Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-11-06
2004-05-25
Nguyen, Hoang V. (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000, C343S767000, C343S770000, C343S846000
Reexamination Certificate
active
06741214
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a Planar Inverted F-Antenna (PIFA), and in particular, to a single feed, multi band (Three, four or five band) PIFA whose radiating/receiving element contains one or more slots.
2. Description of Related Art:
With the rapid progress of cellular communication and the increasing demand for multi systems application, there is a trend toward the design of multi purpose, multi band, cellular handsets, i.e. cellular wireless communications devices.
This demand has advanced from two band cellular antennas to three band antennas that cover the lower US or European cellular band, as well as the digital calling selecting (DCS) and personal communication service (PCS) bands.
It is reasonable to foresee a future requirement for a single antenna that covers the AMPS/PCS and GSM/DCS bands for global cellular communications (wherein AMPS stands for advanced mobile phone service, also called North American cellular phone system, and wherein GSM stands for global system for mobile communications).
There is also a desire to use cellular antennas that are internal to a wireless communication device such as a cellular handset. Since an internal antenna is integrated into, or buried within, the wireless communication device, an internal antenna eliminates any antenna element that protrudes outward from the body of the wireless communication device.
Internal antennas have several advantages, such as being less prone to damage, a reduction in the size of the handset, and increased portability of the handset. When an internal antenna is provided, the wireless communication device's printed circuit board may also serve as a ground plane element for the internal antenna.
Among the choices that are available for internal antennas, a planar inverted-F antenna (PIFA) has great promise. PIFAs have many distinguishing properties, such as being relative lightweight, ease of adaptation and integration into the wireless communication device's chassis, a moderate range of bandwidth, omni directional radiation patterns in orthogonal principal planes for vertical polarization, versatility for optimization, and arrangements to achieve size reduction. The sensitivity of PIFAs to both vertical and horizontal polarization is of practical importance in mobile cellular/RF data communication applications due to the absence of a requirement for a fixed orientation of the antenna, as well as multi path propagation conditions. All of these features make a PIFA a good choice for use as an internal antenna for mobile cellular/RF data communication applications.
In the past, success has been achieved in the design of a single feed PIFA having two resonant frequencies, this resulting in a two band PIFA. In view of the inherent bandwidth limitations that are associated with conventional PIFA designs, most of the prior art single feed, two band, PIFAs exhibit useful and desirable performance that covers only two cellular frequency bands.
U.S. Pat. No. 5,926,139 (incorporated herein by reference), and a paper by Liu. et. al. entitled “Dual Frequency Planar Inverted—F Antenna”, IEEE Trans. Antenna and Propagation, Vol. AP-45, No. 10, pp. 1451-1548, Oct. 1997, are examples of the prior single feed, dual band, PIFAs.
FIGS. 6
a
and
6
b
illustrate a prior art single feed, two band, PIFA
50
. Dual band PIFA
50
that includes a radiating/receiving element
301
(hereinafter radiating element) and a ground plane
302
. An L-shaped open slot
303
within radiating element
301
provides quasi-physical partitioning of radiating element
301
.
The portion of radiating element
301
having the dimensions of length L
1
and width W
1
resonates at the lower frequency band of the PIFA's dual band operation. The portion of radiating element
301
having the dimensions of length L
2
and width W
2
resonates at the upper frequency band of the dual band operation.
A power feedhole
304
is located in radiating element
301
, and a connector feed pin
305
that feeds radio frequency (RF) power to radiating element
301
is inserted through feedhole
304
from the bottom surface of ground plane
302
. Connector feed pin
305
is electrically insulated from ground plane
302
at the point where feed pin
305
passes through a hole that is provided in ground plane
302
. Connector feed pin
305
is electrically connected to radiating element
301
at
306
.
The outer body portion
314
of the connector that includes feed pin
305
is connected to ground plane
302
at
307
, and feed pin
305
is electrically insulated from the outer body portion
314
of this connector.
A hole
308
is provided in radiating element
301
, and a conductive post or pin
309
which provides a short circuit between radiating element
301
and ground plane
302
is inserted through hole
308
. Conductive post
309
is connected to radiating element
301
at
310
, and is connected to ground plane
302
at
311
.
Dual band impedance matching of radiating element
301
is determined by the diameter of connector feed pin
305
, by the diameter of conductive shorting post
309
, and by the separation distance that exists between connector feed pin
305
and conductive shorting post
309
.
A disadvantage of the dual band PIFA
50
illustrated in
FIGS. 6
a
and
6
b
is the lack of a simple means of adjusting the frequency separation between the antenna's lower and the upper resonant frequency bands. A change in the frequency separation of these two resonant frequency bands requires the repositioning of an L-shaped slot
303
that is formed in radiating element
301
. PIFA
50
also provides a constraint on a realizable bandwidth that is centered around the two resonant frequencies of PIFA
50
.
Techniques for enhancing the bandwidth around the two resonant frequencies of PIFA
50
are of practical importance. Depending upon the bandwidth that is achievable around the two resonant frequencies, dual resonant PIFA
50
may potentially cover more than two frequency bands.
For the design of a dual band (i.e. a dual resonance) PIFA that covers the AMPS/PCS and the GSM/DCS bands for global cellular communications, the bandwidth requirement of the lower resonance of a PIFA that covers both the AMPS and the GSM bands is about 15.29%, when compared to about 8.15% for the AMPS band only. Likewise, the bandwidth requirement of the upper resonance of a PIFA that covers both the DCS and PCS bands is about 15.14%, as compared to about 7.29% required for the PCS band only.
Attempts have been made to improve the bandwidth centered around the upper resonant frequency of a dual band PIFA in order to realize three or tri band performance that covers three cellular frequency bands.
Simultaneously enhancing the bandwidth centered around the two resonant frequencies of a dual band cellular PIFA in order to accomplish the four or quad band operation that is essential for global cellular coverage or applications is not known.
Therefore, a single feed, four band, PIFA comprising the four basic frequency bands of global cellular communication is needed by the art, and such a single feed, quad band, PIFA is of practical importance for the emerging trend of a single cellular handset for global cellular coverage.
In order to keep pace with another category of recent advance in cellular communications, there is a requirement for a single antenna that simultaneously covers both cellular and non-cellular applications, examples of non-cellular applications being global positioning system (GPS) and Bluetooth (BT) (wherein Bluetooth is a code name for a proposed open specification to standardize data synchronization between disparate PC and handheld PC devices).
System applications like GPS and BT or IEEE 802.11 have frequency bands that are significantly off of the dual cellular bands of AMPS/GSM and DCS/PCS. An inherent problem is the bandwidth requirement for the upper resonant band of an antenna to simultaneously cover the upper cellular (DCS or PCS) frequencies and the non-cellular (GPS or BT)
Hebron Theodore Samuel
Kadambi Govind Rangaswamy
Meza Antonio Barron
Yarasi Sripathi
Centurion Wireless Technologies, Inc.
Holland & Hart LLP
Nguyen Hoang V.
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