Antenna meshes with compact needs
By Bill Schweber -- EDN, August 7, 2003
The old rule was that if you wanted a better antenna, you had to put up more metal, but that approach is no longer is acceptable or necessary in our portable-product world, as vendors develop new technologies based on monolithic and multilayer ceramics (Picture). Sarantel’s active and passive helix antennas, available for GPS, cellular, 3G, 802.11, and Bluetooth bands, give you electrical and mechanical advantages at modest cost.
Built as a plated, trimmed, and tuned set of spirals on a solid ceramic core, the antennas feature a tight near-field intensity pattern of a few millimeters, which minimizes interaction with the user’s hand or body as well as adjacent circuitry, and avoids resonant-frequency detuning. This also reduces antenna SAR (specific absorption ratio) into conductive tissues, such as a user’s head, for greater efficiency as more radiated energy goes where it is necessary. From an RF perspective, the antenna is balanced, eliminating the need for space-consuming ground planes. The integral balun is an RF trap, which isolates the virtual ground of the antenna from the circuitry ground, thus minimizing the conduction of common-mode noise from the circuitry ground back into the receiver. The antenna also acts as a filter, keeping out-of-band signals from interfering and can eliminate the needs for filter components.
The design allows for bandwidths as wide as about 10% of the center frequency, which many frequency-hopping systems require. Sarantel offers passive units as well as active versions with low-noise amplifier gains of 10 to 24 dB, depending on model. Prices are $3 to $10 (OEM quantities).
Sarantel Inc, 1-425-861-0463, www.sarantel.com.
