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Three microwave garnet phase-shifter designs are used in the AEGIS weapons system. The microwave design is straight-forward except that the toroid assembly is potted with silicone rubber to increase its power-handling capability and the magnetizing wires are shielded with a spiral-wrapped wire to prevent the propagation of higher order modes. The driver circuit uses a new "flux-feedback" concept for improved accuracy and employs monolithic circuits, hybrid circuits, and discrete components. Mechanical and electrical design of the interfaces with mating components are important cost considerations and the chosen designs are described in detail. Several techniques for improving production yield are discussed and a table of production statistics is provided. Performance histograms and data averages as a function of time and operating frequency are also presented.

The influence of the oscillator noise on the minimum detectable signal of a Doppler RADAR with a self-mixing IMPATT-diode oscillator is evaluated. For very short-range RADARs, it is the AM noise which limits the signal-to-noise ratio and thus the range.

Solid-state array radar is of gyeat current interest because of the inherent reliability of solid-state devices and the concomitant promise for improvement in system reliability. However, no extensive reliability base has been established for solid-state devices employed under radar operating requirements. In this paper some of the important factors bearing a device reliability are treated. Accelerated life tests under RF conditions are presented for L-band power transistors. Preliminary life-test and failure-analysis data are also presented with recommendations on how the information can be used by the radar systems designer.

This paper describes the design and development of a double-ridge waveguide designed to propagate both C-band and X-band (5,400 and 9,300 mc) so as to allow for a common waveguide installation in commercial airliners which could use either a C-band or an X-band weather penetration radar. This double-ridge waveguide is capable of propagating over the desired frequency range with single mode operation only; it yields attenuation at C-band which is only slightly higher than that of normal C-band waveguide and has somewhat reduced attenuation at X-band compared to standard 1 X 1/2 rectangular waveguide. This double-ridge guide has been adopted by Aeronautical Radio, Inc. and is specified in their Characteristic No. 529 entitled "5.7 Cm Weather Penetration Airborne Radar." This paper also gives an analysis of the calculated guide wavelength in this double-ridge guide, attenuation, and peak power-handling capabilities; and compares the results of these calculations with measured data. Peak power-handling capability for this double-ridge guide is well within the requirements of this application. The testing procedures used for high-power breakdown measurements are described. This paper also covers the development of double-ridge waveguide flanges, elbows, bends, twists, transitions, and flexible waveguide for use over this extremely broad band.

Needs for nondispersive microwave variable delay devices exist in RADAR, communication, ECM, and test systems. Methods which have been investigated to satisfy these needs are reviewed in this paper. Techniques that employ solid-state microwave acoustic interactions and that have promise of satisfying some of the microwave variable delay requirements are described in detail, and their present capabilities and potential capabilities are discussed. One technique employing magnetoelastic waves is particularly promising and the state of the art of this technique is analyzed thoroughly.

The object of this research is to investigate the feasibility of adapting the conventional pulsed radar technique for closerange back-scattering measurements for obstacles of arbitrary shape and small scattering cross sections. The time-separation or microwave-pulse method described in this paper differs essentially from all previously used laboratory methods in that the scattered field does not mix with the incident field at the detector and is separated from it in time. The essential experimental arrangement of this method is similar to that of the CW magic-T method except that a source generating very short pulses is used instead of CW. Preliminary experimental data for thin circular metallic disks show that the pulse method is a feasible one, since the measured results are in close agreement with the theoretical values. Accurate back-scattering measurements for obstacles of arbitrary shape and small scattering cross sections should be obtainable by this method provided a short microwave pulse of high power level is available.

To achieve optimum performance from a microwave receiver that uses a balanced crystal mixer, matched pairs of crystals should be used. However depending on the reason for choosing the balanced mixer for a particular receiver, the crystal characteristics that should be matched and the degree of balance that is required vary considerably. The three principal reasons for using balanced mixers are: 1. To minimize noise figure by suppressing local-oscillator noise. 2. To suppress local-oscillator power radiation. 3. To reduce receiver sensitivity to certain spurious responses. For radar receivers, the first reason is the only important one, and fortunately it places the least stringent requirement on the degree of balance.

Experimental data and discussion are presented which show the desirability of using thick punch-through PIN diode for high-power limiting. The slower speed of response sets an upper limit on thickness. Data are presented on the maximum thickness allowable as a function of frequency. Results are given for a high-peak-power narrow-pulsewidth receiver protector, and for a high-average-power wide-pulsewidth balanced duplexer. These devices are compared to conventional gas T-R tubes and results suggest that the use of multiple PIN diodes in limiters and duplexers can offer significant improvements in some RADAR applications.

The development of a low-loss broad-band linear FM dispersive filter having a time-bandwidth (TB) product of 1000 is discussed. Two systems applications for highly dispersive linear FM filters--pulse compression RADAR and a microscan receiver--are discussed with emphasis on filter performance requirements. The principal factors which influence the design of surface-wave filters are reviewed and theoretical design procedures are outlined. The 1000:1 filters, which are implemented on strong-coupling YZ lithium niobate, typically meet the design goal of a 100-MHZ rectangular passband and have a CW insertion loss of less than 35 dB. Measured data are presented for the filter performance in a pulse-compression loop and in a prototype broad-band microscan (compressive) receiver.

A method is described for generating simulated microwave frequency RADAR terrain echoes. This method makes it possible for the first time to realistically duplicate in the laboratory the principal characteristics of echoes due to RADAR motion and terrain roughness. These characteristics include variation of echo delay, Doppler shift, random fine structure, and their time variation. The simulation is based on modeling of the RADAR beam propagation and diffuse reflection processes by use of microwave acoustic energy in a solid medium. Scaling relations between RADAR and acoustic model parameters are derived. An experimental program was carried out whose purpose was to develop a practical solution to the problem of varying the distance between a microwave acoustic transducer and a reflecting surface, and to determine the overall feasibility of the simulation method. Results indicating its practicability are presented and directions for further work are suggested.

Pulse testing techniques have been used for many purposes for a long time. In studies of waveguides as radio and radar components and for possible communications systems use, we have employed various types of pulse testing. The need for greater resolution through the use of very short pulses has always been apparent. For this reason, equipment has recently been built to generate and display 9,000 megacycle pulses having a length of about 6 millimicroseconds. In a pulse of this length there are less than 100 cycles of radio frequency energy, and the pulse occupies less than 10 feet of path length in the transmission medium. The r-f bandwidth required is about 500 megacycles.

Theoretical studies at The Aerospace Corporation over the past several years, of the general RADAR resolution problem have been the stimulus for an experimental program aimed at demonstrating the practicability of utilizing the high inherent resolution potential of millimeter-wavelength RADAR. In brief, the large bandwidth available at 94 GHz, for example, (several thousand MHz) should enable a RADAR to obtain a "range profile" of a satellite that shows more details than range profiles at lower frequencies. The high Doppler sensitivity at 94 GHz should permit a precise measurement of the spin rate for spinning satellites; the high carrier frequency offers the possibility of using synthetic aperture processing to "compress" the antenna beam along the track, so that two-dimensional resolution in range and along the track is obtained for better determination of satellite properties.

It is shown how to connect two identical hybrids to obtain a directional coupler of arbitrary power division that operates over a broader band than that of the components. The broad-banding technique is possible with a certain kind of hybrid that includes Riblet couplers, multihole hybrids, coaxial hybrids and semioptical hybrids, but excludes T hybrids and ring hybrids. Riblet couplers have a geometry particularly adaptable to the broad-banding technique. Where the balance of one of these couplers is better than 1 db, the balance of the broad-band hybrid can be made better than 0.16 db. The broad-banding technique is particularly effective in the case of the 100 per cent transfer directional coupler type of circuit used for band separation filters and RADAR duplexers. In the semioptical waveguide band-splitting filters the bandwidth can be increased from about one to about four octaves (35-75 kMc to 35-580 kMc).

An X-band, circularly-polarized, nonreciprocal, ferrite phase shifter has been developed whose size and electrical performance are favorably suited for use in transmission or reflection-type phased arrays requiring element center-to-center spacings of about 0.5 /spl lambda/. The phase shifter has the same configuration as a Faraday rotator with a ferrite rod located at the center of a circular waveguide with an axially applied field. If a circularly polarized wave is passed through this geometry, a nonreciprocal phase-current characteristic is obtained. The array antenna is configured so that no phase-control field reversals are needed between transmit and receive modes of RADAR operation. The radiating element has been designed as an integral part of the beam steering element using waveguide array simulator techniques, this paper will discuss various design problems and performance of the beam steering element. A 1300-element phased array was constructed and tested. Its performance, as it relates to the phase-setting accuracy of 1300 phase-shifter constituents, is stated briefly.

RADAR target scintillation is observed in every type of RADAR system and has generally been analyzed on the basis of the performance of specific types of RADAR systems. However, the target scintillation phenomenon, including Doppler scintillation, may be expressed as distortions of the RADAR echo signal propagating in space, independent of RADAR system parameters. In this form it is convenient for visualizing the overall effects on RADAR systems and how these effects are altered by the RADAR system parameters. Past literature has demonstrated the target angle scintillation as a distortion of the RADAR echo signal phase front. Extension of this approach by a Poynting-vector analysis of the RADAR echo signal from a complex source shows a corresponding deviation of the direction of power flow consistent with the phase-front distortion theory and target scintillation measurements as well as describing all other target scintillation characteristics. The analysis demonstrates that deviations in the direction of the echo signal power flow from a complex target can be so large that the apparent source falls many target spans away from the actual target location. This is demonstrated by both tracking RADAR and single-beam search-t ype RADAR experiments. Although the theoretical angle deviations approach infinite error in target location, RADAR parameters, such as the finite size antenna aperture which perform a space integration of the echo signal, impose practical limitations. Typically, when a complex target such as an aircraft subtends an angle approaching a few tenths of a beamwidth, the antenna aperture integration will significantly limit the rms angle scintillation. Furthermore, the ways in which intentional means, such as diversity techniques, may be employed to reduce the effects of target scintillation on a RADAR are observed in Poynting-vector analysis. The analysis of the echo signal propagating in space provides a readily visualized basis for derivation of the Doppler scintillation caused by the airframe (rigid body portion) of a complex target which spreads the Doppler over a finite bandwidth when it has random yaw, pitch, and roll motion typical of aircraft in flight. The derivation relates the Doppler scintillation to the angle scintillation and the random motions typical of aircraft targets. A typical aircraft target with Gaussian-distributed angle scintillation and Gaussian-distributed rates of random motion will have a spike-shaped Doppler spectrum described by the modified Hankel function K/sub 0/ where the parameters are determined from the values of the rms angle scintillation and the rms angular rates of random motion. These values can be closely approximated without extensive measurements on the target. Experimental results verify the theory. The expressions used to derive the Doppler spectrum may be modified to accommodate non-Gaussian distributed angle scintillation and rates of angle motion.

This paper describes a rain canceller using a turnstile junction to provide the necessary polarization of the fields. It discusses the system from the point of view of adapting an existing radar feed system to one that will permit the reduction of rain return. The turnstile junction is described, and it is shown to have properties that meet the requirements for obtaining circular or elliptical polarizations. Along with this description, the theory behind the effect of elliptical and circular polarization on rain return is discussed in detail as well as the practical limits such a theory can be put to. Other considerations such as aspect ratio of antennas and screening for the antenna surfaces are touched upon.

These subroutines are used in performing Smith-chart analysis. They are also applicable to even-odd mode analysis.

Noise has always played a major role in the design of microwave systems. The tradeoff problems of transmitter power versus receiver sensitivity in RADAR, antenna size versus receiver sensitivity in communications, system noise temperature versus bandwidth and integration time in radiometry, etc., have always challenged the design engineer in the past and will continue to do so in the future. This lecture concerns itself with these tradeoff problems and presents several points of view relative to optimum performance.

Often it is not convenient to measure a reflection coefficient directly. In some such cases, the following procedure may be used. The arrangement of components shown in Fig. 1 will be considered. It will be assumed that lines Nos. 1 and 2 are lossless. These lines may be transmission lines, waveguides, or one of each.

This paper discusses the design and tests of a Microwave Interferometer, an instrument capable of measuring the time-displacement of a projectile within the barrel of a gun. A continuous record of the projectile time-displacement is obtained by using a CW-Doppler radar technique at K-band. A discussion is made of the effect of higher order modes within the gun barrel and of the effect of the leakage of the propellant gases ahead of the projectile.

H. A. Wheeler and H. L. Bachman, authors of "Evacuated Waveguide Filter for Suppressing Spurious Transmission from High-Power S-Band Radar," which appeared on pages 154-162 of the January, 1959 issue of these Transactions, have submitted the following correction.