Varactor element (Dl; D2) having a junction region, in which the depletion capacitance of the varactor element varies when a reverse bias voltage is applied to the varactor element. The varactor element (Dl; D2) has an exponential depletion capacitance- voltage relation, e.g. obtained by providing a predetermined doping profile in the junction region. The varactor element (Dl; D2) can be used in a narrow tone spacing varactor stack arrangement, in which two varactor elements (Dl; D2) are connected in an anti-series configuration. A low impedance path for base band frequency components between a control node and each of two RF connection nodes is provided, while for fundamental and higher order harmonic frequencies, a high impedance path is provided.