SerpApi.Org
A new study in China’s Journal of Microwaves has disclosed the technology behind the world’s only geosynchronous radar surveillance satellite. Ludi Tance-4 01 uses gallium nitride semiconductors as the core of its radar system.
China produces more than 95 percent of the world’s primary gallium supply and has restricted its export since the satellite launched in August 2023. The United States has spent decades attempting to build a comparable system without success.
Scientists at the National Key Laboratory of Space Microwave Communication and the Xi’an Institute of Space Radio Technology conducted the research. Ludi Tance-4 01 orbits 22,370 miles (36,000 km) above Earth, fixed over the same geographic position at all times.
From that altitude, it maintains continuous radar coverage over the Asia-Pacific region and monitors roughly one-third of the Earth’s surface at a resolution of about 65 feet (20 meters), day or night, through any weather.
Why gallium nitride makes geosynchronous radar possible
Radar satellites in low Earth orbit sit about 370 miles (600 km) up. A geosynchronous satellite sits 22,370 miles (36,000 km) up. Because radar signal strength falls off with the square of distance, a satellite at GEO altitude needs vastly more transmit power to achieve the same imaging capability as one in low orbit.
Gallium nitride (GaN) semiconductors solve this problem. GaN handles significantly higher power levels per unit area than conventional silicon or gallium arsenide chips while remaining efficient at microwave frequencies.
The satellite’s AESA radar uses a novel beam-combining technique that synthesizes multiple microwave signals mid-flight to maintain stable performance at extreme range. Without GaN’s efficiency, the power budget would make the whole system unworkable.
The US military is still upgrading the F-35’s radar to GaN-based systems, a program running several years behind schedule, partly because of supply chain constraints.
China controls 95 percent of the world’s gallium supply
Gallium is not independently mined. It is extracted as a by-product of aluminum production, and because China is the world’s largest aluminum producer, it accounts for more than 95 percent of global primary gallium output. Gallium nitride chips are central to AESA radars, electronic warfare systems, 5G and 6G base stations, and next-generation defense platforms.
China restricted gallium exports in August 2023, the same month the satellite launched. The US Geological Survey has flagged gallium as a critical mineral under supply risk. The Pentagon’s dependence on GaN for modern radar and communications systems is a recognized strategic vulnerability, and efforts to build alternative supply chains in Germany, Australia, and Japan remain at early stages.
The satellite the US has spent decades trying to build
Ludi Tance-4 01 is the world’s first and currently only geosynchronous synthetic aperture radar satellite, confirmed by the Center for Strategic and International Studies in a 2024 analysis. China claims it serves civilian purposes including disaster response, meteorology, and agricultural monitoring.
US military analysts have drawn different conclusions. Chief Master Sgt. Ronald Lerch of the US Space Force’s Space Systems Command said the satellite enables persistent surveillance over strategically important areas and could be coordinated with other Chinese reconnaissance satellites to produce what he called a qualitative leap in tracking and targeting. US remote-sensing radar satellites remain in low Earth orbit, where each passes over a given location only a few times per day. Ludi Tance-4 01 never looks away.
