Suppression Of Undesired Modes Research Articles

A Design Method for Mode-Selective Waveguide Couplers in Dual-Polarized Wideband Matched-Feed Antennas

A novel type of multihole directional coupler is presented as well as a design method involving novel procedures. The device couples two orthogonal TE11 modes in a circular waveguide into two orthogonal TE21 modes with specified excitations in a surrounding coaxial waveguide, which has the circular waveguide as the inner conductor. A simple, novel analytical procedure is used to determine azimuthal hole positions, such that each of the input modes couples to only the desired coaxial TE21 mode. The method is applied to a specific coupler which is designed to couple −14 dB to both higher order coaxial modes in the band from 10 to 14 GHz. The suppression of undesired modes is generally better than 40 dB. The coupler is intended for broadband dual-polarized matched feeds, which are able to compensate for the intrinsically high cross polarization of offset single reflector antenna systems.

An alternative method for suppressing undesired transverse modes in longitudinally coupled SAW resonator filters

As known, perturbing transverse modes arising from the waveguide properties of the interdigital transducers and reflectors can appear in SAW resonator filters. Usually, these undesired modes are suppressed by transducer apodization. This method has the disadvantage of increasing the transducer impedance. We propose a longitudinally coupled resonator filter, the basic elements of which are able to guide the two slowest waveguide modes alone, but to excite and receive the first mode only. The basic elements are arranged side by side forming the complete filter permitting coupling with each other weak enough to fulfill the filter specification. The suppression of undesired modes by the construction is demonstrated by transmission measurements.