Abstract: An impedance-matching coupler (1) comprises a dielectric substrate (10) onto which a conducting strip (12) is disposed. A dielectric layer (14), preferably a dielectric film, is formed on top of the conducting strip and the first dielectric layer to encircle the conducting strip. A metallic layer (16, 18) is finally provided on top of the dielectric layer. The dielectric layer has a dielectric constant that is substantially higher that the dielectric constant for the dielectric substrate, preferably more than ten times higher. A dielectric film with a thickness of less than 100 ?m is advantageous, preferably between 5 and 100 ?m, and even more preferably between 10 and 70 ?m. The thickness of the dielectric substrate is preferably larger than for the dielectric film, preferably more than ten time larger. The conducting strip has preferably a constant width. The dielectric film thickness is preferably larger than 10% of the conducting strip width.