The Bell System Technical Journal 



Vol. XXVI April, 1947 No. 2 



Radar Antennas 



By H. T. FRIIS and W. D. LEWIS 



Table of Contents 



Introduction 220 



Part I — Electrical Principles 224 



1 . General 224 



2. Transmission Principles 226 



2 . 1 Gain and Effective Area of an Antenna 226 



Definition of Gain 226 



Definition of Effective Area 226 



2.2 Relationship between Gain and Effective Area 227 



2.3 The Ratio G/A for a Small Current Element 227 



2.4 The General Transmission Formula 230 



2.5 The Reradiation Formula 230 



2.6 The Plane, Linearly Polarized Electromagnetic Wave 231 



3. Wave Front Analysis 232 



3 . 1 The Huygens Source 233 



3.2 Gain and Effective Area of an Ideal Antenna 235 



i.i Gain and Effective Area of an Antenna with Aperture in a Plane and 



with Arbitrary Phase and Amplitude 236 



3.4 The Significance of the Pattern of a Radar Antenna 237 



3.5 Pattern in Terms of Antenna Wave Front 238 



3.6 Pattern of an Ideal Rectangular Antenna 239 



3.7 Effect on Pattern of Amplitude Taper 240 



3.8 Effect on Pattern of Linear Phase Variation 241 



3 . 9 Effect on Pattern of Scjuare Law Phase Variation 242 



3. 10 Effect on Pattern of Cubic Phase Variation 244 



3.11 Two General Methods 245 



3. 12 Arrays 246 



3. 13 Limitations to Wave Front Theory 246 



4. Application of General Principles 247 



Part II — Methods of Antenna Construction 247 



5. General 247 



6. Classification of Methods 248 



7. Basic Design Formulation 250 



7 . 1 Dimensions of the Aperture 250 



7 . 2 Amplitude Distribution 251 



7 . 3 Phase Control 251 



8. Parabolic Antennas 251 



8.1 Control of Phase 251 



8.2 Control of Amplitude 253 



8 . 3 Choice of Configuration 254 



8.4 Feeds for Paraboloids 258 



8.5 Parabolic CyUnders between Parallel Plates 260 



8.6 Line Sources for Parabolic Cylinders 262 



8.7 Tolerances in Parabolic Antennas 264 



9. Metal Plate Lenses 266 



9. 1 Lens Antenna Configurations 269 



9.2 Tolerances in Metal Plate Lenses 269 



9.3 Advantages of Metal Plate Lenses 270 



10. Cosecant Antennas 270 



10. 1 Cosecant Antennas based on the Paraboloid 271 



10.2 Cylindrical Cosecant Antennas 274 



219 



