JPH0326101A - Flash-mounting antenna - Google Patents

Abstract

PURPOSE: To provide an antenna having an effective range of wide frequency band width and a wide angle which matches the shape of a non-planar surface by providing two opposing tapered wall parts in a radiation cavity filled with a dielectric, and allowing the upper surface of this antenna to flow the shape of a surface to which the antenna is attached. CONSTITUTION: A coaxial cable is put through a feeding part 28, and the central conductor is connected with a microstrip horn 16. A dielectric slab 18 is provided with a taper face 34 following the shape of a tapered surface 32 of a base part 12 and a second tapered surface 30 following the shape of a tapered surface in a top part 20, and the top part 20 is fixed to the base part, and a radiation cavity 26 is formed. Thus, an antenna 10 can be placed in the hollow of a planar surface, and the same planar surface can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates generally to antennas, and more particularly to horn antennas.

In many radio frequency systems, limited space is available for antennas. However, from the beginning, antennas designed for small spaces must meet various operational requirements. However, existing antennas may not meet the size and operational requirements of the system.

One common dimensional constraint in airborne systems is that the antenna does not protrude beyond the aircraft carrying the RF system. That is, a "flush mount" antenna is required.

Various types of flush mount antennas are known. For example, annular slot antenna, cavity inductor,
Strip inductors, patch antennas, surface wave antennas and slot antennas can all be mounted horizontally (at the same height) as the surface. However, these types of antennas generally have narrow frequency bandwidths.

These antennas are therefore well suited for systems requiring 3:1 frequency bandwidth.

Printed log periodic die balls can be cavity supported and flush mounted. Although this antenna can be configured with a 3:l frequency bandwidth, it cannot be made small enough to meet the size constraints of certain applications.

SUMMARY OF THE INVENTION It is an object of the invention to provide an antenna that can be mounted flush with a surface.

It is also an object of this invention to provide an antenna that can conform to the shape of a non-planar surface.

It is a further object of the invention to provide an antenna with wide frequency bandwidth and wide angular coverage.

It is a further object of the invention to provide an antenna that fits into a relatively small volume.

It is a further object of the present invention to provide an antenna that can be designed to obtain an end-fire or near-broadside radiation pattern over a 3:1 frequency bandwidth.

The above and other objects are achieved by an antenna having a radiating cavity filled with a dielectric material. The radiation cavity has two opposing tapered walls. Radio frequency energy is delivered to the radiating cavity via a microstrip horn. The dielectric in the radiating cavity follows the shape of the top surface of the antenna. The top surface of the antenna then follows the shape of the surface to which it is mounted.

Embodiment FIG. 1 shows an exploded view of an antenna 10 configured according to the invention. The antenna 10 has a base 12 and a top 20 formed from conductive metal.

The dielectric plate 14 is fixed by, for example, adhesive or mounting screws.
It is attached to the base 12. The relative dielectric constant of the plate 14 is εr8. A microstrip horn 16 is attached to the top surface (not numbered) of the dielectric plate 14 in a known manner.
It is graphically illustrated in . In operation, base 12 is at ground potential and forms the second conductor of the microstrip.

A signal is applied to the microstrip ho/l6 through the power supply 28. For example, a coaxial cable (not shown) could be routed through feed 28 and its center conductor connected to microstrip horn 16.

A dielectric slab 18 with a relative dielectric constant ε7 is also attached to the base 12, for example by gluing or capture by the top 20. The dielectric slab 18 has a microstrip horn, 34, which follows the shape of the microstrip horn, 32, of the base 12. The dielectric slab 18 has a top portion 2
microstrip horn, (element 5 of Figure 3)
0) a second microstrip horn following the shape of 30;
There is.

Top 20 is secured to base 12 by screws passing through threaded holes 22 and 24 or by any other convenient means, such as a proprietary epoxy. With the top 20 fixed to the base, a radiating cavity 26 is bottomed. The radiation cavity 26 is bounded at the bottom by the base 12.

Both sides of the radiation cavity 26 are connected to the tips 42A and 4 of the top portion 20.
It is bounded by the medial surface of 2B. The third side of the radiation cavity 26 is bounded by a microstrip horn, 50 (FIG. 3) on the top 20. The fourth side of the radiation cavity 26 includes a microstrip horn, 3
It is bounded by 2. Dielectric slab 18 therefore fills radiation cavity 26 .

The base 12, the top 20, and the dielectric slab 40 are arranged to form a coplanar top surface.

In particular, when the components of antenna 10 are assembled, top surfaces 36, 38, and 40 form a surface without discontinuities.

In FIG. 1, the surface is shown to be planar. The antenna 10 could therefore be placed in a recess in a planar surface to create a coplanar surface. However, the invention is not limited to planar coplanar surfaces.

FIG. 2 shows additional details of the antenna lO as would be seen by removing the top 20 and looking at the top of the antenna 10 (FIG. 1). Like reference numbers indicate like elements in all drawings. Figure 2
The structure has two axes and an angle ψA measured with respect to them.
Z are superimposed. The angle ψAZ indicates the azimuth direction with respect to the antenna 10.

FIG. 2 also shows various dimensions of the components in the antenna 10. The dielectric plate 14 has a width ti'B and a length Ls.
have. Dielectric slab 18 has a width lV. Top surface 40 has a length L.

The total length of the dielectric plate 14 and the dielectric slab l8 is LT.

FIG. 3 shows a cross-sectional view of antenna 10 taken along line 3--3 of FIG. Details of the top 20 can be seen in FIG. At the top 20 is a microstrip horn 50 following the shape of the microstrip horn 30 of the dielectric slab 18 . Furthermore, a cavity 54 having a height HMC and an extended length LMc is formed above the microstrip horn l6 in the top portion 20. Inside the cavity 54 is an absorber 52, which is any known material that absorbs radio frequency energy.

The cavity 54 and the absorber 52 are the microstrip horn 1
This provides a load on the microstrip horn 16 that is very similar to the load that would exist if 6 were in free space. Additionally, absorber 52 is selected to dampen resonance in cavity 54 and absorb a minimum amount of RF energy.

The top 20 is in electrical contact with the dielectric horn l6.

Electrically, microstrip horn 50 is the same as an extension of microstrip horn 716. The microstrip horn, 50, therefore emits an electrical signal that passes through the microstrip horn 16 and into the radiation cavity 26.

Various other dimensions of antenna 10 are shown in FIG.

Dielectric slab l8 is shown to have a height Hc. The bottom surface of dielectric slab 18, excluding microstrip horn 34, is shown to have a length LB.

Dielectric plate l4 is shown to have a height C. Further, the microstrip horn 50 has an angle αn with the base 12.
I was shown to make a . A microstrip horn, 32, is shown making an angle αf with the two axes.

Also shown is the angle θEL. The angle θEL defines the elevation direction with respect to the antenna 10.

When constructing an antenna in accordance with this invention, the various dimensions of the antenna are selected based on two primary considerations. First of all, the dimensions are the center frequency of the antenna's operation! . wavelength λ. selected based on. Additionally, certain parameters are selected such that antenna 10 projects a beam at the desired azimuth and elevation angles.

EXAMPLE ■ As an example, Table I shows selected values for various parameters of the antenna lO. FIG. 4A shows the azimuthal beam directivity diagram that results when an antenna with the values of Table I is operated at a frequency equal to 0.9177. The horizontal axis of the plot indicates azimuth. The vertical axis is θ
Figure 2 shows the gain for an isotropically radiating antenna measured in the far field at an azimuth angle with an elevation angle of °.

Figure 4B shows that the antenna with the values in Table I is 0.917f0.
FIG. 2 shows an elevational directivity diagram when operated at zero frequency. The horizontal axis of the plot shows the elevation angle. Vertical axis is 0°
Figure 2 shows the gain for an isotropically radiating antenna measured in the far field at an azimuth and elevation angle of .

Table ■ 1.17λ.

0.5lλ0 0.6lλ0 0.31λ.

0.03λ0 0.19λ.

0.18λ0 0.51λ.

0.39λ.

0.36λ.

1.78λ.

40.4° l4, 9° 3.0 2.22 It has a beamwidth of 3 dB in the 60° azimuth plane as seen by A. In FIG. 4B, line 400B indicates that antenna 10 has a beamwidth of 3 dB in an elevation plane of approximately 60°. The beam center in the elevation plane occurs at an elevation of approximately 20'.

The performance of antenna 10 can be modified by changing antenna configuration parameters. If the parameter L is shortened, the 3 dB beamwidth in the elevation plane increases. Furthermore, the beams become more closely centered with a θKLo value equal to 90°. In other words, the antenna has near-broadside antenna directivity. Conversely, increasing L tends to focus the beam in the elevation plane closer to values of θKL near zero. In other words, the antenna has an end-fire antenna pattern.

Furthermore, @W of the dielectric slab l8 can be varied.

Increasing the value of V tends to reduce the 3 dB beamwidth in the azimuthal plane. FIG. 5 shows an alternative embodiment of the antenna. Antenna 10,4 houses an outwardly tapered dielectric slab 10/f away from microstrip horn 16 (not shown). Increasing the width of the taper tends to reduce the 3 dB beamwidth in the azimuthal direction.

Examples ■ A near hemispherical elevation range extending from θEL=O° to θ)11=170° can be achieved by varying some of the parameters shown in Table I.

L=0.53λ. and ε7=6, (θKL,=20
degree and θEL=160°) will result in an 8 bB undropped gain change and a front-to-back ratio of less than 3.5 dB.

An antenna configured with this example value has an impedance matched peak gain of greater than 2 dB4 and a 62°
It is possible to achieve a half-power beamwidth of more than 100%.

Figure 5 shows how the antenna can be mounted flush to the surface. The antennas 10,4 are placed in recesses in the surface 56. In this case the surface 56 is curved. Top surface 36A
, 38A and 40A are formed to follow the shape of the surface 560.

Although embodiments of the invention have been described, it will be apparent to those skilled in the art that various modifications to the disclosed embodiments may be made. For example, although the antenna has been described only in connection with transmitting signals, it could also be used to receive signals.

Additionally, although the antenna has been shown to be mounted flush with a planar or curved surface, it could easily be extended to conform to the shape of any shaped surface. This recessed (flush mount) antenna could be arranged to create a recessed array antenna.

[Brief explanation of drawings]

FIG. 1 shows an exploded view of an antenna constructed in accordance with the present invention. FIG. 2 is a top view of the antenna of FIG. 1 with top portion 20 removed. FIG. 3 is a cross-sectional view of the antenna of FIG. 1 taken along line 3--3. FIG. 4A is a plot showing the azimuthal beam directivity diagram of the antenna of FIG. FIG. 4B is a plot showing the elevation beam directivity diagram of the antenna of FIG. Figure 5 shows another embodiment of the invention attached to an object with a curved surface. (4 other people)

Claims (1)

Claims: 1. a) a conductive structure having an upper surface that conforms to the shape of the surface and in which a cavity is formed; b) a dielectric disposed within the cavity; and c) a conductive structure for discharging radio frequency energy. a surface and horizontally mounted antenna comprising means for coupling to the torso; 2. The antenna of claim 1, wherein the means for coupling radio frequency energy includes a microstrip horn. 3. The antenna of claim 2, wherein the microstrip horn is separated from the top surface by a second cavity. 4. The antenna of claim 3 additionally comprising a radio frequency energy absorbing material disposed in the second cavity. 5. The antenna of claim 1, wherein the cavity is bounded by a first tapered surface of the structure. 6. The antenna of claim 5, wherein the cavity is bounded by a second tapered surface of the structure opposite the first tapered surface. 7. The antenna of claim 6, wherein the means for coupling radio frequency energy includes a microstrip horn electrically connected to the second tapered surface. 8. The antenna of claim 5, wherein the dielectric has a first tapered surface that follows the shape of the first tapered surface of the structure. 9. The antenna of claim 8, wherein the dielectric has a second tapered surface that follows the shape of the second tapered surface of the structure. 10. The antenna of claim 1, wherein the antenna is mounted horizontally to a planar surface. 11. The antenna of claim 1, wherein the antenna is mounted horizontally to the curved surface. 12, a) a base having a top surface and a tapered surface, and b)
An antenna comprising: i) a top surface disposed horizontally with the top surface of the base; and ii) a top having two tips, each tip having an edge that follows the shape of the tapered surface of the base. 13. a) a dielectric having: i) a first surface following the shape of the tapered surface of the base; and ii) second and third surfaces, each surface following the shape of the surface of one of the tips. 13. The antenna of claim 12, additionally comprising a slab. 14, the base has a flat surface adjacent to the tapered surface;
The antenna of claim 13. 15. The antenna of claim 14, further comprising: 15. a) a dielectric plate attached to the flat surface of the base. 16. The antenna of claim 15, additionally comprising: 16. a) a microstrip horn formed on a dielectric plate. 17. The antenna of claim 16, wherein the top has a tapered surface adjacent to and disposed between the two tips. 18. The antenna of claim 17, wherein the dielectric slab has a fourth surface that follows the shape of the top tapered surface.