US3596271A

US3596271A - Microwave antenna having an undulating conductor with variable pitch and amplitude

Info

Publication number: US3596271A
Application number: US822143A
Authority: US
Inventors: Michael Frank Cosslett; Robert Frost; Kenneth Owen Rossiter
Original assignee: EMI Ltd
Current assignee: EMI Ltd; Electrical and Musical Industries Ltd
Priority date: 1968-05-09
Filing date: 1969-05-06
Publication date: 1971-07-27
Anticipated expiration: 1988-07-27
Also published as: GB1269633A

Abstract

The antenna array disclosed comprises an undulatory conductor which is capable of transmission and reception of energy, in which the amplitude and pitch of the undulations are progressively altered along the array to produce an array having directional characteristics, and a main lobe to side lobe ratio, which are those of a Dolph-Tchebycheff array. The undulations are circularly arcuate and blended into one another and the conductor is etched from one copper layer of a strip of low loss copper clad laminate, the other layer of which forms a ground plane.

Description

United States Patent 721 Inventors Michael FrankCoslett App]. No. Filed Patented Assignee Priority Maldon, Essex;

Robert Frost, Wells, Somerset; Kenneth Owen Rositer, Wells, Somerset all of, England May 6, 1969 July 27, 197 1 Electric & Musical Industries Limited Hayes, Middlesex, England Mny 9, 1968 Great Britain MICROWAVE ANTENNA HAVING AN UNDULATING CONDUCT OR WITH VARIABLE PITCH AND AMPLITUDE 3 Claims, 3 Drawing Figs.

Int. Cl. H0111 1/36 Field olseareh 343/731 [56] Relerences Cited UNITED STATES PATENTS 2,759,183 7/1956 Woodward 343/806 2,990,547 6/1961 McDougal... 343/7925 3,302,207 1/1967 Hoffman 343/731 3,369,246 2/1968 Fisk et a1. 343/806 FOREIGN PATENTS 1,118,280 11/1961 Germany 343/806 Primary Examiner-Eli Lieberman Attorney-Fleit, Gipple and Jacobson ABSTRACT: The antenna array disclosed comprises an undulatory conductor which is capable of transmission and reception of energy, in which the amplitude and pitch of the undulations are progressively altered along the array to produce an array having directional characteristics, and a main lobe to side lobe ratio, which are those of a Dolph-Tchebycheff array. The undulations are circularly arcuate and blended into one another and the conductor is etched from one copper layer of a strip of low loss copper clad laminate, the other layer of which forms a ground plane.

PATENTEU JUL2 71971 sum 1 OF 3 LUAD END v i' L.

mvsnrons MICHAEL F. COSSLETT ROBERT FROST KENNETH O. ROSSITER PATENIFD M27 1971 SHEET 2 OF 3 N Q 7 N: u u 2G 92 n 35:85 2? w $252: :23 u u 3:53:28 ENE: 82 22%: J51;

252%; 2265 5x535. 5 384 5:622 24 :E u 25%; Em 5 -25. ZQEI INVENTORS MICHAEL E COSSLETT ROBERT FROST KENNETH O. ROSSITER RNEYJSJ MICROWAVE ANTENNA HAVING AN UNDULATING CONDUCTOR WITH VARIABLE PITCH AND AMPLITUDE The present invention relates to microwave antenna arrays for the purpose of transmission and reception, and especially but not exclusively to such arrays used at microwave frequencies in missiles for guidance by radio means.

An object of the present invention is to provide an antenna array which may be constructed in a simple and cheap form but which has a substantial directivity with a good main lobe to side-lobe ratio.

According to the present invention there is provided a microwave antenna array comprising a conductor adapted to be capable of transmission or reception of en gy. Said conductor being constructed to undulate about an axis so as to form a series of transmitting or receiving elements disposed on alternate sides of said axis, the amplitude and distance from axis point to axis point of said elements being progressively altered along said antenna array, wherein a. the amplitudes of said elements increase, and their axis point to axis point distances decrease, from each end towards the center of said antenna array, I

b. each adjacent pair of elements of said antenna array conforms substantially to an adjacent pair of elements of a respective Dolph-Tchebycheff array of a length equal to the length of said antenna array,

c. each such Dolph-Tchebycheff array has a number of elements related to the axis point to axis point distance of one of the respective pair of elements of said antenna array, and

d. each such Dolph-Tchebycheff array has substantially the same main lobe direction, and substantially the same main lobe to side-lobe ratio.

In order that the invention may be fully understood and readily carried into effect it will now be described with reference to the accompanying drawings of which:

FIG. 1 is a diagram of one form of antenna array according to the present invention,

FIG. 2 is a graph to be used in explaining the design of the array shown in FIG. 1, and

FIG. 3 is another graph to be used in explaining the design of the array shown in FIG. 1.

The example of a microwave antenna array according to the present invention to be described is an antenna array capable of transmission or reception at microwave frequencies, whose overall directivity pattern is substantially that of a Dolph- Tchebychetf array, and in which the transmitting or receiving elements are formed by about an axis conductor of a strip transmission line, constructed so that its undulations about an axis comprise excursions which are circularly arcuate and blended into one another so as to form a series of circularly arcuate transmitting or receiving elements disposed on alternate sides of the axis. In this way such an antenna array can be easily and cheaply constructed from a strip of low-loss copper clad laminate, one copper layer of which forms the ground plane of the transmission line, the low-loss material forms the dielectric and the other conductor can be produced by standard photoetching techniques applied to the other copper layer.

Conventional Dolph-Tchebycheff arrays are well known and have certain criteria which must be met, namely that the elements of the array are equally spaced and fed with excitation currents of different amplitude with a linear phase taper along the array; and in Dolph-Tchebycheff theory it is shown, granted these criteria, how to .determine the element excitation currents so that the side-lobes of the array are of equal magnitude specified in relation to the main lobe. The main lobe beam width is then given, and is shown to be a minimum for the selected side-lobe level.

Thus in the example of the present invention to be described, the radii of the circularly arcuate excursions of the copper strip are progressively altered along the array so as to cause different circularly arcuate elements to radiate at different degrees, and to ensure a linear phase taper along the array, the length of the circularly arcuate elements must also be progressively altered. A typical example is shown in FIG. 1

which shows a conductor 1 which undulates about an axis 4 so as to provide a series of circularly arcuate elements disposed on alternate sides of axis 4. It will be seen that their pitches progressively alter over the length of the array in the direction of arrow 5 as their radii are altered. Conductor 1 is mounted on a slab of low loss material 2, the underside of which is clad with a copper layer 3 which forms the ground plane of the transmission line made up of conductor 1 as the other conductor and slab 2 as the dielectric. However it will be seen from FIG; 1 that the pitch, or distance between axis crossing points by strip 1 progressively alters, with the effect that the criterion of equally spaced elements in a conventional Dolph- Tchebycheff array is no longer met. The design procedure which ensures that the overall directive pattern still substantially conforms to that of a Dolph-Tchebycheff array will now be described.

The angle 6 of the main lobe to thenor mal to the plane of the array'for an array of circularly arcuate elements of a given radius of curvature and a given pitch is given by:

where E is the transmission line effective dielectric constant, d the pitch or distance between axis crossing points, r the 'radius of curvature, n the spatial harmonic and M) the free space wavelength. For a desired angle 0 a curve of individual circularly arcuate element conductance g versus d is plotted, by means of test sections each made up of constant arcs, with different values of d, ensuring at all times that the parameters of the test sections satisfy equation (1) above. From this a curve of g/d versus :1 is plotted, of which a typical example is shown in FIG. 2 for which 0=30, E =2.2, and n -2 at a frequency of 10.5 GHz. For a desired beam width of the main lobe, and main lobe to side-lobe ratio, the length of a suitable conventionalQrray is defined on the basis of a perfect Dolph- Tchebycheff distribution. For a suitable fractional power load a set of suitable conductance distributions is computed and plotted as shown in FIG. 3, which shows a graph of element conductance as a function of distance along the array for different numbers of elements. It must be appreciated that each element conductance is compensated for radiation and dielectric loss. It will be seen from FIG. 3 that all distributions commence at a substantially identical first element conductance regardless of the number of elements in the array. Thus a first conductance (at array length =0), which determines the pitch d of the first arc of the array to be designed, is then converted to the corresponding value of g/d, which using a graph such as is shown in HO. 2 determines a value of d, which specifies the position of the next axis crossing point in the array to be designed. Dividing this distance d into the array length yields the number of circularly arcuate elements in the array to which this part of the array conforms, and thus the next element conductance is defined from a graph such as is shown by FIG. 3, knowing the number of elements and the distance d, another number of elements in the array and hence yet a next element conductance. This procedure is repeated along the length of array, that is to say using each element conductance in turn to determine a new value of d and hence the next element conductance, and in this way'the synthesized array takes on the characteristics of a Dolph-Tchebycheff array. This is also shown in the graph of FIG. 3, which shows how an experimental array whose circularly arcuate element conductances along the array, shown by the shapes cause the array to start off at the input-end as if it were a Dolph-Tchebycheff array of 35 elements passing to such an array of 41 elements at two-thirds along itslength, and then back to a 35 element array. Each part of the array, and therefore the array itself, generates a main lobe at the same angle 6, and the resultant ratio of main lobe level to side-lobe level is substantially that of the chosen Dolph-Tchebycheff array.

The antenna array to which the graph of FIG. 3 conforms, has 31 circularly arcuate elements varying from d =().55 inches to d 0.44 inches; has an'overall length of inches; main lobe to side-lobe ratio of 30 db; an angle of b30; and operates at l0 50GHz. Only a few of the circularly arcuate elements are shown in FIG. I for convenience of illustration, but it will be seen how their amplitude reaches a maximum and distance between axis crossing points at their minimum towards the center of the array.

It will be appreciated that the invention is not limited to undulations comprising circular arcs, indeed any undulatory form may be adopted, for example parts of sinusoids; and nor is it limited to the form of construction described, for example the ground plane may be dispensed with; or a further ground plane may be fitted, above the undulating conductor, but with a slit cut in it, permitting transmission or reception over the length of the slit,

What we claim is:

l. A microwave antenna array comprising a conductor adapted to be capable of transmission or reception of energy, said conductor being constructed to undulate about an axis so as to form a series of transmitting or receiving elements disposed on alternate sides of said axis, the amplitude and distance from axis point to axis point of said elements being progressively altered along said antenna array, wherein a. the amplitudes of said elements increase, and their axis point to axis point distances decrease, from each end towards the center of said antenna array,

h. each adjacent pair of elements of said antenna array con forms substantially to an adjacent pair of elements of a respective Dolph-Tchebycheff array of a length equal to the length ofsaid antenna array, I

2. An array according to claim 1 in which said transmitting or receiving elements disposed on alternate sides of said axis comprise circularly arcuate elements.

3. An array according to claim 1 in which said transmitting or receiving elements disposed on alternate sides of said axis comprise part sinusoidal elements.

Claims

1. A microwave antenna array comprising a conductor adapted to be capable of transmission or reception of energy, said conductor being constructed to undulate about an axis so as to form a series of transmitting or receiving elements disposed on alternate sides of said axis, the amplitude and distance from axis point to axis point of said elements being progressively altered along said antenna array, wherein a. the amplitudes of said elements increase, and their axis point to axis point distances decrease, from each end towards the center of said antenna array, b. each adjacent pair of elements of said antenna array conforms substantially to an adjacent pair of elements of a respective Dolph-Tchebycheff array of a length equal to the length of said antenna array, c. each such Dolph-Tchebycheff array has a number of elements related to the axis point to axis point distance of one of the respective pair of elements of said antenna array, and d. each such Dolph-Tchebycheff array has substantially the same main lobe direction, and substantially the same main lobe to side-lobe ratio.