GB2184605A

GB2184605A - Microwave antenna structure

Info

Publication number: GB2184605A
Application number: GB08531805A
Authority: GB
Inventors: Peter Bradsell
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1985-12-24
Filing date: 1985-12-24
Publication date: 1987-06-24
Also published as: GB8531805D0

Abstract

A microwave antenna structure comprises a plurality of stacked dielectric substrates 1, each substrate being arranged to carry a printed circuit conductor 2, 3. As shown the combination acts to define the dipoles 2 and parasitic elements 3 of a Yagi-Uda array whereby energy may be radiated in the direction of the arrow 4. Log-periodic and multi-element structures are envisaged. In order to provide a progressive match between the dielectric constant of the stack and air, a surface coating may be provided or the substrates may have graded dielectric constants. The conductors may have graded lengths. <IMAGE>

Description

SPECIFICATION Microwave Antenna Structure The invention relates to a microwave antenna structure.

In the provision of a dipole aerial for microwave communications, there is a need to improve the aerial gain and to have a better control if possible over the directivity of the radiated signal output. It would be useful to improve directivity in a way that would be relatively inexpensive to build and would be repeatable in use and, in addition, which would avoid the need to use a lens to direct the radiated signal.

The present invention was devised to provide an improved antenna structure that was capable of being constructed in an inexpensive and robust manner.

According to the invention, there is provided a microwave antenna structure comprising a plurality of stacked dielectric substrates, each substrate being arranged to carry a printed circuit conductor, so as in combination to define the dipoles and parasitic elements of an aerial array.

In one embodiment, at least one of the substrates carries a surface coating effective to afford a progressive match between the dielectric constant of the substrate material and air. The different substrates of the stack may have differing dielectric constants, the arrangement being effective to afford a progressive match between the dielectric constants of the materials of the substrate stack and air.

In a further embodiment, each printed circuit conductor along the body of the stack may have a resonant length which is graded along the length of the stack so as to afford a progressive match between the material of the substrate stack and air.

By way of example, some embodiments of the invention will now be described with reference to the accompanying drawing, in which: Figure 1 shows a microwave antenna structure having a stack of dielectric sheets which are depicted in an exploded view, and Figure 2 is a different antenna structure forming a multi-element array.

Figure 1 shows an antenna structure which had been constructed from a stack of dielectric substrates. Each substrate had been formed from a slice 1 of a high dielectric constant material and for clarity in the drawing, only three of the slices have been shown in full. The slice 1 at the left hand end of the stack carried a printed aerial dipole 2 pattern on its surface. The next slice along the stack carried a printed aerial parasitic element 3. The remaining slices of the stack also carried aerial parasitic elements 3.

When the stack of substrates was clamped together with the slices 1 in close contact with one another, the complete stack formed a microwave antenna structure effective to radiate a flow of microwave power in the direction indicated by the arrow 4.

The resulting stack of dielectric slices, with printed parasitic elements formed a Yagi aerial array. If required, alternative aerial constructions might be used such as the log-periodic (which would need electrical connections to be made between the printed areas on the dielectric slices) or polyrod antennas.

After assembly of the stack, the surface was coated with a 'blooming' layer of suitable material to improve the dielectric match between the material of the dielectric slices and air.

Figure 2 shows how the microwave antenna structure of Figure 1 might be extended to form a multielement array. The array comprised a stack of dielectric slices 5, the lowermost slice of which carried an arrangement of aerial radiating elements 6 on its lower side. The slice above this carried parasitic aerial elements 7 located on its lower side and similar slices 5 carrying parasitic elements 7 were positioned above this.

As depicted in the drawing, the stack of slices carried radiating and parasitic aerial elements which made up six sets of aerial arrays. It will be clear that in a different embodiment, a multielement aerial array could be made up with more or less than this number of elements.

The foregoing description of embodiments of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, it is clear that where the antenna structure has been described as being for use as a transmitting aerial it could equally be put into use as a receiving aerial structure. Although the antenna structure has been stated to have good directional properties, in special circumstances it might still be necessary to use a lens to attain closer control over the directivity of the output.

1. A microwave antenna structure, comprising a plurality of stacked dielectric substrates, each substrate being arranged to carry a printed circuit conductor, so as in combination to define the dipoles and parasitic elements of an aerial array.

2. An antenna structure as claimed in Claim 1, in which at least one of the said substrates carries a surface coating effective to afford a progressive match between the dielectric constant of the substrate material and air.

3. An antenna structure as claimed in Claim 1, in which different substrates of the stack have differing dielectric constants, the arrangement being effective to afford a progressive match between the dielectric constant of the substrate material and air.

4. An antenna structure as claimed in Claim 1, in which each printed circuit conductor along the body of the stack has a resonant length which is graded along the length of the stack so as to afford a progressive match between the material of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Microwave Antenna Structure The invention relates to a microwave antenna structure. In the provision of a dipole aerial for microwave communications, there is a need to improve the aerial gain and to have a better control if possible over the directivity of the radiated signal output. It would be useful to improve directivity in a way that would be relatively inexpensive to build and would be repeatable in use and, in addition, which would avoid the need to use a lens to direct the radiated signal. The present invention was devised to provide an improved antenna structure that was capable of being constructed in an inexpensive and robust manner. According to the invention, there is provided a microwave antenna structure comprising a plurality of stacked dielectric substrates, each substrate being arranged to carry a printed circuit conductor, so as in combination to define the dipoles and parasitic elements of an aerial array. In one embodiment, at least one of the substrates carries a surface coating effective to afford a progressive match between the dielectric constant of the substrate material and air. The different substrates of the stack may have differing dielectric constants, the arrangement being effective to afford a progressive match between the dielectric constants of the materials of the substrate stack and air. In a further embodiment, each printed circuit conductor along the body of the stack may have a resonant length which is graded along the length of the stack so as to afford a progressive match between the material of the substrate stack and air. By way of example, some embodiments of the invention will now be described with reference to the accompanying drawing, in which: Figure 1 shows a microwave antenna structure having a stack of dielectric sheets which are depicted in an exploded view, and Figure 2 is a different antenna structure forming a multi-element array. Figure 1 shows an antenna structure which had been constructed from a stack of dielectric substrates. Each substrate had been formed from a slice 1 of a high dielectric constant material and for clarity in the drawing, only three of the slices have been shown in full. The slice 1 at the left hand end of the stack carried a printed aerial dipole 2 pattern on its surface. The next slice along the stack carried a printed aerial parasitic element 3. The remaining slices of the stack also carried aerial parasitic elements 3. When the stack of substrates was clamped together with the slices 1 in close contact with one another, the complete stack formed a microwave antenna structure effective to radiate a flow of microwave power in the direction indicated by the arrow 4. The resulting stack of dielectric slices, with printed parasitic elements formed a Yagi aerial array. If required, alternative aerial constructions might be used such as the log-periodic (which would need electrical connections to be made between the printed areas on the dielectric slices) or polyrod antennas. After assembly of the stack, the surface was coated with a 'blooming' layer of suitable material to improve the dielectric match between the material of the dielectric slices and air. Figure 2 shows how the microwave antenna structure of Figure 1 might be extended to form a multielement array. The array comprised a stack of dielectric slices 5, the lowermost slice of which carried an arrangement of aerial radiating elements 6 on its lower side. The slice above this carried parasitic aerial elements 7 located on its lower side and similar slices 5 carrying parasitic elements 7 were positioned above this. As depicted in the drawing, the stack of slices carried radiating and parasitic aerial elements which made up six sets of aerial arrays. It will be clear that in a different embodiment, a multielement aerial array could be made up with more or less than this number of elements. The foregoing description of embodiments of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, it is clear that where the antenna structure has been described as being for use as a transmitting aerial it could equally be put into use as a receiving aerial structure. Although the antenna structure has been stated to have good directional properties, in special circumstances it might still be necessary to use a lens to attain closer control over the directivity of the output. CLAIMS

4. An antenna structure as claimed in Claim 1, in which each printed circuit conductor along the body of the stack has a resonant length which is graded along the length of the stack so as to afford a progressive match between the material of the substrate stack and air.

5. A microwave antenna structure, substantially as hereinbefore described with reference to Figure 1 or 2 of the accompanying drawing.