Rotary waveguide phase shifter based on metamaterials

Abstract

A Rotary Waveguide Phase Shifter (RWPS) device adjusts the output phase of a high-power microwave waveguide. The device includes one or more mode converters for converting linear polarization to circular polarization, and a rotary metamaterial element (MME) which may be rotated, either manually or by a servomechanism, about an axis parallel to a direction of propagation. Quarter and half waveplate designs of the MME are provided. Calibration of the RWPS device enables continuous phase shifts from zero to 720 degrees with high accuracy and repeatability. The length of the device in the propagation direction is far less than that required by conventional dynamic phase shifters.

Description

[0001] Rotary Waveguide Phase Shifter based on Metamaterials

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a radiofrequency (RF) device and specifically to a compact, low-loss high-power rotary waveguide phase shifter (RWPS) based on metamaterials.

[0004] BACKGROUND OF THE INVENTION

[0005] Rotary vane phase shifters provide a tunable phase shift by manual or motorized rotation of a low-loss dielectric vane inside a waveguide. The vane changes the guide wavelength giving rise to a change in dynamic phase that is proportional to the length of the waveguide propagation path. At low RF frequencies, e.g. below 20 GHZ, the large size and / or high insertion loss of such phase shifters prevents their use in many high-power microwave applications, such as phased array radar systems and high-energy particle accelerators.

[0006] More compact tunable phase shifters have been proposed based on sub-wavelength patterning of dielectric metamaterials that enable circular polarization mode conversion based on spatial manipulation of geometric phase (GP), or Pancharatnam-Berry (P-B) phase.

[0007] U.S. Patent Application Publication No. US 2022 / 0066082 Al, to S. Young et al., entitled “Polarization Control Devices Using Cascaded Subwavelength Dielectric Gratings”, dated March 3, 2022, presents transmissive and reflective all-dielectric metastructures that offer tailored polarization conversions and spectral responses. The metastructures consist of stacked deeply subwavelength, high contrast gratings of different fill factors and rotations. Plane-wave transfer matrix techniques are employed to model the interactions between gratings, allowing for rapid design and optimization.

[0008] SUMMARY OF THE INVENTION

[0009] The invention provides a compact, low-loss high-power RWPS device including a rotary metamaterial element (MME). The MME and other elements within the device are designed to provide sustained operation at high power levels, such as up to 200 megawatts for nanosecond pulse durations or up to four megawatts for microsecond pulse durations. Calibration of the RWPS device enables continuous phase shifts from zero to 720 degrees with high accuracy and repeatability.

[0010] According to one aspect of the presently disclosed subject matter, there is provided a rotary waveguide phase shifter (RWPS) device including an electromagnetic (EM) waveguide having a propagation axis (Z-axis) and further including: a waveguide input port configured to receive a first EM mode which is linearly polarized in a first direction and has an operating frequency (f) and a first phase angle ( 1); a mode converter for converting the first EM mode to a second EM mode which is circularly polarized; a rotary metamaterial element (MME) which converts the second EM mode to a third EM mode which is circularly polarized in an opposite sense and has a second phase angle (02); and a waveguide output port configured to transmit the third EM mode. The rotary MME is configured to rotate through a rotation angle (0) about the Z-axis, and the second phase angle is shifted with respect to the first phase angle by a phase shift (A0) equal to g(0,f), where g(0,f) is a predetermined calibration function.

[0011] According to some aspects, the rotation angle (6) is adjusted manually or by means of a servomechanism.

[0012] According to some aspects, the phase shift (A<|)) ranges continuously from zero to 720 degrees.

[0013] According to some aspects, the calibration function is a linear function of the rotation angle (0).

[0014] According to some aspects, the mode converter is a quarter-wave plate.

[0015] According to some aspects, the rotary MME is a half-wave plate.

[0016] According to some aspects, the device further includes an RF circulator and an RF reflector; and the rotary MME is a quarter-wave plate.

[0017] According to some aspects, the MME comprises a dielectric material having a relative permittivity at the operating frequency whose real part is greater than or equal to eight and whose loss tangent is less than or equal to 0.0002.

[0018] According to some aspects, the MME comprises one or more materials selected from the group consisting of sapphire, alumina, and magnesium oxide.

[0019] According to some aspects, the device is configured to have an insertion loss whose value is less than or equal to 0.25 decibels at the operating frequency.

[0020] According to some aspects, the EM waveguide is circular.

[0021] According to some aspects, the operating frequency (f) is greater than or equal to the cutoff frequency for a TEn mode and less than the cutoff frequency for a TMoi mode.

[0022] According to some aspects, an interior of the waveguide is in vacuum or is filled with a gas.

[0023] According to some aspects, the device includes an additional mode converter for converting the third EM mode into a fourth EM mode which is linearly polarized in a second direction. According to some aspects, the EM waveguide is coupled to one or more rectangular waveguides.

[0024] According to some aspects, the EM waveguide is configured to operate at power levels up to 200 megawatts for nanosecond pulse durations or up to four megawatts for microsecond pulse durations, without electrical breakdown or overheating.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention is herein described, by way of example only, with reference to the accompanying drawings. Like reference numerals are used to denote similar or like elements in the drawings.

[0027] FIG. 1 is a block diagram of a first exemplary RWPS device comprising a half-waveplate (HWP) metamaterial element (MME) according to the invention.

[0028] FIG. 2A shows a perspective drawing of the MME of FIG. 1.

[0029] FIGs. 2B-2C show cross-sectional drawings of the MME of FIG. 1.

[0030] FIG. 3 shows an intensity plot of the transverse magnetic field inside the RWPS device of FIG. 1.

[0031] FIG. 4 shows a graph of the phase angle shift angle (A(|)) vs. the rotation angle (0) of the MME, for the RWPS device of FIG. 1.

[0032] FIG. 5 is a block diagram of a second exemplary RWPS device comprising a quarter-waveplate (QWP) metamaterial element (MME) according to the invention.

[0033] FIG. 6 shows a graph of the reflection factor vs. frequency (f), for the RWPS device of FIG. 5.

[0034] FIG. 7 shows an intensity plot of the transverse magnetic field inside the RWPS device of FIG.

[0035] 5.

[0036] ABBREVIATIONS AND SYMBOLS

[0037] The following abbreviations and symbols are used in the detailed description.

[0038] RWPS - Rotary Waveguide Polarization Shifter

[0039] EM - Electromagnetic

[0040] MME - Metamaterial Element

[0041] HWP - Half- Wave Plate

[0042] QWP - Quarter- Wave Plate f - frequency of an EM wave (e.g. in GHz)

[0043] (|) - phase of an EM wave (e.g. in degrees)

[0044] A(|) - a phase shift (e.g. in degrees) 0 - a rotation angle of the MME (e.g. in degrees) tan 8 - material loss tangent (dimensionless)

[0045] (£’ + j£”) / £o - material complex relative permittivity (dimensionless)

[0046] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] FIG. 1 is a block diagram of a first exemplary RWPS device 100 comprising a HWP metamaterial element (MME) according to the invention. Waveguide 110 is, for example, a cylindrical waveguide with an input port 120, an output port 160, and a longitudinal Z-axis in the direction of propagation. The input is a linearly polarized EM wave having a frequency (f) and a phase ( 1). The frequency f is preferably above the cutoff frequency of the waveguide TEn mode and below the cutoff frequency of the TMoi mode. For example, for a perfectly conducting waveguide of diameter 8 cm. and having an interior vacuum, the cutoff frequencies are approximately 2.20 GHz for TEn and 2.87 GHz for TMoi.

[0048] Mode converter 130 converts the input polarization from linear to circular polarization. For example, converter 130 may be a QWP oriented at 45 degrees with respect to the electric field of the linearly polarized input, and the sense of the circular polarization may be right circular polarization (as shown explicitly in FIG. 3).

[0049] Metamaterial element (MME) 140 comprises a dielectric grating which is designed according to the principles of the Pancharatnam-Berry (P-B) phase and acts as a rotatable HWP. The axis of rotation is the Z-axis, and the angle of rotation (0) is continuous from zero to, say, 360 degrees. The MME changes the sense of the circular polarization, e.g. from left to right circular (as shown explicitly in FIG. 3) and causes a geometric phase shift equal to 20 (in theory). Thus, a 360-degree rotation angle 0 gives rise to a phase shift of 720 degrees. This large geometric phase shift is achieved within a propagation distance AZ which is much smaller than that required by conventional dynamic phase shifters.

[0050] The junction between the MME 140 and the waveguide 110 is a conducting rotary joint. Rotation unit 145 is, for example, a servomechanism which enables motorized control of the MME rotation angle 0. Alternatively, unit 145 may be simply a rotatable knob providing a manual control of the MME rotation angle.

[0051] The EM wave at the output port 160 is circularly polarized with a frequency (f) and a phase 2- The total phase shift, A0 = 02 - 01, is the sum of the geometric phase shift of the MME, determined by 0, and the dynamic phase corresponding to the optical path length from the input port 120 to the output port 160. The latter generally depends on the operating frequency (f) and the dielectric constant of the gas (if any) inside the waveguide 110. In some embodiments, an additional mode converter 132 converts the circularly polarized electric field back to linear polarization. For example, converter 132 may be a QWP oriented in a direction parallel or perpendicular to that of mode converter 130.

[0052] In some applications, the waveguide 110 may be coupled to one or more rectangular waveguides.

[0053] FIG. 2A shows a perspective drawing of the MME 140 of FIG. 1, and FIG. 2B-2C show cross- sectional drawings of the MME. The MME consists of a ring 142, and a grid with a multiplicity of rungs 144 separated by air gaps 146. The ring 142 has an inner diameter 142a and an outer diameter 142b. The widths of the rungs and gaps are denoted by 144a and 146a. The MME has a thickness 148 in the direction of the Z-axis.

[0054] The MME comprises a low-loss dielectric material which has a relative permittivity whose real part is preferably greater than or equal to eight and whose loss tangent is preferably less than or equal to 0.0002, at the operating frequency. The following table shows the design parameters of an exemplary MME made of at least 95% alumina, which has been designed to operate in the frequency range between the Tn and Moi cutoffs.

[0055] Table 1: Exemplary MME Design parameters

[0056] The dimensions shown in columns three and four have been determined using the CST Studio Suite® software package, which is a three-dimensional EM analysis package, available from Dassault Systemes Simulia Corp. Both the HWP and the QWP MMEs are described by FIGs. 2A-2C. The HWP MME in the third column is associated with the MME element 140 in FIG. 1. The QWP MME in the fourth column is associated with the MME element 140’ shown in FIG. 5, and its operation is described in detail in the subsequent paragraphs relating to FIG. 5.

[0057] FIG. 3 shows an intensity plot of the transverse magnetic field inside the RWPS device of FIG. 1. The color bar on the right shows the scale, in units of volts per meter (V / m). FIG. 4 shows a graph of the phase angle shift ( A(|)) vs. the MME rotation angle (0) for the RWPS device of FIG. 1. The points on line 420 are calculated from the S21 component of the scattering matrix computed at a fixed frequency (f) of 2.86 GHz using the CST simulation software. Over most of the angular range, the slope of line 420 is equal to two. A small departure from linearity is seen inside the dashed oval 430. In general, for applications requiring highly accurate values of the phase angle shift A(|), it is advisable to predetermine a calibration function, g(0,f), by performing an ensemble of CST simulations over a dense grid in the space (0,f) , which includes all of the operational frequencies and MME rotation angles that are intended for use.

[0058] FIG. 5 is a block diagram of a second exemplary RWPS device 500 comprising a QWP metamaterial element (MME) according to the invention. The cylindrical waveguide 110 has an input port 120 and an output port 160’. As in FIG. 1, the input is a linearly polarized EM wave having a frequency (f) and a phase ( 1). The RF circulator 125, which is analogous to an optical polarizing beamsplitter, transmits the input EM wave with close to 100% efficiency in the +Z direction. Mode converter 130 converts the input polarization from linear to circular polarization. MME 140’ is a dielectric grating which is designed according to the principles of the Pancharatnam-Berry (P-B) phase and acts as a rotatable QWP. From Table 1, the thickness of MME 140’ is roughly one-half that of MME 140, which acts as a HWP. The axis of rotation of MME 140’ is the Z-axis, and the angle of rotation (0) is continuous from zero to, say, 360 degrees. The EM wave is then back-reflected by the total reflector 170, and passes again through MME 140’, this time in the -Z direction. The circular polarization change is accompanied by a geometric phase shift equal to 20. On passing through mode converter 130, in the -Z direction, the circular polarization is converted back to the input linear polarization but opposite in direction. The RF circulator 125 then reflects the EM wave by 90 degrees into the output port 160’, with close to 100% efficiency. The embodiment in FIG. 5 is more compact than the one in FIG. 1 because it makes double use of the mode converter 130 and of the QWP MME 140’.

[0059] FIG. 6 shows an exemplary graph of the reflection factor vs. frequency (f) in GHz, for the RWPS device of FIG. 5. The line 620 is calculated from the magnitude of the S 11 component of the scattering matrix, at a fixed MME rotation angle, for frequencies between 2.84 and 2.89 GHz. At the uppermost frequency, the transmission drops to about 0.95, corresponding to an insertion loss of about 0.25 decibels (dB).

[0060] FIG. 7 shows an intensity plot of the transverse magnetic field inside the RWPS device of FIG. 5. The color bar on the right shows the scale, in units of volts per meter (V / m). Although the embodiments of the present disclosure have been described within the context of a circular waveguide, the principles of the present disclosure may be equally applicable to implementations that use non-circular waveguides.

[0061] The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

CLAIMS1. A rotary waveguide phase shifter (RWPS) device comprising an electromagnetic (EM) waveguide having a propagation axis (Z-axis) and further comprising:(a) a waveguide input port configured to receive a first EM mode which is linearly polarized in a first direction and has an operating frequency (f) and a first phase angle ( 1);(b) a mode converter for converting the first EM mode to a second EM mode which is circularly polarized;(c) a rotary metamaterial element (MME) which converts the second EM mode to a third EM mode which is circularly polarized in an opposite sense and has a second phase angle ( 2); and(d) a waveguide output port configured to transmit the third EM mode; wherein, the rotary MME is configured to rotate through a rotation angle (0) about the Z-axis, and the second phase angle is shifted with respect to the first phase angle by a phase shift (A0) equal to g(0,f), where g(0,f) is a predetermined calibration function.

2. The device of claim 1 wherein the rotation angle (0) is adjusted manually or by means of a servomechanism.

3. The device of claim 1 wherein the phase shift (A0) ranges continuously from zero to 720 degrees.

4. The device of claim 1 wherein the calibration function is a linear function of the rotation angle (0).

5. The device of claim 1 wherein the mode converter is a quarter- wave plate.

6. The device of claim 1 wherein the rotary MME is a half-wave plate.

7. The device of claim 1 wherein the device further comprises an RF circulator and an RF eflector; and the rotary MME is a quarter-wave plate.

8. The device of claim 1 wherein the MME comprises a dielectric material having a relative ermittivity at the operating frequency whose real part is greater than or equal to eight and whose loss tangent is less than or equal to 0.0002.

9. The device of claim 1 wherein the MME comprises one or more materials selected from the group consisting of sapphire, alumina, and magnesium oxide.

10. The device of claim 1 configured to have an insertion loss whose value is less than or equal to 0.25 decibels at the operating frequency.

11. The device of claim 1 wherein the EM waveguide is circular.

12. The device of claim 11 wherein the operating frequency (f) is greater than or equal to the cutoff frequency for a TEn mode and less than the cutoff frequency for a TMoi mode.

13. The device of claim 1 wherein an interior of the waveguide is in vacuum or is filled with a gas.

14. The device of claim 1 comprising an additional mode converter for converting the third EM mode into a fourth EM mode which is linearly polarized in a second direction.

15. The device of claim 1 wherein the EM waveguide is coupled to one or more rectangular waveguides.

16. The device of claim 1 wherein the device is configured to operate at power levels of up to 200 megawatts for nanosecond pulse durations or up to four megawatts for microsecond pulse durations, without electrical breakdown or overheating.

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