US2679003A

US2679003A - Heater system for microwave antennas

Info

Publication number: US2679003A
Application number: US164818A
Authority: US
Inventors: Dyke Edwin; Jr Richard Y Hoffman
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1950-05-27
Filing date: 1950-05-27
Publication date: 1954-05-18
Anticipated expiration: 1971-05-18

Description

May 18, 1954 E. DYKE EI'AL 2,679,003

HEATER SYSTEM FOR MICROWAVE ANTENNAS Filed- May 27. 1950 4 Sheets-Sheet 1 FIG. I

IN V EN TOR.

. Edwin Dyke Q BY Richard Y. Hoffman .Tr.

May 18, 1954 E. DYKE ET AL 4 Sheets-Sheet 2 Filed May 27, 1950 INVENTOR. Edwin Dyke B Richard Y. Hoffman Jr.

fly.

iiinw Q. W1 F M May 18 1954 E. DYKE ETAL HEATER SYSTEM FOR MICROWAVE ANTENNAS 4 Sheets-Sheet 3 Filed May 27. 1950 Amplifier *Receiver INVENTOR. Edwin Dyke Richard Y. Hoffman May 18, 1954 E. DYKE ETAL 2,679,003

HEATER SYSTEM FOR MICROWAVE ANTENNAS Filed May 2'7, 1950 4 Sheet s-Sheet 4 FIG. IO

TO AC SOURCE INVENTOR. Edwin Dyke BY Richard Y. HoffmunIr Patented May 18, 1954 HEATER SYSTEM FOR MICROWAVE ANTENNAS Edwin Dyke, Brookfield, and Richard Y. Hoffman, Jr., Northbrook, Ill., assignors to Motorola, Inc., Chicago, 111., a corporation of Illinois Application May 27, 1950, Serial No. 164,818

17 Claims. 1

This invention relates generally to wave reflectors and more particularly to a heated reflector device for electrical microwaves for preventing the collection of ice and snow thereon.

Various reflecting structures have been provided for directing waves which are transmitted from one point to another. These structures have reflecting surfaces which are generally parabolic and operate to convert the waves from a small source into a parallel beam or conversely from a beam to a source. For electrical signalling at microwave frequencies such a reflector is used at the radiating and/or receiving antenna.

When such a reflector is used in the outdoors where it is exposed to rain, snow, sleet and the like, ice and snow will form on the reflecting surface and reduce the effectiveness thereof. Bhis is particularly true when the reflectors are mounted horizontally, as in such cases the reflector forms a container to hold the snow and water which freezes to form ice. Means for draining the reflector have been provided to remove water therefrom but such means are not effective when the temperature is below freezing so that the water forms ice on the reflector surface. Also, falling snow or sleet Will'adhere to the surface and reduce the efiectiveness thereof.

t is therefore an object of the present invention to provide an improved reflector in which the accumulation of ice and snow on the reflecting surface thereof is eliminated.

Another object of this invention is to provide an automatic heating system for a horizontally positioned outdoor antenna reflector which prevents the accumulation of ice and snow on the reflecting surface thereof.

Still another object of this invention is to provide an automatic electric heating system for an antenna reflector having a control circuit for energizing the system so that it utilizes a minimum of power.

A feature of this invention is the provision of a reflector having a parabolic reflecting surface and an elongated heating element positioned adjacent the back or convex surface thereof, with the heating element being substantially uniformly positioned over the convex surface for heating the reflector.

A further feature of this invention is the provision of a horizontal microwave reflector having a drain for removing water therefrom and a heating element with portions adjacent the reflector and extending within the drain for preventing the formation of ice and snow on the reflecting surface and for preventing the blocking of the drain due to the freezing of water therein.

A still further feature of this invention is the provision of a spider-like structure for supporting one or more heater elements closely adjacent the back side of a reflector.

Another feature of this invention is the provision of an automatic control circuit for controlling one or more heating elements on a reflector, with at least one of the elements being controlled by the temperature about the reflector.

Another feature of this invention is the provision of a heating system for a reflector in which a first heating element is controlled by the temperature about the reflector and a second heating element is controlled in accordance with a condition at the reflecting surface. The second heating element may be controlled by the temperature on the reflecting surface, by the effectiveness of reflection surface in reflecting the waves, or by the actual presence of ice or snow on the reflecting surface.

Further objects and features and many advantages of the present invention will be apparent from a consideration of the following description when taken in connection with the accompanying drawings in which:

Fig. 1 illustrates a microwave station using a reflector in accordance with the invention;

Fig. 2 is a bottom view of the reflecting member with the heating element positioned thereon;

Fig. 3 is a perspective View, partly broken away, illustrating the construction of the reflector;

ig. 4 is a cross sectional view illustrating the mounting of the straps for supporting the heating elements;

Figs. 5 and 6 illustrate a modified supporting strap structure;

Fig. 7 illustrates a control system for a reflector heater including main and auxiliary heating elements;

Fig. 8 illustrates a heater control system having an element operated by the reflection characteristics of the reflector;

Fig. 9 illustrates a heating system in which an auxiliary heater is energized when ice or snow forms on the reflecting surface; and

Figs. 10 to 13 inclusive illustrate another embodiment of the system including a device for detecting ice or snow.

In practicing the invention there is provided an antenna reflector which is positioned horizontally to direct waves between an antenna and a flat reflector. The reflector has a concave parabolic reflecting surface which is directed upwardly and a convex back surface on which the heating element is positioned. The heating system may be Wound in the form of a spiral and is positioned substantially uniformly over the area of the reflector. A portion of a heating element extends in, and slightly beyond, the drain for the reflector so that ice and snow melted by the heating element will have a free passage which does not become blocked by freezing of the water therein. It may also be desirable to provide means for heating the end of the antenna horn to prevent the collection of ice or snow thereon. Supporting structures including straps engaging the elongated heating element are provided for supporting the heating element adjacent the convex back surface of the reflector.

The heating element may be made up of a 35. The other coil may be operated by a separate control as for example by a control responsive to the temperature of the reflecting surface itself. A control may also be provided for an auxiliary coil which is operated in accordance with the output of the receiver associated with the reflector. The auxiliary coil will be energized when the received signal falls below a predetermined level indicating defective reflection. Another system which can be used is to control a heating coil by the presence of ice and snow. The presence of ice and snow may be detected by heating a portion of the reflector or an adjacent surface to melt any ice or snow thereon. The water thus produced may be used to control the energization of a heating coil on the reflector.

Referring now to the drawings, in Fig. 1 there is illustrated a microwave system including transmitting and/ or receiving equipment iii having an antenna H extending therefrom. A reflector I2 is provided for directing waves from the antenna ll toward a flat reflector l3. Received Waves are also reflected by the flat reflectors it to th upwardly turned parabolic reflector I2 and thereby directed to the antenna ll. As shown in Figs. 1 to 4 inclusive, the reflector includes a cup shaped member I5 having an upwardly turned concave surface which is of parabolic configuration. A housing It of frusto-conical shape has a rim I! which is secured to the rim it of the reflecting member IS. The housing l6 may be supported on the microwave equipment It] by adjustable supports IE, or may be supported in any other suitable manner. An opening I9 is provided in the cup shaped member l5 and an opening is provided in the housing It through which the antenna 1! from the microwave equipment extends.

Qpenings 2i and 22 are provided in the cup shaped member I5 and the housing I6, respectively, at the center thereof, through which water collecting in the reflector may be allowed to drain. A duct structure 23 is provided for carrying this water to the side so that it does not flow directly on the housing for the microwave equipment !0. To prevent ice and snow from collecting on the reflector member 1 5, an elongated heating element 25 is wound in the form of a spiral on the under side of the reflector member. As shown in Figs. 2 and 3, this heating element extends from connector 26 to the edge of the reflector member and progresses spirally inward to the center of the reflector member. The heating element then continues down the drain and back in a hairpin shaped section with the end being returned to the connector 26.

The heating element is held in position against the under side of the reflector member by a spider like structure including a center ring 30 and a plurality of straps 3| radiating therefrom. The straps are supported at the edge [8 of the reflector member by a bolt and spring assembly 32 which provides continuous tension for the straps. The bolts provide adjustable tension for the straps. The straps therefor hold the heating element firmly against the deflecting member. Projections 33 may be formed in the strap for locating the position of the various turns of the heating element against the reflector member so that the turns will not slip clue to vibration of the member.

The straps 3| of the spider may alternatively be positioned directly against the under surface of the reflector member 15 as shown in Figs. 5 and 6. In this construction, punched out lugs 35 are provided which form projections on which the heating element may be wound or positioned, with the lugs thereafter being bent over to securely hold the element in position. In Fig. 5 the lug 35a is shown in the first position for winding the heating element thereon, and the lug 35b is shown in the position after it has been formed about the heating element 25. In such a construction it may not be necessary to provide tensioning means for the straps and they may be secured to the reflector by rivets as indicated at 31.

Energization of the heating coil 25 may be controlled by a thermostatic switch 40 positioned within the housing I6. This switch is connected through cable 4| to a source of energy and through conductors 42 to the connector 26. The thermostatic switch 40 may be adjusted to connect the heating element 25 when the temperature of the reflector assembly reaches any predetermined value. It has been found that the thermostatic switch should be set to operate at about 35. Therefore, if rain or snow strikes the reflector it will not freeze thereon and be retained but will be melted and will naturally flow through the opening in the center of the reflector member and through the duct structure 23 and will therefor be removed from the reflector unit. The heating element in addition to heating the surface of the reflector member also heats the drain structure 23 so that a free path is provided for the Water to flow away from the structure and the drain will not become blocked by frozen water.

In Fig. 7 there is illustrated a control system which may be used with the reflector heating system disclosed in the prior figures. In this system the heating element is divided into first and second coils or portions. The coil 5!! is connected to the power source through thermostatic switch 5! which may be responsive to the temperature about the reflector structure. Accordingly, when the temperature about the reflector reaches a predetermined value, as for example 35, the coil 59 will be energized to heat the reflector member. The coil 52 is connected to the source of power through the thermostatic switch 5| and a second thermostatic switch 53 connected in series therewith. The thermostatic switch 53 is positioned on the reflector surface and is responsive to the temperature on the reflecting surface of the reflector member l5. This switch may also be set at 35 for example. Therefore, if the outside temperature is such that the coil is not effective to heat the reflector member 15 to such an extent that the temperature of the refleeting surface is 35 or more, the thermostatic switch 53 will close energizing the coil 52. The two coils will therefore operate together to heat the reflecting member IE to a greater extent. Such a system provides the required heating of the reflector member for wide changes in temperature and yet is eiiicient in that only a part of the heating element is energized when the temperature is such that this part will provide all the heating that is necessary.

In Fig. 8 there is disclosed a further embodiment of the invention in which the heating element includes main and auxiliary heating coils or portions. The main coil 55 is connected through thermostatic switch 56 which may be responsive to the temperature about the reflector structure. The auxiliary coil is also connected through the thermostatic switch 56 and is also connected through a relay 58. The relay 58 may be connected to the output of an amplifier 59 which is connected to the output of the limiter of the receiver 68. The output of the limiter of the receiver depends upon the strength of the signal received and when the limiter output is of such value that good reproduction of the receiving signal is possible, the amplified limiter current will hold the relay 58 open so that the coil 5'! is not energized. However, if the output of the limiter falls below this predetermined value, the relay 58 will be deenergized and the coil 57 will be connected to the source of power to provide additional heating of the reflector member [5.

Therefore, if the snow or ice collects on the surface of the reflector member l5 and the temperature is such that the snow or ice is not removed by operation of the heating coil 55, the reflection characteristics of the reflector member will be changed so that the received signal will be great- 1y attenuated. This will cause the relay 58 to drop out so that the heater 5! is energized. When the received signal is increased in strength due to the improved reflection, the coil 5! will be deenergized. It is apparent from the above that this system is highly economical of heater energy and the auxiliary coil 57 will be connected only when necessary to provide the required signal level.

In Fig. 9 there is disclosed a still further system in which the heating element is formed by coils and 6'2. to a source of power through thermostatic switch 5 and is positioned near the center of the reflector member about the center opening therein. A second heating coil 67 is provided extending from the first coil 55 to the edge of the reflector L This second coil is connected to the member. source of power through the thermostatic switch t6 and also through a cell 68 which is in series with the switch and the coil 61. The cell includes a container cc having a pair of electrodes positioned therein. The container 69 is placed below the opening 2! in the reflector member l5 so that any ice or snow on the reflector will be melted by heat from the coil 55, and the water resulting therefrom will flow into the container 69 and provide ciosed circuit between the electrodes lil. This will cause cnergization of the coil 61 to heat the remainder of the reflector member. It is therefore seen that when ice or snow is present on the reflector. and the coil 55 is energized, the ice or snow will be melted causing the circuit through the coil Bl to be energized and the entire reflector member to be thereby heated. Since the coil is also connected through the thermostatic switch 65, the coil 61 will not be energized by the presence of water alone as might be pro- The heating coil 65 is connected duced by rain, when the temperature about the reflector is above that at which the thermostatic switch 66 will be closed.

It may be preferable to provide the snow detector as a separate element instead of incorporating it with the antenna reflector itself. Such an arrangement is shown in Figs. 10 to 13 inclusive. In Fig. 10 the reflector member !5 is provided with a supporting housing to as in the embodiments previously described. A single heating coil 15 is provided on the rear surface of the reflector for heating the same. The coil '55 is energized through. the contacts it of relay ll so that when the relay "H is energized the contacts i6 will close and the heating coil l5 will be energized.

The relay H is part of an external snow detector device which is best shown in Figs. 11 and 12. The device includes a cylindrical housing having a flat base 85 and a conical or funnel-shaped top 82. Within the housing is a frame structure including the insulating

members

83, 84 and 85. Supported on the insulating member 33 is a heating coil 35. As shown in 10 this heating unit 3% is connected through the thermostat 8'! across an alternating current source so that when the temperature falls below a predetermined value the thermostat 8'! will close and the heating unit as will be energized. The housing so is lined with insulating material it to reduce the escape of heat through the cylindrical housing walls, and the heat therefore to heat the funnelshaped member This is effective to melt any ice or snow which may have formed on the funnel-shaped surface 32.

As shown best in Fig. 13, a J-shaped trough 88 is placed below the center of the member 82 so that any water appearing on the surface 82 re sulting from the melting of ice or snow is carried down the trough St to the space between electrodes 88 and 923. The trough to serves as a wind shield and serves to carry any drops from the funnel-shaped surface 32 to the space between the electrodes 89 and st. The bottom wall 8! includes openings 55 therein to permit the escape of water therefrom.

As shown clearly in 19, the electrodes 89 and are connected in a series circuit across the A. C. source, which circuit includes rectifier 9!, resistor 92 and relay 93. The relay 93 is a very sensitive direct current relay which is actuated when a very small current is provided due to the drops of water bridging the

electrodes

89 and 90. It may be desired to provide a coating on the surface 82 which will be partiy dissolved by the water thereon and will render the water more conducting when it flows between the electrodes. The rectifier 9i may be of the selenium type and is connected in a peak rectifying circuit including condenser 9d. manner in which these elements are supported and positioned in the housing is shown in Figs. 11 and 12.

The operation of the system of Figs. 10 to 13 inclusive is believed to be clear from the foregoing description and from a consideration of M Fig. 10. The detector must be located adjacent the reflector with surface 32 positioned so that ice or snow will collect thereon under the same conditions as on the reflector. The heater unit 85 is energized by thermostat 8? when the temperature falls below a predetermined value. The thermostat maybe set to energize the heater when the temperature falls below 35 F. as at higher temperatures than this snow or ice will not form on the antenna reflector. The thermostatic switch 8'3 also closes the circuit through the rec tifler 9i,

electrodes

89 and 90, and relay 93, so that the relay 93 will be actuated in the event that there is moisture on the surface 82 which flows between the

electrodes

89 and 80 to close the circuit therethrough. The relay 93 includes contacts 96 which close to connect the heavy duty relay Tl across the alternating current source and this relay in turn connects the heating coil '15 on the surface of the antenna reflector to the alternating current power source.

It is seen from the above that there is provided a heating system for wave reflectors, such as is used in the transmission of microwaves, which is of relatively simple construction and which provides effective removal of ice and snow from the reflecting surface. lhe heating system may be automatically controlled so that energy is consumed only when heat is actually needed. As described above, this may be done in various ways. The heating element may include one portion which is controlled in accordance with the temperature about the reflector, and a second portion which is controlled in accordance with a condition on the reflecting surface, such as the temperature thereof, the efiiciency of reflection, or the actual presence of ice or snow. The structure for supporting the heating coils provides a secure mounting therefor and is adjustable so that the desired amount of tension can be provided. The provision of a section of the heating coil in the duct which forms a drain insures that the drain will remain open for removal of the melted ice and snow therefrom.

Although certain embodiments of the invention have been described which are illustrative thereof, it is obvious that various changes and modifications can be made therein without departing from the intended scope of the invention as defined in the appended claims.

We claim:

1. An electric wave reflector system adapted to be installed out of doors including in combination, a cup shaped member having a concave reflecting surface and a convex back surface, an elongated heating element positioned in a spiral adjacent said back surface for heating said member to remove ice and snow from said concave refleeting surface, and supporting means holding said element adjacent said convex back surface, said supporting means including a central portion and radially extending strap portions connecting said central portion to the edge of said cup shaped member, said strap portions including adjustable tensioning means for holding the same tensioned.

2. An electric wave reflector system adapted to be installed out of doors including in combination, a cup shaped member having a concave reflecting surface and a convex back surface, an elongated spirally wound heating element positioned adjacent said back surface for heating said member to remove ice and snow from said concave reflecting surface, and supporting means holding said element against said back surface, said supporting means including a central member, strap members extending radially therefrom and tension means securing said strap means to the edge of said cup shaped member, said strap members holding said heating element firmly against said back surface and having projections thereon for restraining lateral movement of said heating element.

3. An electric wave reflector system adapted to be installed out of doors including in combination, a cup shaped member having a concave refleeting surface and a, convex back surface, an elongated heating element positioned adjacent said convex back surface for heating said member to remove ice and snow from said concave reflecting surface, and supporting means holding said element against said back surface, said supporting means including a central portion and radially extending strap portions connecting said central portion to the edge of said cup shaped member, said strap portions having projections thereon engaging said heating element for supporting the same.

4. A wave reflector system including a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, said member having a central opening therein, duct means below said opening forming a drain for liquid flowing through said opening, an elongated heating element having a portion positioned adjacent said convex back surface and being substantially uniformly positioned over the area thereof, and a portion extending in said duct means, mean holding said element against said convex back surface, and means for energizing said heating element including a thermal controlled switch.

5. A wave reflector system including a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, said member having an opening therein for the escape of water which collects therein, duct means adjacent said opening forming a drain for water which flows through said opening, and an elongated heating element having a portion positioned adjacent said back surface and a portion extending in said duct means, said heating element being effective to remove snow and ice from said reflecting surface and from said duct means.

6. A wave reflector system including a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, said member having a central opening therein, duct means adjacent said opening forming a drain for water flowing through said opening, and an elongated heating element having a portion positioned adjacent said convex back surface and a portion extending in said duct means, said heating element serving to prevent the collection of ice and snow on said reflecting surface and said duct means.

7. An electric wave reflector device including in combination, a cup shaped member having a concave reflecting surface and a convex back surface, an elongated heating element positioned adjacent said convex back surface and being substantially uniformly positioned over the area thereof, said heating element having first and second portions and control means for energizing said portions of said heating element, said control means including a thermal controlled switch for selectively energizing said first heating element portion in accordance with the temperature about said device and an auxiliary control for selectively energizing said second heating element portion after said thermal controlled switch has been operated.

8. An electric wave reflector device including in combination, a cup shaped member having a concave reflecting surface and a convex back surface, an elongated heating element positioned adjacent said convex back surface, said elements being substantially uniformly positioned over the area of said convex back surface, said heating element including first and second portions and control means for energizing said heating element portions, said control means including a first control circuit for selectively energizing said first heating element portion in accordance with the temperature about said device and a second control for selectively energizing said second heating element portion in response to a condition of said reflecting surface which affects the reflection characteristic thereof.

9. An electric wave reflector device including in combination, a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, duct means associated with said member for draining water therefrom, an elongated heating element positioned adjacent said convex back surface, said heating element including first and second portions with said first portion having a section thereof extending in said duct means, and control means for energizing said heating element portions, said control means including a thermal controlled switch for energizing said first heating element portion in accordance with the temperature about said device and an auxiliary control for selectively energizing said second heating element portion after said first heating element portion has been energized in response to a condition of said reflecting surface which affects the reflection characteristics thereof.

10. An electric wave reflector system including in combination, a cup shaped member having a concave reflecting surface and a convex back surface, an elongated heating element positioned adjacent said convex back surface and being substantially uniformly positioned over the area thereof, said heating element including first and second portions, and control means for energizing said heating element portions, said control means including a first thermal controlled switch for selectively energizing said first heating element portion in accordance with the temperature about said device and a second thermal controlled switch for selectively energizing said second heating element portion in accordance with the temperature of said reflecting surface.

11. An electric wave reflector system including in combination, a cup shaped member having a concave reflecting surface and a convex back sur face and including means for draining moisture from said concave reflecting surface, a heating element positioned adjacent said convex back surface for heating said cup shaped member and preventing the collection of ice and snow on said reflecting surface, said heating element including first and second portions with said first portion including a part for heating said draining means,

and control means for energizing said heating elements, said control means including a first control circuit for selectively energizing said first heating element portion in accordance with the temperature about said device and a second control circuit for selectively energizing said second heating element portion in accordance with the temperature of said reflecting surface.

12. An electric wave reflector system for reflecting waves to an antenna which is connected to a receiver having a portion producing a signal varying with the strength of the wave received by the antenna, said system including in combination, a cup shaped member having a concave reflecting surface and a convex back surface, an elongated heating element positioned adjacent said convex surface and being substantially uniforml positioned over the area thereof, said heating element including first and second portions, and control means for energizing said heating elements including a control circuit for selectively energizing said first heating element portion in accordance with the temperature about said device, and an auxiliary control circuit for selectively energizing said second heating element portion after said first heating element portion has been energized, said auxiliary control circuit including relay means coupled to said receiver portion providing an open circuit when the signal therein exceeds a predetermined value and providing a closed circuit when the signal therein falls below said predetermined value, so that said second h ating element portion is energized when the signal in said receiver portion falls below said predetermined value.

13. An electric wave reflector system for reecting waves ta an antenna which is connected to a receiver having a portion producing a signal varying with the strength of the wave received by the antenna, said system including in combination, an upwardly extending cup shaped member having a concave reflecting surface and a convex back surface and including means for draining moisture from said concave reflecting surface. an elongated heating element including first and second portions positioned adjacent said convex surface for heating said cup shaped memher, said first heating element portion including a part for heating said draining means, and control means for energizing said heating elements including a thermal controlled switch for energizing said first heating element portion in accordance with the temperature about said device, and auxiliary switching means for selectively energizing said second heating element portion, said auxiliary switching means being coupled to said receiver portion and providing an open circuit when the signal therein exceeds a predetermined value and a closed circuit when the signal therein falls below said predetermined value.

14. An electric wave reflector device adapted to be installed out of doors including in combination, a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, said cup shaped member including means for draining water therefrom, an elongated heating element positioned adjacent said convex back surface and being substantiall uniformly positioned over the area thereof, said heating element including a portion for heating said draining means, and control means for energizing said heating element including a thermal controlled heating unit for heating an exposed surface portion in accordance with the temperature about said device, and a control circuit including spaced electrodes positioned to receive therebetween water drained from said surface portion, to form a closed circuit for energizing said heating element.

15. An electric wave reflector device adapted to be installed out of doors including in combination a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, said cup shaped member having an opening therein and duct means connected thereto for draining water therefrom, an elongated heating element positioned adjacent said convex surface for preventing the collection of ice and snow on said reflecting surface, said heating element having a first portion positioned adjacent said opening and extending along said duct means and a second portion, and control means for energizing said heating elements including a first control circuit for selectively energizing said first heating element portion in accordance with the temperature about said device, and an auxiliary control circuit for selectively energizing said second heating element portion after said first heating element has been energized, said auxiliary control circuit including a container and spaced electrodes therein, said duct means directing water from said opening into said container in contact with said electrodes for closing the circuit therethrough and energizing said second heating element portion.

16. An electric wave reflector device adapted to be installed out of doors including in combination, a cup shaped member having an upwardly extending concave reflecting surface and a convex back surface, said cup shaped member including means for draining water therefrom, an elongated heating element positioned adjacent said convex back surface and being substantially uniformly positioned over the area thereof and having a portion heating said draining means, and control means for energizing said heating element including means positioned adjacent said reflecting surface for detecting the presence of ice or snow.

17. An electric wave reflector system adapted to be installed out of doors including in combination, a cup shaped member having a concave reflecting surface and a convex back surface and including means for draining water from said concave reflecting surface, electric heating means positioned adjacent said convex back surface and adapted to heat said surface substantially uniformly over the area thereof, said heating means including a portion for heating said drain means, and temperature responsive means for controlling the energization of said heating means.

References Cited in the file of this patent UNITED STATES PATENTS