or (JORN) viewed as the number one Over-the-Horizon OTH Radar Air Defense in Asia-Pacific

“Australia's Jindalee Operational Radar Network (JORN) comprises three Over-The-Horizon Radar (OTHR) systems and forms part of a layered surveillance network… (JORN) provides wide area surveillance … at ranges of (621 to 1864 miles) from the radar sites, and is used to conduct air and maritime surveillance in support of…national surveillance effort. (JORN) was designed to detect air targets equivalent in size to a BAE Hawk-127 aircraft or larger, and objects on the surface of the water equivalent in size to an Armidale Class Patrol Boat or larger. The extent of available (JORN) coverage and actual system performance is highly variable and principally dependent on the state of the ionosphere, environmental conditions and an object's size and construction. The ionosphere is the upper part of the atmosphere extending from (47 to 280 miles) above the Earth's surface that consists of particles that have been ionized by solar radiation emitted by the Sun. The state of the ionosphere depends on the level of solar activity. Other more localized phenomena also affect the stability and/or structure of the ionosphere, and the combination of these phenomena and solar events which determines the quality of ionosphere support for (OTHR) operations…”

(OTHR) systems operate on the Doppler principle, where an object can be detected if its motion toward or away from the radar is different from the movement of its surroundings. (OTHR) are made up of very large fixed transmitter and receiver antennas (called ‘arrays’). The location and orientation of these arrays determines the lateral limits or arc of radar’s coverage. The extent of (OTHR) coverage in range within this arc is variable and principally dependent on the state of the ionosphere. They do not continually ‘sweep’ an area like conventional radars but rather ‘dwell’ by focusing the radar’s energy on a particular area – referred to as a ‘tile’ – within the total area of coverage. The transmitted High Frequency energy can be electronically steered to illuminate other ‘tiles’ within the Over the Horizon Radar coverage as required to satisfy operational tasking or in response to intelligence cuing. For an aircraft or maritime vessel to be detected, it must possess a radar reflective (metal) surface of sufficient size so that sufficient HF radar energy is reflected back along the transmission path to the JORN receiver.”

According to Pakistan Defense, “Instead of using the Chinese OTH radars individually, (China) will use radar interferometry to network them together to function as one unit. With massively increased resolution and location identification via triangulation, China should be able to see an incoming stealth aircraft.  Just like radio or laser interferometry, a synchronized system of radars will greatly magnify its power. Networked OTH radars will have resolution equal to the furthest distance between two radars. Interferometry does increase the total signal collected, but its primary purpose is to vastly increase the resolution through a process called Aperture synthesis. This technique works by superposing (interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is equivalent in resolution (though not in sensitivity) to a single antenna whose diameter is equal to the spacing of the antennas furthest apart in the array." (JORN facts provided by the Australian Air Force)