CA2026855A1 - Radome having integral heating and impedance matching elements - Google Patents
Radome having integral heating and impedance matching elementsInfo
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- CA2026855A1 CA2026855A1 CA 2026855 CA2026855A CA2026855A1 CA 2026855 A1 CA2026855 A1 CA 2026855A1 CA 2026855 CA2026855 CA 2026855 CA 2026855 A CA2026855 A CA 2026855A CA 2026855 A1 CA2026855 A1 CA 2026855A1
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- 238000010438 heat treatment Methods 0.000 title claims description 20
- 239000004020 conductor Substances 0.000 claims abstract description 61
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 5
- 230000007613 environmental effect Effects 0.000 claims abstract description 3
- 229910001026 inconel Inorganic materials 0.000 claims description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 239000010949 copper Substances 0.000 claims description 3
- 230000001681 protective effect Effects 0.000 abstract description 2
- 230000008018 melting Effects 0.000 abstract 1
- 238000002844 melting Methods 0.000 abstract 1
- 238000009434 installation Methods 0.000 description 7
- 230000001939 inductive effect Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000005755 formation reaction Methods 0.000 description 3
- 230000002411 adverse Effects 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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Abstract
ABSTRACT
An antenna radome, suitable for use with high precision, environmentally sensitive array antennas, includes a dielectric sheet formed to protect the antenna from environmental conditions and a series of conductors fixed on the sheet in a certain pattern so that the sheet with the conductors provides a lower reflection coefficient to electromagnetic waves at the antenna's operating wavelength than in the absence of the conductors. Current is caused to flow through the conductors, thus generating heat in areas of the dielectric sheet where the conductors are fixed. Accordingly, ice formation on the protective dielectric sheet can be prevented while the antenna array is operational, and accurate antenna performance is ensured. Further, the dielectric sheet presents a significantly lower reflection coefficient at the operating wavelength than radomes in which a conventional grid of heater wires is provided for melting ice.
An antenna radome, suitable for use with high precision, environmentally sensitive array antennas, includes a dielectric sheet formed to protect the antenna from environmental conditions and a series of conductors fixed on the sheet in a certain pattern so that the sheet with the conductors provides a lower reflection coefficient to electromagnetic waves at the antenna's operating wavelength than in the absence of the conductors. Current is caused to flow through the conductors, thus generating heat in areas of the dielectric sheet where the conductors are fixed. Accordingly, ice formation on the protective dielectric sheet can be prevented while the antenna array is operational, and accurate antenna performance is ensured. Further, the dielectric sheet presents a significantly lower reflection coefficient at the operating wavelength than radomes in which a conventional grid of heater wires is provided for melting ice.
Description
2~2~8~
DOCKET H4431.01 EAO:cf 1RADOME HAVING INTEGRAL ~IEATING
2AND .IMPEDANCE MATCHING ELEMENT5 4The present invention relates generally to antenna radomes, and particularly to radome 6 construction providing both low loss and de-icing 7 capability for precision antenna installations at 8 environmentally severe locations.
10Antenna radomes which include heating 11 wires are generally known. Such radomes may include a 12 grid of high resistance Inconel wires for heating the 13 radome to prevent the formation of ice. Problems 14 arise, however, in that the heating wires tend to increase the reflection coefficient at the surf`ace of 16 the radome to incident electromagnetic wave energy at 17 the operating wavelength of the antenna. Thus, the 18 level of energy transmitted through the radome 19 decreases from that which would be transmitted in the absence of the heating wires. Also, depending on the 21 spacing between adjacent wires and the operating - 2~2~8~
1 wavelength, the free space antenna pattern rnay be 2 adversely aft`ected by the radome wires, For example,by 3 -the generation of grating lobes in the antenna 4 pattern. Appropriate precautions must therefo~e be taken with respect to the heating wire grid 6 arrangement. To ensure system compatibility, it may 7 be necessary to provide suitable compensation to 8 signals transmitted or received by the antenna as a 9 function of the antenna scan angle relative to the radome. It may in some cases even be impossible to 11 obtain adequa-te radome heating capability owing to 12 limitations imposed on the heating wire configuration 13 at a given operating wavelength and degree of scan.
14 It is also generally known that highly conductive wires (e.g. copper), when arranged in a 16 certain pattern on or parallel to a major surface of 17 an antenna radome, will serve to enhance the impedance 18 match between the radome material and the surrounding 19 space. A radome having a thickness that is small compared to the antennals operating wavelength will 21 exhibit a capacitive susceptance to incident 22 electromagne-tic wave energy. The inherent capacitive 23 susceptance of the radome material can be cancelled by 24 introducing a corresponding inductive susceptance to the radome by the use of conductive wires that Follow 26 a meandering path in a plane parallel to the surface 27 of the radome.
2~2~5~
1 As Far as is known, no attempts have been 2 made to use conductive wires a:rranged on or in a 3 radome for purposes of impedance matching and also as 4 a means fo:r generating heat sufficient to de-ice the radome during severe weather conditions.
6 SUMMARY 0~ T~IE INVENTION
7 According to the invention, an antenna 8 radome includes a dielectric member shaped -to protect 9 an antenna from environmental conditions, and a plurality of conductors fixed in relation to a major 11 surface of said dialectric member in a predetermined 12 pattern so that the member with the conductors 13 provides a lower reflection coeff`icient to incident 14 electromagnetic waves at the operatiny wavelength of the antenna than in the absence oF the conductor~.
16 Means are provided for causing a desired heating 17 current to flow through the conductors, thereby 18 enabling heat to be generated in the dielectric 19 member.
According to another aspéct oF the 21 invention, an environmentally stable antenna system 22 comprises an array of` antenna elements fixed relative 23 to one another to obtain a desired array pattern when 24 the elements are excited with radio Frequency energy of a certain wavelength and relative phase shift.
2026~
1 A dielectric sheet is used d to protect the array o-F
2 elemen-ts from environrrlental conditions, and means are 3 provided for supportiny the sheet in protective ~ relation to the array. A plurality of` conductors are fixed in relation to a major surface of said 6 dielectric sheet in a predetermined pattern so that 7 the combination of the sheet with the conductors 8 provides a lower reflection coefficient to 9 electromagnetic wave energy at the operating wavelength of the array than in the absence of the 11 conductors. Means are provided for applying a voltage 12 across opposite ends of -the conductors, thereby 13 enabling heat to be generated in the dielectric sheet 14 as a result of a heating curren-t flowing through the conductors.
16 For a better understanding of the present 17 invention, toyether with other and further objects, 18 reference is made to the following description, taken 19 in conjunction with the accompanying drawings~ and its scope will be pointed out in the appended claims.
22 Fig. 1 is a perspective view of an antenna 23 array including a radome constructed according to the 24 present invention;
Fig. 2 is a plan view of a portion of the 26 radome in Fig. l;
2~8~
1 Fig. ~ is an enlarged cross-sectional view 2 taken along line A-A in Fig. 2; and 3 Fig. 4 is an enla:rged detail view of a 4 part of the radome in Fig. 2.
DESCRIPTION OF T~IE INVENTION
6 Fig. 1 is a perspective view o-f a planar 7 array antenna 10 including a radome 12 constructed 8 according to the present invention.
9 Antenna 10 may be, for example, an azimuth (AZ) antenna of the kind used in microwave landing 11 systems (MLS). Such an antenna is generally a planar 12 rectangular array of vertically oriented, slotted wave 13 guides 14 suppor-ted adjacent one another and measuring 14 about 5 feet in height and about 14 feet in width.
The invention is not limited to use with 16 the particular antenna 10 represented in Fig. 1 and 17 may be used with other antennas, such as a line array 18 elevation antenna (EL) used in MLS and other non array 19 antennas.
Until now, it has been the practice to 21 equip radomes for MLS antennas with a grid of Inconel 22 wires to prevent ice from forming on the outer surface 23 of the radome. Any ice allowed -to form on the surface 24 of the radome 12 in Fig.l during operation of the antenna 10 would adversely affect the antenna's 26 performance. In a MLS installation, for example, the 202~8~
1 AZ antenna scans a main beam of electromagnetic wave 2 energy (at a wavelength ~O o-F about 2.33 inches) 3 rapidly "to" and "fro" over an azirnuth scan anyle of, 4 typically, plus and minus 40 degrees with respect to the runway centerline. The EL antenna in a MLS
6 installation scans its beam rapidly "up" and "down"
7 over an elevation scan angle typical~y from about 1 8 degree to 15 degrees relative to the runway. An MLS
9 receiver on board an aircraft approaching the runway receives the beams as scanned by the AZ and EL
11 antennas and calculates the aircraft's heading and 12 angle of descent relative to the runway, 1~ Any malfunction of the MLS antennas, such 14 as may be caused by icing and~or displacement of the radome 12 relative to the antenna elements due to 16 misalignment or motion from high winds, can cause the 17 aforementioned electronically steered beams from the 18 antennas to deviate from their precise location in 19 space. Such deviations may cause significant errors in the positional information derived by the 21 aircraft's MLS receiver during the critical time when 22 the aircra~t is approaching the runway.
2~ Rather than employ the prior art grid of 24 Inconel heater wires arranged perpendicular to the incident FR electric field as a means for preventing 26 ice formation on the radome 12, it has been discovered 27 that a predetermined pattern of conductors 16 (FigO 2) 2~2~85~
1 may be used in a dual role both as a means For 2 generatirlg de-icing heat and for enhancing, rather 3 than degrading, the impedance match oF the radome 4 material with the surrounding space. By reducing the reflection coefficient of the radome 12 to 6 electromagnetic energy at the operating wavelength of 7 the antenna 10 through use of conductors 16, from that 8 obtained in the absence of the conductors 16 or when a 9 conventional grid of heating wires is used, any permanent misalignment or movement of the radome 12 11 relative to the antenna elements 14 will also have 12 less effect on the actual antenna pattern. MLS
13 position errors, introduced by such radome 14 misalignment or movement in the prior installations, will be significantly reduced as the radome 12 itself 16 appears more like free space in its transmiss.ion 17 characteristics.
18 In the embodiment illustrated in Fig.l, 19 the reflection coefficient of the radome 12 is reduced to -36dB from a prior level of -23dB for radomes 21 employing Inconel heater wires. In the antenna 10 of 22 Fig. 1, the radome 12 is supported by suitable 23 brackets 18 so as to extend about 4 inches in front o~
24 the slotted waveguides 14. The bracke-ts 18 fix the radome 12 in position parallel to the antenna elements 26 or ~aveguides 14 in the direction of -the scan plane 27 and apply some tension to the radome 12 to prevent 2~2~8~
1 undesirable movement during high wind conditions.
2 As shown in the embodimen-t illustrated in 3 Fig. 3, radome 12 may be a dielec-tric sheet formed of 4 layers 20 and 22. Layer 20 may be te~lon cloth, such as Raydel type M-26, 0.018 inches thick, for example, 6 Layer 22 rnay be Chemfab Skrimcloth tfiberylass), for 7 example. When bonded by a suitable adhesive such as 8 3M No 2290 (EPO~Y), the two layers 20, 22 form the 9 sheet radome 12 with a thickness of about 0.025 inches. Teflon cloth is preferred as the outside 11 layer (the one exposed to wheather) because of its 12 ability to shed water.
13 Conductors 16 are printed or otherwise 14 fixed on one of the major surfaces oF the radome layers 20, 22 and preferably are sandwiched between 16 the layers when the layers are bonded to one another 17 as shown in Fig. 3.
18 In the illustrated embodiment, each of the 19 conductors 16 follows a meandering path as shown in Figs. 2 and 4. Speci~ically, conductors 16 run 21 parallel to one another and are spaced apart by a 22 distance at most 1/2 the operating wavelength of the 23 antenna 10. Each of -the conductors 16 extends 24 generally in a direction parallel to the E field of electromagnetic wave energy that will be encountered 26 during antenna operation. The maximum spacing limit 27 for conductors 16 prevents undesirable grating lobes 2n~8~
1 from appearing in the ~adiation pattern oF antenna 10 2 as its beam scans relative to the radome 12.
3 At opposite enas of each of the parallel, 4 rneandering conductors 16 are connected terminal bus lines 24, 26 which enable a voltage from a source V
6 ~Fig. 2) to be applied across opposite ends of the 7 conductors 16. The applied voltage causes a heating 8 current to pass through the conductors and generate 9 heat in the radome 12. The heating current should be sufficient to prevent ice forma-tion on the outside 11 surface of the radome 12. The voltage source V may be 12 an AC source located conveniently close to the antenna 13 installation, and typically might have a capacity of 14 several kilowatts or higher.
The conductors 16 are preferably in the 16 form of flat copper strips about 0.055 inches wide, as 17 shown in Fig. 4. A typical heating current for each 18 conductor 16 is then about one-quarter amp. However, 19 other dimensions and conductive materials may be used.
For an operating wavelength of about 2.33 21 inches, such as used in typical MLS ins-tallations, the 22 spacing S between adjacent conductors 16 is preferably 23 about one inch. The length L of inductive regions of 24 the conductors 16 is preferably about 0~41~ inch, and the periodicity P of successive inductive regions 26 along the path of each conductors 16 is about 0.218 27 inch.
202~8~5 1 It will, of course, be urlderstood that the 2 foregoing dimensions for conductor 16 may be varied, 3 depending on the operating wavelength of the antenna 4 with which the radome 12 is used.
The frequency-bandwidth ratio for radome 6 12, having a desired reflection coefficient and 7 dielectric constant, can be derived as shown below.
8 The normalized capacitive susceptance for a 9 dielectric sheet is given by (1) B = (k-1)2~(t/~o)(f/fo), 11 wherein 12 k = dielectric constant 13 ~O _ free space wavelength 14 f = frequency fO = reference frequency 16 t _ dielectric thickness 17 The susceptance for radome 12, including 18 the inductive contribution of the wires 16, then 19 becomes:
(2) B = (k-1)27r(-t/~O)[(f/fO)-(fO/f)J
21 (3) B = (k-1)2~(t!~o)BW, 22 where 23 BW = frequency bandwidth ratio.
_ 10 --202~5~
1 The reflection coeffic.ient is given by 32 (4) P ~ r - ( 1s ~
4 (5) p ~ -jB/2 (~) p = (k~ o)tBW.
6 For 7 p = 0.0158(-36dB) 8 k = 3 9 t = O.Q25"
~O = 2.333", 11 BW = 0~255 or 25.5%
12 In MLS installations, the operational 13 bandwidth ratio is usually taken to be 0.012 or 1.2%.
14 The excess bandwidth afforded by the present radome 12 (24.4%) provides a comfortahle rnargin, such as is 16 desirable required for manufacturing and material 17 tolerances.
DOCKET H4431.01 EAO:cf 1RADOME HAVING INTEGRAL ~IEATING
2AND .IMPEDANCE MATCHING ELEMENT5 4The present invention relates generally to antenna radomes, and particularly to radome 6 construction providing both low loss and de-icing 7 capability for precision antenna installations at 8 environmentally severe locations.
10Antenna radomes which include heating 11 wires are generally known. Such radomes may include a 12 grid of high resistance Inconel wires for heating the 13 radome to prevent the formation of ice. Problems 14 arise, however, in that the heating wires tend to increase the reflection coefficient at the surf`ace of 16 the radome to incident electromagnetic wave energy at 17 the operating wavelength of the antenna. Thus, the 18 level of energy transmitted through the radome 19 decreases from that which would be transmitted in the absence of the heating wires. Also, depending on the 21 spacing between adjacent wires and the operating - 2~2~8~
1 wavelength, the free space antenna pattern rnay be 2 adversely aft`ected by the radome wires, For example,by 3 -the generation of grating lobes in the antenna 4 pattern. Appropriate precautions must therefo~e be taken with respect to the heating wire grid 6 arrangement. To ensure system compatibility, it may 7 be necessary to provide suitable compensation to 8 signals transmitted or received by the antenna as a 9 function of the antenna scan angle relative to the radome. It may in some cases even be impossible to 11 obtain adequa-te radome heating capability owing to 12 limitations imposed on the heating wire configuration 13 at a given operating wavelength and degree of scan.
14 It is also generally known that highly conductive wires (e.g. copper), when arranged in a 16 certain pattern on or parallel to a major surface of 17 an antenna radome, will serve to enhance the impedance 18 match between the radome material and the surrounding 19 space. A radome having a thickness that is small compared to the antennals operating wavelength will 21 exhibit a capacitive susceptance to incident 22 electromagne-tic wave energy. The inherent capacitive 23 susceptance of the radome material can be cancelled by 24 introducing a corresponding inductive susceptance to the radome by the use of conductive wires that Follow 26 a meandering path in a plane parallel to the surface 27 of the radome.
2~2~5~
1 As Far as is known, no attempts have been 2 made to use conductive wires a:rranged on or in a 3 radome for purposes of impedance matching and also as 4 a means fo:r generating heat sufficient to de-ice the radome during severe weather conditions.
6 SUMMARY 0~ T~IE INVENTION
7 According to the invention, an antenna 8 radome includes a dielectric member shaped -to protect 9 an antenna from environmental conditions, and a plurality of conductors fixed in relation to a major 11 surface of said dialectric member in a predetermined 12 pattern so that the member with the conductors 13 provides a lower reflection coeff`icient to incident 14 electromagnetic waves at the operatiny wavelength of the antenna than in the absence oF the conductor~.
16 Means are provided for causing a desired heating 17 current to flow through the conductors, thereby 18 enabling heat to be generated in the dielectric 19 member.
According to another aspéct oF the 21 invention, an environmentally stable antenna system 22 comprises an array of` antenna elements fixed relative 23 to one another to obtain a desired array pattern when 24 the elements are excited with radio Frequency energy of a certain wavelength and relative phase shift.
2026~
1 A dielectric sheet is used d to protect the array o-F
2 elemen-ts from environrrlental conditions, and means are 3 provided for supportiny the sheet in protective ~ relation to the array. A plurality of` conductors are fixed in relation to a major surface of said 6 dielectric sheet in a predetermined pattern so that 7 the combination of the sheet with the conductors 8 provides a lower reflection coefficient to 9 electromagnetic wave energy at the operating wavelength of the array than in the absence of the 11 conductors. Means are provided for applying a voltage 12 across opposite ends of -the conductors, thereby 13 enabling heat to be generated in the dielectric sheet 14 as a result of a heating curren-t flowing through the conductors.
16 For a better understanding of the present 17 invention, toyether with other and further objects, 18 reference is made to the following description, taken 19 in conjunction with the accompanying drawings~ and its scope will be pointed out in the appended claims.
22 Fig. 1 is a perspective view of an antenna 23 array including a radome constructed according to the 24 present invention;
Fig. 2 is a plan view of a portion of the 26 radome in Fig. l;
2~8~
1 Fig. ~ is an enlarged cross-sectional view 2 taken along line A-A in Fig. 2; and 3 Fig. 4 is an enla:rged detail view of a 4 part of the radome in Fig. 2.
DESCRIPTION OF T~IE INVENTION
6 Fig. 1 is a perspective view o-f a planar 7 array antenna 10 including a radome 12 constructed 8 according to the present invention.
9 Antenna 10 may be, for example, an azimuth (AZ) antenna of the kind used in microwave landing 11 systems (MLS). Such an antenna is generally a planar 12 rectangular array of vertically oriented, slotted wave 13 guides 14 suppor-ted adjacent one another and measuring 14 about 5 feet in height and about 14 feet in width.
The invention is not limited to use with 16 the particular antenna 10 represented in Fig. 1 and 17 may be used with other antennas, such as a line array 18 elevation antenna (EL) used in MLS and other non array 19 antennas.
Until now, it has been the practice to 21 equip radomes for MLS antennas with a grid of Inconel 22 wires to prevent ice from forming on the outer surface 23 of the radome. Any ice allowed -to form on the surface 24 of the radome 12 in Fig.l during operation of the antenna 10 would adversely affect the antenna's 26 performance. In a MLS installation, for example, the 202~8~
1 AZ antenna scans a main beam of electromagnetic wave 2 energy (at a wavelength ~O o-F about 2.33 inches) 3 rapidly "to" and "fro" over an azirnuth scan anyle of, 4 typically, plus and minus 40 degrees with respect to the runway centerline. The EL antenna in a MLS
6 installation scans its beam rapidly "up" and "down"
7 over an elevation scan angle typical~y from about 1 8 degree to 15 degrees relative to the runway. An MLS
9 receiver on board an aircraft approaching the runway receives the beams as scanned by the AZ and EL
11 antennas and calculates the aircraft's heading and 12 angle of descent relative to the runway, 1~ Any malfunction of the MLS antennas, such 14 as may be caused by icing and~or displacement of the radome 12 relative to the antenna elements due to 16 misalignment or motion from high winds, can cause the 17 aforementioned electronically steered beams from the 18 antennas to deviate from their precise location in 19 space. Such deviations may cause significant errors in the positional information derived by the 21 aircraft's MLS receiver during the critical time when 22 the aircra~t is approaching the runway.
2~ Rather than employ the prior art grid of 24 Inconel heater wires arranged perpendicular to the incident FR electric field as a means for preventing 26 ice formation on the radome 12, it has been discovered 27 that a predetermined pattern of conductors 16 (FigO 2) 2~2~85~
1 may be used in a dual role both as a means For 2 generatirlg de-icing heat and for enhancing, rather 3 than degrading, the impedance match oF the radome 4 material with the surrounding space. By reducing the reflection coefficient of the radome 12 to 6 electromagnetic energy at the operating wavelength of 7 the antenna 10 through use of conductors 16, from that 8 obtained in the absence of the conductors 16 or when a 9 conventional grid of heating wires is used, any permanent misalignment or movement of the radome 12 11 relative to the antenna elements 14 will also have 12 less effect on the actual antenna pattern. MLS
13 position errors, introduced by such radome 14 misalignment or movement in the prior installations, will be significantly reduced as the radome 12 itself 16 appears more like free space in its transmiss.ion 17 characteristics.
18 In the embodiment illustrated in Fig.l, 19 the reflection coefficient of the radome 12 is reduced to -36dB from a prior level of -23dB for radomes 21 employing Inconel heater wires. In the antenna 10 of 22 Fig. 1, the radome 12 is supported by suitable 23 brackets 18 so as to extend about 4 inches in front o~
24 the slotted waveguides 14. The bracke-ts 18 fix the radome 12 in position parallel to the antenna elements 26 or ~aveguides 14 in the direction of -the scan plane 27 and apply some tension to the radome 12 to prevent 2~2~8~
1 undesirable movement during high wind conditions.
2 As shown in the embodimen-t illustrated in 3 Fig. 3, radome 12 may be a dielec-tric sheet formed of 4 layers 20 and 22. Layer 20 may be te~lon cloth, such as Raydel type M-26, 0.018 inches thick, for example, 6 Layer 22 rnay be Chemfab Skrimcloth tfiberylass), for 7 example. When bonded by a suitable adhesive such as 8 3M No 2290 (EPO~Y), the two layers 20, 22 form the 9 sheet radome 12 with a thickness of about 0.025 inches. Teflon cloth is preferred as the outside 11 layer (the one exposed to wheather) because of its 12 ability to shed water.
13 Conductors 16 are printed or otherwise 14 fixed on one of the major surfaces oF the radome layers 20, 22 and preferably are sandwiched between 16 the layers when the layers are bonded to one another 17 as shown in Fig. 3.
18 In the illustrated embodiment, each of the 19 conductors 16 follows a meandering path as shown in Figs. 2 and 4. Speci~ically, conductors 16 run 21 parallel to one another and are spaced apart by a 22 distance at most 1/2 the operating wavelength of the 23 antenna 10. Each of -the conductors 16 extends 24 generally in a direction parallel to the E field of electromagnetic wave energy that will be encountered 26 during antenna operation. The maximum spacing limit 27 for conductors 16 prevents undesirable grating lobes 2n~8~
1 from appearing in the ~adiation pattern oF antenna 10 2 as its beam scans relative to the radome 12.
3 At opposite enas of each of the parallel, 4 rneandering conductors 16 are connected terminal bus lines 24, 26 which enable a voltage from a source V
6 ~Fig. 2) to be applied across opposite ends of the 7 conductors 16. The applied voltage causes a heating 8 current to pass through the conductors and generate 9 heat in the radome 12. The heating current should be sufficient to prevent ice forma-tion on the outside 11 surface of the radome 12. The voltage source V may be 12 an AC source located conveniently close to the antenna 13 installation, and typically might have a capacity of 14 several kilowatts or higher.
The conductors 16 are preferably in the 16 form of flat copper strips about 0.055 inches wide, as 17 shown in Fig. 4. A typical heating current for each 18 conductor 16 is then about one-quarter amp. However, 19 other dimensions and conductive materials may be used.
For an operating wavelength of about 2.33 21 inches, such as used in typical MLS ins-tallations, the 22 spacing S between adjacent conductors 16 is preferably 23 about one inch. The length L of inductive regions of 24 the conductors 16 is preferably about 0~41~ inch, and the periodicity P of successive inductive regions 26 along the path of each conductors 16 is about 0.218 27 inch.
202~8~5 1 It will, of course, be urlderstood that the 2 foregoing dimensions for conductor 16 may be varied, 3 depending on the operating wavelength of the antenna 4 with which the radome 12 is used.
The frequency-bandwidth ratio for radome 6 12, having a desired reflection coefficient and 7 dielectric constant, can be derived as shown below.
8 The normalized capacitive susceptance for a 9 dielectric sheet is given by (1) B = (k-1)2~(t/~o)(f/fo), 11 wherein 12 k = dielectric constant 13 ~O _ free space wavelength 14 f = frequency fO = reference frequency 16 t _ dielectric thickness 17 The susceptance for radome 12, including 18 the inductive contribution of the wires 16, then 19 becomes:
(2) B = (k-1)27r(-t/~O)[(f/fO)-(fO/f)J
21 (3) B = (k-1)2~(t!~o)BW, 22 where 23 BW = frequency bandwidth ratio.
_ 10 --202~5~
1 The reflection coeffic.ient is given by 32 (4) P ~ r - ( 1s ~
4 (5) p ~ -jB/2 (~) p = (k~ o)tBW.
6 For 7 p = 0.0158(-36dB) 8 k = 3 9 t = O.Q25"
~O = 2.333", 11 BW = 0~255 or 25.5%
12 In MLS installations, the operational 13 bandwidth ratio is usually taken to be 0.012 or 1.2%.
14 The excess bandwidth afforded by the present radome 12 (24.4%) provides a comfortahle rnargin, such as is 16 desirable required for manufacturing and material 17 tolerances.
Claims (23)
- Claim 1. An antenna radome, for use in conjunction with an antenna designed to emit electro-magnetic waves at a given wavelength and having an E
field component, comprising:
a dielectric member formed to protect said antenna from environmental conditions;
a plurality of conductors arranged in a predetermined pattern on a major surface of said dialectric member such that said conductors extend generally in a direction parallel to the E field of incident electromagnetic waves from said antenna at said given wavelength, and follow a predetermined meandering path, whereby the member with said conductors provides a lower reflection coefficient to incident electromagnetic waves at said given wavelength than in the absence of said conductors; and means for causing a desired heating current to flow through said conductors, thereby enabling heat to be generated in said member - Claim 2. An antenna radome according to Claim 1, wherein said conductors are copper.
- Claim 3. An antenna radome according to Claim 1, wherein said conductors are Inconel.
- Claim 4. An antenna radome according to claim 1 wherein said conductors are in the form of flat strips.
- Claim 5. An antenna radome according to claim 1, wherein said conductors are generally parallel and spaced not more than one-half said given wavelength apart from one another.
- Claim 6. An antenna radome according to claim 1, wherein said given wavelength is about 2.33 inches in free space, and the dielectric member is a sheet having a dielectric constant of about 3 and a thickness of about 0.025 inches.
- Claim 7. An Antenna radome according to claim 1, wherein said dielectric member is a sheet formed of two thin layers and said conductors are sandwiched between the two layers.
- Claim 8. An antenna radome according to claim 7, wherein said given wavelength is about 2.33 inches in free space, the thickness of one of the two layers is about 0.018 inches, the thickness of the remaining layer is about 0.007 inches, and the dielectric constant of each sheet is about 3.
- Claim 9. An antenna radome according to claim 1, including means for applying a voltage across opposite ends of said conductors, thereby causing heating current to flow through said conductors at a level which generates sufficient heat to prevent formation of ice on an outside surface of the dielectric member under predetermined conditions.
- Claim 10. An antenna radome according to claim 9, wherein said conductors are in the form of flat strips about 0.055 inches wide, and the heating current through each of the flat strips is about one-quarter amp.
- Claim 11. An antenna radome according to claim 9, wherein said voltage applying means is an AC
source. - Claim 12. An antenna radome according to claim 6, wherein said antenna is a scanning antenna having a predetermined range of scan angles, and wherein the reflection coefficient of the combination of said dielectric sheet with said conductors, at said given wavelength, is about -30dB to -36dB over said range of scan angles.
- Claim 13. An antenna radome according to claim 6, wherein said dielectric sheet exhibits a frequency bandwidth ratio of about 25 percent relative to the operating wavelength.
- Claim 14. An environmentally stable antenna system, comprising:
an array of linearly polarized antenna elements, designed to emit electromagnetic waves of a selected wavelength and having an E field component;
a dielectric sheet formed to shield said array from weather conditions;
means for supporting said dielectric sheet generally parallel to said array and in the path of said electromagnetic waves;
a plurality of conductors arranged in a predetermined pattern on a major surface of said dielectric sheet such that said conductors extend generally in a direction parallel to the E field of incident electromagnetic waves from said array at said given wavelength and follow a predetermined meandering path, whereby the sheet with said conductors provides a lower reflection coefficient to incident electromagnetic waves at said selected wavelength than in the absence of said conductors; and means, coupled to said conductors, for applying a voltage across opposite ends of said conductors, thereby heating the dielectric sheet in response to a heating current passsing through said conductors. - Claim 15. The antenna system of claim 14, wherein said conductors are copper.
- Claim 16. The antenna system of Claim 14, wherein said conductors are Inconel.
- Claim 17. The antenna system of claim 14, wherein said conductors are flat strips.
- Claim 18. The antenna system of claim 14, wherein said conductors are generally parallel and spaced not more than one-half said selected wavelength apart from one another.
- Claim 19. The antenna system of claim 14, wherein said selected wavelength is about 2.33 inches in free space, and the dielectric sheet has a dielectric constant of about 3 and a thickness of about 0.025 inches.
- Claim 20. The antena system of claim 14, wherein the dielectric sheet is formed of two layers and said conductors are sandwiched between the two layers.
- Claim 21. The antenna system of claim 14, wherein said conductors are flat strips about 0.055 inches wide, and the heating current through each of the flat strips is about one-quarter amp.
- Claim 22. The antenna system of claim 19, wherein the reflection coefficient of the dielectric sheet with the conductors at said certain wavelength is about -30dB to -36dB.
- Claim 23. The antenna system of claim 19, wherein the dielectric sheet with said conductors exhibits a frequency bandwidth ratio of about 25 percent relative to said certain wavelength.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2026855 CA2026855A1 (en) | 1990-10-03 | 1990-10-03 | Radome having integral heating and impedance matching elements |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2026855 CA2026855A1 (en) | 1990-10-03 | 1990-10-03 | Radome having integral heating and impedance matching elements |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2026855A1 true CA2026855A1 (en) | 1992-04-04 |
Family
ID=4146100
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2026855 Abandoned CA2026855A1 (en) | 1990-10-03 | 1990-10-03 | Radome having integral heating and impedance matching elements |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2026855A1 (en) |
-
1990
- 1990-10-03 CA CA 2026855 patent/CA2026855A1/en not_active Abandoned
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| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |