Dual-mode MMW/IR simulation of beam combiner
Introduction
With the development of the technique of electrooptical jamming and photoelectronic reconnaissance, the modern warfare environment of missile becomes more and more complicated and wicked. The single-mode homing seeker cannot accomplish the mission of target detecting and tracking, so the dual-mode or multi-mode compound seeker is becoming more and more necessary.
IR/MMW dual-mode compound guidance technology is considered the most promising guidance technology. It combines the IR and the MMW guidance system in a complementary way, which overcomes each weakness and combines advantages of both. The advance of IR/MMW dual-mode compound guidance technology, particularly the advance of IR/MMW dual-mode common-aperture seeker had led to a requirement to develop the simulation tools. The most important techniques for supporting systems development are the hardware-in-the-loop simulation [1], [2], [3]. Compared to single-mode simulation facilities, dual-mode simulation facilities must be able to present simultaneous MMW and IR scene. So it is considered to be the most challenging problem. Currently, dual-mode simulation technology is being researched and developed in the USA and Europe, and a great progress has been made. Research on the dual-mode simulation technology in China is just in the initial stage, and some key technologies still need to be broken through.
In this paper, the dual-mode simulation is researched. The goal is to offer a high-powered simulation method for compound guidance technology. Based on the requirement of dual-mode simulation, two key technologies of dual-mode simulation including dichroic beam combiner (DBC) and IR scene projection system were analyzed and designed.
The main content includes: MMW transmission, insertion phase delay (IPD), size of substrate material, and coating. At last, the substrate material was determined, and the thickness of the substrate material was optimized.
Section snippets
Principle of IR/MMW combiner
The role of IR/MMW combiner is to synthesize the beam of infrared and millimeter waves to compound wave. The basic starting point is to find a substrate, which can transmit through the microwave and reflect the infrared film [4]. Polishing and anti-plating with one- or multi-layer film on the substrate can reflect the infrared light. Choose a suitable point on the incident and the substrate size; the two incident waves of microwave and infrared waves combine to form a compound wave through the
IPD of host material
IPD is a retarding phase which is relative to remove the flat front-to-back variation of transmission wave phasewhere
To low-loss dielectric [5], [6], ,
Here,
The relationship between IPD, dielectric constant, and loss tangent
Fig. 1 shows the three-dimensional solid relation of IPD, εr and tan δ at two polarized states, in which the incident angle is 22.5° and the thickness of dielectric flat is 20 mm.
Fig. 2 shows the three-dimensional solid relation of IPD, εr and tan δ at horizontal polarized state, in which the incident angle is 22.5° and the thickness of dielectric flat is 20 mm.
From Fig. 1, Fig. 2 we can get:
- (1)
IPD is greater with the increase of εr. To the change of tan δ, IPD has minute influence.
- (2)
MMW polarized state
The relationship between IPD, thickness, and incident angle
Fig. 3 shows the relationship between IPD, thickness of host material and incident angle when εr=4, tan δ=0.001. From Fig. 4 we can get:
- (1)
IPD increases with the increase of the thickness of the material, which is almost in direct proportion. IPD increased gradually with the increase of incident angle, especially smaller incident angle, slower speed increase.
- (2)
Polarized state of MMW has little influence on IPD. IPD is almost equal for the two polarized waves.
The relationship between IPD and frequency
Fig. 4 shows the change of IPD relative to incident angle in the frequency of 93, 94, and 95 GHz when εr=4, tan δ=0.001 and the thickness of host material is 20 mm. From Fig. 4 we can see that IPD increases with the increase of frequency.
In the dual-mode simulation of IR/MMW, using quartz glass as a beam combiner host material is realistic.
Thickness optimization of quartz host material
Under the premise of specified fusing quartz glass as the host material, using the transmission function |T|2, we optimize the thickness of the host material. Here, the dielectric constant of quartz glass to MMW is εr=3.33, loss tangent is tan δ=0.001.
If the material is determined, transmission is mainly related to the thickness of host material, incident angle of MMW and frequency of MMW.
When the incident angle is less than 30°, transmission of MMW signal is almost equal at two polarized
Summary
- (1)
The distortion of MMW signal by beam combiner is analyzed. The analysis and calculation method is given.
- (2)
Selection rules of combiner host material are researched. The relationship between the MMW transmission, IPD and host material electricity parameter, thickness of material and incident angle of MMW is studied with numerical simulation method.
- (3)
The feasibility of quartz glass as the host material of beam combiner is confirmed. With quartz glass, the thickness of the material is optimized. The
Acknowledgments
The financial support for this study was provided by Natural Science Foundation of Yunnan Province, China (Grant no. 2008F041M). The authors would like to thank the teacher Baojun Zuo for his suggestions and selfless help.
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