Large-Scale Structures in Acoustics and Electromagnetics Proceedings of a Symposium (1996) / Chapter Skim
Currently Skimming:
7 MODELING OF OPTICALLY 'ASSISTED' PHASED ARRAY RADAR
7 MODELING OF OPTICALLY 'ASSISTED' PHASED ARRAY RADAR
Pages 143-161
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 143... ...
, we have been involved in a long-term effort to determine the efficacy of the use of optical, and more specifically integrated optical, components in phased array radars. There are various reasons why people believe that optics can lead to improved phased array implementations.
|
From page 144... ...
For example, the fabrication of an integrated optical phase shifter requires one to mask off a channel, indiffuse it to obtain an index difference, and then remask and deposit electrodes. The fabrication parameters in such a case are the design dimensions of the masks, the design metal thicknesses, and times of indiffusion.
|
From page 145... ...
The next section will then discuss results of the phenomenological design process employed at GWOL, before turning that discussion to our present attempts to extend the approach to predict end-to-end system performance of phased array radars containing "exotic" components. STATE-OF-THE-ART INDUSTRIAL MODELING In this section we discuss the types of modeling used in industry for design of first digital, then microwave, and last optical systems.
|
From page 146... ...
The upper levels of Me design process are called logical in that the modeling at those levels contains no reference to devices, voltage levels, or wavefonns. The highest of the logical levels will be one in which the system blocks are probably chips, and simulations at this level would be of protocols and perhaps line delays, to see if We pulse length is sufficiently short compared to clock window that timing errors do not occur.
|
From page 147... ...
are well known and run efficiently in the time domain. An ever-growing problem in the digital simulation world, however, is the inclusion of dispersive elements, dispersively coupled lines, and other such artifacts that arise as clock rates increase.
|
From page 148... ...
level can be physical, in the sense that this next level will employ frequency-domain circuit and device models linked together by transmission lines (i.e., refer again to Figure 7.4)
|
From page 149... ...
Parasitic couplings between lines are generally small, and it is often not serious that they do not show up in the transmission line based models. This is not true when the couplings are near active elements where they can provide output to input control, systemlike coupling.
|
From page 150... ...
An optically assisted phased array radar system block diagram appears in Figure 7.7. A salient feature of that diagram is that there needs to be digital, optical and microwave modeling involved in any prediction of the operational characteristics of this microwave optical radar.
|
From page 151... ...
Transmission AE'tive t |Radiation Phase Shifting 'arallel _ Butle l roe. _ Matrix _ Transmission Active Elements Figure 7.7 A block diagram for a phased array radar architecture that employs optical components for phase shifting as well as phase decoding of incoming signals.
|
From page 152... ...
Integrated optical devices, in general, consist of optical channels with electrodes running over them, to effect electrical control of optical stream. To solve exactly for the optical field exiting such a device, given the input optical field, would require a full wave electromagnetic simulation of the electrical field, which involves both the electrodes and feedlines, followed by a calculation of the time varying dielectric constant in the substrate (as caused by the electro-optic effect)
|
From page 153... ...
As was mentioned in the preceding paragraph, uncertainties in the fabrication process preclude the use of models that require sharp parameter definition. The primary processing steps necessary for fabrication of a polymeric integrated optical phase modulator are indicated in Figure 7.10.
|
From page 154... ...
EXp(-i¢) Optical Waveguide Figure 7.9 Block diagram of a system that generates a microwave heterodyne beat note between two optical signals.
|
From page 155... ...
·Substrate Preparation E-O Polymer Spin on Buffer and E-O Polymer Substrate ·Optical Waveguide Formation UV Photo-Bleaching ~ ~ it/ Mask Channel Waveguide C_: _ 1 ·Microwave Electrode Formation Buffer Co-Planar ' Electrodes Rebuker C = , ............. Figure 7.10 Schematic of the processing steps involved in the fabrication of an optical phase modulator.
|
From page 156... ...
: Chromophore Concentration - r~x,y) : E-O Coefficient van ~ Bandwidth _ Linearity Figure 7.11 A block diagram that schematically depicts the phenomenological CAD system used to design optical phase modulators at GWOL.
|
From page 157... ...
"''I tpb Tpb none ~0 ~. _ ~ Corrections · Design Parameters - tpb: Photo-bleaching time - Tpb: Pholo-bleaching temperature - n+nj: Polymer refractive index T: Polymer thickness Figure 7.12 A block diagram of a lower level of the phase modulator design system of Figure 7.11, that level which is used to design the optical waveguide channels.
|
From page 158... ...
· Design Parameters £+£,: Polymer dielectric constant T`1 MetaIlization thickness - w, g: Electrode width and gap | Compare a;; _ Figure 7.13 A block diagram of a second lower-level design subsystem of the design system of Figure 7.1 1, the subsystem for designing the electrode structure of the optical phase modulator. At some point during the effort to employ integrated optics into phased array, it became clear that it was important to be able to mode} both the microwave and microwave optical versions of the system on roughly the same footing, for purposes of comparison.
|
From page 159... ...
to define the system blocks, and then could perform all kinds of quite complex waveform and noise analyses quite simply. To define the blocks would require dropping first one level, to a transmission line modeling level in which the simulation, at least for the standard microwave style software, would be a frequency-domain circuit analysis.
|
From page 160... ...
Klotz, and A.R. Mickelson, 1990, "Integrated optical butler matrices for beam forming in phased array antennas," SPIE Proc.
|
From page 161... ...
Ditto, 1992, Proceedings of the First Experimental Chaos Conference, River Edge, N.J.: World Scientific. Weierholt, A.J., A.R.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.