Reconfigurable beam forming using phase-aligned Rotman lens

The authors describe how a standard Rotman lens design can be readily adapted in order to allow reconfigurable beam
forming. This is achieved by applying concurrent excitations to the modified Rotman lens. A rationale for the design and
underlying behaviour of the modified, phase-aligned, Rotman lens as well as the deficiencies of a conventional Rotman lens
in this mode of operation are provided. Simulated and measured results are provided in order to illustrate the feasibility of the
approach suggested.

Phenomenology and system engineering of micro- and nano-antenna FPA sensors for detection of concealed weapons and improvised explosive devices

The ability of millimetre wave and terahertz systems to penetrate clothing is well known. The fact that the transmission of clothing and the reflectivity of the body vary as a function of frequency is less so. Several instruments have now been developed to exploit this capability. The choice of operating frequency, however, has often been associated with the maturity and the cost of the enabling technology rather than a sound systems engineering approach. Top level user and systems requirements have been derived to inform the development of design concepts. Emerging micro and nano technology concepts have been reviewed and we have demonstrated how these can be evaluated against these requirements by simulation using OpenFx. Openfx is an open source suite of 3D tools for modeling, animation and visualization which has been modified for use at millimeter waves. © 2012 SPIE.

Standoff detection of weapons and contraband in the 100 GHz to 1 THz region

The techniques and technologies currently being investigated to detect weapons and contraband concealed on persons under clothing are reviewed. The basic phenomenology of the atmosphere and materials that must be understood in order to realize such a system are discussed. The component issues and architectural designs needed to realize systems are outlined. Some conclusions with respect to further technology developments are presented.

Amplitude-modulation characteristics of power-combining Class-E amplifier with finite choke

Power back-off performances of a new variant power-combining Class-E amplifier under different amplitude-modulation schemes such as continuous wave (CW), envelope elimination and restoration (EER), envelope tracking (ET) and outphasing are for the first time investigated in this study. Finite DC-feed inductances rather than massive RF chokes as used in the classic single-ended Class-E power amplifier (PA) resulted from the approximate yet effective frequency-domain circuit analysis provide the wherewithal to increase modulation bandwidth up to 80% higher than the classic single-ended Class-E PA. This increased modulation bandwidth is required for the linearity improvement in the EER/ET transmitters. The modified output load network of the power-combining Class-E amplifier adopting three-harmonic terminations technique relaxes the design specifications for the additional filtering block typically required at the output stage of the transmitter chain. Qualitative agreements between simulation and measurement results for all four schemes were achieved where the ET technique was proven superior to the other schemes. When the PA is used within the ET scheme, an increase of average drain efficiency of as high as 40% with respect to the CW excitation was obtained for a multi-carrier input signal with 12 dB peak-to-average power ratio. © 2011 The Institution of Engineering and Technology.

Dual-Reflector Antenna with a Reflectarray Subreflector for Wide Beam Scanning Range at 120GHz

A dual-reflector antenna composed by a small reconfigurable reflectarray subreflector and a large parabolic main reflector is proposed for beam scanning application in the 120 GHz frequency band. The beam scanning is achieved by changing the phase distribution on the reflectarray surface which is supposed to contain reconfigurable cells. The phase distribution for the different beam deflecting states is obtained with a synthesis technique based on the analysis of the antenna in receive mode.

W-Band Planar Wide-Angle Scanning Antenna Architecture

This paper proposes a hybrid scanning antenna architecture for applications in mm-wave intelligent mobile sensing and communications. We experimentally demonstrate suitable W-band leaky-wave antenna prototypes in substrate integrated waveguide (SIW) technology. Three SIW antennas have been designed that within a 6.5 % fractional bandwidth provide beam scanning over three adjacent angular sectors. Prototypes have been fabricated and their performance has been experimentally evaluated. The measured radiation patterns have shown three frequency scanning beams covering angles from 11 to 56 degrees with beamwidth of 10?±?3 degrees within the 88-94 GHz frequency range.

Comparison of frequency-selective screen-based linear to circular split-ring polarisation convertors

This study presents the use of periodic arrays of freestanding slot frequency-selective screens (FSS) as a means for generating circularly polarised signals from an incident linearly polarised signal at normal incidence to the structure. Measured and simulated results for crossed, linear and various ring slot element shapes in single and double-layer polarisation convertor structures are presented for 10 GHz operation. It is shown that 3 dB axial ratio (AR) bandwidths of 21% can be achieved with the one-layer perforated screen design and that the rate of change is lower than the double-layer structures. An insertion loss of 0.34 dB can be achieved for the split circular ring double-layer periodic array, and of the three topologies presented the hexagonal split-ring polarisation convertor gives the lowest variation of AR with angle of incidence 1.8 dB/45° and 3.6 dB/45° for the single and double-screen FSS, respectively. In addition, their tolerance to angle of incidence variation is presented. The capability of the surfaces reported here as twist polariser or spatial isolator components has been demonstrated with up to -30 dB isolation between incident and re-reflected signals for the double-layer designs being measured. © 2010 The Institution of Engineering and Technology.

Design and experimental validation of liquid crystal-based reconfigurable reflectarray elements with improved bandwith in F-band

A reconfigurable reflectarray which exploits the dielectric anisotropy of liquid crystals (LC) has been designed to operate in the frequency range from 96 to 104 GHz. The unit cells are composed of three unequal length parallel dipoles placed above an LC substrate. The reflectarray has been designed using an accurate model which includes the effects of anisotropy and inhomogeneity. An effective permittivity that accounts for the real effects of the LC has also been used to simplify the analysis and design of the unit cells. The geometrical parameters of the cells have been adjusted to simultaneously improve the bandwidth, maximize the tunable phase-range and reduce the sensitivity to the angle of incidence. The performance of the LC based unit cells has been experimentally evaluated by measuring the reflection amplitude and phase of a reflectarray consisting of 52x54 identical cells. The good agreement between measurements and simulations validate the analysis and design techniques and demonstrate the capabilities of the proposed reflectarray to provide beam scanning in F band.

Design of engineered reflectors for radar cross section modification

A technique is proposed for the design of engineered reflectors consisting of doubly periodic arrays printed on thin grounded dielectric substrates that reflect an incoming wave from a given incoming direction to a predetermined outgoing direction. The proposed technique is based on a combination of Floquet theory for propagation in periodic structures and reflect-array principles. A flat surface designed to reflect a TE polarized wave incident at 45 back in the direction of the impinging signal at 14.7 GHz is employed as an example. By means of full-wave simulations, it is demonstrated that the monostatic RCS of a finite reflector is comparable with the specular RCS of a metallic mirror of the same dimensions. It is further shown that comparably high monostatic RCS values are obtained for angles of incidence in the 30-60 range, which are frequency dependent and thus open opportunities for target localization. A prototype array is fabricated and experimentally tested for validation. The proposed solution can be used to modify the radar cross section of a target. Other potential applications are also discussed. © 1963-2012 IEEE.

Split-Ring FSS Spiral Phase Plate

This letter gives the first report of a planar phase plate structure based on frequency selective surface (FSS) technology for the generation of helical far-field radiation patterns with circular polarization properties.The unit cell of the structure comprises two orthogonal split-ring resonators designed to ensure 180$^{\circ}$ phase shift between orthogonal transmission coefficients. This property is exploited to obtain progressive rotational phase shift within the structure and thus synthesize 360$^{\circ}$ spiral phase profile. Measured far-field radiation patterns demonstrate spiral phase front generation for 10-GHz circularly polarized waves transmitted through the structure.

Effect of environmental multipath on line of sight body to body communication at 2.45 GHz

Body to body links are the most scenario dependent form of body centric communications with performance highly dependent on the users' movements, relative positioning and the local operating environment. This paper focuses on line of sight cases which although they should be the most dependent, still have considerable variability depending on local propagation conditions. The results presented in the paper also raise important questions about the statistical characterisation of such links and the effect of different approaches to local mean averaging on fading characteristics. © 2012 IEEE.