## 3 Circuit Level Perspectives of JCRS RF Hardware
### Antenna Implementation
#### 3.2.1 Antennas for Radar  
The characteristics of EM radiation allow for the range to be measured using radars [40]. When EM waves collide with an electrically conductive surface, they are reflected. The presence of an obstruction in the propagation path is indicated in the event these reflected waves are subsequently received at the source. In air, EM radiation moves at a constant speed that is comparable to the speed of light. The preset velocity enables the calculation of the distance amid the radar system, reflecting objects such as aircraft, ships, or automobiles by formulating the elapsed interval for the broadcast signals. Antennas constitute the most important components of the radar system owing to their ability to transmit EM waves to spaceborne signals with the requisite efficiency and to ensure that the signal maintains an appropriate spatial pattern. Additionally, antennas are in charge of providing target position updates at the desired frequency, while offering the pointing direction with the utmost accuracy. Hence, the fundamental performance of the radar system may be demonstrated to be proportional to the product of the antenna extent and the median power being transmitted. Recent developments in the mmWave technology have led to the establishment of trustworthy radars for a variety of applications; for instance, preventing obstacles, landing assistance, autonomous vehicle control, accident avoidance, roadway safety aids, weather surveillance, mapping, healthcare diagnostics, and many more [41; 42; 43]. The commercialization of mmWave radars is primarily attributed to several significant advantages that mmWaves have over lower frequency bands. Radars that operate in the mmWave range are more compact and lightweight [44]. In particular, antenna dimensions and weight can be greatly decreased, while maintaining an identical beam width and gaining performance. Single-element construction, which may include planar, metasurface, transparent material, slot, defected ground, and other types, represents relatively simple and compact mmWave antennas. However, in terms of bandwidth, gain, and efficiency,the single-element configuration performs unfavorably. Additionally, the radiation pattern is mainly omnidirectional, whereas radar applications necessitate a directed radiation pattern. These challenges can be solved by array antennas as they offer numerous benefits such as adaptive BF, wide-angle beam scanning, multiple beams, increased gain, and wide bandwidth. Generally, two modes of operation exist for radar antennas, which include scanning and tracking. All of the objects in a segment are illuminated at regular intervals when the scanning mode is active. The antenna is devoted to one particular target and automatically monitors it while it switches orientation in the tracking mode. The capacity of the antenna to accurately determine the angle error is imperative to enable automatic tracking. The angle error indicates the angle between the antenna beam's peak and the target's direction. A high signal-to-noise ratio allows for precise determination to barely any of the beam width. Two configurations--the parabolic dish and the phased array--have been traditionally used to accomplish the functions of radar antennas. A summary of their underlying concepts is provided below. Parabolic reflector: A dish antenna is made up of a parabolic reflector and a point source feed positioned in its center [45]. The innermost portion of a metal mesh-covered frame often makes up the construction of the parabolic reflector. The metallic covering serves as the reflector for the radar energy. MIMO Antennas: In comparison with single-element antennas, array antennas offer better bandwidth, gain, and radiation performance; however, there has been no significant advancement in the performance of radar systems in dense environments where line of sight communication is impracticable.