Characteristics of electromagnetic disturbance from microwave ovens and interference with digital radio communications systems

Abstract

Microwave ovens operating in the 2.45 GHz band emit broadband noise that could possibly interfere with digital mobile communication systems in the 1-3 GHz band particularly when terminals are used near ovens. Therefore the basic properties of unwanted emissions from microwave ovens were measured in both the time and frequency domains, and it was found that out-of-band emission occurs when magnetron oscillation is transient or unstable. Statistical distributions of the noise envelope in the 1.9 GHz band - amplitude probability distribution, crossing rate distribution, pulse spacing distribution and pulse duration distribution - were also measured to obtain the information necessary to evaluate degradation in the performance of digital radio communication systems. The bit error rate of the pi/4 shift QDPSK (Quaternary Phase Shift Keying Differential Detection) system was evaluated by using the measured time series of noise. It is found that performance is affected by microwave oven noise and that specific channels which synchronize with microwave oven noise are degraded in the case of TDMA-TDD (Time Division Multiple Access/Time Division Duplex) access.

2.45GHz帯で動作するマイクロ波オーブンは広帯域雑音を放射し、1-3GHz帯のデジタル移動通信システムと特にその端子がオーブンの近傍にあるときは干渉する。マイクロ波オーブンからの不要放射の基礎特性を時間および周波数ドメインの両方で測定し、マグネトロンが過渡状態のときや不安定なときには帯域外放射を生ずることがわかった。また、振幅確率分布、交差レート、パルス間隔分布およびパルス幅分布などの1.9GHzの雑音エンベロープの統計的分布を測定し、デジタル無線通信システムの性能劣化を評価するのに必要な情報を得た。π/4シフトQDPSK(4相差動同期PSK)のビット誤り率を、測定した雑音の時系列を使って評価した。マイクロ波オーブン雑音およびマイクロ波オーブンに同期する特定のチャネルの影響により、性能はTDMA-TDDの場合は劣化することがわかった。