relación con elementos mudéjares y los tratados de arquitectura de España
5.1 Arquitectura mudéjar en Chiapas en el siglo XVI
5.1.4 Cubiertas
In general, high-power sources are still not available at MMW for small packaging.
Tube-based transmitters have been used in larger packages to support long-range requirements. For an MMW seeker application, tube transmitters and large power sup-plies are simply not appropriate for small airframe volumes, so only solid-state devices are typically used.
Two of the key performance parameters that are determined by existing technology are transmit power and receiver noise figure. Tables 3-4 and 3-5 illustrate examples of output power for solid-state and tube-type transmitters, and Table 3-6 shows some receiver noise figure values available commercially in the Ka- and W-band regions.
A signal-to-noise ratio (S/N) calculation is presented for an MMW continuous wave (CW) seeker example to illustrate the typical range performance of these types of sys-tems. The MMW seeker parameters are given in Table 3-7.
TABLE 3-4 ¢ Typical Ka Band Transmitter Power – Solid-State Devices
Manufacturer Description Frequency Power
QuinStar Technology QIC Series CW IMPATT Diode amplifier 34–36 GHz 1 W Millitech, LLC IDA Series CW Injection-Locked IMPATT
Diode Amplifier
30–40 GHz 0.7 W QuinStar Technology QTI Series CW Injection-Locked GUNN
Diode Amplifier
26.5–40 GHz 0.3 W Marconi Applied
Technologies
GUNN Diode Oscillator Model DC-1276G 26–40 GHz 0.5 W
TABLE 3-5 ¢ Typical MMW Transmitter Power – Thermionic Devices
Manufacturer Description Frequency Power Bandwidth Duty
CPI CW EIO 35 GHz
95 GHz
1,200 W 50 W
CPI Pulsed EIK 35 GHz
95 GHz
2,000 W pk 1,000 W pk
800 MHz 1,000 MHz
15%
10%
TABLE 3-3 ¢ Antenna Beam Characteristics – Comparison with X-Band
34 GHz 94 GHz 10 GHz
Antenna Diameter Beamwidth Beamwidth Beamwidth
10 cm (4 inch) 0.1 rad (5.9 deg) 0.037 rad (2.13 deg) 0.36 rad (20.7 deg) 15 cm (6 inch) 0.075 rad (4.5 deg) 0.029 rad (1.6 deg) 0.29 rad (15.2 deg) 20 cm (8 inch) 0.05 rad (3.0 deg) 0.019 rad (1.07 deg) 0.18 rad (10.4 deg)
Plugging these data into the radar range equation (equation 3-1 ) allows computa-tion of S/N performance as a funccomputa-tion of range for the –20 dBsm target. The resulting curve is shown in Figure 3-8.
S
N¼ PtG2l2s
ð4pÞ3R4kT0BnFnL (3.1)
Notice that robust detection performance is on the order of 1 km.
A similar result illustrating short-range operation (based on signal-to-clutter ratio) is illustrated in Figure 3-9. The calculations were performed over different clutter types as a function of MMW airborne seeker parameters with the following specifications shown in Table 3-8. In this illustration, coded waveforms are used to achieve a significant level of pulse compression (or signal-processing gain).
As the figure illustrates, the additional waveform duration to allow higher levels of pulse compression (signal-processing gain) can extend the range performance somewhat but at the cost of increased data-collection time and lower effective data rate (updates) by the radar.
Available transmit power, noise figure (S/N), and clutter return (S/C) limitations, combined with increased atmospheric and external propagation effects, tend to restrict MMW applications to shorter ranges compared to lower-frequency systems.
TABLE 3-7 ¢ MMW CW Seeker Performance Parameters – Example
Symbol Description Value Units Value (dB)
Pt Peak transmit power 2.5 Watts 4.0 dBw
Gt Transmit antenna gain 17,647 42.5
Gr Receive antenna gain 17,647 42.5
l2 Wavelength (squared) (0.0086)2 Meters squared –41.3
s Target RCS 0.01 Meters squared –20.0
(4p)3 Constant 1,984 –33.0
R4 (Range)4 (1,000)4 Meters4 –120.0
k Boltzmann constant 1.38e-23 Watts/Hz K 228.6
T0 Standard temperature 290 Degrees K –24.6
B Instantaneous bandwidth 88.2 kHz –49.5
F Noise figure 4.47 –6.5
L System losses 5.50 –7.4
La Atmospheric attenuation 1.02 –0.1
_______
S/N Resulting signal-to-noise ratio 15.2 dB
TABLE 3-6 ¢ Typical Ka Band Noise Figures – Solid-State Devices
Manufacturer Bandwidth Noise Figure
QuinStar Technology QMB series balanced mixers 26.5 to 40 GHz 33 to 50 GHz
6.5 dB Millitech series MXP balanced mixers 26.5 to 40 GHz
33 to 50 GHz
5.0 dB (DSB)
TABLE 3-8 ¢ MMW Airborne Seeker Typical Specifications
Parameter Value
Frequency 95 GHz
Waveform compression (long range) 100:1 (10-ms pulse equivalent) Waveform compression (short range) 10:1 (100-ms pulse equivalent)
Antenna 600diameter Cassegrain
Peak power 10 Watts
Noise figure 8 dB
Target RCS – nominal 20 dBm2
Clutter reflectivity – nominal –8 dBm2/m2 Clutter reflectivity – @ 10grazing –15.6 dBm2/m2 50
40
30
20
10
0
0.1 1.0 10
Range (km) 100 ns clutter
11 dB S/C (SKIN)
100 ns clutter (P.C.) 20 dBm2 TGT
(P.C.) 20 dBm2 TGT
Signal-to-Interference Ratio (dB)
FIGURE 3-9 ¢
Illustration of MMW Seeker
Performance.
0.0 10.0 20.0 30.0 40.0 50.0 60.0
0 200 400 600 800 1,000 1,200 1,400 1,600
Range (m)
Signal-to-Noise Ratio (dB)
FIGURE 3-8 ¢ S/N for an MMW Seeker versus Target Range at Antenna Boresight.
3.5.1 MMW Comparison with Other Systems
Even with all the issues discussed related to power, relative component costs, clutter returns, and atmospheric losses, MMW still offers the best compromise for high resolution with potential imaging capability in many applications compared to systems at different spectral regions. As a comparison, a simple subjective ranking system from 1 to 3, with 3 being the best, can be used to illustrate this compromise. Since a radar must perform many functions (search, detect, acquire, recognize) in a wide variety of conditions (targets, clutter, atmo-spheres), the values shown in Table 3-9 illustrate how MMW may still be the best choice for a selected system application as long as power budget considerations can be maintained.
3.5.2 MMW for Advanced Imaging Technology
The MMW spectrum can be combined in a ‘‘quasi-optical’’ common optics system with IR and visible sensors. The radar offers high-range resolution (inches) and object dimensionality measurements. As such, the basic implementation in the 3-D camera for radar would be for reflectance sensing (concealed ‘‘hard’’ objects and object classifi-cation), gross object geometry (except for range), and gross-and-point materials type electromagnetic (EM) properties. Radar also offers the ability to ‘‘see through’’ denser obstacles than higher wavelength sensors.
The MMW radar (active and passive) can also provide some level of imaging without controlled motion (Narrow Field of View (NFOV) implementation) on its own.
As previously discussed, millimeter wave radar usually serves as a trade-off technology between microwaves and infrared. As such, it has imaging characteristics of both technologies, both good and bad. These trade-offs (and real-life applications) have been realized in many of today’s critical security locations and in military target dis-crimination and classification approaches. Some of the advantages of MMW radar, compared to electro-optical sensors and microwave radar for imaging, include:
● the ability to directly measure range, azimuth angles, and elevation angles;
● the ability to penetrate many nonmetallic surfaces;
● high spatial resolution (as compared to microwaves) and extension to 3-D with controlled geometry changes; and
TABLE 3-9 ¢ MMW Compares Well with Other Systems
Sensor Capability
Microwave (3–30 GHz)
MMW (30–300 GHz)
Optical (0.4–14 microns)
Volume search 3 2 3
Classification, identification 1 2 3
Tracking accuracy 1 2 3
Adverse weather performance 3 2 1
Smoke performance 3 3 1
Covert capability 1 3 3
Day/night performance 3 3 2
Total 15 17 16
Relative performance key: 1¼ poor, 2 ¼ fair, 3 ¼ good
● low resolution (relative to electro-optical), which means less scanning is required to fill a given search volume.
Some of the disadvantages of MMW radar for imaging include:
● nonoptical-quality images due to specular reflections, multipath, and the large dif-ference in reflectance of various shapes (in some ways, this is an advantage in that it is another way to look at things);
● a relatively short range because near-field focusing of antennas is used to obtain high angular resolution; and
● the need for a larger aperture size for NFOV without controlled object motion.
More information on MMW advanced imaging technology (AIT) utilization is provided in the applications section of this chapter.