L. Shafai

The effect of various parameters of circular microstrip antennas on their radiation efficiency and the mode excitation

The numerical solution of circular microstrip antenna is carried out using the method of moment. The effect of the probe position, The dielectric permittivity of the substrate, and the substrate thickness on the radiation pattern and the mode excitation efficiency are studied. It is found that the probe position and the patch size can be used to control the mode excitation efficiency, and heigher order modes can be generated using only one feed location. Also, the finite ground plane can be used to improve the symmetry of the radiation patterns. The technique is general and can be used to investigate other scattering and antenna problems involving axisymmetric geometries.

Design of Multi-Arm Multi-Mode Spiral Antennas for Directional Beams Using Equivalent Array Concept

ABSTRACT Multi-arm spiral antennas can be considered as antenna arrays where the spiral arms constitute the array elements. The proximity of the arms over the full length of the spiral and their direct coupling make such arrays unique in the sense that they operate with very strong mutual coupling. As a consequence, the array performance is dominated by the array configuration, rather than the array elements. In particular, the phase mode concept that is used successfully for the analysis of circular arrays can be used also for investigation of these arrays. For symmetric multi-arm spirals the phase mode excitation is also symmetric and used with Butler matrix type feeds in applications such as the direction finding, where the beam rotation and scanning is achieved with an aid of inter-mode phase shifts. In such applications, however, mostly the first two phase modes are utilized and mode purity has been the dominant requirement, rather than the antenna gain. In this paper the concept of phase modes is re...

INPUT IMPEDANCE AND RADIATION CHARACTERISTICS OF SMALL MICROSTRIP PHASED ARRAYS INCLUDING MUTUAL COUPLING MSAT APPLICATION

ABSTRACT The radiation characteristics of small microstrip arrays is investigated including the mutual coupling effects among the array elements. The mutual coupling of the elements is determined using the reaction theorem, which provides both array patterns and the active Impedances of the elements. The method is then used to study a 19-element array for MSAT application. For the array elements circular patch microstrip antennas are used and optimized to give satisfactory circularly polarized radiation. For the 19-element array, it is shown that the array gain decreases by scanning the array beam towards the endfire direction and a peak gain of 13.73 dBi. is obtained at an elevation angle of 57 degrees. Further scanning of the beam, towards lower elevation angles, reduces the array gain further.

Electromagnetic Scattering from Dielectric Bodies of Revolution: Theoretical and Experimental Results

The scattering of electromagnetic waves from dielectric bodies of revolution in the resonance region is considered. A theoretical solution to the problem is formulated in terms of equivalent currents on the surface of the scatterer, leading to a set of surface integral equations which arc solved numerically using the method of moments. The procedure is applied to dielectric bodies of revolution of various sizes and shapes which simulate ice, and for which experimental results of the backscattering matrix elements are available. Very good agreement between the numerical results and the experimental data is obtained.

Electromagnetic scattering from dielectric bodies of revolution: Theoretical and experimental results

The scattering of electromagnetic waves from dielectric bodies of revolution in the resonance region is considered. A theoretical solution to the problem is formulated in terms of equivalent currents on the surface of the scatterer, leading to a set of surface integral equations which arc solved numerically using the method of moments. The procedure is applied to dielectric bodies of revolution of various sizes and shapes which simulate ice, and for which experimental results of the backscattering matrix elements are available. Very good agreement between the numerical results and the experimental data is obtained.

Simulation and experimental evaluation of the low loss grooved lines

This paper presents a new Grooved Microstrip Line structure(GMLS) for low loss configuration. The dispersion characteristics of this line is determined using the well known numerical technique, the Method of lines(MOL). Finally the conductor and dielectric losses are calculated and compared with the experimental result in the frequency range of 1–16 GHz.

Application of lattice gas automata to electromagnetic scattering and transmission line modelling

In this paper, an LGA algorithm for two-dimensional field simulations was considered. The algorithm approach involves the evolution of linear wave behaviour on a macroscopic scale, resulting from simple interactions within a discrete lattice. Since the LGA cell involves only simple binary operations and a few bits of memory, the technique is best suited for massive parallel processing implementations. Despite memory and computational differences, the operation of the algorithm in comparison with TLM is similar. Algorithm developments include LOA capable of three-dimensional field modelling (10), and multi-bit LGA algorithms to reduce viscosity effects [9].

Efficiency improvement of triplate array

Triplate line fed arrays have been researched extensively over the last 10 years for DBS television subscriber antenna in Japan and Europe. The chief advantage of this type of planar array is the reduction of radiation from the arrays feedlines. One class of triplate fed array employs a thin metal sheet with apertures punched for radiation from patches on the triplate layer [1], Figure 1. This type of triplate array is considered as a candidate for LMCS subscriber antenna. The focus of this research is to identify different methods for increasing the aperture efficiency of this type of triplate fed array, in order to counter the losses that are expected to occur at EHF.

Noncontact internal probing of microwave integrated circuits

A non-contact probing technique for non-invasively performing vector voltage measurements at the internal points of an operating microwave integrated circuit is presented. The internal voltage amplitude and phase are extracted by sensing the localized electrostatic force between a miniature probe and point in the circuit being measured. A force nulling approach allows accurate high frequency voltage measurements to be performed on without the need for complex calibration and on passivated circuits. The non-contact probe introduces a loading of less than 1fF at the test point.

Array thinning in phased arrays using dual mode horns

The authors investigate a new concept in array design, where the level of the grating lobes is controlled by the element pattern. For the array elements circular horns are selected. In standard arrays these horns operate in the TE/sub 11/ mode and beam scanning is achieved fully by element phasing. In the present case, each array element operates in the first two TE/sub 11/ and TE/sub 21/ modes and the element pattern is shaped to place a null in the direction of the grating lobes. Thus, the interelement spacing can be increased beyond that of normal arrays, without a serious pattern degradation due to the appearance of the grating lobes. Also, the array elements in the present study are assumed to be circularly polarized.<<ETX>>