EHF Rotman Lens Fed Linear Array Multibeam Planar Near-Field ...

EHF Rotman Lens Fed Linear Array
Multibeam Planar Near-Field Range
Measurements
A07-0090
Tuesday, November 6, Session 8, 16:30-16:45
Mike Maybell
Planet Earth Communications LLC
1983 San Luis Ave. #31
Mountain View, CA
94043-2900
650-965-7456
mjmaybell@mindspring.com
John Demas
Nearfield Systems Inc.
19730 Magellan Drive
Torrance, CA 90502

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

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

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
19.55 dB/K
18 dB/K
850 Watt
850 Watt
630 lbs
4

Active 8 Element/44 Beam Array &
Passive 44 Element/44 Beam Array Tested
Pyramidal
Horn
HPFL/
Extension
LNA
0.086” 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

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 145-1983:….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

Pyramidal Horn Element CST Computed
and NFR Measured Realized Gain
20
15
Pyramidal Horn Element CST MWS Computed
Realized Gain E-Plane Radiation Pattern
1.79”
CST MWS
Model
10
5
Realized Gain (dBiL)
0
-5
-10
-15
43.5 GHz E-Plane Realized Gain (dBiL)
45.5 GHz E-Plane Realized Gain (dBiL)
0.648”
0.791”
-20
-25
-30
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
-10.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
18.7
Angle From Boresight (deg)
CST H-Plane Radiation Pattern
18.65
18.6
18.55
18.5
18.45
Realized Gain (dBiL)
43.5 GHz H-Plane Realized Gain (dBiL)
45.5 GHz H-Plane Realized Gain (dBiL)
Gain (dBiL)
18.4
18.35
18.3
18.25
18.2
18.15
18.1
CST MWS Computed Realized Gain (dBiL)
NFR Measured horn 7 (dBiL)
NFR Measured horn 8 (dBiL)
18.05
18
43.5 43.7 43.9 44.1 44.3 44.5 44.7 44.9 45.1 45.3 45.5
Frequency (GHz)
Angle From Boresight (deg)
7

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 43.50 44.00 44.50 45.00 45.50 5 Frq
Mean -0.150 -0.027 -0.130 0.170 0.059 -0.015
MAX -0.097 0.172 0.074 0.299 0.151 0.299
MIN -0.188 -0.116 -0.405 0.101 -0.082 -0.405
P-P 0.091 0.287 0.480 0.198 0.233 0.480
1 sigma 0.028 0.080 0.128 0.060 0.062 0.072
8

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

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 43.50 44.00 44.50 45.00 45.50 5 Frq
Mean -0.548 -0.429 -0.141 0.952 0.404 0.048
MAX -0.113 0.128 0.379 1.640 1.097 1.640
MIN -0.860 -0.853 -0.492 0.371 0.072 -0.860
P-P 0.747 0.980 0.871 1.269 1.025 1.269
1 sigma 0.259 0.234 0.241 0.343 0.279 0.271
10

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
0.086” 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

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

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

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 43.50 44.00 44.50 45.00 45.50 5 Frq
Mean 0.214 0.103 0.299 0.454 0.573 0.329
MAX 0.598 0.441 0.572 1.022 0.902 1.022
MIN -0.144 -0.278 -0.274 0.142 0.229 -0.278
P-P 0.742 0.719 0.847 0.879 0.673 0.879
1 sigma 0.164 0.170 0.173 0.177 0.188 0.174
14

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

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
11.25 GHz
LO Source
15.00667 GHz
Multiplier
x4
45.0 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

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 0.048 dB for the active
array and 0.329 dB for the passive array
• Overall NFR peak gain measurement
accuracy is estimated as 0.25 dB
17