Britain and Japan intend to cooperatively research improvements for the MBDA Meteor, raising the possibility of combining that air-to-air missile’s ramjet propulsion and range with an advanced electronically scanned seeker.

Japan could equip its Lockheed Martin F-35 Lightnings with the improved Meteor, Japanese media reported, citing unnamed government officials. It is presumed the weapon will also be available for British F-35s and Eurofighter Typhoons, as well as to export customers.

Ministers in the National Security Council approved the collaborative effort on July 17, expecting to sign the agreement with Britain as soon as September. The program so far seems to be limited to early research and assessment — no schedule for development has been disclosed.

"We welcome the decision by the government of Japan to share information on missile-seeker technology with the U.K.," said a spokesman for the British Ministry of Defense.

The program is likely to focus on the guidance technology in the Mitsubishi Electric AAM-4B air-to-air missile, which entered production in 2010 to equip Japanese Boeing F-15s and Mitsubishi Heavy Industries’s F-2s. Britain has sought "advanced sensor technology" from Japanese companies, says the Japan Times.

The AAM-4B seeker with an active, electronically scanned array (AESA), that should significantly outperform radars with mechanically scanned antennas used in other missiles of medium-and long-range, including the Meteor. The better the missile radar, the greater the distance at which it can detect a target andthe earlier the launching fighter can stop transmitting guidance commands and turn away for safety.

This may be a particularly important issue for a missile with very long effective range such as the Meteor; short seeker detection distance would force the launching aircraft to point toward the target for an unusually long period while the weapon covered the intervening space. The ability to engage at great range and turn away early may be especially valuable for the F-35, which has been criticized for modest flight performance that could make it vulnerable if it flew too close to a high-performance adversary, such as the Sukhoi Su-35S.

Britain is leading a group of European countries in developing the Meteor, thought to have greater effective range than typical rocket-powered air-to-air missiles because its ramjet engine fires for longer; the weapon is still under power in the last few seconds as a target attempts to escape. It is due to enter service in 2015 or 2016.

But the Meteor’s body diameter, at 178 mm (7 in.), is less than the AAM-4B’s 203 mm (8 in.), so the AAM-4B’s seeker would need to be repackaged for installation and the European missile and the antenna would have to be smaller. Mitsubishi Electric makes the "transmitter unit" of the seeker, says the Japanese ministry of defense.

Mitsubishi Electric and the Defense Ministry’s Technical Research and Development Institute are also working on AESA radars that, by using gallium-nitride as a semiconductor, can generate greater power than those of conventional gallium-arsenide technology.

For Japan, the Meteor does not only offer great range and an application for costly seeker technology — MBDA has also proposed a version that will fit into F-35 weapon bays. The AAM-4B will not fit, says Japanese member of parliament Takashi Uto, a former air force fighter controller.

Formal agreement on the joint missile research is expected at a meeting of Japanese and British foreign and defense ministers that will be held as early as September, the Japan Times says.

Companies "involved in the envisioned research collaboration over the Meteor will carry out a simulation of the missile’s performance with the addition of the Japanese technology," the newspaper quoted the officials as saying.

Japan loosened its arms-export policy in April to permit participation in cooperative international programs. Before that, it signed a general agreement with Britain on joint developments. Until then, Japan’s international cooperation had been limited to work on ballistic-missile defense with the U.S. The new export policy permits sales of collaboratively-developed equipment to countries that do not violate international treaties, U.N resolutions, and are not engaged in conflict.

At the July 17 meeting, the National Security Council also approved the sale of PAC-2 missile parts by Mitsubishi Heavy Industries to Raytheon.