1 / 93

RECONFIGURABLE ANTENNA USING PIXEL ELEMENTS Oct. 25, 2007 WPAFB

RECONFIGURABLE ANTENNA USING PIXEL ELEMENTS Oct. 25, 2007 WPAFB. Dr. Eric K. Walton, ElectroScience Lab, The Ohio State University 1320 Kinnear Road; Columbus OH 43212-1191; (614) 292-5051; walton.1@osu.edu IN PARTNERSHIP WITH SYNTONICS LLC, Mr. Bruce Montgomery, President; Columbia, MD.

merton
Download Presentation

RECONFIGURABLE ANTENNA USING PIXEL ELEMENTS Oct. 25, 2007 WPAFB

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. RECONFIGURABLE ANTENNA USING PIXEL ELEMENTSOct. 25, 2007WPAFB Dr. Eric K. Walton, ElectroScience Lab, The Ohio State University 1320 Kinnear Road; Columbus OH 43212-1191; (614) 292-5051; walton.1@osu.edu IN PARTNERSHIP WITH SYNTONICS LLC, Mr. Bruce Montgomery, President; Columbia, MD

  2. WE NEED A CONFORMAL MULTIMISSIONRECONFIGURABLE ANTENNA

  3. PARCA Concepts

  4. Pixel Concepts

  5. RECONFIGURABLE ANTENNA GOALS(WE ARE SERIOUS ABOUT THIS; prototype in 12 months) • Freqs: • 200 MHz to 18 GHz • (ya gotta be kidding ) • Gain: >30dBi goal • Polarization Goals: • V, H, RH Circular, LH Circular, Slant • I.E. “any” • Transmit power: +63dBm CW (2 kW) • Mechanical • Mechanically strong • Conformal • Speed • Complete reconfiguration in < 1 ms

  6. Predict Approach to Establishing Feasibility • Phase I Experiments • Used hex and square “coarse pitch” COTS pixels and simple fixtures • Measured antenna patches • Measured transmission lines • Predict Phase II Performance • Simulated antenna patches using fine-pitch pixel • Simulated transmission lines using fine-pitch pixel Compare, Iterate, • Phase I Analysis • Used hex and square pixels • Simulated patch antennas using dimensions of “coarse pitch” COTS pixels • Simulated transmission lines using dimensions of “coarse pitch” COTS pixels

  7. Highlights to date • Analytic highlights: • Use HFSS (by Ansoft Corp) to model Cap-on-Post concept • Model the transmission lines based on finite dielectric • Good agreement between experimental testing and HFSS models • Experimental highlights: • We created effective pixel-based microstrip transmission lines • Pixel-based t-lines were shown to be reconfigurable and effective • We successfully demonstrated pixel based t-lines feeding patch antennas • single patch • two element steered beam array • Therefore, PARCA antenna concept is feasible! • Pixel size ≤ l/10 continues to seem appropriate • Determines high frequency limit • Precision inter-pixel gaps are critical to performance • Determines low frequency cut-off • Triangular, square, and hexagonal pixels are candidates

  8. Example plot from Smith and Chang

  9. w εr H WIDTH VS. HEIGHT THAT WILL YIELD A 50 OHM TRANSMISSION LINE. From the literature: We note that a 6/32 nut is7 mm across (flat to flat or “average” and 3 mm thick for a W/H ratio of 2.3. It can be supported on a nylon 6/32 nut (nylon εr is 4). Such a transmission line will be very close to 50 ohms. This will be our “standard” test pixel. HFSS model

  10. Example HFSS geometries WE HAVE DONE SEVERAL STUDIES BASED ON THIS MODEL

  11. EXPERIMENTAL TESTING Measure the transmission line impedance and loss. • As a function of shape • As a function of Epsilon • As a function of the thickness of the metal on top Dielectric Metal Movable 6/32 nuts on 6/32 nylon nuts on ground plane with various coaxial connections. SIDE VIEW OF EXAMPLE TEST FIXTURE

  12. TRANSMISSION LINES EARLY EXPERIMENTAL TESTING EARLY TEST LINE PATH 2 (REFERENCE) PATH 1 (2-WIDE NUT ROW)

  13. PRELIMINARY TRANSMISSION DATA • Thru = coax adapter • Barcover = solid metal strip • 2wide = hex geometry with two hex nuts wide (see photo) • 1gap = T-Line with a gap of a pair of hex nuts • Allgone = all of the T Line removed. The rolloff is caused by the characteristics of the coax lines used to feed the structure.

  14. IMPROVED TEST FIXTURE • LARGER SPACING PERMITS TIME DOMAIN STUDIES. • ELIMINATION OF SIDE WALLS SUPPRESSES MULTIPLE REFLECTIONS. WE HAVE A LOT OF RESULTS BASED ON THIS STRUCTURE Ground plane = 25.1 x 18.4 cm

  15. VARIOUS SIZES OF PATCH ANTENNAS WERE TESTED (IMPEDANCE (S11) AND GAIN (S21) PIXEL-BASED PATCH ANTENNAS ARE PRACTICAL EXAMPLE: 6X13 NUT PATCH ANTENNA

  16. analytic modeling

  17. analytic modeling • Modeling allows us to extend simulations to beyond what is possible in these feasibility experiments. • Different dielectrics (including variations in the loss tangent) • Different pixel geometries • Different spacing between pixels • Antenna array modeling

  18. Technical approach to modeling Used HFSS by Ansoft Corp. • 3D electromagnetic field simulation • 3D full-wave Finite Element Method (FEM) • extract parasitic parameters (S, Y, Z) • visualize 3D electromagnetic fields (near- and far-field) • generate broadband SPICE models • optimize design performance. • HFSS evaluates • transmission path losses • reflection loss due to impedance mismatches • parasitic coupling • Radiation

  19. HFSS MODEL EXAMPLE • Nut over washer • Nylon washer with hole • Measured dielectric is 2.0 for washer • This assumes there is no hole, • i.e. measures effective dielectric • Models will use a washer w/o internal hole

  20. Washer/nut prototype

  21. Varying inter-pixel gaps, pixel holes vs. solid, pixel shapes, patch feed schemes

  22. 0 0 -5 -5 -10 -10 -15 -15 -20 -20 -25 -25 -30 -30 -35 -35 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 COMPARISON TO MEASUREMENTS DISCRETE SWEEP 1x34 TL CRES/Nylon w/ Brass feed 1x34 TL CRES/Nylon w/ Brass feed Sim (0.03 mm) ) ) B B measured d d ( ( 1 1 1 2 S S Sim (0.2 mm) Simulated at s=0.031mm Simulated at s=0.031mm Simulated at s=0.2mm Simulated at s=0.2mm measured measured frequency (MHz) frequency (MHz) S11 S21 WE LEARN THAT OUR MEASUREMENTS CORRESPOND TO 0.2 mm SPACING.

  23. 0 0 -5 -5 -10 -10 -15 -15 -20 -20 -25 -25 -30 -30 -35 -35 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 HFSS study of different geometries and separations 1x10 TL hex nuts, s = 0.1 mm 1x10 TL hex nuts, s = 0.005 mm hex nuts, s = 0.0025 mm square nuts, s = 0.1 mm square nuts, s = 0.005 mm square nuts, s = 0.0025 mm hex nuts, s = 0.1 mm squares, s = 0.1 mm hex nuts, s = 0.005 mm squares, s = 0.005 mm hex nuts, s = 0.0025 mm squares, s = 0.0025 mm square nuts, s = 0.1 mm S11 S21 square nuts, s = 0.005 mm square nuts, s = 0.0025 mm squares, s = 0.1 mm squares, s = 0.005 mm squares, s = 0.0025 mm NOTE: LOW FREQ. EXTENDS TO 10 MHZ NOTE: LOW FREQ. EXTENDS TO 10 MHZ frequency (MHz) frequency (MHz) • LOW FREQ. PERFORMANCE: • SQUARE NUTS ARE BETTER THAN HEX • THE HOLE IN THE NUT MAKES LITTLE DIFFERENCE

  24. 10 hex nuts 10 hex nuts 0 0 s = 0.1 mm s = 0.005 mm -5 -5 s = 0.0025 mm -10 -10 s = 0.1 mm s = 0.005 mm -15 -15 s = 0.0025 mm (dB) (dB) 21 11 -20 S -20 S -25 -25 -30 -30 -35 -35 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 frequency (MHz) frequency (MHz) Hex nuts PUSH THE LOW FREQUENCIES BY LOWERING THE GAP SPACING

  25. 1x5 Transmission Line – Varying Geometry • 1x5 TL • Simulations only a few minutes long • Change nut geometry from • Thin PEC strips • Full height PEC nuts no holes • Full height nuts with holes

  26. IMPORTANT PARAMETERS FOR SIMULATION • Smaller separations • S = 0.0050mm • S = 0.0025mm • Behavior for wider TL • 2x43 • 3x43 • Interpolated sweep • Square pixels • Square nuts • Hexagon nuts

  27. S parameters for smaller separation transmission line • S = 0.005 mm • 35 min • S = 0.025 mm • 92 min • S = 0.100 mm • 43 min • Cutoff frequency decreases as separation between nuts is reduced “nuts” @ stainless steel

  28. SQUARE PIXEL STUDY Geometry for square pixels Square pixel side is same length as short diameter of hexagon Shared surface area between square pixels is 1.7x that of hexagon

  29. S parameter for square pixels 0.2 mm

  30. SIMULATION STUDY – QUICK IMPRESSIONS • Separation between pixels • Smaller is much better • Results in a lower cutoff frequency • Allows operation at the lower frequencies that we have been reaching for • Multi-width TL • Single width transmission line is closest to 50 ohms. • Switch from capacitive to inductive • Square pixels • Switch from capacitive to inductive • Lower cutoff freq.

  31. [1] Conclusions drawn from simulations • Inter-pixel gap dimension sets low-frequency cut-off • High frequency: 18 MHz is feasible • Low frequency: 100 MHz seems feasible, 50 MHz may be feasible (but challenging) • Jagged edge formed by hex pixels does not seen to effect performance • Relative surface area of adjacent pixel faces effects performance at low frequencies • E.g., square pixels with same width as hexagon pixels have faces with more surface area

  32. [2] Conclusions drawn from simulations • Discrete versus interpolated scans in HFSS • Interpolated scans — which calculate much faster — are adequate for preliminary design calculations • Detail is lost but general trends are calculated adequately • Discrete scans of large designs will require more computer horsepower • Simulation of feed point deserves careful study • Feed geometry effects S11, S21 performance • We need to better understand how the software is treating this important detail

  33. experimental results

  34. Phase I experimental results • Technical approach to experiments • Test setups • Transmission line experiments • Patch antenna experiments • Conclusions drawn from experiments

  35. Technical approach to experiments • Fixture • Feed structures through (finite) copper ground planes • S11, S21, and pattern measurements taken indoors in laboratory • Pixels • 6-32 nuts in steel, CRES • Some nuts filled with 6-32 screw • Dielectric • Nylon washers, nylon nuts, Plexiglas strips, glass strips • Patch antennas • Hand-formed, inter-pixel gaps controlled by roughness of nuts • Transmission lines • Hand-formed, inter-pixel gaps controlled by roughness of nuts • Various feed point designs

  36. OPEN ENDED LENGTH OF TRANSMISSION LINE (A STUDY OF LOSS EFFECTS) RADIATION ZONE STANDING WAVE ZONE 5 nuts7 nuts11 nuts 2-HIGH LAYER OF HEX NUTS OVER NYLON

  37. OPEN ENDED LENGTH OF TRANSMISSION LINE (A STUDY OF LOSS EFFECTS) CONCLUSIONS • WE CAN SEE THE TRANSITION • T-LINE WITH A MISMATCHED TERMINATION • Below 9 GHz • T-LINE WITH A MATCHED TERMINATION (RADIATION) • Near 11 GHz • RADIATION OCCURS WHERE THE T-LINE IS NEAR RESONANCE AT 11 GHZ (LAMBDA = 2.7 cm) We can speculate that the open end of the line radiates near 11 GHZ.

  38. TRANSMISSION LINE HEX vs. SQUARE NUTS • A SQUARE NUT T-LINE WAS TESTED WITH AND WITHOUT A COPPER COVER • OUR REGULAR HEX LINE WAS TESTED WITH AND WITHOUT A COPPER COVER • FINALLY, A THRU CONNECTION WITH A KNOWN COAXIAL CABLE IN PLACE OF NUTS WAS OBSERVED

  39. TRANSMISSION LINE DIRECT COMPARISON “With cover” is a surrogate for very small gaps. 10 dB loss Good agreement with EYL’s theoretical SEPT 27, 2006 DATA

  40. TRANSMISSION LINES • The coaxial cable gives a “best we can expect” result • The “with cover” results should be approximations for the case of a very small gap. • The square nut case and the hex nut case are quite similar • Eugene Lee’s theoretical results are in very good agreement.

  41. INTRINSIC IMPEDANCE STUDY Input impedance of a device under test based on S11. (Where it is assumed that the cable feeding the device is 50 ohms.) THEN: WHERE Zshort and Zopen are the transmission line input impedances when the far end is either open or shorted.

  42. INTRINSIC IMPEDANCE STUDY COMMENTS • WE HAVE SHOWN THAT MUCH OF THE RADIATION FROM THE LINE IS FROM THE END CONNECTION. (So the line itself may not be very lossy.) • THE END CONNECTION CAN BE SPECIALLY DESIGNED TO INTERFACE WITH THE PIXEL LINE TO SUPPRESS FEED RADIATION. (The “real thing” should do this.)

  43. INTRINSIC IMPEDANCE STUDY • THESE RESULTS ARE INFLUENCED BY RADIATION FROM THE LINE AND THE FEED POINT CONNECTOR • RADIATION FROM THE LINE LOOKS LIKE LINE LOSS • THE BEST BEHAVIOR HERE IS THE 2-NUT WIDE FILLED HOLE EXAMPLE. (But that is only if 50 ohms is considered desirable.) (50 ohms is an arbitrary number in any case.) • MUCH OF THE IMPEDANCE IS SOMEWHAT CLOSE TO 50 OHMS • BUT THE REACTIVE LINE IMPEDANCE VARIES FROM CAPACITIVE TO INDUCTIVE

  44. PUSH FREQUENCY LOWER TRANSMISSION LINE MEASUREMENTS EXTENSION TO LOWER FREQUENCIES GEOMETRY

  45. STACK NUTS 1 – 2- 3 HIGH NOTE MOVE TO LOWER FREQUENCIES

  46. MAKE T-LINES WIDER NOTE COMPARISON TO “BRIDGE” WASHERS

  47. T-LINE LOW FREQUENCY STUDY  GEOMETRY  CONCLUSIONS • STACKING THE NUTS HIGHER IMPROVES THE LOW FREQ. BEHAVIOR • WIDER TRANSMISSION LINE IMPROVES THE LOW FREQ. BEHAVIOR (THIS IS THE MOST EFFECTIVE LOW FREQ. CONCEPT.) • THE “BRIDGE” CONCEPT IS USEFUL, BUT NOT PROVEN TO BE AS EFFECTIVE AS THE WIDER T-LINES IN EXTENDING THE LOW FREQ. BEHAVIOR.

  48. TRANSMISSION LINE DIELECTRIC STUDY WE WILL COMPARE NYLON (εr=4) AND GLASS (εr=6) SUBSTRATES

  49. S11 --- NYLON (εr=4) AND GLASS (εr=6) SUBSTRATES

  50. TRANSMISSION LINE DIELECTRIC STUDY S21 -- NYLON (εr=4) AND GLASS (εr=6) SUBSTRATES

More Related