Radar Performance Assessment Research Articles

Compact Duplexing for a 680-GHz Radar Using a Waveguide Orthomode Transducer

A compact 680-GHz waveguide orthomode transducer (OMT) and circular horn combination has been designed, tested, and characterized in a radar transceiver's duplexer. The duplexing capability is implemented by a hybrid waveguide quasi optical solution, combining a linear polarization OMT and an external grating polarizer. Isolation between the OMT's orthogonal ports' flanges was measured with a vector network analyzer to exceed 33 dB over a >10% bandwidth between 630 and 710 GHz. Calibrated Y-factor measurements using a mixer attached to the OMT ports reveal losses through the transmit and receive paths that sum to an average of 4.7 dB of two-way loss over 660-690 GHz. This is consistent with radar sensitivity measurements comparing the new OMT/horn with a quasi-optical wire grid beam splitter. Moreover, the radar performance assessment validates the OMT as a suitable compact substitute of the wire grid for the JPL's short-range 680-GHz imaging radar.

Parabolic equation modelling of the effects of multipath and ducting on radar systems

The parabolic equation approach to the modelling of clear-air propagation, and in particular to the assessment of radar performance in the presence of multipath and ducting, is described. The derivation and solution of the parabolic equation by means of the split-step algorithm are described. A discussion of the radar equation is given to provide a connection with conventional assessment methods. The model is applied to the problem of anomalous propagation and the influence of the ground. One of the main advantages of the parabolic equation approach over alternative ray and mode methods is its ability to make quantitative predictions for two-dimensional refractiveindex structures without the need for a priori identification of the structures. New applications, such as wideband effects and the influence of refractive-index fluctuations and measurement errors on prediction accuracy, are discussed. Current work on clutter modelling and other extensions to the model are briefly mentioned.

Technique of microwave measurements

The following are described: Power measurements using the torque vane wattmeter, Hall effect, thermistor and bolometer, and calorimetry (vaporization of liquid gases); attenuation measurements using rotary attenuators, cut-off attenuators, resistive film attenuators; general considerations of accuracy of measurement of attenuation; impedance measurements using directional couplers, swept-frequency reflectometers, slotted waveguide standing wave meters, ‘three probe line’ method, substitution methods; frequency measurements using resonant cavities; echo boxes for assessment of radar performance; noise source measurements; particle accelerator measurements using perturbation techniques; dielectric loss measurements; mechanical construction aspects including materials used, and choke coupling. A select bibliography of thirteen relevant papers published in the Brit.I.R.E Journal is appended and numerous other references are given.