US3718933A

US3718933A - Microwave antenna

Info

Publication number: US3718933A
Application number: US00170711A
Authority: US
Inventors: H Huele
Original assignee: Thales Nederland BV
Current assignee: Thales Nederland BV
Priority date: 1971-08-11
Filing date: 1971-08-11
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27

Abstract

A MICROWAVE ANTENNA OF THE ARRAY ANTENNA TYPE IS PROVIDED WITH A TRANSMISSION LINE NETWORK COMPRISING TWO SUPPLY LINES FOR PRODUCING A CORRESPONDING NUMBER OF BEAMS. THE ANTENNA IS FORMED BY VARIOUS PARALLEL LINEAR ARRAYS. A SEPARATE FREQUENCY BAND IS ALLOCATED TO EACH OF THE SUPPLY LINES. THE SUPPLY LINES ARE CONNECTED TO ALL LINEAR ARRAYS BY MEANS OF FREQUENCY-SELECTIVE COUPLERS (E.G. DIPLEXERS), EACH SO DESIGNED THAT THEY FEED THE COMBINED SIGNALS OF VARIOUS FREQUENCY BANDS TO BE TRANSMITTED TO THE ASSOCIATED LINEAR ARRAYS, WHILE THEY FEED THE RECEIVED SIGNALS SEPARATED ACCORDING TO FREQUENCY BAND TO THE VARIOUS SUPPLY LINES.

Description

Feb. 27, 1973 H. T. HUELE MICROWAVE ANTENNA 3 Sheets-Sheet 1 Filed Aug. 11, 1971 INVENTOR HENDRIK TEUNIS HUELE AGENT H. T. HUELE Feb. 27, 1973 MICROWAVE ANTENNA 5 Sheets-Sheet 2 Filed Aug. l l., 1.971

Feb. 27, 1973 H. T. HUELE 3,718,933

MICROWAVE ANTENNA Filed Aug. 11, 1971 3 Sheets-Sheet 3 United States Patent O ce lands Filed Aug. 11, 1971, Ser. No. 170,711 Int. Cl. H01q 13/10 US. Cl. 343-768 3 Claims ABSTRACT OF THE DISCLOSURE A microwave antenna of the array antenna type is provided with a transmission line network comprising two supply lines for producing a corresponding number of beams. The antenna is formed by various parallel linear arrays. A separate frequency band is allocated to each of the supply lines. The supply lines are connected to all linear arrays by means of frequency-selective couplers (e.g. diplexers), each so designed that they feed the combined signals of various frequency bands to be transmitted to the associated linear arrays, while they feed the received signals separated according to frequency band to the various supply lines.

The invention relates to a microwave antenna of the planar array type, comprising a number of radiating elements and a transmission line network, which contains two supply lines, a number of frequency-selective coupling members and a number of directional couplers, each of the supply lines, suitable for producing microwave energy in an own frequency band, being connected to a number of common frequency-selective coupling members via a number of directional couplers, said coupling members combining the supplied microwave energy and transmitting this energy to the radiating elements in order to produce a number of beams corresponding with the number of supply lines, whereas the incoming signals are separated by the coupling members according to frequency band and supplied to the corresponding supply lines.

Such antennae are known, for example, from US. Pat. No. 3,518,689 issued to I. A. Algeo et al. The antenna decribed by Algeo is employed to provide two directionally frequency-scanned energy beams, the one beam scanning in elevation with little appreciable motion in azimuth and the other beam scanning in azimuth with little appreciable motion in elevation. Therefore, this antenna comprises a matrix array of radiating elements, the rows of which are fed by a first frequency-scanned feed and the columns of which are fed by a second frequencyscanned feed, whereby two controlled cross-scanning bearns may be simultaneously produced.

Such antennae, particularly the frequency-selective coupling members between the feeds and the radiators are unsuited for simultaneously producing two beams of different but neighbouring frequency bands; in that case the supply lines afiect each other so that the antenna efficiency and the antenna gain are adversely affected. Such antennae further require many radiating elements and the construction of the employed horn is difiicult to realize and very expensive.

The invention has for its object to construct a microwave antenna of the kind set forth for producing simultaneously two beams with high efficiency and maximum antenna gain.

According to the invention the radiating elements in such an antenna consist of a number of slotted waveguides corresponding with the number of frequency-selective coupling members, the slots having a bandwidth suited for transmission of the microwave energy of two different but neighbouring frequency bands and each of the fre- Patented Feb. 27, 1973 quency selective coupling members being constituted by a diplexer.

The invention and its advantages will be described more fully with reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating the embodiment of the microwave antenna according to the invention;

FIG. 2 is a perspective view, partly cut away, of the embodiment of said microwave antenna.

FIG. 3 is a perspective view of one arrangement of a coupler, which connects a supply line to a frequency-selective coupling member.

In FIGS. 1 and 2 reference numeral 1 designates a microwave antenna of the array type formed by slotted waveguides and connected to a transmission line network 2 having two

supply lines

7 and 8. Each of the

supply lines

7, 8 has its own frequency band I and II respectively,

slightly differing from each other. The two supply lines are each terminated at one end by a

non-reflecting load

15 and 16 respectively. Said supply lines are connected to all linear arrays of the antenna through a number of frequency-selective coupling members corresponding with the number of parallel linear arrays. For the sake of simplicity it is assumed here that the planar array antenna comprises only four parallel

linear arrays

3, 4, 5 and 6 and, therefore, four frequency-

selective coupling members

9, 10, 11 and 12. These

members

9, 10, 11 and 12 are each constructed so that they feed the signals of different frequency bands to be transmitted together to the associated linear arrays, whereas they supply the received signals separated according to frequency band to the corresponding supply line.

Said parallel

linear arrays

3, 4, 5 and 6 form one planar array antenna. Each of these linear arrays consists of a waveguide having slots 13 and closed in a conventional manner at one end by a non-reflecting load 14, the other end forming the input or the output of the waveguide.

Since the antenna according to the invention uses signals in two frequency bands, transmission line network 2 has to be provided with means for feeding the signals of said frequency bands together to all linear arrays of the planar array antenna, and with means for separating the received echo signals according to frequency band. This is achieved in a particularly simple manner since both for joining and for separating, one and the same frequency-selective coupler known from the frequency-diversity technique, termed diplexer may be employed. Since the employed

diplexers

9, 10, 11 and 12 are identical, it may sufiice to describe only diplexer 9. It comprises two

Waveguides

17 and 18, which are coupled by two directional couplers 19 and 19' (so-called short slot hybirds) arranged at a given distance from each other.

Each of the

waveguides

17 and 18 comprises a

filter

20 and 20, which may be of any suitable type, provided that they pass signals from supply line 8 in band H and stop signals from supply line 7 in band I. So the characteristics of the filters 20, 20- are determined in accordance with the operational frequency of the two

supply lines

7, 8 which have to be coupled to the linear array of radiators. The filters have a negligible reactance for frequency band II and a very high reactance for frequency band I and may be of any suitable type, e.g. a waveguide internally provided with one or more irrisses. Waveguide 18 is terminated at one end by a non-reflecting load 21.

Apart from said

supply lines

7 and 8 and

diplexers

9, 10, 11 and 12 the transmission line network 2 comprises four

directional couplers

22, 23, 24 and 25 associated with supply line 7 and four directional couplers 22', 23', 24', and 25' associated with supply line '8. These directional couplers are coupled with the associated supply line at a given distance from each other.

FIG. 3 shows how directional coupler 22 is coupled with supply line 7. If it is assumed that a signal in frequency band II occurs at the input of supply line 8, a directional coupler such as 22' feeds a given quantity of signal energy from the supply line 8 to the diplexer 9 to which said coupler 22' is connected.

The signal energy fed into waveguide 17 is divided into two equal quantities at the short slot hybrids 19; one quantity A is transmitted to the filter 20' and the other quantity B to filter 20 through hybrid 19'. Said energy quantity A has a wave amplitude which is times as large as the wave amplitude of the original signal energy, coupled into waveguide 17 by directional coupler 22'. This energy quantity A is not shifted in phase. Energy quantity B transmitted through hybrid 19', has also a wave amplitude which is times as large as the wave amplitude of the the original energy, however, the phase of this energy quantity has increased by 90 degrees.

Both energy quantities A and B pass the filter part of the diplexer, after which each energy quantity A and B is split at hybrid 19. Quantity A is split into two equal portions A and A A is the energy portion which is transmitted to the linear array 3 and has a Wave amplitude which is times as large as the wave amplitude of energy portion A therefore, this energy portion A has a wave amplitude which is /2 times as large as the wave amplitude of said original energy; the phase of the energy portion A remains 90 degrees. After energy portion A has passed the hybrid 19 in the direction of the directional coupler 22, the corresponding wave amplitude is also /2 times as large as the wave amplitude of said original energy. However, the phase shift is increased to 180 degrees. After energy quantity B passed the filter 19', said quantity B is divided into two equal portions B and B at hybrid 19.

Energy portion B remaining in the same waveguide, has a wave amplitude which is /2 times as large as the wave amplitude of quantity B and so a wave amplitude which is /2 times as large as the wave amplitude of the original energy from supply line 8; the phase of this energy portion B remains degree.

The energy portions A and B have the same wave amplitude, but the corresponding waves are in phase opposition; therefore the waves of the energy portions A and B are quenched and nothing of the original energy from supply line 8 can be transmitted to the other supply line 7. After the energy portion B has passed hybrid 19, this energy portion has also a wave amplitude which is /2 times as large as the wave amplitude of the original energy, while its phase-shift is increased to 90 degrees. Therefore, energy portions A and B have the same wave amplitude, each of which is /2 times as large as the Wave amplitude of the original wave energy; also the phase of waves A and B are the same. By superposition of the two waves, it is obvious that the whole wave energy from supply line 8 is transmitted to linear array 3.

An analogous argument applies to the wave energy fed from supply line 7 to diplexer 9 by directional coupler 22. This microwave energy is first split into two equal quantities C and D at hybrid 19, energy quantity C being transmitted to filter 20 and energy quantity D to filter 20'. After reflection by the filters 20, 20' each of the quantities of energy C and D is divided into two equal portions C and C or D and D respectively. Energy portions C and D are gathered in the part of waveguide 17, which is connected to supply line 7; these energy portions C and D have the same amplitude, but the corresponding waves are in anti-phase; therefore, the waves of the energy portions C and D are quenched. However, energy portions C and D which are transmitted to linear array 3 are identical in wave amplitude and phase; therefore the whole energy fed from supply line 7 by directional coupler 22 is transmitted to linear array 3. Each of said diplexers joins the signal energy of the two frequency bands I and II derived from the two supply lines and supplies the joined energy to one of the parallel linear arrays. Since the required frequencies for producing the cosecF-shaped beam and the pencil-shaped beam do not differ much, one type of slots can be used in the linear arrays. The bandwidth of the slots is such that both frequencies are passed.

Echoes from remote targets are received by the antenna and fed to the

respective diplexers

9, 10, 11 and 12. These diplexers operate as frequency splitters for the incoming signals so that the latter are separated according to frequency band, the signals of frequency band I being fed to supply line 7 through

directional couplers

22, 23, 24 and 25 and the signals of frequency band H being fed to supply,

line 8 through directional couplers 22', 23', 24' and 25.

The antenna described above permits of transmitting and receiving within one and the same antenna aperture in two frequency bands I and II, the signals of frequency band I being transmitted and received in a first, for example, cosec. -shaped beam and the signals of frequency band II being transmitted and received in a second, for example, pencil-shaped beam. The plane of the cosec. shaped pattern has to be perpendicular to the planar array while the pattern of the pencil-shaped beam has to be positioned in said plane of the coscF-shaped pattern. The cosec. -shape of the first beam and the position of its plane is determined by the amplitude and phase ratio of the signals of frequency band I, when a suitable center frequency is used, as supplied to the respective linear arrays. Also the pencil-shape of the second beam and its position in the plane of the cosec. -beam are determined by the amplitude and phase ratio of the signals of frequency band II, which are fed to the respective linear arrays. The correct amplitude and phase ratio for each of these beams is obtained by a correct choice of the coupling factor of the consecutive directional couplers and of each of the supply lines and by a correct choice of the length of the piece of supply line between each pair of consecutive directional couplers. However, there is only one frequency for the pencil-shaped beam, whereas the amplitude and phase ratio is such that the beam is entirely in the plane of the cosec.'--shaped pattern. For other frequencies the pencil-shaped beam is not exactly in said plane. Since the pencil-shaped beam should be kept as much as possible in the plane of the cosec. -shaped pattern, only slight variations in the frequency of band II are allowed. However, to obtain a beam for scanning in elevation, the amplitude and phase ratio has to vary considerably. This is obtained when a rectangular waveguide shaped as a so-called serpentine is used as supply line 8, as shown in FIG. 2; consequently the physical distance between the consecutive directional couplers is considerably shorter than the length of the piece of waveguide between said consecutive directional couplers. As is known, it is possible, when using such a serpentine waveguide for feeding a planar array antenna, to obtain a frequency-controlled beam. The direction of the beam then depends upon the frequency of the signals supplied to the serpentine waveguide. This property may be utilized for controlling the pencil-shaped beam so that the latter can perform a scanning movement in the plane of the cosec. -shaped beam pattern. It will be obvious that this makes a three-dimensional target position indication possible. The loops of the serpentine waveguide provide the desired dispersion. If, however, the beam has to be independent of the frequency, as is, for example, the case with the cosecF-shaped beam, it is necessary for the supply line 7 not to be dispersive.

Frequency-independent phase shifters such as 26 must then be provided to bring about the desired phase variation across the antenna aperture. Since the microwave antenna according to the invention uses supply lines each having its own frequency band, these supply lines cannot influence each other so that a high antenna efficiency and a maximum antenna gain can be obtained.

The microwave antenna according to the invention is not restricted to the embodiment described above. For example, a fan-shaped beam pattern may be employed instead of a cosecP-shaped beam pattern.

What I claim is:

1. A microwave antenna of the planar array type, comprising a number of radiating elements and a transmission line network, which contains two supply lines, a number of frequency-selective coupling members and a number of directional couplers, each of the supply lines, suitable for producing microwave energy in its own frequency band, being connected to a number of common frequency-selective coupling members via a number of directional couplers, said coupling members combining the supplied microwave energy and transmitting this energy to the radiating elements in order to produce a number of beams corresponding with the number of supply lines, whereas the incoming signals are separated by the coupling members according to frequency band and supplied to the corresponding supply lines, wherein the radiating elements consist of a number of slotted waveguides, corresponding with the number of frequency-selective coupling members, the slots having a bandwidth suited for transmission of the microwave energy of two different but neighbouring frequency bands, and each of the frequency-selective coupling members being constituted by a diplexer.

2. A microwave antenna as claimed in claim 1, wherein the directional couplers are arranged at a given relative distance along the waveguide the amplitude and phase ratio of the quantities of energy, coupled out for the one supply line, being chosen so that the planar array antenna has a cosecP-shaped transmitting-receiving pattern, whereas for the other supply line the amplitude and phase ratio of the quantities of energy coupled out are chosen so that the planar array antenna has a pencil-shaped transmitting-receiving pattern in the plane of the said cosecP- shaped beam.

3. A microwave antenna as claimed in claim 2, wherein said other supply line is formed by a rectangular waveguide shaped into a so-called serpentine supply line so that the physical distance between consecutive directional couplers is considerably shorter than the length of the piece of waveguide between said consecutive directional couplers, whilst, when the carrier frequency of the signal fed to said supply line is varied within the frequency band allotted to said supply line, the pencil-shaped beam produced performs a scanning movement in the plane of said cosec. -shaped beam.

References Cited UNITED STATES PATENTS 3,270,336 8/1966 Birge 343854 3,434,139 3/1969 Algeo 343-854 3,518,689 6/1970 Algeo et a1 434854 JOHN S. HEYMAN, Primary Examiner US. Cl. X.R. 34377l, 854