The challenge for mobile phone makers is to create a single small antenna, that can be used for multiple frequency bands. At the 2004 International Symposium on Antennas, NEC announced a new antenna that can operate across two frequency bands, 800MHz and 2GHz. The antenna was jointly developed with Anten Corp.
“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.”
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