Modelling, simulation and

research projects

Using programs such as MATHCAD and PSPICE, it is possible to model virtually any electrical engineering problem providing the system can be described mathematically. Specialised models and simulations have been developed for Customers, where no commercial tools were available. The following projects have been undertaken:

• Multipath and diversity receiver investigation

• Inverse Chirp Z and IFFT transforms for frequency to time domain conversion in radar systems

• Prediction of phase and amplitude inbalance effects in a gradiometer antenna

• Prediction of VCO non linearity effects and bandwidth limitations in a swept synthesiser for a fast scanning receiver

• PSPICE evaluation of mutual coupling in close coupled RFID (magnetic) circuits

• Fresnel zone clearance calculations

• Okumura-Hata path prediction

• Model of ringing artefacts in a SAW based transducer

Chirp Z modelling on MATHCAD

An example using MATHCAD (Mathsoft Inc) to demonstrate the

inverse chirp-Z transform of stepped-FMCW radar data. The model allows the effects

of dispersion and band limitation to be observed on the range data

Diversity reception research

As part of a project, it was necessary to investigate whether simple diversity (dual antenna) reception

was able to remove the effects of standing wave nulls from an amplitude based

range finding system. The system operates in a domestic situation, so the

RF propagation conditions are difficult to predict.

Using a miniature RF source and the rather Heath Robinson dual-antenna receiver below, it was shown

that two antennas spaced one quarter wave apart could reduce the effects of nulls considerably. Ideally, the ground plane should be symmetrical,

as the current setup makes the radiation pattern of the antennas non omnidirectional.

diversity receiver

The RF relay switches back and forth between the two antennas with a 70/30 duty cycle. Using

zero Hz span on the analyser with a 10s sweep rate, the plot below was obtained whilst

carefully walking around (the time axis is effectively distance). The effects

of the diversity antenna pair ensure that while one antenna is in a fade, the other is not.

The peak on one is not exactly at the dip on the other, even though the spacing

is very accurate:

Twin antenna outputs with walk test

SAW based strain sensor, RF interrogated

Another example to simulate oscillations and triple transit time in a SAW-based strain sensor.

The effect was noted practically during trials and the model developed to confirm the

measured response was due to ringing in the sensor itself

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Communications projects

Antenna projects

Radar Projects

Video projects

Renewable Energy

Digital TV

Contact details:

JWD Ltd

Telephone/Fax: +44 (0)1403 261251, Mob: 07973 173808

email:

julian @ jwdltd.demon.co.uk