JPS6390204A - Heated dish-type antenna - Google Patents

Abstract

A dish antenna (12) for receiving or transmitting signals, eg. via a satellite, is heated by means of radiant heat from electrical heater (2-5) located behind the antenna and spaced apart therefrom. This keeps the antenna free from ice and snow and minimizes distortion. The heater is preferably a self-regulating sheet heater comprising a PTC conductive polymer.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a dish antenna for receiving signals and/or transmitting signals from, for example, a microwave antenna of a satellite station or a ground station. Concerning means for heating such an antenna.

[Prior Art] The use of dish antennas, especially for receiving signals from satellite stations, is rapidly increasing. The dimensions of dish antennas vary widely depending on the application, but many dish antennas are
to 7 m, such as 1.2 m and 1.8 m.
Antennas with an aperture of m are most often used for 12 to 14 GIIz signals, which are widely used for private networks transmitting data, voice, and image communications. Many countries specify requirements for both transmitting and receiving antennas, such as requirements for the sidelobe envelope of the radiation pattern.
There are regulations, such as US FCC Regulation 25.209, and a major concern for antenna manufacturers and users is not only that the antenna meets those requirements when it is first manufactured, but also that it subsequently The goal is to ensure that the requirements are not distorted to meet the requirements. If ice or snow is present on a dish antenna, it often causes distortion in the shape of the antenna.
and/or signal attenuation often occurs, which may be more of a problem with larger antennas. Therefore, much effort has been directed toward ways to heat dish antennas so that water and snow can be removed from the antenna.

Unfortunately, however, no technically and economically acceptable method has been found which, if not taken care of, will cause the heating to cause distortion in the antenna.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a dish-shaped antenna assembly that can remove ice and snow from an antenna without causing distortion to the antenna due to heating.

[Means for Solving the Problem] Now, we have developed a method of heating the dish by means of an electric heater provided at a predetermined distance behind the antenna so that the antenna is heated by radiation from the heater. It has been discovered that it is possible to very satisfactorily heat a type antenna and remove water and snow from the antenna.

According to one concept of the invention, the invention provides a dish antenna having (1) a concave front surface and a convex rear surface; (2) a second surface opposite the first surface; a thin plate-shaped electric heater having a thin plate shape, the first surface being adjacent to the rear surface of the antenna such that heat generated by the heater is radiated from the first surface and radiated to the rear surface of the antenna. a dish-shaped antenna assembly characterized in that it is substantially separated from said antenna by a medium, typically air, which is substantially transparent to thermal radiation;

As will be described later, the heater used in the present invention preferably includes a thin plate (sheet)-shaped resistance element. However, the heater alternatively comprises one or more strip heaters fixedly fixed to a thermally conductive sheet, preferably of metal. All such heaters are included within the term "laminar heater" or "laminar heater" as used herein.

[Effects of the Invention] Therefore, according to the present invention, there is provided a dish-shaped antenna having a concave front surface and a convex rear surface, and a second surface opposite to the first surface.
a thin plate-shaped electric heater having a surface of the antenna, and the first surface is attached to the antenna so that the heat generated by the heater is radiated from the first surface and radiated to the rear surface of the antenna. By being substantially separated from said antenna by a medium adjacent to the rear surface but substantially transparent to thermal radiation and typically air, ice and snow can be avoided without causing distortion of the antenna by heating. A dish antenna assembly can be provided that can be removed from the antenna.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

so that the heat generated by the thin plate heater radiates from the heater through the medium and to the rear surface of the antenna;
The thin plate heater is provided such that the medium, which is substantially transparent to thermal radiation and typically air, causes the thin plate heater to be substantially spaced from the antenna. Typically, the distance between the first surface of the heater and the rear surface of the antenna is 3 to 6 inches (7.6 to 15.5 inches).
2cm). In known methods in which electrically resistive heaters are provided in direct contact with the antenna, heating of the antenna occurs primarily or exclusively by conduction. On the other hand, in the present invention there is little or no heating of the antenna as a result of conduction, and a substantial proportion of the heating of the antenna as a result of radiation is preferably at least 40%, in particular at least 60%. The antenna is also typically heated by free convection from air (or gas) between the antenna and the heater.

The air is preferably still air, and the movement of the air occurs solely as a result of convection.

We have found that by heating the antenna in the manner described above, the antenna is heated with remarkable uniformity, even when the cooling effect of water or snow is locally limited, resulting in Depending on appropriate rules, signal reception and transmission can be improved. This is clearly due to a combination of two factors. Firstly, not only directly to the opposite cold spot from said heater section, but also through adjacent parts of the heater that can "see" the cold spot (albeit to a gradually decreasing extent). , heat can be transferred to locally confined cold spots. Second, the heat transferred from the heater to the antenna by radiation is not directly proportional to the temperature difference between the heater and the antenna (as if heat were transferred by conduction), but Tll'-TA' is proportional to. where TH is the temperature of the first surface of the heater (°K) and 'rA is the temperature of the rear surface of the antenna (°K).

Another important advantage of the present invention is that the dish antenna includes a plurality of ribs extending from the rear surface of the antenna.
This is due to the fact that the aim is high.

As a result, if an electrical resistance heater is placed in direct contact with the antenna, a number of heaters of specially shaped and interconnected components are used, which are substantially in contact with the antenna. Touch the whole thing. When heating by radiation is used, as in the present invention, the heaters can be provided remote from the ribs, thereby providing one or a relatively small number, for example less than eight, for example four.
It is possible to use between six and six sheet heaters, each sheet heater having an easily manufactured shape, for example rectangular. Furthermore, the hinata does not necessarily need to cover the entire rear surface of the antenna. The ratio of the area of the heater to the area of the rear surface of the antenna (ignoring ribs) is typically at least 0.3, but 1.0
It is not necessary (of course possible) to have a large amount of potash, so the above ratio is preferably from 0.4 to 0.9, in particular from 0.5 to 0.8.

Direct physical contact between the antenna and the heater is preferably minimized, especially when the antenna comprises metal or other thermally conductive materials. This is because heating of the antenna by conduction through the ribs tends to cause irregular heating of the front surface and consequent distortion. Therefore, at least 90%, in particular at least 95%,
In particular, substantially 100% of the first surface of the heater is exposed to air (
or other medium separating the dish antenna and heater). If the heaters are fixed firmly to the ribs on the rear surface of the antenna, they should be made of polymeric material or of low thermal conductivity, spaced a certain distance from each other and preferably preventing direct contact between the heaters and the ribs. The heater is preferably securely secured to the rib by a fastener constructed of another material having a material. Preferably, however, the heater is secured to a back shell which is secured to the dish antenna around the antenna. This back shell is preferably environmentally sealed to the antenna to minimize heat loss.

The first surface of the heater and/or the rear surface of the dish antenna is preferably treated in some way to improve the radiation properties of the antenna, for example by painting with flat black paint. On the other hand, the second surface of the heater preferably has low radioactivity. Furthermore, the second surface is preferably substantially made of a thermally insulating material, such as foamed polymer, fiberglass, or other hollow polymeric materials alone or with a metal foil applied to their back side. covered.

Any form of thin plate heater can be used in the present invention such that it radiates heat sufficiently uniformly to warm the antenna without substantially distorting the antenna. For this purpose, the radiated heat power preferably does not exceed ±20% from its average value,
In particular, it is preferable not to change by more than ±lO%, in which case the heat load is the same at all points on the heater, ie the antenna has a uniform temperature. A preferred heater comprises a resistive element in the form of a thin plate with electrodes fixed (directly or indirectly) to the resistive element. Preferably, each electrode is also in the form of a sheet, for example a metal foil, and the resistive element is placed between said electrodes so that current normally flows through the resistive element. However, other electrode arrangements are also possible.

A satisfactory heater can also be formed by combining one or more strip heaters with a sheet of metal, such as aluminum or other material with high thermal conductivity. One or more strip heaters can be firmly fixed to one surface of the metal sheet, with the opposite surface acting as a radiating surface, or the strip heater can be sandwiched between two metal sheets. It may be sandwiched, or it may be fitted or embedded in the sheet. The placement and spacing of the strip heater or strip heaters should be such that the radiant heat output is sufficiently uniform. Thus, one or more strip heaters may be provided, for example in the shape of a snake,
Alternatively, a plurality of strip heaters may be provided parallel to each other, for example with an electrical bus connector for supplying power to the heaters.

The heater preferably self-regulates, i.e. as the thermal load at any particular point on the heater (or at any particular zone that is small compared to the overall size of the heater) increases, the ( or in the zone) the heat output of the heater is greater. This makes it possible to prevent overheating of the antenna in areas not cooled by ice or snow, resulting in very good thermal uniformity in the dish antenna, thereby reducing antenna distortion. can be minimized. The isolation of the antenna and the self-adjusting heater can have the expected result of reducing the sensitivity of the heater's thermal output to the temperature of the antenna. However, in fact, its sensitivity increases, which is clearly due to the nature of the auto-adjustment and the combination of the two factors mentioned above. (i.e. (1) locally limited changes in the temperature of the antenna are not only due to parts of the heater exhibiting directly opposite changes;
Measured from adjacent parts of the heater. (2) The heat transferred by radiation from the heater to the antenna is T1
It is proportional to 1'-TA'. ) A preferred self-regulating heater for use in the present invention forms part or all of a resistive heating element, or has a zero temperature coefficient (hereinafter referred to as ZTC), i.e. the heat output is substantially (hereinafter referred to as PTC ) comprising a conductive polymer composition. Self-adjustment can be achieved through other PTC materials or by means of (tl!) (such as the skin effect or the Curie point effect).

If a self-regulating heater is not used, one or more thermostats may be used to control the ZTC heater.

For more information on heaters, including self-regulating heaters, and conductive polymer compositions, see U.S. Pat.
No. 384, No. 3,296,364, No. 4,072,8
No. 48, No. 4.117,312, No. 4,304,98
No. 7, No. 4,330,703, No. 4.425,497
No. 4,429,216, No. 4,534,889, and No. 4,560,498, and European Patent Publication Box No. 158,410 (MP0897), No. 197,
No. 759 (MPIO39), No. 223,404 (MPIO39)
No. 1090), No. 227.405 (MP1034), and No. 231,068 (MP1095 and 1100).

Hereinafter, referring to the drawings, FIGS. 1 and 2 show a dish-shaped antenna having a concave front surface 11, a convex rear surface 12, and a plurality of ribs 13 extending from the rear surface. . An electric heater comprising four rectangular panels 2, 3, 4.5 is fixed firmly to the ribs by means of straps 6 made of polymer.

FIG. 3 is a view similar to FIG. 2, but showing a dish antenna assembly further comprising an environmentally sealed backshelf around the dish antenna 1. FIG. The heater panels 2, 3, 4 and 5 are fixed firmly to the fillet 7 instead of the ribs 13, and a layer 8 of fiberglass insulating material, which is firmly fixed to the metal foil 9, provides a connection between the heater and said insulating material. provided in between.

As shown in detail in FIG. 4, the heater comprises metal foil electrodes 41 and 42 with a PTC conductive polymer resistance heating element 43 sandwiched between the metal foil electrodes 41 and 42. There is. The front face of the heater has a flat black paint coating 44 painted onto the front face.

FIG. 5 shows a metal plate 1 made of, for example, aluminum and having a strip heater 100 fixed to one surface of the metal plate.
00 shows a variant of the thin plate heater for use in the present invention. The first (radiating) surface of the heater is the opposite surface. FIG. 6 shows a cross-sectional view of a preferred strip heater with linear electrodes 61 and 62 embedded in a strip 63 of PTC conductive polymer and a polymeric insulating material 64 surrounding the strip 63. .

The invention is further illustrated by the following experimental examples.

Cold 1 PTC conductive polymer powder was 56% by weight Marlex 50100 (Philips P etr
high-density polyethylene) manufactured by oleum) and Startex (StaLex) with a weight ratio of 43%.
) G H (Columbian Chemicals Co.
carbon black (manufactured by Bian Chemi-cals) and 1% by weight panberry
Prepared by mixing with antioxidant in a mixer (Banbury mixer).

The compound obtained by mixing is mixed so that all the particles are 187
It was pulverized by irradiating it with a 50 M radian radiation ff1 (dose) using a 3 MeV electron beam until it became smaller than μm (80 mesh). This P.T.
The C powder was stirred and mixed with an equal amount of FA750 (a high density polyethylene manufactured by LISI Chemicals, Inc.), and the mixture was rolled into a powder measuring 2 inches long and 0.040 inches wide (30.5 cm x 0.10 cm).
m) was extruded.

Using a belt laminator machine at a temperature of 1100°F (204°C), a 0.001 inch (
0,0025 cm) of TEX-1 foil (electronically deposited copper on inert nickel/zinc, manufactured by Yates) was laminated.

A heater for a 1.8 m diameter antenna was manufactured as follows. The laminated sheets are approximately 10 inches long and 60 inches wide (25.4 cm long and 152.4 cm wide).
cm) and cut into 5 panels. 0.020" long and 0.5" wide (0.05cm long and 1.27cm wide) terminated with 16 AWG copper conductors
Electrical busbars are attached to the two front faces of each panel by soldering copper strips of ) onto the copper foil. Adjacent panels were electrically connected in parallel using appropriate standard connection methods to connect to a 120V power source. The panels and the connections were electrically insulated by completely covering all surfaces with adhesive-backed mylar-type (M>'Jar) tape. The first surface (ie the emitting surface) of the heater thus produced was then painted with flat black paint (Krylon) in order to improve its thermal radiation properties.

To avoid direct contact of the heater with any structural ribs, a two-legged heater was firmly fixed to the back of the dish antenna using plastic straps. A backshell for the antenna is provided in pair with the antenna, with polyurethane foam placed between the rear surface of the heater and the backshell to reduce heat loss.

[Brief explanation of the drawing]

Fig. 1 is a rear front view of a dish-shaped antenna assembly that is an embodiment of the present invention, Fig. 2 is a sectional view taken along line A-A in Fig. 1, and Fig. 3 is a modification of the dish-shaped antenna assembly. 4 is a partially enlarged detailed sectional view of FIG. 3, FIG. 5 is a plan view showing a modification of the thin plate heater that can be used in the present invention, and FIG. FIG. 2 is a sectional view of a strip heater. l... dish-shaped antenna, 2.3.4.5... panel, 6... strap, 7... back shell, 8... fiber glass insulation layer, 9... metal foil, 11...Front surface of concave surface, 12...Rear surface of convex surface, ! 3... Rib, 41.42... Metal foil electrode, 43... Resistance heating element, 44... Coating, 61.62... Wire electrode, 63... Strip, 64... Polymer insulation Materials: 100...Metal plate, 101...Strip heater. Patent Applicant: Raychem Corporation

Claims (7)

[Claims] (1) (a) a dish-shaped antenna having a concave front surface and a convex rear surface; and (b) a thin plate-shaped electric heater having a first surface and a second surface opposite to the first surface. A dish antenna assembly, wherein the first surface is adjacent to a rear surface of the antenna but substantially separated from the antenna by a medium that is substantially transparent to thermal radiation generated by the heater. 2. A dish-shaped antenna assembly, wherein heat radiated from said first surface and radiated to a rear surface of said antenna. (2) A patent characterized in that the antenna includes a plurality of ribs extending from the rear surface of the antenna, and the heater is fixed to the ribs by fixing members made of a polymer material and spaced apart from each other by a predetermined distance. A dish antenna assembly according to claim 1. (3) The dish-shaped antenna assembly includes a back shell fixed to the dish-shaped antenna around the periphery of the dish-shaped antenna and provided with a heater. Dish antenna assembly. (4) The heater includes two metal foil electrodes and a sheet-shaped resistance heating element made of a conductive polymer element exhibiting positive temperature coefficient (PTC) behavior and provided between the foil electrodes. A dish-shaped antenna assembly according to any one of claims 1 to 3, characterized in that it is a self-adjusting heater. (5) Claims 1 to 4 characterized in that the ratio of the area of the first surface of the heater to the area of the rear surface of the dish-shaped antenna is 0.4 to 0.9. A dish antenna assembly according to any of the paragraphs. (6) The dish-shaped antenna assembly includes a plurality of heaters connected in parallel, and at least one of the heaters includes a resistive heating element substantially in the shape of a rectangular sheet. A dish-shaped antenna assembly according to any one of the ranges 1 to 5. (7) A dish antenna assembly according to any one of claims 1 to 6, wherein at least 40% of the heat received by the dish antenna is radiated heat.