A novel, three-in-one antenna system suitable for WLAN operation in the 5 GHz band is presented. The design is based upon incorporating one slot and two dipole antennas into a compact multi-antenna system that has comparable dimensions of a single mobile-unit antenna element. The three antennas are arranged parallel to each other with the two dipoles set on the right and left sides of the slot respectively. With this arrangement, not only can compact integration of three individual antennas be realized, pattern diversity and polarization diversity are also obtained. A design prototype has been constructed and tested. The results show that the coupling or the antenna port isolation is below –20 dB and good radiation characteristics have been observed.
2. Figure 4 Measured isolation (S21, S31, S32) between any two of the three
antennas of the proposed, diversity antenna system. [Color figure can be
viewed in the online issue, which is available at www.interscience.wiley.
com]
Figure 2 Photo of a design prototype constructed from a 1-mm-thick To achieve polarization diversity, the slot and dipole antennas
FR4 substrate. [Color figure can be viewed in the online issue, which is are used and arranged to be parallel to each other. This horizontal
available at www.interscience.wiley.com] configuration of the slot and dipole antennas allows the two
antenna ports to be easily decoupled (port isolation 20 dB),
feeding (denoted as Port 2 in Fig. 1) for the slot antenna is about and at the same time, orthogonal polarization is realized. As for the
7.5 mm from the bottom of the slot. This distance effects imped- effect of pattern diversity, the radiation of the two dipoles are
ance matching and center operating frequency in the 5 GHz band expected to cover space on both sides (right and left) of the slot,
largely. Further, the two dipole antennas are put on the right and whose main radiation is in the front and back directions of the
left sides of the slot antenna and to be symmetrical in arrangement. proposed multiantenna system. Finally, to feed the design proto-
The near optimal value of the dipole-antenna length and feed gap type, three short, 50- mini-coaxial cables with I-PEX connectors
is found to be 17 mm and 1 mm respectively. Usually, for two are utilized.
parallel dipoles, to obtain isolation well below 15 dB between
the dipoles that have good input matching of 10 dB return loss, a 3. RESULTS AND DISCUSSION
minimal space of 0.65 c (that’s 36 mm versus 23 mm here) is On the basis of design dimensions given in Figure 1, the proposed,
required between the antennas [12]. However, the slot antenna three-in-one, diversity antenna system was constructed and tested.
here can be treated as a reflector, which not only reflects the dipole Figure 3 shows the measured reflection coefficients (S11 for dipole
radiation but decouples the two dipole antennas. Also notice that antenna 1, S22 for slot antenna, S33 for dipole antenna 2). Port
further moving the dipole antenna towards the ground plane of the isolation (S21, S31, S32) between any two of the three antennas for
slot antenna can lead to deteriorating bandwidth for the dipole the proposed design is shown in Figure 4. It can easily be seen that
antenna. A near optimal distance of 4 mm is selected in this study. measured impedance bandwidth of the three antennas meets the
required bandwidth specification for 5 GHz WLAN operation with
Figure 3 Measured reflection coefficients (S11 for dipole antenna 1, S22
for slot antenna, S33 for dipole antenna 2) of the proposed, diversity Figure 5 Calculated envelope correlation for the three 5 GHz antennas.
antenna system. [Color figure can be viewed in the online issue, which is [Color figure can be viewed in the online issue, which is available at
available at www.interscience.wiley.com] www.interscience.wiley.com]
2478 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop
3. Figure 6 Measured 2-D radiation patterns at 5490 MHz for dipole antenna 1 studied in Fig. 3. [Color figure can be viewed in the online issue, which is
available at www.interscience.wiley.com]
reflection coefficient well below 10 dB. The isolation between (simulated) as described in [13] for sufficiently accurate results in
the two dipoles is found to be below 20 dB over the 5 GHz band. many practical cases [13, 14]. The correlation values remain under
This good decoupling is expected because the ground plane of the 0.002 in the band, which is better than the value of 0.3 demanded
slot antenna is considered as a reflector lying in between the two widely by industry specification.
dipole antennas. As for the isolation between the dipole and slot Figures 6 – 8 plot the far-field, 2-D radiation patterns at 5490
antennas, due to symmetrical structure of the proposed, diversity MHz, the center operating frequency of the 5 GHz band, for the
antenna system, the curves of S21 and S32 are about the same. In three antennas. Firstly, for the two dipole antennas, directional
addition, better decoupling in the band of interest, compared with radiation patterns are found in the x-y and x-z planes with maxi-
the isolation between the two dipoles, has been observed largely mum radiation (peak antenna gain) in the x directions ( x for
because of the dipole and slot antennas set to be of orthogonal dipole 1 and x for dipole 2, see Figs. 6 and 8). This behavior is
polarization. Figure 5 gives the envelope correlation between port expected due largely to the ground plane of the slot antenna acting
1 (of dipole antenna 1) and port 2 (of slot antenna). Notice that the as a reflector. On the contrary very little effect of the reflector is
envelope correlation here is determined by the use of S parameters given on the radiation in the y-z plane of the two dipoles. Secondly,
Figure 7 Measured 2-D radiation patterns at 5490 MHz for the slot antenna studied in Fig 3. [Color figure can be viewed in the online issue, which is
available at www.interscience.wiley.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 2479
4. Figure 8 Measured 2-D radiation patterns at 5490 MHz for dipole antenna 2 studied in Fig 3. [Color figure can be viewed in the online issue, which is
available at www.interscience.wiley.com]
the slot antenna yields typical, bi-directional radiation patterns in cations. To attain the proposed design, one slot antenna and two
the x-y and y-z planes with peak antenna gain around the y dipoles antennas have been employed and integrated into a com-
directions as seen in Figure 7. Worth noticing that along the y pact structure on a substrate of 30 mm 27 mm. Experimental
axes at the intersection of three principal-polarization radiation of results show that good isolation of less than 20 dB between any
the slot and dipole antennas, the maximum radiation in the E field two antenna ports has been obtained, along with envelope corre-
of the dipole is at the right angle to the maximum radiation in the lation well below 0.002 over the 5 GHz band. Directional radiation
E field of the slot. The properties indicate that orthogonal waves patterns have been observed to cover complementary space in
of polarization diversity take place. Figure 9 presents the peak addition to orthogonal waves formed by the slot and dipole anten-
antenna gain against frequency for the antennas studied in Figure nas. The design of the proposed, three-in-one antenna system is a
3. The peak gain over the 5 GHz band for the three antennas is seen promising solution to internal diversity antennas in the 5 GHz
to be at a constant level of about 4 dBi. In addition, it can easily band.
be seen that the antenna gain of the two dipole antennas is similar
due to symmetrical structure of the proposed design.
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