Modern radars systems for anti-air and anti-ship application naturally had born interest how to do the antidote against of it. Stealth or how to do the reduction of the radar cross section concerns mainly two decisions: a) The creation specially oriented surfaces which reflect radar radiation to the space or down – some kind as “in milk” (on technical language). b) Using special absorption coating on the surfaces and places which is impossible or very difficult to exclude from the reflection of the radar radiation. Absorption in this case means – sounding radar power will be absorbed by the material/s of such coating. Such coating works as black body or matched loading if to talk on microwave language. For the microwave radiometer such surfaces and coating are not antidote for the disclosing according to the physics of radiometer’s job. Nature produces radiation, which re-reflect from the various surfaces to an antenna of the radiometer from the appropriated directions from the sphere of sky or the earth with power depending on, so named, radio-brightness temperatures. And the coating if it the matched loading produces microwave radiation corresponding to her physical temperature. For the both cases a) and b), Stealth object can be disclosed by radiometer in some real cases. Keywords: stealth coating, microwave radiometer,
Abstract—Main difference of radiometer in comparing with the receiving systems for the communication or the radar is noise character of the radiometric signal. Principal for the all receiving items is the attainment of the low noise parameters of system. According to classic theory it is principle for radiometer to expand the entrance band before the detector. In this case it is possible to reach more big value of the so named radiometric win, which is proportional to the square root from the multiplication of the entrance band with the time of a storage.
For the case of the Josephson Junction (JJ) receiver we have principal peculiarity according to the own generation of the JJ, which can be conveniently used for the simple radiometric measuring or for the creation modern passive millimeter and terahertz imaging matrix system with electronic tuning of the receiving frequency band.
Practically, JJ is the electronically monitoring mixer (correlator by math) without special heterodyne. It is better to consider JJ as a device with high nonlinearity to external electromagnetic radiation and meanwhile a device suitable as a local heterodyne signal generator. However, comparing with the traditional understanding of a local heterodyne (oscillator) such as a monochromatic generator in case of JJ, we have to deal with the reality of the noise heterodyne. Accordingly, this study presents the theoretical basis and calculation of the possible sensitivity in the radiometer (“pixel” in case of matrix) consisting in the JJ and IF amplifier in the radiometric regime.
Figure 1. Schematic representation of the frequency conversation
I.
The specially designed and produced Stealth coating for the aircrafts and for the ships must be effective by their direct tasks against of the radar (by the way for the laser, optical and IR remote control too). But it is not antidote in some cases for the passive device as the microwave radiometers, because their job is to evaluate natural radiation of an object at the background of the environment/s (sky is cold, Earth is warm). More to say such specially calculated surfaces which avoids the vertical ones for the radar beams and reflect this radiation “to the milk” can promote and to be convenient for the remote radiometric detection, because the sky radiates from any direction. For the case of Stealth coating with full microwave absorption it was interesting to do simplest evaluation and background of such possible passive method of the remote sensing at the sample of using the microwave discriminator. Short explanation and the simplest evaluation were performed about possible real distances for the disclosing.
Radiometric discriminator is the simplest device for comparing the radiometric brightness temperature of two following spots of antenna beam on the observed remote scene. In this case, the real signal from discriminator can be similar to the radar imaging in form of the bright points based on the difference between the metal object and the background of an absorbing or semi-absorbing environment. To realize the function of finding objects, the scanning antenna is symmetrically decided into two parts. This signal arises only when the two parts generate different levels of brightness temperatures because of a target captured in alternative pixel scanning along the observed scene. In this paper, the device named discriminator is proposed, and the operating principle and possible application is introduced for the object with Stealth coating.
The specially calculated and prepared antiradar surfaces on special ships is very good for detecting them by the
microwave radiometers. It is interesting to evaluate the possibility of using a passive millimeter wave (PMMW)
radiometric discriminator for the remote controlling and finding such objects at real distances and also for
environmental monitoring.
One of the priority trend in electronics is the design of the imaging system in various spectral band of the electromagnetic waves. Multi-spectrum system is one of the critical technologies. It is principal to direct efforts for the creation multi-spectrum system in single block with simple regulation of the receiving band. First question in this field is to do the receiving pixel with tunable band for the matrix imaging system. Best candidate for this aim is Josephson Junction (JJ). The using of the JJ for this purpose can stay the new trend for the creation modern multi-spectrum passive terahertz imaging system. There proposed some analysis at the base of theoretical and experimental results of the possible noise parameters of the such pixel.
Combination of superconductive and semiconductor technologies on the one substrate in any case will give birth to principal trends of critical electronic technologies, including the realization of superconductive Josephson junction near the gate of a semiconductor transistor. Further development will allow us to realize passive imaging systems with main advantage - electronic tuning of the receiving frequency.
Josephson junction (JJ) can be used as the criterion in single-block super wide band frequency-meter and as the
sensitive element in the super wide band panoramic receiver. There presented the theoretical and experimental
investigations and described the innovation decision about to combine both devices in one new microwave device. JJ in
this case works in self-pump mode regime. New device can be especially convenient for the experimental purposes with
new generation structures when radiated power is small and frequency are unknown correctly.
Integration of plurality of radiometers into a panoramic receiving systems seems efficient for realization of `radiovision' (imaging) systems without scanning if small- sized sensors with good operating parameters are available. The use of Josephson Junctions (JJ) in self-pumping mode as one of various heterodyne detection methods is of principally new particular interest and trend, when we consider the properties such as the sensitivity, possibilities of frequency electronic tuning in big band, integrations with HEMT's and other nontraditional technical decisions, including the measuring of frequency of active signals on JJ. According to experimental and theoretical results it is possible to get the sensitivity not less than 0,01 K in 3 mm wave band at cooling temperature 20 - 30 K in passive imaging system at the base of matrix of JJ + HEMT's `pixels'.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.