The equivalent circuits of a compact Quasi-Elliptic low-pass filter (QELPF) are derived from the Chebyshev prototype circuits by introducing an attenuation pole

which has excellent performance in selectivity and harmonic suppression. The inductances in series branch circuits of QELPF are realized by dumb-bell-shaped defected ground structures(DB-DGSs)

the high external quality factor of LC parallel resonance circuits in series branch circuits are realized by spiral-shaped defected ground structures (SP-DGSs)

and the shunt capacitances are realized by broadened microstrip lines. Since the design expressions are all analytical

this design process of QELPF is fast and accurate. Finally

a five-pole QELPF for 2.4GHz is developed. The simulated and measured results show that passband insert-loss is less than 0.5dB and the stopband width with 20dB attenuation is over 13GHz.Furthermore

its size in the lengthwise direction is only about 1/4 wavelength.