RF and Microwave Technology: Applications and History

RF and Microwave Technology: Applications and History

The Rise of Wireless Telephony

“Anywhere, at any time.” Modern wireless telephony is based on the concept of cellular frequency reuse, a technique first proposed by Bell Labs in 1947 but not practically implemented until the 1970s. By this time, advances in miniaturization, as well as increasing demand for wireless communications, drove the introduction of several early cellular telephone systems in Europe, the United States, and Japan.

• The Nordic Mobile Telephone (NMT) system was deployed in 1981 in the Nordic countries.
• The Advanced Mobile Phone System (AMPS) was introduced in the United States in 1983 by AT&T.
• NTT in Japan introduced its first mobile phone service in 1988.

All of these early systems used analog FM modulation, with their allocated frequency bands divided into several hundred narrowband voice channels. These early systems are usually referred to now as first-generation cellular systems, or 1G.

Second-generation (2G) cellular systems achieved improved performance by using various digital modulation schemes, with systems such as GSM, CDMA, DAMPS, PCS, and PHS being some of the major standards introduced in the 1990s in the United States, Europe, and Japan. These systems can handle digitized voice, as well as some limited data, with data rates typically in the 8 to 14 kbps range. In recent years, there has been a wide variety of new and modified standards to transition to handheld services that include voice, texting, data networking, positioning, and Internet access. These standards are variously known as 2.5G, 3G, 3.5G, 3.75G, and 4G, with current plans to provide data rates up to at least 100 Mbps. The number of subscribers to wireless services seems to be keeping pace with the growing power and access provided by modern handheld wireless devices; as of 2010, there were more than five billion cell phone users worldwide.

Satellite Systems

Satellite systems also depend on RF and microwave technology, and satellites have been developed to provide cellular (voice), video, and data connections worldwide.

Wireless Local Area Networks (WLANs)

Wireless local area networks (WLANs) provide high-speed networking between computers over short distances, and the demand for this capability is expected to remain strong. One of the newer examples of wireless communications technology is ultra-wideband (UWB) radio, where the broadcast signal occupies a very wide frequency band but with a very low power level (typically below the ambient radio noise level) to avoid interference with other systems.

Radar Systems

Radar systems find application in military, commercial, and scientific fields. Radar is used for detecting and locating air, ground, and seagoing targets, as well as for missile guidance and fire control. In the commercial sector, radar technology is used for air traffic control, motion detectors (door openers and security alarms), vehicle collision avoidance, and distance measurement. Scientific applications of radar include weather prediction, remote sensing of the atmosphere, the oceans, and the ground, as well as medical diagnostics and therapy.

Microwave Radiometry

Microwave radiometry, which is the passive sensing of microwave energy emitted by an object, is used for remote sensing of the atmosphere and the earth, as well as in medical diagnostics and imaging for security applications.

A Brief History of Microwave Engineering

Fundamental concepts were developed more than 50 years ago, probably because radar, the first major application of microwave technology, was intensively developed as far back as World War II. However, recent years have brought substantial and continuing developments in high-frequency solid-state devices, microwave integrated circuits, and computer-aided design techniques. The ever-widening applications of RF and microwave technology to wireless communications, networking, sensing, and security have kept the field active and vibrant.