A combined isolator diplexer device 100 comprising: a combining circuit having first and second inputs 120,112 to respectively receive radiation from radio frequency (RF) and microwave channels； an output 116 for conveying the RF and microwave radiation to a common signal-pathway； and a waveguide isolator to isolate the microwave-channel from the RF radiation. The waveguide isolator comprising respective conductive input and output sections 102,106 and a conductive intermediate section 104. Intermediate-section 104 comprising: first and second ends to respectively mate with input & output sections 102,106； a first DC isolation barrier between input & intermediate sections 102,104； and a second DC isolation barrier between intermediate & output sections 104,106. Input, intermediate and output sections 102,104,106 form a waveguide cavity, where the combining-circuit output includes signal and ground conductors, where the first and second DC isolation barriers provide a pair of series connected capacitive structures between the ground-conductor and waveguide-isolator input section 102, the capacitive structure being arranged to inhibit RF coupling and leakage of microwave energy. At the first DC isolation barrier, an insulating layer may be positioned between input and intermediate sections 102,104 and the second DC-isolation-barrier may have an insulating layer between the output and intermediate sections 106,104.L'invention concerne un dispositif combiné isolateur-diplexeur pour fournir de l'énergie radiofréquence (RF) et de l'énergie micro-onde obtenues à partir de sources séparées à une sonde par l'intermédiaire d'un trajet de signaux commun. L'invention combine en une seule unité tous les composants nécessaires pour isoler un canal hyperfréquence d'un canal RF tout en fournissant une tension de tenue élevée (par exemple supérieure à 10 kV). Le dispositif comprend un isolateur de guide d'ondes pour isoler le canal de micro-ondes ayant une paire de barrières d'isola
