This thesis aims to develop a chipless passive sensor capable of accurately measuring the time-varying electric field up to 14 kVpp/m with a dynamic range of 3 Hz to 1 kHz near high-voltage apparatus. It also has a sensitivity of 1.86 (kHz)/(V/m), and can be interrogated from a distance of 80 cm. The feasible maximum bandwidth of the external electric field is up to 50 kHz overall. As a passive device, the sensor requires no power source or batteries. The design features a multi-layered stacked printed circuit board (PCB) structure with a chipless cavity resonator in the industrial, scientific, and medical band of 2.4-2.5 GHz, that is based on contactless air-filled substrate integrated waveguide (CLAF-SIW) technology and includes an air cavity surrounded by a low-impedance electromagnetic band gap (EBG) structure. This design simplifies the fabrication of AF-SIW structures and offers a measured high unloaded Q-factor of up to 1340 while reducing dielectric loss. An aperture-coupled microstrip patch antenna is integrated with the CLAF-SIW resonator creating a compact, robust structure that does not require an external commercial antenna. Calibration techniques and far-field measurement results are presented using a wireless experimental setup to assess the performance of the compact sensor. The sensor resonant frequency is measured using a ringback-based wireless interrogation system. The CLAF-SIW sensor provides a high unloaded quality factor necessary for long- distance ringback-based interrogation. It is designed to detect fast time-varying measurands, such as AC electric fields. The multi-layered stacked sensor design allows easy replacement and modification of ground planes, allowing its use for other sensing applications, such as temperature and strain sensing. This thesis also explores wireless temperature sensing in a far-field scenario, where temperature variations cause shifts in the resonant frequency due to changes in the dielectric constant and dimensions of the structure.