Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2003-01-28
2004-12-14
Chen, Shih-Chao (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06831607
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of wireless communication, and more specifically to the construction of planar inverted-F antennas (PIFAs) for use in wireless communication devices such as mobile telephone handsets.
BACKGROUND OF THE INVENTION
The Advanced Mobile Phone Service (AMPS) and the Personal Communication Service (PCS) frequency bands, and the Global System for Mobile Communications (GSM) and the Digital Cellular System (DCS) frequency bands, form the basic dual cellular frequency bands within the US and within Europe, respectively.
There is a demand for wireless communication devices that will accommodate both the US AMPS/PCS frequency bands and the European GSM/DCS frequency bands within a single wireless communications device, so that a single wireless communications device, such as a cellular handset, can be used worldwide. This evolution toward a single cellular handset having global utility results in a need for cellular antennas that will simultaneously cover the AMPS/PCS/GSM/DCS frequency bands.
In addition, use of an antenna that is buried within, or is internal to, a cellular handset is desirable. Among the choices for an internal antenna for use within cellular handsets, a PIFA is very versatile in terms of its physical size and its performance.
In the past, multi-band PIFAs (for example two band or three band) have been provided having two or more RF feeds. However multi-feed PIFAs encounter disadvantages such as increased cost and increased mutual coupling that results from poor isolation.
Extension of a multi-feed multi-band PIFA in order to provide a global cellular PIFA (i.e. a PIFA that covers the AMPS/PCS/GSM/DCS frequency bands), cannot easily be accomplished due to the fact that the lower cellular frequency bands AMPS and GSM are close to each other, and in fact they have a region of frequency overlap, and the same is true for the upper frequency cellular bands DCS and PCS. Due to this close frequency proximity of the relevant frequency bands, as well as the region of frequency overlap, the use of two PIFAs that operate separately in the AMPS/PCS frequency bands and the GSM/DCS frequency bands can be provided within a cellular handset. But this two-PIFA assembly requires that the two antennas occupy about twice the physical volume within a cellular handset that a single PIFA would require. In addition, partitioning the physical antenna-volume that is normally available within a practical and realistic cellular handset does not usually provide a desired separate resonance in both the AMPS frequency band and the GSM frequency band. Even if one were to succeed using such a two-PIFA design, providing adequate isolation between the two PIFAs is difficult. In view of these practical design constraints, the use of two PIFAs, having two feeds and having multiple frequency bands, is not a logical choice for the realization of a global cellular PIFA construction and arrangement.
Progress has been made in the cellular technology to provide a single-feed two-band PIFA. There also has been progress in the bandwidth enhancement of single feed two-band and three-band PIFAs.
Prior art PIFAs include a radiating/receiving element (hereinafter called a radiating element) having a length and a width that is optimized to approximate a quarter-wavelength within its semi perimeter. In order to reduce the resonant frequency of the PIFA without increasing its physical size, slots of different shapes have been used within the PIFA's radiating element. With the judicious choice of a slot configuration, and by optimizing the position of the radiating element's shorting post, PIFA designs have emerged for single-feed multi-band operation.
In prior art single-feed multi-band PIFAs, the multi-band operation is the result of a combination of the quasi physical partitioning of a single band PIFA's radiating element, wherein the radiating element is a derivative of a corresponding single-feed, single-band, PIFA.
In prior art dual-feed multi-band PIFAs having two radiating elements, the two radiating elements are physically isolated from each other.
In multi purpose cellular handsets that are usable in both cellular and non-cellular applications, a multi-band antenna that simultaneously operates in both the cellular and the GPS/Bluetooth frequency bands is of interest, wherein Bluetooth (BT) is a code name for a proposed open specification to standardize data synchronization between disparate PC and handheld PC devices. Single-band PIFAs have proven to be useful in meeting the demand of GPS/BT applications.
In prior art designs, an internal GPS band antenna has been used along with a dual-band cellular antenna, to thereby provide a dual-feed, three-band, two-antenna assembly. Such dual-feed three-band two-antenna assemblies have to encounter design complexities in order to ensure adequate isolation between the two feed ports that support the two cellular frequencies and the GPS frequencies.
Conventionally, a single-feed dual-band PIFA requires only one shorting post. In the prior art, slots of different shapes have been used in the radiating element of a PIFA, mainly to lower the resonant frequency of the radiating element without increasing the physical size of the PIFA. Although attempts have been made to provide a three-band PIFA by improving the bandwidth of a two-band PIFA, little or no success has been achieved relative to providing a single-feed four-band PIFA, or in providing for a simultaneous non-cellular band (GPS/ISM) resonance within the same four-band PIFA.
In certain PIFA designs, parasitic elements have been used in a dual-band PIFA to generate an additional resonance for non-cellular application.
In order to meet the demand of a global cellular antenna, U.S. Pat. No. 6,255,994, provides for the multiple resonance of a PIFA by providing frequency-selecting switches for different resonant frequencies, so that the same telephone and antenna can be used globally. However, such a design results in an increased cost and additional complexities due to the increased number of electrical connections/components that are required for the antenna. In addition, and apart from the higher cost, the possibility exists for a gain degradation of the antenna when additional electrical components are introduced into the antenna.
SUMMARY OF THE INVENTION
This invention provides a single-feed four-band virtual two-PIFA assembly (hereinafter more conveniently called a two-PIFA assembly) that is responsive to the AMPS, PCS, GSM and DCS frequency bands, wherein this multi-band operation is realized by inserting the metal radiating element of one PIFA (i.e. an inner radiating element) within the metal radiating element of another PIFA (i.e. an outer radiating element).
A generally C-shaped slot separates the metal inner radiating element from the metal outer radiating element, and two spaced-apart metal stubs define the two ends of the C-shaped slot. That is, these two metal stubs are located in the discontinuity area of the C-shaped slot. These two metal stubs (the C-shaped slot's discontinuity area) physically and electrically connect the inner radiating element to the outer radiating element.
Separate metal shorting posts are provided for each of the inner and outer radiating elements, to thereby connect both of these radiating elements to a metal ground plane element that is located under, and generally parallel to, a plane that contains the two radiating elements.
The non-radiating edge of the outer radiating element is electrically connected to a single feed post, and one of the two metal stubs that connect the outer radiating element to the inner radiating element is located relatively close to this feed post, to thus provide a virtual feed to the inner radiating element.
RF energy is fed to and taken from the two-PIFA assembly by way of this single feed post, wherein at least one of the two metal stubs acts as a virtual RF feed for the inner radiating element.
The outer radiating element, having the single RF feed post and a shorting po
Hebron Theodore Samuel
Kadambi Govind Rangaswamy
Yarasi Sripathi
Centurion Wireless Technologies, Inc.
Chen Shih-Chao
Holland & Hart LLP
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