Abstract
Abstract In this paper, a compact elliptic-response microstrip low pass filter (LPF) is presented with a wide stop-band using stepped impedance resonators. With high attenuation in the stop-band, the overall size reduction of the proposed filter is achieved using a novel defected ground structure technique using an interdigital capacitor and complementary split ring resonator (CSRR). A 4.2 GHz LPF is designed and simulated on FR4 substrate and a stop band of 8.8 GHz is obtained by utilizing interdigital and complementary split ring resonator. Results further show that the use of U-shaped high impedance line on the top layer of filter enhances the stop-band bandwidth by 2.2 GHz. In the final design, the passband insertion loss is found below 0.5 dB, and –10 dB is obtained over a band from 5.06 GHz to 17.06 GHz between input and output ports. The normalized circuit size of the filter is 0.417× 0.202 and the figure of merit is calculated about 55 at the cut-off frequency. These proposed LPFs have promised significant advantages in the stop-band characteristics with an acceptable roll-off rate for spurious-free communications.
Highlights
Microwave filter is designed to filter out undesired signals like outside band frequencies, harmonics, and spurious mixing products to reduce the system noise
For an improvement in the stop-band, we introduced a simple rectangular shape slot as a defected ground structure (DGS) just below the three high-impedance lines of top layer [3]
The results showed that the insertion loss in the low frequency passband is less than 0.5 dB from DC to 4 GHz and the stop-band of 6.1 GHz BW is obtained corresponding to the 10 dB attenuation for the initial filter design
Summary
Microwave filter is designed to filter out undesired signals like outside band frequencies, harmonics, and spurious mixing products to reduce the system noise. A stepped impedance or high-low (hi-lo) microstrip low-pass filter (LPF) is usually preferred due to properties like low insertion loss, easier design and fabrication Such microstrip filters have some disadvantages like gradual cut-off frequency (fC) response, larger size due to inductance realization, harmonics of higher order and poor stop-band characteristics [1]-[3]. A square-shaped complementary split ring resonator (CSRR) filtering can be used for isolation improvement [33] Such CSRR offers high filtering (band-rejection) capability which is generally required for coupling suppression along with compact size and ease of fabrication.In this way the search for compact filter design structure with smooth curve of group delay and wide stop-band can over to use in the extensively spread microwave and millimeter-wave systems.
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