A miniaturization of compact band-pass filter with radial stubs utilizing modified composite right/left-handed structure

摘要

A novel compact band-pass filter (BPF) with radial stubs (RS) utilizing modified composite-right/left-handed (CRLH) structure is proposed. A pair of microstrip RS is loaded as a combination of inductance and capacitance, which creates a transmission zero at the upper stop band. By introducing the magnetic coupling to the traditional interdigital coupled lines, two more transmission zeros are created. In addition, the fractional bandwidth is just more than 30% contrasted with super-wide BPF implemented by traditional CRLH transmission lines(CLRH-TL). Due to the good performance of out-of-band rejection and to guarantee the compactness in size, only one unit cell is adopted. The interdigital coupled lines are used to realize the strong coupling for the design which is shown to have the compact size of 0.132λ_g × 0.183λ_g (λ_g is the guided wavelength at the center frequency of 2.45 GHz). The insertion loss is no more than 1.7 dB in the pass band from 2.28 GHz to 2.62 GHz, and the spurious response up to 2f_0 is controlled effectively with more than 20 dB attenuation from 3.5 GHz up to 6.0 GHz, where f_0 is the pass band center frequency. Simulated and measured results are in good agreement with each other.