Heinrich Hertz:

Experimentally confirmed Maxwell's theory in 1886, generating and detecting radio waves.
Demonstrated wave properties like reflection, refraction, interference, and polarization for these "invisible" waves.

Microwave Definition: EM radiation with wavelengths from 1mm to 30cm (1 GHz to 300 GHz), though modern radar extends this.

Early Radio: Guglielmo Marconi's transatlantic radio transmission (1901) ushered in global communication.
Echolocation Concept: Nikola Tesla (1900) conceived of using radio waves for object detection and movement tracking. Christian Hülsmeyer (1904) patented an obstacle detector.
Radar Development:
- Robert Watson-Watt: Pioneered operational pulsed radar systems in the UK, leading to the "Chain Home" network.
- WWII Impact: Radar became crucial for air defense (Battle of Britain) and anti-submarine warfare (Battle of the Atlantic).
- Cavity Magnetron: A key breakthrough allowing generation of powerful 10cm waves, making airborne radar feasible (e.g., H2S system for ground mapping).
Radar Nomenclature: Wartime secrecy led to arbitrary letter designations for frequency bands (P, L, S, C, X, Ku, Ka, V, W, mm bands), which persist today.

Radio and Radar Astronomy:
- Jodrell Bank: Sir Bernard Lovell's facility became a leading radio observatory.
- Discoveries: Quasars, pulsars (LGM-1), and the cosmic microwave background radiation (Penzias and Wilson, 1965) revolutionized astronomy.
- Planetary Radar: Used to map Venus and other solar system bodies, improving distance measurements (e.g., Astronomical Unit).

Side-Looking Airborne Radar (SLAR): Developed for military reconnaissance in the 1950s, providing images through darkness and clouds.
Doppler Beam Sharpening (Carl Wiley, 1952): Concept that led to Synthetic Aperture Radar (SAR), improving spatial resolution by using Doppler shifts.
Civilian Applications: Large-scale mapping projects in Panama (1967) and the Amazon (Project Radam, 1971) demonstrated SAR's utility for resource management and inaccessible regions.

Early Atmospheric Sounding: Soviet Cosmos 243 (1968) and US Nimbus-5 (1972) carried microwave radiometers for atmospheric measurements.
Spaceborne Radar:
- Altimeters and Scatterometers: Used for Apollo moon landings (1969-70) and Skylab missions (1973-74).
- Seasat (1978): Carried the first civilian spaceborne imaging SAR, revolutionizing oceanography.
- Modern SAR Missions: ERS-1/2, JERS-1, Radarsat, Envisat, ALOS, TerraSAR-X, SRTM, Marsis, Cassini Radar.

Wave-Particle Duality: EM radiation can be described as waves (frequency, wavelength, refraction, diffraction, interference, polarization, scattering) or particles (photons). Wave theory is dominant for microwaves.
Harmonic Waves: Simplest mathematical description, based on sine/cosine functions.
Wave function: $\psi(z, t) = A \sin \kappa (z - \upsilon t)$
- $A$: Amplitude (maximum disturbance).
- $\kappa$: Wavenumber (spatial frequency) $[\text{rad/m}]$.
- $z$: Position along propagation directi