# An Efficient Digital Channelized Receiver for Low SNR and Wideband Chirp Signals Detection
## 1 Introduction  
Radar reconnaissance uses reconnaissance receivers to monitor the electromagnetic environment, intercept radiation source signals, and measure and analyze radiation source parameters [1]. Radar reconnaissance is an essential means of obtaining battlefield intelligence and a prerequisite for implementing electronic jamming and destruction [2]. Synthetic aperture radar (SAR) is capable of all-weather imaging reconnaissance and plays a vital role in high-tech warfare. Anti-SAR reconnaissance is an important research topic [3, 4, 5]. Wideband chirp signals with a low signal-to-noise ratio (SNR) are widely used in SAR [6, 7, 8]. Intercepting low SNR wideband chirp signals with high estimation accuracy is challenging. On the one hand, wide instantaneous bandwidths lead to high signal sampling rates, resulting in high processor speeds. However, the digital signal processing equipment's processing rate always lags behind the analog-to-digital converter's sampling rate (ADC) [9]. On the other hand, the low SNR will affect signal detection and increase the estimation error. In addition, computational efficiency should be taken into consideration due to the time-sensitive nature of radar reconnaissance. This paper aims to investigate wideband receiver architecture to intercept low SNR chirp signals efficiently. Digital channelization techniques are a good solution for processor rate mismatch [10; 11; 12]. However, to have continuous coverage across the instantaneous bandwidth (IBW), the responses of adjacent channels are overlapped. For many traditional uniform channelization structures, such as polyphase filter structures [13; 14] and FFT-based filter structures [15; 16], overlapped channel response will cause signal spectrum aliasing due to the filter bandwidth being greater than the channel sampling rate, resulting in inaccurate spectrum measurement. A simple and efficient solution uses a non-critically sampled channelization structure [17; 18; 19]. By reducing the signal extraction multiple, the channel sampling rate is increased to ensure that the channel sampling rate is greater than the filter bandwidth [19]. However, existing non-critically sampled channelization structures cannot minimize the channel sampling rate because the channel number is multiple of the decimation number [17]. Another solution is to use a dynamic channelization structure [20; 21; 22; 23]. Dynamic channelization adopts an analysis-synthesis structure. The original signal is channelized by the uniform filter bank first. Then, the output of the uniform filter bank is analyzed to judge the effective signals in channels. Finally, the effective signal is sent to the comprehensive filter bank to complete the reconstruction. The reconstructed wideband signal is used to measure the signal parameters The dynamic channelization method requires one more step of wideband signal reconstruction than the conventional method, which consumes many computing resources to meet the complete reconstruction conditions. They are not suitable for flexible and efficient radar countermeasure systems. The channelization filter bank decomposes the wideband signal into multiple low-rate narrowband signals, requiring a frequency measurement module placed at the output of each channel due to the frequency estimation accuracy being limited to \(\pm 1/2\) the channel bandwidth. The frequency measurement module is mainly implemented by the Coordinate Rotation Digital Computer (CORDIC) algorithm in the digital channelized receiver [24; 25; 26], which is simple and efficient. Nevertheless, the frequency measurement error cannot meet the requirement when the SNR is low. The advanced frequency estimation algorithms have great estimation accuracy [27; 28; 29], but they are unsuitable for the signal interception application due to the low calculation efficiency. Wideband signals are decomposed into narrowband signals through channelization filter banks, and the parameter measurement results of narrowband signals need to be combined to obtain wideband signal parameters.