material it is connected to three lateral microstrips 58 60 and 62 constituting branches disposed transversely relative to the microstrip 56 and having the same width and the same nature thereas to be more precise a first end of the lateral microstrip 58 is connected to the end 51 of the transmission microstrip 56 a first end of the lateral microstrip 60 is connected to a central portion 61 of the transmission microstrip 56 and a first end of the lateral microstrip 62 is connected to the other end 55 of the microstrip 56 in this embodiment the second ends of the microstrips 58 60 62 are not connected to anything the resonators 64 and 66 are of standard design they are ceramic cylinders made of alloys containing magnesium calcium titanium barium zinc zirconium or tin these ceramic materials have high dielectric constants u03b5 r i e dielectric constants at least equal to 10 the microstrips 58 60 62 and the dielectric resonators 64 and 66 have characteristics such that and are disposed so that some frequencies are attenuated by dissipation of energy due to resonance of the lateral micro strips 58 60 62 and the resonators 64 and 66 coupled to the lateral microstrips 58 60 62 in particular the lateral microstrip 60 is coupled both to the resonator 64 and to the resonator 68 in this embodiment the microstrips 58.