Advanced Extremely High Frequency (AEHF) is a constellation of communications satellites operated by the United States Space Force. They are used to relay secure communications for the United States Armed Forces, the British Armed Forces, the Canadian Armed Forces, the Netherlands Armed Forces and the Australian Defence Force. The system consists of six satellites in geostationary orbits. The final satellite was launched on 26 March 2020. AEHF is backward compatible with, and replaces, the older Milstar system and will operate at 44 GHz uplink (extremely high frequency (EHF) band) and 20 GHz downlink (super high frequency (SHF) band). The AEHF system is a joint service communications system that provides survivable, global, secure, protected, and jam-resistant communications for high-priority military ground, sea and air assets.

AEHF satellites use many narrow spot beams directed towards the Earth to relay communications to and from users. Crosslinks between the satellites allow them to relay communications directly rather than via a ground station. The satellites are designed to provide jam-resistant communications with a low probability of interception. They incorporate frequency-hopping radio technology, as well as phased array antennas that can adapt their radiation patterns in order to block out potential sources of jamming.

AEHF incorporates the existing Milstar low data-rate and medium data-rate signals, providing 75–2400 bit/s and 4.8 kbit/s–1.544 Mbit/s respectively. It also incorporates a new signal, allowing data rates of up to 8.192 Mbit/s. When complete, the space segment of the AEHF system will consist of six satellites, which provides coverage of the surface of the Earth between latitudes of 65° north and 65° south. For northern polar regions, the Enhanced Polar System acts as an adjunct to AEHF to provide EHF coverage.

The initial contract for the design and development of the AEHF satellites was awarded to Lockheed Martin Space Systems and Northrop Grumman Space Technology in November 2001, and covered the System Development and Demonstration phase of the program. The contract covered the construction and launch of three satellites, and the construction of a mission control segment. The contract was managed by the MILSATCOM Program Office of the Space and Missile Systems Center. Like the Milstar system, AEHF are operated by the 4th Space Operations Squadron, located at Schriever Space Force Base and the 148th Space Operations Squadron at Vandenberg SFB.

It extends the "cross-links" among AEHF of earlier Milstar satellites, which makes it much less vulnerable to attacks on ground stations. As a geosynchronous satellite over the equator, it still needs to be supplemented with additional systems optimized for polar coverage in high latitudes.

In the April 2009 Defense Department budget request, Secretary of Defense Robert Gates said he planned to cancel the Transformational Satellite Communications System, still in the design phase, in favor of additional AEHF capacity. Individual AEHF satellites, exclusive of launch expenses, cost US$850 million.

Prior to the AEHF, United States and allied military satellite communications systems fell into one of three categories:

AEHF, however, converges the role of its wideband Defense Satellite Communications System (DSCS) and protected MILSTAR predecessors, while increasing bandwidth over both. There will still need to be specialized satellite communications for extremely high data rate space sensors, such as geospatial and signals intelligence satellites, but their downlinked data will typically go to a specialized receiver and be processed into smaller amounts; the processed data will flow through AEHF.