Abstract: This paper presents two types of microstrip bandpass
filter (BPF) at microwave frequencies. The first one is a tunable BPF
using planar patch resonators based on a varactor diode. The filter is
formed by a triple mode circular patch resonator with two pairs of
slots, in which the varactor diodes are connected. Indeed, this filter is
initially centered at 2.4 GHz; the center frequency of the tunable
patch filter could be tuned up to 1.8 GHz simultaneously with the
bandwidth, reaching high tuning ranges. Lossless simulations were
compared to those considering the substrate dielectric, conductor
losses and the equivalent electrical circuit model of the tuning
element in order to assess their effects. Within these variations,
simulation results showed insertion loss better than 2 dB and return
loss better than 10 dB over the passband. The second structure is a
BPF for ultra-wideband (UWB) applications based on multiple-mode
resonator (MMR) and rectangular-shaped defected ground structure
(DGS). This filter, which is compact size of 25.2 x 3.8 mm2, provides
in the pass band an insertion loss of 0.57 dB and a return loss greater
than 12 dB. The proposed filters presents good performances and the
simulation results are in satisfactory agreement with the
experimentation ones reported elsewhere.
Abstract: In this paper, three types of defected ground structure
(DGS) units which are triangular-head (TH), rectangular-head (RH)
and U-shape (US) are investigated. They are further used to low-pass
and band-pass filters designs (LPF and BPF) and the obtained
performances are examined. The LPF employing RH-DGS geometry
presents the advantages of compact size, low-insertion loss and wide
stopband compared to the other filters. It provides cutoff frequency of
2.5 GHz, largest rejection band width of 20 dB from 2.98 to 8.76
GHz, smallest transition region and smallest sharpness of the cutoff
frequency. The BPF based on RH-DGS has the highest bandwidth
(BW) of about 0.74 GHz and the lowest center frequency of 3.24
GHz, whereas the other BPFs have BWs less than 0.7 GHz.