In this paper, a low-cost compact omnidirectional antenna is presented. By directly folding a rectangular-shaped copper plate into an open-loop structure, two resonant modes are generated for tri-band operation. The shape of the rectangular has the highest yield in stamping processes for massive production. Two shorting stubs are loaded symmetrically to reduce the height of the antenna while keeping omnidirectional radiation. Moreover, a compact ground is utilized, making it more suitable to be installed on the PCB of routers. To validate the design, a prototype has been fabricated and measured. The measured −10 dB impedance bandwidths are 2.38–2.52 GHz (4.90%) and 4.16–7.40 GHz (56.06%). The gain variation in the whole operating band is less than 2.5 dB. The antenna profile and ground size are miniaturized to 0.14λ₀ and 0.52λ₀, respectively. The proposed antenna is a good candidate for Wi-Fi 6 and 6E routers, with the merits of low cost, compact size, and ease of massive production.