GB2097196A

GB2097196A - Millimeter Wave Arrays

Info

Publication number: GB2097196A
Application number: GB8112466A
Authority: GB
Inventors: Mehmet Tuncay Birand
Original assignee: ERA Patents Ltd
Current assignee: ERA Patents Ltd
Priority date: 1981-04-22
Filing date: 1981-04-22
Publication date: 1982-10-27
Also published as: GB2097196B

Abstract

A millimeter wave array comprises a conducting ground plane (1), a flat layer (2) of insulating material mounted on the ground plane, a linear dielectric waveguide (3) mounted on the insulating layer (2), and a row of spaced dielectric resonator type radiating elements (4) mounted on the insulating layer parallel to but spaced from one side of the waveguide (3) so that the elements are excited and caused to radiate by energy propagated in the waveguide. A similar row of radiating elements may be located on the opposite side of the waveguide. <IMAGE>

Description

SPECIFICATION Improvements relating to millimeter wave arrays This invention reiates to antenna systems which are of the type known as millimeter wave arrays.

Millimeter wave systems are currently being considered as replacements for or to augment infrared and microwave systems in a number of applications. The majority of these applications demand the use of antennae which are many wavelengths in size, and because of the need for low profile, light weight designs, millimeter wave arrays may be more attractive than conventional reflector or lens configurations.

There are a number of different known types of millimeter wave arrays, such as slotted metallic waveguide arrays, microstrip arrays, and leaky wave dielectric structures.

However, an examination of the losses of these systems at the higher millimeter wave frequencies suggest that only the slotted metallic waveguide arrays are suitable for extremely large arrays (for example greater than 50 wavelengths), but these are not generally compatible with light weight, low profile requirements. Microstrip arrays are extremely lossy at millimeter wavelengths and also suffer from problems associated with the presence of trapped slab modes. Their application therefore seems to be limited to smaller arrays.

With the aim of providing an arrangement which combines ease of manufacture with acceptable losses allowing reasonable efficiency to be realised, particularly in moderately sized arrays, according to the invention, a millimeter wave array comprises a linear dielectric waveguide alongside of which there is a row of dielectric resonator type radiating elements which are spaced from each other and from the waveguide so that the elements are excited and caused to radiate by energy propagated in the waveguide.

Preferably the dielectric waveguide and the dielectric radiating elements are mounted on an insulating layer which in turn is mounted on a conducting ground plane. The main function of the insulating layer is to reduce losses, and it also provides some control over the dispersion characteristics of the system. It is not however essential to the system, and in some cases it may be omitted altogether.

The array in accordance with the invention may comprise a second row of spaced dielectric resonator type radiating elements on the opposite side of the dielectric waveguide from the first row of radiating elements, the first and second rows preferably being arranged symmetrically about the waveguide.

The array generates a fan-beam which is broad in the plane perpendicular to the axis of the array and narrow in the plane passing through the array axis and orthogonal to the former plane. Thus, it is essentially a linear array the main beam direction of which depends on the choice of various design parameters. Broadside radiation (normal to the array axis) can be obtained when the array is operated as a resonant one by placing a short circuit at the load end of the dielectric waveguide and choosing the spacing between the resonators to be equal to the guide wavelength. It is possible to realize a planar array having a "pencil-beam" by arranging a number of linear arrays side by side and parallel to each other.

The energy coupling between the waveguide and the radiating elements, and the performance of the array, is determined by the parameters of the system, that is the permittivity, height and width of the waveguide, the permittivity, height, width and length of the radiating elements and also their spacing from each other and from the waveguide, and the permittivity of the insulating layer (when included). If desired the permittivity of the insulating layer may be the same as that of the dielectric waveguide. Generally the interelement spacing, that is the distance from one end of each of the radiating elements to the corresponding end of the next element, will be made equal to the waveguide wavelength, and the length of each of the radiating elements will be made slightly less than half the waveguide in order to account for the end effects which generate the radiation from the array.However, different combinations for the element lengths and the inter-element spacing may be chosen depending on the array performance required. Control of the excitation coefficients of the array may be effected by varying the coupling between the waveguide and the elements simply by varying the spacing of individual elements from the waveguide.

Usually the waveguide and the radiating elements will have a rectangular cross-section taken in a plane perpendicular to the waveguide axis, but other cross-sectional shapes, for example semi-circular, may be used. In addition, the upper surface of the radiating elements may be partially or fully metallised for the purpose of enhancing the radiation characteristics of the array.

The dielectric waveguide may be operated in the travelling wave or the standing wave mode by appropriate selection of the load connected to one end of the guide. The energy may be launched into the guide using a suitable horn of conventional design.

An example of a millimeter wave array in accordance with the invention is illustrated in the accompanying drawing which shows a perspective view of part of the array. As shown, the array comprises a conducting ground plane in the form of a flat metal plate 1, a flat layer 2 of insulating material mounted on the ground plane 1, a continuous linear dielectric waveguide 3 having a rectangular cross-section mounted on the insulating layer 2, and a linear row of identical, equally spaced dielectric resonator type radiating elements 4 mounted on the insulating layer 2 parallel to but spaced from one side of the waveguide 3.In the drawing: a is the width of the waveguide 3; b is the height of the waveguide; end is the permittivity of the waveguide; c is the width of each radiating element 4; d is the height of each radiating element; I is the length of each radiating element; IT is the Spacing of the radiating elements; eR is the permittivity of the radiating elements; s is the spacing between the waveguide 3 and each of the radiating elements 4; e iS the permittivity of the insulating layer 2: and, t is the thickness of the insulating layer.

In operation, energy which is launched into the dielectric waveguide 3 is coupled to the resonator type radiating elements 4 which generate a fan beam in the desired direction (e.g., in the direction of the arrow 5). In this example, the inter-element spacing IT is equal to the wavelength of the dielectric waveguide 3, and the length 1 of each element 4 is slightly less than half this wavelength (to account for end effects).

The millimeter wave array in accordance with the invention provides a light weight, flat profile array which is cheap and easy to manufacture, is efficient, and is suitable for integration with dielectric waveguide integrated circuit front ends.

Claims

1. A millimeter wave array comprising a linear dielectric waveguide alongside of which there is a row of dielectric resonator type radiating elements which are spaced from each other and from the waveguide so that the elements are excited and caused to radiate by energy propagated in the waveguide.

2. An array according to claim 1, in which the dielectric waveguide and the dielectric radiating elements are mounted on an insulating layer which in turn is mounted on a conducting ground plane.

3. An array according to claim 1 or claim 2, comprising a second row of dielectric resonator type radiating elements which are spaced from each other and from the waveguide on the opposite side of the waveguide from the first row of radiating elements.

4. An array according to claim 3, in which the two rows of radiating elements are arranged symmetrically about the waveguide.

5. An array according to any one of the preceding claims, in which the radiating elements are identical to each other.

6. An array according to claim 5, in which the length of each of the radiating elements is slightly less than half the waveguide wave length.

7. An array according to claim 5 or claim 6, in which the interelement spacing, that is the distance from one end of each of the radiating elements to the corresponding end of the next element in the row, is uniform.

8. An array according to claim 7, in which the interelement spacing is equal to the waveguide wavelength.

9. An array according to any one of the preceding claims, in which the radiating elements are equally spaced from the waveguide.

10. An array according to any one of claims 1 to 8, in which the radiating elements are variably spaced from the waveguide.

11. An array according to any one of the preceding claims, in which the waveguide and the radiating elements are each of rectangular cross section.

12. An array according to any one of claims 1 to 10, in which the waveguide and the radiating elements are each of semi-circular cross-section.

1 3. An array according to any one of the preceding claims, in which the upper surface of each of the radiating elements is partially or fully metallised.

14. An array according to any one of the preceding claims, arranged side by side and parallel to a number of similar arrays to form a planar array.

1 5. An array according to claim 1 substantially as described with reference to the accompanying drawing.