Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-05-17
2001-03-06
Vo, Nguyen (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S129000, C343S702000
Reexamination Certificate
active
06198943
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mobile terminals for use in analog and digital-based cellular communication systems, and, in particular, to an improved antenna configuration for dual-band operation.
BACKGROUND OF THE INVENTION
Mobile terminals, and especially mobile telephones and headsets, are becoming increasingly smaller. These terminals require a radiating element or antenna for radio communications. Conventionally, antennas for such terminals are attached to and extend outwardly from the terminal's housing. These antennas are typically retractably mounted to the housing so that the antenna is not extending from the housing when the terminal is not in use. With the ever decreasing size of these terminals, the currently used external antennas become more obtrusive and unsightly, and most users find pulling the antenna out of the terminal housing for each operation undesirable. Furthermore, these external antennas are often subject to damage during manufacture, shipment and use. The external antennas also conflict with various mounting devices, recharging cradles, download mounts, and other cooperating accessories.
Application Ser. No. 09/189,890 describes an internal loop dipole antenna for a cellular telephone. The antenna includes extra traces and tuning elements on the same physical plane as the antenna element to enable dual-band operation. As phone designs become increasingly smaller and the antenna is brought closer to the ground plane (PCB) of the phone, the antenna begins to lose its effectiveness. It has been discovered that the effective bandwidth of the antenna is narrowed as the antenna is brought closer to the ground plane of the antenna. Also, tuning of the resonance frequencies becomes problematic due to the strays and parasitics caused by the antenna's close proximity to the ground plane. The extra traces and tuning elements did not provide sufficient bandwidth in both bands of operation. Also, lumped elements such as capacitors and inductors did not adequately eliminate the strays and parasitics.
Accordingly, there remains a need for a dual band antenna that will operate effectively in two distinct operating bands even when the antenna is brought in close proximity to the ground plane of the phone.
SUMMARY OF THE INVENTION
The present invention provides an internal antenna for mobile terminals that provides performance comparable with externally mounted antennas, even when placed in close proximity to the ground plane. The antenna includes a resonating element and a parasitic tuning element. The resonating element has a looped, dipole configuration including first and second tuning loops and a ground loop. The tuning loops and ground loop are electrically connected by tuning elements which, preferably, are in the same plane as the tuning loops and ground loop. The loops of the resonating elements may be placed around other components of the phone without significantly impinging on precious physical space. For example, the loops may be disposed around the keypad or display in the housing, in a flip portion pivotally connected to a main section of the housing, or in a distinct printed circuit board enclosed in the housing.
The parasitic element is disposed in a plane spaced from the plane of the resonating element. The parasitic element includes a first portion that generally follows the contour of the ground loop on the resonating element, and a second portion that bisects one of the tuning loops on the resonating element. First and second tuning arms extend along opposing ends of the parasitic tuning. The parasitic element is shifted in the x-y plane to tune the resonant frequency of the antenna to a first operating band. The length of the tuning arms is adjusted in order to tune the antenna to a second operating band.
An advantage of the present invention is that it allows the design engineer to match the antenna to a VSWR of approximately 2:1 in two distinct operating bands (typically the 900 MHz and 1800 MHz bands) even at the band edges. This allows the antenna to obtain broad bandwidth in both bands of operation and prevents loss of gain due to mismatch of the VSWR. No prior art antennas have been able to obtain these advantages in an antenna spaced in close proximity to the ground plane.
REFERENCES:
patent: 5854970 (1998-12-01), Kivela
patent: 5923305 (1999-07-01), Sadler et al.
patent: 6011519 (1998-12-01), Sadler et al.
Hayes Gerard
Sadler Robert A.
Coats & Bennett PLLC
Ericsson Inc.
Vo Nguyen
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