Advantages of rapid bipolar planar near-field scanner for millimetre-wave antenna measurement

Planar near-field measurement of small antennas operating at millimetre-wave frequencies are often wrought with difficulty. Over-sized ranges, cable loss, expensive equipment, long measurement times, and positional accuracy are just some of the issues that contribute to making measurements inefficient and cumbersome for most laboratories. As more compact millimetre-wave antenna designs are introduced, these measurement issues must be addressed to better allow cost-effective and efficient measurements to facilitate the antenna design cycle. The bipolar planar scanning technique for millimetre-wave antennas was introduced by the authors and demonstrated to be a viable option for cost-effective measurement [1-2]. Its simple mechanical design allows for many of the issues associated with millimetre-wave antenna measurement to be effectively mitigated or even eliminated. One example is its dual rotary stage design that allows for minimal cable movement, reducing cable phase errors that can perturb the measurement. Other distinct advantages of the bipolar scanner can tackle the issues of expensive equipment, positional accuracy, and range size. This paper will describe and elaborate on the advantages of the bipolar scanner for millimetre-wave antenna measurement, including at introduction of new scanning modes that can help dramatically reduce measurement time over previously implemented scanning modes. These new modes are the most natural and rapid mode of scanning and involves simultaneous and continuous motion of both rotational axes of the scanner. This motion results in a data grid with a spiral geometry. Two spiral geometries, the linear spiral and the bipolar spiral, have been implemented for the bipolar scanner. Representative measurements using our millimetre-wave bipolar planar near-field antenna measurement system will show the capabilities of the bipolar scanner and verify its viability for efficient and accurate millimetre-wave antenna measurements.