The SIR-C/X-SAR synthetic aperture radar system

The SIR-C/X-SAR synthetic aperture radar, a three-frequency radar to be flown on the Space Shuttle in September 1993, is described. The SIR-C system is a two-frequency radar operating at 1250 MHz (L-band) and 5300 MHz (C-band), and is designed to get four-polarization radar imagery at multiple surface angles. The X-band synthetic aperture radar (X-SAR) system is an X-band imaging radar operating at 9600 MHz. The discussion covers the mission concept; system design; hardware; RF electronics; digital electronics; command, timing, and telemetry, and testing     

On the EMC dipole feed-line parasitic radiation

A rigorous analysis of the electromagnetically coupled microstrip dipole based on potential integral equations, Green's functions, and the moment method is presented. The computations of the antenna's radiated field using the steepest descent technique is then detailed, and the theoretical results are compared with experimental measurements in the X-band. By considering the feed as an antenna part, the excitation line parasitic radiation is shown clearly. Two possibilities to reduce this parasitic phenomenon are proposed. Also, it is shown that in any microstrip structure (one or two layers) excited by a microstripline, the feed parasitic radiation is nonnegligible     

An X-band spacecraft transponder for deep spaceapplications-design concepts and breadboard performance

The design concepts and measured performance characteristics of an X-band breadboard deep-space transponder (DST) for future spacecraft applications are summarized. The DST consists of a double-conversion, superheterodyne, automatic phase tracking receiver, and an X-band exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X-band uplink carrier signal. The exciter phase modulates the X-band downlink signal with composite telemetry and ranging signals. The measured tracking threshold, automatic gain control (AGC), static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB     

Analysis of coplanar E-H planeT-junction using dissimilar rectangular waveguides

An analysis of a T-junction that differs from conventional H -plane T-junctions in that the T arm is rotated by 90° and coupling takes place through an inclined slot is presented. Since use of standard X-band waveguides results in such a T-junction operating above 11.7 GHz, nonstandard waveguide dimensions have been considered to bring down the operating frequency to 9.375 GHz. The effect of a change of the broad dimension of the primary feed waveguide on the resonant conductance is evaluated. The variations of resonant length with the angle of inclination of the slot, and coupling with frequency, are presented     

A new method for obtaining antenna gain from backscattermeasurements

A method is presented for determining the gain of an antenna from analysis of backscatter data of the antenna. This approach is different from those which have been presented in the past because it accounts for the presence of resonances which can occur in the antenna during a backscatter measurement. In particular, this type of resonance appears in the backscatter measurement of symmetric reflector antennas. This technique is applied to determine the gain of a Ka-band Cassegrain antenna and an X-band prime focus-fed antenna     

A periodic second harmonic spatial power combining oscillator

The authors present a periodic second-harmonic spatial power combining oscillator. The power combining is achieved by phase locking the oscillators at the fundamental frequency and combining the second-harmonic power in space through an array of microstrip patch antennas. The effect of moding and multiple device-circuit interaction is investigated. This circuit is planar, and therefore simplifies the design of monolithic circuits, X-band Gunn diodes are used for the purpose of demonstration     

Dual passband dichroic plate for X-band

A need arose in the NASA Deep Space Network, a worldwide tracking system, for a dichroic plate that would be transparent at two desired frequency bands in the X-band region and be totally reflective at S-band. The dual-passband dichroic plate that was developed to meet the technical requirements is a thick metallic plate having an array of periodic round holes filled with Teflon plugs. Test results on an experimental prototype plate indicate that it is technically possible to design a dielectrically filled dichroic plate that meets all of these technical requirements     

Quasi-optical HEMT and MESFET self-oscillating mixers

Planar quasi-optical receivers that compactly integrate a coupled slot antenna and a HEMT or MESFET balanced self-oscillating mixer and on the same substrate for applications in microwave and millimeter-wave receiver arrays are discussed. Both the HEMT and the MESFET circuit are designed and demonstrated at X-band. The HEMT circuit exhibits an isotropic conversion gain of 4.5 dB and a noise figure of 6.5 dB. The isotropic conversion gain of the HEMT circuit is 7.5 dB higher than the mixer diode circuit previously reported     

X-band 0.5, 1, and 2 watt power amplifiers with markedimprovement in power-added efficiency

Very efficient X-band MESFET power amplifiers, showing greater power-added efficiency over a wider bandwidth than any X-band amplifiers of comparable output reported to date, are discussed. The amplifiers were designed with attention given to optimum bias, proper harmonic termination, and efficient power combining. These device and design issues are discussed, and a straightforward design method which achieved the increased levels of efficiency is described     

FETs and HEMTs at cryogenic temperatures-their properties and usein low-noise amplifiers

Typical DC characteristics and X-band noise parameters are presented and qualitatively correlated wherever possible with other technological or experimental data. While certain general trends can be identified, further work is needed to explain a number of observed phenomena. A design technique for cryogenically cooled amplifiers is briefly discussed, and examples of realization of L-band, C -band, X-band, and K-band amplifiers are described. The noise temperature of amplifiers with HEMTs in input stages is usually less than half of that for all-FET realizations, setting new records of performance for cryogenically cooled, multistage amplifiers     

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     

Analysis of a centered-inclined waveguide slot coupler

Integral equations are developed for a centered-inclined coupling slot (including the effect of finite wall-thickness of the common broad-wall) and the slot-aperture electric intensity field is found using the method of moments. Numerical results for resonant length, backscattered wave amplitude, and phase variation off-resonance are presented over a range of values of the waveguide b dimension, wall thickness, slot width, and frequency. It is shown that the resonant length is relatively insensitive to slot tilt, &thetas;, for a standard-height X-band waveguide, whereas its dependence on &thetas; is significant for reduced-height waveguides. The phase variation of scattered TE₁₀ waves in both waveguides off-resonance is less for wider slots and smaller b dimensions. Shunt-series coupling slots exhibit greater phase variation off resonance when compared to a centred-inclined coupling slot. Also, the former has a longer resonant length for a smaller b dimension and for a wider slot. Thus the centred-inclined slot coupler possesses superior characteristics. The higher-order mode coupling between a centred-inclined slot coupler and a pair of straddling radiating slots in the branch waveguide is significant     

Quasi-optical integrated antenna and receiver front end

A quasioptical receiver front end applicable to both microwave and millimeter-wave receiver arrays is presented. Two planar microwave integrated circuit (MIC) quasioptical receiver circuit designs that integrate a coupled slot antenna, a Schottky-diode balanced mixer, and a local oscillator on the same substrate are described. The even-mode/odd-mode characteristics of the coupled slotlines are used to achieve intrinsic RF/LO and RF/IF isolation. To demonstrate circuit feasibility, X-band scaled models of the circuit unit using a Gunn-diode oscillator on an Epsilam-10 substrate, and MESFET local oscillator on a R/T Duroid substrate were built and tested. Results of these tests are included     

Antenna Designer's Notebook-thinned arrays: some fundamentalconsiderations

The idea of using a thinned version of an array of active elements in an early version of an X-band radar system is explored. The motivation is to hedge against the time when the T/R modules become less expensive. The idea is to design the manifold for the antenna as if all modules were present, and to load the missing ports. All radiating elements would be present and located on the ultimate regular grid but those not actively fed would be terminated in matched loads     

Planar FET oscillators using periodic microstrip patch antennas

An integrated oscillator/antenna is presented that uses a single microstrip leaky-wave structure as both the resonant and the radiating element. This resonant antenna is connected to a GaAs metal-semiconductor field-effect transistor which acts as the negative resistance element in the oscillator circuit. This type of oscillator is similar in its operating principle to one reported using Gunn diodes and a periodically notched dielectric image guide. This circuit exhibits the high DC-RF conversion efficiency that is typical of field-effect transistor oscillators. The planar circuit is simple and inexpensive to construct, occupies a small volume, and can conform to different surface profiles. Such circuits are suitable for use in millimeter-wave systems as well as at microwave frequencies. A design procedure is given, and the performance of X-band prototype circuits is reported. Prototype circuits showed a 9 dB isotropic conversion gain and 40 MHz tuning range at 9.5 GHz     

Conservation of complex power technique for waveguide junctionswith finite wall conductivity

Scattering at the junction of two waveguides with finite wall conductivity is rigorously treated using E-field mode matching and the conservation of complex power technique. At the transverse junction discontinuity between the two waveguides, the complex power absorbed by the junction wall is taken into account along with the usual transfer of complex power from one guide to the other. This leads to a generalized form of the scattering matrix [S] of the lossy junction which incorporates the surface impedance Z_m of the transverse metallic wall, assumed to be a good conductor. The specific case of a copper transverse diaphragm with centered circular iris in an X-band guide is considered and the equivalent TE₁₀ shunt admittance is computed. Numerical results are also given for lossy X-band cavity resonators with circular coupling holes     

Calibration of the CCRS airborne scatterometers

A series of experiments and associated analyses which were designed to lead to an end-to-end calibration of the Canada Centre for Remote Sensing (CCRS) fanbeam scatterometers are described. The method followed was originally introduced in 1984 by A. Yizhar et al. for the Ku-band scatterometer at one incidence angle. This work was extended to yield a full calibration for the Ku-band and C -band scatterometers over the complete range of incidence angles accessible to the instruments. An array of 12 trihedral corner reflectors was deployed in a grassy field near Ottawa. The CCRS CV-580, equipped with two scatterometers, repeatedly overflew the array collecting radar replicas of the targets proportional to the unknown two-dimensional antenna pattern. Data from inertial navigation systems and aerial photographs from a Wild RC-10 mapping camera were used to determine the exact track of the aircraft during the acquisition. This data, with a field survey, alloyed the reduction of the scatterometer data from the reflector array to yield the unknown antenna pattern of the instruments. The cross-polarized antenna patterns were then deduced from the like-polarized results. The results show consistency within 0.5 dB and overall calibration accuracy is estimated to be better than 1 dB     

Microstrip Yagi array antenna for mobile satellite vehicleapplication

A novel antenna structure formed by combining the Yagi-Uda array concept and the microstrip radiator technique is discussed. This antenna, called the microstrip Yagi array, has been developed for the mobile satellite (MSAT) system as a low-profile, low-cost, and mechanically steered medium-gain land-vehicle antenna. With the antenna's active patches (driven elements) and parasitic patches (reflector and director elements) located on the same horizontal plane, the main beam of the array can be tilted, by the effect of mutual coupling, in the elevation direction providing optimal coverage for users in the continental United States. Because the parasitic patches are not connected to any of the lossy RF power distributing circuit the antenna is an efficient radiating system. With the complete monopulse beamforming and power distributing circuits etched on a single thin stripline board underneath the microstrip Yagi array, the overall L -band antenna system has achieved a very low profile for vehicle rooftop mounting, as well as a low manufacturing cost. Experimental results demonstrate the performance of this antenna     

Waveguide-fed parallel plate slot array antenna

A novel planar antenna in which radiating slots are arrayed on one side of a square parallel plate waveguide and coupling slots occupy the other side is proposed. The antenna is excited via the coupling slots by a rectangular waveguide. In order to suppress unwanted reflections and to assure the purity of the transverse electromagnetic traveling-wave mode in the parallel plate waveguide, all the slots are arrayed in pairs. An X-band model antenna was fabricated, and uniform aperture illumination was demonstrated with 48% antenna efficiency. These results demonstrate the feasibility of antennas of this type