GB2213995A

GB2213995A - Coplanar patch antenna

Info

Publication number: GB2213995A
Application number: GB8729874A
Authority: GB
Inventors: Peter John Gibson
Original assignee: Philips Electronic and Associated Industries Ltd
Current assignee: Philips Electronics UK Ltd
Priority date: 1987-12-22
Filing date: 1987-12-22
Publication date: 1989-08-23
Also published as: GB8729874D0

Abstract

A coplanar patch antenna in the form of a slot line ladder array is etched in a metal layer on a dielectric base 1. A linear array of individual metal patches 11 to 15 are spaced from a ground plane 3 and from each other by an interconnected ladder network of slot lines 18 to 25. The array is fed at the centre A of a transverse slot line 20 at one end of the array which is made resonant at the operating frequency, e.g. by making each side of the square patches a quarter of a wavelength long. The squint angle of the array is determined by the interpatch distance d and the illumination function by tayloring the widths W of the transverse slot lines 20 to 25. <IMAGE>

Description

DESCRIPTION COPLANAR PATCH ANTENNA The invention relates to a coplanar patch antenna including a continuous layer of dielectric material, a patch of conductive material supported on a major surface of the layer of dielectric material, a ground plane of conductive material supported on said major surface of the layer of dielectric material and substantially surrounding and spaced from the patch of conductive material, and means for feeding electrical signals to the antenna.

A form of coplanar patch antenna of the kind specified is disclosed in an article "Coplanar Stripline Antenna" by John W. Greiser in Microwave Journal, October 1976, pages 47 to 49, and in US Patent Number 4,063,246.

It is an object of the invention to provide an improved form of coplanar patch antenna in the form of an array.

In accordance with the invention there is provided a coplanar patch antenna of the kind described, characterised in that the antenna comprises a linear array of uniformly spaced substantially rectangular patches of conductive material arranged so that a respective longitudinal slot line is formed between the ground plane and the corresponding side of the linear array of patches, and respective transverse slot lines are formed between each adjacent pair of patches in the array and between the ground plane and each end patch of the array, said transverse slot lines communicating at each end with the corresponding longitudinal slot line to form a ladder arrangement, and said means for feeding signals to the antenna is coupled to the centre of a said transverse slot line at one end of the array, the respective coupling factors between the longitudinal slot lines and the corresponding transverse slot lines and the centre to centre spacing d of the transverse slot lines being arranged to provide a desired illumination function and angle of squint for the antenna array.

Each patch can be square in shape. If it is desired to provide a broadside radiation beam direction, i.e. normal to the surface of the array, the patches can be made square with sides one quarter wavelength long. The antenna array can be formed by selectively etching a printed circuit board or by vapour deposition of metal on an alumina base. The antenna can be fed via a strip line, a microstrip line, a tr;-pLate line or a coaxial line.

Since an antenna is reciprocal in nature, any reference herein to means for feeding radio-frequency energy to the antenna is to be understood to mean additionally or alternatively means for transferring signals received by the antenna to a feeder.

A patch antenna array in accordance with the invention can provide an effective degree of radiation when formed on a substrate having a high dielectric coefficient. This has been found difficult to achieve hitherto.

An embodiment of the invention will now be described by way of example, with reference to the accompanying drawing, of which: Figure 1 illustrates diagrammatically a coplanar patch antenna array in accordance with the invention, and Figure 2 represents a longitudinal section through Figure 1.

Referring to Figures 1 and 2, the antenna is formed on a continuous layer 1 of a suitable dielectric material having a high dielectric coefficient, such as DUROID 6010 which can comprise the supporting dielectric substrate for a printed circuit. The antenna is formed by selectively etching the metal cladding of the printed surface board using conventional photoresist techniques. The antenna comprises a linear array of uniformly spaced rectangular patches 11 to 15 of electrically conductive material, namely the etched metal cladding. Five patches are shown in the present example but a different number may be employed, a larger number will give a narrower beamwidth.

A ground plane 3 is formed by the remainder of the metal cladding and it surrounds and is spaced from the patches 11 to 15.

The space between the ground plane 3 and the patches 11 to 15 forms a network of slot lines 18 to 25. Thus, between the ground plane 3 and the corresponding sides of the array of patches, respective upper and lower longitudinal slot lines 18 and 19 are formed, as shown in Figure 1. Respective transverse slot lines 21,22,23 and 24 are formed between corresponding adjacent pairs of patches. Further transverse slot lines 20 and 25 are formed between the ground plane 3 and the corresponding end patches 11 and 15 of the array.

The transverse slot lines 20 to 25 each communicate at each end with the corresponding longitudinal slot line 18,19, thus forming a ladder arrangement. The intermediate transverse slot lines 21 to 24 are respectively coupled to the corresponding longitudinal slot lines 18,19, via a series tee slot line junctions.

Radio-frequency energy is coupled to or from the antenna array at the centre of a transverse slot line 20 at one end of the array by means of a strip line 5 on the reverse of the substrate, the strip conductor being connected to the corresponding patch 11 by means of a through connection pin 6.

Alternative feed arrangements can be employed such as a microstrip line, a trip lathe line or coaxial line connection provided that the feed is applied at the centre of a transverse slot line at one end of the array.

A radio-frequency signal applied at the centre A of the transverse slot line 20 will divide into two equal components of the same phase and propagate in opposite directions, one passing along the upper longitudinal strip line 18 and the other along the lower longitudinal strip line 19 to opposite ends of the transverse strip line 25 at the other end of the array, where they will meet at the centre point B, in phase, and by interference, generate a virtual open circuit. Reflection will occur and corresponding standing waves will be set up along the longitudinal slot lines 18 and 19, which will energise the intermediate transverse slot lines 21,22,23 and 24, via the associated series tee slot line junctions.

Since the slot line currents and voltages in the upper and lower longitudinaL lines 18,19 when viewed as in Figure 1, are in phase but are inverted with respect to one another, radiation will tend to cancel. The relative phase of radiation from the transverse slot lines 20 to 25 will determine the direction of reinforcement, i.e. the angle of squint, of the radiated beam in a plane normal to the plane of the array and through the longitudinal axis 8 of the array. This will be determined by the slot spacing d. Thus, if the patches 11 to 15 were made as squares having sides equal to one quarter of a wavelength at the operational frequency, all the slots formed by the transverse slot lines 20 to 25 would be energised in phase and the radiation pattern would be directed in a broadside manner, i.e. normal to the plane of the array.This is because, taking for example the first patch 11, the phase delay from the point A to the mid-point S of the transverse slot 21 will be pi radians but from the point of view of the direction of currents in the sides of the slot lines 20,21, and of the electric fields across the slot lines 20,21, the slot geometry will be rotated through 180 degrees so that the reversed slot 21 fed by an inverted signal will radiate in phase with the slot 20. A similar description applies to the remaining slots 23 to 25 which will all radiate in phase with one another.

The angle of squint can readily be altered at the design stage by modifying the phase delay between adjacent patches namely by aLtering the length of the patches and hence the centre to centre transverse slot line spacing d.

The illumination function of the antenna array which depends on the relative intensities of radiation from the individual transverse slot elements, can be tailored by adjusting the coupling factors between the longitudinal slots lines 18,19, and the transverse slot lines via the series tee slot line junctions, for example by modifying the width W of the transverse slot line. For a larger adjustment of the slot coupling the height of the patches can be adjusted. In fact, provided account is taken of the delay, the longitudinal slot lines can be stepped sideways to accommodate patches of various width along the array.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of planar patch antennas, slot lines and component parts thereof and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

CLAIM(S)

1. A coplanar patch antenna including a continuous layer of dielectric material, a patch of conductive material supported on a major surface of the layer of dielectric material, a ground plane of conductive material supported on said major surface of the layer of dielectric material and substantially surrounding and spaced from the patch of conductive material, and means for feeding electrical signals to the antenna, characterised in that the antenna comprises a linear array of uniformly spaced substantially rectangular patches of conductive material arranged so that a respective longitudinal slot line is formed between the ground plane and the corresponding side of the linear array of patches, and respective transverse slot lines are formed between each adjacent pair of patches in the array and between the ground plane and each end patch of the array, said transverse slot lines communicating at each end with the corresponding longitudinal slot line to form a ladder arrangement, and said means for feeding signals to the antenna is coupled to the centre of a said transverse slot Line at one end of the array, the respective coupling factors between the longitudinal slot lines and the corresponding transverse slot ines and the centre to centre spacing d of the transverse slot lines being arranged to provide a desired illumination function and angle of squint for the antenna array.

2. A coplanar patch antenna as claimed in Claim 1, characterised in that each patch is square.

3. A coplanar patch antenna as claimed in Claim 2, characterised in that the length of the sides of each of the squares is a quarter wavelength at the operating frequency.

4. A coplanar patch antenna as claimed in any one of the preceding claims, characterised in that the dielectric layer comprises the dielectric support of a printed circuit board and the conducting material forming the ground plane and the patches is the metal cladding layer after selective etching.

5. A coplanar patch antenna as claimed in any one of Claims 1,2 and 3, characterised in that the dielectric material is alumina and the conducting material forming the ground plane and the patches, is metal applied to the alumina by vapour deposition.

6. A coplanar path antenna as claimed in any one of the preceding claims, characterised in that signals are fed to the antenna by means of a strip line.

7. A coplanar patch antenna array substantially as herein described with reference to the accompanying drawing.