Compact balanced bandpass filter using isosceles right triangular patch resonator

A compact balanced bandpass filter (BPF) by using the isosceles right triangular patch resonator is presented. Stemming from the mode degeneration properties of the square patch resonator with single excitation located at its corner, the specific current distribution on this square patch resonator is investigated. Based on that, a new type of half-mode square patch resonator named as the isosceles right triangular patch resonator is derived and proposed. Afterwards, resonant properties of the new patch resonator under different excitation forms are also investigated. Subsequently, balanced BPF has been implemented by adopting appropriate coupling structure among four isosceles right triangular patch resonators. Finally, to verify the design concept, a second-order Chebyshev balanced BPF centred at 2.44 GHz with 3 dB fractional bandwidth of 6.15% is designed and fabricated. Good agreement can be observed between the simulated and the measured results.