Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-03-27
2002-11-19
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000, C343S702000
Reexamination Certificate
active
06483463
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a diversity antenna system which includes two planar inverted F antennas which have a small common ground plane. Four embodiments of the invention are disclosed herein.
2. Description of the Related Art
In its simplest form, the diversity technique, as it applies to antennas for RF data and wireless communication devices, provides a means of achieving reliable and enhanced system performance through the use of an additional antenna. A diversity antenna system utilizes two antennas which sample the RF signal to determine the strongest signal to enable the communication device to utilize the strongest RF signal. To meet the requirement of sustained and fast rate of data transfer, specific emphasis has been recently placed on diversity antennas in RF data communication. Despite the enhanced reliability and the improved performance of an antenna system with the diversity scheme, its adoption to a compact wireless system is not widespread. Theoretically, the spatial diversity technique requires a physical separation of one wavelength between the two antennas. In many practical applications, it may not be feasible to provide the required separation between the two antennas of a spatial diversity scheme. The requirement of a wide separation between the two antennas of a diversity scheme also requires a longer feed cable to the individual antennas from a common RF source point. The resulting longer feed cable leads to the problem of ensuring effective shielding of the cable, the consequent RF power loss in the cable and the undesirable interference effect on system performance particularly at a higher frequency band. The above-mentioned shortcomings apply to diversity schemes consisting of conventional external antennas which have been in existence for a long time as well as with the recently evolving internal antenna. In view of the above constraints associated with the conventional diversity scheme, emphasis is being shifted to arrive at a compactness of the overall spatial diversity scheme which meets acceptable performance standards.
Of late there has been an increasing emphasis on internal antennas instead of a conventional external wire antenna. The concept of internal antenna stems from the avoidance of a protruding external radiating element by the integration of the antenna into the device itself. Internal antennas have several advantageous features such as being less prone for external damage, a reduction in overall size of the handset with optimization, and easy portability. The printed circuit board of the communication device serves as the ground plane of the internal antenna. Among the various choices for internal antennas, the PIFA appears to have great promise. The PIFA is characterized by many distinguishing properties such as relative lightweight, ease of adaptation and integration into the device 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. Its sensitivity to both vertical and horizontal polarization is of immense practical importance in mobile cellular/RF data communication applications because of the absence of the fixed antenna orientation as well as the multi-path propagation conditions. All these features render the PIFA to be a good choice as an internal antenna for mobile cellular/RF data communication applications.
The PIFA also finds useful applications in diversity schemes. Despite all of the desirable properties 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 (sum of the length and the width) of its radiating element equal to one-quarter of a wavelength at the desired frequency. With the rapidly advancing size miniaturization of the radio communication devices, the space requirement of a conventional PIFA is a severe limitation for its practical utility. Further, the internal antenna technology is relatively new and is in an evolving stage of development. The combination of inherent shortcomings associated with the size of the PIFA and the requirement of even larger space or volume for multiple PIFAs seems to be the primary reason for the non-feasibility of the use of PIFA for diversity schemes of modern wireless communication systems.
To assist in the understanding of a conventional PIFA, a conventional single band PIFA assembly is illustrated in
FIGS. 9A and 9B
. The PIFA
110
shown in FIG.
9
A and
FIG. 9B
consists of a radiating element
101
, a ground plane
102
, a connector feed pin
104
a,
and a conductive post or pin
107
. A power feed hole
103
is located corresponding to the radiating element
101
. The 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 and 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
, with the conductive post or pin
107
being 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 feed pin
104
a
and the shorting pin
107
. The impedance match of the PIFA
110
is achieved by adjusting the diameter of the connector feed pin
104
a,
by adjusting the diameter of the conductive shorting post
107
, and by adjusting the separation distance between the connector feed pin
104
a
and the conductive shorting post
107
.
SUMMARY OF THE INVENTION
In this invention, several new embodiments of compact diversity PIFAs having a small and common ground plane are disclosed. This invention demonstrates that it is possible to retain the performance of individual antennas of a spatial diversity antenna scheme even when the separation between the antennas is only a fraction of a wavelength. In the first embodiment of this invention, two PIFAs are placed back to back on a small rectangular ground plane. The two PIFAs are placed such that the shorted ends of the PIFAs face each other. Such an arrangement ensures better isolation between the two PIFAs despite being placed in close proximity to one another. In the second embodiment of this invention, the ground plane is bent at its opposite ends to form vertical sections. The two PIFAs are placed (outward) on the vertical sections at the opposite ends of the ground plane. Such an arrangement of PIFAs allows the placement of some system components between the two vertical sections of the bent ground plane. The distortion of the radiation patterns of the PIFAs is also minimized despite the presence of some components between the two PIFAs. This is mainly due to the blockage effect offered by the vertical sections of the ground plane. With a significantly different design configuration, in the third embodiment of this invention, there is no physical separation between the two PIFAs placed on a common rectangular ground plane. Only a single shorting pin or post partitions the two diversity PIFAs resulting in
Kadambi Govind R.
Simmons Kenneth D.
Yarasi Sripathi
Centurion Wireless Technologies, Inc.
Clinger James
Thomte Dennis L.
Thomte Mazour & Niebergall
Wong Don
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