Communication employing triply-polarized transmissions

Details Communication employing triply-polarized transmissions Communication employing triply-polarized transmissions

1999-08-23

2001-02-27

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Balanced doublet - centerfed

C342S361000

Reexamination Certificate

active

06195064

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to wireless communication. More particularly, this invention relates to use of polarized communication signals.
Prior art systems accept the long-recognized constraint imposed by Maxwell's equations that signals which are transmitted from point A to point B over a free space path that directly connects points A and B, and which differ only in their polarization modes, can comprise at most two independent channels. The reason for this constraint lies in the fact that the polarized transmission coefficients between points A and B form a matrix, T, of rank 2. The prior art, therefore, were always of the view that signals can be usefully transmitted from a point A to point B at most with two polarizations, and realizing thereby at most two independent channels of communication. This is demonstrated in the prior art system of
FIG. 1
, where a transmitter
10
has one dipole antenna
11
and another dipole antenna
12
and a receiver
20
has one dipole antenna
21
and another dipole antenna
22
. Typically, dipole antennas
11
and
12
perpendicular to each other, and so are dipole antennas
21
and
22
. The most efficient transfer of information from the transmitter to the receiver occurs when antennas
11
and
12
are in a plane that is perpendicular to the line connecting points A and B, antennas
21
and
22
are in a plane that is parallel to the plane of antennas
11
and
12
, and antenna dipole
11
is also in a plane that contains antenna
21
. Of course, any other spatial arrangement of antennas
11
,
12
,
21
and
22
may be used for communicating information from the transmitter to the receiver, except that the effectiveness of the communication is reduced (a greater portion of the transmitted signal energy cannot be recovered), and the processing burden on the receiver is increased (both antennas
21
and
22
detect a portion of the signal of antenna
11
and of antenna
12
).
Whether a transmitter has a single antenna (polarized or not) or two polarized antennas (as in FIG.
1
), it remains that multi-pathing presents a problem. Specifically, multiple paths can cause destructive interference in the received signal, and in indoor environments that presents a major problem because there are many reflective surfaces that cause multiple paths, and those reflective surfaces are nearby (which results in the multiple path signals having significant amplitudes).
SUMMARY OF THE INVENTION
The problems of fading in a multi-path environment are ameliorated, and the presence of reflective surfaces is turned from a disadvantage to an advantage by employing a receiver that accepts and utilizes signals that are polarized to contain energy in the three orthogonal directions of free space. Even more improved operation is obtained when the transmitter transmits information in three independent communication channels with signals that are polarized so that there is transmitted signal energy in the three orthogonal directions of free space, in a third independent communications channel, The third communication channel can be used to send more information, or to send information with enhanced polarization diversity to thereby improve the overall communication efficiency. A transmitted signal with the third polarization direction is created, illustratively, with a transmitter having a third antenna dipole that is orthogonal to the transmitter's first and second antenna dipoles. To take advantage of the signal with the third polarization direction, the receiver illustratively also comprises three mutually orthogonal antenna dipoles.


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