Coincidence Apple's OS X Lion upgrade advertisement prominently displays the MacBook Air.

Apple's refresh of the MacBook Air should come in July packing Apple's newest OS X Lion operating system, a Deutsche Bank analyst said today.

"Our checks suggest a forthcoming MacBook Air refresh in July where we believe units could ramp to as high as 1.5M units per [quarter] or 50 percent of the MacBook business," analyst Chris Whitmore wrote in a research note distributed via e-mail.

If the MacBook Air garnered half of all of Apple's MacBook business, that would be a significant milestone, as early versions of the Air, dating back to January 2008, were not that popular compared with other MacBook offerings.

The most significant upgrade to the Air is expected to be the switch to Intel's new Sandy Bridge processors. Less certain is whether the new models get the high-speed Thunderbolt port, though it has been widely reported that they will.

Whitmore's note continued: "We also believe Lion will drive a strong upgrade cycle due to: 1) low ASP' 2) significant enhancements/feature upgrades' and 3) arrives in conjunction with MacBook Air refresh."

Whitmore also commented on OS X Lion, saying that among its 250-plus new features, the most important improvements include iCloud, multitouch gestures, "mission control," and "resume." These will "spur a large part of the 54 [million] Mac installed base to upgrade," he wrote.

OS X Lion also benefits Apple because it is available only through Apple's App store, which means no retail distribution costs for Apple, Whitmore said.