Microwave filter consisting of at least three composite resonators located in a same reference plane or in parallel reference planes, and at least one coupling means (V; 4, 8) between any two adjacent composite resonators, each composite resonator comprising a cavity (A; B; 2; 21-24) and a dielectric resonator (R; 3) housed inside said cavity, wherein: - the composite resonators are configured to have a first and a second resonant frequencies corresponding respectively to a first and a second degenerated orthogonal HEM11 modes comprising electric field and magnetic field patterns, the first resonant frequency corresponding to the central frequency of the filter; - each reference plane is perpendicular to the height dimension of the cavities and sections the respective dielectric resonator into two symmetrical halves, the electric field patterns of the two degenerated orthogonal HEM11 modes being turned 90° with respect to each other on the respective reference plane, - any composite resonator comprises a same asymmetry means configured to provide a separation in resonant frequency between the two degenerated orthogonal HEM11 modes, such that the filter can be operated with the first HEM11 mode as a single mode, the respective electric field patterns of each of said composite resonators being in a parallel arrangement, said asymmetry means being an asymmetrical geometric shape of the cavity, or a symmetrical geometric shape of the cavity with an aspect ratio other than unity between the dimensions on different axes of symmetry of the cavity, or an asymmetrical or off-centred arrangement of the dielectric resonator in the cavity, or an off-centred arrangement of an adjustment element with respect to the centre of the composite resonator; - part of the coupling means (V; 4, 10) define a sequential order of the composite resonators, corresponding to a main path of the signal, by a coupling between the first HEM11 modes of said composite resonators, and the rest of the coupling means comprise at least one cross coupling between two composite resonators spatially adjacent and not consecutive in the sequence by a coupling between the first HEM11 modes of said two composite resonators. - the composite resonators are configured to have a first and a second resonant frequencies corresponding respectively to a first and a second degenerated orthogonal HEM11 modes comprising electric field and magnetic field patterns, the first resonant frequency corresponding to the central frequency of the filter; - each reference plane is perpendicular to the height dimension of the cavities and sections the respective dielectric resonator into two symmetrical halves, the electric field patterns of the two degenerated orthogonal HEM11 modes being turned 90° with respect to each other on the respective reference plane, - any composite resonator comprises a same asymmetry means configured to provide a separation in resonant frequency between the two degenerated orthogonal HEM11 modes, such that the filter can be operated with the first HEM11 mode as a single mode, the respective electric field patterns of each of said composite resonators being in a parallel arrangement, said asymmetry means being an asymmetrical geometric shape of the cavity, or a symmetrical geometric shape of the cavity with an aspect ratio other than unity between the dimensions on different axes of symmetry of the cavity, or an asymmetrical or off-centred arrangement of the dielectric resonator in the cavity, or an off-centred arrangement of an adjustment element with respect to the centre of the composite resonator; - part of the coupling means (V; 4, 10) define a sequential order of the composite resonators, corresponding to a main path of the signal, by a coupling between the first HEM11 modes of said composite resonators, and the rest of the coupling means comprise at least one cross coupling between two composite resonators spatially adjacent and not consecutive in the sequence by a coupling between the first HEM11 modes of said two composite resonators.