Patrick Mannion
TechOnline

The importance of antenna design
While Wisair has spent years perfecting its RF and MAC/baseband chips, and has lots of intellectual property and patents surrounding its signal acquisition, detection, automatic gain control and timing on the front end, when it came down to system implementation, antenna design became the make-or-break factor.

"We had to redesign the antenna to meet the real estate and had to make sure the antenna worked in such close proximity to the board," said Shor. The design team also had to cope with meeting expectations for a slick design with a low profile, no external antennas and with pre-defined locations for the connectors. According to Menshulam, Wisair's partnership with antenna maker In4tel had already given them a head start with a low-cost design based on FR4 material, small size and positive gain that was flat over the 3- to 5-GHz band. While FCC rules require a transmit EIRP of 0 dBi, having a positive gain in the receive path improves the link budget. "We have 2 dBi gain, that's very impressive: the norm is 0 to 1 [dBi]," said Yurdakul.

However, for a real-world implementation, the team had to make sure the antenna worked on different surfaces and in different environments. "To do this, we had to reshape the antenna, check it in free space and then optimize it for the design," said Menshulam. The result is an omni-like effective antenna that allows the user to place the hub in different orientations and which also keeps positive gain despite the close proximity to the to the board. The company also leveraged its own antenna diversity expertise and In4tel's internal antenna design expertise. Despite the compromises made in the redesign to make it effective in the real world of varying surfaces, orientations and environments, Yurdakul said the team was able to keep a positive gain of approximately 2 dBi. For antenna diversity, the team placed the two redesigned wideband omni antennas at 90 degrees to each other which made the design less sensitive to the environment. Additional acceptance tests were added to make sure the effective pattern from the two antennas would be omni-like.

Figure 4: Final antenna patterns. Placing the two omni antennas at right angles helped mitigate orientation and environmental effects.

Figure 5: Hub antennas gain over 360 degrees.

Figure 6: Single antenna gain versus frequency response shows flat gain over the 3- to 5-GHz band.

Figure 7: Single antenna group delay, representing the phase response of the antenna and the quality of In4tel's anechoic chamber with its good absorption characteristics.

Figure 8: In4tel's 3D anechoic chamber where free-space tests were performed before the final tweaks were made in the antenna design before the final system implementation.

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