Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-09-19
2003-01-21
Nguyen, Hoang (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S745000
Reexamination Certificate
active
06509875
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to antennas.
More particularly, the present invention relates to integrated antennas used in portable communication systems.
BACKGROUND OF THE INVENTION
An antenna is an essential element in most communication systems. This is particularly true for portable communication systems, such as cell phones, pagers, and laptop computers, where the size, weight, cost, and efficiency of the systems are critical design parameters. Types of antennas include monopole and dipole antennas, but these tend to be too large and obtrusive for the desired high operating frequencies, and, consequently, there is a need for elegant non-obtrusive antennas for portable communications systems.
FIG. 1
illustrates a plan view of an antenna
5
typically used in the prior art. Antenna
5
includes a voltage source
10
and a dipole antenna
20
. Dipole antenna
20
has a length
25
, a current distribution
30
and a radiation field pattern
40
. For the antenna
5
, most of the current is distributed within the middle section of the antenna and the ends do not radiate as effectively as the middle section. The two most important design parameters of antenna
5
is the electrical length, L, and the thickness parameter, t. The electrical length of a dipole antenna is given by
L
=
λ
ol
λ
,
where l is the physical length of the antenna element, &lgr; is the resonant wavelength, and &lgr;o is the wavelength in free space. The thickness parameter of a dipole antenna is given by
t
=
a
l
,
where
2
a
is the diameter or width of the dipole antenna.
FIG. 2
illustrates a capacitively loaded antenna
43
. Since most of the current is closer to the center of antenna
5
, it is possible to decrease the length of antenna
5
by capacitivly loading it without significantly distorting the current distribution. Capacitively loaded antenna
43
includes a voltage source
10
and a dipole antenna
50
. Capacitively loaded dipole antenna
43
has a length
35
, a current distribution
33
, and a radiation field pattern
15
. Further, the capacitive loading is provided by capacitors
45
which are electrically connected to dipole antenna
50
. The result of the capacitive loading is to make length
35
less than length
25
while achieving the same resonance frequency. Also, current distribution
33
is more evenly distributed over the length of dipole antenna
50
. A problem with capacitively loaded dipole antenna
43
is that the m resonance frequency is determined by length
35
and the values of capacitors
45
. Once these parameters are set, the resonance frequency cannot be actively tuned.
A common type of antenna that is small and efficient for high frequency portable applications is the microstrip antenna. Microstrip antennas can be fabricated using inexpensive printed circuit board technology and can easily be integrated with other circuitry and electronic components. A patch antenna is a type of microstrip antenna that finds wide use in portable communication systems. However, most of the patch antennas in today's communication devices have very limited tuning capability and a relatively large physical size. Therefore, it is desirable to have a small electronically tunable antenna for use in portable communication systems.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved electronically active antenna apparatus.
It is an object of the present invention to provide a new and improved electronically active antenna apparatus which has a small size.
It is another object of the present invention to provide a new and improved electronically active antenna apparatus which has an improved radiation efficiency.
It is another object of the present invention to provide a new and improved electronically active antenna apparatus which can be tuned over a wide range of frequencies.
A further object of the invention is to provide a new and improved electronically active antenna apparatus which is inexpensive to manufacture.
SUMMARY OF THE INVENTION
To achieve the objects and advantages specified above and others, an electrically active antenna apparatus is disclosed which includes a substrate, a RF feed positioned on the substrate, a radiator element positioned on the substrate and adjacent to the RF feed such that the radiator element and the RF feed are electromagnetically coupled, and a plurality of active devices that make electrical contact with the radiator element.
The antenna is actively tuned by incorporating a varactor, a negative differential resistance device, a resonant tunneling device, or micro-electro-mechanical system (MEMS) component, or combinations of these devices in the plurality of active devices. The integration of a negative differential resistance device reduces the antenna resistance and improves the efficiency of radiation. The plurality of active devices changes the capacitive loading and, consequently, the resonant frequency of the active antenna. The capacitance and the resistance of an active device can be tuned by applying a DC bias. The MEMS devices allow loading of the antennas with low loss capacitors which minimizes the power loss and increases the efficiency of the antenna. The magnitude of operational DC voltage applied to the MEMS in general is larger than the magnitude of the RF signal that is fed to the antenna. Therefore the capacitance of the MEMS devices will not be modulated by the RF signal and hence the harmonic signal generation will be minimized. Further, the placement of the active devices in relation to the antenna affects the resonant frequency and tuning characteristics. Thus, the physical size of the active antenna can be decreased and the resonant frequency can be tuned without significantly decreasing the effective resonant length.
REFERENCES:
patent: 4780724 (1988-10-01), Sharma et al.
patent: 5394159 (1995-02-01), Schneider et al.
patent: 5511238 (1996-04-01), Bayraktaroglu
patent: 6049308 (2000-04-01), Hietala et al.
patent: 6061025 (2000-05-01), Jackson et al.
patent: 6069587 (2000-05-01), Lynch et al.
patent: 6198438 (2001-03-01), Herd et al.
El-Ghazaly Samir
Nair Vijay K.
Gilmore Douglas W.
Koch William E.
Nguyen Hoang
LandOfFree
Electronically tuned active antenna apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electronically tuned active antenna apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electronically tuned active antenna apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3026341