Cristian I. Coman

Implementation of polarization agility in planar phased-array antennas by means of interleaved subarrays

A method for ensuring polarization agility in conjunction with beam steering in planar array antennas is proposed. It relies on interleaving two subarrays with orthogonal, linear polarizations that, together, can generate arbitrary polarization states: adjustable linear, elliptical, and left- or right-handed circular. The complexity of the resulting system is comparable with that of standard, fully populated array antennas consisting of identical, linearly polarized elements. By dynamically controlling the amplitude and the phase of the signals fed to the subarrays, a stable polarization state can be maintained during beam steering. The concept is validated by numerically investigating an architecture obtained by interleaving nonuniform subarrays designed by means of a deterministic placement strategy. The effects of the mutual coupling between the different radiating elements are modeled and discussed.

Interleaving sparse arrays: a new way to polarization-agile array antennas?

A new strategy to obtaining polarization-agile array antennas was discussed. It makes use of the interleaving of sparse (complementary) sub-arrays characterized by mutually orthogonal, linear polarizations. The validity of this approach was demonstrated by examining two examples of arrays designed for obtaining adjustable linearly-polarized waves. The advocated technique allows a significant reduction of the control circuitrys complexity and the use of simple radiators, while guaranteeing the possibility to obtain complex and reconfigurable polarization states of the radiated field.

Synthetic aperture antenna procedure for a SFCW sensor

The use of electromagnetic waves for detection of shallowly buried objects has some advantages over other types of detection systems. The most important is the fact that the detection process can be remote controlled, so the risks associated with this activity can be minimized. Also an airborne radio sensor can scan a larger surface with a higher speed. Any detection process supposes a certain accuracy which has to provide the location of the object as precise as possible. In the case of an electronic device the interface between the propagation media and the device is assured by the antenna systems, which plays a critical role for the system resolution. The paper describes a simple procedure to create a synthetic aperture antenna by using the data acquired with a moving transmitting and receiving antenna system.

The relativity of bandwidth - the pursuit of truly ultra wideband radiators for communication applications

An overview on the design of increasingly wider bandwidth radiators that are amenable to being integrated in array configurations is presented. The initial step is represented by moderate bandwidth radiator of the cavity backed patch antennas. The bandwidth characteristics are then substantially increased by combining coplanar waveguide (CPW) feedings and profiled dipoles, the result being radiators with unprecedented performances. This type of radiators are further refined for improving their time-domain adequacy or for ensuring intrinsic filtering properties.

Body-borne IED detection: NATO DAT#10 BELCOAST 09 demonstration results

Belgium leads the tenth initiative in the CNAD Programme of Work for the Defense Against Terrorism (PoW DAT), dealing with Critical Infrastructure Protection (CIP). The BELCOAST 09 event, comprising a series of technology demonstrations, was organized to tackle the need for an event that brings together the operational, armaments and technological communities in the field of CIP. A counter terrorism scenario has been created: Terrorist with body-borne IED approaching the entrance of an installation, and a millimeter-wave imagers ability to detect IEDs has been demonstrated. The results of this scenario-based demonstration are presented in this paper.

Interleaved Array Antennas Design | (Almost) Deterministic Strategies

The synthesis strategies to be used for designing array antennas implementing the shared-aperture concept are described and discussed. The presented techniques range from fully deterministic approaches to semi-deterministic ones up to purely statistical design strategies. The pros and cons of each technique are ascertained. 1. INTRODUCTION The quest for increasingly performing antenna front-ends has been stimulated in the last years by the necessity of implementing complex functions in radars and communication systems. In particular, modern sensing systems require the (array) antennas to be able to perform a number of concurrent tasks, such as, for instance, operating at difierent frequency bands, difierent polar- izations, difierent scanning directions, etc. The coexistence of several array antennas performing concomitantly the difierent tasks often results in bulky antenna systems that are di-cult to deploy on moving platforms such as ships, airplanes or satellites. A convenient way to address this problem is to co-locate the array antennas responsible for the difierent services (functionalities) to be concurrently provided. The so-called shared-aperture concept (1,2) can then be adopted to realize multi-functional array antennas. The difierent func- tionalities are ascribed to sub-arrays of elementary radiators, the sub-arrays sharing a common physical area that constitute the complete antenna aperture. An early implementation of this concept is reported in (3) where the elementary antennas com- posing the sub-arrays are deployed on interleaved, uniform grids. A later contribution (4) proposed a complementary partition of a linear array in two sub-arrays exhibiting narrow radiation beams and grating lobes free operation. The shared-aperture concept was successively exploited to achieve multi-frequency operation (2) and polarization-agility capability (5). Moreover the possibility to integrate the transmitter and the receiver antennas of a frequency modulated, continuous wave (FMCW) radar by making use of the shared-aperture concept was demonstrated in (6). In this paper, some techniques that can be used to design interleaved array antennas imple- menting the shared-aperture concept are described. The reader is conducted through a path that, starts from strictly deterministic methods, passes through an intermediate step, and leads to fully stochastic approaches. The advantages and drawbacks introduced by the difierent techniques are analyzed in detail. It is worth noting that none of the techniques described in this work invokes any kind of iterative optimization procedure, this enabling a time efiective design strategy for any of the presented methods.

Measurement of electrically large array antennas in small anechoic chambers [Measurements Corner]

A post-processing procedure that yields accurate array-antenna radiation-pattern estimations is described. By resorting to this strategy, measurements of large array antennas inside small anechoic chambers become feasible. The method employs an adequate phase-correction derived from an optical ray approach, under the assumption that the elementary radiators themselves are electrically small and can be measured under far-field conditions inside the relevant anechoic chamber. The effectiveness of the proposed technique is demonstrated by examining the case of a nonuniform linear array antenna.