CROSS-REFERENCE TO RELATED APPLICATIONS
This is the first application filed for the present invention.
TECHNICAL FIELD
The present invention relates to the field of line sources.
BACKGROUND OF THE ART
A line source may be used in a waveguide antenna to expand a point source in one direction. Such a line source can be used as an input source to feed a larger two-dimensional aperture antenna, such as a sectoral horn. The line source may also be used solely as a line source emitter.
When used to expand an input electromagnetic field over a large frequency bandwidth, structures used to create conventional line sources typically introduce arbitrary phase errors and ohmic losses. Complex assembly is also required, making it difficult to achieve a low weight and compact size antenna, as desired for aeronautical applications and the like.
There is therefore a need for an improved line source.
SUMMARY
In accordance with a first broad aspect, there is provided a reflective line source comprising at least one region adapted to receive thereat an input electromagnetic field and to expand the input electromagnetic field in at least one dimension and at least one reflective phase compensator coupled to the at least one region, the at least one reflective phase compensator adapted to fold a direction of propagation of the expanded electromagnetic field and correct a phase error thereof.
In accordance with a second broad aspect, there is provided a method for manufacturing a reflective line source, the method comprising providing at least one region adapted to receive thereat an input electromagnetic field and to expand the input electromagnetic field in at least one dimension and coupling at least one reflective phase compensator to the at least one region, the at least one reflective phase compensator adapted to fold a direction of propagation of the expanded electromagnetic field and correct a phase error thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:
FIG. 1 is a perspective view of a folded reflective line source in accordance with an illustrative embodiment of the present invention;
FIG. 2
a is a schematic diagram of a taper region of FIG. 1;
FIG. 2
b is a bottom view of the folded reflective line source of FIG. 1;
FIG. 2
c is a schematic diagram of a reflective phase compensator of FIG. 1;
FIG. 3
a is a perspective cross-sectional view of the folded reflective line source of FIG. 1;
FIG. 3
b is a perspective view of the folded reflective line source of FIG. 1 with an input beam propagating through a first taper region;
FIG. 3
c is a schematic diagram of a reflector of FIG. 3a;
FIG. 3
d is a perspective view of the folded reflective line source with the input electromagnetic field of FIG. 3b propagating through the first and a second taper region;
FIG. 3
e is a perspective view of the folded reflective line source with the input electromagnetic field of FIG. 3b propagating through a second, a third and a fourth taper region;
FIG. 4
a is a plot of the phase error for the folded reflective line source of FIG. 1 prior to compensation using the reflective phase compensator;
FIG. 4
b is a plot of the phase error for the folded reflective line source of FIG. 1 after compensation;
FIG. 5
a is a bottom perspective view of a folded reflective line source integrated with an E-plane sectoral horn in accordance with an illustrative embodiment of the present invention;
FIG. 5
b is a front perspective view of the folded reflective line source integrated with the E-plane sectoral horn of FIG. 5a;
FIG. 6 is a plot of modeled and measured results of the azimuth far field gain pattern for the folded reflective line source integrated with the E-plane sectoral horn of FIG. 5a; and
FIG. 7 is a flow diagram of a method for manufacturing a folded reflective line source in accordance with an illustrative embodiment of the present invention.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
DETAILED DESCRIPTION
Referring to FIG. 1, a folded reflective line source 100 in accordance with an illustrative embodiment will now be described. As will be discussed further below, the line source 100 may be used to expand in one direction, e.g. the X direction, a point source fed thereto. As such, the line source 100 may be used as an input source to feed an antenna (not shown), such as an aperture antenna, e.g. a horn, waveguide aperture, reflector, or the like, that emits electromagnetic waves through an opening or aperture. The line source 100 illustrative comprises an input 102, a plurality of expansion regions 104 used to guide therethrough an electromagnetic field received at the input 102, a plurality of 180 degrees elongate reflectors 106 used to fold the direction of propagation of the field by 180 degrees, and a reflective phase compensator 108.
In particular, as illustrated in FIG. 2a, in some embodiments, each expansion region 104 flares away from a first edge 1101 towards a second edge 1102 opposite to the first edge 1101. In this manner, a field 1121 that has a width w1 and enters the expansion region 104 at the first edge 1101 is expanded when propagating down the expansion region 104 towards the second edge. As such, the width w2 of the field 1122 exiting the expansion region 104 is illustratively greater than the width w1 of the field 1121 entering the expansion region 104. The flare angle θ may be adjusted to achieve the desired flare in the expansion region 104. By increasing the flare angle θ, the rate of flare of the expansion region 104 may be increased, resulting in a faster expansion of the input electromagnetic field 1121. The flare angle θ of the expansion regions 104 is illustratively comprised between zero and ninety (90) degrees. In one embodiment, one expansion region 104, and more particularly the last expansion region through which the field exits the line source 100, is a straight region that is provided with no taper.
In addition to expanding the field 1121, propagation down each tapered one of the expansion regions 104 introduces a phase error between the field 1121 entering the tapered expansion region 104 and the field 1122 exiting the tapered expansion region 104. Indeed, the difference between the length d1 from the center point of the first edge 1101 of the tapered expansion region 104 to the center point of the second edge 1102 and the length d2 along each one of the side edges as in 114 of the tapered expansion region 104 results in a difference between the phase of the field 1121 and the phase of the field 1122. In particular, the length d2 is substantially greater than the length d1. It should be understood that the greater the flare angle θ of each expansion region 104, the greater the phase error and the higher the need for phase compensation. Indeed, a gentle width expansion would likely not require phase correction. Still, such a gentle expansion would result in the line source as in 100 being several meters in length so as to achieve a half-meter wide output field. In order to ensure the compactness of the line source 100, it is therefore desirable for the width expansion to be rapid and accordingly for phase compensation to be implemented using the reflective phase compensator 108. Although the expansion region 104 has been illustrated in FIG. 2a as comprising side edges 114, e.g. metal walls, it should be understood that the expansion regions 104 may be provided without such edges 104.
Referring now to FIG. 2b and FIG. 2c, the reflective phase compensator 108 may be used to compensate for the above-mentioned phase error. For this purpose, the phase compensator 108 may be provided to couple a pair of consecutive expansion regions as in 104 of the line source 100. In the embodiment illustrated in FIG. 2b, the phase compensator 108 is provided at the end of the second to last expansion region 104. Still, it should be understood that the phase compensator 108 may be provided at the end of any tapered one of the expansion regions 104 and thus may couple any pair of consecutive expansion regions 104. In such cases, the phase compensator 108 may be designed to overcompensate the phase error. In this manner, although the electromagnetic field exiting the phase compensator 108 will propagate through the remaining expansion regions 104, thereby introducing additional phase error, the overcompensation initially effected by the phase compensator 108 illustratively results in an overall phase error cancellation. It should further be understood that multiple phase compensators 108 may be provided for coupling to more than one pair of expansion regions 104.
The reflective phase compensator 108 illustratively has an arcuate profile and comprises an arcuate edge 116. The complex shape of the reflective phase compensator 108 illustratively introduces a complex phase correction factor, i.e. a non-uniform phase. It should be understood that the reflective phase compensator 108 may have a simple conic profile, may be of high order aspherical type, or any other suitable profile known to those skilled in the art. For example, the phase compensator 108 may be shaped as an arc of circle, a conic section, a polynomial surface, a parabola, or the like. It should also be understood that the shape of the phase compensator 108 may or may not be smooth continuous. For instance, the phase compensator 108 may have a discontinuous curvature, be piecewise arcuate, or otherwise segmented. Other profiles may also apply.
As shown in FIG. 2c, when an expansion region 104 is provided with such a phase compensator 108 having the arcuate edge 116, the length along each one of the side edges 114 of the expansion region 104 is illustratively reduced from the value d2 to the value d3, with the length d1 along the center line (not shown) of the expansion region 104 being longer than the length d3 along the edges 114 thereof. Thus, the difference between the lengths d1 and d3 may be reduced, resulting in a compensation of the phase error.
Referring now to FIG. 3a in addition to FIG. 2a, in one embodiment, the reflective line source 100 may comprise five (5) connected expansion regions 1041, 1042, 1043, 1044, and 1045. It should be understood that any suitable number of expansion regions may also apply. The expansion regions 1041, 1042, 1043, 1044, and 1045 may be provided in a vertically, i.e. along the Z direction, stacked relationship and connected by the elongate reflectors 106 to create a compact folded structure. In particular, a first expansion region, as in 1041, and a second expansion region, as in 1042, are connected such that a first reflector, as in 1061, is provided between the second edge 1102 of the first expansion region and the first edge 1101 of the second expansion region. In addition, in the embodiment of FIG. 3a, expansion regions 1041, 1042, 1043, and 1044 are illustratively tapered waveguides with a flare angle θ while the fifth expansion region 1045 through which the electromagnetic field exits the line source 100 is a straight waveguide, i.e. is not tapered. It should be understood that other configurations may apply. As the width of the electromagnetic field exiting each one of the tapered expansion regions 1041, 1042, 1043, and 1044 is illustratively expanded compared to the field received at the input 102, the tapered expansion regions 1041, 1042, 1043, and 1044 illustratively have an increasing size. Indeed, the width w2 of the second edge 1102 of a first tapered expansion region, as in 1041, is illustratively equal to the width w1 of the first edge 1101 of the tapered expansion region, as in 1042, which is connected and consecutive to the first tapered expansion region, as in 1041.
Referring to FIG. 3b in addition to FIG. 3a, a guided electromagnetic field 1121 illustratively enters the line source 100 at the input 102 along a direction A. The field 1121 then travels along a direction B through the first expansion region 1041 found on the top layer 118 of the line source 100. While traveling through the first expansion region 1041, the field 1121 gets expanded into a field 1122. At the end of the first expansion region 1041, the first reflector 1061 redirects the expanded field 1122 into the second expansion region 1042 found below the top layer 118. For this purpose, and as illustrated in FIG. 3c, the reflector 1061 illustratively comprises a first angled facet 1201 and a second angled facet 1202. The first and the second angled facets 1201 and 1202 illustratively act as reflective surfaces oriented at forty-five (45) degrees to the incident field. As such, the field 1122 incoming along the direction B is illustratively turned through 90 degrees by each one of the first angled facet 1201 and the second angled facet 1202. Thus, the field 1123 exiting the first reflector 1061 into the second expansion region 1042 along direction C is illustratively turned by 180 degrees by the pair of angled facets 1201 and 1202, as illustrated in FIG. 3d. It should be understood that the first reflector 1061 may comprise more than two angled facets as in 1201 and 1202 and that the angled facets 1201 and 1202 may be oriented at angles other than forty-five (45) degrees. Still, regardless of the design of the first reflector 1061 and remaining ones of the reflectors as in 106, it is desirable for the incoming field to be reflected by 180 degrees.
Referring to FIG. 3e, the field 1123 may then continue to travel down the second expansion region 1042 of the reflective line source 100 along the direction C. The field 1123 may get redirected by a second reflector 1062 found at the end of the second expansion region 1042. The second reflector 1062 illustratively comprises a first and a second angled facet similar to the facets 1201 and 1202 of the first reflector 1061 of FIG. 3c. As such, the field 1124 exiting the second reflector 1062 is illustratively turned by 180 degrees upon entering into the third expansion region 1043 along the direction D. When so redirected, the field 1124 travels through the third expansion region 1043 towards the end thereof. The field 1124 may then be redirected as a field 1125 towards the fourth expansion region 1044 by a third 180 degree reflector 1063 comprising angled facets similar to the facets 1201 and 1202 of the first reflector 1061.
Referring back to FIG. 3a in addition to FIG. 3e, the field 1125 may then travel through the fourth expansion region 1044 along the direction E. When traveling through the fourth expansion region 1044, the field 1125 may further encounter the reflective phase compensator 108, which illustratively corrects errors induced by the finite length tapered expansion regions as in 1041, 1042, 1043, 1044. In particular and as discussed above with reference to FIG. 2c, upon reaching the arcuate edge 116, the field 1125 has illustratively traveled through an expansion region 1044 where the length (reference d1 in FIG. 2c) along the center line is longer than the length (reference d2 in FIG. 2c) along the edges (reference 114 in FIG. 2c). As such, it is desirable, using the reflective phase compensator 108, to achieve phase compensation for the distances traveled by the signal through the expansion regions 1041, 1042, 1043, and 1044. In particular, the phase compensator 108 may correct the phase error so that a planar phase front is achieved at an output of the line source 100. The phase compensator may alternatively correct the phase error so that a target value phase front is achieved.
The arcuate edge 116 illustratively comprises a first and a second reflective phase compensating surface 1221 and 1222. In one embodiment, the reflective phase compensating surfaces 1221 and 1222 are arcuate angled facets each oriented at substantially forty-five (45) degrees for turning an electromagnetic field impinging thereon by substantially ninety (90) degrees. It should be understood that the phase compensator 108 may comprise more than two reflective phase compensating surfaces 1221 and 1222 and that the latter may be oriented at angles other than forty-five (45) degrees. Upon reaching the arcuate edge 116, the field 1125 thus successively encounters the first and the second reflective phase compensating surfaces 1221 and 1222. As such, the field 1125 is folded by 180 degrees and redirected towards the fifth expansion region 1045 found on the bottom layer 124 of the folded structure 100. The field 1126 exiting the reflective phase compensator 108 may then propagate along the direction F through the fifth expansion region 1045.
FIG. 4
a and FIG. 4b illustrate results obtained by simulating a 600 mm by 700 mm reflective line source (reference 100 in FIG. 1). Such a line source 100 is then used as an input source to feed an antenna (not shown). Simulations were performed using electromagnetic simulation software, such as CST Microwave Studio™. It should be understood that any other suitable software known to those skilled in the art may be used. FIG. 4a shows a plot 200 of the phase error in the reflective line source 100 without phase error compensation. Due to the periodic nature of electromagnetic waves, phase jumps 202 of substantially 360 degrees occur due to phase wrapping. The unwrapped total phase error of the uncompensated expansion regions (reference 104 in FIG. 1) is in excess of 2600 degrees or approximately 7.2 wavelengths.
FIG. 4
b shows a plot 300 of the phase error after compensation using a reflective phase compensator (reference 108 in FIG. 1). After the field propagates through the reflective phase compensator 108, a non-uniform and complex phase correction factor is introduced. As a result, the peak-to-peak phase error is reduced to less than five (5) degrees over half of the width of the antenna aperture. The phase correction factor being non-uniform, a residual phase error remains across the full width of the antenna aperture. Still, this phase error is reduced to approximately sixty (60) degrees or 0.17 wavelengths. A phase error less than one-quarter of a wavelength can therefore be achieved using the reflective line source architecture 100 described above. As known to those skilled in the art, a phase error of lambda/6, with lambda being the wavelength of the electromagnetic wave, or sixty (60) degrees is typically sufficient for most antenna applications.
As discussed above, the reflective line source 100 may be coupled to a plurality of antenna types. FIG. 5a and FIG. 5b show a proof-of-concept reflective line source 400 integrated with an E-plane sectoral horn 402. The proof-of-concept line source 400 and the sectoral horn 402 may be fabricated using any suitable manufacturing process, such as rapid prototyping. The rapid prototyping process illustratively uses a laser to cure polymer into a specific geometry. In the embodiment shown in FIG. 5a and FIG. 5b, the resulting polymer part is then metalized with copper. An input waveguide 404 as well as two (2) expansion regions 4061 and 4062 of the line source 400 can be seen in FIG. 5a. FIG. 5b shows the output radiator 408 of the sectoral horn 402 with the line source 100 attached on top and to the back of the horn 402.
FIG. 6 illustrates a comparison between modeled and measured results of the azimuth far field gain pattern at 19.7 GHz for the folded reflective line source 400 and E-plane sectoral horn 402 of FIG. 5a and FIG. 5b. The gain pattern plot 500 shows the agreement of the integration of the line source 400 with the sectoral horn 402. Indeed, well-behaved and low sidelobe levels 502 are obtained due to the fact that the phase error is reduced to less than one-quarter of a wavelength using the reflective phase compensator (reference 108 in FIG. 1).
Referring to FIG. 7, a method 500 for manufacturing a folded reflective line source, such as the line source 100 of FIG. 1, will now be described. The method 500 comprises providing at step 502 one or more expansion regions (reference 104 in FIG. 1). As described above, each expansion region may be such that an input field may be received at a first end thereof and an output field output through a second end thereof opposite the first end. When a plurality of expansion regions are provided, the next step 504 may then comprise arranging the expansion regions in a vertically stacked relationship. In particular, the expansion regions may be arranged such that the second end of each expansion region is adjacent the first end of the consecutive expansion region.
When a plurality of expansion regions are provided, the method 500 may then comprise coupling at step 506 a reflector (reference 106 in FIG. 1) to each consecutive pair of expansion regions. In particular, the step 506 may comprise, as discussed above, coupling the reflector between the second end of the first expansion region of each pair and the first end of the second expansion region of the pair. In this manner, any electromagnetic field exiting through the second end of the first expansion region of each pair may be redirected towards the first end of the second expansion region of the pair, thereby connecting the expansion regions. The step 506 may, for instance, comprise providing a reflector having a first and a second angled facet each oriented at forty-five (45) degrees to an incident electromagnetic field for folding the direction of propagation of a field incident on the reflector by 180 degrees.
The next step 508 may then be to couple at least one reflective phase compensator (reference 108 in FIG. 1) to at least one of the expansion regions. It should be understood that the order of steps 506 and 508 may be interchanged. The phase compensator may be coupled to the second end of a first expansion region and the first end of the second expansion region consecutive to the first expansion region. The phase compensator may be provided with an arcuate or other suitable shape for compensating a phase error due to propagation of a field through the taper regions connected at step 506. In particular, the phase compensator coupled at step 508 to the expansion region(s) may be provided with at least two reflective phase compensating surfaces for folding by 180 degrees a field incident on the phase compensator.
Referring back to FIG. 1, the folded reflective line source architecture illustratively compensates for arbitrary phase errors over a very large frequency bandwidth. In particular, broadband response over 50% of the bandwidth may be achieved and the design may be scalable from 5 GHz to 75 GHz operating frequency. The line source 100 may further allow for superior phase control and provide continuous and smooth phase responses as well as a symmetric and well controlled phase and amplitude field distribution. Moreover, a reduction of losses and a loosening of assembly tolerances may be achieved. Also, the reflective line source 100 illustratively enables a compactness and a reduction in the weight of the overall antenna structure. The design may further be compatible with conventional high speed machining, extrusion, injection molding, arc-machining, stamping, or other manufacturing processes known to those skilled in the art.
The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.
Patent Application
20140198015
