《ULTRA HIGH FREQUENCY PROPAGATION》求取 ⇩

CHAPTER 1.AN INTRODUCTION TO UHF COMMUNICATIONS AND THE SYSTEM CONCEPT1

1.1.Meanings of VHF,UHF,and SHF1

1.2.Noise and the Desirability of Higher Frequencies in Communications1

1.3.Regions of Propagation3

1.4.Use of High-Power Transmitter to Give Rceeption in the Far Reaches of the Diffraction Region4

1.5.Ray vs.Wave Theories5

1.6.Variations in Predicted Values of Signal Strength6

1.7.Limitations at UHF and the"Systems Concept"12

CHAPTER 2.GENERAL ASPECTS OF PROPAGATION23

2.1.A Basic Procedure for the Development of a Radiation Pattern as Applied to a Flat Earth24

2.2.Equation of Constant Path-Length Difference Loci26

2.3.Example.A Particular Hyperbolic Equation27

2.4.Lobe Structure27

2.5.Relation between Path-Length Difference and Grazing Angle for a Particular Antenna Height28

2.6.Phase Lag28

2.7.Reflection Coefficient,R29

2.8.Directivity30

2.9.Gain32

2.10.Lobe Structure for Half-Wave Vertical Dipole.R=0.5,φ=180°32

2.11.Lobe Structure for Half-Wave Vertical Dipole.Use of Actual Re-flection Coefficient34

2.12.The ILS(Instrument Landing System)36

2.13.Equivalent Earth Radius37

Problems40

CHAPTER 3.METEOROLOGICAL THEORY42

3.1.The Standard Atmosphere42

3.2.Snell’s Law for Spherical Boundary Surfaces44

3.3.Curvature of Radio and Light Waves47

3.4.Modified Earth Radius.4/3 Earth Radius Diagram50

3.5.Earth as a Parabolic Arc52

3.6.The Non-standard Atmosphere53

Problems57

CHAPTER 4.ANTENNAS AND RADIATION PHENOMENA(GROUND REFLECTION BEHAVIOR)58

4.1.The Wave Equation and Its Solution for Free Space Propagation58

4.2.Poynting Vector63

4.3.Radiation from a Short Wire65

4.4.Radiation and Induction Fields69

4.5.Radiated Power from Short Wire69

4.6.The Half-Wave Dipole71

4.7.Radiation Resistance of the Half-Wave Dipole77

4.8.Field at a Distance from the Half-Wave Dipole77

4.9.Antenna Gain77

4.10.Reciprocity78

4.11.Effective Area of Antenna79

4.12.Example.Effect of Change in Effective Area81

4.13.Inverse Law of Radiation81

4.14.Reflection Coefficient82

4.15.Properties of the Medium83

4.16.Fundamental Considerations84

4.17.Horizontal Polarization88

4.18.Vertical Polarization90

4.19.Effect of Earth Curvature91

4.20.Evaluation of n2 in MKS Units91

4.21.Example.Calculation of Reflection Coefficient91

4.22.Surface Roughness98

4.23.Approximate Expressions for Reflection Coefficients99

4.24.Physical Path-Length Difference99

4.25.Equation for Constant Path-Length Difference100

4.26.Example.Calculation of Total Angle of Lag of Reflected Ray101

4.27.Divergence Factor102

4.28.Radio Horizon and Value of △h1 from Curved-Earth Geometrical Relationships108

4.29.Example.Calculation of Divergence Factor109

4.30.Gain.Earth Gain Factor110

4.31.Example.Calculation of the g(θ)Function110

4.32.4/3 Earth Radius Charts112

Problems115

CHAPTER 5.MULTIPATH PROPAGATION(GROUND-TO-AIR,AIR-TO-GROUND,AND GROUND-TO-GROUND PROPAGATION)117

5.1.Elementary Wave Theory117

5.2.Ray Theory121

5.3.Waves and Rays122

5.4.Validity of Ray Theory126

5.5.Multipath Propagation127

5.6.Two-Path Propagation128

5.7.Example.Calculation of a Typical Microvolt Contour136

5.8.Free Space Maximum Range of Dipole137

5.9.Radio Horizon Line139

5.10.Errors140

5.11.Tabulated Procedure for Calculation of Theoretical Lobe Structure141

5.12.Deviation from Theoretical Predictions148

5.13.A Short-Cut Procedure for Calculating Signal Strength and Its De-ficiencies149

5.14.Fallacy in Believing Maximum Height Provides Maximum Coverage Range154

5.15.Calculation of UHF Radio Field Strength in the Diffraction Region155

5.16.Calculation of the Surface Wave Field Strength for Short Ranges171

5.17.Conditions under Which the Surface Wave May Be Neglected172

5.18.Field Strength in the Turbulent Region175

5.19.Range-Microvolt Curve at Constant Elevation175

5.20.Deficiencies in Knowledge of the Art and the Use of Safety Factors178

Problems179

CHAPTER 6.COMPAIRISON OF VHF AND UHF PROPAGATION,DIPOLE-TO-DIPOLE(GROUND-TO-AIR AND AIR-TO-GROUND PROPAGATION)183

6.1.Vertical Lobe Structure185

6.2.Theoretical and Experimental Lobe Structures191

6.3.Field Strength vs.Range218

6.4.Circular Polarization220

6.5.Comparison of Horizontal with Vertical Polarization229

6.6.Over Land vs.Over Sea Water Propagation231

6.7.Theoretical vs.Experimental Reflection Coefficients.Surface Rough-ness233

6.8.Analysis of Frequency and Antenna Height238

6.9.Optimum Height for Antenna242

6.10.Example.Calculation of Solid Coverage Range246

6.11.Example.Optimum Antenna Height247

6.12.Example.Calculation of Solid Coverage Range250

6.13.Conditions Necessary to Obtain a Given Radiation Pattern at a Higher Frequency250

Problems252

CHAPTER 7.COMPLEX ANTENNAS(LINEAR ARRAYS)254

7.1.Arrays254

7.2.Broadside Array255

7.3.End-Fire Array256

7.4.Colinear Array256

7.5.Two-Element Array257

7.6.Three-Element Array259

7.7.n-Element Linear Array261

7.8.Free Space Field Strength Patterns of Colinear Arrays263

7.9.Colinear Array in Proximity of Earth267

7.10.Four-Element Colinear Array in Proximity of Earth270

7.11.Solid Coverage Range277

7.12.Electrically Tilted or"Dished-up"Antenna280

7.13.Null Positions for Linear Arrays of n Elements284

7.14.Nine-Element Linear Array285

7.15.Calculation of Radiation Pattern.Nine-Element Array292

7.16.Broadband Operation of a Given Array296

7.17.Diversity Antennas301

7.18.Two Half-Wave Vertical Dipoles in Height Diversity.Vertical Po-larization304

7.19.Two Four-Element Colinear Arrays in Height Diversity.Vertical Polarization308

Problems311

CHAPTER 8.COMPLEX ANTENNAS(CIRCULARLY POLARIZED ANTENNAS)313

8.1.Wave Polarization313

8.2.Circular Polarization.Free Space Conditiohs317

8.3.In Proximity of Earth319

8.4.Illustrative Example,Circular Polarization320

8.5.Crossed-Dipole Antenna323

8.6.Practical Design of a Circularly Polarized Antenna System324

8.7.System Improvement Obtained by Use of Circularly Polarized An-tennas329

Problems335

CHAPTER 9.SYSTEM COMPARISON,OPERATION,AND DESIGN OF UHF COMPLEX ANTENNAS336

9.1.Comparison of UHF Propagation from Four Types of Complex An-tennas.Ground-to-Air and Air-to-Ground Propagation336

9.2.Comparison Based on Range and Altitude of Critical Null337

9.3.Disadvantages of Complex Antennas345

9.4.System Operation and Application349

9.5.Installation Losses,Airborne and Ship351

9.6.Responsibilities of the Design Engineers and Operating Personnel352

9.7.Reciprocity in Communication Systems355

9.8.Shipboard Antenna Design Elements355

9.9.The"Sector"Antenna358

9.10.The Basic Sector Antenna(Manually Switched)System359

9.11.Automatic Sequential Sector Antenna Switching361

9.12.High-Speed(Supersonic)Switching362

9.13.Paralleled Sector Antennas362

9.14.Sector Diversity Systems363

9.15.Squelched Sector System366

9.16.Personnel Diversity System367

9.17.General Considerations368

Problems370

CHAPTER 10.AIR-TO-AIR PROPAGATION371

10.1.General Considerations,Geometry of the Problem372

10.2.Derivation of Equation of Carrier Signal374

10.3.Lobe Modulation Concept377

10.4.Magnitude of dφ/dt379

10.5.Magnitude of ωm380

10.6.Characteristics of the Carrier Angular Frequency383

10.7.Frequency Analysis of the Modulation Envelope384

10.8.Experimental and Theoretical Results of Air-to-Air Propagation over Sea Water388

10.9.Lobe Modulation Factor,m388

10.10.Lobe Modulation Frequency391

10.11.Magnitudes of Received Signals392

10.12.Doppler-Beat Modulation Concept392

10.13.Fresnel Zone Variations396

10.14.Propagation over Rough Terrain397

Problems401

CHAPTER 11.LOBE MODULATION INTERFERENCE AND DESIGN CONSIDERATIONS402

11.1.Discussion of Modulation Factor m403

11.2.Lobe Modulation Interference Frequency405

11.3.Lobe Modulation Interference to Amplitude-Modulated Communica-tion Systems405

11.4.Lobe Modulation Interference to Frequency-Modulated and Sub-carrier Amplitude-Modulated Communications Systems408

11.5.Reduction of Lobe Modulation through Antenna Design411

11.6.Practical Approaches to Idealized Antenna Design413

11.7.Reduction of Lobe Modulation by AVC424

11.8.Dynamic Sensitivity429

11.9.Dynamic Characteristics of Squelch and Automatic Relay Circuits432

Problems432

CHAPTER 12.EFFECTS OF METEOROLOGICAL CONDITIONS ON EXPERIMENTAL FLIGHT DATA434

12.1.Experimental Flight Data434

12.2.Ray Paths Determined by Meteorological Conditions437

12.3.Path Length and Phase Difference438

12.4.Phase Shift Due to Change in dn/dh439

12.5.Phase Shift Due to Change in n440

12.6.Grazing Angle Change Due to Change in dn/dh440

12.7.Effects of Duct Formation441

12.8.Experimentally Determined Values of Modulation Factor and Re-flection Coefficient442

12.9.Calculation of Reflection Coefficient from Experimental Data444

12.10.Radio Horizon Line Distance445

12.11.Irregularities in Radio Field Strength445

12.12.Experimental Determination of dn/dh449

12.13.Radio Holes in Air-to-Air Radio Wave Propagation451

Problems453

CHAPTER 13.GENERAL OPERATIONAL CONSIDERATIONS455

13.1.Theoretical Approach to Operational Ranges455

13.2.Definitions of the Various Communication Ranges455

13.3.Loci of Interference Maxima and Minima457

13.4.Factors Affecting Optimum Communication Coverage459

13.5.Theoretical Air-to-Air Communication Ranges463

13.6.Theoretical Air-to-Relay-to-Ground Communication Ranges471

13.7.Actual Operational Ranges472

13.8.System Parameter Measurement474

13.9.Frequency Netting474

13.10.Radio Interference and Squelch Adjustment476

13.11.Transmission Line Losses477

13.12.Impedance Matching and VSWR477

13.13.Measurement of Free Space Radiation Patterns480

13.14.Directivity Pattern Measurement of Aircraft in Flight483

13.15.A Recommended Test Procedure for Flight Evaluation of Azimuth Directivity484

13.16.Flight Test Procedure for Determination of Elevation Pattern in Equatorial Belt488

13.17.Spherical Directivity Patterns489

13.18.A Method of Obtaining the Spherical Coverage Pattern of a UHF Antenna While It Is Installed on a Full-Scale Airplane490

13.19.Correlation between Model and Full-Scale Spherical Directivity Pat-terns495

13.20.Factors Affecting Choice of Frequency and Polarization in System Design497

13.21.Multipath Propagation Effects in Pulse Systems507

Problems517

CHAPTER 14.ILLUSTRATIVE SYSTEMS DESIGN PROBLEMS519

14.1.Problem 1.Design for Gapless Communication within Specified Altitude and Range519

14.2.Determination of the Frequency Which Yields the Minimum Cover-ages521

14.3.Solid Coverage Range through Use of Curves523

14.4.Radiation Pattern Using Vertical Dipoles on Ship and Aircraft523

14.5.Four-Element Colinear Array on Shipboard529

14.6.Optimum Spacing for Broadband Operation534

14.7.Three-Element Colinear Array534

14.8.Four-Element Colinear Array and 9-db Added System Loss534

14.9.Eight-Element Tilted Array and 9-db Added System Loss535

14.10.Problem 2.Effect of Antenna Height on Ranges536

14.11.Problem 3.Antenna Height to Give Maximum Range at a Specified Ceiling539

14.12.Problem 4.Calculation of Television Field Strength in Rural and Fringe Areas544

Problems552

INDEX555