RADIO ANTENNAS AND PROPAGATION pot

[...]... short-range radio systems Cellular radio telephones are the most obvious example Short-range radio has the important advantage that it enables more users to be accommodated in the same radio bands without interfering with each other All of this explosive technological development depends on the transmission, propagation and reception of radio energy So what is radio energy? 1.1 What radio energy really is Radio. .. equations) that describe the electromagnetic field, how it is produced by charges and currents, and how it is propagated in space 6 Radio Antennas and Propagation ,, J i,, ,, and time The electromagnetic field is described by two quantities, the electric component E and the magnetic flux B, both of which change in space and time The equations (in modern vector notation) are: V D = p p is electric charge... , ,, , Notes: 1 In the early days of radio the LF, MF and HF bands were referred to as Long Wave (LW), Medium Wave (MW) and Short Wave (SW), respectively These names are obsolete, but still found on mass-produced broadcast receivers 2 Sometimes SHF is called the centimetre wave band, and EHF the millimetre wave band; together they constitute the microwave bands Radio technology is concerned with the... reception and will have broadly the same characteristics In reality there may be differences between transmitting antennas 20 Radio ntennasand Propagation A and their receiving counterparts, but these are of an entirely practical nature, such as the need for higher voltage insulation in transmitting antennas working at high power levels, or the need for particularly compact structures in personal radio. .. visible light Fig 1.2 • The electromagnetic spectrum 10 i ,'" n.,uv , i" I ~ i ~ .X-lrlays 10- -7 "'-">~ Known in Maxwell's day 10 -10 m 14 Radio Antennas and Propagation |,,,, ,,,,= , ,,, , i Table 1.1 The radio bands ,, i ,, i ,, Frequencies Name of band ,, Extra High Frequency, EHF Super High Frequency, SHF Ultra High Frequency, UHF Very High Frequency, VHF High Frequency, HF Medium Frequency,... therefore, later, radio) was a stream of particles, and those, following Christiaan Huygens (1629-95), who thought that it was waves Now we know that it is composed of particles (photons) which have wave properties, so there was something to be said for both points of view Some people (and textbooks) still speak of 'radio waves', 4 Radio Antennas and Propagation J I I I Illl I I I I I I I but strictly... to interact with the gas and water vapour molecules of the atmosphere, which is therefore transparent to radio signals This is a great practical advantage As a matter of convenience, the radio part of the electromagnetic spectrum is further subdivided into a series of bands, each covering a 10" 1 frequency range, as in Table 1.1 Each band has a particular range of uses and demands its own distinctive...2 Radio Antennas and Propagation radio, to some extent, for communication between fixed locations, but for all situations in which one or both ends of a communication link may be mobile or subject to movement, radio remains the only information-bearer technology Early radio engineers struggled to get the maximum possible range from their... which to compare other, more 24 Radi Antennasand Propagation o complicated, antennas In practice people refer to it a great deal in just this way g ~ The isotrope as a receiving a n t e n n a As we have seen, antennas can both transmit, emitting quanta when driven by electrical energy, or they can equally well receive, capturing radio quanta as they approach the antenna and converting their energy into... ONE ANTENNAS There were vast numbers of radio quanta in the universe long before Hertz performed his famous experiments They are generated naturally whenever electric charges are accelerated or decelerated All hot objects, in which charged particles are in rapid random motion, radiate quanta of radio energy, along with heat (infrared) quanta, and light too if they are hot enough The stars are potent .