Popular Articles (March 2015)
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1. A new antenna feed having equal E and Hplane patterns
Publication Year: 1954 , Page(s): 113  119
Cited by: Papers (29)  Patents (1)When two complementary sources are combined in the proper amplitude and phase, desirable radiation characteristics for feeding a circular aperture are obtained. It is shown that when the feed is achieved there results a circular beam cross section which optimizes the efficiency of illumination of a circular aperture. The back radiation from the feed is down 30 db from that in the forward direction, minimizing interference effects between feed and aperture. It is the purpose of this thesis to show how a feed composed of complementary sources has been physically realized and to present and discuss experimental radiation and impedance data. It is well known that the radiation pattern of an electric dipole is a circle in the plane and a figure 8 in the plane. An openended coaxial line carrying the mode is similar to a magnetic dipole; i.e., the plane is nearly circular while the plane is like a figure 8. These two sources have been combined to produce a feed whose  and plane patterns are of equal width. The complementary source idea has been applied to feeds of both linear and circular polarization. The linearly polarized feed is excited from rectangular waveguide and is simple to fabricate. It can be easily matched over a broadband. This feed has been used to illuminate a 20inch parabola with the result that the secondary and planes are of equal width and the side lobes are 30 db down from the main radiation. The circularly polarized feed is excited from a circularly polarized mode in coaxial line. The radiating structure maintains circular symmetry and the axial ratio remains essentially constant over a large portion of the beam. View full abstract»

2. Design of linesource antennas for narrow beamwidth and low side lobes
Publication Year: 1955 , Page(s): 16  28
Cited by: Papers (129)  Patents (3)It is well known that the phenomenon of radiation from linesource antennas is very similar to that of the diffraction of light from narrow apertures. Unlike the optical situation, however, antenna design technique permits the use of otherthanuniform distributions of field across the antenna aperture. Line source synthesis is the science of choosing this distribution function to give a radiation pattern with prescribed properties such as, for example, narrow angular width of the main lobe and low side lobes. In the present article the mathematical relationships involved in the radiation calculation are studied from the point of view of function theory. Some conclusions are drawn which outline the major aspects of synthesis technique very clearly. In particular, the problem of constructing a line source with an optimum compromise between beamwidth and sidelobe level (analogous to the Dolph  Tchebycheff problem in linear array theory) is considered. The ideal pattern is cos π √ {u /sup 2/  A/sup 2/} , where u = (2a/λ) cos θ, a is the halflength of the source, and cosh π A is the sidelobe ratio. Because of theoretical limitations, this pattern cannot be obtained from a physically realizable antenna; nevertheless its ideal characteristics can be approached arbitrarily closely. The procedure for doing this is given in detail. View full abstract»

3. On the theory of corrugated plane surfaces
Publication Year: 1954 , Page(s): 71  81
Cited by: Papers (40)  Patents (1)An analysis is given of an electromagnetic system composed of a rectangular waveguide in tandem with a corrugated waveguide which feeds a flat, corrugated surface of arbitrary length terminated by a ground plane, whose length is also arbitrary. An improved procedure of field determination is used which combines Floquet's theorem and the variational principle, thus revealing an additional requirement on the corrugation geometry. Factors influencing a match at the feed mouth, and satisfactory launching of the surface wave are discussed. The degree of suppression of the feed radiation is given in db as a function of the geometry of the system. Approximate radiation patterns are derived for two cases, (a) when the system is terminated by an infinite ground plane, and (b) when the system is terminated by a finite ground plane. For the latter case, an upper bound on the tilt angle of the main beam and a lower bound on its beamwidth result from an approximate theory. For both cases, the HansenWoodyard endfire relation is found to provide beam sharpening even when the feed radiation is considered. The presence of higher order surface modes, their effect, and their elimination are discussed. Comparison of the theory with experiment is reasonably good. View full abstract»

4. A twodimensional microwave luneberg lens
Publication Year: 1953 , Page(s): 12  23
Cited by: Papers (13)  Patents (9)SummaryA twodimensional microwave model of the Luneberg lens has been designed employing the TE
10 mode. It consists of two 36inch diameter, almostparallel, conducting plates with the space between plates filled with polystyrene. Its thickness varies with the normalized radius, T, to give the desired index of refraction n = Due to symmetrp about the center, this lens maintains constant gain and beam shape as a feed is scanned over its circumference, while the side lobe level remains at least 18 db below peak power. Experimental patterns show good agreement with computed patterns in the two principal planes. View full abstract» 
5. Radiation from a vertical dipole over a stratified ground (Part II)
Publication Year: 1954 , Page(s): 144  146
Cited by: Papers (3)Further results are given for the problem of a vertical electric dipole situated over a horizontally stratified conductor. It is pointed out that under certain conditions the surfacewave field intensity for a stratified conducting ground is greater than the corresponding case for a perfectly conducting ground. Numerical values for the attenuation factor are also given. View full abstract»

6. UHF omnidirectional antenna systems for large aircraft
Publication Year: 1954 , Page(s): 6  15
Cited by: Papers (1)This paper discusses the problem of obtaining omnidirectional coverage from antennas operating between 1,000 and 3,000 megacycles on large aircraft. Electromagnetic modeling was used to determine the limitations of several single antenna sites on typical commercial aircraft. Considering all azimuth angles and in elevation to be equally important, the best coverage obtainable from a single radiator is equivalent to the radiation from a freespace dipole for 50 per cent of the time. To improve this, dual antenna systems must be used. Dual antenna requirements depend on whether or not the airborne equipments know when they should be receiving a signal. The distancemeasuring equipment (DME) is a typical system that knows when it should be receiving a signal, while radar safety beacon equipment does not know when or from what direction it is being interrogated. Direct parallel feed, the least complicated method of operating dual antennas, allows simple hybrid multiplexing to be used. With this type of operation interference occurs where the individual patterns overlap. Performance in this region is investigated on a probability basis for beacon operation and found favorable; for DME this region is uncertain. In addition, performance is predicted when the RF voltage in one of the dual antennas is (a) shifted periodically in phase, (b) delayed, and (c) interrupted periodically. Considerations involved in an antenna system common to DME and beacon are discussed. View full abstract»

7. Measurement of the effect of irregular terrain on VHF and UHF directive antenna patterns
Publication Year: 1952 , Page(s): 167  178
Cited by: Papers (4)Measurements of antenna patterns of directive antennas were made while driving around transmitters at relatively constant distances of 0.4, 10, and 30 miles. The transmitting antennas for pattern measurement were located at Fort Dix, N.J., and operated at frequencies of 49, 141.75, 239, and 460 mc. The receiving antennas used for recording were groundplane antennas mounted on a retractable mast in the mobile recording unit and could be operated as high as 30 feet, road obstacles permitting. Because of the great number of wires and trees over the road, most measurements were made at 12 and 15 feet. In addition to the measurements made around the transmitters, receiving antenna pattern measurements were made at spot locations around the transmitter with a 460mc corner reflector antenna. View full abstract»

8. A rotary joint for two microwave transmission channels of the same frequency band
Publication Year: 1952 , Page(s): 136This dualchannel rotary joint consists of two pairs of rectangular waveguide terminals, a circular waveguide which transmits both channels, and coupling elements between the rectangular waveguide terminals and the circular waveguide which convert the rectangular H
10 mode into the circular H01 and E01 modes. If pure H01 and E01 modes can be excited, perfect separation of the channels as well asconstant amplitudes and phases can be obtained when the Joint rotates. While the conversion into the circular E01 mode is performed by a conventional method, a new method had to be developed for the conversion of the rectangular H10 mode into the circular H01 mode. View full abstract» 
9. Microwave radio reflection from ground and water surfaces
Publication Year: 1952 , Page(s): 37  45Reflection of microwaves from ground and water surfaces for a number of wavelengths between 0.86 and 26.5 centimeters have been measured over paths of a few thousand feet and grazing angles of the reflected ray up to 5 degrees. Antennas with comparable patterns large enough to illuminate a large surface area were used. A variety of surface conditions including bare ground and smooth and choppy water were studied. For the particular overland path used, the ground appeared smooth at 26.5 and 9 centimeters wavelength, evidenced considerable roughness to 3.2 centimeters and appeared very rough to 0.86 centimeters. The mean reflection coefficient decreased with decreasing wavelength. For the overwater paths, the reflection for all wavelengths was that associated with a smooth surface when the conditions were calm. For a choppy surface, the millimeter signal showed large time variations and its apparent reflection coefficient decreased. View full abstract»

10. Electrically small antennas and the lowfrequency aircraft antenna problem
Publication Year: 1953 , Page(s): 46  54
Cited by: Papers (7)This paper is concerned with the properties of antennas which are small relative to their operating wavelength. A brief analysis based upon quasistatic principles is presented, and two experimental procedures suggested by the nature of the analytical results are described. The application of these experimental procedures is illustrated with examples of measurements made in connection with the design of lowfrequency aircraft antennas. View full abstract»

11. The geometrical optics field at a caustic
Publication Year: 1952 , Page(s): 262The asymptotic expansion of a wave field in powers of , where is the wave number, for large k has as its lowest order term what is commonly known as the geometrical optics field. The caustics of geometrical optics are those point sets on which the zero order teen becomes infinite. It is well known that caustics may exist even where the exact wave field is perfectly regular. An investigation of reflection from cylindrical walls of arbitrary cross section shows that the occurrence of caustic points means a change in character of the asymptotic expansion of the true field such that the lowest order term is no longer independent of , but actually contains a factor raised to a positive power. There also occurs a Jump in phase along a ray passing through a caustic which, as is well known, equals in the case of a focal point, but which may differ from in the case of more general types of caustics. In addition, the geometric optics field is worked out in detail for the case of a plane wave incident on a parabolic cylinder, and the field is obtained in its lowest order at the focus and in the neighborhood of the focus. View full abstract»

12. Radiation from a vertical electric dipole over a stratified ground
Publication Year: 1953 , Page(s): 9  11
Cited by: Papers (9)Expressions for the radiation fields at low frequencies of a vertical electric dipole situated on a horizontally stratified ground are derived. It is indicated that the wellknown numerical results for the homogeneous ground can also be employed for ground wave propagation over a plane couductor composed of any number of parallel layers by suitably defining an "effective numerical distance." View full abstract»

13. Thickness effects in slots located in various positions in rectangular waveguide
Publication Year: 1952 , Page(s): 107Theoretical expressions for the equivalent circuit parameters of slots of finite Â¿ wall thickness are obtained in terms of the parameters of aerothickness slots of identical crosssection dimensions. The thick slots are treated as composite structures consisting of appropriate junctions and lengths of connecting waveguide, and the parameters of the junctions are determined from those of corresponding zerothickness slots. The latter parameters have been developed in previous work by our group. The thick slots considered include transverse slots coupling identical guides, transverse slots radiating from the end of the guide, slotcoupled Eplane Tees, and slots radiating from the broad face of the guide. Precision measurements have been taken at a wavelength of 3.2 cm as a function of nail thickness, and excellent agreement is obtained with the theoretical predictions. View full abstract»

14. On spherically symmetric lenses
Publication Year: 1952 , Page(s): 66  71
Cited by: Papers (7)First Page of the ArticleView full abstract» 
15. Random processes in wave propagation
Publication Year: 1952 , Page(s): 143Part I. Transmission: For wave propagation through a randomly scattering medium, theory predicts statistical averages of certain measurements. Familiar theories are discussed in terms of the measurements to which they relate. For instance, the "extinction cross section" of a large opaque object is simply shown to be twice its geometric cross section; the relevant measurement is not one of transmitted power flux, but an interferometric measurement of the average phase and amplitude of a coherent wave passing through a cloud of such objects. A similar interferometric measurement relates to the attenuation currently calculated from the BookerGordon scattering formula. This is shown by two new derivations of the propagation constant of a "blobby" medium. The simpler measurement of average transmitted powerflux requires a complicated theory of photon transport. Theory and measurements relating to angleofarrival are intermediate between those relating to powerflux and propagation constant. Part II. Reflection: Similar considerations hold for reflection from a rough surface. Specular reflection is an interferometric concept. Lambert's law and backscatter are powerflux concepts. A theory of specular reflection is logically prior to a theory of backscatter. The requirements for such theories are discussed through simple examples. View full abstract»

16. A further study of the patterns of single slots on circular conducting cylinders
Publication Year: 1952 , Page(s): 240  250
Cited by: Papers (1)The azimuthal patterns of both axial and circumferential slots on circular conducting cylinders have been carefully calculated in both magnitude and phase and some experimental checks have been obtained. The calculated patterns show that in the semicircle over which the slot is optically visible, the magnitude, and particularly the phase, of the patterns, are very similar to those, of a similarly situated slot in an infinite ground plane. This conclusion has significant implications in the design of an antenna involving several slots on a cylinder. On the semicircle over which the slot is optically invisible, and partioularly near the midpoint of this range, the pattern is very well represented by where is the value of the pattern at (the point opposite the slot) and is complex. Thus the field of either one of the rear quadrants resembles the voltage of an opencircuited lossy transmission line. The implications of the abovenoted form of the field pattern behind the slot led to the consideration of an expression for the field which is quite different from the usual one originally employed. By an exact transformation of the usual expression it is possible to show that the far field is given by the expansion , where is complex. Near , the first term of this series is dominant, and the results of this approach agree with those noted above. The procedure and its significance are quite closely related to the problem of electromagnetic wave propagation over a sphere, which has been of considerable interest for some time. The various aspects of the cylindrical problem are discussed in some detail. View full abstract»

17. Factors affecting the performance of linear arrays
Publication Year: 1952 , Page(s): 85  106The primary problem in the design of antennaarrays is the satisfaction of the requirements of sidelobe level and beamwidth. An additional major consideration which has only recently received an analytical treatment1 is the problem of the deterioration of the beamwidth and sidelobe level arising from the variations in the excitation of each element. These variations are due primarily to the inaccuracies inherent in the manufacturing processes used to produce the array. The first problem has been discussed in great detail by many authors,2 and it will be the purpose of this paper to analyze the second problem. The analysis is formulated in general for a symmetrically excited broadside array and then, as a specific example, is applied to a linear shunt slot array which uses a DolphTchebyscheff3 distribution for the element excitations. This distribution optimizes the relationship between beam width and sidelobe level. However, the method of analysis is general and may be applied to any linear array of radiators with arbitrary excitation, if the total mutual coupling between individual radiators may be neglected and no cross correlation exists between the inaccuracies of any two sources. Consideration will be given to these fundamental assumptions to show that the general method will yield useful results for slot arrays. View full abstract»

18. Guided wave concept in electromagnetic theory
Publication Year: 1952 , Page(s): 231  239First Page of the ArticleView full abstract» 
19. Discussion on optimum patterns for endfire arrays
Publication Year: 1955 , Page(s): 40  43
Cited by: Papers (7)The method of synthesizing an equalminorlobe directivity pattern suggested by Riblet for the broadside array was applied recently by DuHamel to the case of the endfire array. In the present paper, an alternative synthesis procedure is described, based directly on Dolph's method of synthesis for the broadside array. Advantages of this alternative procedure include (a) applicability to arrays having even as well as odd numbers of elements, and (b) somewhat simpler equations for calculating relative currents for the elements of the array. This alternative procedure is described here in detail, together with numerical examples for the sevenelement array used by DuHamel and for a fourelement array. A tabulation of equations for relative current amplitudes for arrays of 5, 7, 9, 11, and 13 elements is given in an Appendix. In conclusion, an alternative method of overdesigning a supergain antenna is described. View full abstract»

20. Instantaneous prediction of ionospheric transmission circuits by the communication Zone Indicator ("COZI")
Publication Year: 1952 , Page(s): 202  209
Cited by: Papers (1)Detection of longdistance echoes by an obliqueincidence hf sounder with directive antenna provides a novel technique for predicting ionospheric transmission conditions to remote points. Measurements on oscilloscopic echo patterns can be correlated with (a) field strength of remote cw stations, (b) response of remote beacons synchronously triggered by the sounder, or (c) predictions based upon CRPLSignal Corps worldwide contours of ionospheric layer heights and muf s. The results indicate that most of the echoes are due to energy backscattered at the earth, lonospherically reflected en route. Further, the transmission time (slant range) to the leading edge of the backscatter pattern measures reasonably well the skip distance (ground range) for long distances. Thus the backscatter echoes may be attributed to a ground area near and somewhat beyond skip distance to which communication is possible. A PPI echo display with a rotating directive antenna reveals in a striking manner the azimuthal variation of skip distance, giving at a glance the possible distant conmunication zones. Transmission modes, such as Flayer and sporadicE layer reflections are readily discernible. Diurnal variation of the communication zones may be determined by comparing PPI photographs taken throughout the day. Results, recently declassified by the government, are given in a series of PPI photographs and corresponding azimuthal maps, commencing more than four years ago. Early equipment consisted of 20 kw peak power pulsers, with nominal lO0microsecond pulse width and 20 per second repetition rate. Horizontal rhombics and multielement rotatable Yagi antennas were employed. Later, longer pulse widths up to 2 milliseconds and peak powers less than I kw were employed with results equally useful for many applications. Backscatter patterns have been observed on 9, 12, 16, and 22 mc. The first demonstration of the PPI technique is shown in a nighttime photograph taken at . Dartmouth, Mass. on May 6, 1948 at 16 mc. A typical diurnal variation of PPI patterns is shown in a series of photographs taken at 15minute intervals, at 22 mc, on January 19, 1950. Effect of different frequencies is shown in a series of PPI photographs taken at 12, 16, and 22 inc. Flayer and sporadicE  modes are noted. Suggested applications of the "COZI" technique includes assisting communication services in better circuit utilization, for implementing ionospheric prediction services, and as a new tool for ionospheric research. View full abstract»

21. Modified magic tee phaseshifter
Publication Year: 1952 , Page(s): 126  134A magic tee may be used as a microwave phaseshifter by placing adjustable short circuits in its symmetrical arms. A perfect impedance match will exist through the E and Hplane arms if the distances from the shortcircuits to the tee junction differ by (2n + 1)Â¿ g/4. The phase is shifted by simultaneously varying the distances from the short circuits to the tee junction. Orienting the symmetrical arms parallel to each other and replacing the E and Hplane arms by coupling slots on opposite sides of the stucture simplifies the shortcircuit driving mechanism and allows cascading of several phaseshifters. This modification is useful as a precision laboratory phaseshifter and allows the construction of a wideangle scanning array. View full abstract»

22. An experimental investigation of the singlewire transmission line
Publication Year: 1954 , Page(s): 46  56
Cited by: Papers (3)The results of some measurements made on a dielectric coated wire are presented and compared with theoretical results. These measurements indicate that the singlewire line can be considered as a simple transmission line provided account is taken of the "endeffect." View full abstract»

23. Factor of merit for aircraft antenna systems for the frequency range from 3 to 30 MC
Publication Year: 1952 , Page(s): 67  73
Cited by: Papers (3)First Page of the ArticleView full abstract» 
24. Dielectric sheet radiators
Publication Year: 1954 , Page(s): 152  158
Cited by: Papers (2)A class of electromagnetic radiators is described which employs the principle of waveguiding along a flat surface by means of dielectric coating. Radiation occurs as a result of nonuniformities in the guiding system. The efficiency of the feeding arrangements and diffraction over the edge of the flat surface are factors in the sidelobe level observed. A unit is described which has been used aboard missiles. A series of tests are reported which illustrate some of the characteristics of the radiators. Data for comparison with corrugated surface antennas is given. Problems for further investigation are listed. An experimental unit is described with a gain of 25 db and an efficiency compared to conventional aperture radiators of about 60 percent. This unit has linear dimensions comparable to a hem producing the same beamwidth. View full abstract»

25. An exact stepup impedanceratio chart of a folded antenna
Publication Year: 1954 , Page(s): 163
Cited by: Papers (4)First Page of the ArticleView full abstract» 
26. An atmospherics analyzer
Publication Year: 1955 , Page(s): 9  12The enormously powerful radiation from lightning discharges has been used as a tool for the study of the ionosphere at very low frequencies. Previous workers have calculated the height of the ionosphere and the distance to the radiation source by application of the ray theory of multiple ionospheric reflections. Time measurements for use in the height and distance formulas were obtained by direct measurement of recorded oscillograms. Time resolution was limited and the calculations were extremely tedious. This paper describes a complete system which records the received atmospheric wave form and simultaneously derives a plot of the time intervals between peaks of the wave form vs time. The timeinterval plot greatly facilitates data reduction by means of a simple curvefitting technique. Accuracy of measurement of height and distance is limited chiefly by the validity of the multiple reflection theory and the assumption of a simple layer structure in the ionosphere. The time differences are measured more accurately than is ordinarily possible with direct measurement on the waveform. The system automatically derives frequencytime plots for whistling atmospherics and relates the whistler to preceding impulsive atmospherics. Consumption of photographic film is low. The system can be used to visually monitor taperecorded atmospherics. View full abstract»

27. Some methods for evaluating trends in time series of tropospheric radio field strength data
Publication Year: 1952 , Page(s): 144  151This paper presents a short review of several methods for evaluating the "seasonal trend" in a series of hourly median field strengths corresponding to one hour of the day. The presentation is from the viewpoint of descriptive statistics, and no discussion is given of the difficult problem of statistical tests of significance for appraising the components of trend found by these methods. Of three methods investigated in CRPL, a type of harmonic analysis was found to be the most successful. The other two methods were an adaptation of the smoothing theory of Wiener and Levinson and a method using orthogonal polynomials. The tools of the statistician, the autocorrelation function and the variate difference method, enable us to refine our analysis of time trends to a point where we hope to obtain a maximum amount of correlation with similar trends in relevant meteorological information. View full abstract»

28. News and views
Publication Year: 1955 , Page(s): 1  3First Page of the ArticleView full abstract» 
29. Distant radio communication theory
Publication Year: 1952 , Page(s): 212
Cited by: Papers (2)Distant radio communication at high frequencies is difficult because the transmission medium, the earth ionosphere duct, is time variable, noisy, and shows dispersive or multipath transmission with consequent fading of the received signal. Because most of these factors are random and not under design control, one can treat the ionospheric communication problem only on a statistical basis in terms, for example, of such things as the probability that a transmitted pulse or bit of information will be received correctly. On this basis it is shown that, by a purely numerical experiment wherein random number tables are used to simulate fading and noise, it is possible to appraise various telegraph transmission systems without the costly process of building them and then testing their performance. An approximate, but simple, analysis is given of receiver signal detection, by which is meant generation of dc for operation of an output printing device. It is shown that the important parameter here is the average or expectation of the difference in dc between a received space and mark signal, divided by the square root of the variance of this difference. Incoherent square law detection is compared with coherent detection using the matched filter or, what is the same thing, correlation. The use of diversity transmission to overcome signal fading at the receiver is considered. The important statistical data regarding timevarying ionospheric transmission are obtained from the auto and crosscorrelation functions of the received signal envelopes for the various diversities. For the correlated fading of signal s in two transmission channels, a simple de sign formula is shown which predicts the improvement in the use of diversity. A brief description is also given of a simple acoustic ionosphere analog simulating timevarying multipath transmission. View full abstract»

30. Fregion effects of solar eclipse at sunrise, September 1 , 1951
Publication Year: 1952 , Page(s): 210The annular eclipse of September 1, 1951 started before ground surmise along the east coast of the United States but did not reach maximum phase until later. Three highspeed ionospheric stations were operated by the D.T.M., C.I.W. for the eclipse observations. Locations at Charlottesville, Virginia, Derwood, Maryland, and Chincoteague, Virginia established a westtoeast chain with local time difference of approximately twelve minutes. The maximum phase of eclipse occurred at a time (twenty to thirty minutes after ground sunrise) when normal rate of production of ionization (established by control observations) was very high. The results show absence of any ion production at any station for a period of approximately onehalf hour centered on time of eclipse maximum. From the moment when twothirds of the sun was covered, through the maximum phase ( per cent), and until onethird of the sun was uncovered, no ionization was generated. Several possible explanations are discussed: (1) Emitting sources near center of sun's disc; (2) Uniform solar emission, but an effective limb darkening; (3) An atmosphere on the moon. View full abstract»

31. Sweep frequency backscatterSome observations and deductions
Publication Year: 1954 , Page(s): 56  63
Cited by: Papers (3)Sweepfrequency backscatter records have proved to be of great value in identifying the sources of backscatter seen on a fixed frequency by demonstrating the development of the echo as frequency and range increase. The most commonly observed scatter is ground scatter propagated via the F2 layer, but it is also evident that the other layers propagate ground scatter and that scatter from the distant E region may at times be important. In one group of observations over an 1,150km path on three undisturbed days, the values of F2layer maximum usable frequency scaled from midpoint verticalincidence ionospheric records and those determined by backscatter delay assuming ground scatter agreed almost within experimental error. In another threeday group characterized by a lowlatitude ionospheric disturbance with low geomagnetic indexes but considerable sporadic activity, values of muf determined from scatter were much too high under the groundscatter assumption, errors of about 30% being not uncommon. View full abstract»

32. Refraction of radio waves in arbitrary atmosphereraytracing picture
Publication Year: 1952 , Page(s): 36A development following Hartree, etc., is carried out of ray tracing using REAC differential analyzer. Ray families, on 2kinch by 32inch paper, are obtained for an atmosphere with a single n profile (index of refraction versus altitude curve), and for an atmosphere with three n profiles over the region of interest. The n profiles used were measured up to 10,000foot altitude. The variation in radio field strength with separation between airplanes as measured in a recent airtoair propagation flight is correlated with a variation or ray density based on index of refraction data taken during the flight. This was a flight which encountered a radio hole followed by its antihole (region of erulanced and interfering signals) within the geometrical horizon, and then a second hole and antihole at an anomalously large range beyond the horizon. The second antihole is accounted for by an anomalousranee layer near the ground and one in which the refractive gradient has a negative value nearly equal to l/(radius of earth}. In some respects the correlation is striking between raytracing picture and observed radio data. View full abstract»

33. A singlecontrol tuning circuit for electrically small antennas
Publication Year: 1955 , Page(s): 12  15
Cited by: Papers (2)It is often desirable to tune electrically small antennas at their feed terminals. An "L" matching circuit for this purpose is considered. It is shown that one fixed element and one variable tuning element are adequate for certain small antennas. The manner in which losses affect the circuit effiiciency and the singlecontrol tuning feature is discussed. Application of the technique to a tunable cavity antenna is noted. View full abstract»

34. The design of circularly polarized aperture antennas
Publication Year: 1952 , Page(s): 136By using equivalent circuits, the polarization transmitted from an aperture is analized in terms of the reflection properties of the aperture, the length of the Waveguide, and pertinent parameters of the exciting antenns. The techniques described afford a systematic procedure for designing antennas which are circularly polarized at one frequency or which have a low axial ratio over a band of frequencies, This procedure may be used to solve which have been applicable to lessless antennas are derived. Systems for measuring all pertinent parameters are developed and theoretical predictions are correlated with experimental measurements. View full abstract»

35. A theoretical and experimental study of the recombination coefficient in the lower ionosphere
Publication Year: 1954 , Page(s): 99  102The problem of recombination of electrons and ions in the lower ionosphere is studied both experimentally and theoretically. The experimental study involves analysis of new experimental data such as 150kc radio wave absorption, polarization, and phase heights; absorption of shortwave galactic radiation; and Eregion critical frequency, as well as recombination values already published. Then, by use of the theories of dissociative recombination and negative ions, a theoretical model is derived which is consistent with the experimental results. The values of the coefficient during nighttime and during sudden ionospheric disturbances are discussed. View full abstract»

36. Turbulence in the lower ionosphere as deduced from increments in absorption and phase path at 150 KC
Publication Year: 1952 , Page(s): 139It is important in the study of ionospheric winds to determine the height of the "diffraction screen" which produces the variations in radio wave field strength, or other characteristics, measured at ground level. A method which may be used to determine this height is developed. It is shown that, under proper conditions, the mean electronic collisional frequency associated with the electron clouds which are presumed to form the "diffraction screen" may be determined by studying change in phase path records obtained simultaneously with absorption records. This value of collisional frequency may then be related to height through an ionospheric model. Single recording stations are used in this comparison of the phase pattern and the amplitude pattern at ground level. The statistical information necessary to the theoretical development is obtained, in the usual way, from a triangular arrangement of receiving stations which record the amplitude of the signal. Preliminary calculations show that the screen which produces the daytime ionospheric winds measured at 150 kc lies in a collisional frequency range from to sec^{1}. This would correspond to a height range from 70 to 80 km for our ionospheric model. These results appear to be in good agreement with recent work by Kellogg (1951) from the meteorological viewpoint. View full abstract»

37. Theory of waveguidefed slots radiating into parallelplate regions
Publication Year: 1952 , Page(s): 63  66Slotted waveguide arrays feeding into parallelplate regions have been used in some high speed scanners. Parallelplate regions also have been used for the suppression of secondorder beams of highgain arrays. A theoretical expression is derived for the conductance of a longitudinal shuntslot in a rectangular guide when the slot is radiating into a parallelplate region of arbitrary plate spacing. Some peculiarities of the theoretical results are discussed. There is good agreement between theory and experiment. View full abstract»

38. Slot radiators and arrays at Xband
Publication Year: 1952 , Page(s): 62  84Experimental verification of the validity of Stevenson's expression for a longitudinal shunt slot has been obtained. The theoretical expression has been found to be valid throughout Xband. Substantiating curves are shown, Resonant slot lengths as functions of slot dimensions and position on the waveguide are given. Correlation. between the phase angle of the admittance and the phase angle of the radiated field of a slot has been established. The behavior of the radiation pattern as a function of the position of the slot on the waveguide is shown. The characteristics of linear arrays of these slots are given, and some of the applications are indicated. View full abstract»

39. Strip transmission line study
Publication Year: 1952 , Page(s): 37A TEM transmission line having a circular or rectangular center conductor placed between two parallel plates or inside a rectangular tube, has been used in the construction of a number of uhf antennas and Â¿ wave filters. The characteristic impedance of the class of transmission lines, of which the abovementioned are particular examples, can be theoretically calculated by a number of methods. A review of the theoretical methods using the above transmission lines as examples will be given. Comparison between theoretical and measured results will be given to show the usefulness of the different theoretical methods. View full abstract»

40. Sessions on diffraction and electromagnetic theory
Publication Year: 1953 , Page(s): 58  60First Page of the ArticleView full abstract» 
41. Mutual impedance of stacked rhombic antennas
Publication Year: 1954 , Page(s): 39
Cited by: Papers (1)First Page of the ArticleView full abstract» 
42. Double parabolic cylinder pencilbeam antenna
Publication Year: 1955 , Page(s): 4  8
Cited by: Papers (2)Radiation from a point source placed on the focal line of a parabolic cylinder is reflected in succession from this cylinder and from a second parabolic cylinder crossed so that its focal line coincides with the directrix of the first cylinder. The two reflections result in a parallel beam. The theory is applicable to both microwaves and light. The advantages of shipping the cylinders in the form of flat sheets and the possibilities of independent control of horizontal and vertical beamwidths and shapes are pointed out. Experimental models have been built and tested. View full abstract»

43. Symmetrical waveguide junctions
Publication Year: 1952 , Page(s): 106Dicke and Kerns have shown that from a knowledge of the geometrical symmetry of a junction one can deduce the form of the scattering matrix. The synthesis problem; given a desired scattering matrix, to determine whether it is physically realizable in a symmetrical structure, and to find the possible structures, has not been solved completely, although several useful things can be said about the general problem. However, the number of cases that are ever likely to arise in practice is finite, and by solving the analysis problem for each of them and tabulating the results we have effectively given a "bruteforce" solution of the synthesis problem for junctions of six or fewer waveguides. View full abstract»

44. Transmission loss of space waves propagated over irregular terrain
Publication Year: 1952 , Page(s): 152  166
Cited by: Papers (3)First Page of the ArticleView full abstract» 
45. Nodal shift impedance measurements in periodic waveguides
Publication Year: 1952 , Page(s): 106The nodal shift method of measuring the properties of a Coupling system connecting two transmission lines is a convenient and accurate method which does not require the existence of good terminations to match the lines. Using a generalized definition of impedance in a periodically loaded waveguide, such as is encountered in the Stanford linear accelerator or in travelingwave tubes, this technique can be extended to determining the properties of a coupling system connected between a smooth waveguide and the periodic one, and when these are known, one can measure impedances in the periodic structure by observing those in the smooth guide. In addition, this impedance relation permits one to deduce the phaseshift constant of the structure at any frequency in the passband. View full abstract»

46. A broadband microwave quarterwave plate
Publication Year: 1952 , Page(s): 123  125A differential phase shift between two orthogonal TE11 waves in circular hollow waveguide may be achieved with capacitive pins which affect one mode and not the other. Representing the two modes in the guide by two equivalent transmission lines and the pins by shunt susceptances, an analysis of an array of pins may be made to determine, as a function of pin spacing, the required values of susceptance to produce a given phase shift Â¿ with no reflection. By making use of the transmission matrix giving voltage and current at one point in terms of voltage, and current at another point on the line, the following formulas for a threeelement array are derived: View full abstract»

47. On the input construction of thin antennas
Publication Year: 1955 , Page(s): 29  32
Cited by: Papers (1)Input conductances of thin antennas are computed by evaluating separately input voltage and radiated power for a prescribed value of the current near the maximum. The current distribution required to evaluate the radiated power and the input voltage is obtained by solving Hall??n's equation for the prescribed value of the current. First and second order computations were carried out for full wave antennas, and the results compared with those obtained by others. View full abstract»

48. Internal reflection in the troposphere and propagation well beyond the horizon
Publication Year: 1952 , Page(s): 19
Cited by: Papers (5)A simple estimate of the feeble internal reflection from the normal troposphere explains remarkably well long puzzling fields well beyond the horizon throughout the VHF and microwave spectrum. Even in the absence of ducts, the continuous decrease with height of the index of refraction under gravitational influence makes the troposphere an inhomogeneous continuously stratified medium. The effective earth's radius notion allows for the refractive effect of this inhomogeneity in calculating the diffracted field beyond the horizon, but not for internal reflections. A bilinear model for the index profile of the normal atmosphere gives modes with db/mi attenuation rates in approximate agreement with the experimental one of roughly 1/7 db/mi at 50,400 and 3000 Mc. To a considerable extent, the internal reflection idea obviates the need for hypothesizing omnipresent atmospheric turbulence up to heights of several miles in the troposphere, a phenomenon once erroneously thought also to cause "angel" echoes on radars. View full abstract»

49. A waveguide array for solar noise studies
Publication Year: 1954 , Page(s): 147  152
Cited by: Papers (5)A description is given of a 150foot slotted waveguide array which was built for solar noise studies at wavelengths near 10.3 centimeters. Some of the problems associated with the design of such an array are discussed. View full abstract»

50. Theoretical and experimental investigation of the group heights of reflection of 150KC radio waves vertically incident on the ionosphere
Publication Year: 1952 , Page(s): 136  137This paper is concerned with the theoretical and experimental determination of the group heights of reflection of long radio waves vertically incident on the ionosphere. The theoretically expected group heights for 250microsecond Gaussian shaped pulses are determined utilizing: (1) a wave theory treatment including coupling, (2) a Chapmanlike ionospheric model including all variables and their height variations and (3)a fundamental radio frequency or carrier component of 150 kc. From the theoretical viewpoint the continuous wave (cw) results of Gibbons and Nertney(1951) (1952) are extended by including the dispersive characteristics of the above model. This is accomplished by determining the received pulse characteristics by means of a response function developed from a suitable FourierHermite series which includes the frequency dependent effects of the model. It is Found that the rapid changes in polarization near the lower edge of Eregion, called the "coupling region", are very effective in generating reflected waves or pulses under suitable conditions; i.e., late night hours associated with low Elayer critical Frequencies. However, the dispersive characteristics are small so that almost negligible group retardation is to be expected. At a higher level in the layer, rapid variations in the index of refraction for one of the characteristic wave components occur in what is called the "reflection region". Here the time delays are large for low critical frequency models. Some geometrical discussion is included concerning polarization and coupling Factors. If not considered, then the ordinary and extraordinary modes can be given a representation (in a certain complex space) as orthogonal principal directions. The above theory is compared with the experimentally observed group heights on a diurnal and seasonal basis. Good agreement is obtained and is further strengthened by comparison with some recent measurements of R.E. Jones on the diurnal change in phase (cw) paths. The occurrence of a third echo in addition to the regular First hop Eechoes is reported. This apparently occurs from levels above the maximum ionization density of the layer, height range 100 to 200 km, and appears to be associated with low nighttime layer critical frequencies and magnetically disturbed conditions. Correlations of experimental results with sunrise, solar flares, etc. are also considered. View full abstract»
Aims & Scope
This Transactions ceased publication in 1955. The current retited publication is IEEE Transactions on Antennas and Propagation.