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MicrowaveMicrowaves are electromagnetic waves with wavelengths longer than those of Terahertz (THz) wavelengths, but relatively short for radio waves. Microwaves have wavelengths approximately in the range of 30 cm (frequency = 1 GHz) to 1 mm (300 GHz). However, the boundaries between far infrared light, Terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The term microwave generally refers to "alternating current signals with frequencies between 300 MHz (3 x 108 Hz) and 300 GHz (3 x 1011 Hz)." Pozar 1998 Microwave Engineering [text]. The existence of electromagnetic waves, of which microwaves are part of the higher frequency spectrum, was predicted by James Clerk Maxwell in 1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF region. The design necessarily used horse-and-buggy materials, including a horse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter whose parabolic cross-section worked as a reflection antenna. The microwave range includes ultra-high frequency (UHF) (0.3-3 GHz), super high frequency (SHF) (3-30 GHz), and extremely high frequency (EHF) (30-300 GHz) signals. Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is effectively opaque , until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. Microwaves can be generated by a variety of means, generally divided into two categories: solid state devices and vacuum-tube based devices. Solid state microwave devices are based on semiconductors such as silicon or gallium arsenide, and include field-effect transistors (FET's), bipolar junction transistors (BJT's), Gunn diodes, and IMPATT diodes. Specialized versions of standard transistors have been developed for higher speed, which are commonly used in microwave applications. Microwave variants of BJT's include the heterojunction bipolar transistor (HBT), and microwave variants of FET's include the MESFET, the HEMT (also known as HFET), and LDMOS transistor. Vacuum tube based devices operate on the ballistic motion of electrons in a vacuum under the influence of controlling electric or magnetic fields, and include the magnetron, klystron, traveling wave tube (TWT), and gyrotron. The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. Microwave Frequency Bands are defined in the table below: Microwave frequency bands Designation Frequency range L band 1 to 2 GHz S band 2 to 4 GHz C band 4 to 8 GHz X band 8 to 12 GHz Ku band 12 to 18 GHz K band 18 to 26.5 GHz Ka band 26.5 to 40 GHz Q band 30 to 50 GHz U band 40 to 60 GHz V band 50 to 75 GHz E band 60 to 90 GHz W band 75 to 110 GHz F band 90 to 140 GHz D band 110 to 170 GHz Check out the following recipes that are tagged "Microwave":
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