Radar Cross Section RCS

Evaluation of RCS can also in principle be carried out using measurements similar to those above. However, additional factors such as the dimensions and shape of the sample, and a strong directional component (incident and re-scattered radiation) come into play. It cannot be proposed to enter into a detailed discussion of these here reference is made to excellent volumes available for the purpose, such as the Radar Cross Section Handbook [478, 479]. 

Most work to date has concentrated on a particular aspect of microwave properties, e.g. conductivity or dielectric constant, with few studies of the complete spectrum of properties over broad frequency ranges. For example. Fig. 12-2a.b show the DC vs. microwave (6.5 GHz) conductivity and the microwave (6.5 GHz) dielectric constant vs. temperature for a series of poly(anilines) measured by Javadi et al. [195]. The behavior observed- microwave conductivity greatly exceeding DC conductivity for higher doping levels, and dielectric constant being independent of temperature for low doping levels- is typical of CPs. Buckley and Eashoo [430] obtained relatively poor values for e and e , ca. 90 and 60 (at the Ka band, ca. 33 GHz) for compacted P(Py)/Cl powder. 

Fig 12-3 Loss Tangent at 6.5 GHz vs. temperature for four-folded stretched emeraldine hydrochloride parallel to the stretch direction (x), perpendicular to the stretch direction ( ), unoriented poly(orthotoluidine) hydrochloride (o) and unoriented self-doped sulfonated polyaniline (+). After Reference [190], reproduced with permission. 

Temperature dependent microwave frequency dielectric constant of poly(aniline)-camphor sulfonic acid (PAN-CSA) prepared in CHCI3 and m-cresol. Inset microwave frequency conductivity of PAN-CSA (m-cresol). Data were recorded at 6.5 X 10 . After Reference [482], reproduced with permission. 

Many workers have measured microwave properties of blends of CPs with thermoplastics or with materials such as teflon. Fig. 12-6 shows e and e for P(Py)/teflon blends measured at 2 GHz by Lafosse [342]. It is seen that the rise in permittivity closely approximates the percolation threshold for DC conductivity, and that for the more conductive blends (P(Py) ca. 0.15) the Loss Tangent is of the order of 10, indicating good absorption. Hourquebie et al. [483] studied P(Py) blends with a butyl elastomer, an epoxy, and teflon emulsion, and showed that a plot of log(e ) vs. log(frequency) was linear over the 130 MHz to 18 GHz range their data however showed attenuation to be poor or moderate. In a study of P(Py) latexes , Henry et al. [484] obtained typical values of e and e at 5 GHz of ca. 945 and 1086. In a study of P(Py) blends with PVC, Jousse et al. [340] observed that for a pressed blend, classical microwave behavior, i.e. a monotonic fall of permittivities with frequency (Fig. 12-7a) is observed, whilst for injection-molded blends (Fig. 12-7b) 

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The most common mode of aircraft detection is radar. Essentially, radar is the detection of radio waves that have been thrown out and which bounce off objects returning to the site of origin. Today s radar, if properly used, can help identify the location, speed, and identity of the aircraft. The radar cross-section (RCS) of an aircraft is how much echo the plane sends from radar. Birds have an RCS of about 0.01 m. The Stealth Bomber has an RCS of 0.75 m. The Stealth Bomber and many stealth aircraft gain their stealth character from both the shape of the aircraft and the presence of radar absorbing material (RAM), which is made to absorb and eliminate radio waves rather than reflect them. Most of the RAM materials are polymeric. 

The definition of the radar cross section (RCS) is illustrated in Fig. 2.5. Here a fictitious flat plate, with area a ant, intercepts an incident plane wave with power density —that is, the intercepted power is dant b,. 

In this book, Ben treats a number of subjects related to antennas and both their intended usage as transmission or reception devices, as well as the important (these days) radar cross section (RCS) that they can contribute. A constant theme behind the presented results is how often investigators approach the problem with no apparent understanding of the real-world factors that bear heavily on the practicality and/or quality of the result. He takes issue with those who have become so enchanted with high-powered computers that they simply feed the machine some wonderful equations and sit back while it massages these and optimizes a result. Sad to say, Ben has been able to document all too many examples to prove his point. 

MICROWAVE ABSORPTION AND RADAR CROSS SECTION (RCS) REDUCTION... 

In order to achieve dynamic, microwave region modulation, the primary parameter varied is the conductivity of the CP. In addition to this basic parameter, however, other considerations include the geometry of the object doing the modulation, important for radar cross section (RCS) control the thickness of the CP and dimensions of the underlying conductive electrode grid, important in determining resonance and thus whether the modulation is broad-band or only for a narrow range of frequencies. Some of these factors were discussed briefly in the previous chapter, to which the reader is referred. 

Expression (2.8) will in general not constitute the entire RCS of an antenna. In fact, it is only a component of the total radar cross section, which implies that there may be something else. This is usually called the residual (or structural) component a res- It was defined earlier as whatever must be added to the field associated with a am as given by (2.8) in order to obtain the field associated with the total antenna RCS, that is. 

It was pointed out in Chapter 2 that arrays possess unique features from a radar cross section point of view. To reduce the RCS outside the operating band of an antenna in general, a bandpass radome is often placed in front of it (see Chapter 2, Fig. 2.1). In the case of an array we recall from Chapter 2 that a low RCS is obtained when the terminal reflection coefficient is low in other words, the bandwidth of the array should ideally exceed that of the radome. Furthermore, due to the high price tag of arrays in general, it is desirable to pass on as much information through them as possible. Thus, we shall in this chapter consider the principles for broadband arrays, which is of interest to the communication community. 

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