Antenna Theory and Arrays
Antennas convert guided signals into radiated waves and back, characterized by pattern, gain, and impedance, and combined into arrays for directivity.
Definition
Antenna theory studies devices that efficiently radiate or receive electromagnetic waves, quantifying their performance through radiation pattern, directivity, gain, impedance, and polarization, and arrays combine multiple elements to control the shape and direction of the radiated beam.
Scope
This topic covers the engineering of radiating structures: linear and aperture antennas, radiation pattern, directivity and gain, radiation resistance, input impedance and bandwidth, polarization, the reciprocity of transmitting and receiving, and antenna arrays with their array factor, beam steering, and beamforming. It applies radiation theory to practical communication and sensing systems.
Core questions
- How is an antenna's radiation pattern and gain determined?
- Why are transmitting and receiving properties related by reciprocity?
- How do arrays of elements steer and shape the beam?
Key concepts
- radiation pattern
- directivity
- gain
- radiation resistance
- input impedance
- reciprocity
- array factor
- beamforming
Key theories
- Antenna parameters and reciprocity
- An antenna is described by radiation pattern, directivity, gain, radiation resistance, and impedance, and by reciprocity its transmitting and receiving patterns are identical.
- Array factor and beamforming
- The combined pattern of an antenna array is the element pattern times an array factor set by element spacing and phasing, allowing the beam to be narrowed and electronically steered.
Clinical relevance
Antenna design enables mobile and satellite communications, radar and remote sensing, radio astronomy arrays, wireless power and RFID, and the phased-array and coil designs used in radar medicine and magnetic resonance imaging.
History
Hertz's dipole and loop were the first antennas, and Marconi scaled them up for long-distance wireless. Twentieth-century work produced directive arrays such as the Yagi-Uda design, and Jansky's antenna detected cosmic radio waves, founding radio astronomy; phased arrays later enabled electronic beam steering.
Key figures
- Guglielmo Marconi
- Heinrich Hertz
- Karl Jansky
Related topics
Seminal works
- balanis2016
- kraus2002
Frequently asked questions
- What is antenna gain?
- Gain measures how strongly an antenna concentrates radiated power in its preferred direction compared with an isotropic radiator, combining directivity with efficiency.
- How can an array steer its beam without moving?
- By adjusting the relative phase of the signal fed to each element, an array shifts the direction in which the element contributions add constructively, electronically steering the beam.