Single feed tri-band PIFA with parasitic element

Details Single feed tri-band PIFA with parasitic element Single feed tri-band PIFA with parasitic element

2002-04-29

2003-10-28

Clinger, James (Department: 2821)

Communications: radio wave antennas

Antennas

Microstrip

C343S702000

Reexamination Certificate

active

06639560

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 PIFA having an internal parasitic element for tri-band operation including the dual cellular and non-cellular frequency bands.
2. Description of the Related Art
Cellular communication technology has witnessed a rapid progress in the recent past. Of late, there is an enhanced thrust for internal cellular antennas to harness their inherent advantages. The concept of an internal antenna stems from the avoidance of protruding external radiating element by the integration of the antenna into the device itself. Internal antennas have several advantageous features over external antennas such as being less prone to 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, 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. The PIFA also finds useful applications in diversity schemes. The sensitivity of the PIFA to both vertical and horizontal polarization is of immense practical importance in mobile cellular/RF data communication applications because of the absence of fixed orientation of the antenna 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.
In the rapidly evolving cellular communication technology and ever increasing demand for multi-systems applications, there is a growing trend towards the design of a multi-purpose cellular handset. A cellular handset with system capabilities of both the dual cellular and non-cellular (such as GPS or Bluetooth [BT]) applications has become a new feature. Therefore, there is an enhanced interest for the design of a single feed cellular antenna which operates in both the dual cellular and non-cellular frequency bands. The inherent problem facing such a design is the bandwidth requirement of the upper resonant band of the antenna to simultaneously cover upper cellular (DCS or PCS) and the non-cellular (GPS or BT) frequencies. In most of the research publications/patents on PIFA technology, the major success has been the design of a single feed PIFA with dual resonant frequencies resulting essentially in a dual band PIFA. Depending upon the achievable bandwidth around the two resonant frequencies, the dual resonant PIFA can potentially cover more than 2 bands. However, system applications like GPS and BT or IEEE 802.11 have frequency bands that are significantly off from the dual cellular bands (AMPS/GSM, DCS/PCS). The extension of the currently available cellular dual band PIFA designs to additionally cover the GPS or BT (ISM) band imposes rather non-realizable bandwidths centered around the dual resonant cellular frequencies. For example, to extend the operation of a cellular dual band (AMPS/PCS) PIFA to cover the GPS band would imply the bandwidth requirement of 23.35% for the upper resonance combining GPS and PCS bands (1575 to 1990 MHz). The corresponding bandwidth requirement of the (GSM/DCS/GPS) PIFA for its upper resonance combining GPS and DCS bands (1575 to 1880 MHz) is 17.72%. Likewise, to extend the operation of the cellular dual band (AMPS/PCS) PIFA to cover the BT/ISM application would require 29.89% bandwidth for its upper resonance comprising both PCS and ISM bands (1850 to 2500 MHz). It is very difficult to achieve such a wide bandwidth out of the currently reported PIFA designs. A dual feed multi-band PIFA with separate feeds exclusively for dual cellular bands and non-cellular band has not proved to be an attractive choice because of the mutual coupling between the individual feeds. Therefore the design technique of a multi-band (dual cellular and non-cellular) PIFA devoid of the problem of mutual coupling is called for. The design scheme of a single feed PIFA, which can effectively overcome the enormity of bandwidth requirement centered around any specific resonant frequency to simultaneously cover dual cellular and non-cellular bands, will be of significant practical importance from a system point of view. It is also desirable that the alternative design techniques of a single feed PIFA for the simultaneous inclusion of the dual cellular and non-cellular resonant bands should not involve an increase in the overall volume of the antenna.
The instant invention proposes a new technique for designing a single feed tri-band (dual cellular and non-cellular) PIFA which overcomes the enormity of the bandwidth requirement for its upper resonant band covering both upper cellular and non-cellular frequencies. The serious problem of the mutual coupling encountered in the dual feed multi-band PIFA is a non-entity in the proposed design scheme of this invention. A possible practical recourse to design a single feed tri-band PIFA that covers the cellular and non-cellular systems applications lies in the realization of three distinct resonant frequencies at the respective bands and to achieve the requisite bandwidths centered around the resonant frequencies of interest. This invention proposes the placement of a shorted parasitic element internal to the dual cellular band PIFA structure to realize a third and an exclusive non-cellular resonant frequency band of the PIFA.
In conventional designs of a microstrip antenna or PIFA with a parasitic element, the parasitic element is usually placed adjacent to the radiating element which leads to increased linear dimensions and volume of the antenna. In the proposed single feed tri-band PIFA design of this invention, the parasitic element is placed in the area between the radiating element and the ground plane thereby resulting in neither an increased volume nor increased linear dimensions thus accomplishing the compactness of the multi-band PIFA structure. Thus the single feed multi-band PIFA design of this invention also has the desirable feature of compactness of the overall volume of the PIFA.
A conventional single band PIFA assembly
100
is illustrated in
FIGS. 5
a
and
5
b
. The PIFA
100
shown in
FIG. 5
a
and
FIG. 5
b
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
. A 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
104
a
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 the 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
100
is determined by th

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