US2712603A

US2712603A - Aircraft receiving antennae

Info

Publication number: US2712603A
Application number: US224870A
Authority: US
Inventors: Bridges Donald Edward; O'brien William Joseph
Original assignee: Decca Record Co Ltd
Current assignee: Decca Record Co Ltd
Priority date: 1950-05-10
Filing date: 1951-05-07
Publication date: 1955-07-05
Anticipated expiration: 1972-07-05
Also published as: GB682274A

Description

y 5, 1955 D. E. BRIDGES ET AL 2,712,603

AIRCRAFT RECEIVING ANTENNAE Filed May 7, 1951 19 REEF? fl 1:1: \/H F 15 17 I Rm 379 2g lA/Vf/VMRS D. BRIDGES W. J. O'BRIEN By: h/Llluhnow +797 A TTORIIE United States Patent Office 2,712,603 Patented July 5, 1955 2,112,603 AIRCRAFT RECEIVING ANTENNAE Donald Edward Bridges and William Joseph. QBrien, London, England, assignors to The Decca Record Company Limited, London, England, a British company This invention relates to radio receiving antennae for aircraft and more: particularly to antennae, having dimensions and effective height small compared with the wavelength of the signals to be received.

' Particularly when receiving relatively low frequency signals, if an exposed metal antenna is used considerable noise is experienced due to precipitation static i. e., due to charged particles of rain, dust or the like striking the antenna. A thin skin of insulation applied to an antenna gives no improvement although, as the thickness of the insulation (or the distance between the insulation and the antenna) is increased, the static level is decreased. The size of an insulated antenna which would substantially eliminate static, however, is too great to make. such a system of practical value. These facts may be explained in the following manner: approaches the antenna, there is a transfer of charge which is, at first, very small. As the droplet reaches a distance from the antenna approximately ten times the diameter of the droplet, the rate of transfer increases appreciably although still remaining too slow to produce a component of radio frequency energy. However, when the droplet reaches the sparking distance, the transfer of energy is rapidly completed so producing a radio frequency dis- Iurbance in the receiver. The sparking distance is dependent to'a large degree on the radius of the antenna and thus the proportion of charge transferred by spark as distinct from slow proximity transfer will be greater for small radii antennae. An insulated wire is equivalent to an insulated series of concentric metallic rings concentric'with the wire. The increased diameter compared with uncovered wire tends to reduce the spark energy. Also the capacity between the surface of the insulation and the wire considered in combination with the effective antenna capacity acts as a capacity divider to reduce the amplitude of the disturbance at the receiver. Covering the antenna with insulation thus reduces precipitation static to a certain extent but as mentioned above it cannot be eliminated completely in this manner since the bulk of the insulation required would not be practicable. According to this invention, a non-directional receiving antenna for an aircraft comprises two adjacent conductors, one of which forms an antenna member and is adapted to be coupled to the input of a receiver and the second of which is so constructed and disposed in front of the antenna member as to form a shield member which, when connectedto the ground terminal of a receiver, either directly or through an impedance. of small value, shields the antenna member electrically from chargedv particles of dust, rain or the like impinging upon the antenna system. The earthy terminal of the receiver is that connected to the main metallic structure of the aircraft. Impedance of small value is to be understood to mean an impedance small compared with that of the capacity between the shielding conductor and the effective ground, i; e., the body of the aircraft.

By this arrangement, precipitation static may be sub- As a charged droplet of rain also caused by corona.

stantially reduced or eliminated. This may be explained in the following manner: A complete metallic screen around an antenna wire offers no advantage over an insulated antenna having the same outside diameter but it is well known that, if such a screen were grounded, both the received signal and the static will be suppressed. In an aircraft, however, practically all the droplets or particles striking an antenna or other object will impinge on the leading part. it thus becomes possible to provide a grounded shield for the antenna which is effective in preventing a charge transfer from charged rain droplets or other particles onto the receiving antenna without causing an undue loss in the strength of the received signal. Provided the antenna dimensions are small compared with the wavelength, for example, not greater than one-thirtieth of the wavelength, the antenna currents produce only negligible voltage drops in the antenna conductors compared with the received open circuit voltages and the system may be treated as a capacity network, the self and mutual inductances being negligible. Thus, if the screen is connected directly to the body of the aircraft, it can be. regarded as being wholly at ground potential and the screening is completed. Also provided the antenna dimensions are small compared with the wavelength, the system will be non-directional and free from phase diiferences between the received waves and the output signal.

In addition to precipitation static, radio interference is It is. well known that the static from corona discharge from an antenna may be prevented by using wick dischargers or by enclosing the antenna in insulating material. Thus, in one arrangement according to the invention, a non-directional receiving antenna comprises a hollow structure of insulating material adapted to surround an upright conducting element forming an antenna member and having a layer of conducting mate.- rial forming a shield member on the surface of or embedded within the leading portion of the insulating structure to shield the antenna member. electrically from charged particles of dust or rain impinging on the antenna system. In this construction the insulating material prevents static from corona discharge and may conveniently be shaped to form a streamlined antenna system. It-will be appreciated that a covering of insulating material over the shielding conductor does not affect its ability to shield the antenna electrically from charged particles.

According to another aspect of the invention, a non- I directional receiving antenna for an aircraft comprises a hollow mastof insulating material formed of streamlined section, an antenna member formed by a conducting element inside said mast and a shield member of conducting material disposed in front of the antenna member.

It is found that with a structure of conventional streamlined section, practically all the charged particles will strike the antenna structure in an are extending for about around the leading edge. .Thus in an arrangement in which. the hollow structure or mast is of streamlined section, the shield member may be arranged to extend around the leadingportion, of said hollow structure or mast for an arc of approximately 120. Conveniently the structure is closed at the top and the conducting material arranged to extend around the-top part of the mast.

The mast may be built of laminated insulating material in which case, the conducting material for the shield may conveniently be a sheet of metal disposed between two of the layers of the insulating material.

The conducting member inside the made in the form of a blade or plate.

According to a further feature of the invention, a radio mast is preferably receiving system for an aircraft comprises a non-directenna member directly to the input terminal and means coupling the shield member either directly or through a small resistance to the ground terminal.

It will be appreciated that there will be some loss in the antenna output compared with a simple antenna of similar dimensions and disposition because of the capacity of the antenna member to the shield member. This loss may be substantially reduced by providing a valve ampli fier, the antenna member and the shield member being connected to the input terminals of the amplifier which is arranged to have a low impedance output and to provide an output voltage of amplitude slightly less than the input voltage and in phase therewith, and by providing means for applying the amplifier output signal between the shield member and ground so as to reduce the effect of the capacity of the shield member to the antenna member, By ground is meant the main metallic structure of the air craft. If the output is applied between the shield member and ground, the capacity loading of the antenna member caused by its capacity to the shield member is reduced in a ratio which is equal to the reciprocal of the difference of the gain from unity.

Conveniently the valve amplifier may comprise a valve arranged as a cathode follower with the antenna member connected to the input grid of the valve and the shield member connected to the cathode of the valve.

If desired, the shield member may be used as an aerial for very high frequencies; this may be done by connecting, in the leads from the antenna and shield members to the receiver, impedance elements havin a high impedance to signals of very high frequency. it will readily be appreciated that with a large difference of frequencies. it is possible to isolate a low frequency receiver from the very high frequency signals in this Way without affecting the reception of the desired low frequency signals. As there is no ultra high frequency component in the rain static, the anti-static considerations, including the dimension limitations with regard to wavelength. do not apply at these frequencies.

The following is a description of a number of embodiments of the invention, reference being made to the accom-- panying drawings, in which:

Figure l is a diagrammatic representation of part of an aircraft showing the radio receiving system,

Figure 2 is a horizontal section through the antenna system of Figure 1 along the line 22, and

Figures 3 and 4 are diagrammatic representations of part of an aircraft showing modified forms of the radio receiving system of Figure 1.

Referring to Figure 1, there is shown, diagrammatically, part of the body of an aircraft which is adapted to travel in the direction of the arrow 11. Carried on the upper surface of the body 10 is a hollow mast 12 which is closed at the top and is of streamlined section. as is seen in Figure 2. This mast is formed of insulating material. and may. for example, be constructed of layers of glass fibre cloth bonded together with a suitable resin. Around the leading portion of the mast is arranged a conducting sheet 13, which forms the shield member and which extends through an arc of about 120 as seen in Figure 7.. This sheet 13 is shown, for clarity. as beinrr on the inner surface of the mast but when the latter is formed of laminated insulating material. the sheet 13 is conveniently disposed between two of the layers of in sulating material. The shield member 13 may be a sheet. of metal but conveniently is formed of metal gauze. Inside the mast is an antenna member comprising an upright blade 14 which extends rearwardly from about the rearward edge of the shield member 13.

In the arrangement illustrated in Figure l, the shield member 13 is connected directly to ground, that is, to the main metallic structure of the aircraft. The antenna member 14 is connected to the grid of an amplifier valve 15, the output of which is fed to a receiver indicated diagrammatically by the rectangle 16. With this antenna system, any charged particles of dust, rain or the like will strike the leading portion of the mast 12 in the region of the shield member 13, due to the forward motion of the aircraft. Since the shield member is grounded, the charges on the particles will not be transferred to the antenna and thus will not cause static noise in the receiver. As previously stated, the present invention relates to antenna systems having dimensions and an effective height small compared with the wavelength. The antenua currents produce, therefore, only negligible voltage drops in the antenna conductors. The shield member 13, therefore, can be regarded as being wholly at ground potcntial and the screening is effective over the whole length of the antenna. It will also be noted that the insulating mast 12 totally encloses the antenna and thus will prevent static interference from corona discharge.

In the modified form of receiving system illustrated in Figure 3, the antenna member 14 is connected, as in Fig ure 1, to the grid of the valve 15. The valve in Figure 2 is arranged as a cathode follower, the cathode being connected to ground through a bias resistance 17 and a load resistance 18. The shield member 13 is connected not to earth but to the junction of the resistors 17 and 18. The output voltage of the cathode follower developed across the resistance 18 is in phase with the input signal, that is the signal between the antenna member 14 and the shield member 13, but is of slightly smaller amplitude. This output signal is applied between the shield member 13 and ground and this reduces the effect of the capacity loading of the antenna member by its capacity to the shield member. As previously explained, the capacity loading is reduced in a ratio which is equal to the reciprocal of the difference of the gain from unity. The feed to the receiver 16 may be taken from the anode of the valve as before.

In Figure 4 there is illustrated a modification of the arrangement of Figure 3 in which provision is made for utilising the shield member 13 as a very high frequency antenna. For this purpose, inductances 19, 20 are connected in the leads from the shield member 13 and the antenna member 14 to the input circuit of the valve 15. These inductances are arranged to present a high impedance to the very high frequency signals but to have a low impedance for the relatively low frequency signals such as are to be received by the receiver 16. These

inductances

19, 20 therefore isolate the input circuit of the valve 15 from the very high frequency signals which can be fed through a condenser 21 to a very high he quency receiver indicated by the rectangle 22. It will be appreciated that since there are no very high frequency components in the rain static, anti-static considerations do not arise so far as the very high frequency system is concerned.

We claim:

I. A radio receiving system for an aircraft comprising two adjacent conductors one of which forms an antenna member and the second of which is so constructed and disposed around the front of and wholly forward of the rear edge of the antenna member as to form a shield member, a receiver having an input terminal and a ground terminal for receiving a signal applied between said input terminal and said ground terminal, means coupling said antenna member to said input terminal and an impedance of negligible value connecting said shield member to said ground terminal.

2. A radio receiving system for an aircraft comprising a hollow mast of insulating material formed of stream-lined section, a conducting element forming an antenna member inside said mast, a shield member of conducting material disposed around the front of and wholly forward of the rear edge of the antenna member, a receiver having an input terminal and a ground terminal for receiving a signal applied between said input terminal and said ground terminal, means coupling said antenna member to said input terminal and an impedance of negligible value connecting said shield member to said earthy terminal.

3 A radio receiving system for an aircraft according to claim 2 wherein saidshieldmember is embedded within the insulating material forming the leading portion of the hollow mast. I

4. A radioreceiving system for an aircraft according to claim 2 wherein said shield member extends around the leading portion of said hollow mast for an arc of approximately 120.

5. A non-directional radio receiving system for an aircraft comprising a hollow mast of laminated insulating material formed of stream-lined section, a conducting element forming an antenna member inside said mast, a shield member of conducting material disposed between two of the layers of said insulating material and extending around the front of and wholly forward of the rear edge of said mast, a receiver having an input terminal and a ground terminal for receiving a signal applied between said input terminal and said ground terminal, means coupling said antenna member to said input terminal and an impedance of negligible value connecting said shield member to said ground terminal.

6. A non-directional radio receiving system for an aircraft comprising a hollow mast of insulating material, a shield member of conducting material extending around the front part of said mast, a blade antenna member inside said mast and disposed so as to extend rearwardly from substantially the rear edges of the shield member, a receiver having an input terminal and a ground terminal for receiving a signal applied between said input terminal and said ground terminal of the receiver, means coupling said antenna member to said input terminal and an impedance of negligible value connecting said shield member to said ground terminal.

7. A non-directional radio receiving system for an aircraft comprising an upright antenna member, a conducting shield member extending around an arc in front of and wholly forward of the rear edge of the antenna member, a receiver having an input terminal and a ground terminal for receiving signals applied between said input and said ground terminals, a low impedance circuit connecting the antenna member to the input terminal and an impedance of negligible value connecting the shield member to the ground terminal.

8. A non-directional radio receiving system for an aircraft for receiving signals of a given frequency comprising an upright antenna member having dimensions not exceeding one thirtieth of the wavelength corresponding to said given frequency, tending around an arc in front of and wholly forward of the rear edge of the antenna member, a receiver having an input terminal and a ground terminal for receiving signals applied between said input and said ground terminals, a circuit having a low impedance at said given frequency connecting the antenna member to said input terminal and a circuit having a negligible impedance at said given frequency connecting the shield memberto said ground terminal.

9. A non-directional radio receiving system for an aircraft comprising an upright antenna member, a conducting shield member extending around an arc in front of said antenna member, said antenna member and said shield member being insulated from the aircraft structure, a valve amplifier having a pair of input terminals and arranged to have a low impedance output and to provide an output voltage of amplitude slightly less than and in phase with the input voltage across said input terminals, low impedance circuit means connecting the antenna member and the shield member respectively to the two input terminals and means for applying the amplifier output signal between the shield member and the aircraft structure.

10. A non-directional radio receiving system according to claim 9 wherein said valve amplifier comprises a a conducting shield member exvalve having an input grid and a cathode and arranged as a cathode follower with the antenna member con.- nected to the input grid and the shield member connected to the cathode.

11. A non-directional radio receiving antenna for an aircraft comprising a hollow mast of insulating material formed of stream-lined section, a conducting element forming an antenna member inside said mast and a shield member of conducting material grounded through an impedance of negligible value extending around the leading portion of said mast for an arc of less than 12. A non-directional radio receiving antenna according to claim 11 wherein said antenna member comprises an upright blade with its front edge to the rear of the rear edges of the shield member.

13. A non-directional radio receiving antenna for an aircraft comprising a hollow mast of laminated insulating material formed of stream-lined section, a conducting element forming an antenna member inside said mast and a shield member of conducting material disposed between two of the layers of said insulating material and extending around the front part only for an are less than 180 of said mast, said shield being grounded by an impedance of negligible value.

14. A radio receiving system for an aircraft comprising two adjacent upright conductors one of which forms an antenna member of length less than one-thirtieth of a wavelength of the signal to be received and the second of which is so constructed and disposed in front of the antenna member to form a shield member which shield member extends around the front of the antenna member and has its rear edge forward of the rear edge of the antenna member by a distance not greater than the thickness, in the front of rear direction, of the antenna member, a receiver having a pair of input terminals, and means connecting one of said terminals to said antenna member and the other of said terminals to said shield member, the impedance of said connecting means being of negligible value at the frequency of the signals to be received.

15. In an aircraft, a non-directional radio receiving system comprising an upright antenna conductor, a discharging surface forward of the antenna conductor, a capacity shielding conductor disposed between said surface and said antenna conductor such as to provide substantially perfect electrostatic shielding between said antenna conductor and said surface, which shielding conductor lies in an arc around the front of the antenna conductor of extent limited such that the antenna conductor to aircraft structure capacity is not reduced by a factor of greater than ten by the introduction of said shielding conductor, a receiver having a pair of input terminals and means connecting one of said terminals to said antenna conductor and the other of said terminals to said shielding conductor, the impedance of the connecting means being of negligible value at the frequency of the signals to be received.

16. In an aircraft, a radio receiving antenna system comprising an antenna conductor, a shielding conductor, and means connecting the shielding conductor to the aircraft structure, the shielding conductor extending in an are around the front of the antenna conductor and having a surface of sufiicient area to receive substantially all of rain droplets impinging on the antenna system, thereby providing a sparking surface for charged droplets, the orientation and dimensions of the two conductors being such that the capacity from said antenna conductor to the inner surface of said shielding conductor shall not ex ceed ten times the capacity from said antenna conductor to the aircraft structure and shall not be less than one hundred times the capacity from said antenna conductor to said sparking surface and said connecting means being arranged to have an impedance which is less than one hundredth of the impedance, at the operating frequency, of the capacity between the shielding member and aircraft structure.

References Cited in the file of this patent Bouvier et a1. .June 8, 1937 Carlson Sept. 17, 1940 Hefele Aug. 5, 1941 Harris Jan. 30, 1945 Busignies Feb. 5, 1946 Bennett Feb. 25, 1947