Practical_Antenna_Handbook_0071639586

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466 P a r t V I : A n t e n n a s f o r O t h e r F r e q u e n c i e s A Figure 20.12 End terminations. Permanent plate at end Contact is at point of minimum current / 4 0 W, or nearly so. Thus, a virtual short exists at the points shown. By this means, the contact (or joint) resistance problem is overcome. B C Removable / 4 wave end piece Removable short circuit Actual short here Virtual short here / 4 Half wave channel Adjustable plunger Thumb screw Waveguide Joints and Bends Joints and bends in any form of transmission line or waveguide are seen as impedance discontinuities, and so are points at which disruptions occur. Thus, improperly formed bends and joints are substantial contributors to a poor VSWR. In general, bends, twists, joints, or abrupt changes in waveguide dimension can deteriorate the VSWR by giving rise to reflections. Extensive runs of waveguide are sometimes difficult to make in a straight line. Although some installations do permit a straight waveguide, many others require directional change. This possibility is especially likely on shipboard installations. Figure 20.13A shows the proper ways to bend a waveguide around a corner. In each case, the radius of the bend must be at least two wavelengths at the lowest frequency that will be propagated in the system. The “twist” shown in Fig. 20.13B is used to rotate the polarity of the E- and H-fields by 90 degrees. This type of section is sometimes used in antenna arrays for phasing the elements. As in the case of the bend, the twist must be made over a distance of at least two wavelengths. When an abrupt 90-degree transition is needed, it is better to use two successive 45-degree bends spaced one quarter-wavelength apart (see Fig. 20.13C). The theory (be- 0111057 FIG 18-12 hind this kind of bend) is to deliberately cause interference between the direct reflection of one bend and the inverted reflection of the other. The resultant relationship between the fields is reconstructed as if no reflections had taken place. Joints are necessary in practical waveguides because it simply isn’t possible to construct a single length of guide that is practical for all situations. Three types of common joints are used: permanent, semipermanent, and rotating. To make a permanent joint, the two waveguide ends must be machined extremely flat so that they can be butt-fitted together. A welded or brazed seam bonds the two sections together. Because such a surface represents a tremendous discontinuity, reflections and VSWR will result unless the interior surfaces are milled flat and then polished to a mirrorlike finish. A semipermanent joint allows the joint to be disassembled for repair and maintenance, as well as allowing easier on-site assembly. The most common example of this class is the choke joint shown in Fig. 20.14.
C h a p t e r 2 0 : M i c r o w a v e W a v e g u i d e s a n d A n t e n n a s 467 A At least 2 B / 4 / 4 / 4 Narrow dimension Wide dimension Side view C Figure 20.13 Bends in waveguide must be gentle. Flanges Short circuit 0111057 FIG 18-13 / 4 / 4 A / 4 Flanges B C Figure 20.14 Choke joint.
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Practical Antenna Handbook
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Practical Antenna Handbook Joseph J
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Contents Preface . . . . . . . . .
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C o n t e n t s vii 12 The Yagi-Uda
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C o n t e n t s ix Switched-Pattern
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Preface My paternal grandfather was
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P r e f a c e xiii this book repres
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Acknowledgments As with other field
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Background and History Part I Chapt
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CHAPTER 1 Introduction to Radio Com
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C h a p t e r 1 : I n t r o d u c t
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Fundamentals Part II Chapter 2 Radi
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CHAPTER 2 Radio-Wave Propagation To
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C h a p t e r 2 : r a d i o - W a v
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R N-1 C h a p t e r 2 : r a d i o -
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Figure 2.29C Monthly averaged sunsp
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CHAPTER 3 Antenna Basics An antenna
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C h a p t e r 3 : A n t e n n a B a
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CHAPTER 4 Transmission Lines and Im
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C h a p t e r 4 : T r a n s m i s s
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Chapter 5 Antenna Arrays and Array
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C h a p t e r 5 : a n t e n n a A r
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A. B. C. D. E. F. G. H. Figure 5.9
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B. C. D. E. F. G. H. Figure 5.10 Gr
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High-Frequency Building-Block Anten
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CHAPTER 6 Dipoles and Doublets A co
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C h a p t e r 6 : D i p o l e s a n
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CHAPTER 7 Large Wire Loop Antennas
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C h a p t e r 7 : L a r g e W i r e
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CHAPTER 8 Multiband and Tunable Wir
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C h a p t e r 8 : M u l t i b a n d
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CHAPTER 9 Vertically Polarized Ante
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C h a p t e r 9 : V e r t i c a l l
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Quarter-wave vertical radiator Insu
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Directional High-Frequency Antenna
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CHAPTER 10 Wire Arrays When a singl
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C h a p t e r 1 0 : W i r e A r r a
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Wire 2 C h a p t e r 1 0 : W i r e
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CHAPTER 11 Vertical Arrays Despite
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C h a p t e r 1 1 : V e r t i c a l
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CHAPTER 12 The Yagi-Uda Beam Antenn
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C h a p t e r 1 2 : T h e Y a g i -
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CHAPTER 13 Cubical Quads and Delta
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C h a p t e r 1 3 : C u b i c a l Q
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Figure 13.5 Multiband quad “spide
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High-Frequency Antennas for Special
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CHAPTER 14 Receiving Antennas for H
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C h a p t e r 1 4 : r e c e i v i n
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351 Figure 14.12 Remote tuning sche
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CHAPTER 15 Hidden and Limited-Space
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C h a p t e r 1 5 : H i d d e n a n
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CHAPTER 16 Mobile and Marine Antenn
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C h a p t e r 1 6 : M o b i l e a n
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CHAPTER 17 Emergency and Portable A
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C h a p t e r 1 7 : E m e r g e n c
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Antennas for Other Frequencies Part
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CHAPTER 18 Antennas for 160 Meters
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C h a p t e r 1 8 : a n t e n n a s
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Page 517 and 518: CHAPTER 22 Radio Astronomy Antennas
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Page 529 and 530: Figure 22.9 Interferometer pattern.
Page 531 and 532: CHAPTER 23 Radio Direction-Finding
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C h a p t e r 2 3 : R a d i o D i r
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Figure 23.9 Adcock array RDF antenn
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Figure 23.11 Watson-Watt Adcock arr
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Tuning, Troubleshooting, and Design
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CHAPTER 24 Antenna Tuners (ATUs) Th
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C h a p t e r 2 4 : a n t e n n a T
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CHAPTER 25 Antenna Modeling Softwar
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C h a p t e r 2 5 : A n t e n n a M
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Figure 25.3B Bent dipole wire and s
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CHAPTER 26 The Smith Chart The math
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Figure 26.2 Normalized impedance li
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A Figure 26.3 Constant resistance c
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A Figure 26.4A Constant inductive r
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C h a p t e r 2 6 : T h e S m i t h
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D C B A Figure 26.5 Radially scaled
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0.165 Y ' 1.0 j1.1 G' 1.0 Y ' 0.2
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CHAPTER 27 Testing and Troubleshoot
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C h a p t e r 2 7 : T e s t i n g a
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Mechanical Construction and Install
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CHAPTER 28 Supports for Wires and V
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C h a p t e r 2 8 : S u p p o r t s
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CHAPTER 29 Towers At some point, th
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C h a p t e r 2 9 : T o w e r s 655
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C h a p t e r 2 9 : T o w e r s 667
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CHAPTER 30 Grounding for Safety and
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C h a p t e r 3 0 : G r o u n d i n
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CHAPTER 31 Zoning, Restrictive Cove
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C h a p t e r 3 1 : Z o n i n g , R
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C h a p t e r 3 1 : Z o n i n g , R
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Appendices
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APPENDIX A Useful Math The material
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A p p e n d i x A : U s e f u l M a
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Appendix B Suppliers and Other Reso
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A p p e n d i x B : S u p p l i e r
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B.1.6 Rotators and Controllers Alfa
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Index Note: Boldface numbers denote
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I n d e x 747 Binns, Jack, first ma
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I n d e x 749 dipole (Cont.): slopi
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I n d e x 751 grounding and ground
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I n d e x 753 ionospheric propagati
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I n d e x 755 maximum effective len
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I n d e x 757 noise (Cont.): sky no
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I n d e x 759 reactance: cancellati
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I n d e x 761 standing waves: on an
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I n d e x 763 transmission lines, 1
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I n d e x 765 vertically polarized
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I n d e x 767 Yagi antennas (Cont.)
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