennas together. Omnidirectional in horizontal plane, controllable in vertical plane.

Antenna Gain (dBi) Beamwidth Polarization Bandwidth Lower F Upper F λ/2 Dipole 2 80x360 Linear 10% None 6GHz λ/4 Monopole 2-6 45x360 Parabolic 20-30 1-10 33% 400MHz 13GHz Yagi 5-15 50x50 5% 50MHz 2GHz Patch 8-18 Varies Array varies 10MHz 10GHz Sector 8-21

Review What are lobes and nulls? If you have a right handed circularly polarized transmission antenna, what is the best kind of antenna to use as the reception antenna? If the gain of an antenna is 5dBi for transmission, and its beamwidth for transmission is 90°x45°, what would the gain and beamwidth be if it was used for reception? What is this principle called? A 1 watt signal is input to an antenna, but 200mW is reflected. The gain of the antenna is 10dBi, and the loss of power due to resistance is 50mW. What is the efficiency of this antenna?

Review What happens if there is an impedance mismatch between the antenna, and the cable coming into the antenna? The center frequency of an antenna is 104.7MHz, and at 104.7MHz it radiates 50 Watts of power. If it radiates a 100MHz signal, it can only output 12.5W of power, and at 110MHz, it can only output 12.5W of power. What is the bandwidth of this antenna?

Review In terms of directionality, what kind of antenna is this ? What are the horizontal and vertical beamwidths? In the vertical plane, what is the signal strength at 45° if the strength at 90° is 50mW?

Review Describe at least two ways to provide full wireless coverage to a large rectangularly shaped warehouse. Explain the types of antennas you would use and why. If you have need for long distance point to point communications, what kind of antenna would you use. What would you use a Yagi antenna for?

Resources http://www.arrl.org/tis/info/whyantradiates.html http://www.hp.com/rnd/pdf_html/antenna.htm http://www.connect802.com/wcu_articles.htm