Communications Fundamentals FAQ

Chapter 12 FAQ

1. 12.9.1 Why Do Radio Systems Need Antennas
   1. Why Can't a Radio Be Connected Directly to Free Space?
   2. What Does an Antenna Actually Do?
   3. Why Can the Same Antenna Usually Transmit and Receive?
   4. How Does an Antenna "Focus" Radio Waves?
   5. Why Are Antennas Different Shapes?
   6. Why Is Antenna Size Related to Frequency?
   7. What Happens If the Antenna Is Poorly Designed?
   8. Why Is the Antenna Often the Most Important Part of a Radio System?
   9. Where Are Antennas Used?
   10. How Has Antenna Technology Changed?
   11. What Should You Remember?
2. 12.9.2 Why Are Some Antennas Much Larger Than Others
   1. Why Does Wavelength Determine Antenna Size?
   2. How Are Frequency and Wavelength Related?
   3. Why Are AM Broadcast Antennas So Tall?
   4. Why Are Mobile Phone Antennas So Small?
   5. Can an Antenna Be Made Smaller Than Its Wavelength?
   6. Why Are Satellite Dishes So Large?
   7. Why Do Radar Systems Often Use Flat Panels?
   8. Why Can't Engineers Ignore Antenna Size?
   9. Have New Materials Changed This Relationship?
   10. Why Do Some Antennas Seem Smaller Than They Really Are?
   11. Why Is Understanding Antenna Size Important?
   12. What Should You Remember?
3. 12.9.3 What Determines How Far an Antenna Can Communicate
   1. Does a Bigger Antenna Always Mean Greater Range?
   2. What Is a Radio Link?
   3. How Does Transmitter Power Affect Range?
   4. What Role Does Antenna Gain Play?
   5. Why Does Frequency Influence Communication Distance?
   6. Why Is Receiver Sensitivity Important?
   7. How Does the Environment Affect Communication?
   8. Why Isn't Line of Sight Always Enough?
   9. What Is Fade Margin?
   10. Why Can Small Antennas Sometimes Communicate Over Enormous Distances?
   11. How Do Engineers Estimate Maximum Range?
   12. Why Is Communication Range Always a Trade-Off?
   13. Why Is Understanding Range So Important?
   14. What Should You Remember?
4. 12.9.4 Why Do High-Gain Antennas Have Narrow Beams
   1. What Is Antenna Gain?
   2. Does a High-Gain Antenna Produce More Power?
   3. Why Does Concentrating Energy Produce a Narrow Beam?
   4. What Is Beamwidth?
   5. Why Are Large Antennas Usually More Directional?
   6. Why Is a Narrow Beam Useful?
   7. Why Isn't Every Antenna Highly Directional?
   8. What Are Side Lobes?
   9. Why Must Satellite Dishes Be Pointed So Accurately?
   10. How Do Phased Arrays Steer Narrow Beams?
   11. Is There a Limit to Antenna Gain?
   12. Why Is Understanding Gain and Beamwidth Important?
   13. What Should You Remember?
5. 12.9.5 Why Must Antennas Be Matched to Their Transmission Lines
   1. What Is Impedance?
   2. Why Does a Mismatch Cause Problems?
   3. What Are Standing Waves?
   4. What Is VSWR?
   5. What Happens to the Reflected Power?
   6. Why Is Matching More Important at High Power?
   7. How Is an Antenna Matched?
   8. What Is a Balun?
   9. Does Matching Increase Antenna Gain?
   10. Why Do Antenna Tuners Exist?
   11. Why Is Matching Also Important for Receivers?
   12. How Do Engineers Measure Antenna Matching?
   13. Why Is Understanding Matching Important?
   14. What Should You Remember?
6. 12.9.6 Why Are There So Many Different Types of Antennas
   1. Why Isn't There One Perfect Antenna?
   2. What Factors Influence Antenna Selection?
   3. Why Is the Dipole So Popular?
   4. When Is a Monopole a Better Choice?
   5. Why Are Yagi Antennas So Common?
   6. Why Do Satellite Systems Use Reflector Antennas?
   7. Why Are Patch Antennas So Popular?
   8. Why Are Loop Antennas Still Used?
   9. What Is a Log-Periodic Antenna?
   10. Why Are Arrays Becoming More Common?
   11. Can One Antenna Cover Every Frequency?
   12. Why Is There No Universal Antenna?
   13. What Should You Remember?
7. 12.9.7 How Do Smart Antennas and Phased Arrays Work
   1. What Is a Phased Array?
   2. Why Does Changing the Phase Steer the Beam?
   3. Why Is Electronic Steering Better Than Mechanical Steering?
   4. What Is Beamforming?
   5. What Makes an Antenna "Smart"?
   6. How Do Smart Antennas Reduce Interference?
   7. Why Are Phased Arrays Ideal for Radar?
   8. How Are Phased Arrays Used in Satellite Communication?
   9. Why Are Smart Antennas Important for 5G?
   10. Can One Antenna Form Several Beams?
   11. Are Phased Arrays More Expensive?
   12. Will Mechanical Antennas Disappear?
   13. Why Are Smart Antennas One of the Most Important Developments in Modern Communications?
   14. What Should You Remember?
8. 12.9.8 What Is MIMO and Why Does It Increase Wireless Capacity
   1. What Does MIMO Mean?
   2. Why Isn't One Antenna Enough?
   3. How Does MIMO Work?
   4. What Is Spatial Multiplexing?
   5. How Does MIMO Improve Reliability?
   6. Isn't Multipath Supposed to Be a Problem?
   7. How Is MIMO Used in Wi-Fi?
   8. Why Is MIMO Important for Cellular Networks?
   9. What Is Massive MIMO?
   10. Does MIMO Increase Communication Range?
   11. Can Satellite Systems Use MIMO?
   12. Does MIMO Have Any Limitations?
   13. Why Has MIMO Changed Wireless Communications?
   14. What Should You Remember?
9. 12.9.9 Why Are Satellite Antennas So Different from Mobile Phone Antennas
   1. Why Can't Every Communication System Use the Same Antenna?
   2. Why Do Satellite Antennas Need High Gain?
   3. Why Are Mobile Phone Antennas Almost Omnidirectional?
   4. Why Are Satellite Dishes So Large?
   5. Why Don't Mobile Phones Use Reflector Dishes?
   6. Why Are Radar Antennas Different Again?
   7. Why Are Wi-Fi Antennas Different?
   8. Why Is Polarization Important?
   9. Why Must Satellite Antennas Be Pointed So Accurately?
   10. Why Are Flat-Panel Satellite Antennas Becoming Popular?
   11. What Can We Learn from Comparing Different Antennas?
   12. What Should You Remember?
10. 12.9.10 How Are Future Antennas Changing Wireless Communications
    1. Why Are Antennas Changing?
    2. What Is Driving Antenna Development?
    3. What Are Electronically Steerable Antennas?
    4. What Are Flat-Panel Satellite Antennas?
    5. What Are Reconfigurable Intelligent Surfaces?
    6. Will Artificial Intelligence Control Antennas?
    7. How Will Antennas Change Mobile Networks?
    8. Are Antennas Becoming Part of Electronic Circuits?
    9. What About New Materials?
    10. Will Antennas Be Used for More Than Communication?
    11. Will the Fundamental Principles Change?
    12. Why Is Antenna Engineering More Important Than Ever?
    13. What Should You Remember?