# Functionality Investigation of the UAV Arranged FMCW Solid-State Marine Radar
## 1 Introduction  
Unmanned aerial vehicle (UAV) related applications most frequently apply optical sensors, which provide visibility from above. Unfortunately, the abilities of such sensors are limited by atmospheric conditions and illumination. Radar sensors can be used at night and in poor visibility conditions. Radars on manned aircraft are considered conventional means for various purposes, such as surveillance of weather, ground, or other aircraft [1, 2]. The same features became a standard on UAVs [3, 4, 5], especially for specific tasks, such as ground penetration [6].  
Due to high costs and heavy weight, radars are not widely used with UAVs. There are solutions based on fixed-wing UAV platforms carrying the radars, such as the IAI Searcher or the IAI Heron, however, both of those platforms are extremely large (up to 1.2 t in case of the IAI Heron), have an extremely high price, and are used solely in military operations. The millimetre-wave radar provides an alternative solution to overcome the shortcomings of optical solutions because data in the microwave range can be acquired independently of atmospheric conditions and time of day [7, 8].  
The latest developments of mmWave technologies provide good potential for applications using UAVs due to decreased costs and weight. Usage of mmWaves allows reduction of the size of the antenna to get good range and angular resolution, but the range is limited by the order of hundreds of meters. Cheap low-power C or K-band radars can only be used as terrain estimation and altitude sensors [9, 10, 11, 12, 13]. A similar application of low power higher frequency W-band radars usually achieves slightly more detailed results [14, 15]. Another small range task for which radars are very suitable is collision avoidance and all mentioned band radars were tested for this purpose [16, 17].  
For radar applications in marine traffic or ice monitoring, the range of the order of kilometres or tens of kilometres is needed. Marine radars fulfil this requirement [17; 18].  
A concept for a scalable radio frequency (RF) sensor payload for small UAVs that can perform multiple RF functions such as a synthetic aperture radar (SAR), ground moving target indication (GMTI), and electronic support measures (ESM) was analysed and presented in [19]. The digitization of the antenna signals on transmission and reception at the antenna element level was essential to the scalable multi-function RF payload concept. The architecture of a technology demonstrator based on an X-band SAR that can perform radar and ESM functions was introduced and usage of the X-band radar on the small UAV was justified.  
In recent times, the technologies of marine radars have been rapidly growing and becoming more and more advanced. The marine radar market is big enough to provide low-cost radars for customers. The development of technologies of semiconductors such as high power transistors, integrated circuits, field-programmable gate arrays (FPGA) allows for improved radar parameters such as range, power consumption, weight, as well as decreasing the cost of radar equipment. At this time, solid-state FMCW and pulse compression radars are permanently replacing magnetron pulse radars. For our experiments, we have chosen the Simrad 4G(tm) FMCW marine radar, which we adapted to provide a possibility to integrate it on the UAV.