###### Abstract  
This contribution handles a single-channel radar method that utilizes frequency-coded sub-channels for enabling cross-range resolution. Because of the sub-channel coding, the whole area of interest (AOI) is scanned within a single radar measurement. To further enhance the cross-range resolution, the sub-channels' antenna beams are overlaid in this work, resulting in multiple coding signatures. Next to the operation theory, hardware components, such as coding filters and antennas, as well as signal processing methods, are presented and discussed in detail. A final measurement campaign that investigates several radar scenarios reveals high detection properties and proves the applicability of the proposed radar method.  
scanning radar; radar resolution; frequency coding; FMCW +
Footnote †: journal: Sensors  
0000-0001-5000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-0000-00000-00000-00000-00000-00000-00000-000000-000000-00000-00000-000000-0  
The above-mentioned methods have in common that the actual scanning process is performed in time-multiplex, which means that scans of different areas are carried out consecutively. Consequently, the overall scanning time hardly relies on the number of scanning directions and the system's reconfiguration speed. This however leads to the obvious contradiction of scanning resolution, system complexity, and scanning speed. In order to overcome this drawback, the time-multiplex scanning philosophy can be changed to a frequency- or code-multiplex, leading to instantaneous scanning and single measurement scanning coverage. In [18; 19], the authors propose a dispersive scanning antenna, which distributes the available bandwidth to different radiation directions. In terms of scanning speed, this approach is promising, because a single radar measurement covers the whole AOI. Unfortunately, the proposed bandwidth distribution leads to strongly reduced range resolution as the total bandwidth was split up and is reduced in every cross-range direction. Most recently, a radar channel frequency coding method was introduced in [20], which overcomes this drawback. Here, the scanning directions are divided into radar sub-channels, each containing a unique, passive coding filter and antenna. All sub-channels are summed up so that a single measurement from a radar transceiver covers the whole AOI by preserving maximum range resolution. However, in this previous work, antenna beams were strictly decoupled to avoid cross-talk. Consequently, every scanning direction demanded a unique sub-channel. Hence, the cross-range resolution cells corresponded to the number of sub-channels, leading to complex hardware requirements.  
Therefore, we propose an advanced, cross-range resolution enhancing method in this contribution. By investigating radar beam overlapping areas, the amount of cross-resolution cells can be increased by keeping the number of sub-channels constant. Moreover, we introduce several hardware components which are mandatory for the proposed method and discuss their performances in detail. Finally, an unsupervised signal-processing method is introduced and compared to the supervised signal processing from [20] in an open range test scenario. The work is structured as follows: Section 1 explains the fundamentals of the radar-channel frequency coding method and discusses possible multi-target scenarios. In Section 2, essential hardware components, i.e., antennas and coding filters are presented, and their performance is demonstrated in simulations and measurements. While Section 3 introduces two different signal processing methods for target classification, Section 4 proves the proposed concept in a wide range measurement campaign. Finally, Sections 5 and 6 discuss the presented results and conclude the paper, respectively.