Electronic Design

Helical Antenna Makes Satellite Reception Reliable And Easy

Receiving a signal from a geosynchronous satellite 22,300 miles out or a GPS satellite over 10,000 miles away is a challenge. Big gain antennas usually are necessary. But that’s just the opposite of what developers need for their handheld designs.

Benefon’s TWIG Discovery smart phone uses Sarantel’s GeoHelix helical antenna in its full-blown GPS receiver and navigation system. This GSM cell phone with GPS targets security, personnel, and fleet management applications. The antenna makes GPS incorporation practical with uncompromised performance.

Meanwhile, satellite radio receiver perofrmance depends more on the antenna than the chip. The GeoHelix’s SkyTune design targets portable XM satellite radios. Samsung’s and Pioneer’s new XM2go portable XM receivers use it to pick up satellite signals from almost anywhere. It offers the benefits of reduced size and 30% to 50% better performance over previously used conventional patch antennas.

The Sarantel helix antenna comprises a four-conductor helix (quadrifilar) on a ceramic substrate. This high-dielectric base does a super job of constraining the near field to the antenna, so hands and faces won’t detune the cell phone anymore. The helix is a balanced antenna, meaning that it does not need a ground plane for proper operation like the common patch antenna. The balanced design also offers the usual balanced benefits of common-mode noise reduction.

The antenna has a circular polarization with a voltage standing-wave ratio (VSWR) of less than 2:1. A built in balun translates the balanced antenna to a standard 50-Ω single-ended output. Overall efficiency is over 25%, which is significantly higher than the 3% to 5% typical with patch and other types of portable antennas. Its high Q resonance limits its bandwidth, making the antenna a great bandpass filter that helps reduce noise and interference. And, its cardoid radiation pattern makes it virtually omnidirectional.

The SkyTune antenna is a cylinder that’s 10 mm in diameter and 17 mm long. It comes with a variety of mounts and connections, including surface mount. Check out the various models on Sarantel’s Web site.

Sarantel Ltd and Sarantel USA Inc.

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