###### Abstract  
Radars are used to retrieve physical parameters related to clouds and fog. With these measurements, models can be developed for several application fields such as climate, agriculture, aviation, energy, and astronomy. In Chile, coastal fog and low marine stratus intersect the coastal topography, forming a thick fog essential to sustain coastal ecosystems. This phenomenon motivates the development of cloud radars to boost scientific research. In this article, we present the design of a Ka-band cloud radar and the experiments that prove its operation. The radar uses a frequency-modulated continuous-wave with a carrier frequency of 38 GHz. By using a drone and a commercial Lidar, we were able to verify that the radar can measure reflectivities in the order of \(-60\) dBZ at 500 m of distance, with a range resolution of 20 m. The lower needed range coverage imposed by our case of study enabled a significant reduction of the instrument cost compared to existent alternatives. The portability and low-cost of the designed instrument enable its implementation in a distributed manner along the coastal mountain range, as well as its use in medium-size aerial vehicles or balloons to study higher layers. The main features, limitations, and possible improvements to the current instrument are discussed. cloud radar; boundary layer; frequency modulated continuous wave radar; Ka-band radar 20202020  
range. Close interaction with coastal fog facilitates studies not only of macro characteristics of clouds, but also allows the study of its microphysics by using in situ measurements with multiple instruments. The possibility of interception of clouds with the coastal range motivates the establishment of an in situ regional fog observatory to obtain continuous measurements of cloud properties in the Fray Jorge national park, north of Chile. Continuous measurements can improve the understanding of physical interactions driving the fog life cycle, improving the quality of fog forecast models [1]. These models have a wide range of applications such as climate [2], aeronautics [3], and solar energy studies due to the effect of clouds in Earth radiation budget [4] and in astronomy not only for site testing, but also for observatories operation [5]. In addition, this facility is expected to serve as a calibration site for new developed remote sensing instruments that might be later used along the coastal range, as well as to serve as either calibration or ground truth for satellite products that estimate physical parameters of clouds in larger areas. Remote sensing instruments such as Radars and Lidars are key to study large scale phenomena such as clouds that defy conventional surface and upper air meteorological observations [6]. Cloud radars can estimate profiles of cloud and fog properties such as reflectivity, scatterers doppler speed, liquid water and ice content, and precipitation rate [7; 8; 9; 10; 11]. The combination of both ceilometer (Lidar) and cloud radar can provide relevant information of the internal structure of clouds as well as the boundaries of a cloud layer during continuous operational use. The ceilometer is very precise at detecting the base of a cloud layer, but cannot commonly detect the cloud top due to attenuation of the beam in the cloud. Meanwhile, cloud radars are able to penetrate the cloud, giving internal information as well as detecting the cloud top depending on the range limit of the radar and the thickness of the cloud. In addition, radars could eventually detect higher layers in the case of multilayered clouds. Cloud lower and upper limits are important to study the impact of clouds in a changing climate. High-resolution observations of the cloud and fog boundaries can help modelers verify and improve local fog prediction models or numerical weather prediction climate models.