Radiation field consideration of biconical horn antenna withdifferent flare angles

The radiation fields of a biconical horn antenna with different flare angles are computed from both the fields of an equivalent Huygens source on the spherical-surface aperture and the infinite biconical horn antenna with spherical transverse electromagnetic wave. Numerical data and experimental results are first presented for the symmetrical biconical horn antenna ka=1.57 and 3.14 (where k is the propagation constant and a=cone length) with equal flare angle. Curves of the beamwidth versus cone length are then given for various flare angles. At flare angles above 75°, the beamwidth increases with the cone length, while at flare angles below about 75°, the beamwidth decreases with the cone length in this region of ka. For the asymmetrical biconical horn antenna, with two different flare angles (including a conical coaxial type and a discone type), the numerical and the experimental patterns are both presented. For the asymmetrical biconical horn antenna, the pattern main lobe direction, with respect to the antenna axis, may be adjusted by using suitable flare angles     

Development of highly dense four-stage flat-gain 1-W 6-18-GHz MMICpower amplifier chip

A state-of-the-art dual-channel four-stage MMIC power chip operating over C-X-Ku bands has been produced. The chip, which is only 4.35 mm×5.1 mm, operates over 6-17 GHz with very small gain ripple. At 25°C each one of its channels provides 29.5±0.5 dBm at 2-dB compression (2 dBc) from a small-signal gain of 19.5±1.5 dB. The drain bias is 7 V. and the power added efficiency is 11-14%. At 85°C, power and gain decrease by 0.5-1 and 3.5-4 dB, respectively. The design was iterated once to produce an all-monolithic amplifier chip that operates over the full 6-18-GHz frequency band and provides more than 1 W at 18 GHz. The architecture and size were maintained in the iterated design. The excellent power and gain ripple performances of the C-X-Ku chip extended to 18 GHz with a small-signal gain reduction of 0.5-1 dB. The chip is designed for use with inputs and outputs coupled externally for additional 2-2.5 dB of power. Excellent performance over 6-18 GHz was achieved using Lange couplers on 10-mil alumina     

High aperture efficiency symmetric reflector antennas with up to60° field of view

A microwave single-reflector scanning antenna derived from an ellipse (rather than the usual parabola) which gives a much greater field of view is presented. This reflector combines reasonable scanning in one plane with good focusing in the other, and its scanning ability is superior to the torus and other single reflectors because it has much greater aperture efficiency and is thus smaller while having the same performance. The reflector surface is derived in two steps: a fourth-order even polynomial profile curve in the scan plane is found using least squares to minimize the scanned ray errors; then even polynomial terms in x and y that minimize astigmatism for both the unscanned and maximally scanned beams are added to form the three-dimensional surface. Numerical simulations of radiation patterns for a variety of antenna diameter and field-of-view cases give excellent results. The 60° scan case with 30-λ-diameter aperture has only 0.2-dB peak gain deviation from ideal and first sidelobe levels below 14 dB down from peak gain. The 17°, 500-λ case has only 0.8-dB gain variation and -14 to -11 dB sidelobe levels for approximately ±68 beamwidths of scan, with focal length to aperture diameter ratio equal to about one     

A polarization splitter on LiNbO3 using only titaniumdiffusion

A novel polarization splitter is proposed for use in integrated optical circuits on lithium niobate. In contrast to previously reported devices, its operation is based on the mode sorting effect with no external control, while its fabrication requires only a single technology: the diffusion of titanium. The splitter is formed by a Y junction. The polarization splitting can be achieved by making the output waveguides from two titanium strips with different dimensions. A realistic design of these output guides is presented, and some technological aspects are discussed. The operation of the polarization splitter is investigated with the beam propagation method. The results show that a 15-dB extinction ratio is obtained with branching angles larger than 0.2°. The extinction ratio can be as high as 30 dB with a branching angle of 0.1°. The excess losses are below 0.05 dB     

Performance of packaged near-traveling-wave semiconductor laseramplifier with multilongitudinal mode input

The results for a packaged 1.30-μm InP/InGaAsP optical amplifier used to switch broadband multilongitudinal modes signals are presented. Despite the absence of optical isolators and even with the introduction of additional external reflections (R≈1.0%), the optical fiber-to-fiber gain is stable over a large temperature range at resonance (ΔG⩽0.35 dB ΔT=±0.75°C at G=5.76 dB). Although the amplifier is capable of higher levels of gain (G_max ≈13 dB), it is considered that stable gain, relative to variations in temperature and reflectivity is more critical to the overall system. It has been found that a multilongitudinal mode signal can be amplified by a resonant amplifier without system degradation caused by mode-partition noise, and that junction heating requires a thermal stabilization period up to ≈0.2 ms after the start of a current pulse     

Construction technique and performance of a 2 GHz rectangularcorrugated horn

A large rectangular horn antenna with a center frequency of 2.0 GHz, corrugated on the E-plane walls, made out of aluminium sheet, has been designed, constructed, and tested. A technique has been developed to solder thin aluminium strips onto the back plane to form the corrugations. The radiation beam pattern shows half-power beamwidths of 12° and 14° in the H- and E-planes, respectively, and sidelobe response below -40 dB at angles greater than 50° from the horn axis. The measured return loss is greater than 20 dB (VSWR<1.22) between 1.7 and 2.3 GHz; insertion loss is less than 0.15 dB     

SAR observations and modeling of the C-band backscattervariability due to multiscale geometry and soil moisture

The effect of the multiscale surface geometry on the sensitivity of C band synthetic aperture radar (SAR) data to soil moisture is studied. The experimental data consist of C-band SAR images of an agricultural site, including fields with various combinations of three distinct roughness components from small to large scale. The backscatter variability due to surface roughness has been analyzed. The effect of random roughness associated with soil clods is never less than 2 dB, and the effect of a row pattern can be as strong as 10 dB. In addition, the periodic drainage topography induces a backscatter variability due to soil moisture variation and drainage relief. The results indicate that airborne C-band SAR data cannot be easily inverted into soil moisture data. However, with ERS-1 or Radarsat data at an incidence angle of about 20°, the effect of random and periodic roughness can be reduced to about 2 dB if the look angle is less than 50°     

High-dynamic-range airborne tracking and fire control radarsubsystem

Two high-dynamic-range receiver subsystems for use in airborne radar fire control and tracking applications are described. The X -band dual-channel monopulse tracking receiver operates at 9.36±0.290 GHz with a 6-dB noise figure and a linear instantaneous dynamic range of 42 dB. A total of 80 dB of RF and IF gain control is programmable with less than ±15° phase and ±1 dB amplitude tracking errors. The Doppler radar receiver operates at 9.3±0.15 GHz and has a 4.6-dB noise figure with ⩾80 dB of instantaneous dynamic range. An 18-dB sensitivity time control (STC) circuit and a 60-dB dump attenuator allow close-in target reception     

An ultrahigh-speed GaAs MESFET operational amplifier

A wide-bandwidth GaAs MESFET operational amplifier is reported, with a 65-dB DC gain and a 20-GHz gain-bandwidth product at 500 MHz. The circuit uses a variety of local feedback techniques to enhance the overall gain. The use of an undoped GaAs buffer, grown at a relatively low temperature (≈300°C), eliminates backgating and light sensitivity. The circuit was fabricated in an 80-GHz f_T MESFET process, with 0.2-μm electron-beam defined gates. The high levels of 1/f noise, MESFET frequency-dependent output conductance, and large offset voltage standard deviation limit the application of the circuit to moderate precision applications     

Seasat over-land scatterometer data. I. Global overview of theKu-band backscatterer coefficients

Statistics on the backscatter coefficient σ⁰ from the Ku-band Seasat-A Satellite Scatterometer (SASS) collected over the world's land surfaces are presented. This spaceborne scatterometer provided data on σ⁰ between latitude 80° S and 80° N at incidence angles up to 70°. The global statistics of vertical (V) and horizontal (H) polarization backscatter coefficients for 10° bands in latitude are presented for incidence angles between 20° and 70° and compared with the Skylab and ground spectrometer results. Global images of the time-averaged V polarization σ⁰ at a 45° incidence angle and its dependence on the incidence angle are presented and compared to a generalized map of the terrain type. Global images of the differences between the V an H polarization backscatter coefficients are presented and discussed. The most inhomogeneous region, which contains the deserts of North Africa and the Arabian Peninsula, is studied in greater detail and compared with the terrain type     

The electrical characteristics of a conical horn-reflector antennaemploying a corrugated horn

The electrical properties of a conical horn-reflector antenna of 2-3° beamwidth have been investigated over the frequency range of 12-18 GHz. It is shown that the employment of a corrugated horn reduces the characteristic spillover side lobe of the conical horn-reflector antenna by 15 dB and yields excellent main beam circularity over the full Ku band. This results from the taper of the field amplitude toward the edges of the horn aperture in both the E-plane and the H-plane illumination. The performance of the antenna makes it suitable for use in closely packed interferometers for radio astronomy     

Tensile-strained InGaAs/InGaAsP quantum-well optical amplifierswith a wide spectral gain region at 1.55 μm

A tensile-strained InGaAsP/InP multi-quantum-well optical amplifier is constructed which has ⩾92 nm bandwidth at 16-dB gain for 50-mA drive current. The wide gain bandwidth is a result of both n=1 and n=2 contributions from the e→1 h transition. These results suggest wide tunability for lasers made from this material     

Super-low-noise performance of direct-ion-implanted 0.25-μm-gateGaAs MESFET's

The authors report on advanced ion implantation GaAs MESFET technology using a 0.25-μm `T' gate for super-low-noise microwave and millimeter-wave IC applications. The 0.25×200-μm-gate GaAs MESFETs achieved 0.56-dB noise figure with 13.1-dB associated gain at 50% I_DSS and 0.6 dB noise figure with 16.5-dB associated gain at 100% I_DSS at a measured frequency of 10 GHz. The measured noise figure is comparable to the best noise performance of AlGaAs/GaAs HEMTs and AlGaAs/InGaAs/GaAs pseudomorphic HEMTs     

A 16-b 320-kHz CMOS A/D converter using two-stage third-orderΣΔ noise shaping

The design and measured performance of a two-stage third-order ΣΔ (sigma-delta) analog-to-digital (A/D) converter is described. The A/D converter achieves a 96-dB dynamic range and a maximum signal-to-noise-plus-distortion ratio (S/(N+ D)) r.m.s./r.m.s. of 93 dB with 320-kHz output rate and an oversampling ratio of 64. An analysis of the integrator gain error is presented. The modulator is realized in a 1.2-μm double-metal single-poly CMOS process with an active area of 1.6 mm². This modulator operates from a 5-V power supply and a single reference voltage     

Interference effects on Space Station Freedom and Space Shuttleorbiter Ku-band downlinks

The Space Shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the Space Station Freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. It is shown that a simplified analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit-energy-to-thermal-noise power spectral density ratio to achieve a 10^-5 coded bit-error probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5-dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes. For the Ku -band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I=21.6 dB     

Broadband compact horn feed for prime-focus reflectors

A compact flare angle controlled corrugated horn antenna with a 60° half beamwidth is optimised by using a moment method for bodies of revolution. The horn has corrugations with simple rectangular cross-sections and is excited by a smooth wall circular waveguide. The resulting 15 dB beamwidth varies by <18% and the crosspolar sidelobe levels are more than 26 dB below the mainlobe, both over a 1.8:1 bandwidth. All results are confirmed by measurements. The horn is suited for broadband feeding of e.g. prime-focus reflectors in radioastronomy applications     

Temperature sensitivity of phase-matched second-harmonic generationin LiIO3

Measurements were made of the temperature dependence (between 23 and 65°C) of the phase-matching angle &thetas;_pm for type I frequency doubling of 1064-nm laser light in lithium iodate (LiIO₃). The measured value of d&thetas;_pm/dT is -14.7±1 μrad/°C, which corresponds to a thermal sensitivity β_T =0.24±0.02 cm^-1/°C for this process. Also calculated is a value of d&thetas;_pm/dT using experimentally determined thermooptic data available in the literature. The calculated value of d&thetas;_pm/dT is -31±18 μrad/°C using literature values of n and dn/dT for LiIO₃. The extreme sensitivity of the calculated value of d&thetas;_pm/dT to small errors in the thermooptic coefficients may be the reason for this discrepancy     

AlInAs-GaInAs HEMT for microwave and millimeter-wave applications

The status of lattice-matched high-electron-mobility transistors (HEMTs) and pseudomorphic AlInAs-GaInAs grown on In substrates is reviewed. The best lattice-matched devices with 0.1-μm gate length had a transconductance g_m=1080 mS/mm and a unity current gain cutoff frequency f_T=178 GHz, whereas similar pseudomorphic HEMTs had g_m=1160 mS/mm and f_T=210 GHz. Single-stage V-band amplifiers demonstrated 1.3- and 1.5-dB noise figures and 9.5- and 8.0-dB associated gains for the lattice-matched and pseudomorphic HEMTs, respectively. The best performance achieved was a minimum noise figure of F_min=0.8 dB with a small-signal gain of G_a=8.7 dB     

5-60-GHz high-gain distributed amplifier utilizing InP cascodeHEMTs

A high-gain InP MMIC cascode distributed amplifier was developed which has 12 dB of gain from 5 to 60 GHz with over 20-dB gain control capability and a noise figure of 2.5-4 dB in the Ka band. Lattice-matched InAlAs/InGaAs cascode HEMTs on InP substrate with 0.25-μm gate length were the active devices. Microstrip was the transmission medium for this MMIC with an overall chip dimension of 2.3 mm×0.9 mm. The gain/noise figure advantages of the InP HEMT over the AlGaAs HEMT and the superior gain performance of the cascode HEMT over the common-source HEMT are demonstrated     

Comparisons of microwave performance between single-gate anddual-gate MODFETs

Both a 1.2-μm and a 0.3-μm gate length, n⁺-GaAs/InGa/n⁺-AlGaAs double-heterojunction MODFET have been fabricated with single-gate and dual-gate control electrodes. Extrinsic DC transconductance of 500 mS/mm has been achieved from a 0.3-μm single-gate MODFET. The device also has a current gain cutoff frequency f_T of 43 GHz and 14-dB maximum stable gain at 26 GHz with the stability factor k as low as 0.6 from the microwave S-parameter measurements. At low-frequency dual-gate MODFETs demonstrate higher gain than the single-gate MODFETs. However, the k of dual-gate MODFETs approaches unity at a faster rate. Power gain roll-off slopes of 3-, 6-, and 12-dB/octave have been observed for the dual-gate MODFETs