Theory of coupled monopoles

Accurate numerical values of mutual and self-admittances are obtained for an array consisting of two monopoles having different lengths and radii. The monopoles are actually protrusions of the inner conductors of coaxial cables. The sheaths of the cables are connected to a perfectly conducting ground screen. Restrictions in the theory are the following: the monopoles must be thin,a/lambda ll 1whereais the radius andlambdathe wavelength,b < 3awherebis the radius of the coaxial cable sheath, andd > 10awheredis the separation of the monopoles. The procedure employed to obtain the mutual and self-admittances is to derive simultaneous integral equations for the current distributions and to solve the integral equations numerically. The results are given for the most part in graphical form. Comparisons are made with existing theory and with experimental data. Excellent agreement in all cases is observed.     

An investigation of concentric ring antennas with low sidelobes

An analysis is made of circular antenna arrays with diameters being 2 to9lambda(the minimum inner circle diameter being0.4lambda) containing 3 to 18 concentric circles. For the purpose of computation of the array factor the elements of the array are assumed to be isotropic radiators. The elements of each circle have equal current amplitudes and are phased so that the contributions of all the elements add in phase in the direction of the main beam. The Chebyshev radiation pattern function is approximated by a truncated Fourier-Bessel series, from which the current amplitude of each circle is obtained. From these current amplitudes a method for computing the current amplitude to excite a new distribution of fewer circles is shown. Also, an empirical method is given for improving the sidelobe level of the radiation pattern by adding an element to the center of the array. A number of circles in the array sufficient to avoid pattern deterioration is found to be the integer nearest to5d/4lambdafor -20 and -30 dB sidelobe level and4d/3lambdafor -40 dB, wheredis the diameter of the array. This represents a large reduction in the number of circles needed over the Fourier-Bessel series representation in the case of large antennas. Experimental verification of the computed pattern is made for an array of two concentric circles with diameters of0.8lambdaand1.6at a frequency of 90 Mc/s. The elements of the array were vertical monopoles.     

A spiral antenna backed by a conducting plane reflector

An Archimedean planar spiral antenna is numerically analyzed in the presence of a conducting plane reflector. The analysis shows that the spiral antenna backed by the plane reflector has two distinct regions in the current distribution, which explain the radiation of a circularly polarized wave for the outer circumferenceCranging over about1.3 lambda < C < 1.5 lambdaandC > 2.9 lambda, wherelambdais a free-space wavelength. Further consideration is given to a truncated spiral antenna whose outer circumference is on the order of1.4 lambda. The truncated spiral antenna maintains a decaying current distribution and radiates a circularly polarized wave over a 1:1.2 frequency bandwidth. It is also demonstrated that a power gain on the order of 8.5 dB is realized over the same frequency range.     

The echo area of small rectangular plates with linear slots

The echo area of rectangular plates on the order of1lambda times 1lambdain size and smaller with linear slots is discussed. Approximations are given which allow one to explain qualitatively the experimental results given. Afrac{1}{2} lambda times 1lambdaplate is considered both analytically and experimentally and by choosing the proper length slot or a slot with the proper reactive loading the echo area has been reduced by more than 8 db from the solid plate return.     

Reduction of reradiated field in equatorial plane of parasitic antenna

A suitable impedance connected at the center of a parasitic dipole or the base of a monopole antenna can reduce to zero the reradiated field in the equatorial plane. The two-term theory provides a simple formula for the determination of the required impedance for dipole elements up to 1.25 wavelengths long or monopoles up to0.625lambda. Examples and tables are given.     

Experimental study of the characteristics of top-loaded microstrip monopoles

The characteristics of microstrip monopoles fed at the center with antiphase currents are investigated experimentally. First the impedance is measured as a function of frequency. It is found that the radiation resistance at the resonance nearL simeq 05 lambda, is very low while the radiation resistance at the resonance nearL simeq lambdais very high. For a given physical length of the monopole, the resonant frequency is dependent on the strip width and the substrate thickness. The effect of substrate thickness and strip width on the input impedance and bandwidth has also been studied. Finally theE-plane radiation pattern is found to contain two maxima, occurring at approximatelypm 40degfrom broadside.     

Analysis of the symmetric center-fed V-dipole antenna

A wire antenna moment method using piecewise sinusoidal expansion and testing functions is used to obtain properties of a symmetric center-fedV-dipole antenna driven by a slice generator. The impedance, admittance, current distribution, radiation patterns in the dipole plane, and other properties are computed as functions of the parameters0 < h/lambda leq 0.60,100 leq h/a leq 20 000, and30deg leq psi leq 180deg, whereh= arm length,lambda= free space wavelength,a= wire radius, andpsi= apex angle. The results are checked with experiment and compared with similar results previously reported for the linear dipole. It is shown that 1) omnidirectional patterns over a wide bandwidth are achieved forpsi leq 90deg, but at the expense of reduced resonant radiation resistance and reduced bandwidth, insofar as the impedance is concerned, 2) forpsiless than about75deg-80deg, lowest resonant lengthgeq lambda/4and increases ash/adecreases, and 3) lowest antiresonant length forpsi > 30degis within0.01lambdaof that for a linear dipole with the sameh/a.     

Third-order susceptibility of alkali metal vapors

This paper presents calculations of the third-order susceptibility in the alkali metal vapors involving spin-orbit coupling in the energy spectrum of the alkali atoms and some power transfer between the atoms in the ensemble and their surroundings, including the radiation field. The results are plotted as a function of wavelength in the vicinity of the neodymium and iodine laser lines, and their second, third, and fourth harmonics for each of the alkalies; i.e., 10 520 Å < (lambda, 2lambda, 3lambda, 4lambda) < 10 720 Å, and 13 070 Å < (lambda, 2lambda, 3lambda, 4lambda) < 13 230 Å, respectively.     

Effect of gap length on the input admittance of center fed coaxial waveguides and infinite dipoles

The input admittance of a coaxial waveguide fed by a gap of length2din the center conductor is evaluated using the dyadic Green's function of the guide and a band of equivalent magnetic surface current proportional to the gap's axial electric field via the equivalence principle. The axial electric field is expressed in terms of a rapidly convergent series of ultraspherical polynomials whose weighting function satisfies the edge conditions at each end of the gap. If the inner and outer radii of the coaxial guide areaandb, respectively, then the limiting case ofb rightarrow inftyis an infinite dipole in free space. Numerical results for the admittance are given as a function ofka (0.01 leq ka leq 0.50)with parameterb/a = 2, 5,10and 50 for the coaxial guide. For the infinite dipole the admittance is presented as a function ofd/a (10^{-3} leq d/a leq 10)withkaas a parameter (0.001 leq ka leq 0.1).     

The analysis of general axially symmetric antennas with a coaxialfeed line by the method of lines

The use of the method of lines in the analysis of various circular antennas-circular patch antennas and various forms of monopoles is proposed and substantiated. The antennas considered are fed by coaxial lines. Impedance/admittance transfer procedures are developed, which allow to calculate the antenna input impedance by a successive transfer from the aperture through the different sections. The described relations are also useful for other applications     

A Novel Circularly-Polarized Periodically-Loaded Mast Antenna for Vehicular Satellite Radio Reception

A novel type of short monopole antenna is proposed. Its structure consists of a periodically slotted coaxial line radiating in linear polarization (LP). The structure can be easily modified by the addition of a thin layer of dipoles in order to generate circular polarization (CP). The number of slots along the structure, their periodicity and the tuning of the terminating load allow control of the antenna main beam' angle and width. One advantage of the proposed design over conventional monopoles is that the antenna does not require a ground plane. Both left-hand and right-hand CP are possible with the same design, simply by inverting the symmetry of the printed dipoles. Design details for the annular slotted coaxial line and for the LP and CP mast antennas are given. Prototypes in both LP and CP were fabricated and their characteristics were measured. Simulations and measurement are in good agreement. The proposed CP mast antenna is compliant with the requirements of the XM digital satellite radio system, with a frequency bandwidth of more than 1.7% in which ${rm VSWR}≪ 2$, and an ${rm AR}≪ 4~{rm dB}$ in the elevation range of $pm 30^{circ} ≪ theta ≪ pm 70^{circ}$ .      

The cylindrical antenna as a probe for studying the electrical properties of media

When a base-driven cylindrical monopole (or center-driven dipole) is immersed in an arbitrary medium, the electric and magnetic fields on its surface depend not only on its length and radius but also on the effective conductivity and permittivity of the medium. These fields can be explored and measured with small probes designed to travel along the cylindrical surface of the antenna. The interpretation of the observations depends on the availability of a general theory that correctly describes the distributions of current and charge on the conductor. The results of a new theory that is valid for electrically thin monopoles up to5lambda/8(dipoles up to5lambda/4)in length over all practical ranges of conductivity and permittivity of the ambient medium, including those characteristics of under- and overdense cold plasmas, are described together with their experimental verification.     

A new approach to the problem of wave fluctuations in localized smoothly varying turbulence

In the past, smoothly varying turbulence has been studied by changing the structure constant to the functionC_{n}^{2}(bar{r}). The purpose of this paper is to show that this approach is insufficient, and that a random process developed by Silverman can be used to describe the wave fluctuations in localized smoothly varying turbulence. The localized turbulence is characterized by a correlation function which is a product of a function of the average coordinate and a function of the difference coordinate. The corresponding spectrum is also given by a product of a function of the difference wavenumber and a function of the average wavenumber. They are related to each other through two Fourier transform pairs. Making use of the preceding representations, the fluctuations of a wave propagating through such a turbulence can be given either by the integrals with respect to the two wavenumbers or by a convolution integral of the structure constantC_{n}^{2}(bar{r}) and a function involving the outer scale of the turbulenceL_{0}. It is shown that for a plane wave case, if the distanceLis within (L_{0}^{2}/lambda), then the usual formula given by Tatarski is valid. But if the distance is betweenL_{0}^{2}/lambdaand(bL_{0})/lambdawherebis the total transverse size of the turbulence, the variance of the wave is nearly constant, and ifL gg (bL_{0})/lambda, the variance decays asL^{-2}. Similar conclusions are shown for a spherical wave case. Some examples are shown illustrating the effectiveness of this method.     

Input Admittance of a Circular Waveguide Aperture Covered by a Dielectric Slab

The input admittance of a circular waveguide opening onto an infinite flange with a homogeneous lossy dielectric coating is derived using integral transforms and assuming the dominant TE11mode as the trial field at the aperture. Admittance calculations for low-loss dielectric sheets of various thicknesses are given and compared with measurements obtained using ground planes of varying sizes. Excellent agreement with theory is obtained for the circular waveguide terminated into a square ground plane only1lambdato2lambda. on a side. A quantitative comparison of the surface wave contribution to the total admittance is also given.     

A Wide-Band Balun

Experimental results are given for a transformer from an unbalanced 50-ohm coaxial line to a balanced pair of 50-ohm coaxial lines. The design is one proposed by Marchand. The balance, standing wave ratio, and insertion loss are nearly constant over a 13 to 1 frequency range from 650 mc to 8500 mc. The standing wave ratio is less than 2.1 to one and the insertion loss is about 0.5 db over this band of frequencies.     

Measuring radar cross section at short distance

Radar cross sections (RCS) must be measured at large distance. We exclude here the special near-field methods. The distance (R) must be so large that different RCS contributions are added in the same way as at infinite distance. This leads to the ruleR > 2D^{2}/lambdaif the target cross range is confined withinpm D/2and a phase error ofpi /4is tolerated. It is shown, however, that if the RCS is measured as a function of an angle and is low-pass filtered with a cut off period ofphi_{c}(radians), the distance requirement could be changed toR > 4Dphi^{-1}_{c}(1 - lambda/2phi_{c}D)). All RCS measurements at such distances give approximately the same result after low-pass filtering. We assume that a set of isotropic point scatterers, accurately describes the target.     

Measurement distance effects on low sidelobe patterns

Because of the current strong emphasis on low sidelobe antennas, the effects of measurement distance in distorting patterns are reexamined. Previous calculations have used obsolete or suboptimum aperture distributions. The Taylorbar{n}linear distribution is a versatile highly efficient and robust optimum distribution; its use here allows a single curve of sidelobe measurement error versus measurement distance (normalized to far field distance2D^{2}/lambda) for a given sidelobe level. The calculations give data from a uniform distribution to a 60 dB Taylor. For example, the first sidelobe of a 40 dB Taylor pattern is in error 1 dB at a distance of6 D^{2}/lambda.     

Modeling and Characterization of Microstrip-to-Coaxial Transitions

A simple circuit model for the transition from a Iossy microstrip to coaxial line has been developed on an experimental basis. The proposed model can be used to predict accurately the insertion loss and insertion phase over a wide frequency range. Since explicit formulas for the model element values are given, these elements, representing the parasitic of the transitions, can be taken into account very easify when the microstrip is used as a test fixture for measuring the parameters of solid-state devices. The practical use of the model has been examined for several Z/sub 0/=50-omega lines on both Epsilam-10 and 99-percent alumina substrates with standard SMA coaxial connectors.     

Microwave Circuits for High-Efficiency Operation of Transferred Electron Oscillators

Compact circuits for obtaining high-efficiency operation of high-power transferred electron oscillators (TEOs) in L-band are described. One is a coaxial resonator and the other employs coupled TEM lines. The circuits are shown analytically and experimentally to be capable of matching a wide range of fundamental device impedances. Provisions for independently tuning the second-harmonic impedance over a wide range are included in both types of circuits. Pulsed conversion efficiencies up to 32 percent have been obtained TEOs mounted in the coaxial resonators and up to 27 percent with TEOs in the coupled TEM-line structures. The impedance at the second harmonic has been shown quantitatively to be extremely important in controlling device efficiency. By varying the second-harmonic tuning the device performance can be varied from high-efficiency operation to no output. Oscillators using these cavities were temperature stable over a wide range. The operating frequency of TEOs in the coaxial cavity and the coupled-TEM-line cavity varied less than 30 and 40 kHz//spl deg/C, respectively, over the range from - 54/spl deg/C to +125/spl deg/C.     

Yagi-Uda Array as a Surface-Wave Launcher for Dielectric Image Lines

A Yagi-Uda array of monopoles is embedded in the dielectric of a dielectric image line, with the driven element fed from coaxial cable below the metallic ground plane, in order to launch the dipole-mode surface wave. The launching efficiency is a function of the array length and is relatively independent of the transverse dimension. With a six-element array, a launching efficiency of 62 percent has been achieved over an 18-percent bandwidth at 2.2 GHz. A design procedure for such arrays is described and experimental verification is given.