Abstract: A frequency-scanned end-fire phased-array antenna includes a board, a sinuous transmission line formed on the board, a plurality of end-fire antennas, and a plurality of couplers corresponding to the end-fire antennas, such that the transmission line is selectively coupled to the plurality of end-fire antennas via the plurality of couplers, for selectively coupling energy within the transmission line to the end-fire antennas. By varying the input frequency to the antenna over a narrow range, the direction of a main radiation beam emitted by the antenna can be scanned .+-.90 degrees from broadside. A single antenna board produces a frequency-scanned fan beam. Stacked antenna boards can produce a frequency-scanned pencil beam, or several independent frequency-scanned fan beams at different frequencies. The present antenna can operate in the microwave, millimeter-wave, terahertz, infrared, or optical frequency range.