Showing papers in "IEEE Transactions on Microwave Theory and Techniques in 1955"

The Design of Ridged Waveguides

Abstract: As far as we are aware, the only published design information on ridged guide transmission lines is found in a paper by S. B. Cohn and to some extent in the Waveguide Handbook. Recent applications, however, have indicated a need for additional and, in some cases, more accurate design information. The present paper is largely written with this in mind.

Shielded Coupled-Strip Transmission Line

Abstract: An analysis is made of the odd and even TEM modes on a pair of parallel co-planar strips midway between ground planes. Rigorous formulas are presented for the case of zero-thickness strips, while approximate formulas are given for strips of finite thickness and for strips printed on opposite sides of a thin dielectric sheet supported in air between ground planes (AIL construction). The characteristic impedances and the phase velocities of the two modes are necessary and sufficient information for the design of directional couplers, coupled-line filters, and other components utilizing the coupling between parallel-strip lines. In order to facilitate design work, nomograms are included in the paper which give the dimensions of the coupled-strip cross section in terms of the odd- and even-mode characteristic impedances. The characteristic-impedance scales of these nomograms may be read to an accuracy of better than one per cent over a wide range of values that is sufficient for most purposes.

Optimum Design of Stepped Transmission-Line Transformers

Abstract: This paper describes the optimum stepped-transmission-line transformer structure for matching two unequal characteristic impedances. For any specified bandwidth, the steps are designed to yield a Tchebycheff-type (or equal-ripple) reflection-coefficient response. Over this band, the maximum vswr is less than that obtainable with any other stepped-transformer having the same number of steps. Design method and technique for eliminating discontinuity-capacitance effects are given. The measured results for a coaxial and a waveguide model are presented and found to verify the method.

Problems in Strip Transmission Lines

Abstract: A review is given of characteristic-impedance formulas for shielded-strip transmission lines. From these formulas a set of approximate relationships for the attenuation and Q of a dielectric-filled shielded-strip transmission line is derived. The method makes the standard assumption that the current distribution is that of a lossless line and the surface resistivity that of an infinite-plane condutor. Although this method applies accurately to most other types of lines, in this case an error of the order of 10% is believed to occur due to the failure of the assumptions at the corners of the strip. However, the error is in a direction that makes the computed values conservative, and the accuracy should be sufficient for most practical purposes. The derivation of a correction term is now being attempted. In addition to the discussion of attenuation attention is given in this paper to the design considerations involved in a shielded-strip-line impedance meter, and to some preliminary data obtained with this device. Also the future topics for investigation under this research and development program are mentioned.

A Modulated Scattering Technique for Measurement of Field Distributions

Abstract: Electric field distributions can be measured accurately by passing a short metal dipole through the field and recording the wave scattered by the dipole. Ordinarily the method is difficult to use since the scattered signal is small, critical tuning adjustments are required, and careful attention to stability is necessary. However, by placing a nonlinear impedance at the center of the dipole and applying an audio voltage though slightly conducting threads, the scattered wave can be modulated. This makes it possible to relax the tuning and stability requirements and at the same time to increase the sensitivity of the measurements.

Equivalent Circuits for Discontinuities in Balanced Strip Transmission Line

Abstract: Theoretical formulas are derived for the equivalent circuit parameters of a variety of discontinuties in balanced strip transmission line. These formulas are simple in form and are obtained by employing a small aperture procedure or a Babinet equivalence procedure in conjunction with an approximate model of the line. The results for a number of discontinuities are presented and comparison is made with the available measured data.

Phase Shift by Periodic Loading of Waveguide and Its Application to Broad-Band Circular Polarization

Abstract: A rectangular or square waveguide may be loaded periodically by thin capacitive or inductive irises in order to produce phase delay or phase advance, respectively. The amount of phase shift may be calculated with accuracy by making use of available theoretical values of iris susceptance and of transmission line theory. The phase shifting sections maybe designed for low voltage standing-wave ratio (vswr) over a considerable bandwidth. When a square waveguide capable of supporting two fundamental modes is loaded periodically, the irises act inductively for one mode and capacitively for the other, thus introducing a differential phase shift. This differential phase shift may be made equal to 90°, in order to convert linear to circular polarization. Furthermore such a device may be made, by proper choice of parameters, to yield near-circular polarization over a bandwidth of 1.65:1, because the variation in phase delay for one mode and phase advance for the other tend to compensate each other as the frequency is varied. Several of these circular polarizers have been built and tested at X band and the measured results of ellipticity and vswr, as well as broad-band performance check with theoretical values quite closely.

Applications of the Turnstile Junction

Abstract: The Turnstile Junction is a six-terminal pair microwave network, consisting of four coplanar rectangular arms and a circular arm, orthogonal to the rectangular arms, which is excited in two orthogonal TE 1, 1, modes. The characteristics of the network are such that they lend themselves to some very important and unique applications in the microwave field. Making use of the symmetry conditions and the field division properties of the Junction, this paper describes the operation of the Junction under various conditions, with particular emphasis on the applications to which these characteristics lend themselves.

Microwave Printed Circuits - A Historical Survey

Abstract: The microwave printed circuit, as described in this paper, is an extension of the well-known technique which is of such importance in the lower frequency regions, where lumped element circuits are practical. This new circuit possesses all of the virtues of other printed circuits, such as light weight, cheapness, ease of manufacture, miniaturization, etc., along with the ability to be used at frequencies as high as 10,000 mc. The basis of the new technique is the planar or "flat strip" coaxial transmission system which was developed during World War II but which has remained unpublished and relatively unknown in the postwar period; and for which an adequate theoretical analysis had not been available.

Rigorous Determination of the Parameters of Microstrip Transmission Lines

Abstract: Statement of Problem--The purpose of this paper is to determine explicit expressions enabling calculation of the performance of the recently-introduced open-strip UHF transmission line, now rapidly coming into extensive use.

Step-Twist Waveguide Components

Abstract: The step twist is a number of adjoining sections of straight rectangular waveguide, twisted about their common axis at their junction faces. The technique of designing the step twist resides in the proportioning of the section dimensions and the angles at the twist faces. The resulting design is much shorter than the usual twisted waveguide; it offers further advantages in ease of specifying shape and dimensions, and in their reproducibility in construction. A series of fixed 90-degree step twists has been designed for the rated 40 per cent frequency bandwidths in the standard waveguide sizes for 1 to 40 kmc. The total angle is divided equally among seven faces spaced about 1/8 wavelength in the guide. Each step twist is matched within 0.3 db swr with plain flanges or 0.5 db swr with choke flanges at both ends. Rotary step twists for operation at all angles out to +-90 degrees have been designed for the same bandwidths. The total angle is divided unequally among four faces (choke flanges) spaced about 1/4 wavelength in the guide. The entire unit at maximum rotation is matched within 1.2 db swr with choke flanges at both ends; the matching is closer at lesser rotation.

Probes for Microwave Near-Field Measurements

Abstract: To be satisfactory for microwave near-field measurements, a probe must have desirable polarization characteristics, must have an aperture small enough to indicate the field at a point, must deliver sufficient signal voltage to permit accurate measurement, and yet must not seriously distort the fields. The design of a probe may be simplified if the fields to be measured are known to be almost linearly polarized or to consist only of a traveling wave. Comparison of measurements made with various probes has led to the development of a small open-ended waveguide probe which is simple to construct and has given excellent results.

Characteristics and Applications of Microstrip for Microwave Wiring

Abstract: Microstrip has been developed as a substitute for waveguides or coaxial lines, especially for the development of microwave components and Microwave circuitry.

Slot Array Employing Photoetched Tri-Plate Transmission Lines

Abstract: Microwave printed circuit techniques are readily adapted to the construction of compact antennas ideal for flush mounting on high speed aircraft. This paper describes the development of a two-dimensional X-band array consisting of 16 slots fed by photoetched Tri-plate transmission line. The design of a unity coupled series slot and the resulting mode purity problems are discussed. Several power divider configurations are illustrated and data (on the performance of some of these devices is presented. The construction of a 4 slot E-plane, a 4 slot H-plane and the combination 4x4 E-, H-plane array utilizing these power dividers is shown. Radiation patterns of each of these arrays were measured and a comparison of the individual and combination array patterns is made.

The Use of Scattering Matrices in Microwave Circuits

Abstract: Difficulties arising from the use of the impedance concept in microwave circuitry have led to the introduction of the scattering representation for work at these frequencies. This paper presents a development of the scattering approach in terms of fundamental transmission-line phenomena. The physical meaning of the quantities involved is brought out wherever possible and the relationships among the various elements of the scattering matrix are given. Several examples of the application of scattering techniques to analysis of the properties of microwave junctions are presented, and methods for measuring scattering parameters of such junctions are outlined.

Properties of Dialectric Image Lines

Abstract: The properties of a dielectric rod on an image surface are reviewed, and experimental results on straight sections, various bends, and a twist are presented. Techniques for measuring insertion parameters and field distributions are described.

Measurement Techniques for Multimode Waveguides

Abstract: This paper surveys some of the techniques that have been worked out for multimode waveguide measurements Equipment has been developed for measuring one mode at a time by taking advantage of the differences between the modes Illustrations of its use are given

E-Plane Forked Hybrid-T Junction

Abstract: A novel rearrangement of the waveguides of a microwave hybrid-T junction has been investigated. This junction is formed by the intersection of four rectangular waveguides, two of which (conventionally E and H arms) are mutually perpendicular, cross-polarized, and have their centerlines in one symmetry plane of the junction; the remaining two waveguide arms are formed by symmetric E-plane bifurcation of the E-arm waveguide extended. This hybrid T possesses special advantages with regard to match and pulse power capacity. A special test fixture was constructed of 1.122- X 0.497-inch rectangular waveguide. Experimental design work was carried out over a 12 per cent range of frequencies from 8.5 to 9.6 kmc. The H-arm reflection was reduced to 2.6-db standing-wave ratio (swr) by simple shaping of the bifurcating element. Addition of conventional matching elements resulted in maximum reflections, within the above band, of 0.8 and 0.6 db swr in the H and E arms, respectively. The ultimate limitation on the E-arm power capacity, as fixed by the intensified electric field at the leading (rounded) edge of the center partition, was computed to be 2 db below uniform waveguide. Experimental corroboration has been obtained.

Circuit Components in Dielectric Image Lines

Abstract: Symmetry of dipole mode in a dielectric rod permits use of an image system. By replacing lower half of dielectric and its surrounding field with an image surface, support problem is eliminated. Resulting image provides structural convenience and also has very low loss, provided wave is allowed to occupy a cross section many wavelengths square. In millimeter region this is readily achieved. Possibilities of new types of circuit elements in this image system are explored. Combination of optical and waveguide techniques is a characteristic of resulting components. Properties of several transducers between image line and either rectangular waveguide or coaxial line are described. Attenuators, standing-wave detector, and various directional coupler types for image lines are also discussed.

Measurement of Time-Quadrature Components of Microwave Signals

Abstract: A phase-sensitive coherent detector used for microwave laboratory measurements is described. The receiver measures the real (|E| cos alpha) and imaginary (|E| sin alpha) components of a signal E with equipment which is less elaborate than that required for measuring the amplitude |E| and phase alpha. Furthermore, many calculations are more convenient if E is presented in rectangular rather than polar form. Measurements made with the receiver on known fields in waveguides are included to demonstrate its accuracy. The receiver has a sensitivity of -125 dbw at 9,375 mc.

Planar Transmission Lines

Abstract: This paper derives formulas for the transmission properties--characteristic impedance and attenuation--in the principal mode of a transmission line consisting of one or two long strips of metal foil embedded in a dielectric material between two long metal strips considerably wider than the central ones. The width and spacing of the central strips is arbitrary, and it is also necessary to take account of their thickness in computing the attenuation. A graphical method is given for evaluating the characteristic impedance in general, and analytic approximations are given for a number of special cases. Finally the question of the leakage of power from between the outer strips is considered briefly.

Characteristics and Some Applications of Stripline Components

Abstract: Basic characteristics of Stripline in various frequency bands from 1000 to 16,000 mc are summarized. Various components such as transitions to coaxial line, attenuators, hybrid rings, directional couplers, and filters are shown. Some applications of these components in practical high performance microwave circuits and equipment in the frequency range of 2500-10,000 mc are also described.

Intrinsic Insertion Loss of a Mismatched Microwave Network

Abstract: A brief review is presented of the absolute minimum loss of a two-port, mismatched lossy microwave network. This minimum loss, called the "intrinsic insertion loss" can be attained by adding suitable susceptances at the ports that will yield simultaneous bilateral network match. A measurement procedure is described and convenient graphs are presented.

High-Power Ferrite Load Isolators

Abstract: The principles of ferromagnetic resonance have been well described in literature. It is the purpose of this paper to point out the application of these principles to the design of practical microwave components, especially for high power. The various types of ferrite microwave circuits that can be used in the design of a load isolator are presented. The advantages and disadvantages of each of these circuits are discussed in regard to the electrical, mechanical, thermal, and magnetic field requirements. Experimental data are given for the optimum design of nonreciprocal ferrite absorbers for rectangular guide. Finally, practical design information for a power circulator in rectangular waveguide is presented which has been modified for use as a load isolator. This device has extremely high isolations (50 db) and low insertion loss (.5 db), and has maintained an isolation in excess of 30 db over a 25 per cent bandwidth with a permanent magnet field. Power handling ability of 250 kw peak with a .001 duty cycle is easily accomplished without external cooling. This isolator requires quite small magnetic fields for proper operations and hence packaged isolator is quite lightweight. Use of this power circulator for high-power modulators and duplexers is discussed.

A Waveguide Impedance Meter for the Automatic Display of Complex Reflection Coefficient

Abstract: A waveguide impedance meter has been developed, comprising some specially designed components and some components previously designed for other applications. When this circuit is used in conjunction with the X-band rapid sweep oscillator and suitable display and control circuits, the impedance focus of a waveguide component is automatically and rapidly measured and oscilIographically displayed in the reflection coefficient plane. A waveguide component having a 11/4-inch X 5/8-inch (large X-band) waveguide input port can be continuously measured throughout the frequency range extending from 8.5 to 9.6 kmc (12 per cent X-band). The bandwidth of the system is limited by the design bandwidth of the waveguide components. The plane of the impedance measurement may be referred to a plane internal to or external to the input port of the component under test. An expanded portion of the reflection coefficient plane may be displayed on the crt when small reflections are measured. The measurements of several representative impedances by the waveguide circuit were compared with slotted line measurements of these same components. For measurements of large reflections, standard /spl infin/ db swr full scale display, the maximum observed errors of the magnitude and phase of the reflection coefficient as measured by the waveguide circuit were 10 per cent and 5 degrees respectively. These maximum errors occurred for measurements performed at the ends of the 12 per cent frequency band. The average errors of the magnitude and phase of the reflection coefficient were 2.5 per cent and 2 degrees respectively. For measurements of small reflections, with the crt display of the reflection coefficient plane expanded to 6 db swr full scale, the maximum observed deviation of the waveguide circuit measurements from slotted line measurements was 0.5 db swr, and the average deviation was 0.2 db swr. The maximum errors again occurred at the ends of the 12 per cent frequency band.

Notes on a Crystal Mixer Performance

Abstract: A simple relation between optimum rf source impedance for minimum noise figure and the nominal conversion loss of a mixer is derived. This impedance is related to the input mismatch and its dependence on the type of IF amplifier input circuit is discussed. Relations between the crystal noise temperature and mixer noise temperature as a function of conversion loss are derived for different load conditions at the image frequency terminals.

Simplified Calculation of Antenna Patterns, with Application to Radome Problems

Abstract: Generally, the calculation of antenna far-field patterns from known near-field distributions is tedious and may require the use of a large computer. The calculations are simplified for certain types of antennas having separable near fields. This simplifying assumption is found to yield satisfactory results with pyramidal horns and parabolic reflector antennas. Calculations are further simplified by approximating a complex line integral with two real summations. Measured and calculated far-field patterns are included to indicate the accuracy of the calculations. Results are presented for horns and parabolic antennas and for a horn covered with a hollow dielectric wedge. The method is applicable to both E-plane and H-plane pattern calculations. The main lobe of a far-field pattern is calculated in less than one hour on a desk calculating machine by the simplified method. In radome work an important feature is that it permits rapid evaluation of the far-field distortion associated with any given near-field distortion in any given small region in the near field.

Effect of Ellipticity on Dominant-Mode Axial Ratio in Nominally Circular Waveguides

Abstract: An investigation is made of the effect of ellipticity on the dominant-mode axial ratio (AR) in nominally circular waveguides. Equations for calculating the AR are derived for the case where the difference between the major and minor axes of the guide cross section is small and the waveguide is not too long. Values of AR obtained by calculations are compared with measured values, and a method for improving the AR performance of a waveguide run is demonstrated.

A Method of Measuring Dissipative Four-Poles Based on a Modified Wheeler Network

Abstract: A method of abstracting the parameters of dissipative four-poles from measured data is presented here. This semi-precision method is applicable to symmetric four-poles and results directly in a conveniently symmetric network representation. It is based on the modified Wheeler representation, a new and completely general network, which is introduced in this paper. In addition to the derivation of the network and of the analysis, the relationship that the network bears to its dual, to the impedance Tee, and to the admittance Ri is presented.

Capacity and Characteristic Impedance of Strip Transmission Lines with Rectangular Inner Conductors

Abstract: An example of the rigorous solution of a complex region boundary value problem is presented. The particular problem, the electrostatic capacity and characteristic impedance of a strip transmission line, is solved exactly and numerical results are given for a particular geometrical configuration.