Abstract: Radio frequency identification (RFID) tags have been used for the nondestructive detection of quality deterioration in fresh meat. However, conventional chipless RFID can suffer from insufficient radiation gain, poor directional focusing, and environmental humidity interference due to frequency drift and unstable echo signals. In this study, a spiral-array RFID tag was designed using high-frequency electromagnetic simulation software, according to the rotation phase. The structural parameters of the spiral array were optimized to enhance electromagnetic coupling among array elements. A systematic analysis was also conducted to optimize the resonant characteristics, input impedance matching, and radiation performance of the array tag using electromagnetic simulation. Cooperative radiation improved the directional focusing of the array elements. In the experiment, the ammonia-sensitive layer was selected as an MXene/In₂O₃ composite material, according to the heterojunction synergistic effects. The high electrical conductivity of MXene was effectively combined with the excellent gas-sensing properties of In₂O₃. Volatile ammonia adsorption was enhanced to stabilize the electrical response behavior. The composite material was uniformly deposited onto the sensitive region of the spiral array tag using screen-printing. Thereby, a chipless RFID spiral array ammonia sensor was fabricated to realize integrated coupling between the gas-sensitive material and the radio frequency resonant structure. A radio-frequency sensor system was established to validate practical applicability. Fresh shrimp was taken as the target of quality deterioration in fresh agricultural products. The amplitude response characteristics of the sensor return loss (S₁₁) were obtained before and after ammonia adsorption. Since S₁₁ resonant frequency drift was induced by humidity variations, the coupling mechanism between humidity-induced S₁₁ amplitude response and frequency response was clarified to reduce the influence of humidity interference on the performance. An S₁₁ amplitude-frequency response separation was proposed to effectively decouple the humidity-induced resonant frequency drift signal from the ammonia-induced amplitude response, indicating humidity interference compensation and the reliability of ammonia detection. Simulation and experimental results show that the spiral array structure led to a 20.17% decrease in the S₁₁ magnitude of the tag and a 102.33% enhancement in the radiation gain along the Z-axis, compared with conventional single-tag structures. Electromagnetic energy coupling and radiation capability were effectively strengthened on the tag surface. The sensor exhibited a better linear response relationship with a sensitivity of 0.65 dB·L/mg in an ammonia concentration range of 0~15 mg/L. Humidity variations caused both S₁₁ resonant frequency drift and amplitude fluctuations during testing. By employing the humidity interference compensation strategy, the concentration detection error of the sensor was significantly reduced by 91.89% under 80% relative humidity. The signal decoupling strategy effectively improved detection accuracy under high-humidity conditions. Furthermore, the sensor exhibited excellent packaging penetrability and low-temperature adaptability, where its sensing response was attenuated by only about 2% at low temperature. In summary, the chipless RFID spiral array ammonia sensor shared the high radiation performance, humidity interference, and detection stability. The array structure with the S11 amplitude–frequency decoupling can effectively improve wireless sensing reliability in complex environments. The sensor can be effectively applied to the wireless nondestructive detection of quality deterioration in fresh meat, such as fresh shrimp, during cold chain storage and transportation.