An internal wideband metal-plate monopole antenna for mobile phone applications is presented. The antenna is easily fabricated by bending a single metal plate and suitable to be embedded within the casing of a mobile phone as an internal antenna. Further, the antenna shows a wide operating bandwidth of about 5 GHz (about 1.8−6.7 GHz), making it easy to cover the UMTS band and the 2.4/5.2/5.8 GHz WLAN bands for mobile/WLAN dual-mode operation for a mobile phone.
2. Figure 3 Measured radiation patterns at 2045 MHz. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]
located below a via-hole in the center of the small ground plane. In The proposed antenna, with the asymmetrical two-branch feed-
addition, the length and width of the system ground plane are ing strip and the bending process shown in Figure 1(b), can be
chosen to be 100 and 70 mm, respectively, which are reasonable divided into several portions, which easily makes the obtained
dimensions for a practical PDA phone. impedance bandwidth to have a lower edge frequency less than 2
Figure 4 Measured radiation patterns at 2442 MHz. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]
1742 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 7, July 2008 DOI 10.1002/mop
3. Figure 5 Measured radiation patterns at 5500 MHz. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]
GHz and provide a wide operating bandwidth of about 5 GHz. This and the main ground plane together operate in the high-order
behavior is largely because the several resonant paths are obtained, resonant modes, thus leading to less smooth radiation patterns.
which control the occurrence of the antenna’s different resonant Figures 6 and 7, respectively, plot the measured peak antenna
modes. Moreover, a much more uniform current distribution in the gain and the simulation radiation efficiency against the UMTS
planar monopole antenna is achieved. Note that the asymmetrical band and the 2.4/5.2/5.8 GHz WLAN band for the constructed
two-branch feeding strip can provide additional coupling between prototype. The antenna gain in the UMTS band of about 3.1–3.5
the proposed antenna and the antenna ground plane, which helps dBi is obtained with the simulation radiation efficiency of about
improve the impedance matching of the antenna, leading to a much 79 – 84%. The antenna gain in the 2.4 GHz band has a gain level
wider impedance bandwidth obtained. In addition, owing to the of 3.3 dBi with the simulation radiation efficiency of about
asymmetrical two-branch feeding strip, the proposed monopole 83%. In addition, in the 5.2/5.8 GHz band, the antenna gain
antenna height above the small ground plane is reduced, which varies slightly in a range of about 4.4 – 4.9 dBi and the simu-
helps achieve a compact size for the antenna. lation radiation efficiency exceeds about 84%.
3. EXPERIMENTAL RESULTS AND DISCUSSION 4. CONCLUSION
The proposed antenna was constructed and studied with the design A wideband metal-plate monopole antenna suitable for applica-
dimensions shown in Figure 1. Figure 2 shows the measured and tions of an internal mobile-phone antenna, especially for a PDA
simulation return loss for the constructed prototype. The simula-
tion results are obtained using the Ansoft simulation software
high-frequency structure simulator (HFSS) [9], and good agree-
ment between the experiment data and simulation result is seen. A
very wide impedance bandwidth, defined by 10-dB return loss, is
first obtained. The measured impedance bandwidth is about 5 GHz
(1818 – 6746 MHz), which makes the antenna easily cover the
UMTS band for mobile communications and the 2.4/5.2/5.8 GHz
band for WLAN communications. The radiation characteristics
were also studied. Figure 3 plots the measured radiation pat-
terns at the center frequency (at 2045 MHz) of the UMTS band.
Figures 4 and 5, respectively, show the measured radiation
patterns at the center frequencies (at 2442 and 5500 MHz) of
the 2.4 GHz WLAN band and the 5 GHz (5.2/5.8 GHz) WLAN
band. By comparing the radiation patterns at 5500 MHz to those
at 2045 and 2442 MHz, it is observed that the radiation patterns Figure 6 Measured antenna gain and simulated radiation efficiency for
at 5500 MHz are seen to be less smooth. This characteristic is the UMTS band studied in Figure 2. [Color figure can be viewed in the
largely because, at higher frequencies, the proposed antenna online issue, which is available at www.interscience.wiley.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 7, July 2008 1743