This study is based on the results of a slant-path Ka-band propagation experiment carried out in Madrid, Spain, regarding rain attenuation, which is the main propagation impairment in this frequency band. The experimental and statistical results correspond to seven complete years of measurements, a period large enough to accomplish a comprehensive analysis in order to characterize the variability of rain rate and attenuation. It is shown that year-to-year variability is significant in temperate climates as Madrid's. The aforementioned significance is also apparent with regards to seasonal, monthly, worst-month and hourly variability concerning rain attenuation, which are also discussed and related when possible to the variability of the rain phenomena, either represented by the total amounts of rainfall in the different periods or by rain rate statistics. Copyright © 2015 John Wiley & Sons, Ltd.
A method for computer-aided noise analysis of microwave circuits described by the nodal admittance matrix is discussed. Algorithms for the computation of both the noise figure and the four noise parameters of a circuit with any topology are presented. The method and the algorithms are compatible with existing CAD software based on a nodal admittance matrix formalism. Their direct implementation into computer-aided microwave simulation and optimisation programs should significantly increase their power and computational efficiency.
A perturbation/iterative method (the PPP method) is proposed for the analysis of electromagnetic fields in inhomogeneous media. It consists of increasing the values of the parameters of the medium at all points in small increments, starting from their vacuum values, and computing the induced sources by means of the total field (the incident field, plus that of the induced sources as obtained in the preceding step). Thus, in all the perturbation/iterative steps the total excitation field is known, and therefore the solution of any problem using the method is based solely on the expression for the field of an elemental source in a vacuum. The method appears to be very versatile, conceptually the simplest possible and remarkably rapid. It also has extremely low memory requirements even for very large problems, provided that computing time is not critical. In addition, it can be combined very efficiently with other available methods, e.g. with the method of moments for the analysis of conducting antennas in a vacuum to analyse such antennas in the presence of arbitrary dielectric or magnetic bodies.
A method for the description of the fields in finlines on anisotropic substrates is presented. The method also allows the complex tensor character of all material parameters and the influence of second-order effects, such as metallisation thickness, to be taken into account. The principal boundary value problem can be described with the help of a relatively small eigen-matrix and so the numerical treatment demands little work. Numerical and measurement results are presented, and discussed, for the transmission properties and for the field and power distributions. Furthermore, a suitable definition of the characteristic impedance is introduced, having in mind CAD applications. Design procedure and measurement characteristics for nonreciprocal elements are also included.
Distributions of the current and the surface fields close to the corners of a conducting strip with rectangular cross-section are investigated by an accurate and efficient moment method. The strip is made of either a normal conductor or a superconducting material. Based upon this study, a simple graphical procedure for a rough estimation of the finite maxima of the current densities at the edges (corners) is presented.
Analysis of clear air fading encountered on millimetric wave and infrared radio links are presented. The analysis is based on data obtained during a four-year field study in the city of Riyadh, Saudi Arabia. The region can be considered as a typical arid climate where the rate of evaporation is higher than the rate of precipitation. Maximum rain rate is of the order of 30 mm/h for 0.001% of the year. A brief description of the experimental setup is presented, together with the results of measuring clear air fading experienced by the radio links. Statistical characterisation of fading is given for both the millimetric wave links operating near 40 GHz and the infrared radio link at a wavelength of 0.88 μm. It is shown that fading is dominated by multipath, having a Rayleigh amplitude distribution and an occurrence factor similar to the microwave band. Fades were highly correlated for the two links sharing the same path and separated in frequency by 1%. Multipath fading was also measured on the infrared link. Even at the short hop length at 0.75 km, the occurrence factor was about 1%. Time duration of fades are also analysed, and fade durations were essentially exponentially distributed. Small fades, however, have normal duration distribution
An experimental measurements programme for characterisation of radiowave propagation at UHF band is discussed. Preliminary results on transmission loss, specific attenuation and delay spread are presented and discussed in terms of the biophysical and radio parameters that characterise the propagation path. The results are compared with predictions based on discrete random medium model
A triple modulation technique, applicable to microwave cavity spectrometers, is described, which enables Stark, Zeeman, double resonance or cavity modulation in the cavity gas cell to operate at a relatively low frequency, while satisfying the criterion that the microwave crystal detector should operate at a relatively high frequency. This technique is such that the microwave source is frequency double-modulated by means of a sweeping signal of frequency f 1 and a relatively high-frequency sinusoidal signal of frequency f2 applied to a tuning varactor, while an additional relatively low-frequency modulation such as Stark, Zeeman, double resonance or cavity modulation (frequency f3) is applied in the cavity gas cell. The low-frequency modulation signal ( f3), which contains the salient information of the analyte gas, is carried by the high-frequency signal f2 , the former being extracted and amplified by a series of filters, demodulators and tuned amplifiers
Simple, approximate formulas describing the peak cross-polar characteristics of circular and rectangular microstrip patches are derived from the governing equations using small argument approximations. Results from the formulas compare favourably with those obtained elsewhere using more stringent numerical methods. In the case of the circular patch, a novel approximation is employed to circumvent the use of Bessel functions.
The paper discusses how variations in the pattern of convective plasma flows should be included in self-consistent time-dependent models of the coupled ionosphere-thermosphere system. The author shows how these variations depend upon the mechanism by which the solar wind flow excites the convection. The modelling of these effects is not just of relevance to the polar ionosphere. This is because the influence of convection is not confined to high latitudes: the resultant heating and composition changes in the thermosphere are communicated to lower latitudes by the winds which are also greatly modified by the plasma convection. These thermospheric changes alter the global distribution of plasma by modulating the rates of the chemical reactions which are responsible for the loss of plasma. Hence the modelling of these high-latitude processes is of relevance to the design and operation of HF communication, radar and navigation systems worldwide.
A compact broadband TE/sub 01/-mode generator is presented. It consists of five identical sectorial waveguides which are stepped into an ordinary circular waveguide. These sectorial waveguides are fed by five identical probes at the end of a star-shaped feed line with five arms. This feed line is placed in a trace between the sectorial waveguides. A consequence of the five-fold symmetry is that the lowest parasitic mode which can be generated and propagated has a cutoff far above the frequency range of operation (9.5-10.5 GHz). The measurements show that the return loss is less than -15 dB in the frequency range of operation. The mode purity is better than 99.4%.
A moment-method calculation is described of the maximum mutual coupling (or minimum isolation) between two loop antennas mounted on the tail-cone of a helicopter at the low-frequency end of the aircraft HF band. The wire-mesh mathematical model of the aircraft is constructed with a high sampling density in an attempt to produce estimates of the required near-field dependent parameters with sufficient precision to calculate the maximum mutual coupling with acceptable accuracy. The calculation is a fairly demanding test of the procedure adopted for the construction of the mathematical model, because it depends upon the accuracy with which both near-field and far-field parameters are determined. This mathematical model does not incorporate any empirically derived information, and the calculation was of necessity performed in advance of an aircraft being available for experimental purposes. The difficulty of assessing the credibility of calculated results under such circumstances is considered. NEC was used as the solution code for the wire-mesh model. An independent corroboration of the calculation was made possible by the siting and configuration of the proposed antennas. This allowed a simple equivalent circuit model of the arrangement to be constructed, values of the circuit elements to be estimated, and hence an independent approximate determination of the maximum coupling to be made. The degree of consistency between the results obtained by these two methods is considered to enhance the confidence which can be placed in the results obtained using moment-method mathematical models of this type when applied to near-field aircraft HF antenna problems.
A method is given for the exact synthesis of optimum difference patterns for linear antenna arrays. The technique uses Zolotarev polynomials and is analogous to the Dolph-Chebyshev synthesis of optimum sum patterns. It is shown how, given the number of array elements and the required sidelobe ratio, the array element excitations can be found. Complete computational details are given in an Appendix.
A mixed technique is presented for calculating the radar cross-section characteristics of a dielectric-coated conducting cylinder with TE-wave incidence loaded with periodic metallic strips. The technique is based on the spectral-domain method (SDM), conjugate gradient method (CGM) and fast Fourier transform (FFT). Since the property of circular Toeplitz matrix has been used, only memory directly proportional to NsNb (Ns is the number of strips and Nb is the number of basis functions for approximating the currents on the strips) is needed, which allows treatment of the cylinder loaded with tens or even hundreds of strips. The RCS of a dielectric-coated conducting cylinder loaded with many periodic metallic strips are first calculated. Numerical results show that the RCS can be effectively controlled by adjusting the period or the spaces between strips
A very simple, but almost exact, image method is proposed for the analysis of vertical thin-wire antennas above ground. The method is based on the approximation of the actual field of a current element above and below the ground surface by the field of a few (typically three) images. The relative image current intensities are obtained by stipulating that the tangential components of the electric and magnetic field for the two cases, at a number of points at the interface, satisfy the boundary conditions. The field of these images is next incorporated into the Hallen equation, current distribution is approximated by polynomials, and unknown coefficients are determined by point-matching. The results obtained for the impedance, current distribution and the radiation field of such dipoles are found to practically coincide with the exact results (i.e. those obtained from the Sommerfeld theory), in spite of the proposed method being conceptually much simpler and requiring about ten times less computing time than the exact method.
The feasibility of using diodes in linear microstrip antenna arrays to facilitate electronic beam scanning is investigated. The first concept concerns a microstrip line loaded with varactor diodes serving the dual purpose of phase shifter and feeder for a linear travelling wave array. Theoretical and practical results provide antenna design data on the number and type of diodes, optimisation of the radiating elements and temperature effects. Likely noise figure degradation, transient beam scanning response, and the antenna construction are other design aspects discussed. An array at 7.5 GHz containing 24 varactor diodes demonstrates that some 20-degrees of beam scan is achievable before the travelling wave action is disrupted, and confirms the usefulness of the concept for applications demanding modest beam scan range and a simple low cost construction. The second concept introduced is a novel microstrip patch element with embedded diode and polariser enabling mixer action to take place. The theoretical and practical design of this antenna mixer element, and its deployment in an eight element linear beam scanning array at 2.92 GHz, is presented. Other mixer configurations, using additional diodes offering superior suppression of spectral products, are noted and the possible influence of the polariser on inter-element mutual coupling investigated. Computations and measurements show that coupling effects are not significantly increased and confirm the usefulness of the antenna mixer element concept in beam forming array applications where no premixer low noise amplification is demanded.
A detailed analysis of the capacitance of a subharmonic millimetre-wave mixer diode is presented. The individual components contributing to the total capacitance are identified, with values derived for each component for a 183 GHz Schottky design. A new method is described to determine the shunt capacitance associated with the complicated geometry of the metal bonding pads for planar diodes. It is shown that this component can contribute up to 12 fF towards an overall device capacitance of 25 fF for the 183 GHz design. The inclusion of air bridging and back-etching techniques is shown to reduce this value by 70%, resulting in a lower capacitance, higher cutoff-frequency subharmonic diode device.
Comments on a paper by Chen, Simpson and Ho (see IEE Proc. H vol. 139, p. 7, 1992) that addressed the spherical wave expansion (SWE) technique for solving radiation and scattering problems. As the authors pointed out, this technique is a classical one. However, the authors have overlooked some classic treatments of application of SWE in antenna and scattering problems. The authors reply by discussing the efficiency of the technique, its convergence, and the effects of the ground plane on asymmetrical antenna structures
The paper presents a historical review of gyroelectric devices. It presents the theoretical and experimental performances of nonreciprocal devices using semiconductor materials, and introduces a theoretical approach to circulators using high-mobility layers, applicable to MMIC technology.
A circuit model for the coupling of externally generated electromagnetic fields to coplanar stripline interconnections with resistive and geometric discontinuities on lossy integrated circuit substrates is presented. The simplicity and fast speed of the model enable computer-aided analysis of externally induced electromagnetic noise in integrated circuit interconnects to be carried out. A general CAD algorithm is developed based on this model, and is applied to realistic coplanar strip interconnect line prototypes which are selected from a practical microwave integrated circuit. The effects of dielectric losses in the integrated circuit substrates and the discontinuities in the conducting tracks on the wave coupling are investigated in isolation.
