Filter device (100; 200; 300; 400; 450) with an electrically conducting strip structure, comprising: - a transmission line (102; 202; 302; 402; 452) formed by an electrically conducting strip printed on a surface of an electrically insulating substrate (104; 204; 304; 404; 454), said conducting strip having two ends (102 IN , 102 OUT ; 202 IN , 202 OUT ; 302 IN , 302 OUT ; 402 IN , 402 OUT ; 452 IN , 452 OUT ) respectively forming the two sole input and output connection ports of the filter device (100; 200; 300; 400; 450), - a plurality of resonators (106 1 , ..., 106 M ; 206 1 , ..., 206 M ; 306 1 , ..., 306 M ; 406 1 , ..., 406 M ; 456 1 , ..., 456 M ), each resonator comprising an electrically conducting strip printed on said surface of the substrate (104; 204; 304; 404; 454), - the conducting strip of each resonator (106 1 , ..., 106 M ; 206 1 , ..., 206 M ; 306 1 , ..., 306 M ; 406 1 , ..., 406 M ; 456 1 , ..., 456 M ) has a first end (108 1 , ..., 108 M ; 208 1 , ..., 208 M ; 308 1 , ..., 308 M ; 408 1 , ..., 408 M ; 458 1 , ..., 458 M ) coupled to the transmission line between the two connection ports and at least one second end (110 1 , ..., 110 M ; 210 1 , ..., 210 M ; 310 1 , ..., 310 M ; 410 1 , ..., 410 M ; 460 1 , ..., 460 M ) that is free or connected to a ground so as to create an effective fundamental resonant wavelength specific to each resonator on said surface of the substrate, the filtering device being characterized in that : - for each pair of neighbouring resonators of the plurality of resonators, the distance (e 1 , ..., e M-1 ) between the first ends of two neighbouring resonators of this pair is less than one tenth of the smallest effective fundamental resonant wavelength of the plurality of resonators (106 1 , ..., 106 M ; 206 1 , ..., 206 M ; 306 1 , ..., 306 M ; 406 1 , ..., 406 M ; 456 1 , ..., 456 M ) on said surface of the substrate. - a transmission line (102; 202; 302; 402; 452) formed by an electrically conducting strip printed on a surface of an electrically insulating substrate (104; 204; 304; 404; 454), said conducting strip having two ends (102 IN , 102 OUT ; 202 IN , 202 OUT ; 302 IN , 302 OUT ; 402 IN , 402 OUT ; 452 IN , 452 OUT ) respectively forming the two sole input and output connection ports of the filter device (100; 200; 300; 400; 450), - a plurality of resonators (106 1 , ..., 106 M ; 206 1 , ..., 206 M ; 306 1 , ..., 306 M ; 406 1 , ..., 406 M ; 456 1 , ..., 456 M ), each resonator comprising an electrically conducting strip printed on said surface of the substrate (104; 204; 304; 404; 454), - the conducting strip of each resonator (106 1 , ..., 106 M ; 206 1 , ..., 206 M ; 306 1 , ..., 306 M ; 406 1 , ..., 406 M ; 456 1 , ..., 456 M ) has a first end (108 1 , ..., 108 M ; 208 1 , ..., 208 M ; 308 1 , ..., 308 M ; 408 1 , ..., 408 M ; 458 1 , ..., 458 M ) coupled to the transmission line between the two connection ports and at least one second end (110 1 , ..., 110 M ; 210 1 , ..., 210 M ; 310 1 , ..., 310 M ; 410 1 , ..., 410 M ; 460 1 , ..., 460 M ) that is free or connected to a ground so as to create an effective fundamental resonant wavelength specific to each resonator on said surface of the substrate, the filtering device being characterized in that : - for each pair of neighbouring resonators of the plurality of resonators, the distance (e 1 , ..., e M-1 ) between the first ends of two neighbouring resonators of this pair is less than one tenth of the smallest effective fundamental resonant wavelength of the plurality of resonators (106 1 , ..., 106 M ; 206 1 , ..., 206 M ; 306 1 , ..., 306 M ; 406 1 , ..., 406 M ; 456 1 , ..., 456 M ) on said surface of the substrate. <EOS>