A dual-frequency antenna (100) includes a ground plane (105) that is substantially planar and a radiator (110) that is substantially planar and formed of a conductive material. A slot (115) having first and second ends is formed in the radiator (110), and first and second apertures (120, 125) are formed at the first and second ends, respectively, of the slot (115). The radiator (110) also includes transmission connections (140) for coupling to external transmission circuitry and receiving connections (130) for coupling to external reception circuitry. The transmission connections (140) and the receiving connections (130) are located along the slot and separated by a distance of approximately one-quarter wavelength. Preferably, the height of the antenna (100), i.e., the distance between the radiator (110) and the ground plane (105) is equal to or less than about 1.9 centimeters for low-profile mounting on truck-drawn trailers.
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