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Motorized Self-Tuning Antenna

IP.com Disclosure Number: IPCOM000020185D
Original Publication Date: 2003-Oct-30
Included in the Prior Art Database: 2003-Oct-30
Document File: 3 page(s) / 67K

Publishing Venue

Motorola

Related People

Steven Tan: AUTHOR [+3]

Abstract

This invention relates to handphones or portable two-way radios having an automatically self-tunable antenna. The antenna will have narrow-band characteristics, thus giving better gain, but covers a wide frequency band. A servomotor will provide the drive to enable the antenna coil to reach its designated length.

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Motorized Self-Tuning Antenna

Steven Tan, Alexander Oon and Tan Pek Kai


 

ABSTRACT

This invention relates to handphones or portable two-way radios having an automatically self-tunable antenna. The antenna will have narrow-band characteristics, thus giving better gain, but covers a wide frequency band. A servomotor will provide the drive to enable the antenna coil to reach its designated length.

CURRENT ANTENNA LIMITATIONS

Current antenna designs are limited to either narrow-band or wide-band. Although narrow-band antennas generally give better selectivity as compared to their wide-band cousins, they are band limited, in the sense that their performance will degrade after a certain bandwidth limitation. As the bandwidth of an antenna increases, its Q factor decreases. This decrease in Q factor will cause the gain and selectivity at a particular band to decrease. The relationship between the Q factor and bandwidth (BW) of a narrowband antenna is:

where a is the radius of a sphere enclosing the antenna and . The BW and Q relationship of a wideband antenna shares the same trend. Therefore the generally accepted solution to wideband antenna design is to have a lower gain and lower Q factor antenna, within specification limits, that will function across the desired bandwidth.

SELF-TUNING ANTENNA

The purpose of the self-tuning antenna is to provide a wide-band antenna that is self-

tunable thus providing narrow-band gain and selectivity. This will give it the advantages of a narrow-band antenna plus the bandwidth of a wide-band antenna.

The self-tuning mechanism (Fig. 4) includes a movable coil and a solid metal block. The coil forms the radiating element of the antenna. By altering the length of the coil that is exposed (i.e. not shorted to the metal block), the resonating frequency of the antenna changes, thus allowing the antenna to tune to a particular frequency band. The “tuning” process is achieved by moving the coiled cylinder relative to a stationary solid metal block. A servomotor, preset to reach a designated number of turns, drives the receiver coil on its track. A micro-controller provides the necessary drive voltage to the servomotor to enable/disable as well as to determine the number of turns required to achieve the desired tuning frequency.

Fig. 1 Effective Reception Length of the Antenna

The ability to self-tune is achieved by varying the length of the coil to obtain the Effective Reception Length...