(Sharecast News) - Without mentioning any numbers, Filtronic said it has traded in line with expectations in the first half of its fiscal year but warned that uncertainties regarding the tail-off of its legacy filter sales and the adoption of its new Massive MIMO antennas had made near-term forecasting "very difficult".The AIM-listed manufacturer has inked its first contract wins for its Massive MIMO (multiple-input multiple-output) antennas during the period, alongside further incremental defence contracts.Ahead of its annual shareholder meeting, Filtronic told investors that its mMIMO programme, which is expected to be pivotal to the roll-out of 5G mobile networks, was "strategically significant" to its future and highlighted that successful market acceptance of the product would be material in defining the firm's near-term development."We have devoted significant resources to ensuring that we maximise our opportunity with this product, but we caution that we remain dependent on a number of variables outside our control that will determine the rate of market take-up of mMIMO and hence the timing and rate of sales growth for this product," the West Yorkshire-based outfit said.Filtronic, which opted to exit the OEM base station filter subset of the wireless telecommunications market back in 2016, stated that, over the past two years, it had benefitted from continuing sales of some of these legacy filter products, but warned that it expects those sales to continue to diminish as client programmes come to their natural end."Whilst we continue to enjoy good baseload volumes from our long-term defence contracts, the uncertainties regarding the timing of the market take-up for mMIMO and the rate of tail-off of our legacy filter sales make near-term forecasting very difficult.""However, we are confident that our position overall continues to strengthen and our outlook remains positive."As of 0845 BST, Filtronic shares had plunged 15.44% to 17.97p.