Title of Invention	AN ANTENNA SYSTEM AND METHOD FOR MEASURING AZIMUTH AND ELEVATION ANGLES OF AN ACTIVE SIGNAL SENDING RADIOSONDE .
Abstract	The present invention relates to an antenna system and method. The antenna system for measuring azimuth and elevation angles of an active, signal sending radiosonde (31), comprises a first passive antenna group (13) comprising at least two antenna arrays (11a, 11b), the direction pattern of which is wide at least in elevation plane for measuring azimuth angle of the radiosonde (31) based on the phase differences between the antenna arrays (11a, 11b), a second passive antenna group (12) comprising at least two antenna arrays (10a, 10b), the direction pattern of which is wide at least in elevation plane for measuring the elevation angle of the radiosonde (31) based on the phase differences between the antenna arrays (10a, 10b) and the rotational position of the antenna field (1), and at least one third antenna (8) having high gain for receiving the telemetry signal, the direction pattern of which element (8) is narrow in azimuth plane and wide in elevation plane. According to the invention first (13) and second (12) antenna groups form a solid antenna field (1), and antenna field (1) is fixedly tilted in a predetermined elevation position.

Title of Invention

AN ANTENNA SYSTEM AND METHOD FOR MEASURING AZIMUTH AND ELEVATION ANGLES OF AN ACTIVE SIGNAL SENDING RADIOSONDE .

Abstract

The present invention relates to an antenna system and method. The antenna system for measuring azimuth and elevation angles of an active, signal sending radiosonde (31), comprises a first passive antenna group (13) comprising at least two antenna arrays (11a, 11b), the direction pattern of which is wide at least in elevation plane for measuring azimuth angle of the radiosonde (31) based on the phase differences between the antenna arrays (11a, 11b), a second passive antenna group (12) comprising at least two antenna arrays (10a, 10b), the direction pattern of which is wide at least in elevation plane for measuring the elevation angle of the radiosonde (31) based on the phase differences between the antenna arrays (10a, 10b) and the rotational position of the antenna field (1), and at least one third antenna (8) having high gain for receiving the telemetry signal, the direction pattern of which element (8) is narrow in azimuth plane and wide in elevation plane. According to the invention first (13) and second (12) antenna groups form a solid antenna field (1), and antenna field (1) is fixedly tilted in a predetermined elevation position.

Full Text	AN ANTENNA SYSTEM AND METHOD FOR MEASURING AZIMUTH AND ELEVATION ANGLES OF AN ACTIVE, SIGNAL SENDING RADIOSONDE The present invention relates to an antenna system for measuring the azimuth and elevation angles of an active, signal sending radiosonde, as described hereinafter. The invention relates also to a method for measuring the azimuth and elevation of an active, signal sending radiosonde. The present invention is related to atmospheric sounding systems, in which the properties of the atmosphere are measured in-situ by independent, self powered active components typically called radiosondes including a radio transmitter. Typical features for this technique are inactive (non-sending) receiving antennas and the fact that the measuring device (radiosonde) is either lifted or dropped through the space to be measured. Parameters measured in-situ by sensors of the radiosonde, such as air pressure, temperature and relative humidity, are transmitted through a telemetry link to a receiving station. Other parameters of interest are wind speed and wind direction that can be measured by using navigation aid networks such as GPS or Loran-C, by a primary or secondary radar, or by a passive (non-sending) and independent (no navigation aid networks used) radiotheodolite. Height of the radiosonde can be calculated from the air pressure, temperature and humidity data. The object of the invention is to determine the azimuth and elevation angles of an active radiosonde in a three dimensional space with a passive (non-sending) antenna structure independent of navigation aid networks. A typical application of the invention is to locate a radiosonde launched into the atmosphere with the help of a balloon filled with hydrogen or helium. Radiosonde azimuth and elevation angles are determined from the received radiosonde signal. Wind speed and direction can be calculated from consecutive azimuth and elevation angles and height of the radiosonde. Prior solutions in the 1680 MHz meteorological frequency band track the radiosonde mechanically both in the azimuth and elevation directions. The disadvantage of this solution is the complicated and expensive mechanical receiving antenna structure. Another disadvantage of the prior solutions is the disability to attenuate ground reflections enough when the radiosonde signal is received from a low elevation angle. It is an object of the present invention to overcome the problems of the prior solutions and to provide an entirely novel type of antenna structure and a method for determining the azimuth and elevation angles of a radiosonde. The goal of the invention is achieved by a fixedly backwards tilted antenna field, in which the antenna elements are assembled on an antenna frame. In one typical embodiment the antenna field is rotated around vertical axis approximately to the direction of the radiosonde while the elevation angle remains essentially constant. In another embodiment of the invention there are at least three such fixedly tilted antenna fields that point to different fixed azimuth directions. This solution has no moving parts. Accordingly, the present invention provides an antenna system for measuring azimuth and elevation angles of an active, signal sending radiosonde, which antenna system comprises a first passive antenna group comprising at least two antenna arrays, the direction pattern of which is wide at least in elevation plane for measuring azimuth angle of the radiosonde based on the phase differences between the antenna arrays and the rotational position of the antenna field, a second passive antenna group comprising at least two antenna arrays, the direction pattern of which is wide at least in elevation plane for measuring the elevation angle of the radiosonde based on the phase differences between the antenna arrays, and at least one third antenna element having high gain for receiving the telemetry signal, the direction pattern of which element is narrow in azimuth plane and wide in elevation plane, characterized in that first and second antenna groups form a solid antenna field, and antenna field is fixedly tilted in a predetermined elevation position. The presecnt invention also provides a method for measuring azimuth and elevation angles of an active, signal sending radiosonde, in which method the azimuth angle of the radiosonde is measured based on the phase differences of the received radiosonde signals between the antenna arrays and the rotational position of the antenna field with a first passive antenna group comprising at least two antenna array, the direction pattern of which is wide at least in elevation plane, the elevation angle of the radiosonde is measured based on the phase differences of the received radiosonde signals between the antenna arrays with a second passive antenna group comprising at least two antenna array, the direction pattern of which is wide at least in elevation plane, and the telemetry signal is received with at least one third antenna element having high gain, the direction pattern of which element is narrow in azimuth plane and wide in elevation plane, characterized in that first and second antenna groups form a solid antenna field, and antenna field is fixedly tilted in a predetermined elevation position. The invention offers significant benefits. By attenuating the ground reflection the azimuth and elevation angles of the radiosonde can be measured more precisely especially when the radiosonde is in a low elevation angle. The mechanics of the antenna structure can be simplified and manufactured at a lower cost. Furthermore the reliability of the system is increased as there are less moving parts. In the following, the invention will be examined in greater detail with the help of exemplary embodiments by making reference to the accompanying drawings in which: Figure la shows in a perspective view a rotatable antenna structure in accordance with the invention. Figure lb shows a simplified version of the embodiment of figure la. Figure 2 shows in a perspective view a stationary antenna structure in accordance with the second embodiment of the invention. Figure 3 shows schematically a balloon borne radiosonde, direct signal, ground reflection, rotatable antenna structure and a typical radiation pattern witfi a gain pattern minimum (null) in the direction of the ground reflection. Figure 4 shows a polar-plot of a typical radiation pattern for a two-element antenna array with a gain pattern minimum (null) in the direction of the ground reflection. Figure 5 shows schematically as a side view the phasing of a two-element antenna array. In accordance with figure 1 the essentially planar antenna field 1 comprises a vertical antenna group 12 and a horizontal antenna group 13. The vertical antenna group 12 comprises at least two antenna arrays 10a and 10b positioned above each other. In this solution each array comprises three antenna elements 9. The direction pattern of these arrays 10a and 10b is wide in elevation plane. The vertical antenna group 10a and 10b is used for determining the elevation angle of the radiosonde based on the phase differences of the received radiosonde signal between the antenna arrays 10a, 10b. Respectively horizontal antenna group 13 comprises two horizontal antenna arrays 11a and lib positioned at least essentially symmetrically around the vertical center line of the antenna field 1. In this solution each array comprises two or more antenna elements 9. The direction pattern of these arrays 11a and 1 lb is also wide in elevation plane. The azimuth angle of the radiosonde is determined with arrays 11a and 1 lb based on the phase differences between the antenna arrays 11a, lib and the rotational position of the antenna field 1. One preferable embodiment 1 of the invention includes only one rotatable support frame divided in upper 6 and lower parts 14. The antenna field 1 with its frame 2 is mounted on a stationary tripod 3 having circular support plates 4 at the end of its legs 5. An independent antenna 8 is for radiosonde telemetry. The antenna frame is rotatable around the vertical axis 7 for directing the antenna field 1 approximately to the direction of the radiosonde. The azimuth angle is measured with the horizontal antenna group 13 on the lower part 14 of the frame and elevation angle with help of the vertical antenna group 12 positioned on the upper and lower parts 6 and 14 of the frame. A simplified version of the antenna groups required for the angle measurement is presented is the figure lb. The tilting angle a is typically 30°. The term "fixed tilting" or "fixed tilting angle" in this context means also solutions, where a small vibrational deviation of the tilting angle is allowed for example due to the wind. Due to the antenna group 13 for azimuth measurement, the antenna field 1 forms an inverted T- or L-shape. With this solution a low center of gravity and wind load can be achieved. Obviously, the azimuth antenna group 13 can be positioned also in the upper part 6 or center of the antenna field 1 within the scope of the inventive idea, whereby a T-, inverted L- or plus (+) shape is formed. The invention does not limit the azimuth and elevation antenna groups to be perpendicular to each other or the ground, thereby allowing, for instance, also an X-shape antenna field. Radiosonde telemetry reception is independent of azimuth and elevation measurements. The telemetry signal is received by a separate high gain directional antenna 8. The direction pattern of the antenna 8 is typically narrow in azimuth plane and wide in elevation plane. Figure lb represents a simplified version of the antenna structure of figure la. In this version each antenna array is replaced by single antenna elements 9. Figure 2 represents another embodiment of the invention in a form of a fixed pyramid shaped antenna with four tilted antenna fields 14. The azimuth angle is measured with horizontal antenna group 20 comprising two antenna arrays 18a and 18b at the bottom of the pyramid. Arrays include two or more antenna elements 16. Elevation angle is measured with vertical antenna group 19 comprising two vertically positioned antenna arrays 17a and 17b in the upper and lower parts of the pyramid. The telemetry signal is received by a separate directional antenna 15 positioned on the top of the pyramid. In both of the before described solutions the azimuth angle is determined from the measured phase difference of at least two antenna elements or arrays in the horizontal direction (horizontal groups 13 or 20) and the direction of the antenna field 14. The elevation angle is determined from the measured phase difference of at least two antenna elements or arrays essentially in the vertical direction (vertical groups 12 or 19). In accordance with figure 3 the purpose of the antenna system 34 is to obtain a direct radio signal 32 from the radiosonde 31. When the radiosonde 31 is in a low elevation angle, ground reflection 30 coming from the (negative) mirror angle has been a major factor degrading the performance of prior solutions. The present invention decreases this problem by aligning a gain pattern minimum 35 (null) of the radiation pattern 33 to the direction of the ground reflection 30. The direction is typically determined experimentally for different elevation angles by aligning the main beam by phased array techniques such that the ground reflection is minimized. In accordance with figure 4 the gain pattern minimum (null) is formed by an antenna array (10a, 10b, 11a, 1lb, or 17a, 17b, 18a, 18b) which consists of at least two antenna elements (9 or 16). Gain pattern minimum (null) 30 is directed by modifying the signal phase and amplitude of each antenna element in the array (beamforming). According to figure 5 the sum of the modified signals represents the antenna array that can now be regarded as a single antenna element with a more suitable radiation pattern. A gain pattern minimum (null) is formed separately for each of the antenna arrays in the horizontal and vertical groups (12, 13 or 19, 20). Phase shift is designed experimentally for different elevation angles (radiation patterns). Antenna beam forming is explained in more detail e.g., in reference Robert J Mailloux, Phased Array Antenna Handbook, Chapters 2 and 3, 1994 Artech House, Inc, ISBN 0-89006-502-0. In accordance with figure 6 the angle of arrival can be measured with two identical antennas Al and A2 using interferometric principle explained in more detail e.g., in reference Englar, Mango, Roettcher, Watters, FINAL REPORT FOR THE MININTRACK TRACKING FUNCTION DESCRIPTION, Volume 1, March 1973, NASA-TMX-66213. If the base length (b) is less or equal than half of the wavelength (A/2) the unambiguous angle of arrival (-90 ° can be measured. When the phase difference (0) between antenna Al'&and A2 has been measured (-180 ° calculated as: Instead of the planar antenna field 1 or 14 shown in figures la, lb and 2 the antenna field may be also convex, concave or for example stepped. In the rotatable embodiments of figures la and lb all the antennas, antenna arrays and antenna elements are positioned on this uniform rigid antenna field 1 regardless of the shape of the antenna field. In the embodiment of figure 2 the telemetry antenna 15 is not included to this antenna field 14. In this application with wide beam is meant beam widths greater than 120°. Respectively narrow beam means beam widths smaller than 30°. WE CLAIM: 1. An antenna system for measuring azimuth and elevation angles of an active, signal sending radiosonde (31), which antenna system comprises a first passive antenna group (13) comprising at least two antenna arrays (1 la, 1 lb), the direction pattern of which is wide at least in elevation plane for measuring azimuth angle of the radiosonde (31) based on the phase differences between the antenna arrays (11a, l1b) and the rotational position of the antenna field (1), a second passive antenna group (12) comprising at least two antenna arrays (10a, 10b), the direction pattern of which is wide • at least in elevation plane for measuring the elevation angle of the radiosonde (31) based on the phase differences between the antenna arrays (10a, 10b), and - at least one third antenna element (8) having high gain for receiving the telemetry signal, the direction pattern of which element (8) is narrow in azimuth plane and wide in elevation plane, characterized in that - first (13) and second (12) antenna groups form a solid antenna field (1), and - antenna field (1) is fixedly tilted in a predetermined elevation position. 2. The antenna system as claimed in claim 1, wherein the third antenna (8) belongs to the antenna field (1). 3. The antenna system as claimed in claim 1 or 2, wherein the antenna field is essentially planar. 4. The antenna system as claimed in any of the previous claims or their combination, wherein the gain pattern minimum (35) (null) of each antenna array (10a, 10b, 1 la, 1 lb) is aligned to the direction of the ground reflection (30). 5. The antenna system as claimed in any previous claim or rheir combination, wherein the antenna system comprises means for rotating the antenna field (1) around vertical axis (7) approximately to the direction of the radiosonde (31) while the elevation angle remains essentially constant. 6. The antenna system as claimed in any previous claim or their combination, wherein radiosonde (31) telemetry reception is independent of azimuth and elevation measurements. 7. The antenna system as claimed in any previous claim or their combination, wherein the antenna field (14) is fixed in elevation and azimuth direction, and that the system comprises at least three antenna fields (14) pointing to different azimuth directions. 8. The antenna system as claimed in claim 7, wherein the gain pattern minimum (null) of each antenna array (17a, 17b, 18a, 18b) is aligned to the direction of the ground reflection. 9. The antenna system as claimed in claim 7 or 8, wherein radiosonde telemetry reception (15) is independent of azimuth and elevation measurements. 10. The antenna system as claimed in any previous claim or their combination, wherein the antenna field (1) is fixedly tilted backwards. 11. The antenna system as claimed in any previous claim or their combination, wherein the antenna field (1) forms an inverted letter T. 12. A method for measuring azimuth and elevation angles of an active, signal sending radiosonde (31), in which method - the azimuth angle of the radiosonde (31) is measured based on the phase differences of the received radiosonde signals between the antenna arrays (1 la, 1 lb) and the rotational position of the antenna field (1) with a first passive antenna group (13) comprising at least two antenna arrays (11a, l1b), the direction pattern of which is wide at least in elevation plane, - the elevation angle of the radiosonde (31) is measured based on the phase differences of the received radiosonde signals between the antenna arrays (10a, 10b) with a second passive antenna group (12) comprising at least two antenna arrays (10a, 10b), the direction pattern of which is wide at least in elevation plane, and - the telemetry signal is received with at least one third antenna element (8) having high gain, the direction pattern of which element (8) is narrow in azimuth plane and wide in elevation plane, characterized in that - first (13) and second (12) antenna groups form a solid antenna field (1), and - antenna field (1) is fixedly tilted in a predetermined elevation position. 13. The method as claimed in 12, wherein the third antenna (8) belongs to the antenna field (1). 14. The method as claimed in any previous method claim or their combination, wherein the gain pattern minimum (null) of each antenna array (17a, 17b, 18a, 18b) is aligned to the direction of the ground reflection. 15. The method as claimed in any previous method claim or their eombination, wherein radiosonde telemetry reception is independent of azimuth and elevation measurements. 16. The method as claimed in any previous method claim or their combination, wherein the antenna system is rotated around vertical axis (7) approximately to the direction of the radiosonde (31) while the elevation angle remains essentially constant. 17. The method as claimed in any previous method claim or their combination, wherein the antenna field (1) is fixedly tilted backwards. 18. The method as claimed in any previous method claim or their combination, wherein the antenna field (14) is fixed in elevation and azimuth direction, and that the system comprises at least three antenna fields (14) pointing to different azimuth directions. 19. The method as claimed in claim 18, wherein the gain pattern minimum (null) of each antenna array (17a, 17b, 18a, 18b) is aligned to the direction of the ground reflection. 20. The method as claimed in claim 18 or 19, wherein radiosonde telemetry reception (15) is independent of azimuth and elevation measurements. The present invention relates to an antenna system and method. The antenna system for measuring azimuth and elevation angles of an active, signal sending radiosonde (31), comprises a first passive antenna group (13) comprising at least two antenna arrays (11a, 11b), the direction pattern of which is wide at least in elevation plane for measuring azimuth angle of the radiosonde (31) based on the phase differences between the antenna arrays (11a, 11b), a second passive antenna group (12) comprising at least two antenna arrays (10a, 10b), the direction pattern of which is wide at least in elevation plane for measuring the elevation angle of the radiosonde (31) based on the phase differences between the antenna arrays (10a, 10b) and the rotational position of the antenna field (1), and at least one third antenna (8) having high gain for receiving the telemetry signal, the direction pattern of which element (8) is narrow in azimuth plane and wide in elevation plane. According to the invention first (13) and second (12) antenna groups form a solid antenna field (1), and antenna field (1) is fixedly tilted in a predetermined elevation position.

Full Text

AN ANTENNA SYSTEM AND METHOD FOR MEASURING
AZIMUTH AND ELEVATION ANGLES OF AN ACTIVE,
SIGNAL SENDING RADIOSONDE
The present invention relates to an antenna system for measuring the azimuth and
elevation angles of an active, signal sending radiosonde, as described hereinafter.
The invention relates also to a method for measuring the azimuth and elevation of
an active, signal sending radiosonde.
The present invention is related to atmospheric sounding systems, in which the
properties of the atmosphere are measured in-situ by independent, self powered
active components typically called radiosondes including a radio transmitter.
Typical features for this technique are inactive (non-sending) receiving antennas
and the fact that the measuring device (radiosonde) is either lifted or dropped
through the space to be measured.
Parameters measured in-situ by sensors of the radiosonde, such as air pressure,
temperature and relative humidity, are transmitted through a telemetry link to a
receiving station. Other parameters of interest are wind speed and wind direction
that can be measured by using navigation aid networks such as GPS or Loran-C,
by a primary or secondary radar, or by a passive (non-sending) and independent
(no navigation aid networks used) radiotheodolite. Height of the radiosonde can
be calculated from the air pressure, temperature and humidity data.
The object of the invention is to determine the azimuth and elevation angles of an
active radiosonde in a three dimensional space with a passive (non-sending)
antenna structure independent of navigation aid networks. A typical application of
the invention is to locate a radiosonde launched into the atmosphere with the help
of a balloon filled with hydrogen or helium. Radiosonde azimuth and elevation
angles are determined from the received radiosonde signal.

Wind speed and direction can be calculated from consecutive azimuth and
elevation angles and height of the radiosonde.
Prior solutions in the 1680 MHz meteorological frequency band track the
radiosonde mechanically both in the azimuth and elevation directions. The
disadvantage of this solution is the complicated and expensive mechanical
receiving antenna structure.
Another disadvantage of the prior solutions is the disability to attenuate ground
reflections enough when the radiosonde signal is received from a low elevation
angle.
It is an object of the present invention to overcome the problems of the prior
solutions and to provide an entirely novel type of antenna structure and a method
for determining the azimuth and elevation angles of a radiosonde.
The goal of the invention is achieved by a fixedly backwards tilted antenna field,
in which the antenna elements are assembled on an antenna frame. In one typical
embodiment the antenna field is rotated around vertical axis approximately to the
direction of the radiosonde while the elevation angle remains essentially constant.
In another embodiment of the invention there are at least three such fixedly tilted
antenna fields that point to different fixed azimuth directions. This solution has no
moving parts.
Accordingly, the present invention provides an antenna system for measuring
azimuth and elevation angles of an active, signal sending radiosonde, which
antenna system comprises
a first passive antenna group comprising at least two antenna arrays, the direction
pattern of which is wide at least in elevation plane for measuring azimuth angle of
the radiosonde based on the phase differences between the antenna arrays and the
rotational position of the antenna field, a second passive antenna group
comprising at least two antenna arrays, the direction pattern of which is wide at

least in elevation plane for measuring the elevation angle of the radiosonde based
on the phase differences between the antenna arrays, and at least one third antenna
element having high gain for receiving the telemetry signal, the direction pattern
of which element is narrow in azimuth plane and wide in elevation plane,
characterized in that first and second antenna groups form a solid antenna field,
and antenna field is fixedly tilted in a predetermined elevation position.
The presecnt invention also provides a method for measuring azimuth and
elevation angles of an active, signal sending radiosonde, in which method the
azimuth angle of the radiosonde is measured based on the phase differences of the
received radiosonde signals between the antenna arrays and the rotational position
of the antenna field with a first passive antenna group comprising at least two
antenna array, the direction pattern of which is wide at least in elevation plane, the
elevation angle of the radiosonde is measured based on the phase differences of
the received radiosonde signals between the antenna arrays with a second passive
antenna group comprising at least two antenna array, the direction pattern of
which is wide at least in elevation plane, and the telemetry signal is received with
at least one third antenna element having high gain, the direction pattern of which
element is narrow in azimuth plane and wide in elevation plane, characterized in
that first and second antenna groups form a solid antenna field, and antenna field
is fixedly tilted in a predetermined elevation position.
The invention offers significant benefits.
By attenuating the ground reflection the azimuth and elevation angles of the
radiosonde can be measured more precisely especially when the radiosonde is in a
low elevation angle.
The mechanics of the antenna structure can be simplified and manufactured at a
lower cost. Furthermore the reliability of the system is increased as there are less
moving parts.

In the following, the invention will be examined in greater detail with the help of
exemplary embodiments by making reference to the accompanying drawings in
which:
Figure la shows in a perspective view a rotatable antenna structure in accordance
with the invention.
Figure lb shows a simplified version of the embodiment of figure la.
Figure 2 shows in a perspective view a stationary antenna structure in accordance
with the second embodiment of the invention.
Figure 3 shows schematically a balloon borne radiosonde, direct signal, ground
reflection, rotatable antenna structure and a typical radiation pattern witfi a gain
pattern minimum (null) in the direction of the ground reflection.
Figure 4 shows a polar-plot of a typical radiation pattern for a two-element
antenna array with a gain pattern minimum (null) in the direction of the ground
reflection.
Figure 5 shows schematically as a side view the phasing of a two-element antenna
array.
In accordance with figure 1 the essentially planar antenna field 1 comprises a
vertical antenna group 12 and a horizontal antenna group 13. The vertical antenna
group 12 comprises at least two antenna arrays 10a and 10b positioned above each
other. In this solution each array comprises three antenna elements 9. The
direction pattern of these arrays 10a and 10b is wide in elevation plane.
The vertical antenna group 10a and 10b is used for determining the elevation
angle of the radiosonde based on the phase differences of the received radiosonde
signal between the antenna arrays 10a, 10b.

Respectively horizontal antenna group 13 comprises two horizontal antenna arrays
11a and lib positioned at least essentially symmetrically around the vertical
center line of the antenna field 1. In this solution each array comprises two or
more antenna elements 9. The direction pattern of these arrays 11a and 1 lb is also
wide in elevation plane.
The azimuth angle of the radiosonde is determined with arrays 11a and 1 lb based
on the phase differences between the antenna arrays 11a, lib and the rotational
position of the antenna field 1.
One preferable embodiment 1 of the invention includes only one rotatable support
frame divided in upper 6 and lower parts 14. The antenna field 1 with its frame 2
is mounted on a stationary tripod 3 having circular support plates 4 at the end of
its legs 5. An independent antenna 8 is for radiosonde telemetry. The antenna
frame is rotatable around the vertical axis 7 for directing the antenna field 1
approximately to the direction of the radiosonde. The azimuth angle is measured
with the horizontal antenna group 13 on the lower part 14 of the frame and
elevation angle with help of the vertical antenna group 12 positioned on the upper
and lower parts 6 and 14 of the frame. A simplified version of the antenna groups
required for the angle measurement is presented is the figure lb. The tilting angle
a is typically 30°. The term "fixed tilting" or "fixed tilting angle" in this context
means also solutions, where a small vibrational deviation of the tilting angle is
allowed for example due to the wind.
Due to the antenna group 13 for azimuth measurement, the antenna field 1 forms
an inverted T- or L-shape. With this solution a low center of gravity and wind load
can be achieved. Obviously, the azimuth antenna group 13 can be positioned also
in the upper part 6 or center of the antenna field 1 within the scope of the
inventive idea, whereby a T-, inverted L- or plus (+) shape is formed. The
invention does not limit the azimuth and elevation antenna groups to be
perpendicular to each other or the ground, thereby allowing, for instance, also an
X-shape antenna field.

Radiosonde telemetry reception is independent of azimuth and elevation
measurements. The telemetry signal is received by a separate high gain directional
antenna 8. The direction pattern of the antenna 8 is typically narrow in azimuth
plane and wide in elevation plane.
Figure lb represents a simplified version of the antenna structure of figure la. In
this version each antenna array is replaced by single antenna elements 9.
Figure 2 represents another embodiment of the invention in a form of a fixed
pyramid shaped antenna with four tilted antenna fields 14. The azimuth angle is
measured with horizontal antenna group 20 comprising two antenna arrays 18a
and 18b at the bottom of the pyramid. Arrays include two or more antenna
elements 16. Elevation angle is measured with vertical antenna group 19
comprising two vertically positioned antenna arrays 17a and 17b in the upper and
lower parts of the pyramid. The telemetry signal is received by a separate
directional antenna 15 positioned on the top of the pyramid.
In both of the before described solutions the azimuth angle is determined from the
measured phase difference of at least two antenna elements or arrays in the
horizontal direction (horizontal groups 13 or 20) and the direction of the antenna
field 14.
The elevation angle is determined from the measured phase difference of at least
two antenna elements or arrays essentially in the vertical direction (vertical groups
12 or 19).
In accordance with figure 3 the purpose of the antenna system 34 is to obtain a
direct radio signal 32 from the radiosonde 31. When the radiosonde 31 is in a low
elevation angle, ground reflection 30 coming from the (negative) mirror angle has
been a major factor degrading the performance of prior solutions. The present
invention decreases this problem by aligning a gain pattern minimum 35 (null) of
the radiation pattern 33 to the direction of the ground reflection 30. The direction
is typically determined experimentally for different elevation angles by aligning

the main beam by phased array techniques such that the ground reflection is
minimized.
In accordance with figure 4 the gain pattern minimum (null) is formed by an
antenna array (10a, 10b, 11a, 1lb, or 17a, 17b, 18a, 18b) which consists of at least
two antenna elements (9 or 16). Gain pattern minimum (null) 30 is directed by
modifying the signal phase and amplitude of each antenna element in the array
(beamforming).
According to figure 5 the sum of the modified signals represents the antenna array
that can now be regarded as a single antenna element with a more suitable
radiation pattern. A gain pattern minimum (null) is formed separately for each of
the antenna arrays in the horizontal and vertical groups (12, 13 or 19, 20).

Phase shift is designed experimentally for different elevation angles (radiation
patterns). Antenna beam forming is explained in more detail e.g., in reference
Robert J Mailloux, Phased Array Antenna Handbook, Chapters 2 and 3, 1994
Artech House, Inc, ISBN 0-89006-502-0.
In accordance with figure 6 the angle of arrival can be measured with two
identical antennas Al and A2 using interferometric principle explained in more
detail e.g., in reference Englar, Mango, Roettcher, Watters, FINAL REPORT
FOR THE MININTRACK TRACKING FUNCTION DESCRIPTION, Volume
1, March 1973, NASA-TMX-66213. If the base length (b) is less or equal than
half of the wavelength (A/2) the unambiguous angle of arrival (-90 ° can be measured. When the phase difference (0) between antenna Al'&and A2 has
been measured (-180 ° calculated as:

Instead of the planar antenna field 1 or 14 shown in figures la, lb and 2 the
antenna field may be also convex, concave or for example stepped. In the
rotatable embodiments of figures la and lb all the antennas, antenna arrays and
antenna elements are positioned on this uniform rigid antenna field 1 regardless of
the shape of the antenna field. In the embodiment of figure 2 the telemetry
antenna 15 is not included to this antenna field 14.
In this application with wide beam is meant beam widths greater than 120°.
Respectively narrow beam means beam widths smaller than 30°.

WE CLAIM:
1. An antenna system for measuring azimuth and elevation angles of
an active, signal sending radiosonde (31), which antenna system comprises
a first passive antenna group (13) comprising at least two
antenna arrays (1 la, 1 lb), the direction pattern of which is wide
at least in elevation plane for measuring azimuth angle of the
radiosonde (31) based on the phase differences between the
antenna arrays (11a, l1b) and the rotational position of the
antenna field (1),
a second passive antenna group (12) comprising at least two
antenna arrays (10a, 10b), the direction pattern of which is wide
• at least in elevation plane for measuring the elevation angle of
the radiosonde (31) based on the phase differences between the
antenna arrays (10a, 10b), and
- at least one third antenna element (8) having high gain for
receiving the telemetry signal, the direction pattern of which
element (8) is narrow in azimuth plane and wide in elevation
plane,
characterized in that
- first (13) and second (12) antenna groups form a solid antenna
field (1), and
- antenna field (1) is fixedly tilted in a predetermined elevation
position.

2. The antenna system as claimed in claim 1, wherein the third antenna
(8) belongs to the antenna field (1).
3. The antenna system as claimed in claim 1 or 2, wherein the antenna
field is essentially planar.

4. The antenna system as claimed in any of the previous claims or their
combination, wherein the gain pattern minimum (35) (null) of each antenna array
(10a, 10b, 1 la, 1 lb) is aligned to the direction of the ground reflection (30).
5. The antenna system as claimed in any previous claim or rheir
combination, wherein the antenna system comprises means for rotating the
antenna field (1) around vertical axis (7) approximately to the direction of the
radiosonde (31) while the elevation angle remains essentially constant.
6. The antenna system as claimed in any previous claim or their
combination, wherein radiosonde (31) telemetry reception is independent of
azimuth and elevation measurements.
7. The antenna system as claimed in any previous claim or their
combination, wherein the antenna field (14) is fixed in elevation and azimuth
direction, and that the system comprises at least three antenna fields (14) pointing
to different azimuth directions.
8. The antenna system as claimed in claim 7, wherein the gain pattern
minimum (null) of each antenna array (17a, 17b, 18a, 18b) is aligned to the
direction of the ground reflection.
9. The antenna system as claimed in claim 7 or 8, wherein radiosonde
telemetry reception (15) is independent of azimuth and elevation measurements.
10. The antenna system as claimed in any previous claim or their
combination, wherein the antenna field (1) is fixedly tilted backwards.
11. The antenna system as claimed in any previous claim or their
combination, wherein the antenna field (1) forms an inverted letter T.
12. A method for measuring azimuth and elevation angles of an active,
signal sending radiosonde (31), in which method

- the azimuth angle of the radiosonde (31) is measured based on the
phase differences of the received radiosonde signals between the
antenna arrays (1 la, 1 lb) and the rotational position of the antenna
field (1) with a first passive antenna group (13) comprising at least
two antenna arrays (11a, l1b), the direction pattern of which is
wide at least in elevation plane,
- the elevation angle of the radiosonde (31) is measured based on the
phase differences of the received radiosonde signals between the
antenna arrays (10a, 10b) with a second passive antenna group (12)
comprising at least two antenna arrays (10a, 10b), the direction
pattern of which is wide at least in elevation plane, and
- the telemetry signal is received with at least one third antenna
element (8) having high gain, the direction pattern of which element
(8) is narrow in azimuth plane and wide in elevation plane,
characterized in that
- first (13) and second (12) antenna groups form a solid antenna
field (1), and
- antenna field (1) is fixedly tilted in a predetermined elevation
position.

13. The method as claimed in 12, wherein the third antenna (8) belongs
to the antenna field (1).
14. The method as claimed in any previous method claim or their
combination, wherein the gain pattern minimum (null) of each antenna array (17a,
17b, 18a, 18b) is aligned to the direction of the ground reflection.
15. The method as claimed in any previous method claim or their
eombination, wherein radiosonde telemetry reception is independent of azimuth
and elevation measurements.
16. The method as claimed in any previous method claim or their
combination, wherein the antenna system is rotated around vertical axis (7)

approximately to the direction of the radiosonde (31) while the elevation angle
remains essentially constant.
17. The method as claimed in any previous method claim or their
combination, wherein the antenna field (1) is fixedly tilted backwards.
18. The method as claimed in any previous method claim or their
combination, wherein the antenna field (14) is fixed in elevation and azimuth
direction, and that the system comprises at least three antenna fields (14) pointing
to different azimuth directions.
19. The method as claimed in claim 18, wherein the gain pattern
minimum (null) of each antenna array (17a, 17b, 18a, 18b) is aligned to the
direction of the ground reflection.
20. The method as claimed in claim 18 or 19, wherein radiosonde
telemetry reception (15) is independent of azimuth and elevation measurements.

The present invention relates to an antenna system and method. The
antenna system for measuring azimuth and elevation angles of an active, signal
sending radiosonde (31), comprises a first passive antenna group (13)
comprising at least two antenna arrays (11a, 11b), the direction pattern of which
is wide at least in elevation plane for measuring azimuth angle of the radiosonde
(31) based on the phase differences between the antenna arrays (11a, 11b), a
second passive antenna group (12) comprising at least two antenna arrays (10a,
10b), the direction pattern of which is wide at least in elevation plane for
measuring the elevation angle of the radiosonde (31) based on the phase
differences between the antenna arrays (10a, 10b) and the rotational position of
the antenna field (1), and at least one third antenna (8) having high gain for
receiving the telemetry signal, the direction pattern of which element (8) is
narrow in azimuth plane and wide in elevation plane. According to the invention
first (13) and second (12) antenna groups form a solid antenna field (1), and
antenna field (1) is fixedly tilted in a predetermined elevation position.

Documents:

1020-kolnp-2005-granted-abstract.pdf

1020-kolnp-2005-granted-assignment.pdf

1020-kolnp-2005-granted-claims.pdf

1020-kolnp-2005-granted-correspondence.pdf

1020-kolnp-2005-granted-description (complete).pdf

1020-kolnp-2005-granted-drawings.pdf

1020-kolnp-2005-granted-examination report.pdf

1020-kolnp-2005-granted-form 1.pdf

1020-kolnp-2005-granted-form 18.pdf

1020-kolnp-2005-granted-form 3.pdf

1020-kolnp-2005-granted-form 5.pdf

1020-kolnp-2005-granted-pa.pdf

1020-kolnp-2005-granted-reply to examination report.pdf

1020-kolnp-2005-granted-specification.pdf

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Patent Number

228368

Indian Patent Application Number

1020/KOLNP/2005

PG Journal Number

06/2009

Publication Date

06-Feb-2009

Grant Date

04-Feb-2009

Date of Filing

30-May-2005

Name of Patentee

VAISALA OYJ

Applicant Address

P.O. BOX 26, FIN-00421 HELSINKI

Inventors:

#	Inventor's Name	Inventor's Address
1	ANDERSSON HENRY	LUHTATIE 38, FI-02760 ESPOO
2	KARHUNEN PENTTI	AINONTIE 7 G 21, FI-01630 VANTAA
3	KORTE JARKKO	OHRAKASKENSYRJA 11 G, FI-02340 ESPOO
4	JAATINEN JUHANA	NIITTYVILLANKIERTO 13, FI-05800 HYVINKAA

PCT International Classification Number

H01Q 3/04,21/29

PCT International Application Number

PCT/FI2003/000963

PCT International Filing date

2003-12-16

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	20022202	2002-12-16	Finland