The radar meteoroid orbit data set obtained from the AMOR facility in Christchurch, New Zealand (longitude 172°39′ E, latitude 43°34′ S) between 1995 May and 1999 October contains ∼5 × 105 high‐quality meteor records. The system was very sensitive compared with previous surveys, with a limiting radio magnitude of +14 corresponding to a 3 × 10−10 kg meteoroid mass limit (40‐μm diameter) being achieved. This data set is here examined to determine and remove biases inherent in the radar method. The fully corrected meteoroid orbital distribution at 1 au from the Sun is derived. This distribution replaces a previous, much used, orbital distribution produced by the earlier Harvard Radio Meteor Program (HRMP). Anomalies have been found in the original debiasing of the latter which strongly favoured meteoroids observed at low speeds. Three forms of output orbital element distributions have been produced in the present study. To aid comparisons, these forms are identical to those produced by the HRMP: the ‘directly observed’ output is that with no corrections applied, the ‘atmospheric’ sample is corrected for all in‐atmosphere effects, which includes electromagnetic wave propagation and ionospheric effects and the influence of the particular form of the radar system, and the ‘space sample’ is additionally corrected for collision probability with the Earth. The space sample has rather higher eccentricity and larger semimajor axis length orbits than directly observed by AMOR. Its inclination distribution shows a general decrease in number with inclination: with a peak at ∼20° and few meteors at inclinations very close to the ecliptic; a small population remains from the original ∼50 per cent of orbits in retrograde orientations. Comparison with the original HRMP space distributions shows little agreement, however the revised HRMP orbital element distributions of Taylor and Elford compares well. The higher number of orbits in the AMOR data set and the uncertainty involved in re‐reducing the older HRMP data shows a strong direction for the use of the AMOR as a standard.

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A large data set provided by the highly sensitive Advanced Meteor Orbit Radar (AMOR) facility is used to investigate the structure of the sporadic meteor complex. The helion, antihelion and apex apparent sources are clearly found. Observational bias is then removed to reveal the true source distributions as observed on Earth. A long‐standing problem in meteor science has been the difference in observed meteor flux between the helion and antihelion source directions. Consideration of the effects of atmospheric interference and Faraday rotation is found to lead to a closer balance between these. The orbital distributions present within the different regions are also discussed. The apex region is found to have a strong retrograde component and a weaker prograde component that exists at high southerly latitudes and that contains orbits with particularly high inclinations. The retrograde component reduces substantially after inclusion of observational bias corrections. Care should be taken in comparing the results presented here with those from other radar systems: AMOR is sensitive to dust as small in diameter as ∼40 μm, while the limiting sensitivity of most contemporary systems is an order of magnitude larger.

In order to determine stream structure within the meteoroid orbital dust cloud, which may help in our understanding of progenitor comet and asteroid bodies, a method involving dissimilarity functions called D‐criteria must be used. It is important to understand the response of these criteria to particular orbital orientations. Simulations are performed to determine the applicability of four D‐criteria functions in retrieving meteor stream members, with due regard for sporadic background intrusion, in radar detected data sets. The AMOR data set is used as a particular example of the latter. It is found that the Southworth & Hawkins’ criterion (DSH) performs satisfactorily but requires quite different cut‐off levels depending on the orbital inclination angle of the stream. Valsecchi et al.'s criterion (DN) performs more evenly over different prograde orbital orientations. The modifications to DSH proposed by Drummond (DD) and Jopek (DH) are also explored. For low prograde inclination streams , , , cut‐off levels are found to retrieve 70 per cent of a simulated stream. For higher prograde inclination streams , , , cut‐off levels are used. For retrograde orbits and are found to retrieve 70 per cent of the members in the case of three retrograde streams studied. DSH and DH require such high cut‐off values, especially in the case of the η Aquarids, that a value is not listed here.

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