Abstract: A slot antenna structure includes a metal trough and two metal plates. The metal trough includes a metal bottom plate, two metal sidewalls erected on two opposite long sides of the metal bottom plate respectively, two metal closing walls erected on two opposite short sides of the metal bottom plate respectively, and an opening formed and surrounded by the metal sidewalls and the metal closing walls. The metal plates are provided on the opening. A slot is formed between the metal plates and extends in a straight line to separate the metal plates. An electrical unit is provided on the metal plates and astride the slot. The metal plates and the metal trough form a resonance chamber in communication with the slot. The depth from the opening to the inner bottom side of the metal trough is generally one eighth of the wavelength of an input signal.

Abstract: A SINR-based intrusion detection system comprises a first antenna, a second antenna, and an arithmetic unit connected to the second antenna. The first antenna simultaneously transmits one or plural beams having mutually different frequencies in an enclosed space so as to cover the enclosed space. The second antenna receives signals of the one or plural beams so as to capture signal parameters of the beam. The arithmetic unit is connected to the second antenna and detects the signal parameters in an always-on manner so as to obtain a SINR value from the signal parameters, comparing the SINR value to a predetermined threshold range, and determining that there is object intrusion when the SINR value falls within the predetermined threshold range.