Realisation of compact quasi‐elliptic bandpass filters based on coupled eighth‐mode SIW cavities

Abstract

A novel basic quasi‐elliptic response bandpass filter in quadruplet based on coupled TE101‐mode‐based eighth‐mode substrate integrated waveguide (EMSIW) cavities is proposed and analysed firstly. The negative cross coupling is achieved by the nature of coupled fringe electric‐field components of the first and fourth cavities. Then, based on the proposed basic quadruplet structure, two methods using a step‐impedance resonator and meandered feeding lines, respectively, are introduced and analysed to realise S‐L coupling to improve the upper stopband performance further. Finally, two possible structures with quasi‐inline and quasi‐folded layouts, respectively, are proposed to realise sixth‐order EMSIW filters. Five EMSIW filters are designed, fabricated, and measured to demonstrate and verify the proposed structures. The proposed filters have the advantages of compact size, good out‐of‐band rejection and realisation of higher‐order filtering function. The size of the realised 4th‐/6th‐order filter is less than 0.13/0.17λg2. The out‐of‐band rejection higher than 28 dB can reach 2.32f0.

A Low-Profile Half-Mode Substrate Integrated Waveguide Filtering Antenna With High Frequency Selectivity

“…Various antennas have been developed to obtain excellent filtering performances, including Yagi Uda antennas [1], dielectric resonator antennas [2][3][4][5][6], microstrip patch antennas [7][8][9][10][11], and substrate integrated waveguide (SIW) antennas. Due to the virtues of low loss and high radiation efficiency, SIW has been widely applied to design excellent filtering antennas [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. By vertically stacking the resonators, multilayered 3-D configurations are designed in [14][15][16][17][18][19].…”

“…Although these multilayered configurations make the frequency selectivity improved, they bring about high profile and fabrication complexities. Given this, the filtering antenna using a single-layered SIW cavity was proposed in [20][21][22][23][24][25]. Conventional SIW cavities were employed to enhance the selectivity of channel responses in [22].…”