Lars Josefsson

Analysis of longitudinal slots in rectangular waveguides

An accurate computation of the admittance characteristics of longitudinal shunt slots in a rectangular waveguide is presented. A moment method with entire basis functions is used for solving the electric field in the slot. The waveguide wall thickness is accounted for by introducing higher order waveguide modes in the short waveguide connecting the inner and outer regions. Particular attention is given to the resonant length of the slot, which is a critical parameter in the design of waveguide slot array antennas. Computed resonant lengths compare very well with measured results.

A waveguide transverse slot for array applications

The characteristics of a radiating rectangular transverse slot in a rectangular waveguide have been studied. A moment method solution is used with entire basis expansion and testing functions (Galerkin) including the effect of wall thickness. The results are presented in terms of normalized resistance and reactance versus slot length and frequency. Excellent agreement with a previous pulse basis solution is found, as well as with measured data. An array of resonantly spaced transverse slots radiates large grating lobes. A spatial filter using baffles to suppress the grating lobes is described, suppressed. The effect of the baffles on the transverse slot impedance is analyzed for the case of baffles with infinite height. >

Calculating the mutual coupling between apertures on a convex circular cylinder using a hybrid UTD-MoM method

The problem of calculating the mutual coupling between apertures on a perfectly conducting circular cylinder is considered. The mutual coupling is calculated by a combination of the uniform theory of diffraction (UTD) and the method of moments (MoM). This hybrid method makes it possible to include higher order aperture modes in order to improve the accuracy. It is found that the UTD-MoM solution gives accurate results, even for small cylinders. The results are verified against results found in the literature, as well as against measurements performed at Ericsson Microwave System in Molndal, Sweden. For this purpose, a cylindrical test antenna with 54 apertures was built. Using a single-mode approximation, good agreement, down to about -60 dB, with comparisons to measured data has been obtained. If additional modes are added the results improve significantly, both in amplitude and phase. In several cases, the agreement is good down to coupling levels of about -80 dB. This requires that about six modes are included. However, the most important mode, besides the fundamental TE/sub 10/ mode is the TM/sub 11/ mode.

Waveguide-Fed Slot Antennas and Arrays: A Review

ABSTRACT Conceived in the forties, slot array antennas have reached a state of maturity. However, there are still many problems addressed in the current literature. This paper presents an overview of the significant publications on waveguide-fed slot antennas and arrays.

Moment method analysis of circular-cylindrical array of waveguide elements covered with a radome

We have developed a moment method program that analyzes arrays of waveguide elements on circular-cylindrical surfaces. The presence of a radome is rigorously taken into account by using the Greens function of a multilayer circular cylindrical structure. Special attention is given to numerical treatment of the Greens function when analyzing cylindrical antennas of large radii. The calculated results are compared with the measured S-parameters of the array with 54 waveguide elements. The agreement between measured and calculated results is very good.

A broad-band twist reflector

Polarization twisting reflectors, or twist reflectors, consisting of a wire grid spaced approximately 3 \lambda/8 from a ground plane [1], [2] have a bandwidth of at most 30 percent. It is shown that the inclusion of an additional wire grid in front of the first grid makes bandwidths of 100 percent possible. Design formulas, theoretical performance in terms of cross polarization attenuation, and some experimental results for a twist reflector with two wire grids are given.

The RCS of a cylindrical array antenna coated with a dielectric layer

The scattering properties of dielectric coated waveguide aperture antennas mounted on circular cylinders are investigated. Both the single element antenna and the array case are treated. The array antenna consists of 4 /spl times/ 32 rectangular apertures placed in a rectangular grid on the surface of an infinitely long circular cylinder. The problem is formulated in terms of an integral equation for the aperture fields which is solved with the method of moments using rectangular waveguide modes as basis and test functions. An efficient uniform asymptotic technique is used to calculate the excitation vector and the backscattered far-field. The asymptotic solution is valid for large cylinders coated with thin dielectric layers away from the paraxial (i.e. near axial) region. A similar asymptotic solution is used to calculate the mutual coupling in the nonparaxial region. For the self coupling terms and for the mutual coupling in the paraxial region a planar approximation is used with a corresponding spectral domain technique. Numerical results are presented as a function of frequency, angle of incidence, cylinder radius, and electrical thickness of the coating.

Radiation Performance of an Experimental Phased Array

The radiation performance of an experimental phased array has been investigated. The antenna system consists of a nine element X-band linear array, digital phase shifters and a beam steering computer. Beamwidth, gain and beam direction error have been evaluated versus scan angle for 3- and 4-bit phase approximation. Results for E- and H-plane scan are compared. A phase monopulse tracking system has been added to the antenna and beam steering logic. With this system tracking of several independent targets is possible. Search and track information may be displayed simultaneously. Examples of tracking performance with digital beam steering are given. The work reported is a part of a research program jointly carried out by the MI Division of L M Ericsson in Molndal and the Division of Network Theory at Chalmers University of Technology in Gothenburg, Sweden.

A perspective on array antenna developments

Although the first array antennas were developed long ago, it took considerable time and effort before the electronically phased array antennas reached the marketplace. Their full potential could initially not be exploited without the availability of advanced integrated circuits and computer technology. The developments of electromagnetic analysis methods and simulation tools have of course also played a significant role. Still, a phased array antenna is costly, and it has to be proven that the improvements in system functionality and performance are worth the extra cost. The modern trend is towards digital processing of the received array element signals, i.e. using the spatial dimension in addition to the traditional time/frequency (range & doppler, coding...) dimensions. In this way the desired information can be extracted more efficiently and at the same time provide interference rejection, improved signal quality, higher resolution etc. A corresponding scheme is not possible on the transmit side, but the spatial dimension can also here be used advantageously. Thus, the modern antenna array is typically integrated with other subsystems, forming an antenna system where the critical parts are optimized together. The development of new system simulation tools and subsystem interface descriptions will be necessary to facilitate the interdisciplinary efforts needed.