Two promising, internal, shorted monopole antennas for 700 MHz and WLAN/WiMAX operation are combined in an arrangement with minimized mutual coupling for palm-sized mobile applications. The two stamped, metal-plate antennas with a 2 mm gap therein between can be integrated into a compact configuration and are then mounted near one side of the system circuit board. With the suitable shorting locations and arrangement of the two antennas, good isolation (S21 < –20 dB) between the two ports can easily be obtained. Analysis of placing a CCD shielding cylinder between the two antennas and the two shorting strips joined to form a shorting wall are also conducted. Detailed designs of the two antennas are described, and the results thereof are discussed.
2. Figure 2 The photo of the antenna working samples made of a 0.3-mm
thick alloy [Color figure can be viewed in the online issue, which is
available at www.interscience.wiley.com]
Figure 4 Measured 3D radiation patterns at 752 MHz for the 700 MHz
antenna studied in Figure 3 [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com]
(width 2 mm) for lowering the operating frequency is utilized. This
patch-like monopole antenna is also operated as a quarter-wave-
length resonant structure, and in general, both the length and the 3. RESULTS AND DISCUSSION
width of the plate determine the center frequency about 2545 MHz Figures 3(a) and 3(b) show the measured and simulated reflection
of the resonant mode for 2.4-GHz WLAN/2.5-GHz WiMAX op- coefficient (S11 for the 700 MHz antenna, S22 for the WLAN/
eration. WiMAX antenna) and isolation (S21). It is first noticed that, in
general, the experimental data compare favorably with the simu-
lation results, which are based on the finite element method. The
impedance matching for frequencies across the 700-MHz band, the
2.4-GHz WLAN band, and the 2.5-GHz WiMAX band is all less
than 6 dB (3:1 VSWR) and even well below 10 dB in both the
WLAN and WiMAX bands. The isolation between the two anten-
nas remains less than about 20 and 30dB over the 700-MHz
band and the WLAN/WiMAX band, respectively. Notice that the
second resonant mode of the 700-MHz antenna is found at about
1.45 GHz. That is, the frequency ratio of the antenna upper to
lower resonant mode is close to 2, which is largely due to the
effects of the meandered structure in the 700-MHz antenna.
Figures 4– 6 give the measured radiation patterns at 752, 2442,
and 2593 MHz. The far-field 3D radiation patterns were measured
at a fully anechoic chamber (dimensions 3 3 7 m3) at Lite-On
Technology. The 3D measurement system uses the great-circle
method and is equipped with a dual-polarized horn as a receiving
(a) antenna. The radiation characteristics for the 700-MHz antenna
resemble those of the mobile-phone antenna for GSM operation, in
(b)
Figure 3 Reflection coefficients (S11 for the 700 MHz antenna, S22 for
the WLAN/WiMAX antenna) and isolation (S21) between the two anten- Figure 5 Measured 3D radiation patterns at 2442 MHz for the WLAN/
nas: (a) measured results; (b) simulated results [Color figure can be viewed WiMAX antenna studied in Figure 3. [Color figure can be viewed in the
in the online issue, which is available at www.interscience.wiley.com] online issue, which is available at www.interscience.wiley.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 11, November 2008 2949
3. is seen to be in the direction of the system ground plane ( x
direction here), which behavior shows no particular distinction
between the proposed and other small 2.4-GHz antennas for PDA
phone applications [10 –13]. Figures 7(a) and 7(b) present the
measured peak antenna gain and radiation efficiency for 700 MHz
and 2.4-GHz WLAN/2.5-GHz WiMAX operation. In the 700-
MHz band, the peak gain is in the range of 1.5–2.6 dBi with the
radiation efficiency above 64%. As for the WLAN/WiMAX bands,
Figure 6 Measured 3D radiation patterns at 2593 MHz for the WLAN/
WiMAX antenna studied in Figure 3 [Color figure can be viewed in the
online issue, which is available at www.interscience.wiley.com]
which dipole-like radiation is obtained with omnidirectional pat-
tern in the plane (the y–z plane in this study and two nulls in the
x axis direction) perpendicular to the ground plane at the longer
side [6 –9]. Also, no major difference is observed for radiation
patterns at 2442 and 2593 MHz, which suggests stable radiation
properties for the WLAN/WiMAX antenna. In addition, the max-
imum radiation over the 2.4-GHz WLAN/2.5-GHz WiMAX bands
(a)
(a)
(b) (b)
Figure 7 Measured peak antenna gain and radiation efficiency for the Figure 8 Simulated reflection coefficients (S11, S22) and isolation (S21)
two antennas studied in Figure 3: (a) for the 700 MHz antenna; (b) for the for the case with (a) a common shorting wall and (b) a CCD shielding
WLAN/WiMAX antenna [Color figure can be viewed in the online issue, cylinder [Color figure can be viewed in the online issue, which is available
which is available at www.interscience.wiley.com] at www.interscience.wiley.com]
2950 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 11, November 2008 DOI 10.1002/mop