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Antennas for Mobile Communications: CDMA, GSM, and WCDMA 115

Figure 3.12. This arrangement can enhance the cancellation effect of the
first method. For instance, “wall a” mainly affects the coupling between
probes 1 and 3 so as to increase the total input port isolation between
lower frequency bands (ports 1 and 2). Similarly, the auxiliary “wall b” and
“wall c” are mainly used for the upper frequency band isolation enhance-
ment. By optimizing the dimensions and positions of these walls, high
input port isolation can be achieved over the frequency band.

3.2.3.3 Measurement Results Because the size of the array is quite
large in terms of wavelength, simulating its performance with a com-
mercial simulation package is difficult. Therefore, only measurement
results are presented here. Figures 3.14a and 3.14b show the measured
return loss and input port coupling of the array in the lower and upper
frequency bands, respectively. It is observed that, for RL < −14 dB, the
bandwidth is 22% (0.81–1.01 GHz) for port 1 and 19% (0.81–0.98 GHz)
for port 2 in the lower frequency band. Over the frequency range of 0.82
to 0.96 GHz, the input port coupling is less than −30 dB. For the upper
frequency band, the bandwidth is 40% (1.48–2.23 GHz) for port 1 and
42% (1.53–2.34 GHz) for port 2. The input port coupling is less than
−30 dB over the frequency range of 1.68 to 2.2 GHz. In the same figures,
it can also been seen that the peak gain is around 10.5 dBi in the lower
band and 14 dBi in the upper band.
Figures 3.15 and 3.16 depict the measured far-field radiation patterns of
the two input ports, corresponding to the ± 45° polarizations, at the center
frequency of the lower frequency band (0.9 GHz) and the upper frequency
band (2.0 GHz), respectively. We define the x-z plane as the vertical plane
and the y-z plane as the horizontal plane. For the lower frequency band
(port 1), the 3-dB beamwidths are 30° and 61° in the vertical and hori-
zontal planes, respectively. The corresponding values for the lower band
(port 2) are 30° and 66°. In both planes, the cross-polarization level is less
than −17 dB in the broadside direction. Also, the backlobe level is less
than –20 dB. For the upper frequency band (port 1), the 3-dB beamwidths
are 12° and 67.5° in the vertical and horizontal planes, respectively. The
corresponding values for the upper frequency band (port 2) are 13° and
75°. In both planes, the cross-polarization level is less than −19 dB in the
broadside direction. Moreover, the backlobe level is less than −25 dB.

3.2.3.4 Summary A dual-band dual-polarized patch antenna array was
designed and implemented successfully. The measured results demon-
strate that it has an input return loss of less than −14 dB, input port iso-
lation of more than 30 dB, and a cross-polarization level of less than −15
dB over the 0.82 to 0.96-GHz and 1.71 to 2.17-GHz bands. This array is
suitable for CDMA, GSM, PCS, and UMTS bands simultaneously.