What Is Microwave Communication?

Microwave communication is the transmission of information using electromagnetic signals in the microwave frequency range, broadly from 1 GHz to 100 GHz. These signals propagate primarily along line-of-sight paths between directional antennas, making microwave links a reliable means of carrying high-capacity point-to-point and point-to-multipoint traffic where installing fiber-optic cable is impractical or cost-prohibitive. The field draws from radio propagation theory, modulation and coding, microwave circuit design, and network engineering, with practical systems relying on narrowband channelization, frequency reuse, and adaptive modulation to maximize spectrum efficiency.

Terrestrial microwave communication has its origins in the late 1940s, when AT&T and other carriers built transcontinental relay networks across the United States and Europe using tower-mounted parabolic dish antennas spaced 30 to 50 kilometers apart. Satellite communication extended the same principles to intercontinental and global links beginning in the 1960s. Today, terrestrial microwave remains the dominant backhaul technology for mobile networks in regions where fiber penetration is limited, carrying traffic from cell towers to core network nodes over links that operate across bands from 6 GHz to beyond 80 GHz.

Line-of-Sight Links

A microwave communication link requires unobstructed line-of-sight propagation between the transmitting and receiving antennas, with additional clearance around the direct path to prevent diffraction losses from terrain or structures entering the first Fresnel zone. Free-space path loss increases with both frequency and distance, following the Friis transmission equation, which means that higher-band links must compensate with larger antenna gains, higher transmit power, or shorter hop distances. Typical terrestrial hops in the 11 GHz to 23 GHz range span 5 to 30 kilometers, while E-band (71 to 86 GHz) links are optimized for shorter distances of 1 to 3 kilometers with very high throughput. Non-line-of-sight microwave backhaul techniques described in IEEE conference proceedings address scenarios where terrain or urban density prevents true line-of-sight alignment, using reflected or diffracted paths at lower frequencies. Microstrip filters in the intermediate-frequency chain of a microwave radio suppress image frequencies and adjacent-channel interference, contributing to the clean frequency selectivity that makes dense frequency reuse feasible.

Modulation and Spectral Efficiency

Modern microwave radios employ high-order quadrature amplitude modulation (QAM) to maximize the bits per hertz carried over a given channel. Commercial point-to-point systems routinely use 256-QAM or 1024-QAM in favorable propagation conditions, achieving spectral efficiencies of 8 to 10 bits per hertz. Adaptive modulation schemes automatically reduce modulation order during rain fades or atmospheric multipath events, maintaining link availability at the cost of reduced throughput. Channel coding, typically using low-density parity-check (LDPC) codes, provides additional margin against burst errors. The Ericsson Technology Review article on microwave backhaul evolution beyond 100 GHz surveys how the industry is extending throughput toward terabit-class links by combining wider channel bandwidths at millimeter-wave frequencies with advanced modulation and multi-carrier techniques.

Network Integration and Backhaul

Microwave links are most often used as the access or aggregation segment of a larger transport network that ultimately connects to fiber. A single microwave hop may terminate at a hub site where traffic from several cell towers aggregates before entering the fiber core. Packet-based microwave radios carry Ethernet frames directly, aligning with the all-IP architecture of 4G and 5G networks. Synchronization is delivered using IEEE 1588 Precision Time Protocol or Synchronous Ethernet over the microwave bearer, allowing cell towers to maintain the timing accuracy required for interference coordination and handover. The ACM proceedings on geospatial planning of wireless backhaul links describe the network-level optimization tools used to plan frequency assignments and antenna orientations across large microwave networks.

Applications

Microwave communication has applications in a wide range of fields, including:

• Cellular network backhaul connecting base stations to the core network
• Enterprise campus and building interconnects where trenching is impractical
• Emergency and public-safety communication networks requiring rapid deployment
• Satellite ground station uplinks and inter-facility trunking
• Military tactical communication links requiring quick setup and portability