Film Type Wide-Band Antenna for Next-Generation Communi- cation

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					Film Type Wide-Band Antenna for Next-Generation Communi-
cation Systems at Frequency Range from 2.3 to 6 GHz
Keisuke Fukuchi*                                                ABSTRACT: Ultra Wide Band (UWB) communication (now being standardized by
Kenichi Sato*                                                   IEEE802.15 TG3a) is expected to be widely adopted for high-speed communication
                                                                systems by 2006. A transfer rate as high as 1 Gbps will be realized in the future, thus
Hisashi Tate*                                                   enabling the speedy transmission of such high-density files as high definition TV
Ken Takei**                                                     images.
                                                                We designed and developed a film type of UWB antenna that is small and thin, and
                                                                able to oscillate in a wide-band frequency range of 2.3 to 6 GHz, including the wire-
                                                                less LAN (Local Area Network) region. This includes the frequency ranges of 2.4 to
                                                                2.5 GHz (IEEE 802.11b/g), 5 to 6 GHz (IEEE 802.11a), and WiMAX (2.3, 2.5, 3.5, and
                                                                5.8 GHz being standardized by IEEE802.16). The antenna achieved the omnidirec-
                                                                tional radiation pattern and high average gain. The group delay fluctuations of this
                                                                antenna was less than 1.2 nanoseconds in the field of 2 to 6 GHz.

                                                                              (IEEE 802.11a/b/g) region.
     Wireless LAN antennas have recently been installed in more
                                                                              [2] WIDE-BAND ANTENNA DESIGN
than 80% of newly developed laptop PCs. This means that wire-
less communication is now widely used in the consumer field.                  2.1 Optimization for each element
Although the maximum transfer rate of wireless LANs is theo-                      We defined the antenna specifications suitable for installa-
retically 54 Mbps, the actual rate is up to 20 Mbps based on                  tion in mobile devices, as well as our wireless LAN antenna2)-5)
IEEE802.11g or 11a.                                                           specifications. To satisfy these specifications, we designed the
     On the other hand, there is a growing need for faster file               antenna in line with to the following parameters: 1) small size
transmission given the quality of files required, such as movie               and thin structure, 2) self-grounding design, and 3) omnidirec-
files and high quality images. In particular, the transfer of digi-           tional radiation pattern (particularly on the azimuth plane). Our
tal data of high definition TV (HDTV) images between elec-                    film-type antenna has an originally thin structure2)-5) because it's
tronic consumer products poses the most prominent and impor-                  made of thin copper alloy plate (0.1 or 0.2 mm thick) and lami-
tant challenge in the near future because consumers want to                   nated with polyimide film (typically 25 µm thick).
connect HDTVs, laptop computers, and other digital consumer                       We considered three elements of the antenna to satisfy all
electronic products for creating a more comfortable personal                  three design parameters above. Figure 1 shows the basic antenna
environment. This kind of communication requires a transfer                   design. We set two open stubs and one short stub to ground to
rate exceeding 40 Mbps to produce the high quality and smooth                 achieve wide-band characteristics, and optimized the length of
action scenes on a TV, especially when transmitting multiple                  each stub using a transmission-line model to make each length
images and information. Existing wireless LANs can not basi-                  accommodate the appropriate frequency6). Figure 2 shows the
cally achieve this kind of high-speed transmission.                           antenna design as the result of our calculations. The first open
     UWB communication systems can satisfy these consumer                     stub from the feeding point is 16 mm long; the second open stub
needs thanks to the original high-speed transfer rates. The                   is 13 mm long in the same way. The third stub makes a loop
chipset and module necessary to achieve a rate of 110Mbps have                between the feeding point and grounding point, and is 45 mm in
been commercially available since late 2004. In the first stage
of UWB communication system, a maximum transfer rate of
480 Mbps is possible by using the frequency range from 3 to 5
GHz(What is called low band).
     We have studied various types of antennas for mobile de-
vices since the latter half of 20001)-4), and accumulated much
know-how on antenna design and manufacture. This paper ex-
amines the design and development of a film type wide-band
antenna that is suitable for first-stage UWB communication. For
this antenna, we targeted the frequency range to be covered from
2.4 to 6 GHz, which encompasses the UWB and wireless LAN
                                                                              Fig. 1 − Transmission-line model of wide-band antenna
* Electronic & automotive products group, Hitachi Cable, Ltd.                 We set three elements (two open stubs and one short stub) to achieve
** Research & development group, Hitachi Cable, Ltd.                          wide-band characteristics.

loop length. The total antenna size is 40 mm (W) x 33 mm (H).                            Wave Ratio) of 2.5, at the frequency range from 2.8 to 6.6 GHz.
Figure 3 shows the calculated return loss of this antenna design.                        Figure 4 shows the calculated resonant part at each resonance
This calculation shows that the designed antenna covers return                           frequency (3.32, 4.86, and 5.97 GHz). As designed, the first and
loss less than -7.36 dB, which is an important indicator of an-                          second stubs mainly oscillate at the lowest and middle frequen-
tenna characteristics and equal to a VSWR (Voltage Standing                              cies of 3.32 GHz and 4.86 GHz, respectively. The third stub
                                                                                         mainly oscillates at the highest frequency at 5.97 GHz. Based on
                                                                                         the calculation results, we confirmed that wide-band resonance
                                                 2nd stub
                                                                                         covering the first-stage UWB frequency region could be
                                  3rd stub                    1st stub                   achieved.
                                                                                             We made a prototype antenna based on the calculated re-
                                                                                         sults. Figure 5 shows a photograph of an actual antenna. The
                                                                                         antenna conductor is made of copper alloy and is laminated with
                                                                                         polyimide film. The total thickness of the antenna is less than
                                                                                         0.3 mm. Signals are fed via a mini coaxial cable (1.1 mm in
                                                                                         diameter). Figure 6 compares the measured return loss of this
                                                                                         antenna with the calculated return loss. The lowest and middle
                                                                                         measured resonance frequencies are almost same as those cal-
                                                                                         culated, but the resonance matching itself is much deeper than
                                                                                         that calculated. The highest resonance frequency measured
Fig. 2 − Schematic diagram of calculated result                                          shifts slightly lower than that calculated. These differences are
The 1st stub from the feeding point is 16 mm long; the 2nd stub is 13 mm                 caused by the different signal feeding procedures employed for
long; the 3rd stub is 45 mm long along the loop between the feeding and                  the calculation and in actual application. Despite the slight dif-
grounding points.                                                                        ferences, the measured return loss remained at the wide-band

     Return Loss (dB)



                        -20                                     RL; -7.36 dB

                              2      3       4        5      6      7          8
                                                  Frequency (GHz)

Fig. 3 −Calculated return loss                                                           Fig. 5 − Photo of the radiator
The designed antenna covers return loss less than -7.36 dB at the fre-                   The antenna conductor is made of copper alloy and laminated with
quency range from 2.8 to 6.6 GHz.                                                        polyimide film. The total antenna thickness is 0.3 mm.




Fig. 4 − Calculated resonant part in each resonance frequency
The 1st stub oscillates at 3.32 GHz (a); the 2nd stub oscillates at 4.86 GHz (b);the 3rd stub makes a loop oscillating at 5.97 GHz (c).

                                                                                                     HITACHI CABLE REVIEW No.24 (AUGUST 2005)            7
                                                                                                               because these devices must work normally at any location and
                                                                                                               any position. Thus, this wide-band antenna can satisfy this re-
    Return Loss (dB)

                        -5                                                                                     quired specification.
                                                                                                                   We then calculated the average gain at each frequency by
                                                                                                               summing up all azimuth angle gain values of the radiation pat-
                       -15                                                                                     tern. We used the following equation to calculate the average
                       -20                                                 Calculated                                                                  N-1
                       -25                                                 RL; -7.36 dB                                                                      (PVi + PHi)
                                                                                                                      Average Gain (dBi) = 10 log      i=0                           (1)
                       -30                                                                                                                                       N
                                     2         3     4       5       6        7           8
                                                         Frequency (GHz)

Fig. 6 − Comparison of calculated and measured return loss
Both results correspond well except for the total resonance depth and
                                                                                                               where, PVi , and PHi respectively denote the gain values of the
the frequency of the highest resonant part. These differences are caused                                       vertical and horizontal polarized waves, i denotes the number
by different signal feeding procedures employed by the calculation and                                         of the azimuth angle (0, 1, 2, ---, 359) and N denotes the step
in actual application.                                                                                         counts of measurement (= 360).
                                                                                                                    Figure 8 shows the average gain results. The antenna had a
resonance frequency range from 3 to 6 GHz.                                                                     high (almost 0 dBi even when including 1 dB cable loss) and
                                                                                                               flat gain profile from 2.5 through 6 GHz. This is important for
2.2 Antenna Estimation and Discussion                                                                          UWB systems, especially for the antenna to achieve a flat gain
    We measured the radiation pattern and average gain of the                                                  response throughout the appropriate frequency range. Because
developed wide-band antenna on the azimuth plane. Figure 7                                                     the UWB signal has wide-band frequency components, the flat
shows the results of the radiation pattern measurement at 3.0                                                  gain response should be needed to avoid inducing a time delay
and 5.0 GHz. These results show the vertical (in blue) and hori-                                               throughout its frequency range of use during signal transmis-
zontal (in red) polarized waves separately. Each result at 3.0                                                 sion and reception.
and 5.0 GHz shows an almost omnidirectional radiation pattern                                                       Figure 9 shows the setup used to measure the group delay
without any null-point. These omnidirectional patterns are an                                                  of this antenna. The group delay was measured between two of
important consideration for such mobile devices as laptop PCs,                                                 our UWB antennas. Antennas were set face to face in free space,

                                                                  x                                                                          x                    Vertical
                                                                  0                                                                          0
                                          10                                                                     10
                                           0                                                                      0
                                         -10                                                                    -10
                                         -20                                                                    -20
                        Gain (dBi)

                                         -30                                                                    -30
                                                                                                  Gain (dBi)

                                         -40                                                                    -40
                                         -50   270                                    90y                       -50    270                                             90y
                                         -40                                                                    -40
                                         -30                                                                    -30
                                         -20                                                                    -20
                                         -10                                                                    -10
                                           0                                                                      0
                                          10                                                                     10                                          -Micro coaxial cable;
                                                                                                                                                              OD 1.13 mm,
                                                                 180                                                                        180               L = 180mm
                                                              (a) 3.0 GHz                                                                (b) 5.0 GHz


                                                                                      x                               y

                                                                                          Measurement plane

                                                                                  (c) Definition of the azimuth angle

Fig. 7 − Measured radiation pattern of the antenna
The antenna has an omnidirectional radiation pattern at both frequencies.

8                  HITACHI CABLE REVIEW No.24 (AUGUST 2005)
and the distance between both antennas was changed from 40,                                            veloped wide-band antenna is suitable for UWB communica-
60, and 80 cm. Figure 10 shows the results. The group delay of                                         tion systems.
the antenna was less than 1.2 nanoseconds from 2 to 6 GHz even
at a distance of 80 cm. From the standpoint of UWB communi-
                                                                                                       [3] ACTUAL USE ON A LAPTOP PC CHASSIS
cation, a group delay (one of the important factors for UWB
communication) of less than a few nanoseconds is good enough                                                We modified the developed antenna for actual usage by con-
for the antenna characteristics. This result indicates that our de-                                    sidering its installation in laptop PCs. In particular, the height
                                                                                                       of the antenna radiator part should be lowered for installation in
                          2                                                                            a narrow space. To lower the height of the radiator, the second
                          1                                                                            stub was bent perpendicularly. We recalculated the length of
    Average Gain (dBi)

                          0                                                                            each stub and optimized the antenna resonance frequency for
                         -1                                                                            actual application.
                         -2                                                                                 We then installed the recalculated antenna on a dummy LCD
                                                                                                       chassis4) that we normally use for basic estimation of our anten-
                                                                                                       nas. Figure 11 and 12 show the conditions of installing the
                                                                                                       antenna on the dummy LCD chassis. We used cable (1.1 mm in
                                                                                                       outer diameter and 500 mm in length) made by Hitachi Cable,
                         -7                        Including 1 dB cable loss @ 5.0 GHz
                                                                                                       and a miniature coaxial connector for feeding signals. Figure
                                 2.0    2.5       3.0    3.5    4.0 4.5 5.0 5.5          6.0     6.5   13 and (a) and (b) in Fig. 14 show the return loss and average
                                                               Frequency (GHz)                         gain in this situation. By re-optimizing the antenna configura-
                                                                                                       tion, resonance matching less than -7.36 dB in the return loss
Fig. 8 − Measured average gain
The result shows that the antenna has a high and flat gain profile from
                                                                                                       properties was expanded from 2.2 to over 7 GHz even in the
2.5 through 6 GHz.                                                                                     case of actual installation. In this case, the antenna needs a win-
                                                                                                       dow size (i.e., size of a nonmetal material area) of 60 mm (W) x
                                                                                                       7 mm (H) to achieve this characteristic. The average gain shown
                                                                                                       in (a) and (b) in Fig. 14 achieved a practicable level enough, in

                                                                                                                                           296 mm
                                       UWB Antenna                       UWB Antenna
                                                                                                        Cover = Plastic                          UWB Antenna

                                                                                                          Copper film
                                                                                                                               Dummy LCD panel = Steel              210 mm
                                                                                                          attached to
                                                                                Coaxial Cable
                                                        Network Analyzer                                Base = Plastic
Fig. 9 − Setup for group delay measurement
Two antennas were set face to face in free space, with the distance be-
tween both being changed from 40, 60, and 80 cm.
                                                                                                       Fig. 11 − Dummy LCD dimensions
                                                                                                       This is our standard equipment used for antenna development and evalua-
                  10                                                                                   tion. The antenna was attached to the cover with tape.
                         9                                                               40 cm
                                                                                         60 cm
    Group delay (nsec)

                         7                                                               80 cm
                                                                                                               10 mm                40 mm               10 mm
                                                           1.2 ns
                                                                                                                                                                  7 mm
                         3                                                                                                           x              y

                             2                3                4           5         6             7
                                                                   Frequency (GHz)                     Fig. 12 − Antenna window dimensions
Fig. 10 − Group delay results                                                                          This antenna needs 10 mm of metal-free space on both sides, and 7 mm
The group delay of the antenna was less than 1.2 nsec from 2 to 6 GHz,                                 between the top of the antenna and upper edge of the LCD panel.
even at a distance of 80 cm.                                                                           Thus, the antenna was almost directly attached to the plastic cover.

                                                                                                                    HITACHI CABLE REVIEW No.24 (AUGUST 2005)                9
                                 0                                                                        [4] CONCLUSION
                                                                                                               We have developed a new film type wide-band antenna suit-
                         -10                                                                              able for UWB, wireless LAN, and WiMAX. The antenna has an
      Return Loss (dB)

                         -15                                                                              omnidirectional pattern and average gain (0 dBi including cable
                                                                                                          loss) that is sufficiently high and flat on the azimuth plane .
                                                                                                               This antenna is also applicable for practical use, even in such
                                                                                                          narrow spaces as around the LCD panel of a laptop PC. By using
                         -30                                                                              this antenna, the number of antennas mounted in laptop PCs and
                                                                     Including cable reflection
                         -35                                         Eliminating cable reflection         other portable devices can be reduced due to the antenna's wide-
                                                                     RL; -7.36 dB                         range resonance frequency.
                                                 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
                                                                  Frequency (GHz)
Fig. 13 − Return loss of improved antenna                                                                                          REFERENCES
Resonance matching the bandwidth less than -7.36 dB is from 2.2                                           1) Tate et al.: "New Method for Designing Internal Antennas
through over 7 GHz.                                                                                          of Mobile Phones," HITACHI CABLE REVIEW No. 20 (Au-
                                                                                                             gust 2001).
                                                 0                                                        2) Ikegaya et al.: "Film Type Antenna for Mobile Devices for
                                                -1                                                           2.4 GHz Range," HITACHI DENSEN No. 21 (2002).
                          Average Gain (dBi)

                                                                                                          3) Ikegaya et al.: "Development of Film Type Antenna for Mo-
                                                -4                                                           bile Devices," HITACHI CABLE REVIEW No. 21 (August
                                                -5                                                           2002).
                                                -6                                                        4) Fukuchi et al.: "Wide-Band Wireless LAN Antenna for IEEE
                                                -7                                                           801.11 a/b/g," HITACHI CABLE REVIEW No. 23 (August
                                                -9         Including 1.5 dB cable loss @ 2.4 GHz
                                               -10                                                        5) Tate et al.: "Film Type Wideband Antenna for UWB Com-
                                                  2.25   2.3     2.35 2.4 2.45            2.5      2.55      munication," IEEE 802.15-<15-04-0087-00-003a> (03
                                                                Frequency (GHz)
                                                                                                             March, 2004).
                                                               (a) 802.11b/g band
                                                                                                          6) Takei et al.: Patent Application No. 2003-383647 (Novem-
                                          -1                                                                 ber 2003, Japan)
                            Average Gain (dBi)

                                          -3                                                                                 Keisuke Fukuchi
                                          -4                                                                                 Engineering dept., Electronic & Automotive Products
                                          -5                                                                                 Group
                                          -6                                                                                 Joined the company in 1991.
                                                                                                                             Currently engaged in design of wireless communication
                                          -8                                                                                 Member of the Japan society of applied physics
                                          -9              Including 2.4 dB cable loss @ 5.0 GHz
                                                   2.5      3.5      4.5            5.5           6.5
                                                            Frequency (GHz)                                                   Kenichi Sato
                                                         (b) UWB and 802.11a band                                             Engineering dept., Electronic & Automotive Products
Fig. 14 − Average gain in dummy LCD chassis                                                                                   Joined the company in 2000.
Average gain in both (a) and (b) are sufficiently flat and high for practi-                                                   Currently engaged in design of wireless communica-
cal use. Cable (1.1 mm in outer diameter and 500 mm long) was used for                                                        tion antenna.
signal feeding.

the 802.11b/g (2.4 to 2.5 GHz), UWB (3 to 5 GHz), and 802.11a
(4.9 to 6 GHz) ranges.                                                                                                       Hisashi Tate
    The results mentioned above suggest that this antenna is                                                                 Engineering dept., Electronic & Automotive Products
applicable for use as a combo antenna with wireless LAN (IEEE                                                                Joined the company in 1985.
802.11a/b/g) and UWB (IEEE 802.15 TG3a). Although the fre-                                                                   Currently engaged in development and design of wire-
                                                                                                                             less communication antenna.
quency specification has yet to be defined, WiMAX (IEEE
802.16) would also be a target for using this antenna, because
this antenna covers WiMAX scheduled frequencies (2.3, 2.5,
3.5, and 5.8 GHz). As already mentioned, our newly developed
                                                                                                                             Ken Takei
wide-band antenna is suitable for practical use with several
                                                                                                                             Cross technology development center, Research & de-
next-generation wireless communication systems. At the same                                                                  velopment group
time, the number of antennas mounted in laptop PCs can be                                                                    Joined the company in 2004.
                                                                                                                             Currently engaged in development of antenna embed-
reduced by using this antenna, although a module combining                                                                   ded RF module.
wireless LAN and UWB, or a switching device is required for                                                                  Member of IEEE and IEICE

such use.