Presentation - Modeling of a 192-Way Waveguide Power Divider
Presentation - Modeling of a 192-Way Waveguide Power Divider
Presentation - Modeling of a 192-Way Waveguide Power Divider
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Lockheed Martin<br />
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MODELING OF A <strong>192</strong>-WAY<br />
WAVEGUIDE POWER DIVIDER<br />
Eric Marx<br />
Lockheed Martin M&DS<br />
Reconnaissance Systems<br />
Goodyear, AZ, USA<br />
eric.l.marx@lmco.com<br />
Ans<strong>of</strong>t HF Users’ Workshop, Los Angeles, CA, January, 2002<br />
Management & Data Systems<br />
Reconnaissance Systems
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Abstract<br />
A <strong>192</strong>-way, waveguide power divider is designed, modeled and<br />
validated through prototype dividers. The structure is part <strong>of</strong><br />
the power distribution network that controls the Taylor<br />
amplitude weighting for a Synthetic Aperture Radar antenna.<br />
Ans<strong>of</strong>t High Frequency Structure Simulator with Optimetrics<br />
was used to determine the optimal design for each transition.<br />
The design process relies on heavy use <strong>of</strong> the macro language to<br />
maximize model reuse and minimize design cycle. The described<br />
procedure is suitable to any large power distribution network<br />
with non-uniform amplitude distribution.<br />
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Background<br />
Lockheed Martin M&DS – Reconnaissance Systems division in Goodyear,<br />
AZ develops and produces airborne Synthetic Aperture Radar (SAR)<br />
Systems. The waveguide power distribution network described in this<br />
presentation is part <strong>of</strong> an antenna for a podded SAR system.<br />
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Examples <strong>of</strong> SAR Images<br />
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SAR System in a Pod<br />
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SAR POD<br />
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Antenna Design<br />
� The SAR Antenna discussed in this presentation has stacked<br />
patch radiators that are fed with both a waveguide power<br />
distribution network and a microstrip distribution network.<br />
� There are a total <strong>of</strong> 1536 radiating elements.<br />
� The antenna weighting requirements are uniform amplitude in<br />
elevation and 20 dB, n_bar=3, Taylor weighting in azimuth.<br />
� The waveguide power distribution network is the means by<br />
which the non-uniform amplitude weighting is achieved. This<br />
requires a 1-to-<strong>192</strong> network and many unequal power splits.<br />
� The system is Ku-Band and both WR-62 and WR-51 waveguide<br />
are used.<br />
� The antenna aperture is 38” x 14.25”.<br />
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<strong>Waveguide</strong> <strong>Power</strong> <strong>Divider</strong><br />
14.25”<br />
Input Ports(2)<br />
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38”<br />
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Output Ports<br />
(<strong>192</strong>)
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Amplitude Weighting<br />
� 16 waveguide power dividers are needed to achieve the 1-to-32<br />
azimuth distribution. The number <strong>of</strong> unequal power divider types was<br />
reduced to 6 for the azimuth power division to simplify the design.<br />
Six was determined to be sufficient (see the following page). The<br />
power split ratio and location were chosen such that the resulting<br />
amplitude weighting was close to the ideal weighting.<br />
� A 2-to-1 power split was used for the elevation power distribution<br />
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30/70<br />
40/60 43/57<br />
Magic Tee<br />
47/53 43/57 45/55 49/51<br />
49/51 47/53 47/53 47/53 47/53 47/53 49/51 49/51<br />
Azimuth <strong>Power</strong> Division<br />
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Amplitude Weighting<br />
� The following plot shows the ideal azimuth Taylor weighting and the<br />
weighting generated using a reduced number <strong>of</strong> power divider types.<br />
Normalized Magnitude<br />
1.0<br />
0.9<br />
0.8<br />
0.7<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
0.0<br />
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Azimuth Amplitude Weighting<br />
1 6 11 16 21 26 31<br />
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Ideal<br />
Approximate
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Far Field Patterns<br />
� Amplitude approximation due to reduced number <strong>of</strong> power dividers<br />
types has little impact on the far field antenna patterns.<br />
� The first two sidelobes are reduced by ~0.5 dB.<br />
0<br />
-5<br />
-10<br />
-15<br />
-20<br />
-25<br />
-30<br />
-35<br />
-40<br />
-5 -4 -3 -2 -1 0 1 2 3 4 5<br />
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Taylor<br />
Approx
<strong>Waveguide</strong> <strong>Power</strong> <strong>Divider</strong><br />
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� Determined logical points to break the problem into pieces<br />
that can be modeled using Optimetrics.<br />
• Single power dividers<br />
• <strong>Waveguide</strong> bends: H-plane and E-plane<br />
• WR-62 to WR-51 transformer<br />
� An H-plane waveguide power divider was chosen for its<br />
geometrical advantages.<br />
� The double-iris H-plane T-junction configuration[1] was chosen<br />
because it is relatively easy to manufacture and integrate.<br />
� Prototypes were made and tested to validate the design<br />
concept and the HFSS modeling.<br />
[1] J. Joubert & S.R. Rengarajan, "Design <strong>of</strong> Unequal H-plane <strong>Waveguide</strong> <strong>Power</strong> <strong>Divider</strong>s for Array Applications", Proceedings <strong>of</strong> the IEEE<br />
Antennas and Propagation Society International Symposium 1996, Vol. 3, pp 1636-1639, Baltimore, USA, 21-26 July 1996.<br />
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Double-Iris H-Plane T-Junction<br />
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Port<br />
#2<br />
Design Variables<br />
dy = power split <strong>of</strong>fset<br />
ir1L = power split iris length<br />
ir1W = power split iris width<br />
ir2L = matching iris length<br />
ir2W = matching iris width<br />
dpath = delta path length<br />
a<br />
<strong>Power</strong> Split Iris<br />
dpath<br />
Matching Iris<br />
ir1L<br />
ir2W<br />
a<br />
Port<br />
#1<br />
dy<br />
ir1W<br />
ir2L<br />
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Port<br />
#3
HFSS Models<br />
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� The T-Junction model was<br />
used to determine the iris<br />
geometry, <strong>of</strong>fset, and phase<br />
differential.<br />
� This was completed for each<br />
power divider type.<br />
� A macro was built for this<br />
model and Optimetrics was<br />
used to iterate to the<br />
optimum geometry.<br />
Machining Radius<br />
� The inside corners that are left by the milling process have a<br />
measurable impact on the electrical performance and were included in<br />
the model.<br />
� Prototypes <strong>of</strong> this type <strong>of</strong> power divider were manufactured and the<br />
RF performance matched the simulated data very well.<br />
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HFSS Models<br />
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� The next step is to take<br />
the individual 3-port<br />
power dividers and create<br />
the next higher level<br />
model.<br />
� Using the baseline model,<br />
more complex models<br />
were built to capture the<br />
effects <strong>of</strong> nearby<br />
transitions.<br />
� <strong>Power</strong> division and phase<br />
were adjusted at this<br />
level.<br />
� The Filter Cost Function is used to achieve a flat amplitude response<br />
across the entire bandwidth (use the Equal To curve) and minimize<br />
the return loss (use the Below curve). These filter cost functions<br />
were combined into a single cost function to optimize to the required<br />
performance.<br />
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<strong>Waveguide</strong> <strong>Power</strong> <strong>Divider</strong><br />
14.25”<br />
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38”<br />
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HFSS Models / Results<br />
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HFSS Model “pd4_4”<br />
E-Field Plot<br />
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Magnitude (dB) HFSS Model “pd4_4”<br />
Return Loss<br />
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0<br />
-5<br />
-10<br />
-15<br />
-20<br />
-25<br />
-30<br />
-35<br />
-40<br />
-45<br />
-50<br />
Return Loss<br />
16.3 16.4 16.5 16.6 16.7 16.8 16.9 17.0 17.1 17.2 17.3 17.4 17.5<br />
Frequency (GHz)<br />
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<strong>Power</strong> Split<br />
HFSS Model “pd4_4”<br />
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Magnitude (dB)<br />
-5.5<br />
-5.6<br />
-5.7<br />
-5.8<br />
-5.9<br />
-6.0<br />
-6.1<br />
-6.2<br />
-6.3<br />
-6.4<br />
Output Magnitude<br />
-6.5<br />
16.3 16.4 16.5 16.6 16.7 16.8 16.9 17.0 17.1 17.2 17.3 17.4 17.5<br />
Desired Amplitude<br />
Frequency (GHz)<br />
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S12<br />
S13<br />
S14<br />
S15
Phase Matching<br />
HFSS Model “pd4_4”<br />
Phase (Degrees)<br />
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180<br />
150<br />
120<br />
90<br />
60<br />
30<br />
0<br />
-30<br />
-60<br />
-90<br />
-120<br />
-150<br />
-180<br />
S12<br />
S13<br />
S14<br />
S15<br />
Phase Match<br />
Frequency Phase (Degrees)<br />
(GHz)<br />
S12 S13 S14 S15<br />
16.86 -147.94 -147.78 -148.10 -147.96<br />
16.88 -152.51 -152.35 -152.68 -152.53<br />
16.90 -157.07 -156.92 -157.25 -157.11<br />
16.92 -161.63 -161.48 -161.81 -161.68<br />
16.94 -166.19 -166.04 -166.37 -166.24<br />
16.96 -170.75 -170.59 -170.93 -170.81<br />
16.3 16.4 16.5 16.6 16.7 16.8 16.9 17.0 17.1 17.2 17.3 17.4 17.5<br />
Frequency (GHz)<br />
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Top Layer <strong>Power</strong> <strong>Divider</strong>s<br />
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� The amplitude and phase optimization <strong>of</strong> the 4-way power dividers<br />
determined the location <strong>of</strong> the 180 degrees E-plane bends that<br />
transition to the top layer <strong>of</strong> waveguide power dividers.<br />
� Two 5-port models and the 7-port model shown here complete the<br />
waveguide hogout power divider modeling.<br />
PHASE (DEG)<br />
PHASE BALANCE<br />
180<br />
150<br />
120<br />
90<br />
60<br />
30<br />
0<br />
-30<br />
-60<br />
-90<br />
-120<br />
-150<br />
-180<br />
16.3 16.8 17.3<br />
FREQUENCY (GHz)<br />
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Top Layer <strong>Power</strong> <strong>Divider</strong>s<br />
� Results are from the 7-port model pictured on the previous slide.<br />
� The desired amplitudes are –10 dB and –6.32 dB.<br />
� This model includes the two greatest unequal power splits.<br />
� Also included is the transformer from WR-62 to WR-51.<br />
� This was the largest waveguide power divider modeled.<br />
AMPLITUDE (dB)<br />
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0<br />
-10<br />
-20<br />
-30<br />
-40<br />
-50<br />
INPUT POWER DIVIDER STRUCTURE<br />
-60<br />
16.3 16.5 16.7 16.9 17.1 17.3 17.5<br />
FREQUENCY (GHz)<br />
AMPLITUDE (dB)<br />
-4<br />
-5<br />
-6<br />
-7<br />
-8<br />
-9<br />
-10<br />
AMPLITUDE BALANCE<br />
-11<br />
16.3 16.8 17.3<br />
Desired Amplitude<br />
FREQUENCY (GHz)<br />
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Photos <strong>of</strong> the <strong>Waveguide</strong> <strong>Power</strong> <strong>Divider</strong><br />
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Layer 1<br />
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Layer 2
Summary<br />
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� Large power divider networks with non-uniform amplitude<br />
distributions require many different power splits.<br />
� Depending on the performance requirements, some<br />
simplifications may be made by simply reducing the number <strong>of</strong><br />
power split types.<br />
� Design a generic power divider design and identify the<br />
parameters that can be varied to meet all the requirements.<br />
� Generating a baseline model using the macro language with<br />
variable parameters minimizes model development time by<br />
maximizing model reuse. This has positive impacts on cost,<br />
schedule, and repeatability<br />
� Using Optimetrics allows the user to reach the best design in<br />
the least amount <strong>of</strong> time.<br />
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