Efficiency metrics quantify how much power delivered to the antenna is actually radiated as electromagnetic waves:

Radiation efficiency – Ratio of radiated power to total accepted power

Total efficiency – Ratio of radiated power to net input power

Losses such as I^2R heating, dielectric absorption, and impedance mismatches reduce efficiency below 100%. Highly efficient antennas minimize internal losses and maximize radiated power.

Typical Antenna Applications

Antennas enable wireless connectivity, broadcasting, sensing and observation across the radio spectrum:

• Communications – Connecting cell phones, WiFi devices, Bluetooth headsets, emergency radios, and other electronic systems wirelessly. Antennas are embedded or external.
• Broadcasting – Transmitting radio, television, satellite TV and mobile audio programming to individual receivers and cell sites. High gain outdoor antennas used.
• Radio astronomy – Large specialized antennas like Arecibo and Very Long Baseline Arrays gather faint cosmic microwave signals for scientific observation.
• Radar – Detecting objects by analyzing reflected EM waves. Directional high gain antennas required for long range radar. Used for air traffic control, meteorology, and target tracking.
• Satellite – Parabolic dish antennas transmit and receive signals over huge distances to communicate with Earth orbiting satellites for data, video, telephony, and military uses.
• RFID – Small antennas in UHF or microwave bands transfer data to/from RFID tags for item identification and tracking.
• Medical – RF and microwave signals applied in body imaging techniques including MRI and diathermy therapeutic tissue heating.

These key applications demonstrate the indispensable role antennas play in any system involving transmission, reception or interaction with electromagnetic waves across the radio spectrum.

Frequently Asked Questions

1. What is an antenna?

An antenna is a device used to transmit and receive radio frequency signals by converting electromagnetic waves in space to electrical currents and vice versa. They provide the air interface for wireless communications.

2. What are the key properties of an antenna?

Important antenna parameters are gain, directivity, radiation pattern, impedance, bandwidth, VSWR, beamwidth, polarization and efficiency. These determine suitability for particular applications.

3. What are the main types of antennas?

Common antenna types include wire antennas like monopoles and dipoles, aperture antennas like horns and dishes, microstrip patch antennas, and antenna arrays combining multiple elements.

4. How does an antenna concentrate radiated power?

By focusing the emitted electromagnetic waves in a particular direction, an antenna concentrates signal power into a narrow solid angle for increased gain and directivity.

5. What applications use antennas?

Antennas are essential components enabling technologies including communications, broadcasting, radar, radio astronomy, satellite links, RFID, medical RF, and any application involving transmission/reception of radio waves.