Spurious free independently controllable compact quad‐band filter using folded T‐shaped stub loaded modified ring resonator

Abstract

A compact spurious free, quad‐band, band‐pass filter (BPF) having independently controllable and widely spaced frequency bands is proposed. The design consists of a basic BPF to which the authors introduce transmission zeros (TZs) in the frequency response using T‐shaped stubs loaded with a modified ring resonator (MRR) thereby creating the four passbands. This design results in very high band‐to‐band isolation. The TZs are obtained by transversal signal path cancellation and also due to the loaded T‐shaped stubs. The BPF consists of a stepped impedance low‐pass filter which provides spurious free out of band characteristics up to 20GHz. By changing the tapping position of the MRR, the frequencies of the TZs can be adjusted to get the desired pass band characteristics. The proposed quad‐band filter provides low‐insertion loss (<1dB) at the four passbands centred at 2.4, 5.1, 7.7 and 10.1GHz. The simulation results of the filter are verified experimentally.

A novel asymmetrical interdigital coupled line‐based penta‐band bandpass filter design with enhanced selectivity employing square complementary split ring resonator

“…The RT/Duroid 5880 substrate is used to fabricate the proposed penta‐band BPF and its electric proprieties are ε r = 2.2, and δ = 0.0009. The overall dimension of the filter is 17.5 × 28.5 mm 2 that match with 0.10λg × 0.17λg, where λg is the guided wavelength, which is comparable to the multi‐band BPF configurations dealt by the earlier literature 2,5,7,8,10,12 . HFSS and ADS numerical simulation software are used to perform the simulation of this filter.…”

“…A compact multi‐layered four‐band BPF with improved selectivity and low‐insertion loss is demonstrated in Reference 2. Subsequently, a single layer configuration with multi‐band BPF using multimode resonator, 3–5 short stub loaded E‐shape resonator 6,7 and multi‐set of resonators 8,9 have been defined to reduce the circuit complexity and size. However, the selectivity of these filters is not impressive enough as the number of TZs are restricted.…”

“…Multiband BPF proves to be a promising member ensuring competitive insertion loss and high selectivity 1 with miniaturized dimensions 2–6 . So far, all literatures have reported on dual and quad‐band BPFs with remarkable filtering characteristics 2–8 . A compact multi‐layered four‐band BPF with improved selectivity and low‐insertion loss is demonstrated in Reference 2.…”

Design of compact quad‐band bandpass filter with good selectivity using two‐/tri‐section SIRs and stepped impedance inverters

“…The corresponding external quality factors of input and output sections, which are equivalent to the J s1 and J 2L functions in Fig. 10b can be extracted by utilising (11), (12) and the prescribed filter responses. Subsequently, the dimensions of the admittance inverter can be further deduced.…”

“…For examples, four pairs of resonators with different fundamental frequencies [8], E-shaped resonators [9], two sets of stepped impedance resonators (SIRs) with meandering structures [10,11] and negative refractive-index transmission-line metamaterials were employed to form quad-band BPFs. Another category to realise a quad-band BPF is to introduce several notches in the passbands, such as by introducing transmission zeroes (TZs) among the passbands using T-shaped stubs loaded with a modified ring resonator [12], and dual-mode notch elements in dual-band BPF [13]. However, all of the aforementioned quad-band BPFs suffer from a larger circuit area and high design/installation complexity.…”