## 1 Introduction  
To date, radio frequency (RF) harvesters offer exceptional advantages over other sources of ambient solar energy, such as solar, acoustic, and mechanical vibration harvesters. The various notable characteristics of RF energy harvesting technology, including reliability, predictability, controllability, and the ability to simultaneously supply energy to different nodes, have made it the preferable option for certain areas or applications [1, 2]. Interestingly, the marginal total energy harvested allows it to be applied in many applications that expect lower power consumption and contain many nodes [3]. The RF energy can be divided into ambient and intended RF [3]. The intended RF emits an RF signal from an RF transmitter directly to a specific area [4]. The advanced development of semiconductor technology and the fabrication process allow for the RF-EH concept realization. The conversion of energy in electromagnetic waves (EM) into valuable electrical energy in RF-EH facilitates the real application of continuous operating sensors [5]. On the other hand, however, the ambient radiofrequency energy is accessible over a broad range of frequency bands, such as LTE (750-800 MHz), DTV (550-600 MHz), UMTS (2150-2200 MHz), GSM-900 (850-910 MHz), GSM-1800 (1850-1900 MHz), Wi-Fi (2.4-2.45 GHz), band for television (TV) and radio applications (900 MHz-2 GHz), ISM (2.1-2.6 GHz), UWB (3.1-10.6 GHz), WLAN (3.1-4.4 GHz), HIPERLAN (5.1-5.3 GHz), and C-BAND (4.4-5 GHz) [6]. Increasing attention is being paid to energy-harvesting technologies that use ambient power sources, including heat, vibration, and electromagnetic waves. The self-sustaining \"Zero-Power\" standalone electronics have been developed in various energy harvesting systems, such as circuitries, topologies, and energy harvesting devices [7]. Currently, Wi-Fi, Wi-MAX, and GSM applications are more favored because of the services provided, including voice and video calls, short message service (SMS), high-speed data transfer, and broadly accessible internet access. These functional applications are utilized in mobile phones, laptops, and other portable devices that radiate plentiful amounts of RF energy, which can be harvested [8]. Harvesting RF energy is all about protecting RF energy from the radio environment and putting it to use in low-voltage electronic devices. Antennas-like patches with ultra-wideband properties or narrow-band antennas are required to detect radio frequency energy emitted by the radio environment. However, the utilization of the latter depends on the frequency bands that are going to be detected. For instance, an antenna with narrowband properties is required to detect GSM-900 frequencies. In addition, multiple-input-multiple-output systems are employed to improve the functional properties of wireless communication systems [9]. Meanwhile, the disposal of battery waste has become a significant issue in the last few years. Battery waste is mainly disposed of in landfills, which would lead to land pollution and the contamination of underground water due to the dissipation of harmful chemicals from the battery. Besides applying wireless power harvesting (WPH) technology to minimize the reliance on batteries, avoiding the use of batteries is the most effective solution to reduce the issue of battery waste, although it is not ideal [6]. In view of this, wireless RF power harvesting is considered a promising approach to replace or increase the lifespan of batteries. In fact, the ability of RF-EH via ambient RF energy provides an alternative method to reduce the cost of regular maintenance in terms of device improvement [10]. It has been explored [11; 12; 13; 14; 15] if radiofrequency energy can be used to replace batteries in low-power embedded systems, given the various energy sources available in the environment. Although the main perspective is to improve the lifespan of multipurpose electronic components, the RF-EH technology is feasible and distinguished through the required applications and its ability in philosophical design.