A generalised stubs-integrated-microstrip (SIM) antenna with wide coverage circularly polarised (CP) radiation is proposed for radio-frequency energy harvesting applications. The antenna consists of a microstrip patch radiator with four integrated asymmetric/symmetric-stubs and a coaxial feed. Four stubs are integrated at the corners of a square microstrip radiator. The stub lengths or stub gaps from the microstrip radiator are optimised for wide-beam CP radiation. Four different combinations of asymmetric/symmetric based SIM antennas are designed, fabricated, and tested. The proposed antennas are able to cover upper-half area with CP radiation across the 3-dB axial ratio bandwidth.
target was clear of clutter was used, thus removing the effect of clutter from the outdoor measurements. A first order multipath analysis was conducted and it was determined that the effects of multipath was negligible for this setup. The slight differences between the outdoor data and compact range data can be attributed to alignment inaccuracies of the tri-copter toward the radar, especially in elevation. A stabilizing gimbal can be attached to the tricopter as a mounting platform for the target or its antennas to reduce the fluctuations due to the roll, pitch and yaw of the tricopter. CONCLUSIONResults were presented for a relatively small and light weight cost effective airborne active calibration target, suitable for the calibration of a ground to air RCS measurement system. It was demonstrated that the calibration target had wide bandwidth and wide beamwidth properties. The static RCS characteristics of the airborne active calibration target were measured in a compact range and compared to outdoor measurements of the active calibration target mounted on a small remote controlled tricopter. The major advantages of the active calibration target are that it has a large beamwidth; is easy to deploy; is low cost as well as being wideband; and has a relatively large absolute RCS making it a suitable alternative over passive calibration targets for ground based radar systems. Another advantage of being airborne and in motion is that calibration measurements are out of ground clutter. This calibration system is also useful for independent verification of radar specifications by defence evaluation and research institutes. The airborne capability could also give the opportunity to verify the minimum detectable velocity of a target of a specified RCS. The RCS of the calibration target can be varied which could also be used to test deployed/ installed radar systems.ABSTRACT: A circularly polarized (CP) microstrip antenna with four strips is proposed for wide beamwidth and RF energy harvesting applications. Four strips along the diagonal directions are integrated symmetrically onto a square patch radiator for CP radiation with wide beamwidth. To improve the impedance matching of the antenna, a stub is integrated along the orthogonal direction of the patch radiator. The antenna is designed on FR4 substrate and an antenna prototype shows a measured 10-dB return loss bandwidth of 120 MHz (2.53-2.65 GHz) with a maximum gain of 4.6 dBic. The measured 3-dB axial ratio (AR) bandwidth is 65 MHz (2.540-2.605 GHz) with a 3-dB AR beamwidth of around 1808 across the band. Overall antenna volume is 0.475k o 3 0.475k o 3 0.013k o at 2.5 GHz.
Numerical studies have been carried out using a validated two-dimensional standard k-omega turbulence model for the design optimization of a thrust vector control system using shock induced self-impinging supersonic secondary double jet. Parametric analytical studies have been carried out at different secondary injection locations to identifying the highest unsymmetrical distribution of the main gas flow due to shock waves, which produces a desirable side force more lucratively for vectoring. The results from the parametric studies of the case on hand reveal that the shock induced self-impinging supersonic secondary double jet is more efficient in certain locations at the divergent region of a CD nozzle than a case with supersonic single jet with same mass flow rate. We observed that the best axial location of the self-impinging supersonic secondary double jet nozzle with a given jet interaction angle, built-in to a CD nozzle having area ratio 1.797, is 0.991 times the primary nozzle throat diameter from the throat location. We also observed that the flexible steering is possible after invoking ON/OFF facility to the secondary nozzles for meeting the onboard mission requirements. Through our case studies we concluded that the supersonic selfimpinging secondary double jet at predesigned jet interaction angle and location can provide more flexible steering options facilitating with 8.81% higher thrust vectoring efficiency than the conventional supersonic single secondary jet without compromising the payload capability of any supersonic aerospace vehicle.
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