Polarisation Agile Microstrip Array Antenna Element

A new microstrip antenna element is described which exhibits polarization agility. This is achieved by employing a T-slot radiator which is driven by the edge fields of a balanced microstrip line. The balanced line can support two propagating modes. namely. an even mode and an odd mode, and be switching between these modes. the orthogonal arms of the T-slot radiator are separately excited thus forming orthogonally polarized radiated fields. A nucrostrip patch antenna, which displays polarization agility using the sane mechanism, is also described

Modifications of secondary reflector antenna patterns due to shaped beams from flanged primary horn feeds

With the advent of satellite communication and radio astronomy, the need for large and efficient reflector antennas had triggered a widespread investigation in reflector feed design techniques. Major improvements sought are reduction in spill-over, cross polarization losses and the enhancement of aperture efficiency. The search for such a feed culminated in the corrugated horn. The main idea behind the present work is to use the H-plane sectoral horns fitted with,corrugated flanges as feeds of a paraboloid and see how the secondary pattern of the reflector antenna varies with different parameters of the feed. An offset paraboloid is used as the secondary reflector in order to avoid the adverse effect of aperture ‘blocking by the feed horn structure on the secondary radiation pattern. The measurements were repeated for three different H-plane sectoral horns with the same set of corrugated flanges at various X-band frequencies. The following parameters of the whole system are studied: (a) Beam shaping. (b) Gain. (c) Variation of VSWR and (d) Cross polarization

A Multi-Objective Antenna Placement Genetic Algorithm for Matched Array Synthesis on Complex Platforms

A Multi-Objective Antenna Placement Genetic Algorithm (MO-APGA) has been proposed for the synthesis of matched antenna arrays on complex platforms. The total number of antennas required, their position on the platform, location of loads, loading circuit parameters, decoupling and matching network topology, matching network parameters and feed network parameters are optimized simultaneously. The optimization goal was to provide a given minimum gain, specific gain discrimination between the main and back lobes and broadband performance. This algorithm is developed based on the non-dominated sorting genetic algorithm (NSGA-II) and Minimum Spanning Tree (MST) technique for producing diverse solutions when the number of objectives is increased beyond two. The proposed method is validated through the design of a wideband airborne SAR

Antenna Simulations and Measurements of Focal Plane Array Facet Reflectors

We present a conceptual prototype model of a focal plane array unit for the STEAMR instrument, highlighting the challenges presented by the required high relative beam proximity of the instrument and focus on how edge-diffraction effects contribute to the array's performance. The analysis was carried out as a comparative process using both PO & PTD and MoM techniques. We first highlight general differences between these computational techniques, with the discussion focusing on diffractive edge effects for near-field imaging reflectors with high truncation. We then present the results of in-depth modeling analyses of the STEAMR focal plane array followed by near-field antenna measurements of a breadboard model of the array. The results of these near-field measurements agree well with both simulation techniques although MoM shows slightly higher complex beam coupling to the measurements than PO & PTD.

A Compensating Anastigmatic Submillimeter Array Imaging System for STEAMR

In this paper, we present a novel technique for the removal of astigmatism in submillimeter-wave optical systems through employment of a specific combination of so-called astigmatic off-axis reflectors. This technique treats an orthogonally astigmatic beam using skew Gaussian beam analysis, from which an anastigmatic imaging network is derived. The resultant beam is considered truly stigmatic, with all Gaussian beam parameters in the orthogonal directions being matched. This is thus considered an improvement over previous techniques wherein a beam corrected for astigmatism has only the orthogonal beam amplitude radii matched, with phase shift and phase radius of curvature not considered. This technique is computationally efficient, negating the requirement for computationally intensive numerical analysis of shaped reflector surfaces. The required optical surfaces are also relatively simple to implement compared to such numerically optimized shaped surfaces. This technique is implemented in this work as part of the complete optics train for the STEAMR antenna. The STEAMR instrument is envisaged as a mutli-beam limb sounding instrument operating at submillimeter wavelengths. The antenna optics arrangement for this instrument uses multiple off-axis reflectors to control the incident radiation and couple them to their corresponding receiver feeds. An anastigmatic imaging network is successfully implemented into an optical model of this antenna, and the resultant design ensures optimal imaging of the beams to the corresponding feed horns. This example also addresses the challenges of imaging in multi-beam antenna systems.

On the design of a planar phased array radar antenna architecture for space debris situational awareness

The Space Situational Awareness (SSA) program from the European Space Agency (ESA) protects Europe's citizens and their satellite-based services by detecting space hazards. ESA Ground Systems (GS) division is currently designing a phased array radar composed of thousands of radiating elements for future stages of the SSA program [1]. The radar shall guarantee the detection of most of the Low Earth Orbit (LEO) space debris, providing a general map of space junk. While range accuracy is mainly dictated by the radar waveform, the detection and tracking of small objects in LEO regimes is highly dependent on the angular accuracy achieved by the smart phased array antenna, demonstrating the important of the performance of this architecture.

GEODA-SARAS: Multi-Phased array planar antenna for satellite communications

Nowadays, earth stations have as a common feature the use of large reflector antenna for downloading data from satellites. Large reflectors have impairments such as mechanical complexity, low flexibility and high cost. Thus, the feasibility of other antenna technologies must be evaluated, such as conformal adaptive antennas based on multiple planar active arrays. In the scenery under study, the capability to track several satellites simultaneously, higher flexibility, lower production and maintenance cost, modularity and a more efficient use of the spectrum; are the most important advantage to boost up active antenna arrays over large dishes.

Combating interference in an indoor wireless-communication system using a phased-array antenna with switched-beam elements

A phased-array antenna with switched-beam elements used to combat interference in an indoor wireless communication system is described. The array uses I-bit phase shifters applied to its elements in order to point its main beam in a desired direction and internal switching of elements in order to form nulls towards interference. The array's capability of suppressing interference is verified by studying its radiation patterns and by performing interference-rejection experiments in an indoor multipath environment. (c) 2005 Wiley Periodicals, Inc.

A wideband array antenna with beam-steering capability using real valued weights

This article presents an array antenna with beam-steering capability in azimuth over a wide frequency band using real-valued weighting coefficients that can be realized in practice by amplifiers or attenuators. The described beamforming scheme relies on a 2D (instead of 1D) array structure in order to make sure that there are enough degrees of freedom to realize a given radiation pattern in both the angular and frequency domains. In the presented approach, weights are determined using an inverse discrete Fourier transform (IDFT) technique by neglecting the mutual coupling between array elements. Because of the presence of mutual coupling, the actual array produces a radiation pattern with increased side-lobe levels. In order to counter this effect, the design aims to realize the initial radiation pattern with a lower side-lobe level. This strategy is demonstrated in the design example of 4 X 4 element array. (C) 2005 Wiley Periodicals. Inc.

A dual band 2.4/5.2GHz antenna including a radial line slot array and a patch

The design of an antenna that combines a radial line slot array and a circular patch to operate as a dual band (2.4/5.2 GHz) antenna at the access point of a WLAN is presented. The design has been accomplished using commercially available Ansoft HFSS and in-house developed software. The designed antenna shows good performance in terms of return losses, radiation pattern and circular polarization in the two, 2.4 and 5.2 GHz, frequency bands. Due to its good electrical performance and a relatively low profile and low developmental cost, it should be found attractive for use as an access point antenna for dual band operation.