ARRL天线手册21版(英文版)20.pdf

Chapter 20 Antenna MaterialsAntenna Materials Antenna Materials Antenna MaterialsAntenna Materials and Accessoriesand Accessories and Accessories and Accessoriesand Accessories This chapter contains information on materials dipole, for example. In this chapter we’ll look at materials amateurs use to construct antennas—what types of material for those applications, too. Structural supports such as to look for in a particular application, tips on working with towers, masts, poles, etc. are discussed in Chapter 22. and using various materials. Chapter 21 contains There are two main types of material used for antenna information on where to purchase these materials. conductors, wire and tubing. Wire antennas are generally Basically, antennas for MF, HF, VHF and the lower simple and therefore easier to construct, although some UHF range consist simply of one or more conductors that arrays of wire elements can become rather complex. When radiate (or receive) electromagnetic waves. However, an tubing is required, aluminum tubing is used most often antenna system must also include some means to support because of its light weight. Aluminum tubing is discussed those conductors and maintain their relative positions— in a subsequent section of this chapter. the boom for a Yagi antenna and the halyards for a wire Wire Antennas Although wire antennas are relatively simple, they can smaller, have been used quite successfully in the constitute a potential hazard unless properly constructed. construction of “invisible” antennas in areas where more Ant