GB2131232A

GB2131232A - Microstrip antenna and method of manufacture thereof

Info

Publication number: GB2131232A
Application number: GB08227490A
Authority: GB
Inventors: G Wilson
Original assignee: Rogers Corp
Current assignee: Rogers Corp
Priority date: 1982-09-27
Filing date: 1982-09-27
Publication date: 1984-06-13
Also published as: DE3334944A1; FR2533764A1; JPS5989006A; FR2533764B1; GB2131232B

Abstract

A microstrip antenna 10 is presented having the construction of a circuit pattern 20 formed on a polymeric film 18, a foam or honey comb material 16 serving both as a dielectric and support for the circuit pattern, and a carrier or container 12 which serves both as a ground plane 14 and as a carrier or container to house the dielectric 16 and the circuit pattern 20, the assembly all being bonded together to form a rigid structure. <IMAGE>

Description

SPECIFICATION Microstrip antenna and method of manufacture thereof This invention relates to the field of microstrip or stripline antennas. More particularly, this invention relates to a planar microstrip antenna for use primarily as a receiver antenna for receiving broadcasted microwave signals. Whilethis invention may have general utility in microwave transmission or reception, the invention will be described in the environment of wheat is known as a TV receive only (TVRO) antenna in a direct satellite broadcasting (DSB) system. However, itwill be understood thatthe invention may have general utility as eithera receiver antenna ortransmitter antenna in microwave communication systems.

With the growing potential for satellite transmission of microwave signalsforTV broadcasting and receiving systems, there is an increasing need for a reliable, durable and reasonably inexpensive antenna for household and other commercial use forth reception of satellite transmitted microwave signals. Parabolic antennas aretraditionally used intransmissionsys- temsofthistype, butthey present many problemsfor an effective and commercially viable TV microwave reception system. Among other problems, parabolic antennas are relatively expensive, and are not suffi cientlystable in low winds to guarantee consisent signal reception and hence picture quality.Thus, they are not particularly suitable for everyday use in home or other commercial TV reception systems.

Stripline or microstrip antannas for microwave transmission or reception are known in the art. Such antannes are shown,for example, in GB-PS 1,529,361, US-PS 3,995,277, US-PS 3,987,455 and US-PS 3,803,623. In all of these prior patents the antenna structure consists of a laminate structure of a dielectric material with an electrically conductive ground plane on one surface of the dielectric and a stripline or microstrip pattern on the othersurface ofthe dielectric. It is well known thatthe properties ofthe dielectric material are important to the performance ofthe antenna, especially the properties of dielectric constantand dissipation factor.Those considerations make these conventional microstrip antennas practicably unsuitable forTVRO antennas because they severely limitthe choice of suitable dielectric materials to very expensive materials, especially when one considers that a TVRO antenna must be relatively large, such as on the order of a square structure 76cm to 102cm on each side or a circular structure having a diameter of 76cm to 102cm. Also, since TVRO antennas will be used outdoors, they must be weatherized to protect them from exposure to the elements. This is particularly so with the conventional prior art stripline or microstrip antennas where the circuit pattern and the ground plane are on the exterior ofthe dielectric surfaces. This weatherizing req uire mentfurtheraddstothe economic and practical problems of using prior art microstrip antennas in TVRO systems.

The combined requirements of electrical properties and weathering resistance limitthe choice of dielectric materials that may be effectively employed in a practicable TVRO antenna if one were constructed in accordance with conventional prior art techniques.

Low loss ceramics would offer good performance for the dielectric materials, but the cost and limited size of ceramic substrates would rule them out. PTFE (polytetrafluoroethylene) based substrates or subs trates based o n on otherfluoropolymerswould also be acceptable choices from the standpoint of dielectric properties, but the cost of such substrates would make them unsuitable for home and general commercial use. Thus, because ofthe economic and other practical drawbacks, the art has not developed a commercially practicable and acceptable planarTVRO antenna.

The above-discussed and other problems of the prior art are overcome or reduced by the antenna of the present invention. In accordance with the present invention there is provided a microstrip antenna comprising a polymeric film means having a circuit pattern on one surface thereof, a layer of dielectric material supporting said polymeric film means with said circuit pattern on the surface of said polymeric film means facing said layer, and carrier means including a ground plane, for carrying said layer of dielectric material. The components may be assembled and bonded together to form a rigid assembly which constitutes a planarTVRO antenna.

Viewed from another aspect the invention provides a method of making a microstrip antenna including the step offorming a laminate film of a sheet of polymeric material and a microwave circuit pattern, forming a carrier means having a metal surface suitable to serve as a ground plane, locating a dielectric material on the carrier means on said metal surface, locating said sheet of polymeric material on said dielectric material with the circuit pattern facing said dielectric material, and bonding said dielectric material to said sheet of polymericfilm material and to said carrier means.

Thus, a ground plane may be defined by the base surface of a tray or other carrier, the tray or carrier either being metal or a metal coated reinforced resin material. The microstrip circuit pattern may consist of a conductive pattern formed on a surface of a polymeric film in accordance with any standard printed circuittechnique. The dielectric may be positioned on the ground plane and may be bonded to the ground plane. The dielectric may be either a rigid foam material, fused powder, a honeycomb material or any other self-supporting dielectric material. The microstrip circuit pattern may be bonded to the dielectric, with the circuit pattern facing the ground plane and the polymeric film serving as a protective cover to seal the unit and provide protection against the weather.The microstrip antenna in a preferred embodimentthus consists of the ground plane, which is part ofthe carrier tray, the dielectric bonded to the carrier and the circuit pattern bonded to the dielectric.

The protective cover formed by the polymeric sheet of the circuit pattern significantly increases the life expectancy of this TVRO antenna.

In orderthatthe invention may be readily understood certain embodimentsthereofwill now be described by way of example with referencetothe accompanying drawings in which: FIGURE lisa blockflow diagram of the method of the present invention, FIGURE 2 is a partial sectional elevation view of a planar microwave antenna in accordance with the present invention, and FIGURE 3 is a viewsimilarto FIGURE 2 showing a second embodiment of a planarTVRO antenna of the present invention.

Referring first to FIGURE 2, one embodiment of a planarTVRO antenna in accordance with the present invention is shown. The planar antenna 10 has a lower tray 12 with base surface 14. Base surface 14 constitutes the ground plane of a microwave antenna.

Tray 12 is either a metal tray, such as aluminium, or it may be a moulded unit, such asfibreglass reinforced resin, with surface 14 being metallized. Tray 12 contains a dielectric material 16, which in the FIGURE 2 embodiment is a foam material (either a self ortwo partfoaming material) foamed in place and adhering to the innersurfaces of tray 12. Foam 16 defines the dielectric media forthe microwave antenna. Foam 16 will typically have a dielectricconstantoffrom about 1 to about4and a losstangent in the range of about 0.001 to 0.01.Thefoam may also be formed as a foam in a separate operation, trimmed to size and adhered to the tray. The dielectric material may also be a fused powder or equivalent. Alternatively the dielectric may be a synthetic resinlg lass mixture, including glass microbubbles.

Dielectric material 16 is covered by a sheet 18 of polymericfilm on which is defined a microwave circuit pattern 20. Polymericfilm 18 and circuit pattern 20 may be formed by any conventional printed circuit technique, and they are bonded to dielectric material 16 to form a rigid assembly. As can be seen in FIGURE 2, tray 12 forms a housing which contains the other components (i.e., the dielectric material and the circuit pattern ofthe antenna). Thus, a fully contained integral structure is formed which is rigid. In addition, the polymeric film 18 serves as a protective layer to protect the dielectric pattern 20 from weathering.

Appropriate electrical connections (not shown) will be connected to the ground plane and circuit pattern for operation ofthe TVRO antenna.

FortheTVRO antenna application primarily evisioned forthe present invention, the structure will be relatively large, such as on the order of a square or rectangle 76cm to 102cm on each sideora circle 76cm to 102cm in diameter. Itis importantfor proper signal reception and the maintaining of consistent picture quality in the television setto which the antenna is connected thatthe spatial relationship between electronic components remain constant. Accordingly,the dimensionally stable and rigid nature ofthe construction ofthe present invention is of particular importance in achieving that objective. Tray 12 is either metal or a rigid polymeric material, preferably a fibre reinforced material, with a metallized inner surface.

Foam 16,when properly cured, is rigid and dimensionally stable. Circuit pattern 20 and polymeric sheet 18, althoughflexiblewhen unsupported, are firmly and rigidly supported on the upper surface of foam 16.

Thus, the entire assmbly becomes rigid and dimensionally stable.

The microstrip pattern 20 is designed and selected so that it would generate a plane wave if it were a microwave transmitter. Since microwave transmitters and receivers are reciprocal, circuit pattern 20 will receive a plane wave from a specific direction, such as an equatorial or geostationary satellite. Polymeric sheet 18 should, ideally, have a thickness of approximately 1/2 wavelength of the signal being received (12-14 GHzforthe stationary OTS satellite now in operation) however,that ideal configuration may not be practical. Therefore, sheet 18 may be on the order of between 0.0025cm and 0.25cm thick, which will result in some reflective losses but will still result in an acceptable antenna unit.

The dielectric constant of foam 16should be maintained within an acceptable limit of between approximately 1 to 4 and should have a low loss factor of a loss tangent of 0.01 or less to be acceptable for use in the TVRO antenna ofthe present invention.

Referring nowto FIGURE 1, a block diag ram is shown ofthe process forforming the antenna of FIGURE 1. A laminate of a sheet of polymeric material and a metal coating are formed instep A and then etched in step B to form the radiator or microwave circuit pattern 18. Separately, and eithersimultaneously or at some selected time interval,tray 12 is formed in step C. Tray 2 is then filled with a suitable dielectric material, such as in the form of a curable powder orfoam material.The tray may be filled with a dielectric material to a level slightly above the top of thetray.Thepolymericfilm laminatewiththecircuit pattern formed thereon is then placed on top of the dielectric with the circuit pattern 20 face down, i.e., facing the base of tray 12 which serves as the ground plane. This occurs in step E. Next, in step F, the assembly is placed under a slight pressure so thatthe film 18 is maintained parallel to the base of tray 12.

While under pressure the composite assembly is heated to cure and cross linkthe dielectric, which then adheres to both the inner surfaces of the tray and to the polymericfilm to thereby seal the entire assembly.

Referring to FIGURE 3, a modified TVRO antenna is shown wherein a honeycombed material 22 is housed within tray 12 and serves as the supportforthe microwave circuit of film 18 and conductors 20. The honeycomb material has wall 24which define air spaces or cells 26. In the configuration of FIGURE 3, air in the cells 26 forms the primary dielectric material for the microwave antenna unit. Of course, the material from which the honeycomb structure is formed also serves as a part of the dielectric system, and hence the honeycomb material must have suitable dielectric constant and loss characteristics.

As can be seen from both the configurations of FIGURES 2 and 3, the dielectric material 16 and the honeycomb structure 22 serve as a supportforthe microwave circuit structure of film 18 and conductors 20 as well as the microstrip transmission media. Also, it will be seen thatthefilm 18 is not a component ofthe microwave circuit system per se; rather, it provides environmental protection forthe assembly as well as serving as a convenient way for defining the microwave circuit array.

From the foregoing description it will be recognized that a particularly effective, practical and economical planarTVRO antenna has been achieved bythe present invention. The antenna is dimentionally stable, and, hence, it may be mounted on the exterior of buildings, (such as roof houses or other similar structures) and it may be mounted in rotational structure for directional alignment without impairing the reception ofthetransmitted signal, and hence the consistency ofthe picture displyed on the TV screen to which the antenna isconnected.Aparticularlyimpor- tant and useful feature for outdoor antennae is that the antenna is protected from the weather by the overall unitary and sealed structure ofthe antenna; and the upperfilm 18 protects both the circuit pattern and dielectric from the effects of weather. Thus, the antenna will lastfor many years of outdoor use.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described byway of illustrations and not limitation.

Claims

1. A microstrip antenna comprising a polymeric film means having a circuit pattern on one surface thereof, a layer of dielectric material supporting said polymericfilm means with said circuit pattern on the surface of said polymeric film means facing said layer, and carrier means, including a ground plane, for carrying said layer of dielectric material.

2. A microstrip antenna according to claim 1 wherein said polymeric film means is bonded to said dielectric material, and said dielectric material is bonded to said carrier means.

3. A microstrip antenna according to claim 1 or2 wherein said carrier means is a tray which contains said dielectric material.

4. A microstrip antenna according to claim 4 wherein said tray has a base portion and sides, said ground plane being in said base portion.

5. A microstrip antenna according to claim 3 or4 wherein said tray is metallic.

6. A microstrip antenna according to claim 3 or4 wherein said tray is a rigid polymeric material with a metallized surface.

7. A microstrip antenna according to any of the preceding claims wherein said dielectric material has a dielectric constant of between approximately 1 and 4.

8. A microstrip antenna according to any of the preceding claims wherein said dielectric material has a loss tangent of 0.01 or less.

9. A microstrip antenna according to any of the preceding claims wherein said dielectric material is a honeycomb material and air in air cells of the honeycomb material.

10. A microwave antenna according to any ofthe preceding claims wherein said polymericfilm means is a sheet of material having a thickness of approximately 112 wavelength ofthe microwavesignalto be received by the antenna.

11. A microwave antenna according to any ofthe preceding claims wherein said polymeric film means is a sheet of material having a thickness between about 0.0025cm and 0.25cm.

12 A method of making a microstrip antenna including the step offorming a laminate film ofa sheet of polymeric material and a microwave circuit patter, forming a carrier means having a metal surface suitable to serve as a ground planer, locating a dielectric material on the carrier means on said metal surface, locating said sheet of polymeric material on said dielectric material with the circuit pattern facing said dielectric material, and bonding said dielectric material to said sheet of polymeric film material and to said carrier means.

13. A method according to claim 12 wherein said dielectric material is in the form of a curable powder or foam when located on said carrier means, and said step of bonding the dielectric material to the sheet of polymeric material and to the carrier means includes curing the powder or foam to form a rigid layer of dielectric material.

14. A method according to claim 13 wherein said carrier means is a tray having a base and sides, and the step of locating the dielectric material on the carrier means includes filling the tray with a curable powderorfoam.

15. A method according to claim 12 or 13 wherein said laminate film is maintained parallel to said carrier means during the curing of the dielectric material.

16. A microstrip antenna substantially as hereinbefore described with reference to the accompanying drawings.

17. A method of making a microstripantenna substantially as hereinbefore described with reference to the accompanying drawings.