REFLECTIVE LINE SOURCE

There is provided a reflective line source for an antenna system. The reflective line source comprises at least one region adapted to receive an electromagnetic field and to expand the field in at least one dimension. The reflective line source further comprises a reflective phase compensator that is coupled to the region. The reflective phase compensator is adapted to correct a phase error resulting from propagation of the field through the region as well as to fold a direction of propagation of the field. For this purpose, the reflective phase compensator comprises at least two reflective phase compensating surfaces oriented at ninety degrees relative to one another.

DETAILED DESCRIPTION

Referring toFIG. 1, a folded reflective line source100in accordance with an illustrative embodiment will now be described. As will be discussed further below, the line source100may be used to expand in one direction, e.g. the X direction, a point source fed thereto. As such, the line source100may 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 source100illustrative comprises an input102, a plurality of expansion regions104used to guide therethrough an electromagnetic field received at the input102, a plurality of 180 degrees elongate reflectors106used to fold the direction of propagation of the field by 180 degrees, and a reflective phase compensator108.

In particular, as illustrated inFIG. 2a, in some embodiments, each expansion region104flares away from a first edge1101towards a second edge1102opposite to the first edge1101. In this manner, a field1121that has a width w1and enters the expansion region104at the first edge1101is expanded when propagating down the expansion region104towards the second edge. As such, the width w2of the field1122exiting the expansion region104is illustratively greater than the width w1of the field1121entering the expansion region104. The flare angle θ may be adjusted to achieve the desired flare in the expansion region104. By increasing the flare angle θ, the rate of flare of the expansion region104may be increased, resulting in a faster expansion of the input electromagnetic field1121. The flare angle θ of the expansion regions104is illustratively comprised between zero and ninety (90) degrees. In one embodiment, one expansion region104, and more particularly the last expansion region through which the field exits the line source100, is a straight region that is provided with no taper.

In addition to expanding the field1121, propagation down each tapered one of the expansion regions104introduces a phase error between the field1121entering the tapered expansion region104and the field1122exiting the tapered expansion region104. Indeed, the difference between the length d1from the center point of the first edge1101of the tapered expansion region104to the center point of the second edge1102and the length d2along each one of the side edges as in114of the tapered expansion region104results in a difference between the phase of the field1121and the phase of the field1122. In particular, the length d2is substantially greater than the length d1. It should be understood that the greater the flare angle θ of each expansion region104, 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 in100being several meters in length so as to achieve a half-meter wide output field. In order to ensure the compactness of the line source100, it is therefore desirable for the width expansion to be rapid and accordingly for phase compensation to be implemented using the reflective phase compensator108. Although the expansion region104has been illustrated inFIG. 2aas comprising side edges114, e.g. metal walls, it should be understood that the expansion regions104may be provided without such edges104.

Referring now toFIG. 2bandFIG. 2c, the reflective phase compensator108may be used to compensate for the above-mentioned phase error. For this purpose, the phase compensator108may be provided to couple a pair of consecutive expansion regions as in104of the line source100. In the embodiment illustrated inFIG. 2b, the phase compensator108is provided at the end of the second to last expansion region104. Still, it should be understood that the phase compensator108may be provided at the end of any tapered one of the expansion regions104and thus may couple any pair of consecutive expansion regions104. In such cases, the phase compensator108may be designed to overcompensate the phase error. In this manner, although the electromagnetic field exiting the phase compensator108will propagate through the remaining expansion regions104, thereby introducing additional phase error, the overcompensation initially effected by the phase compensator108illustratively results in an overall phase error cancellation. It should further be understood that multiple phase compensators108may be provided for coupling to more than one pair of expansion regions104.

The reflective phase compensator108illustratively has an arcuate profile and comprises an arcuate edge116. The complex shape of the reflective phase compensator108illustratively introduces a complex phase correction factor, i.e. a non-uniform phase. It should be understood that the reflective phase compensator108may 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 compensator108may 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 compensator108may or may not be smooth continuous. For instance, the phase compensator108may have a discontinuous curvature, be piecewise arcuate, or otherwise segmented. Other profiles may also apply.

As shown inFIG. 2c, when an expansion region104is provided with such a phase compensator108having the arcuate edge116, the length along each one of the side edges114of the expansion region104is illustratively reduced from the value d2to the value d3, with the length d1along the center line (not shown) of the expansion region104being longer than the length d3along the edges114thereof. Thus, the difference between the lengths d1and d3may be reduced, resulting in a compensation of the phase error.

Referring now toFIG. 3ain addition toFIG. 2a, in one embodiment, the reflective line source100may comprise five (5) connected expansion regions1041,1042,1043,1044, and1045. It should be understood that any suitable number of expansion regions may also apply. The expansion regions1041,1042,1043,1044, and1045may be provided in a vertically, i.e. along the Z direction, stacked relationship and connected by the elongate reflectors106to create a compact folded structure. In particular, a first expansion region, as in1041, and a second expansion region, as in1042, are connected such that a first reflector, as in1061, is provided between the second edge1102of the first expansion region and the first edge1101of the second expansion region. In addition, in the embodiment ofFIG. 3a, expansion regions1041,1042,1043, and1044are illustratively tapered waveguides with a flare angle θ while the fifth expansion region1045through which the electromagnetic field exits the line source100is 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 regions1041,1042,1043, and1044is illustratively expanded compared to the field received at the input102, the tapered expansion regions1041,1042,1043, and1044illustratively have an increasing size. Indeed, the width w2 of the second edge1102of a first tapered expansion region, as in1041, is illustratively equal to the width w1 of the first edge1101of the tapered expansion region, as in1042, which is connected and consecutive to the first tapered expansion region, as in1041.

Referring toFIG. 3bin addition toFIG. 3a, a guided electromagnetic field1121illustratively enters the line source100at the input102along a direction A. The field1121then travels along a direction B through the first expansion region1041found on the top layer118of the line source100. While traveling through the first expansion region1041, the field1121gets expanded into a field1122. At the end of the first expansion region1041, the first reflector1061redirects the expanded field1122into the second expansion region1042found below the top layer118. For this purpose, and as illustrated inFIG. 3c, the reflector1061illustratively comprises a first angled facet1201and a second angled facet1202. The first and the second angled facets1201and1202illustratively act as reflective surfaces oriented at forty-five (45) degrees to the incident field. As such, the field1122incoming along the direction B is illustratively turned through 90 degrees by each one of the first angled facet1201and the second angled facet1202. Thus, the field1123exiting the first reflector1061into the second expansion region1042along direction C is illustratively turned by 180 degrees by the pair of angled facets1201and1202, as illustrated inFIG. 3d. It should be understood that the first reflector1061may comprise more than two angled facets as in1201and1202and that the angled facets1201and1202may be oriented at angles other than forty-five (45) degrees. Still, regardless of the design of the first reflector1061and remaining ones of the reflectors as in106, it is desirable for the incoming field to be reflected by 180 degrees.

Referring toFIG. 3e, the field1123may then continue to travel down the second expansion region1042of the reflective line source100along the direction C. The field1123may get redirected by a second reflector1062found at the end of the second expansion region1042. The second reflector1062illustratively comprises a first and a second angled facet similar to the facets1201and1202of the first reflector1061ofFIG. 3c. As such, the field1124exiting the second reflector1062is illustratively turned by 180 degrees upon entering into the third expansion region1043along the direction D. When so redirected, the field1124travels through the third expansion region1043towards the end thereof. The field1124may then be redirected as a field1125towards the fourth expansion region1044by a third 180 degree reflector1063comprising angled facets similar to the facets1201and1202of the first reflector1061.

Referring back toFIG. 3ain addition toFIG. 3e, the field1125may then travel through the fourth expansion region1044along the direction E. When traveling through the fourth expansion region1044, the field1125may further encounter the reflective phase compensator108, which illustratively corrects errors induced by the finite length tapered expansion regions as in1041,1042,1043,1044. In particular and as discussed above with reference toFIG. 2c, upon reaching the arcuate edge116, the field1125has illustratively traveled through an expansion region1044where the length (reference d1inFIG. 2c) along the center line is longer than the length (reference d2inFIG. 2c) along the edges (reference114inFIG. 2c). As such, it is desirable, using the reflective phase compensator108, to achieve phase compensation for the distances traveled by the signal through the expansion regions1041,1042,1043, and1044. In particular, the phase compensator108may correct the phase error so that a planar phase front is achieved at an output of the line source100. The phase compensator may alternatively correct the phase error so that a target value phase front is achieved.

The arcuate edge116illustratively comprises a first and a second reflective phase compensating surface1221and1222. In one embodiment, the reflective phase compensating surfaces1221and1222are 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 compensator108may comprise more than two reflective phase compensating surfaces1221and1222and that the latter may be oriented at angles other than forty-five (45) degrees. Upon reaching the arcuate edge116, the field1125thus successively encounters the first and the second reflective phase compensating surfaces1221and1222. As such, the field1125is folded by 180 degrees and redirected towards the fifth expansion region1045found on the bottom layer124of the folded structure100. The field1126exiting the reflective phase compensator108may then propagate along the direction F through the fifth expansion region1045.

FIG. 4aandFIG. 4billustrate results obtained by simulating a 600 mm by 700 mm reflective line source (reference100inFIG. 1). Such a line source100is 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. 4ashows a plot200of the phase error in the reflective line source100without phase error compensation. Due to the periodic nature of electromagnetic waves, phase jumps202of substantially 360 degrees occur due to phase wrapping. The unwrapped total phase error of the uncompensated expansion regions (reference104inFIG. 1) is in excess of 2600 degrees or approximately 7.2 wavelengths.

FIG. 4bshows a plot300of the phase error after compensation using a reflective phase compensator (reference108inFIG. 1). After the field propagates through the reflective phase compensator108, 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 architecture100described 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 source100may be coupled to a plurality of antenna types.FIG. 5aandFIG. 5bshow a proof-of-concept reflective line source400integrated with an E-plane sectoral horn402. The proof-of-concept line source400and the sectoral horn402may 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 inFIG. 5aandFIG. 5b, the resulting polymer part is then metalized with copper. An input waveguide404as well as two (2) expansion regions4061and4062of the line source400can be seen inFIG. 5a.FIG. 5bshows the output radiator408of the sectoral horn402with the line source100attached on top and to the back of the horn402.

FIG. 6illustrates a comparison between modeled and measured results of the azimuth far field gain pattern at 19.7 GHz for the folded reflective line source400and E-plane sectoral horn402ofFIG. 5aandFIG. 5b. The gain pattern plot500shows the agreement of the integration of the line source400with the sectoral horn402. Indeed, well-behaved and low sidelobe levels502are obtained due to the fact that the phase error is reduced to less than one-quarter of a wavelength using the reflective phase compensator (reference108inFIG. 1).

Referring toFIG. 7, a method500for manufacturing a folded reflective line source, such as the line source100ofFIG. 1, will now be described. The method500comprises providing at step502one or more expansion regions (reference104inFIG. 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 step504may 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 method500may then comprise coupling at step506a reflector (reference106inFIG. 1) to each consecutive pair of expansion regions. In particular, the step506may 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 step506may, 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 step508may then be to couple at least one reflective phase compensator (reference108inFIG. 1) to at least one of the expansion regions. It should be understood that the order of steps506and508may 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 step506. In particular, the phase compensator coupled at step508to 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 toFIG. 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 source100may 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 source100illustratively 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.