Microwaves

Saja Ghazi Omar

What is a MicrowaveHistory of MicrowaveMicrowave SourcesUses of a Microwave Microwave Frequency

MeasurementsTheoryEffect on HealthReferfnces

What Is a Microwave

HISTORY

1846 Maxwell predicted the radio waves from

his equations.

1888,  Hertz  was the first to demonstrate

the existence of radio waves by building

a spark gap radio transmitter that produced

450 MHz microwaves, in the UHF region.

1894 Indian radio pioneer Jagdish Bose publicly demonstrated radio control of a bell using millimeter wavelengths, and conducted research into the propagation of microwaves.

1943, the Hungarian engineer Zoltán Bay sent ultra-short radio waves to the moon.

MICROWAVE SOURCES High-power microwave sources use

specialized vacuum tubes to generate microwaves.

Low-power microwave sources use solid-state devices such as thefield-effect transistor (at least at lower frequencies) tunnel diodes, Gunn diodes

USES

CommunicationRadarRadio astronomyHeating and power application

Spectroscopy

MICROWAVE FREQUENCY BANDS

The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 100 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range.

Letter Designati

on

Frequency range (GHz)

Wavelength range (mm)

Typical uses

L band 1 – 2 150 – 300 military telemetry, GPS, mobile phones (GSM), amateur radio

S band 2 – 4 75 - 150 weather radar, surface ship radar, and some communications satellites

(microwave ovens, microwave devices/communications, radio

astronomy, mobile phones, wireless LAN, Bluetooth, GPS)

C band 4 – 8 37.5 – 75 long-distance radio telecommunications

X band 8 – 12 25 – 37.5 satellite communications, radar, terrestrial broadband, space

communications

Ku band 12 – 18 16.7 – 25 satellite communications

K band 18 – 26.5 11.3 – 16.7 radar, satellite communications, astronomical observations

Ka band 26.5 – 40 5 – 11.3 satellite communications

Q band 33 – 50 6 – 9 satellite communications, terrestrial microwave communications, radio

astronomy

U band 40 – 60 5 – 7.5

V band 50 – 70 4 – 6 millimeter wave radar research and other kinds of scientific research

E band 60 – 90 3.3 – 5 UHF transmissions

W band 75 – 110 2.7 – 4 satellite communications, millimeter-wave radar research, military radar targeting and tracking applications

F band 90 – 140 2.1 – 3.3 SHF transmissions: Radio astronomy, communications, wireless LAN,

communications satellites, satellite television broadcasting,

D band 110 - 170 1.8 – 2.7 EHF transmissions: Radio astronomy, microwave remote sensing, amateur

radio, directed-energy weapon, millimeter wave scanner

MICROWAVE FREQUENCY MEASUREMENT

Microwave frequency can be measured by either electronic or mechanical techniques.

Frequency counters or high frequency heterodyne systems can be used. Here the unknown frequency is compared with harmonics of a known lower frequency by use of a low frequency generator, a harmonic generator and a mixer. Accuracy of the measurement is limited by the accuracy and stability of the reference source.

Mechanical methods require a tunable resonator such as an absorption wavemeter, which has a known relation between a physical dimension and frequency.

THEORY

The amount of radiation that can be absorbed by a body can be determined according to Beer’s Law:

Energy transferred from an electromagnetic wave which travels through space into a receiver objects, The rate of energy transferred per unit area called power density:

S = E × H

Specific absorption rate (SAR) is defined as the time derivative of the incremental energy (dW) absorbed by an incremental mass (dm) contained in volume (dv) of a given mass density (ρ).

EFFECTS ON HEALTH

Microwaves do not contain sufficient energy to chemically change substances by ionization, and so are an example of non ionizing radiation. The word "radiation" refers to energy radiating from a source and not to radioactivity. It has not been shown conclusively that microwaves (or other non ionizing electromagnetic radiation) have significant adverse biological effects at low levels. Some, but not all, studies suggest that long-term exposure may have a carcinogenic effect. This is separate from the risks associated with very high intensity exposure, which can cause heating and burns like any heat source, and not a unique property of microwaves specifically.

REFERENCES  Pozar, David M. (1993). Microwave

Engineering Addison–Wesley Publishing Company. ISBN 0-201-50418-9.

R. Sorrentino, Giovanni Bianchi, Microwave and RF Engineering, John Wiley & Sons, 2010, p. 4

 Microwave Oscillator notes by Herley General Microwave

 Sisodia, M. L. (2007). Microwaves : Introduction To Circuits,Devices And Antennas. New Age International. pp. 1.4–1.7. ISBN 8122413382.

Liou, Kuo-Nan (2002). An introduction to atmospheric radiation. Academic Press. p. 2. ISBN 0-12-451451-0. Retrieved 12 July 2010.

 "IEEE 802.20: Mobile Broadband Wireless Access (MBWA)". Official web site. Retrieved August 20, 2011

 "the way to new energy". ITER. 2011-11-04. Retrieved 2011-11-08.

 "Electron Cyclotron Resonance Heating (ECRH)". Ipp.mpg.de. Retrieved 2011-11-08.

 Raytheon's Silent Guardian millimeter wave weapon

"eEngineer – Radio Frequency Band Designations". Radioing.com. Retrieved 2011-11-08.

PC Mojo – Webs with MOJO from Cave Creek, AZ (2008-04-25). "Frequency Letter bands – Microwave Encyclopedia". Microwaves101.com. Retrieved 2011-11-08.

 Merrill I. Skolnik, Introduction to Radar Systems, Third Ed., Page 522, McGraw Hill, 2001.

Goldsmith, JR (December 1997). "Epidemiologic evidence relevant to radar (microwave) effects". Environmental Health Perspectives 105 (Suppl. 6): 1579–1587. doi:10.2307/3433674.JSTOR 3433674. PMC 1469943. PMID 9467086.

Philip L. Stocklin, US Patent 4,858,612, December 19, 1983

 "''The work of Jagdish Chandra Bose: 100years of MM-wave research'', retrieved 2010 01 31"