This paper presents a new architecture of a compact multimode FMCW radar for general purpose short-range applications. The radar can operate in CW as well as in FMCW modes. The transmitted RF frequency or frequency range can be arbitrarily selected using an inbuilt SPI control over 2.25-2.50 GHz with a frequency resolution of at least 100 kHz. A modified VCO-PLL loop with a stable reference source of 10 MHz improves the frequency stability. Other than the audio signal generator, all modules like RF blocks, base-band block DC power management block, and control and synchronization and data acquisition blocks are integrated into a single module using a three-layer PCB configuration. Fabrication and measurement of the radar unit in both the modes are presented.

A non-coherent passive six-port receiver system is presented for accurate amplitude, phase and frequency measurement of a RF signal. The system uses the six-port network and a new wideband phase delay line with known phase profile. The phase delay unit uses a number of openstubs connected to a microstrip line. Detail design steps of the phase delay line is presented. The whole receiver is fabricated in PCB technology. No local oscillator or DC biasing are used. Thus, it is an all-passive system, which does not require any power source. It can be used as a real time and fast demodulator for both analog and digital signals.

Present article reviews the early and recent developments in skid resistance measurement techniques at asphalt concrete pavement. Suitability and limitations of various methods used for capturing skid characteristics of the surface has been outlined. The harmonization of laboratory and field-testing methods has been summarized briefly. Harmonization is agreement of test outcomes reported from field as well as laboratory. Correlation analysis of various in-situ and laboratory test data has been made to maintain the better harmony of measurement either in field or in laboratory. Measurement of skid resistance in field is time consuming, labor intensive and requires use of costly, advanced and sophisticated instruments. Lab measurement lags in accuracy and still needs improvement in design and working methodology which compelled researchers for looking into modelling as an alternative option. In the subsequent sections, progress in modelling approach (analytical to numerical) has been discussed in brief. Analytical and numerical solutions of asphalt concrete pavement for modelling skid resistance have been reviewed and emphasis for choosing a particular solution has been justified on the basis of accuracy as well as efficacy of the output model. Critical factors affecting skid resistance model like hydroplaning, tire related parameters, temperature, surface texture has been highlighted in this manuscript. Skid data obtained from any model whether it is analytical or numerical, needs to be validated against field measurement or some established data. Validation of skid resistance model using field test and experimentally derived equations in various research studies has been summarized in later section of this article. Few key research directions have been suggested as scope of future study so as to predict a more reliable skid resistance model (1) For predicting dynamic frictional properties with higher accuracy at tire pavement interface, tire pavement interaction modelling still needs improvement considering all field constraints (2) Influence of surface texture, hydroplaning, temperature and pavement ageing needs to be studied in depth for modelling skid resistance as these are critical parameters & contributes significantly.

This paper presents a compact continuous wave Doppler radar architecture at 2.4 GHz. The system provides a low-cost solution to remotely monitor vibrations of any object. In the RF system, two separate antennas are used for the transmitter and receiver. The receiver works in homodyne mode. A single microwave oscillator is used to transmit continuous wave signal as well as the synchronized local oscillator for the receiver. An opamp base band electronics separate the small receiver output signal from a large dc offset due to homodyne operation. In comparison to other approaches, number of components are minimized.