Analysis of Mobile Phone antenna Impedance Variations With User Proximity

hongse2005

Analysis of Mobile Phone antenna Impedance Variations With User Proximity
【文件名】:071220@52RD_04084732.pdf
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【简　介】:Analysis of Mobile Phone antenna Impedance Variations With User Proximity

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john019

Abstract—The impedance change that occurs when the user
holds a mobile phone antenna is a well-known problem. This
paper analyses the contributions to this change for a dual-band
PIFA. In particular, the contribution of the slot is shown and a
method of reducing it is proposed and analyzed.
Index Terms—Antenna, impedance, interaction, planar inverted
F antenna (PIFA).
I. INTRODUCTION
WHEN a mobile phone call takes place there is a degree
of interaction between the user and the antenna housed
within the phone. For example, many calls occur with the phone
in “talk position” that is, with the phone held next to the head.
In such circumstances there is a strong interaction between the
antenna and the user’s head and hand, which, broadly speaking,
act as lossy dielectrics. This causes a significant reduction in the
antenna radiation efficiency [1]–[3].
User interaction also causes a change in the antenna driving
point impedance that leads to a further, often significant, loss of
performance [4]–[8]. The design of circuitry that can adaptively
recover some of this lost performance has been the subject of
research for many years [9]–[16]. However, a cheap solution
that is easy to implement is yet to be proposed. The main reasons
for this are two-fold:
• Measurement
Accurate measurement of the complex antenna impedance
by a circuit that is both small and cheap remains a challenge.
Such measurement techniques are an active area of
research [11].
• Variable components
To date variable components, that also meet all of the
linearity and quality requirements of mobile phones, have
not been commercially available. It is expected that this
restriction will be alleviated to some extent in the coming
years by microelectromechanical systems (MEMS) devices
[17]–[20].
Both of these problems are lessened if the antenna impedance
variation is known and, if possible, reduced. However, there are
no published results on how the complex impedance of a dual-
Manuscript received May 15, 2006; revised October 17, 2006.
K. R Boyle is with NXP Semiconductors, Redhill, Surrey RH1 5HA, U.K.
(e-mail: kevin.boyle@philips.com).
Y. Yuan was with Philips Research Laboratories, Kerry Everbright City,
Shanghai, China. She is now with Philips Research Program Office, 5656 AE
Eindhoven, The Netherlands (e-mail: carrie.y.yuan@philips.com).
L. P. Ligthart is with the International Research Centre for Telecommunications.............................

lihuansir

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