EHF Rotman Lens Fed Linear Array Multibeam Planar Near-Field Range Measurements CST 5 th NORTH AMERICAN USERS FORUM 4th FEBRUARY 2008 SANTA CLARA, CA

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1 EHF Rotman Lens Fed Linear Array Multibeam Planar Near-Field Range Measurements CST 5 th NORTH AMERICAN USERS FORUM 4th FEBRUARY 2008 SANTA CLARA, CA 3:40 pm - 4:05 p.m. Mike Maybell Planet Earth Communications LLC 1983 San Luis Ave. #31 Mountain View, CA mjmaybell@mindspring.com John Demas Nearfield Systems Inc Magellan Drive Torrance, CA 90502

2 AGENDA 2/4/2008 Rotman Lens-True Time Delay Beamformer Rotman Lens Application Example Rotman Lens CST MWS Analysis Rotman Lens Analysis vs. Measurements AMTA Paper A Presented 11/6/07 1A

3 Rotman Lens Physical Optics Design 2/4/2008 Rotman 1 lens parameters Four basic parameters; α, β, γ, f1 TEM transmission line lengths w computed using Rotman & Turner formulas The focal arc is a circle defined by Rotman & Turner formulas The beam pointing angles are frequency independent 3 focal points y L2 f1 f2 y2 L1 α (X2,y2) w y3 Ψ x Parameter Definition Formula α Focal Angle β Focal Ratio f2/f1 γ Beam to Ray Angle Ratio sinψ/sinα Ψm Maximum Beam Angle f1 Focal Length d Array Element Spacing Na Number of Array Ports Nb Number of Beam Ports εr Rel. Dielectric Constant Note: γ is the compression factor if <1 γ is the expansion factor if <1 >1 [1] Rotman, W. and Turner, R. F., Wide-Angle Microwave Lens for Line Source Applications, Trans. IEEE, Vol. AP-11, Nov. 1963, pp B

4 Rotman Lens Application: AN/SLQ-32(V) 2/4/2008 SLQ-32 is the primary EW suite used on over 450 US Navy Ships. Each ship has one port and one starboard antenna enclosure equipped with a Band 2 receive, Band 3 receive, and Band 3 transmit (V)3 pair of quadrant linear sectoral horn arrays fed by Rotman lenses providing 360 instantaneous azimuth coverage. Thus there are 12 Rotman lenses per (V)3 ship set. AN/SLQ-32(V)2 Outboard Array Enclosure Sidekick Transmitter AN/SLQ-32 Band 3 Rotman Lens Fed Receive Array Measured Multibeam Rosette AN/SLQ-32 Band 3 Receive Rotman Lens Fed Array 1C

5 EHF Rotman Lens CST MWS Analysis 2/4/2008 In 2005 when analysis was required, available CST hardware & software was marginal Using Dell Precision Workstation with 16 GB RAM, A planar array was successfully analyzed using CST MWS TDS in Oct cubic wavelengths 40.6 M mesh cells Acceleware ClusterInABox D30WL should help make CST MWS solution practical Fmax 45.5 GHz λ 0.26 inch L W H inch inch 0.41 inch L/λ W/λ H/λ LWH/λ 3 = cubic wavelenghts 9.9 M mesh cells D

6 EHF Rotman Lens TE Mode Lens Multi- Port S-Matrix Analysis 2/4/2008 We selected TE1 and TE2 mode contour integral lens analysis 2 in conjunction with CST MWS modeling of the isolated waveguide tees including TE1/TE2 mode coupling due to resistance card and other asymmetries within the tees The results 3 compared well with measured lens data TE1 Mode TE1/TE2 Mode 44.5 GHz Composite Beams 1-44 TE1/TE2 Overlay 44.5 GHz [2] A. F. Peterson and E. O. Rausch, Scattering matrix integral equation analysis for the design of a waveguide Rotman lens, IEEE Trans. Antennas Propagat., vol. 47, pp , May 1999 [3] M. J. Maybell et al, EHF Waveguide Rotman Lens for Minimum Frequency Scan and Low Loss Design, Analysis, Test, Paper #2215 submitted to 2008 IEEE International Symposium on Antennas and Propagation & 2008 USNC/URSI National Radio Science Meeting 1E

7 ABSTRACT Objective Measure Realized gain for 44 beam 44 element linear array 43.5 to 45.5 GHz Single column of 50 column multibeam 2200 element planar active receive array for geostationary satellite communications payload 1760 simultaneous 0.4 degree beams/1463 earth beams Multibeam single prototype column realized gain tested at the Nearfield Systems Inc.'s (NSI) facility using a 12 x 12 Planar Near-Field Range Two linear array configurations tested using same WR-19 waveguide fed 44 beam 44 element Rotman lens and integrated RF distribution network (RFD). Active receive array utilizing only the center 8 array elements of the Rotman lens feed Passive 44 element array demonstrating narrow 0.4 degree half power beamwidth Summary & examples of the NFR test results presented Compared with that predicted using the previously measured lens array factor gain (AFG) and CST computed embedded element realized gain 2

8 Introduction EHF uplink array for TSAT spiral applications Beamformers for satellite payloads create simultaneous high gain pencil beams feeding 2200 element rectangular planar arrays from geostationary orbit Beamformers use column and row 2D Rotman lens stacks feeding elements in an equilateral triangular lattice Equilateral triangular beam lattice covering the entire 17.4º earth disc with 1760 pixel beams At each lens stack beam port, a 0.4 HPBW pixel beam is formed with frequency independent beam pointing angle due to Rotman lens true time delay RF Beam switch/combiner results in 64 simultaneous independent communication beams 18 db/k minimum G/Ts Constant communication beam pointing angles over the full bands Performance can be easily scaled, resulting in reduced size weight and prime power 3

9 EHF Uplink 2200 Element Active Planar Array Design Goals Receive Active Array Design Goals Parameter Value Units Receive Array Size Aperture Length 35.5 inch Aperture Width 34.9 inch Aperture Payload Depth 60 inch Column Spacing 2.6 λ Number Array Elements 2200 Array Beam Performance Operating Frequency (min.) 43.5 GHz Operating Frequency (max.) 45.5 GHz Peak Gain 52.2 dbi Half Power Beamwidth 0.4 Degree Number Pixel Earth Beams 1463 Number Simultaneous Comm. Beams 64 FOV Radius (Geo) 8.5 Degree Receive Active Array Design Goals Parameter Value Units Element Aperture Efficiency 85 % Element FOV Relative Gain (min.) -1.5 dbi Array G/T Performance LNA RF Loss before LNA 0.5 db LNA Noise Figure 2 db Peak G/T at 0.0 deg. Scan Peak G/T at max. Scan EOC beam box G/T at max. scan Array Power And Weight DC Power Dissipation Weight 21 db/k db/k 18 db/k 850 Watt 850 Watt 630 lbs 4

10 Active 8 Element/44 Beam Array & Passive 44 Element/44 Beam Array Tested Pyramidal Horn HPFL/ Extension LNA Semi-Rigid Coax WR-19/2.4mm End Launch Transition Rotman lens/rfd WR-19 Shim EHF Active Uplink Array 8 Element RF Chain and Lens/RFD 44 Element Passive Array & lens/rfd at NSI NFR with Mounting Fixture & Near Field Probe 5

11 Predicted Realized Gain Formulation Realized gain (G R ) was predicted using the previously measured lens array factor gain (AFG) and computed embedded element realized gain (G E ) G G R R ( θ ) = ( θ ) = A G n= 1 G E E ( θ ) ( θ) S A S n= 1 nb nb e e n2πd j sin( θ ) λ S nb : measured lens/rfd transmission S parameter from beam port B to array port n d/λ = 2.6 and low coupling therefore isolated and embedded element gain equal G G AFG n2πd j sin( θ ) λ ( θ ) ( θ ) ( θ ) R = E G R (θ) dbi = G E (θ) dbi + AFG(θ) db (4) IEEE Std :.When..radiation patterns of..array elements are identical.product of the array factor and the element radiation pattern gives the radiation pattern of the entire array (1) (2) (3) 6

12 Pyramidal Horn Element CST Computed and NFR Measured Realized Gain Pyramidal Horn Element CST MWS Computed Realized Gain E-Plane Radiation Pattern 1.79 CST MWS Model 10 5 Realized Gain (dbil) GHz E-Plane Realized Gain (dbil) 45.5 GHz E-Plane Realized Gain (dbil) Angle From Boresight (deg) CST H-Plane Radiation Pattern Realized Gain (dbil) 43.5 GHz H-Plane Realized Gain (dbil) 45.5 GHz H-Plane Realized Gain (dbil) Gain (dbil) CST MWS Computed Realized Gain (dbil) NFR Measured horn 7 (dbil) NFR Measured horn 8 (dbil) Frequency (GHz) Angle From Boresight (deg) 7

13 CST MWS Computed E-Plane Realized Gain G E (θ) Used for Realized Gain Prediction To Compute Realized Gain of the 8 Element Active Array & 44 Element Passive Array Integrated with the Rotman lens/rfd CST MWS computed E-Plane element realized gain G E (θ) dbi in (4) Measured lens array factor AFG(θ) db using HP8510C ANA Required Data at 44 beam peak angles from -8º to +8º Pyramidal Horn Element NFR Measured CST Computed Realized Gain Difference Statistics Two Horn S/N s & 220 Data Points Pyramidal Horn Element NFR Measured - CST Computed Realized Gain 44 Beam Port F (GHz) F (GHz) F (GHz) F (GHz) F (GHz) Angles Frq Mean MAX MIN P-P sigma

14 Eight Element Lens/RFD Active Array NFR Test Results; AFG(θ) Used for Realized Gain Prediction 8 element active array integrated with lens/rfd & S-parameters measured with HP8510C ANA Array Factor computed 13 Beam Ports: B02, B06, B10, B14, B18, B22, B23, B27, B31, B32, B35, B39, and B43 8 element active Array Factor rosettes computed HPBW for the 8 element active beams is about 2º HPBW for the 44 element passive beams is 0.4º due to the 5.5 x passive array aperture Array Factor Calculated Lens/RFD 8 Element Active Rosette at 44.5 GHz 13 Beam Ports 9

15 8 Element Active Array lens/rfd Calculated and NFR Measured Realized Gain 8 Element Active Array lens/rfd Calculated and NFR Measured Realized Gain overlay for the same 13 beam ports as those computed for AFG(θ) db in previous slide. G R (θ) dbi =G E (θ) + AFG(θ) (Slide 7) (Slide 9) Calc Bench(---), vs. Meas NFR( _ ) 44.5 GHz 13 BP Gain Statistics 8 Elt Active Array ([NFR Measured Realized Gain] -[AF + CST MWS Computed Horn Gain]) 13 Beam Port F (GHz) F (GHz F (GHz) F (GHz) F (GHz) Angles Frq Mean MAX MIN P-P sigma

16 Eight Element Active Array lens/rfd Measured Realized Gain at NSI NFR 44.5 GHz for all 44 Beam Ports Pyramidal Horn HPFL/ Extension LNA Semi-Rigid Coax WR-19/2.4mm End Launch Transition Rotman lens/rfd WR-19 Shim EHF Active Uplink Array 8 Element RF Chain and Lens/RFD 11

17 44 Element Lens/RFD Passive Array NFR Test Results; AFG(θ) Used for Realized Gain Prediction 44 element passive array integrated with lens/rfd & S- parameters measured with HP8510C ANA Array Factor computed All 44 Beam Ports 44 element passive Array Factor rosettes computed HPBW for the 44 element passive beams is 0.4º as expected Array Factor Calculated Lens/RFD 44 Element Passive Rosette at 44.5 GHz 44 Beam Ports 12

18 44 Element Passive Array & Lens/RFD Tested for realized gain using a NSI Planar 12 x12 NFR. Gain for All 44 Beam Ports was Measured 13

19 44 Element Passive Array lens/rfd Calculated and NFR Measured Realized Gain 44 Element Passive Array lens/rfd Calculated and NFR Measured Realized Gain overlay for all 44 beam ports as for AFG(θ) db in slide 12 G R (θ) dbi =G E (θ) + AFG(θ) (Slide 7) (Slide 12) Realized Gain (dbil) Calc Bench(---), vs. Meas NFR( _ ) 44.5 GHz 44 BP Gain Statistics 44 Elt Passive Array ([NFR Measured Realized Gain] -[AF + CST MWS Computed Horn Gain]) 44 Beam Port F (GHz) F (GHz) F (GHz) F (GHz) F (GHz) Angles Frq Mean MAX MIN P-P sigma

20 44 Element Passive Array lens/rfd Calculated and NFR Measured Realized Gain 44 Element Passive Array lens/rfd Calculated and Measured Realized Gain Overlay Bench (dashed lines), NFR (solid lines) 43.5 GHz & 45.5 GHz 44 Beam Ports Realized Gain (dbil) Realized Gain (dbil) 15

21 NFR Measurement Accuracy The NFR testing was performed at Nearfield Systems Inc., Torrance, CA on 5/8/07-5/11/07, using their Planar 12 x 12 NFR Considered Error Sources Gain Standard Uncertainty Considered Largest Source Calibrated at PSNA Impedance Mismatch Factor Peak Far-Field Peak Amplitude for Gain Standard Multiple Reflections between the horn and probe Truncation of the near-field data for the standard gain horn Bias error leakage within the receiver Room scattering RF Source GHz LO Source GHz Multiplier x GHz LO LO to Ref Coupler LO to Test Mixers operate in 3 rd harmonic mode -10 db Ref Mixer Ref IF Probe Ref AUT Panther Receiver Sig Pad Test Mixer LO LO/IF Unit NFR RF Test Block Diagram Term db Gain Standard 0.20 Mismatch 0.05 SGH FF Peak 0.15 Total (RSS) 0.25 Test IF Receiver displays Sig/Ref Probable Uncertainties in Peak Far-Field Gain 16

22 Summary Primary emphasis of this paper was to compare the accuracy of predicting the realized gain using fundamental array theory with NFR measurements An 8 element active array and a 44 element passive array were both tested The mean gain difference between model and measured data is db for the active array and db for the passive array Overall NFR peak gain measurement accuracy is estimated as 0.25 db 17