The Balanced Design Of The Balanced Filter Based On The Laminated Substrate Integrated Waveguide Structure

Balanced bandpass filter(BPF)is widely used in modern communication system,due to their superior immunity to the environmental noise.Meanwhile,the substrate integrate waveguide(SIW)has become popular for its great performance at the microwave and millimeter wave band.In order to realize the miniaturation,the balanced BPF based on HMSIW and multi-mode structure have been proposed.The stacked structure can reduce the size by increasing the height of the substrate and this method can be used to design the three-dimensional circuit.Several balanced filters are mentioned in this paper,which have about 50 percent reduction in size with great performance.The details are as follows:1.A four-order Chebyshev filter based on double-layer structure is presented,which verifies the feasibility of this method.In order to improve the selectivity of this filter,we add a new coupling path to introduce the cross-coupling,resulting in quasi-elliptic filtering response.A four-order protopype is designed for demonstration with two TZs.The proposed filter exhibits high selectivity with 254.1 and 206.2 dB/GHz,and 48.4 percent reduction in size.2.Two methods are mentioned in this paper to design dual-band bandpass filter.The DM passband is designed by ultilizing the TEioi and TEiO2-mode of cavity.The desired coupling coefficients of both bands can be achieved respectively by properly setting positions and sizes of the coupling slots,and slotlines are etched to improve the common-mode(CM)suppression.The CM suppression is greater than 41 dB over the DM passband with 50 percent reduction in size.3.A dual-band balanced filter with high CM rejection is achieved by the ports distributed in different layers.Controlled TZs are generated by coupling between the two modes of cavity.The proposed filter exhibits high CM suppression of 47 dB from 1 to 17 GHz,band-to-band isolation is better than 45 dB.