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An overview is presented of research carried out at TNO Physics and Electronics Laboratory in the field of phased anay antennas. Started is with a brief historical overview and a presentation of the antenna measurement facilities. Then full wave analysis methods for infinite planar waveguide arrays are discussed and ways to use these methods for analysing finite arrays. A design approach for microstrip patch array antennas, employing reduced analysis methods and commercially available full wave software is discussed next, followed by a presentation of analysis techniques for faceted and curved array antennas, together with the first reduced analysis results.

For printed antenna systems, microstrip feeding networks may become quite complex, including several right-angled bends. In designing feed networks we have to consider reflection levels at and electrical lengths of the bends. Removing a part of the area of metallization in the bend's corner can compensate for the excess capacitance and reduce the reflection level of the bend. Full wave simulations have been performed for unmitered and (50%) mitered right-angled bends in microstrip on FR4 and FR4 -like substrates in the frequency range 868MHz - 60GHz. The simulations revealed that for reflection levels below -15dB, up to 10GHz mitering is unnecessary. For reflection levels below -20dB, mitering must be applied for frequencies in excess of 2.5GHz. A slight modification of the centreline approach for unmitered bends leads to an equivalent electrical length for unmitered bends with an absolute accuracy of less than one degree for all frequencies and substrates, where the reference planes may be brought back all the way to the bend. Applying this modification to 50%-mitered bends, having the reference planes at 0.2 λg distance from the bend, λg being the wavelength in the substrate, leads to an absolute error in electrical length of less than two and a half degrees for all frequencies and substrates.

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In this paper we present an efficient theoretical formulation for a full-wave analysis of phased Arrays conformal to cylindrical structures. The theory is based on an integral equation formulation and the Unit Cell Approach. Thanks to its generality and efficiency, this method represents a good starting point for the development of accurate CAD tools for the analysis of integrated cylindrical structures including radome, coaxial excitations and tuning elements in waveguide.

Conformal array antennas are required whenever an antenna must be located on a vehicle, e.g. the skin of an aircraft, missile or superstructure of a ship. Conforming the array antenna to the existing structure avoids compromising aerodynamic or stealth characteristics, but at the cost of an increase in effort in designing the antenna.

In this paper an alternative approach for the design of open-ended waveguide array antennas is presented. The approach is based on microwave filter concepts. The exploitation of this alternative viewpoint has been made possible by the availability of a very efficient computer-aided design (CAD) tool which is based on a full-wave modal analysis technique. In this paper we first outline the technique for the efficient analysis of open-ended waveguide array antennas. Using the software developed and following the alternative design approach two different application examples are then shown indicating how the alternative viewpoint introduced gives indeed significant additional degrees of freedom

Future space-borne SAR systems should feature wider bandwidth, scanning capability in azimuth and elevation, and above all they should provide full polarisation information because polarimetry is one of the most promising tools for the interpretation of radar signatures. Within the context of these considerations, a couple of years ago TNO-FEL conducted a case-study for a C-band space-borne SAR antenna. In the remainder of this paper we will discuss the design considerations, the strong and weak points of the final design and ideas about reducing the costs of SAR array antennas.

Results of two software packages for analysis and synthesis of waveguide phased array antennas are shown. The antennas consist of arrays of open-ended waveguides where irises can be placed in the waveguide apertures and multiple dielectric sheets in front of the apertures in order to accomplish a wide band wide scan angle impedance match. One of the packages is restricted to the use of infinitely thin aperture irises, but has the advantage of fast calculation times. The other package, which has been completed recently, is very versatile and allows multiple (finite thickness) obstacles in the waveguides, but at the cost of longer computation times. The validity of the new software package is demonstrated and a design strategy, using both packages, is discussed. With the newly developed software we expect to have a better control over scan blindness effects.

A modal technique is employed to evaluate the suitability of a square waveguide element for use in a dual polarized phased array. The element is found to possess low active reflection coefficient and high cross-polar isolation over the bandwith and scan volume that are typically required for SAR applications.

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