Abstract
A substrate integrated waveguide (SIW) for phase shifter for millimeter wave applications has a waveguide with a plurality of curved sections and which passes through the substrate from a wave entry port to a wave exit port. The plurality of curved sections forms a serpentine path of curves in a first direction followed by curves in a second direction which are opposite the first direction. Phase shifting elements are positioned in the waveguide in each of the curved sections. The phase shifting elements may take the form of PIN diodes or a pattern of liquid metal filled vias in the waveguide.
Claims
1. A substrate integrated waveguide (SIW) for millimeter wave applications, comprising: a substrate having length, width, and height dimensions; a wave entry port on a first end of the substrate and a wave exit port on a second end of the substrate, wherein the first and second ends are opposite ends of the substrate; a waveguide comprising a plurality of curved sections and which passes through the substrate from the wave entry port to the wave exit port, wherein the plurality of curved sections forms a serpentine path of curves in a first direction followed by curves in a second direction which is opposite the first direction, a plurality of radiating members which extend into the waveguide between curves in the first direction and curves in the second direction; and phase shifting elements in the waveguide in each of the curved sections, wherein the phase shifting elements are comprised of a plurality of spaced apart vias which extend into the waveguide.
2. The SIW of claim 1 wherein at least some of the plurality of spaced apart vias are filled with the liquid metal.
3. The SIW of claim 1 wherein at least some of the plurality of spaced apart vias are empty holes in a dielectric.
4. The SIW of claim 1 wherein the radiating members are each semicircular.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1A are plan and side views of a prior art of a switch based phase shifting configuration.
(2) FIG. 1B is a plan view of a prior art of a liquid crystal based phase shifting configuration.
(3) FIG. 2 shows the geometry of an exemplary SIW waveguide with phase shifter.
(4) FIG. 3 is a close up view of the SIW waveguide of FIG. 2 and shows features of the proposed radiating elements of the array.
(5) FIG. 4 is a view of the curved SIW of FIG. 2 without the phase shifter elements.
(6) FIG. 5 is a view of one curved section of the SIW including spaced apart metallized vias, wherein the vias are designed to provide the different phase shifters.
(7) FIG. 6 is a view of one curved section of the SIW including switches, wherein the switches are designed to provide the different phase shifters.
(8) FIG. 7 is a graph showing a simulated reflection coefficient.
(9) FIG. 8 is a graph showing a simulated gain showing the scan capability.
DETAILED DESCRIPTION OF THE INVENTION
(10) A lightweight, low profile array antenna with wide-angle scan capability is desired for the rising demands of 5G communication. To address the design challenge, the inventive phase shifter utilizes a curved substrate integrated waveguide. The proposed design utilizes physics which is totally different from the design that forms the basis of legacy phase shifting devices, e.g., ferrite phase shifters. The low-cost phase shifter may be integrated in 5G communication systems.
(11) FIG. 2 shows an exemplary SIW phase shifter geometry according to the invention. In particular, there is shown a substrate having length, width and height dimensions. For exemplary purposes, the SIW guide is fabricated by using a Rogers Duroid 5880 substrate with a thickness of 3 mm, and a dielectric constant of 2.2. Other materials having different thicknesses and dielectric constants may also be employed. Typically a substrate is included in an SIW for mechanical reasons to provide support and the choice of the material is not critical as long as the material is low loss at the frequency of interest. The substrate has a wave entry port on a first end (i.e., port 1, shown in FIGS. 2 and 4) and a wave exit port on a second end (i.e., port 2, shown in FIGS. 2 and 4) of the substrate, wherein the first and second ends are opposite ends of the substrate. The waveguide includes a plurality of curved sections which form a serpentine path of curves in a first direction followed by curves in a second direction which is opposite the first direction. A plurality of radiating members (sometimes referred to as elements) extend into the waveguide between curves in the first direction and curves in the second direction. The radiating elements of the array, in some embodiments, are semi-circular radiating slots spaced approximately one half-wavelength apart in free space.
(12) The effective width of the straight sections of the SIW waveguide is “a” (see FIG. 2). The distance between radiating elements is “b” (see FIG. 3). In some embodiments a=b. In the figures, “a” the width of the SIW and “b” the separation distance between radiating elements are both close to half wavelength, “c” and “e” are the length and width of the rectangular part of the slots, respectively. The relevant dimensions of the exemplary device shown in FIGS. 2 and 3 are as set forth in Table I.
(13) TABLE-US-00001 TABLE I THE DIMENSIONS OF THE SIW PHASE SHIFTER Length Width a b c e 50 mm 24 mm 6 mm 6 mm 3.66 mm 0.5 mm
“a” and “b” are close to half wavelength to make an acceptable side lobe level and c and e are optimized to keep the reflexion coefficient under −10 dB for all phase shifters. The propagation constant in the waveguide varies as a function of the width of the guide. If the value of the width of the guide is changed, the resonance frequency varies because the propagation constant varies.
(14) In FIG. 2, each of the curved SIW sections between the slots contain phase shifters. In FIG. 2, the phase shifters are metalized vias of a diameter equal to 0.8 mm and they are spaced 0.4 mm apart. The via thickness is preferably the same for all vias. The spacing between vias that present the waveguide and curved waveguide is the same and is equal to 1.2 mm from center to center vias. But for the vias which are representing the phase shifters, the spacing depends on the desirable phase shifter. The phase shift is realized by switching the metalized vias inside the curved waveguide sections. The vias which are presenting the different phase shifters (see FIG. 5) may be configured and operated by a control mechanism to have mutually exclusive combinations of being filled with a conductor or being devoid of a conductor filling.
(15) In the fabrication process the curved SIW with slots, but without any phase shifters, is preferably produced first as shown in FIG. 4. Next, the phase shifter is inserted inside the curved sections to scan the array (i.e., scan the beam). FIGS. 4 and 5 show different exemplary alternatives for the phase shifter shown in FIG. 2. The alternative shown in FIG. 5 is based on the use of liquid metal deposited in at least some of the vias. The via configuration is varied to realize different phase shifts, which in turn determine the scan angle of the array. The liquid metal is used to fill the dielectric tubes which are positioned inside the curved waveguide sections. As noted above, the vias presenting the different phase shifters (see FIG. 5) may be configured and operated by a control mechanism to have mutually exclusive combinations of being filled with a liquid metal or being devoid of filling by a liquid metal.
(16) Another alternative phase shifter design is shown in FIG. 6 and is based on the use of switching diodes. The switching diodes could be PIN diodes, which are basically comprised of a p-type semiconductor region separated from an n-type semiconductor region by a wide, undoped intrinsic semiconductor. An advantage of the PIN is the switching time. Using the PIN, the switching time becomes very fast comparing to the liquid metal switching mechanism. The switching diodes are turned on or off, to effectively change the electrical length of the wave path, and thus to change the phase. In either embodiment, to realize one phase shifter we there needs to be a number of vias or diodes not just one via or one diode for each phase shifter. In the second technique (see FIG. 6), which approach is faster than the liquid metal approach, phase shifting is based on the use of multiple PIN diode switches (e.g., switches 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, as shown in FIG. 6) that are either on or off depending upon their bias levels. This is, similar to the FIG. 5 embodiment, achieved by positioning or depositing the switches inside the curved sections, just as for the case of liquid metal vias. The advantage of the PIN is the switching time: using the PIN, the switching time becomes very fast comparing to the liquid metal switching mechanism.
(17) The proposed general design shown in FIG. 2, with variations shown in FIGS. 5 and 6 effectively varies the electrical length between the adjacent radiating elements, and it does this by using switchable vias inside the waveguide which connects the two adjacent radiating elements. FIG. 4 highlights the curved SIW without any phase shifter, while FIG. 2 highlights an example of one phase shifter presented by 6 vias inserted in the curved sections. Variable phase shifts are realized by placing and arranging the vias in various locations to alter the effective width of the guide and thereby control the wave propagation in the guide. Low loss is achieved by using high quality PIN diodes that are still low cost (see FIG. 6). This type of phase shifter provides a stepwise phase shift, e.g. 30 deg. 60 deg., 90 deg., etc. Though not shown here, a separate and auxiliary phase shifting mechanism can be added to the stepwise phase shifters, if desired.
(18) The proposed design utilizes physics which is totally different from the design that forms the basis of legacy phase shifting devices, e.g., ferrite phase shifters. A desired phase shift can be achieved by varying the configuration of the vias inserted in the curved sections of the waveguide. As noted above to have mutually exclusive combinations of being filled with a liquid metal or being devoid of filling by a liquid metal. Varying the configuration of the vias, in turn, changes the propagation constant within the guide and thus achieves different electrical lengths of the curved sections of the SIW guide, even though their physical lengths remain unchanged. The via patterns inside the curved web guide sections are reconfigured to realize different phase. It is possible after configuring the control mechanism of the wave propagation in the guide to have mutually exclusive combinations of being filled with a liquid metal or being devoid of filling by a liquid metal.
(19) In some embodiments, as shown in FIG. 7, seven different phase shifters (phase shifter 1, 2, 3, 4, 5, 6, and 7) are used. The simulated reflection coefficients for all the seven phase shifters are plotted in FIG. 7, for the frequency range (i.e., “Frequency (GHz)” shown in FIG. 7) as of 25 GHz to 26.7 GHz. The return loss (S.sub.11) for all the phase shifters is seen to be better than −10 dB in the frequency range of interest mentioned above. The proposed phase shifter introduced in the curved SIW can provide phase shifts in the range of 0 to 360°.
(20) FIG. 8 shows the simulated the gain plots in dB at 26 GHz for different scan angles (i.e., Theta in °), and we observe that the gain varies only moderately, between 9.5 dB and 11 dB as different phase shifters are actuated, which is highly desirable for a scanning array. To have the seven different lobe directions as presented in FIG. 8, we need seven different phase shifters (phase shifter 1, 2, 3, 4, 5, 6, and 7). The switching from a phase shifter to another is being performed by filling of some vias with a liquid metal or by activating some diodes for the PIN diodes case. Furthermore, when we activate one phase shifter at a time, the return loss (S11) is seen to be better than −10 dB in the frequency range 25 to 26.7 GHz and the gain varies only moderately, between 9.5 dB and 11 dB.
(21) The novel proposed microwave scanning array system offers “low-cost” platforms that can be ground-based or mounted on mobile platforms, e.g., airplanes, ships and buses for SATCOM systems. The main beneficiary of the proposed scanning array system will be broadband mobile communication industry because the proposed “low-cost” platforms can be ground-based or mounted on mobile platforms, e.g., airplanes, ships and buses for SATCOM systems offering broadband, wide connectivity, high capacity, high speed data transfer, without using conventional ferrite type phase shifters that can be prohibitively costly as well as lossy. The phase shifting system can be fabricated relatively easily using existing electronic components and it is both low loss and relatively low cost.
