RCS of a coated circular waveguide terminated by a perfect conductor

The radar cross section (RCS) of a circular waveguide terminated by a perfect electric conductor is calculated by the geometrical theory of diffraction (GTD) for the rim diffraction and by a physical optics approximation for the interior irradiation. The interior irradiation is generally more than 10 dB higher than the rim diffraction fora/lambda geq 1(ais the waveguide radius,lambdais the free-space wavelength). At low frequencies (a/lambda sim 1), the interior irradiation can be significantly reduced over a broad range of incident angle if the interior waveguide wall is coated with a thin layer (1 percent of the radius) of lossy magnetic material. Our theoretical prediction is confirmed by measurements. At higher frequencies (a/lambda sim 3), a thin layer of coating is effective for the case of near axial incidence, provided that a good transition of theTE_{11}mode near the waveguide opening to theHE_{11}mode inside the waveguide is made. A thicker layer of coating is required for the RCS reduction over wider incident angle.     

Multipath Fading Effects on Digital Radio

An experimental study of multipath fading effects on an 8-PSK 6 GHz digital radio system was conducted on a 26.4 mi test link near Atlanta, Georgia. Results were obtained for a non-diversity arrangement and a space-diversity arrangement employing a cophasing combiner operating at 70 MHz and fed by two antennas separated by 30 ft. Multipath fading was found to have a significant impact on bit error rate performance, i.e., the digital radio system was fragile by comparison to conventional analog FM radio. Modest in-band linear amplitude dispersion, 0.2 dB/MHz for example, was sufficient to cause aBERgeq10^{-3}. Such dispersion occurred at (average power) fade depths as shallow as 20 dB. However, average fade depth was a poor indicator of BER performance. The measured hop missed short haul outage objectives by an order of magnitude without space-diversity, and was close to acceptable when diversity was activated.     

Backscatter from snow and ice surfaces at near incident angles

The radar backscatter of natural snow surfaces was measured at 10 GHz and 35 GHz and at grazing angles from1degto0.3deg. For horizontal polarized radiation the terrain clutter per unit area (m²) at 10 GHz of a flat snow terrain decreases from -50 dB at1degto -70 dB at0.4deg. The return is approximately 10 dB lower for vertical polarized radiation. The terrain clutter was found to depend on the free water content of the snow. The radar cross sections of ice blocks placed on the snow surface is roughly proportional to the square of the area of the ice block facing the radar at 10 and 35 GHz and is approximately 20 dBsm below the return expected for a perfectly reflecting plane surface. At 95 GHz the ice blocks become diffuse reflectors.     

Second breakdown of double epitaxial transistors

This paper deals with the second breakdown of transistors with epitaxial collector, epitaxial base, and diffused emitter. Transistors were fabricated with base width WBin the range of 2 to 18 µ and resistivity in the range of 0.1 to 10 ohm . cm. The optimum values of the resistivity and the thickness of these regions were calculated by computer techniques. The devices were mounted onto a TO-63 header and the base and the emitter leads were bonded onto the device ultrasonically. The electrical characteristics, including the frequency response ftand secondary breakdownS/Bcapability, were tested. For the measurement of second breakdown current IM, forward bias condition was used. It was found that for fixed collector and emitter parameters, IMwas controlled by the product of base resistivity ρBand base width WB. The value of IMwas found to increase withrho_{B}W_{B}. However, for a specified device characteristic, an optimum value ofrho_{B}W_{B}was found to exist. For transistors withV_{CEO} =150volts,f_{t}=20mHz andh_{FE}=20, the optimum value ofrho_{B}W_{B}was found to be 6 × 10^-4ohm . cm².     

High-frequency backscatter from terrain with trees

The standing-wave method was used to measure the radar cross section σ of a flat piece of ground on which stood a single tree. Measurements were made at 26 MHz at angles of elevation γ up to 22.5 degrees, by raising the transmitting antenna with a balloon and moving the receiving probe along the transmitter-target line by means of ropes. For horizontal polarization, σ was a smoothly increasing function of γ. For "vertical" polarization (polarization parallel to the plane of incidence on the ground), σ increased rapidly up to 10 degrees, then became fairly constant with a value of 6 m². The sudden change in the slope of σ(γ) is the knee effect suggested by previous observations. The Brewster angle was 14 degrees, consistent with a theory that the knee should occur a few degrees below the Brewster angle. Below 15 degrees, the cross section for vertical polarization was greater than that for horizontal polarization by as much as 30 dB.     

The radar cross section of ogives, double-backed cones, double-rounded cones, and cone spheres

Experimental measurements have been made of the nose-on backscattering radar cross section over a range of diameters from 0.05 to 1.0 wavelengths of a series of ogives with total included nose angles of40deg,75deg, and120deg; of cone spheres with nose angles of15deg,30deg,40deg60degand120deg; of double-rounded cones with nose angles of15deg,40deg, and75deg; and of double-backed cones with nose angles of40deg. Further, a series of ogives of approximately the same diameter and with nose angles of25deg,40deg,60deg,75deg,95deg,120deg,160degand180deghave also been measured. All the present results have been obtained using two monostatic phase-locked CW balanced-bridge model measurement radars operating at frequencies of 9 Gc and 35 Gc. For targets with maximum dimensions less than two inches, cross sections of less than10^{-7}square meters at 9Gc and10^{-6}square meters at 35 Gc can be measured with an accuracy of pm0.5 db. The experimental data is sufficiently comprehensive to provide qualitative explanations of the scattering mechanism in the Rayleigh and resonance regions, and to make rigorous tests of the various theoretical predictions. An extension of the physical optics theory of Adachi was found to predict accurately the echo area of the ogive, the double-rounded cone, and double-backed cone in the resonance region. The Rayleigh theory was found to be generally accurate for all the models considered. The impulse analysis of Kennaugh and Moffatt was found to be accurate for the cone sphere.     

Back-scatter by dielectric spheres (Refractive index approx 1.6

Two independent sets of experimental results are presented on the back-scatter from plexiglass spheres. These are compared with theoretical computations for refractive indices m = 1.60, 1.61 and 1.61-0.0025i. Foralpha(ratio of perimeter to wavelength)leq 7.5, the upper limit of the experimental data, the theoretical values are practically identical to one another and agreement with experiment is excellent. Foralpha >7.5, the theoretical values diverge from one another. The small absorption coefficient has an increasingly important effect as the spheres grow larger, but even atalpha simeq 100, the cross section remains above its asymptotic value. Except for the interval30< alpha <40, plexiglass spheres have larger cross sections than metal ones between6 < alpha < 60. This is due to the focusing action of the dielectric sphere and the back surface reflection.     

A 0.13 $mu$ m CMOS Quad-Band GSM/GPRS/EDGE RF Transceiver Using a Low-Noise Fractional-N Frequency Synthesizer and Direct-Conversion Architecture

This paper presents a single-chip CMOS quad-band (850/900/1800/1900 MHz) RF transceiver for GSM/GPRS/EDGE applications which adopts a direct-conversion receiver, a direct-conversion transmitter and a fractional-N frequency synthesizer with a built-in DCXO. In the GSM mode, the transmitter delivers 4 dBm of output power with 1$^{circ}$ RMS phase error and the measured phase noise is ${-}$164.5 dBc/Hz at 20 MHz offset from a 914.8$~$MHz carrier. In the EDGE mode, the TX RMS EVM is 2.4% with a 0.5 $~$dB gain step for the overall 36 dB dynamic range. The RX NF and IIP3 are 2.7 dB/ ${-}$12 dBm for the low bands (850/900 MHz) and 3 dB/${-}$ 11 dBm for the high bands (1800/1900 MHz). This transceiver is implemented in 0.13 $mu$m CMOS technology and occupies 10.5 mm$^{2}$ . The device consumes 118 mA and 84 mA in TX and RX modes from 2.8 V, respectively and is housed in a 5$,times,$ 5 mm$^{2}$ 40-pin QFN package.      

Resonant third-harmonic generation a low-loss medium

The linear and nonlinear susceptibilities for resonant third-harmonic generation in an Mg-Kr system using the3s^{2}-3s3dtwo-photon resonance at 431 nm are presented. The Mg-Kr system is shown to be a suitable low-loss medium because of its small one-photon and two-photon absorption cross section. A detailed quantitative analysis up to a power conversion efficiency of1.2 cdot 10^{-4}was carried out. The phase-matching curves and the intensity dependence are in excellent agreement with a nonstationary modification of the theory of resonant third-harmonic generation in high density, phase-matched systems recently presented by Puell et al. [4].     

On the polarization and the wavelength dependence of sea echo

Data on radar cross section per unit areasigmadegof the sea at 6.3 Gc/s and 35.0 Gc/s and for grazing angles between1.5degand4.0degare reviewed. The data were obtained by simultaneously receiving both horizontally and vertically polarized echo components for transmitted polarizations which were sequentially changed between horizontal and vertical. Results indicate that sea echo is primarily caused by two scattering mechanisms: 1) a wind-dependent fine structure of the sea (presumably ripples) that partly depolarizes and has a scattering cross section which depends on wavelength in accordance withlambda^{-1}, and 2) a gross structure of the sea (presumably smooth facets between the ripples) that does not depolarize and has a scattering cross section which is independent of wavelength. The cross sections for transmitting and receiving vertical polarization (sigmadeg VV) and for transmitting and receiving horizontal polarization (sigmadeg HH) are caused by the sum of the contributions from the two mechanisms. Therefore, although dependent on sea state and polarization, it seems thatsigmadeg VVandsigmadeg HHwill tend to be independent of wavelength at the lower frequency end of the microwave spectrum and will tend to depend on wavelength in accordance withlambda^{-1}at the higher end of the spectrum. A comparison of data at 6.3 Gc/s and 35.0 Gc/s and for grazing angles between1.5degand4.0degindicates that the wavelength dependences ofsigmadeg VVandsigmadeg HHare functions of sea state but are greater thanlambdadegand are considerably less thanlambda^{-1}.     

Tunable alexandrite lasers

Wavelength tunable laser operation has been obtained from the solid-state crystal alexandrite (BeAl2O4:Cr³⁺) over the continuous range from 701 to 818 nm. The tunable emission was observed at room temperature and above in a homogeneously broadened, vibronic, four-level mode of laser action. In this mode the laser gain cross section increases from7 times 10^{-21}cm²at 300K to2 times 10^{-20}cm²at 475K, which results in improved laser performance at elevated temperatures. Efficient 2.5 percent, low-threshold (10 J) operation has been obtained with xenon-flashlamp excitation of the 6 mm diameter × 76 mm length laser rods. Output pulses of greater than 5 J and average power outputs of 35 W have been demonstrated, limited by the available power supply. The emission is strongly polarizedEparallelb, with a gain that is 10 times that in the alternate polarization. The 262 μs, room-temperature fluorescence lifetime permits effective energy storage andQ-switched operation. TunableQ-switched pulses as large as 500 mJ have been obtained with pulsewidths ranging between 33 and 200 ns depending on the laser gain. Laser action has also been demonstrated on the high-gain (3 times 10^{-19}cm²emission cross section)Rline at 680.4 nm and is also polarizedEparallelb. This three-level mode is analogous to the lasing in ruby except that the stimulated emission cross section in alexandrite is ten times larger than for ruby.     

A CMOS 1 Gb/s 5-Tap Fractionally-Spaced Equalizer

This paper presents the design of a 1 Gb/s 5-tap T/2 fractionally-spaced equalizer. The T/2 delay lines are based on third-order linear-phase double terminated sections that offer a tunable group delay of 500 ps with less than 10% ripple and a 3 dB bandwidth greater than 600 MHz. Furthermore, the equalizer architecture introduces a broadband summing circuit using a transimpedance $I/V$ converter that increases the bandwidth by a factor of 3.6 over a conventional resistive loaded analog adder. The topology's performance is demonstrated in the equalization of 1 Gb/s binary data through CAT5e twisted-pair cables for up to 23 meters. The vertical eye-opening increases from 0% to 58%. Implemented in CMOS 0.35 $mu{hbox{m}}$, the transversal equalizer occupies an area of 26 ${hbox{mm}}^{2}$ and consumes 32 mA.      

A millimicrosecond pulse-generator tube

This paper describes the theory and testing of a 100- Mc repetition-rate millimicrosecond pulse-generator tube utilizing klystron bunching. The optimum operation of the generator was obtained with a drift-tube transit angle Θ0of approximately 150°; depth of modulationalpha = V_{1}/V_{0} = 1; and the reduced plasma-anglePhi_{q}was less than 20°. Observations and data were determined with an Edgerton, Germeshausen and Grier traveling-wave oscilloscope and a comparison measurement technique. The generator has a measured pulse rise time of 130 µµsec (0-100 per cent), and a pulse duration of 300 µµsec at the half-voltage point. A pulse height of 20 volts on a 50-ohm coaxial line is possible. The analysis applied in predicting the shape of the pulse was based on large signal ballistic bunching theory and a quantized collector gap theory. A comparison between analysis and measurement indicates an error of about 20 per cent. Theory predicts that little improvement can be made in the pulse duration, but the pulse rise time may be improved with increased circuit complexity.     

Radar ground-clutter shields

Metal shields (or fences) are useful in reducing the ground clutter received by a radar. The design of a clutter shield for an L-band monopulse radar employing a 60-ft parabolic reflector with Cassegrainian geometry is verified by scale-model measurements at Ka-band. It is shown that a 100-ft fence, at a distance 500 ft from the radar, will give a nominal one-way clutter reduction of 20 dB. Tracking is expected to be virtually unaffected down to about 7.8° in elevation, but the low limit on useful performance is about 4.8°. More than 10 dB additional clutter reduction can be achieved by cutting rectangular slots in the top edge of the fence. However, polarization dependence and antenna geometry yield an average clutter suppression of 5 dB. In addition, the slots as other periodic structures are subject to "grating lobes." These place a restriction on the fence geometry. This is investigated experimentally on the scale model and explained by a mathematical analysis. A nonperiodic edge treatment is expected to be free of this troublesome effect.     

2 MHz AO $Q$ -switched ${rm TEM}_{00}$ Grazing Incidence Laser With 3 at.% Neodymium Doped Nd:YVO$_{4}$

We present a detailed experimental and theoretical study of the ultrahigh repetition rate AO $Q$ -switched ${rm TEM}_{00}$ grazing incidence laser. Up to 2.1 MHz $Q$-switching with ${rm TEM}_{00}$ output of 8.6 W and 2.2 MHz $Q$ -switching with multimode output of 10 W were achieved by using an acousto-optics $Q$ -switched grazing-incidence laser with optimum grazing-incidence angle and cavity configuration. The crystal was 3 at.% neodymium doped Nd:YVO$_{4}$ slab. The pulse duration at 2 MHz repetition rate was about 31 ns. The instabilities of pulse energy at 2 MHz repetition rate were less than ${pm}6.7hbox{%}$ with ${rm TEM}_{00}$ operation and ${pm}3.3hbox{%}$ with multimode operation respectively. The modeling of high repetition rate $Q$-switched operation is presented based on the rate equation, and with the solution of the modeling, higher pump power, smaller section area of laser mode, and larger stimulated emission cross section of the gain medium are beneficial to the $Q$-switched operation with ultrahigh repetition rate, which is in consistent with the experimental results.      

A Highly Linear SAW-Less CMOS Receiver Using a Mixer With Embedded Tx Filtering for CDMA

An embedded filtering passive (EFP) mixer is used to overcome transmitter power leakage in a receiver without the use of a SAW filter. The receiver IC exhibits more than ${+}$ 60 dBm of Rx IIP$_{2}$ , 2.4 dB Rx noise figure, and ${+}$77 dB of Triple Beat (TB) with 45 MHz offset transmit leakage at 900 MHz Rx frequency while consuming only 18 mA from a 2.1 V supply. Thanks to the embedded filtering passive mixer, the proposed receiver IC shows an additional 15 dB Tx rejection compared to a conventional receiver. The additional Tx rejection improved the IIP $_{2}$ by 10 dB and TB by 30 dB. The complete receiver consists of a differential LNA employing an active post-distortion (APD), I/Q embedded filtering passive mixer, two TIAs for I/Q outputs. The fabricated receiver IC occupies 2.25 mm$^{2}$ including bonding pads, ESD devices, local oscillator (LO) input buffer, frequency divider, and mixer drivers. The receiver is fabricated using a 0.18 $mu$m CMOS process with 5 metal and 1 poly (5M1P) layer.      

Copper-Airbridged Low-Noise GaAs PHEMT With$hboxTi/hboxWN_x/hboxTi$Diffusion Barrier for High-Frequency Applications

A GaAs pseudomorphic HEMT (PHEMT) with Cu-metallized interconnects was successfully developed. Sputtered$hboxWN_x$was used as the diffusion barrier and Ti was used as the adhesion layer to improve the adhesion between$hboxWN_x/hboxCu$interface in the thin-metal structure. After copper metallization, the PHEMTs were passivated with silicon nitride to avoid copper oxidation. The Cu-airbridged PHEMT showed the saturation$I_ DS$was 250 mA/mm and the$g_m$was 456 mS/mm. The Ti adhesion layer plays a significant role on the$g_m$and$V_p$uniformity of the Cu-metallized PHEMTs. The GaAs PHEMTs with$hboxTi/hboxWN_x/hboxTi/Cu$multilayer have better noise figure and associated gain than those of the devices without the Ti adhesion layer. The fabricated Cu-metallized GaAs PHEMT with$hboxTi/hboxWN_x/hboxTi/Cu$multilayer has a noise figure of 0.76 dB and an associated gain of 8.8 dB at 16 GHz. The cutoff frequency$(f_T)$is 70 GHz when biased at$V_ DS = hbox1.5 V$. These results show that the$hboxTi/hboxWN_x/hboxTi$multilayer can serve as a good diffusion barrier for Cu metallization process of airbridge interconnects on GaAs lownoise PHEMTs.     

Measurement of the microwave structure constant profile

Measurements of the microstructure of refractivity at 9.4 GHz were made in Colorado and Florida up to altitudes of about 29000 ft. The structure function parameterC_{n}^{2}was calculated from these data. Examples of the resulting profiles are presented with corresponding profiles of refractivity and temperature. Values ofC_{n}^{2}varied from about10^{-13}to10^{-17}m^-2/3. The heights of occurrence of maximum and minimum values are summarized.     

A 63 mA 112/94 dB DR IF Bandpass $DeltaSigma$ Modulator With Direct Feed-Forward Compensation and Double Sampling

We developed a 10.7 MHz intermediate frequency bandpass discrete-time 4th-order 4-bit $DeltaSigma$ modulator for AM/FM car radio tuners. Using direct feed-forward compensation and double sampling, we have achieved a dynamic range (DR) of 112 dB in the 3 kHz AM bandwidth (BW) and a DR of 94 dB in the 200 kHz FM BW. The modulator occupies 3 ${hbox {mm}}^{2}$ , in 0.15 $mu{hbox {m}}$ CMOS technology, and draws 63 mA of current.      

Theoretical and experimental investigation of rhodamine B-dopedpolymer optical fiber amplifiers

High-power (620 W) and high-gain (28 dB) amplification was achieved by a rhodamine B (RB)-doped GI polymer-optical fiber amplifier (POFA) with a l-m length. A theoretical analysis of the amplification in the RE-doped GI POFA was carried out using the rate equation for the fast three level system. The calculated gain behaviour reasonably fit the experimental data. The possibility of higher power (more than 620 W) and higher gain (more than 28 dB) amplification covering a wide range in the visible region is shown from the calculation. Absorption and emission cross sections of RE in poly(methyl methacrylate) bulk were determined and used in the calculation. The values of the cross sections (σ_{a max}=3.4·10^-20m² ,σ_{e max}=3.4·10^-20 m ²) were approximately 10,000 times larger than those of Er ³⁺ in GeO₂-SiO₂ glass