A Compact Dual-band Antenna for WLAN Applications
In the world of portable electronics, antennas are problematic. They need to be small, light weight and possess the ability to perform well in a variety of conditions. It also helps if they can be neatly integrated into the product without protrusions that can be easily damaged or broken off, rendering the device useless. Toward this end a new miniature antenna fabricated using low temperature co-fired ceramic (LTCC) technology has been developed that accepts both 2.45 and 5.5 GHz inputs, and provides good performance at both frequencies without sacrificing additional board space. The model 2450AD46A5400 2.45/5.5 GHz antenna is specifically designed and optimized for use in both frequency bands, and is compatible with WLAN 802.11 a, b, g, h, i, j and Bluetooth® operation.
The complete antenna measures only 8.5 x 1.5 x 1.2 mm and incorporates individual feeds for the 2400 to 2500 MHz (low band) and 4900 to 5900 MHz (high band) elements simplifying the electrical feed relative to a single feed design. It can be used in either the vertical (perpendicular) or horizontal (parallel) orientation relative to the PCB. Figure 1 shows the mechanical configuration of the antenna alone. The inner terminals are for the RF feeds and the outer terminations are provided for additional mechanical anchoring. Polarization is linear and the antennas exhibit excellent gain and diversity.
The new dual-band antenna's performance specifications have a typical peak gain of 1.0 dBi in the low band and -1.5 dBi in the high band, and a minimum return loss within each band of 8.5 dB. Typical radiation patterns depending on mounting orientation are displayed in Figure 2 . Figure 3 shows the typical return loss across both frequency bands. Maximum input power is 3 W into 50 and its operating temperature is specified at -40° to +85°C.
The ground plane of the PCB must be removed from the immediate area of the antenna. A recommended feed structure and PCB layout is included in the data sheet. Due to the variety of circuit boards, thickness and dielectric constants that are employed, matching using high Q capacitors and ceramic inductors is recommended to optimize the center frequency to the bands of interest. Matching can also be used to widen the bandwidth. JTI offers a service to its customers to optimize the match and placement if the user will provide a fully populated board and exterior housing.
The terminations are lead free and are compatible with standard volume assembly practices. Hand soldering is not recommended; a belt furnace or hot gas reflow are preferred for lab and prototype assemblies. If the user chooses to use a soldering iron it should be of the controlled temperature variety and used to proximally heat the connection. Ceramic devices should never be touched with the tip of the soldering iron.
A compact dual-band LTCC chip antenna has been introduced with a frequency combination that covers any conceivable integration of 802.11 and Bluetooth operation. The new antenna is easy to incorporate and features high performance in a low cost, space saving design.
Johanson Technology Inc., Camarillo, CA (805) 389-1166, www.johansontechnology.com. Circle No. 304