Communications: radio wave antennas – Antennas – High frequency type loops
Reexamination Certificate
2003-01-03
2004-11-23
Nguyen, Hoang V. (Department: 2821)
Communications: radio wave antennas
Antennas
High frequency type loops
C343S866000, C343S870000
Reexamination Certificate
active
06822614
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a loop antenna, and particularly to a loop antenna making use of a ground conductor plate for inducing image charge to enhance radiation efficiency.
2. Description of the Related Art
For emerging wireless transmission devices, dimensions of antennas have great effects on wireless transmission and must be in the order of the radio wavelength for transmission efficiency. However, in some bandwidths, radio wavelengths are much longer than the length of antenna that wireless transmission devices can afford, such that radiation efficiency is very low. In order to improve radiation efficiency, It is necessary to use complicated antennas and RF circuits. That will causein the wireless system in high cost, low yield, and high power consumption. Thus, the benefits of wireless transmission are lost. To improve radiation efficiency, it is necessary to make use of ground conductor plates within wireless devices and polarization of signal source of an antenna.
Most conventional loop antennas are magnetic dipoles. When the conventional loop antennas are using near a ground metallic plate, their radiation efficiencies will be reduced by the ground metallic plate.
A block diagram of a wireless mouse with a conventional magnetic dipole loop antenna is shown in FIG.
1
. RF module
220
includes an amplifier
520
, a phase lock loop circuit
450
, a filter
470
, and a voltage control oscillator
480
. The base band circuit includes a CPU
420
, a shift encoder
300
, a memory
440
such as non-volatile memory EEPROM, and a switch
550
. The first end of the loop antenna
240
is coupled to the signal end of the amplifier
520
. The second end of the loop antenna
240
is coupled to the ground end of the amplifier
520
.
When the wireless mouse operated, the CPU
420
reads out the channel frequencies, the sampling frequencies of the photo detector
310
, and the identification code from the memory
440
. The identification code identifies different wireless mice in the same transmission region and the same transmission frequency. For a same computer, each wireless mouse has a unique identification code. When the wireless mouse is powered up, the memory
440
records and updates the peripheral identification code of the computer.
The CPU
420
controls the channel frequencies by controlling the modulation frequency by the phase lock loop circuit
450
. The CPU reads the data of the transmission channel frequency from memory
440
, and sends the data to the phase lock loop circuit
450
to generate the carrier signal of the transmission channel. The user can use the channel select key
500
to select the transmission channel from the memory
440
.
The CPU
420
provides a determined information to modulator
560
to modulate the transmitted signal. The modulator
560
comprises a voltage control conciliator (VCXO) in series with a crystal to generate a reference frequency and uses this frequency to work as a FSK modulator. The modulator
560
, the phase lock loop circuit
450
, the filter
470
, and the voltage control oscillator form a feedback loop which generates a RF carrier signal with precise frequency. The RF carrier signal is fed into the circular loop antenna
241
through the amplifier
520
. The modulated reference frequency of the modulator
560
is generated by switching over resonance capacitors of the reference oscillator. The reference frequency is changed by the resonance capacitor that is FSK modulation. The signals of switching over is the encode data of the mouse operation. The filter must have enough bandwidth to track the modulation of the reference frequency.
When the wireless mouse used on a metallic table which acting as a ground conductor plate, that causes cancellation of the magnetic dipole source. The input impedance of the loop antenna
240
changes, that will shorten the transmission distance of the wireless mouse. A diagram of the loop antenna
240
and the ground conductor plate
230
is shown in FIG.
2
. The wireless mouse is used on the ground conductor plate
230
. The first end of the loop antenna is coupled to the signal end of the amplifier
520
, and the second end of the loop antenna
240
is coupled to the ground end of the RF module
220
. The loop antenna
240
is using upon the ground conductor plate
230
and parallels closely to the ground conductor plate
230
. The current of the loop antenna
240
is parallel to the ground conductor plate
230
. Owing to good conduct characteristic of the ground conductor plate
230
, the current of the loop antenna
240
induces an image current distribution in the ground conductor plate which makes the tangential electric field is zero. The image magnetic dipole source caused by the image current is opposite to the magnetic dipole source in the current of the loop antenna
240
, as shown in FIG.
3
. Therefore, the image magnetic dipole reduced the radiation intensity of the loop antenna
240
. Usually, the wireless mouse is used on the surface of a table. The distance between the wireless mouse and the table is small. Thus, as the desk-top of the table is made by conduct plate
230
, when the distance between the loop antenna
240
and the ground conductor plate
230
is smaller the effect of reduced radiation intensity is more significant.
It is necessary to design an antenna system not only reduced but also enhanced radiation intensity. It is also necessary to take advantage of a conductor plate when a wireless transmission device is using on it.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a loop antenna enhanced by an environment with a ground conductor plate.
To achieve the above objects, the present invention provides a loop antenna system. According to the embodiment of the invention, the loop antenna system includes a ground conductor plate coupled to a ground end and a loop antenna having a helix wire wounded on a toroid. The helix wire has a first end coupled to the ground end. The toroid has a principal axis AX
1
and a minor axis AX
2
. The principal AX
1
is perpendicular to the ground conductor plate. The minor AX
2
is parallel to the ground conductor plate.
When the radio wavelength of the transmission signal is beyond the dimensions of the loop antenna, the magnetic current is distributed along the minor axis AX
2
, and the electric dipole is along the principal axis AX
1
and perpendicular to the ground conductor plate.
REFERENCES:
patent: 2375593 (1945-05-01), Sontheimer et al.
patent: 3495264 (1970-02-01), Spears
patent: 5442369 (1995-08-01), Van Voorhies et al.
patent: 5633648 (1997-05-01), Fischer
patent: 6204821 (2001-03-01), Van Voorhies
patent: 6218998 (2001-04-01), Van Voorhies
patent: 6437751 (2002-08-01), Craven et al.
Darfon Electronics Corp.
Ladas & Parry LLP
Nguyen Hoang V.
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