PLL with secondary loop control for self tracking antennas

This paper shows a simple, yet highly effective, tracking phase locked loop circuit which has applications for self steered antenna arrays. The tracking PLL has been demonstrated to accurately phase track signal levels as low as -120 dBm, making it suitable for applications such as SATCOM ground terminals. The implementation is simple requiring a low Q voltage controlled oscillator, a downconverting mixer and a PLL circuit.

Self-aligning wireless link using modulated backscatter

A self-tracking (aligning) radio communications system based on the principle of modulated backscatter detection is presented here. Using amplitude-modulated backscatter from a co-operating target, a modified IQ demodulation scheme is used to reproduce automatically and in real time both the received and conjugate of the received phase of an incoming signal. The phase conjugated demodulated IF signal can have incoming backscattered data removed and new data are inserted before being up-converted using IQ single side-band generation so that retro-directive re-transmission can be made to occur. In the absence of the backscattered modulation signal, no phase conjugation and hence no retro-directed re-transmission can occur. The system reported is therefore inherently self-authenticating a facility not readily available from previously reported retro-directive self-tracking systems. © 2010 © The Institution of Engineering and Technology.

Modulation Insensitive PLL for Tracking Antenna Applications

This article shows practical results of a self-tracking receiving antenna array using a new phase locked loop (PLL) tracking configuration. The PLL configuration differs from other architectures, as it has the new feature of being able to directly track phase modulated signals without requiring an additional unmodulated pilot carrier to be present. The PLLs are used within the antenna array to produce a constant phase intermediate frequency (IF) for each antenna element. These IF's can then be combined in phase, regardless of the angle of arrival of the signal, thus utilizing the antennas array factor. The article's main focus is on the phase jitter performance of the modulation insensitive PLL carrier recovery when tracking phase modulated signals of low signal to noise ratio. From this analysis, it is concluded that the new architecture, when optimally designed, can produce phase jitter performance close to that of a conventional tracking PLL.

Retro-transceiver array using monopole antennas

In this paper, we show how a self-tracking antenna array constructed using gimel /4 monopoles can be constructed, which is capable of receiving with gain over an entire 360 degrees azimuthal cut. It is also shown how the self-tacking receive unit can be used in conjunction with a self-phased transmitter so that self-steered spatially selective receive and transmit functions ran be formed simultaneously. The resulting array is capable of maintaining spatially selective receive and transmit functions to a roaming target without prior knowledge of its physical location.

Dual-mode retrodirective/phased array

A method for producing a retrodirective (self-tracking) antenna, which can also be operated as a phased (selectively pointed) array through the addition of a simple switching circuit and DC bias offset adjustment, is presented. Phase adjustment to individual antenna elements is shown to be readily carried out by a simple frequency pushing technique, applied to a PLL circuit, thus replacing the requirement for additional phase shifters. Practical results when applied to a ten-element array operating at 2.4 GHz are shown for both modes of operation.

Rotman lens based-retrodirective array

A new type of broadband retrodirective array, which has been constructed using a microstrip Rotman lens, is presented. Automatic tracking of targets is obtained by exploiting the conjugate phase response of the beamforming network which is exhibited when the input ports are terminated with either open or short circuits. In addition, the true time-delay property of the Rotman lens gives broadband operation of the self-tracking array when used in conjunction with Vivaldi antennas. The simulated and measured bistatic and monostatic radar cross-section (RCS) patterns of a structure consisting of 13 beamports and 12 array ports are presented at frequencies in the range 8-12 GHz. Significantly enhanced RCS within the scan coverage ±40° is demonstrated by comparing the retrodirective behavior of a 12-element Vivaldi array terminated with and without the Rotman lens. © 2006 IEEE.

CP retrodirective antenna array performance degradation at large elevation angles

At large elevation angles away from boresight the performance of planar phased antenna arrays for circularly polarized, CP, signals suffers from significant gain reduction, worsening of the circular polarization purity, increased pointing error and unwanted dominantly specular lobe radiation. The mechanisms governing this performance deterioration and suggestions for possible rectification are for the first time elaborated in this paper. The points raised in this paper are important when CP retrodirective arrays are to be deployed in self-tracking satellite and terrestrial communication systems mounted on mobile platforms.

SATCOM Retrodirective Array

We present an in depth look at the challenges involved in using analogue retrodirective arrays for satellite communications. The main technical issues surrounding the development of a retrodirective (self-steering) Satellite Communications (SATCOM) system are given and techniques for mitigating these issues provided. Detailed results are given for a prototype high performance circularly polarized retrodirective array architecture suitable for mounting on an un-stabilized mobile platform. The paper concludes with practical retrodirective L-band array results with the array used to acquire actual broadband satellite data signals from a commercial L-band satellite system. Received satellite signals as low as -130dBm at the antenna elements are tracked. Accurate self-tracking occurs over the azimuth range of up to +/- 40 degrees.

Mean field approach for tracking similar objects

In this paper, we consider the problem of tracking similar objects. We show how a mean field approach can be used to deal with interacting targets and we compare it with Markov Chain Monte Carlo (MCMC). Two mean field implementations are presented. The first one is more general and uses particle filtering. We discuss some simplifications of the base algorithm that reduce the computation time. The second one is based on suitable Gaussian approximations of probability densities that lead to a set of self-consistent equations for the means and covariances. These equations give the Kalman solution if there is no interaction. Experiments have been performed on two kinds of sequences. The first kind is composed of a single long sequence of twenty roaming ants and was previously analysed using MCMC. In this case, our mean field algorithms obtain substantially better results. The second kind corresponds to selected sequences of a football match in which the interaction avoids tracker coalescence in situations where independent trackers fail.

Self-Feedback Motion Control for Cable-Driven Parallel Manipulators

This article proposes a closed-loop control scheme based on joint-angle feedback for cable-driven parallel manipulators (CDPMs), which is able to overcome various difficulties resulting from the flexible nature of the driven cables to achieve higher control accuracy. By introducing a unique structure design that accommodates built-in encoders in passive joints, the seven degrees of freedom (7-DOF) CDPM can obtain joint angle values without external sensing devices, and it is used for feedback control together with a proper closed-loop control algorithm. The control algorithm has been derived from the time differential of the kinematic formulation, which relates the joint angular velocities to the time derivative of cable lengths. In addition, the Lyapunov stability theory and Monte Carlo method have been used to mathematically verify the self-feedback control law that has tolerance for parameter errors. With the aid of co-simulation technique, the self-feedback closed-loop control is applied on a 7-DOF CDPM and it shows higher motion accuracy than the one with an open-loop control. The trajectory tracking experiment on the motion control of the 7-DOF CDPM demonstrated a good performance of the self-feedback control method.

Obsessive-compulsive symptoms and attentional bias: An eye-tracking methodology

Background and objectives: Cognitive models suggest that attentional biases are integral in the maintenance of obsessive-compulsive symptoms (OCS). Such biases have been established experimentally in anxiety disorders; however, the evidence is unclear in Obsessive Compulsive disorder (OCD). In the present study, an eye-tracking methodology was employed to explore attentional biases in relation to OCS.
Methods: A convenience sample of 85 community volunteers was assessed on OCS using the Yale-Brown Obsessive Compulsive Scale-self report. Participants completed an eye-tracking paradigm where they were exposed to OCD, Aversive and Neutral visual stimuli. Indices of attentional bias were derived from the eye-tracking data.
Results: Simple linear regressions were performed with OCS severity as the predictor and eye-tracking measures of the different attentional biases for each of the three stimuli types were the criterion variables. Findings revealed that OCS severity moderately predicted greater frequency and duration of fixations on OCD stimuli, which reflect the maintenance attentional bias. No significant results were found in support of other biases.
Limitations: Interpretations based on a non-clinical sample limit the generalisability of the conclusions, although use of such samples in OCD research has been found to be comparable to clinical populations. Future research would include both clinical and sub-clinical participants.
Conclusions: Results provide some support for the theory of maintained attention in OCD attentional biases, as opposed to vigilance theory. Individuals with greater OCS do not orient to OCD stimuli any faster than individuals with lower OCS, but once a threat is identified, these individuals allocate more attention to OCS-relevant stimuli.

Learning outcomes tracking system (L.O.T.S):seeing student progress as term progresses

At QUB we have constructed a system that allows students to self-assess their capability on the fine grained learning outcomes for a module and to update their record as the term progresses. In the system each of the learning outcomes are linked to the relevant teaching session (lectures and labs) and to [online] resources that students can access at any time. Students can structure their own learning experience to their needs to attain the learning outcomes. The system keeps a history of the student’s record, allowing the lecturer to observe how the students’ abilities progress over the term and to compare it to assessment results. The system also keeps of any of the resource links that student has clicked on.