This article presents a temperature sensor tri-delta appended Complementary Split Ring Resonator (CSRR) loaded circular antenna with twelve-polygon sides. A monopole Compressed Reduced Ground Plane (CRGP) along width and length, respectively, is used to improve the antenna bandwidth from narrow band to wide band, from 1.71 GHz to 3.66 GHz. The appended tri-delta to dodecagon-structure increases the patch’s overall electrical length and plays a significant role in improving bandwidth and resonance frequency close to the solution frequency 2.45 GHz. The antenna uses transformer-feed and a CSRR that result in excellent reflection coefficient ( \(\:{\text{S}}_{11}\) ) value below \(\:-\) 20 dB. This leads to an enhancement in the antenna gain, and the antenna achieves a peak gain of 5.22 dBi and a peak radiation efficiency of 95.71%. The proposed antennas not only cover applications like Internet of Things (IoT) (2.39–3.15 GHz), WLAN/Bluetooth (2.3/2.5 GHz), Wi-Fi (2.4 GHz), Wi-Bro (2.3–2.4 GHz), GSM (1.9 GHz), Bluetooth, public safety and ISM band (2.4–2.5 GHz), 3G (2100 MHz), WCDMA (1.9–2.1 GHz), 4G-LTE (2.1/2.3/2.5 GHz), PCS applications but also Wi-MAX (3.3/3.5 GHz) and 5G NR band n78 (3.2–3.6 GHz), n77 (3.3–4.2 GHz) applications. The low-cost FR-4 substrate is used ( \(\:{\epsilon\:}_{r}\) = 4.4, thickness = 1.6 mm) for designing two antennas. The metal (Cu) thickness of the patch and ground is considered as 35 μm. The fabricated antenna was miniaturized to 30.41% in comparison to the fundamental antenna. The temperature sensitivity is analyzed and investigated on cold and hot water in terms of reflection coefficient sensitivity, resonance frequency sensitivity, and their relative sensitivities. The cold water shows the negative sensitivities, while the hot water shows the positive sensitivities.
