DESIGN OF LOW-PASS FILTER USING MEANDER INDUCTOR AND U-FORM HI-LO TOPOLOGY WITH HIGH COMPACTNESS FACTOR FOR L-BAND APPLICATIONS

In this paper, novel compact low-pass filters using Hi-Lo technique and meander method are proposed. Series of the proposed filters are designed by adding modifications along the microstrip line (meander inductor) and by using U-form topology. The size of the proposed filter can be reduced by 15% compared to the conventional filter while maintaining the optimal low-pass features. The compact meander LPF consists of two thin microstrip lines, which are connected with 50 Ω microstrip feed lines and a microstrip patch placed in the middle of the structure. The thin lines and the microstrip patch correspond to inductance and capacitance, respectively. The proposed meander Hi-Lo topology has been mounted on an RO4003 substrate with a relative dielectric constant εr = 3.38, thickness h = 0.813 mm and loss tangent 0.0027. The compact L-band low-pass structure has a size of (0.263λg ×0.175λg) where λg = 57 mm is the wavelength at the cutoff frequency 2.85 GHz. In addition to a good compactness, the structure exhibits a simple design, very low insertion loss in the passband (L-band) of less than 0.3 dB, and it achieves a wide rejection bandwidth with a 20 dB attenuation from 5.3 to 6.3 GHz. The excellent LPF characteristics are verified through simulations and measurements where a good consistency can be observed. Such compact filter structures are expected to be used in various microwave system applications.