Which of the following devices can be used for impedance matching at radio frequencies?
Why Impedance matching just means transforming one impedance into another so power transfers efficiently, and several components do that at RF. A transformer changes impedance by the square of its turns ratio (a 2:1 turns ratio gives a 4:1 impedance ratio). A Pi-network of two capacitors and an inductor, the classic tube amplifier output network, transforms the plate impedance down to 50 ohms and filters harmonics at the same time. A length of transmission line also transforms impedance, the best known case being the quarter-wave matching section where Z0 equals the square root of the two impedances being matched.
Watch out Picking only the transformer is the usual trap because it is the familiar low frequency example, but at RF the LC network and the quarter-wave line section are just as standard.
Turns ratio, LC network, or a piece of coax: all three can transform impedance.