Communications: radio wave antennas – Antennas – With aircraft
Reexamination Certificate
1999-08-12
2001-11-27
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With aircraft
C343S706000
Reexamination Certificate
active
06323813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates generally to communication systems and methods. More particularly, this invention relates to communication systems and methods for communicating with a moving vessel.
2. Description of Related Art
Avionics (aviation electronics) systems perform many functions. For both military and civil aircraft, avionics are used for flight controls, guidance, navigation, communications and surveillance. An ever-increasing portion of avionics equipment is being dedicated to communications. Much of the increase comes in the form of digital communications equipment for either digitized voice or data transfer. Military aircraft typically use digital communications to improve security. Civil aircraft use digital communications to transfer data for improved efficiency of operations and radio frequency (RF) spectrum utilization. Regardless of the rationale for implementing digital communication technology, both the civil and military arenas are focusing more on enhanced communications to fulfill the requirements for better operational capability.
The requirements for digital communications for civil aircraft have grown so significantly that the industry, as a whole, has embarked on a virtually total upgrade of the communications systems elements. The goal is to achieve a high level of flexibility in processing various types of information as well as attain compatibility between a wide variety of communications devices. Bandwidth availability poses a special problem for aircraft designers due to weight and electromagnetic interference (EMI) considerations. Generally, a single unit, commonly identified as a communications management unit (CMU), will perform buffering and distribution of the information received by the aircraft. The CMU can receive information via RF transceivers operating in conjunction with terrestrial, airborne, or space-based transceivers. Additionally, it is often advantageous to have several antennas operating on the same vessel or building.
FIG. 1
is a schematic partial cross-sectional view of an aircraft incorporating an antenna system according to the prior art. In
FIG. 1
, a fuselage
100
of an aircraft
10
bears a right wing
110
and a left wing
120
, an upper antenna
140
and a lower antenna
130
. Antennas
130
and
140
are placed on opposite sides of the fuselage aircraft, in order to provide additional electrical isolation between them by virtue of the electrical shielding effect of the intervening metal. Antennas
130
and
140
are placed symmetrically about the circumference of the fuselage
100
; the top-mounted antenna
140
is the counterpart of antenna
130
which is mounted on the bottom of the fuselage
100
.
The fuselage
100
of the aircraft
10
contains a first transceiver
141
electrically coupled to the upper antenna
140
and a second transceiver
131
electrically coupled to the lower antenna
130
. The transceivers
141
and
131
and the antennas
140
and
130
are well known in the art. In this example, transceiver
141
and antenna
140
perform VHF data transmission and reception and transceiver
131
and antenna
130
perform VHF voice radio. However, any other types of transceivers and antennas may be used.
The upper antenna
140
is positioned at the top of the fuselage
100
, along the vertical axis (Y) of the fuselage
100
. The upper antenna
140
transmits a signal having a wavelength &lgr;.
The lower antenna
130
is positioned at the bottom of the fuselage
100
, on the opposite side of the fuselage
100
with respect to antenna
140
, along the vertical axis (Y) of the fuselage
100
. As a consequence, the distance between the antennas
140
and
130
along the right side of the fuselage is equal to the distance between the antennas along the left side of the fuselage.
The radio wave transmitted by the antenna
140
clockwise, along the fuselage
100
is shown with dashed lines
160
. The radio wave transmitted by the antenna
140
counterclockwise along the fuselage
100
is shown with dashed lines
150
. Arrow
170
represents the electric field received by antenna
130
from antenna
140
by radiowaves
150
and arrow
180
represents the electric field received by antenna
130
from antenna
140
by radiowaves
160
.
FIG. 2
is a schematic side view of an aircraft incorporating an antenna system according to the prior art. As shown in
FIG. 2
, the aircraft includes a fuselage
100
and wings
110
. In order to reduce the interference level between antennas
230
and
240
, the distance between those antennas is maximized. Thus, antenna
230
is located proximate to the nose of the aircraft and antenna
240
is located proximate to the tail of the aircraft.
SUMMARY OF THE INVENTION
When two or more radio transceivers are operated simultaneously, the transmissions of one radio transceiver can interfere with the reception of signals by another radio transceiver. The level of interference is dependent upon many factors, including the difference between the frequencies of the transmitted and received signals, receiver selectivity, and both physical and electrical separation of antennas. For example, as shown in
FIG. 1
, because the distances between antennas
130
and
140
along both sides of the fuselage
100
are equal or approximately so, the signals transmitted by antenna
140
along both sides of the fuselage
100
and received by antenna
130
are in phase. Therefore, a constructive interference occurs between the two radiowaves
150
and
160
, resulting in a high level of noise on antenna
130
produced by the signals emitted by antenna
140
. This is represented by arrows
170
and
180
extending along the same direction. Also, as shown in
FIG. 2
, because antennas
230
and
240
are both positioned on a symmetrical vertical plane, the constructive interference explained above still occurs.
Recent technological advances in air-ground communications have aggravated the need for improved radio frequency isolation between multiple very high frequency (VHF) transceivers on board a mobile vessel. The interference potential between a VHF data radio and a VHF voice radio is significantly greater than that between two voice radios. This increased potential is primarily due to the broader bandwidth of data emissions in comparison to those of voice transmitters.
To permit simultaneous operation of two voice transceivers on board the same vessel, hull manufacturers have attempted to provide as much physical separation between the antennas as practicable. They have also placed antennas on opposite sides of the vessel hull, to provide additional electrical isolation between the antennas by virtue of the electrical shielding effect of the intervening material.
FIG. 1
shows an example of a typical antenna placement on a commercial aircraft fuselage. Typically, antennas are placed symmetrically about the circumference of the fuselage or on opposite sides of the vertical stabilizer or other empennage. A top-mounted antenna for one transceiver usually has a counterpart antenna which is mounted on the bottom of the fuselage for the second transceiver.
FIG. 2
is a schematic side view of an aircraft incorporating an antenna system according to the prior art, where, as stated above, one antenna is located proximate to the nose of the aircraft and the other antenna is located proximate to the tail of the aircraft. However, both of the antenna mounting practices shown in
FIGS. 1 and 2
have had only limited success in permitting simultaneous operation of two VHF radios within the same aircraft.
Thus, this invention relates to methods and systems that provide improved radio frequency isolation between multiple antennas. For example, the antenna system may include a first transmitting antenna and a second antenna positioned away from each other on a hull by half the circumference of the hull, offset by an odd multiple of one quarter wavelength of a signal transmitted by the first antenna.
Alternatively, a first transmitting antenna and a second antenna may be p
Aeronautical Radio, Inc.
Clinger James
Oliff & Berridge PLC.
Wong Don
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