Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-02-01
2004-12-28
Chen, Shih-Chao (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06836246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to Planar Inverted-F Antenna (PIFA) and, in particular, to a method of designing a single and multi-band PIFA with a single feed.
2. Description of the Related Art
The cellular communication industry has experienced an enormous growth in recent years. Of late there has been an increasing emphasis on internal antennas for cellular handsets instead of a conventional external wire antenna. The conventional external wire antenna on a cellular handset exhibits an Omni directional radiation pattern in the azimuth plane. This results in a portion of transmitted power being lost by absorption into the user's head and consequently leads to a higher value of Specific Absorption Rate (SAR). Internal antennas have several advantageous features such as being less prone for external damage, a reduction in overall size of the handset with optimization, easy portability, and potential for low SAR characteristics. The concept of internal antenna stems from the avoidance of protruding external radiating element by the integration of the antenna into the handset. The printed circuit board of the cellular handset serves as the ground plane of the internal antenna, and also acts to shield RF energy from user's head. This shielding/blockage effect reduces the power radiated in the direction of the user's head resulting in an improvement in the front to back (F/B) ratio of the radiation pattern of the internal antenna and lower value of SAR. Among the various choices for cellular internal antennas, PIFA appears to have great promise. The PIFA is characterized by many distinguishing properties such as being relatively lightweight, ease of adaptation and integration into the phone chassis, moderate range of bandwidth, Omni directional radiation patterns in orthogonal principal planes for vertical polarization, versatility for optimization, and multiple potential approaches for size reduction. A possible placement for PIFA inside a typical cellular handset to function as an internal antenna is shown in FIG.
10
. The PIFA also finds useful applications in diversity schemes. Its sensitivity to both the vertical and horizontal polarization is of immense practical importance in mobile cellular communication applications because the antenna orientation is not fixed. All these features render the PIFA to be a good choice as an internal antenna for mobile cellular handsets. Despite all of the desirable features of a PIFA, the PIFA has the limitation of a rather large physical size for practical application. A conventional PIFA should have the semi-perimeter of its radiating element (sum of the length and the width) equal to ¼ of a wavelength at the desired frequency. One-quarter of a wavelength at the center of AMPS frequency band (824-894 MHz) is 87.31 mm while the corresponding value at the center of GSM frequency band (880-960 MHz) is 81.52 mm. With the rapidly advancing size miniaturization of the cellular handset, the space requirement of a conventional PIFA is a severe limitation for practical application. Thus, there is a need for an efficient design technique to reduce the size of the PIFA, in order to realize a practical utility of the PIFA for cellular frequency bands.
Rapid expansion of the cellular communication industry in the recent past has created a need for multi-frequency band operation cellular handsets to meet the ever-increasing subscriber demand. In a typical multi-frequency band cellular handset with a single Duplexer, a multi-frequency band antenna with a single feed is the most viable option. Few attempts have been made in the past to design multi-frequency band PIFA with a single feed due to the complexity of design and difficulty in achieving acceptable bandwidths for the resonant bands desired. Multi-band PIFA designs have been realized in the past by using a separate feed path for each band. There is a great concern for a multi-band PIFA design with multiple feed paths having its performance compromised due to the mutual coupling and poor isolation of the various resonant bands. Therefore, the multi-band PIFA with multiple feed paths has not been a logical choice for practical applications in multi-frequency band cellular operations. Therefore, the design of single feed multi-band PIFA has been a topic of specific emphasis and special relevance to cellular communication.
A typical placement of a PIFA placed inside the housing of a typical cellular handset to function as an internal antenna is illustrated in FIG.
10
.
FIG. 10
is a schematic cut-away side view of a typical cellular handset
40
with an internal antenna
42
. Cellular handset
40
includes a housing
41
in which antenna
42
and other accessories are enclosed. Among other things, the accessories of a cellular handset include a speaker
43
, display
44
, keypad
45
, microphone
46
, battery
47
and a printed circuit board
48
containing various electronic cards. Speaker
43
and microphone
46
define a user direction. When the cellular handset is in use with the keypad
45
pointing towards user's head, the speaker
43
is placed in the vicinity of user's ear and the microphone
46
is placed in the close proximity of the user's mouth. In
FIG. 10
, the internal antenna
42
is placed directly over the printed circuit board
48
implying that the printed circuit board
48
also serves as a ground plane for the antenna
42
. The internal antenna may also have a separate ground plane. In such a case, the ground plane of the internal antenna
42
is placed over the printed circuit board
48
. The radiating element of the internal antenna
42
is oriented in a direction away from user's head. The printed circuit board
48
which is located in the region between the internal antenna
42
and the user's head, blocks a significant amount of the RF field radiated by the antenna
42
in the direction of the user's head. Such a blockage effect offered by the printed circuit board
48
results in a dip or null in the radiation pattern of the antenna over an angular sector comprising the direction of the user's head also. Consequently, the amount of RF power of the internal antenna
42
transmitted in the direction of the user's head is considerably reduced resulting in low value of specific absorption rate (SAR).
A conventional prior art single band PIFA assembly is illustrated in
FIGS. 11A and 11B
. The PIFA
110
shown in FIG.
11
A and
FIG. 11B
consists of radiating element
101
, ground plane
102
, connector feed pin
104
a
, and conductive post or pin
107
. A power feed hole
103
is located corresponding to the radiating element
101
. Connector feed pin
104
a
serves as a feed path for radio frequency (RF) power to the radiating element
101
. The connector feed pin
104
a
is inserted through the feed hole
103
from the bottom surface of the ground plane
102
. The connector feed pin
104
a
is electrically insulated from the ground plane
102
where the pin passes through the hole in the ground plane
102
. The connector feed pin
104
a
is electrically connected to the radiating element
101
at
105
a
with solder. The body of the feed connector
104
b
is electrically connected to the ground plane at
105
b
with solder. The connector feed pin
104
a
is electrically insulated from the body of the feed connector
104
b
. A through hole
106
is located corresponding to the radiating element
101
, and a conductive post or pin
107
is inserted through the hole
106
. The conductive post
107
serves as a short circuit between the radiating element
101
and the ground plane
102
. The conductive post
107
is electrically connected to the radiating element
101
at
108
a
with solder. The conductive post
107
is also electrically connected to the ground plane
102
at
108
b
with solder. The resonant frequency of the PIFA
110
is determined by the length (L) and width (W) of the radiating element
101
and is slightly affected by the locations of the f
Kadambi Govind R.
Masek Thomas F.
Simmons Kenneth D.
Centurion Wireless Technologies, Inc.
Chen Shih-Chao
Holland & Hart LLP
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