Abstract A Ku band 4×1 linear slot array antenna design based on recently developed gap waveguide technology is presented. The complete antenna has been built using two parallel plates where the. An ultralow cross-polarization slot array antenna in the narrow wall of ridge waveguide is presented. In the first, a non-angled slot which is created to the narrow wall of ridge waveguide is suggested to be used as radiating resonance slot. The normalized resistance and normalized reactance curves are presented for design purposes.
- Geometry of the most common slotted waveguide antenna. The front end (the open face at the y=0 in the x-z plane) is where the antenna is fed. The far end is usually shorted (enclosed in metal). The waveguide may be excited by a short dipole (as seen on the cavity-backed slot antenna) page, or by another waveguide.
- Abstract: A novel waveguide slot filtering antenna with an embedded metamaterial is presented. This filtering antenna consists of a common waveguide slot antenna with longitudinal slots cut on the top broad wall of its rectangular waveguide and a metamaterial surface embedded in the bottom broad wall.
A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut out. When the plate is driven as an antenna by an applied radio frequency current, the slot radiates electromagnetic waves in a way similar to a dipole antenna. The shape and size of the slot, as well as the driving frequency, determine the radiation pattern. Slot antennas are usually used at UHF and microwave frequencies at which wavelengths are small enough that the plate and slot are conveniently small. At these frequencies, the radio waves are often conducted by a waveguide, and the antenna consists of slots in the waveguide; this is called a slotted waveguide antenna. Multiple slots act as a directivearray antenna and can emit a narrow fan-shaped beam of microwaves. They are used in standard laboratory microwave sources used for research, UHF television transmitting antennas, antennas on missiles and aircraft, sector antennas for cellular base stations, and particularly marine radar antennas. A slot antenna's main advantages are its size, design simplicity, and convenient adaptation to mass production using either waveguide or PC board technology.
Structure[edit]
As shown by H. G. Booker in 1946, from Babinet's principle in optics a slot in a metal plate or waveguide has the same radiation pattern as a driven rod antenna whose rod is the same shape as the slot, with the exception that the electric field and magnetic field directions are interchanged; the antenna is a magnetic dipole instead of an electric dipole; the magnetic field is parallel to the long axis of the slot and the electric field is perpendicular. Thus the radiation pattern of a slot can be calculated by the same well-known equations used for rod element antennas like the dipole. The waves are linearly polarized perpendicular to the slot axis. Slots up to a wavelength long have a single main lobe with maximum radiation perpendicular to the surface.
Antennas consisting of multiple parallel slots in a waveguide are widely used array antennas. They have a radiation pattern similar to a corresponding linear array of dipole antennas, with the exception that the slot can only radiate into the space on one side of the waveguide surface, 180° of the surrounding space. There are two widely used types:
- Longitudinal slotted waveguide antenna - The slots' axis is parallel to the axis of the waveguide. This has a radiation pattern similar to a collinear dipole antenna, and is usually mounted vertically. The radiation pattern is almost omnidirectional in the horizontal plane perpendicular to the antenna over the 180° azimuth in front of the slot, but narrow in the vertical plane, with the vertical gain increasing approximately 3 dB with each doubling of the number of slots. The radiation is horizontally polarized. It is used for vertical omnidirectional transmitting antennas for UHF television stations. For broadcasting, a cylindrical or semicircular waveguide is sometimes used with several columns of slots cut in different sides to give an omnidirectional 360° radiation pattern.
- Transverse slotted waveguide antenna - The slots are almost perpendicular to the axis of the waveguide but skewed at a small angle, with alternate slots skewed at opposite angles. This radiates a dipole pattern in the plane perpendicular to the antenna, and a very sharp beam in the plane of the antenna. Its largest use is for microwave marine radar antennas. The antenna is mounted horizontally on a mechanical drive that rotates the antenna about a vertical axis, scanning the antenna's vertical fan-shaped beam 360° around the water surface surrounding the ship out to the horizon with each revolution. The wide vertical spread of the beam ensures that even in bad weather when the ship and the antenna axis is being rocked over a wide angle by waves the radar beam will not miss the surface.
History[edit]
The slot antenna was invented in 1938 by Alan Blumlein, while working for EMI. He invented it in order to produce a practical type of antenna for VHF television broadcasting that would have horizontal polarization, an omnidirectional horizontal radiation pattern and a narrow vertical radiation pattern.[1][2]
Prior to its use in surface search radar, such systems used a parabolic segment reflector, or 'cheese antenna'. The slotted waveguide antenna was the result of collaborative radar research carried on by McGill University and the National Research Council of Canada during World War II.[3] The co-inventors, W.H. Watson and E.W. Guptill of McGill, were granted a United States patent for the device, described as a 'directive antenna for microwaves', in 1951.[4]
Other uses[edit]
In a related application, so-called leaky waveguides are also used in the determination of railcar positions in certain rapid transit applications. They are used primarily to determine the precise position of the train when it is being brought to a halt at a station, so that the doorway positions will align correctly with queuing points on the platform or with a second set of safety doors should such be provided.
See also[edit]
- Microwave Radiometer (Juno) (has a slot array antenna)
- RIMFAX (radar for Mars rover has slot antenna design)
References[edit]
- ^Blumlein, Alan (1938-03-07), 'Improvements in or relating to high frequency electrical conductors or radiators', British patent no. 515684
- ^Burns, Russell (2000). The life and times of A.D. Blumlein. Institution of Engineering and Technology. ISBN0-85296-773-X.
- ^Covington, Arthur E. (1991). 'Some recollections of the radio and electrical engineering division of the National Research Council of Canada, 1946-1977'. Scientia Canadensis: Canadian Journal of the HIstory of Science, Technology and Medicine. 15 (2): 155–175. doi:10.7202/800334ar.
- ^Watson, William Heriot; Guptill, Ernest Wilmot (6 November 1951), Directive Antenna for Microwaves, retrieved 20 December 2016
External links[edit]
- 'Slot Antennas'. Antenna Theory.
- Slotted Waveguide Antennas Antenna-Theory.com
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to planar array antennas, and particularly to the slotted waveguide planar array antennas.
The performance of planar arrays comprising longitudinal (shunt) slot radiators in the broad wall of conventional rectangular waveguides has a number of limitations: The scan range in the plane perpendicular to the waveguide axis (E-plane) is restricted because of the relatively large width of the waveguide which translates into a wide inter-element spacing in this plane. This wide spacing also hampers sidelobe control. The purpose of sidelobe control would have been best served by an arrangement of columns of collinear slots with narrow spacing between the columns; however this arrangement is not possible in conventional rectangular waveguides because longitudinal slots must be arranged in staggered configuration. Moreover, polarization is limited to the plane perpendicular to the waveguide axis.
Transversal (series) slots, on the other hand, while potentially providing orthogonal polarization, are not used in conventional arays because of the difficulty associated with their incorporation into a serial waveguide array.
The ridged waveguide may have a much narrower cross section than the rectangular waveguide, and as such it holds promise for constructing slot arrays with narrower inter-element spacing in the E-plane, thus providing a solution to the scan and sidelobe limitations of conventional rectangular waveguides. However, symmetrical ridge waveguides are limited in the area over which longitudinal slots can be cut; therefore the dynamic range is limited. In addition, polarization is still limited to the E-plane.
The idea of asymmetric ridge waveguides is described in H. Shnitkin and J. Green, 'Asymmetric Ridge Waveguide Collinear Slot Array Antenna', U.S. Pat. No. 4,638,323, Jan. 20, 1987, and the paper J. Green, B. Shnitkin and Paul J. Bertalan, 'Asymmetric Ridge Waveguide Radiating Element for a Scanned Planar Array', IEEE Trans. on Antennas and propagation Vol. 38, No. 8. pp. 1161-1165, August 1990. In order to increase the dynamic range of the slots, the ridge is constructed in an asymmetric manner, thereby allowing a wider region on one of its sides for placing longitudinal slots, but includes alternating side chambers on opposite sides of the ridge alternating between high and low level. Longitudinal slots are fed out of phase every one-half a waveguide wavelength (λg); therefore they must be placed at opposing sides of the broad walls of conventional or symmetrical ridge waveguides.
In the array antenna described in U.S. Pat. No. 4,638,323, ridge asymmetry is obtained by including, on opposite sides of the ridge, side chambers alternating between high and low levels. The above patent and the publication relating thereto also disclose the idea of providing a meandering ridge to produce ridge asymmetry. However, the structures described in that patent and publication are difficult to construct mechanically; moreover, they may generate high order modes at the bends of the ridges.
Slotted waveguide array antennas of this type are also described in U.S. Pat. Nos. 3,189,908, 4,658,261, 4,873,528, 3,193,830, 3,183,511, 4,513,291, 4,821,044, 4,554,550 and 4,554,551.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a slotted waveguide array antenna of a novel construction having advantages over the previously known antennas as will be described more particularly below.
According to the present invention, there is provided a slotted waveguide array antenna comprising a plurality of waveguide elements extending in a parallel side-by-side relation, each waveguide element having a longitudinal axis, a radiating side including a broad wall formed with a plurality of slots, a non-radiating side opposite to the radiating side, and a single asymmetric ridge in the non-radiating side; characterized in that the single asymmetric ridge is a straight continuous ridge extending parallel to, laterally of, and asymmetrical with respect to, the longitudinal axis of the waveguide element. Such an asymmetric ridge construction has advantages over the meandering ridge construction described in the above-cited U.S. Pat. No. 4,638,323, in that mechanically, it is simpler to construct, and electrically, it avoids the generation of high order modes at the bends of the ridges.
According to further features in the described preferred embodiments of the invention, the antenna is further characterized in that the slots are slanted to the longitudinal axis of the antenna in alternating directions and are spaced λg/2 apart such as to offset phase reversal between each pair of adjacent slots.
In One described embodiment, the slots in each waveguide element are slanted in alternating directions. In this described embodiment, the antenna includes means for feeding the slanted slots at locations where the ridge traverses the slot, to provide control over the slot impedance and the amount of power lea into each slot, to thereby produce a high-dynamic range of the slots.
A second embodiment is described wherein the plurality of waveguide elements are arranged in pairs in which the slots of one waveguide element in each pair are slanted parallel to each other and to the axis of the respective waveguide element, and the slots of the other waveguide element in each pair are also slanted parallel to each other and to the axis of the respective waveguide element, but in the opposite direction to that of the one waveguide element of the respective pair. In this described embodiment, the antenna includes: a first power network for feeding the one waveguide element of all the pairs; a second power network for feeding the other waveguide element of all the pairs; and a phase shifting network between the first and second power networks. The arrangement is such that:
Waveguide Slot Antenna Gain
(a) when the two waveguides of each pair are in phase, linear polarization is generated perpendicular to the waveguide axis; (b) when the two waveguides of each pair are out of phase, orthogonal linear polarization is generated; and (c) when the waveguides are fed in phase quadrature, circular polarization is generated.
Waveguide Slot Array Antenna
Further features and advantages of the invention will be apparent from the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
FIG. 1 schematically illustrates a part of one waveguide element which may be used in constructing a slotted waveguide array antenna in accordance with the present invention;
FIG. 2 is a top plan view of FIG. 1;
FIG. 3 illustrates a slotted waveguide array antenna including a plurality of the waveguide elements of FIGS. 1 and 2;
FIG. 4 illustrates a pair of waveguide elements in another form of slotted waveguide array antenna constructed in accordance with the present invention;
FIG. 5 is an end view of the waveguide elements of FIG. 4;
and FIG. 6 illustrates a slotted waveguide array antenna including a plurality of pairs of waveguide elements according to FIGS. 4 and 5.
DESCRIPTION OF PREFERRED EMBODIMENTS
The invention will be better understood by reference first to the part of the waveguide element illustrated in FIG. 1 and 2, and therein generally designated 2, which may be used in constructing a slanted waveguide array antenna in accordance with the present invention.
The part of the waveguide element 2 illustrated in FIGS. 1 and 2 has a radiating side including a broad wall 4 formed with a plurality of slots 6a, 6b, and a non-radiating side, opposite to the radiating side of broad wall 4, and formed with a single ridge 8 which is asymmetric to the longitudinal axis 10 of the waveguide element. As clearly seen in FIGS. 1 and 2, the asymmetric ridge 8 is a continuous ridge extending parallel to and laterally of the longitudinal axis 10; also, the slots 6a, 6b are slanted to the longitudinal axis of the waveguide element 2 in alternating directions. They are spaced λg/2 apart. The alternating directions offset the phase reversal between any two adjacent slots.
The slots are fed at the locations where the ridge 8 traverses the respective slot, as shown at points 12a and 12b for slots 6a, 6b, respectively. In this way, resonant slots can be cut in the broad wall 4 of the ridge waveguide, which is narrower than the broad wall of a rectangular waveguide and which therefore does not accommodate transversal slots.
The polarization in the construction illustrated in FIGS. 1 and 2 is perpendicular to the waveguide axis, similar to longitudinal slots. However, better control can be obtained of the slot impedance and the amount of power fed into each slot by selecting these feed point, resulting in high dynamic range of the slots.
FIG. 3 illustrates a slotted waveguide array antenna including a plurality of the waveguide elements 2 of FIGS. 1 and 2. Spacing between adjacent waveguides in the antenna of FIG. 3 is smaller than in the conventional rectangular waveguide antenna, thereby facilitating wider scan range and lower sidelobes, especially in the inter-cardinal planes.
FIG. 4 illustrates a pair of waveguide elements for use in a switchable multi-polarization array antenna constructed in accordance with the present invention.
The pair of waveguide elements illustrated in FIG. 4 are generally designated 20a, 20b, respectively. Each includes a plurality of slots 26a, 26b formed in the broad wall of the radiating side of the waveguide element. In this case, however, the slots 26a, 26b in adjacent waveguide elements extend in opposite directions. The slots in each element are spaced apart λg, so that the spacing between the slots in adjacent elements is λg/2, thereby providing in-phase excitation. Each pair of such waveguides thus form a single antenna 'element' whose width is smaller than a wavelength and is thus suitable for limited scan in the plane perpendicular to the waveguide axis.
FIG. 6 illustrates a plurality of pairs of such waveguide elements arranged in parallel relationship to produce a switchable multi-polarization array antenna, generally designated 30. Each pair thus includes the two elements 20a, 20b. It will be seen that all the waveguide elements 20a, constituting one element of each pair, are connected to power dividing network 32, and that all the elements 20b, constituting the other elements of the waveguide pairs, are connected to a separate power dividing network 34 via a phase-shift network 36.
The arrangement illustrated in FIG. 6 enables the polarization of the antenna to be controlled. Thus, when the group of waveguide elements 20a are energized in phase with the group of waveguide elements 20b, the polarization is linear and perpendicular to the waveguide axis. When the energization of the two groups of waveguides is out of phase, orthogonal linear polarization is generated; and when the energization of the two groups is in phase quadrature, circular polarization is generated. In this manner, the phase shift network 36 may be used to control the polarization of the antenna to enable it to be switched dynamically from one polarization to another.
Following is one example of dimensions in millimeters for an antenna operating in the C-band: the width (W) of each waveguide element 20a, 20b is 2.80 mm; the width (w) of each slot 26a, 26b is 1.60 mm; the length (1) of each slot 26a, 26b is 20.75 mm; λg/2 is 21.40 mm; the distance (S) between the radiating and non-radiating sides of the antenna is 8.0 mm; and the distance (s) between the top of the ridge and the non-radiating side of the antenna is 5.5 mm.
History[edit]
The slot antenna was invented in 1938 by Alan Blumlein, while working for EMI. He invented it in order to produce a practical type of antenna for VHF television broadcasting that would have horizontal polarization, an omnidirectional horizontal radiation pattern and a narrow vertical radiation pattern.[1][2]
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Prior to its use in surface search radar, such systems used a parabolic segment reflector, or 'cheese antenna'. The slotted waveguide antenna was the result of collaborative radar research carried on by McGill University and the National Research Council of Canada during World War II.[3] The co-inventors, W.H. Watson and E.W. Guptill of McGill, were granted a United States patent for the device, described as a 'directive antenna for microwaves', in 1951.[4]
Other uses[edit]
In a related application, so-called leaky waveguides are also used in the determination of railcar positions in certain rapid transit applications. They are used primarily to determine the precise position of the train when it is being brought to a halt at a station, so that the doorway positions will align correctly with queuing points on the platform or with a second set of safety doors should such be provided.
See also[edit]
- Microwave Radiometer (Juno) (has a slot array antenna)
- RIMFAX (radar for Mars rover has slot antenna design)
References[edit]
- ^Blumlein, Alan (1938-03-07), 'Improvements in or relating to high frequency electrical conductors or radiators', British patent no. 515684
- ^Burns, Russell (2000). The life and times of A.D. Blumlein. Institution of Engineering and Technology. ISBN0-85296-773-X.
- ^Covington, Arthur E. (1991). 'Some recollections of the radio and electrical engineering division of the National Research Council of Canada, 1946-1977'. Scientia Canadensis: Canadian Journal of the HIstory of Science, Technology and Medicine. 15 (2): 155–175. doi:10.7202/800334ar.
- ^Watson, William Heriot; Guptill, Ernest Wilmot (6 November 1951), Directive Antenna for Microwaves, retrieved 20 December 2016
External links[edit]
- 'Slot Antennas'. Antenna Theory.
- Slotted Waveguide Antennas Antenna-Theory.com
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to planar array antennas, and particularly to the slotted waveguide planar array antennas.
The performance of planar arrays comprising longitudinal (shunt) slot radiators in the broad wall of conventional rectangular waveguides has a number of limitations: The scan range in the plane perpendicular to the waveguide axis (E-plane) is restricted because of the relatively large width of the waveguide which translates into a wide inter-element spacing in this plane. This wide spacing also hampers sidelobe control. The purpose of sidelobe control would have been best served by an arrangement of columns of collinear slots with narrow spacing between the columns; however this arrangement is not possible in conventional rectangular waveguides because longitudinal slots must be arranged in staggered configuration. Moreover, polarization is limited to the plane perpendicular to the waveguide axis.
Transversal (series) slots, on the other hand, while potentially providing orthogonal polarization, are not used in conventional arays because of the difficulty associated with their incorporation into a serial waveguide array.
The ridged waveguide may have a much narrower cross section than the rectangular waveguide, and as such it holds promise for constructing slot arrays with narrower inter-element spacing in the E-plane, thus providing a solution to the scan and sidelobe limitations of conventional rectangular waveguides. However, symmetrical ridge waveguides are limited in the area over which longitudinal slots can be cut; therefore the dynamic range is limited. In addition, polarization is still limited to the E-plane.
The idea of asymmetric ridge waveguides is described in H. Shnitkin and J. Green, 'Asymmetric Ridge Waveguide Collinear Slot Array Antenna', U.S. Pat. No. 4,638,323, Jan. 20, 1987, and the paper J. Green, B. Shnitkin and Paul J. Bertalan, 'Asymmetric Ridge Waveguide Radiating Element for a Scanned Planar Array', IEEE Trans. on Antennas and propagation Vol. 38, No. 8. pp. 1161-1165, August 1990. In order to increase the dynamic range of the slots, the ridge is constructed in an asymmetric manner, thereby allowing a wider region on one of its sides for placing longitudinal slots, but includes alternating side chambers on opposite sides of the ridge alternating between high and low level. Longitudinal slots are fed out of phase every one-half a waveguide wavelength (λg); therefore they must be placed at opposing sides of the broad walls of conventional or symmetrical ridge waveguides.
In the array antenna described in U.S. Pat. No. 4,638,323, ridge asymmetry is obtained by including, on opposite sides of the ridge, side chambers alternating between high and low levels. The above patent and the publication relating thereto also disclose the idea of providing a meandering ridge to produce ridge asymmetry. However, the structures described in that patent and publication are difficult to construct mechanically; moreover, they may generate high order modes at the bends of the ridges.
Slotted waveguide array antennas of this type are also described in U.S. Pat. Nos. 3,189,908, 4,658,261, 4,873,528, 3,193,830, 3,183,511, 4,513,291, 4,821,044, 4,554,550 and 4,554,551.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a slotted waveguide array antenna of a novel construction having advantages over the previously known antennas as will be described more particularly below.
According to the present invention, there is provided a slotted waveguide array antenna comprising a plurality of waveguide elements extending in a parallel side-by-side relation, each waveguide element having a longitudinal axis, a radiating side including a broad wall formed with a plurality of slots, a non-radiating side opposite to the radiating side, and a single asymmetric ridge in the non-radiating side; characterized in that the single asymmetric ridge is a straight continuous ridge extending parallel to, laterally of, and asymmetrical with respect to, the longitudinal axis of the waveguide element. Such an asymmetric ridge construction has advantages over the meandering ridge construction described in the above-cited U.S. Pat. No. 4,638,323, in that mechanically, it is simpler to construct, and electrically, it avoids the generation of high order modes at the bends of the ridges.
According to further features in the described preferred embodiments of the invention, the antenna is further characterized in that the slots are slanted to the longitudinal axis of the antenna in alternating directions and are spaced λg/2 apart such as to offset phase reversal between each pair of adjacent slots.
In One described embodiment, the slots in each waveguide element are slanted in alternating directions. In this described embodiment, the antenna includes means for feeding the slanted slots at locations where the ridge traverses the slot, to provide control over the slot impedance and the amount of power lea into each slot, to thereby produce a high-dynamic range of the slots.
A second embodiment is described wherein the plurality of waveguide elements are arranged in pairs in which the slots of one waveguide element in each pair are slanted parallel to each other and to the axis of the respective waveguide element, and the slots of the other waveguide element in each pair are also slanted parallel to each other and to the axis of the respective waveguide element, but in the opposite direction to that of the one waveguide element of the respective pair. In this described embodiment, the antenna includes: a first power network for feeding the one waveguide element of all the pairs; a second power network for feeding the other waveguide element of all the pairs; and a phase shifting network between the first and second power networks. The arrangement is such that:
Waveguide Slot Antenna Gain
(a) when the two waveguides of each pair are in phase, linear polarization is generated perpendicular to the waveguide axis; (b) when the two waveguides of each pair are out of phase, orthogonal linear polarization is generated; and (c) when the waveguides are fed in phase quadrature, circular polarization is generated.
Waveguide Slot Array Antenna
Further features and advantages of the invention will be apparent from the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
FIG. 1 schematically illustrates a part of one waveguide element which may be used in constructing a slotted waveguide array antenna in accordance with the present invention;
FIG. 2 is a top plan view of FIG. 1;
FIG. 3 illustrates a slotted waveguide array antenna including a plurality of the waveguide elements of FIGS. 1 and 2;
FIG. 4 illustrates a pair of waveguide elements in another form of slotted waveguide array antenna constructed in accordance with the present invention;
FIG. 5 is an end view of the waveguide elements of FIG. 4;
and FIG. 6 illustrates a slotted waveguide array antenna including a plurality of pairs of waveguide elements according to FIGS. 4 and 5.
DESCRIPTION OF PREFERRED EMBODIMENTS
The invention will be better understood by reference first to the part of the waveguide element illustrated in FIG. 1 and 2, and therein generally designated 2, which may be used in constructing a slanted waveguide array antenna in accordance with the present invention.
The part of the waveguide element 2 illustrated in FIGS. 1 and 2 has a radiating side including a broad wall 4 formed with a plurality of slots 6a, 6b, and a non-radiating side, opposite to the radiating side of broad wall 4, and formed with a single ridge 8 which is asymmetric to the longitudinal axis 10 of the waveguide element. As clearly seen in FIGS. 1 and 2, the asymmetric ridge 8 is a continuous ridge extending parallel to and laterally of the longitudinal axis 10; also, the slots 6a, 6b are slanted to the longitudinal axis of the waveguide element 2 in alternating directions. They are spaced λg/2 apart. The alternating directions offset the phase reversal between any two adjacent slots.
The slots are fed at the locations where the ridge 8 traverses the respective slot, as shown at points 12a and 12b for slots 6a, 6b, respectively. In this way, resonant slots can be cut in the broad wall 4 of the ridge waveguide, which is narrower than the broad wall of a rectangular waveguide and which therefore does not accommodate transversal slots.
The polarization in the construction illustrated in FIGS. 1 and 2 is perpendicular to the waveguide axis, similar to longitudinal slots. However, better control can be obtained of the slot impedance and the amount of power fed into each slot by selecting these feed point, resulting in high dynamic range of the slots.
FIG. 3 illustrates a slotted waveguide array antenna including a plurality of the waveguide elements 2 of FIGS. 1 and 2. Spacing between adjacent waveguides in the antenna of FIG. 3 is smaller than in the conventional rectangular waveguide antenna, thereby facilitating wider scan range and lower sidelobes, especially in the inter-cardinal planes.
FIG. 4 illustrates a pair of waveguide elements for use in a switchable multi-polarization array antenna constructed in accordance with the present invention.
The pair of waveguide elements illustrated in FIG. 4 are generally designated 20a, 20b, respectively. Each includes a plurality of slots 26a, 26b formed in the broad wall of the radiating side of the waveguide element. In this case, however, the slots 26a, 26b in adjacent waveguide elements extend in opposite directions. The slots in each element are spaced apart λg, so that the spacing between the slots in adjacent elements is λg/2, thereby providing in-phase excitation. Each pair of such waveguides thus form a single antenna 'element' whose width is smaller than a wavelength and is thus suitable for limited scan in the plane perpendicular to the waveguide axis.
FIG. 6 illustrates a plurality of pairs of such waveguide elements arranged in parallel relationship to produce a switchable multi-polarization array antenna, generally designated 30. Each pair thus includes the two elements 20a, 20b. It will be seen that all the waveguide elements 20a, constituting one element of each pair, are connected to power dividing network 32, and that all the elements 20b, constituting the other elements of the waveguide pairs, are connected to a separate power dividing network 34 via a phase-shift network 36.
The arrangement illustrated in FIG. 6 enables the polarization of the antenna to be controlled. Thus, when the group of waveguide elements 20a are energized in phase with the group of waveguide elements 20b, the polarization is linear and perpendicular to the waveguide axis. When the energization of the two groups of waveguides is out of phase, orthogonal linear polarization is generated; and when the energization of the two groups is in phase quadrature, circular polarization is generated. In this manner, the phase shift network 36 may be used to control the polarization of the antenna to enable it to be switched dynamically from one polarization to another.
Following is one example of dimensions in millimeters for an antenna operating in the C-band: the width (W) of each waveguide element 20a, 20b is 2.80 mm; the width (w) of each slot 26a, 26b is 1.60 mm; the length (1) of each slot 26a, 26b is 20.75 mm; λg/2 is 21.40 mm; the distance (S) between the radiating and non-radiating sides of the antenna is 8.0 mm; and the distance (s) between the top of the ridge and the non-radiating side of the antenna is 5.5 mm.
While the invention has been described with respect to two preferred embodiments, it will be appreciated that these are set forth merely for purposes of example, and that many other variations, modifications and applications of the invention may be made.
