The first known use of an interferometer was in the work of Michelson and Morley in 1890 and again in 1920, where they used interference patterns from light emitted by stars to measure the diameter of large stars. The stellar image creates an interference pattern related to the diameter of the star and the size of the optical aperture. Shortly thereafter, in 1946, Ryle and Vonberg transferred the principles of optical interferometry to radio waves for solar observations. These early interferometers combined coherent analog signal to create amplitude interference patterns to achieve enhanced angular resolution for stellar measurements and imaging. With advances in radio frequency transmitter and receiver technology and in analog-to-digital converters, interferometers have entered the digital age. The digital interferometer spatially samples signals at rates greater than or equal to the Nyquist rate for the bandwidth limited signals and uses phase, as opposed to amplitude, information to measure angle-of-arrival with high precision. As a result, these digital radio frequency (RF) interferometers have found application in several areas that include military, commercial, and scientific endeavors. In this chapter, five applications are presented that illustrate the diversity and versatility of interferometry: military, sports, synthetic aperture radar (SAR), radio astronomy, and geostationary satellite tracking. Both SAR and radio astronomy are imaging interferometer techniques that take advantage of large aperture separations, whereas military and sports applications are tracking radars that use interferometry to achieve high angle accuracy as opposed to high angle resolution. In addition, radio astronomy is an example of a passive interferometer whose signal is generated from an external source (stellar objects). The other three interferometer applications are active radars that generate specific waveforms or signals that facilitate interferometer angle estimation. This book focuses on active tracking interferometers where angle accuracy is the driving requirement. The distinction between tracking and imaging interferometers is made in this chapter using the five examples.

Chapter Contents:

• 1.1 Military Applications
• 1.2 Sports Applications
• 1.3 Synthetic Aperture Radar
• 1.4 Radio Astronomy
• 1.4.1 Stellar Imaging Using Radio Astronomy
• 1.5 Near-Geostationary Interferometric Tracking
• References

Inspec keywords: radiofrequency interference; radiowave interferometers; radio transmitters; synthetic aperture radar; radar interferometry; radio receivers

Other keywords: aperture separations; angular resolution; Nyquist rate; interference pattern; optical interferometry; radio waves; amplitude interference patterns; radio receiver technology; RF interferometry applications; digital radio frequency; interference patterns; analog-to-digital converters; solar observations; radio frequency transmitter; radio astronomy; SAR astronomy; stellar image; stellar measurements; optical aperture; analog signal

Subjects: Radioastronomical techniques and equipment; Radio links and equipment; Electromagnetic compatibility and interference; Radar equipment, systems and applications