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REPORT DOCUMENTATION PAGE

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Form Approved REPORT DOCUMENTATION PAGE OMB No Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions,
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Form Approved REPORT DOCUMENTATION PAGE OMB No Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of lhis collection of nformation, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports ( ), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA Respondents should be aware that notv.ithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information ~it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YyyY) I 2. REPORT TYPE 3. DA TES COVERED (From - To) Final 01 /02/2013 to 30/04/ TITLE AND SUBTITLE Sa. CONTRACT NUMBER Slotted Waveguide and Antenna Study for HPM & RF Applications N Sb. GRANT NUMBER N Sc. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Sd. PROJECT NUMBER Christos Christodoulou Se. TASK NUMBER Sf. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT University of New Mexico NUMBER 9. SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) AFRL 11. SPONSOR/MONITOR'S REPORT NUMBER(S) 12. DISTRIBUTION I AVAILABILITY STATEMENT Public 13. SUPPLEMENTARY NOTES 14. ABSTRACT An S-band longitudinal slotted waveguide antenna was designed to perform as a uniform array. The antenna was investigated for its power handling capability. The input power threshold for both air breakdown and multipaction were studied. The radiation pattern measured in high power testing with a magnetron providing 500 ns long and 0.8 MW peak pulses, demonstrated good agreement with the simulated radiation pattern. This source power level was below the predicted maximum input power handling capability of 1.8 MW, at high elevation (in Albuquerque, NM). No breakdown was observed during the experiment. To further reduce the size of the antenna array, a narrow-band, rugged, complementary-split-ring (CSR) slotted waveguide antenna (SWA) was designed and fabricated. Both simulation and experimental results showed that the complementary-split-ring slot radiates a linearly polarized wave with high efficiency. The CSR slotted waveguide antenna provided, approximately, 55% size reduction, compared to currently available SWA designs, with high directivity, low return loss, and very high power handling capability for S-band applications Finallv, a new approach to prototypinq CSR-SWA antennas for hiqh-power microwave applications bv usinq 3D printinq 1 S. SUBJECT TERMS Slotted waveguide arrays, High power microwaves, 30 printed antennas, multipaction, complementary-split-ring waveguide arra 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT a. REPORT b. ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER (include area code) Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39. 18 Department of Electrical & Computer Engineering Slotted Waveguide and Antenna Study for HPM & RF Applications Final Technical Report ONR Grant#: N February April 2017 July Submitted by: Christos Christodoulou- Principal Investigator Department of Electrical and Computer Engineering University of New Mexico Albuquerque, NM Tel. (505) This material is based on research sponsored by the Office of Naval Research under agreement number N000!4-13-I The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. Distribution Statement A: Approved fo r public release; distribution un limited TABLE OF CONTENTS LIST OF ACRONYMS... 3 LIST OF FIGURES... 4 I. SUM!v1ARY OF ACHIEVEMENTS... 6 IL INT.RODUCTION III. DETAILED RESULTS OF THE PROJECT I. Narrow-wall longitudinal slotted wavegu ide antenna design for HPM applications S-band narrow-wall longitudinal-slot array waveguide antenna... l 0 I.2 Collaboration with NSWC Dahlgren Collaboration with Air Force Research Laboratory Power handling capabili ty estimation for slotted waveguide antennas Power handling capability estimation determined by air break down (outside the antenna) Power handling capabi lity estimation determined by multipaction (inside the antenna) Miniaturization of narrow-wall slotted waveguide antenna designs l Periodic structures applied for antenna miniaturization and beam-steering.. 23 Split-ring-loaded waveguide: Double narrow-wall longitudinal-slot array waveguide antenna: A Compact S-band narrow-wall complementary-split-ring slotted waveguide antenna Complementary-split-ring slots in the narrow-wall of a rectangular waveguide Microwave network analysis... 30!\arrow-wall complementary-split-ring slotted waveguide antenna Complementary-split-ring slotted waveguide antenna loaded with periodic air-filled corrugations Complementary-split-ring slotted wavegu ide antenna array D printed HPM antennas printed HPM antennas on ABS printed HPM antennas on Bluestone (SLA printing) IV. CONCLUSIONS V. List of publications APPENDIX J Slotted circular cylinder resonators REFERENCES LIST OF ACRONYMS Acronym ABS APS CRLH CSR CST ECCS EMI HPB HPM HFSS IEEE RF RFI SCCR SLA SRR SWA URSl USNC Definition Acrylonitrile Butadiene Styrene Antennas and Propagation Society Composite Right/left-Handed Complementary Split Ring Computer Simulation Technology European Cooperation for Space Standardization Electromagnetic Frequency Interference H-plane Bend High Power Microwave High Frequency Structure Simulator Institute of Electrical and Electronics Engineers Radio Frequency Radio Frequency Interference Slotted Circular Cylinder Resonator Stereo lithography Split Ring Resonator Slotted Waveguide Antenna International Union of Radio Science United States National Committee 3 LIST OF FIGURES Figure 1 S-band & X-band narrow-wall longitudinal slot array waveguide antenna.. 10 Figure 2 Simulated and measured S parameter Figure 3 Radiation Pattern Set-up Figure 4 Normalized radiation pattern of narrow-wall longitudinal-slot array waveguide antenna: a) I-I-plane, b) -plane Figure 5 Schematic and H-plane rad iation pattern of double-array design Figure 6 Schematic and axial ratio of circularly-polarized-array design Figure 7 Measured return loss of the S-band narrow-wall longitudinal-slot array waveguide antenna Figure 8 Simulated and measured H-plane radiation pattern of the S-band narrow-wall longitudinal-slot array waveguide antenna Figure 9 Simulated and measured E-plane radiation pattern of the S-band narrow-wall longitudinal-slot array waveguide antenna Figure 10 Block diagram of hottest setup Figure LI High power microwave source: S-Band Magnetron F igure 12 Radiation pattern measurement setup inside anechoic chamber Figure 13 Diagram ofh-plane radiation pattern measurements Figure 14 Antenna gain within the main-beam Figure 15 E field distribution simulated by HFSS Figure 16 Power threshold estimation by CST Figure 17 Number of electrons inside the antenna for input power of2.35mw, 2.54MW and 2.75MW Figure 18 Distribution of the electrons inside the antenna (P;n=2.35MW) Figure 19 Distribution of the electrons inside the antenna (Pin=2.54MW) Figure 20 Schematic of HPB-radiator loaded with an SRR-array (overlapping placement of rings) Figure 21 S 11 of H-plane-bend radiator loaded with an SRR-array Figure 22 3D radiation pattern & E-field polarization of HPB-radiator loaded with an SRR array Figure 23 Schematic of double narrow-wall longitudinal-slot array waveguide antenna and its 3D radiation pattern Figure 24 Configuration of CRLH waveguide structure Figure 25 Azimuth plane radiation pattern for different lengths of short stubs of left-handed/right-handed waveguide Figure 26 Desig11 parameters of the CSR slot Figure 27 SJ 1 vs R F igure 28 S 11 vs a Figure 29 SJ l vs w Figure 30 Equivalent microwave network of the slot array Figure 31 Comparison of the CSR-SWA with the longitudinal slot artay (same inter-ele1nent spacing) Figure 32 schematic of the CSR-SWA Figure 33 aluminum plates fabricated by Waterjet Cutting Figure 34 Simulated and measured SJ 1 of the CSR-SWA Figure 35 Comparison of the CSR-SWA and the longitudinal SWA Figure 36 Radiation pattern measurement set-up for the CSR-SWA Figure 37 Measured & simulated normalized radiation pattern of the CSR-SWA Figure 38 Periodic corrugations added to the other narrow-wall of the CSR-SWA Figure 39 H plane rad iation pattern of the CSR-SWA and the CSR-SWA loaded with corrugations Figure 40 E plane radiation pattern of the CSR-SWA and the CSR-SWA loaded with corrugations Figure 4 l Schematic of the CSR-SWA double array Figure 42 E-plane radiation pattern of the CSR-SWA double array and the longitudinal slotted waveguide antenna Figure 43 H-plane radiation pattern of the CSR-SWA double array and the longitudinal slotted waveguide antenna Figure 44 Normalized E-plane radiation pattern of the CSR-SWA double array and the single CSR-SWA Figure 45 Normalized H-plane radiation pattern of the CSR-SWA double array and the single CSR-SWA Figure 46 3D printed CSR-SWA and aluminum CSR-SWA (on the right). Antenna one the left is the metallic version Figure 47 A 30 printed CSR-SWA applied with MG chemical 843 conductive coating Figure 48 Schematic of3d printed CSR-SWA with conductive coatings Figure 49 Sl l values of JD printed CSR-SWA with MG chemical Figure 50 I-I-plane radiation pattern of3d printed modified CSR-SWA with conductive coating Figure 51 E-plane radiation pattern of30 printed modified CSR-SWA with conductive coating Figure 52 SLA printed CSR-SWA plated with copper Figure 53 Geometry of SCCR structure with nonzero thickness I. SUMMARY OF ACHIEVEMENTS This technical report presents the work performed during the time span of of ONR NOOO contract. The achievements can be listed as follows: a) Narrow-wall longitudinal slotted waveguide antenna design for HPM applications i) A high-gain, S band narrow-wall, longitudinal-slot array waveguide antenna design was proposed. The proposed antenna model was fabricated and tested at the University of New Mexico. Further research on a double array design, a curved antenna design, and a circularly polarized antenna design was performed through HFSS simulations. ii) The University of New Mexico has collaborated with NSWC Dahlgren on fabricating and testing an S-band, narrow-wall, longitudinal-slot array waveguide antenna. Its high power handling capability has been tested. iii) The University of New Mexico has also collaborated with the Air Force Research Laboratory in Albuquerque, NM on testing the high power capabilities of the S-band narrow-wall longitudinal-slot array waveguide antenna. A paper was submitted to the APS/URSI 2017 reporting the experiments performed both at the University of New Mexico and at the Air Force Research Laboratory in Albuquerque. iv) The power handling capability estimation for slotted waveguide antenna was performed, thjough ANSYS HFSS and CST Particle-in-cell solver. A paper was submitted to the journal of IEEE Antennas and Wireless Propagation Letters. b) M iniaturization of narrow-wall slotted waveguide antenna designs i) A periodic structure using split-ring-resonators was applied to the narrow-wall slotted waveguide antenna for size miniaturization in either transverse cross section or longitudinal length of the waveguide. A paper was submitted to and presented at 2014 USNC-URSI, National Radio 6 Science meeting. A new double narrow-wall longitudinal-slot array design was proposed to reduce the side-lobe level. A paper was submitted to and presented at the APS/URSI 2014 conference. ii) A narrow-wall, complementary-split-ring slotted waveguide antenna design was proposed for antenna size reduction. This was the first time that such a slot structure was used as a radiating element in slotted array waveguide antennas. The proposed narrow-wall complementary-split ring slots provide similar radiation characteristics, i.e. efficiency, gain, polarization etc., as the conventional, half-wavelength longitudinal slots, while reducing the slot dimension to 0.229A. An antenna prototype was fabricated and tested at the University of New Mexico. A paper was submitted to and presented at the APS/URSl Additionally, a journal paper was submitted to the IEEE Transactions on Antennas and Propagation in c) 3D printing technology fo r fast prototyping of complex, light weigh RPM antenna structures i) 3D printing technology has been applied to the fabrication of the narrow-wall complementary-split-ring slotted waveguide antenna design, due to the complexity of its design, and precision required of the fabrication of the CSR-slots. A couple of antenna prototypes were built at UNM and tested. The 3D printed antenna models were either spray painted with conductive paint or electro-plated. A paper was submitted and presented at the APS/URSl II. INTRODUCTION 1. High-power microwave antennas Recently, high power microwave (HPM) structure technology has seen major developments in size reduction as well as increase in efficiency [1]. Electronics have 7 been proven to be vulnerable to various high power generated waveforms (2-5]. Key devices to develop HPM systems are high power microwave antennas. HPM antennas can provide very intense electric field ( -field) covering a narrow band to ultra-wideband spectrums. Such antennas require a gain as high as possible, side lobes as low as possible, and withstand input power as high as possible. Depending on the application and mainly on the feeding HPM source (magnetrons, backward-wave oscillators (BWO), magnetically insulated line oscillators (MILO), Marx generators, etc.), designs ofhpm antennas have been proposed in the form of parabolic antennas [6], slotted waveguide antennas [7], lens antennas (8], reflect array antennas [9], radial transmission helix arrays [ l OJ, etc. In this work, the design of an air-filled slotted rectangular waveguide antenna has been considered for its ruggedness and high-power handling capability. This type of antenna provides high directivity, low return loss as well as mechanical structural strength. The need to miniaturize the antenna size to fit the platform also leads us to the design of slotted waveguide antennas due to their compact structure. 2. Miniaturization of the slotted waveguide antenna designs This type of half-wavelength slotted waveguide antennas tend to be bulky and heavy due to its all metallic structure. The reduction of the array size without losing its radiation performance is limited by the size of the half-wavelength longitudinal slots. Recently, single split-ring resonators have been placed underneath longitudinal slots to reduce slots size while maintaining a similar gain and efficiency [ll-12]. The split-ring resonators must be designed to match the desired resonant frequency, as well as be precisely placed underneath the slot, to increase the field intensity. Thus, the complexity of manufacturing increases significantly. Also, the reduction in size is li mited to 0.25A. 0 without a loss of radiation performance. To fu1ther reduce the size of the slot dimensions and to overcome the associated manufacturing complexities, an alternative approach is required. A split-ring slot cut 8 in the broad-wall of a rectangular waveguide was proposed and investigated [13-14]. The outer diameter of such split ring slot cuts was shown to reduce the individual slot dimensions from 0.5il. 0 to 0.186il. 0, yielding a more compact array antenna whit similar radiation characteristics as the conventional half-wavelength slot arrays. 3. 3D printing technology (Or high-power-microwave applications Additive manufacturing or 3-D printing is a technology that enables the fabrication of complex objects directly from a digital model. Three-dimensional printing is achieved by laying down successive layers, each of slightly different shape. This technology has been evolving quite rapidly in recent years and is nowadays seen an alternative to traditional manufacturing methods. Potential applications of 3-D printing have expanded from its origins in the fabrication of mechanical objects to the incorporation of electrical circuits in the manufacturing process [15]. It has the potential to provide a number of benefits to high power microwave (HPM) systems, including weight reduction, rapid prototyping, or the fabrication of extremely complex shapes. An obvious concern is that these benefits may come at the cost of a reduction in performance or durability. Recently, the performance of two 3D printed anode structures, metallized via electroplating and thermal spraying, in a relativistic planar magnetron was reported in [ 16]. It was shown that both 3 D printed anode structures provide similar microwave performance compared to a machined aluminum anode. Over a limited set of shots, no damage or degradation was observed. A slow wave structure (metamaterial-like) was fabricated using 30 printing in [17]. This structure was tested in the mega watt class and no breakdown, attributable to the surface roughness, introduced by additive manufacturing, was observed in the experiments. 9 Ill. DETAILED RESULTS OF THE PROJECT 1. Narrow-wall longitudinal slotted waveguide antenna design for HPM applications 1.1 S-band narrow-wall longitudinal-slot array waveguide antenna A high-gain, S-band narrow-wall longitudinal-slot array waveguide antenna design for high-power microwave applications was proposed in [ l 8]. The proposed antenna operates at 3.17GHz with a return loss of -32dB. Measurement results show that the antenna provides a fan-beam radiation pattern, as predicted by HFSS simulations. Figure I shows the S-band, narrow-wall longitudinal-slot array waveguide antenna model along with the X band antenna model. Figure 2 presents simulated and measured return loss results of the S-band narrow-wall longitudinal-slot array. Figure l. S-band & X-band narrow-wall longitudinal slot array waveguide antenna...., ~ O F OQ~ncy Figure 2. Simulated and measured S parameter Figure 3 shows the radiation pattern measurement set-up and Figure 4 depicts the 10 simulated and measured radiation pattern of the S-band narrow-wall longitudinal-slot array design. Table J shows predictions of the power handling capability for the S-band narrow-wall longitudinal-slot a1rny design in different air pressure cases. Figure 3. Radiation Pattern Set-up 1.0 ~ ~ 0.8 a; ~ Simulation Ex eriment ~ (ij 0.4 E 0 z Theta a) I-I-plane 1.0 E Q) ::::: 0.8 '!':- 0.6 Q) ~ 8.. al 0.4.~ 'iij ~ Simulation - Ex eriment Phi(degree) b) E-plane Figure 4. Normalized radiation pattern of narrow-wajj longitudinal-slot array waveg.uide antenna: a) H-plane, b) E-plane. 11 Table I Maximum input power for narrow-wall longitudinal-slot array design in HFSS simulation SEA LEVEL ALBUQUERQUE Maximum Input Power 2.SMW l.8mw Figures 5 and 6 show further research conducted based on the S-band narrow-wall longitudinal-slot array design. The double-array design presents a low side-lobe level, whereas the circularly polarized antenna presents circular polarization within the range of the main beam. a) Schematic of the double-array ~ ~ (i) 0.8.9:! c: 0 ii) ~ 0.6 E '6 c -~ ro E c: It i ~.. l J l I i - Double Array -- Slot Arra Theta( degrees) b) H-plane radiation pattern Figure 5. Schematic and H-plane radiation pattern of double-array design 12 a) Schematic of the circular-polarized-array design ii) 15 O 0 ~ 12 a: (ij 9 ~ 6 \ \ \ \ l--axial Ratiol! I! l I 3 O+-~~~~~~~~~~~~~~~~~--l Phi(degre) b) Axial ratio of the circular-polarized-array design in the H-plane Figure 6. Schematic and axial ratio of circularly-polarize
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