**Wantian Wang, Ziyue Tang, Yichang Chen \*, Yuanpeng Zhang and Yongjian Sun**

Air Force Early Warning Academy, Wuhan 430019, China; laodifang0120@126.com (W.W.); tang\_zi\_yue@163.com (Z.T.); zhangyuanpeng312@163.com (Y.Z.); bmdsun@126.com (Y.S.) **\*** Correspondence: cyc\_2007@163.com; Tel.: +86-134-7620-2876

Received: 27 September 2019; Accepted: 15 November 2019; Published: 18 November 2019

**Abstract:** For a conventional narrow-band radar system, the detectable information of the target is limited, and it is difficult for the radar to accurately identify the target type. In particular, the classification probability will further decrease when part of the echo data is missed. By extracting the target features in time and frequency domains from multi-wave gates sparse echo data, this paper presents a classification algorithm in conventional narrow-band radar to identify three different types of aircraft target, i.e., helicopter, propeller and jet. Firstly, the classical sparse reconstruction algorithm is utilized to reconstruct the target frequency spectrum with single-wave gate sparse echo data. Then, the micro-Doppler effect caused by rotating parts of different targets is analyzed, and the micro-Doppler based features, such as amplitude deviation coefficient, time domain waveform entropy and frequency domain waveform entropy, are extracted from reconstructed echo data to identify targets. Thirdly, the target features extracted from multi-wave gates reconstructed echo data are weighted and fused to improve the accuracy of classification. Finally, the fused feature vectors are fed into a support vector machine (SVM) model for classification. By contrast with the conventional algorithm of aircraft target classification, the proposed algorithm can effectively process sparse echo data and achieve higher classification probability via weighted features fusion of multi-wave gates echo data. The experiments on synthetic data are carried out to validate the effectiveness of the proposed algorithm.

**Keywords:** narrow-band radar; target classification; signal reconstruction; features extraction; weighted features fusion
