The mobile phone market is stepping up demand for a single antenna with dual-band capabilities that can cover two or more frequency bands.
This reflects the global shift of mobile communications from 2G to 3G, which is driving development and marketing of dual-band mobile phones. To use two frequency bands, a simple solution is implementing two antennas in a handset.
However, a problem is that of larger dimensions. Mobile phone makers and antenna manufacturers are tackling the challenge, aiming at a single, small antenna for use across multiple frequency bands.
At the "2004 International Symposium on Antennas and Propagation" (ISAP '04) held in Sendai, Japan, from August 17 through 21, NEC Corp announced a new antenna that can operate across two frequency bands: 800MHz and 2GHz. The antenna results from joint development work done by NEC and its group company, Anten Corp.
The two companies adopted a special structure of an antenna made of a single conducting wire that is bent and folded, so that one part of the wire can handle 800MHz signals and another part 2GHz signals. It has dimensions of 7mm high x 5mm deep x 27mm wide (photo).
The structure is unique in that a metal strip (stub) is applied to the 2GHz-receiving portion of the antenna. Moreover, the length of the stub is made variable to enable a frequency change within the 2GHz band according to receiving conditions. However, this technique does not apply to the 800MHz band, because its 2GHz range signals are susceptible to factors such as differences in structures of handsets.
This structure, NEC verified, resulted in a reflection loss of -6dB both in a bandwidth of 120MHz for the 800MHz band (the ratio of the spectrum to a receiving frequency is actually 14.2%) and in a bandwidth of 210MHz for the 2GHz band (the ratio is 10.3%). According to parties concerned, stable communications requires -6dB or lower reflection loss.
Via:neasia.nikkeibp.com
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