Compact lowpass filters with very sharp transition bands based on open complementary split ring resonators

Abstract

It is shown that open complementary split ring resonators (OCSRRs) are useful particles for the design of lowpass filters with very narrow transition bands in microstrip technology. Owing to the small electrical size of OCSRRs, the filters are also very small. These filters are implemented by cascading several OCSRR stages in a microstrip line. The OCSRR stages can be modelled as parallel resonators in series configuration, thus providing a transmission zero at their resonance frequency. By designing the OCSRRs with small inductance and high capacitance, very sharp cutoffs are achieved. To illustrate the possibilities of the approach, a prototype device example is provided. It consists on a five-stage periodic microstrip lowpass filter with 3 dB insertion losses at 1.33 GHz and 40 dB rejection at 1.45 GHz. To improve out-of-band rejection, four additional OCSRR stages tuned at the spurious frequency band have been cascaded. Filter dimensions are 39  7.4 mm (i.e. 0.46l 0.087l, where l is the guided wavelength at the cutoff frequency). These filters are of interest in applications where small size and severe cutoff requirements are required. Introduction: Open complementary split rings resonators (OCSRRs) have been reported recently (e.g. [1]) as useful particles for the synthesis of planar metamaterials and for the miniaturisation of microwave components in coplanar waveguide (CPW) technology. The OCSRR is the complementary counterpart of the open split ring resonator (OSRR) [2]. OCSRRs and OSRRs are open resonators, i.e. both particles can be excited by means of a voltage or current source connected to their terminals. The OCSRR (see Fig. 1) can be modelled as an open parallel resonant tank, where the inductance L o is the inductance of the strip connecting the internal and external metallic regions of the particle, and the capacitance C c is equivalent to the capacitance of a disk of radius r o 2 c/2 surrounded by a metallic plane at a distance c of its edge [1]. Such element values can be roughly inferred from the geometry of the particle (following the model reported in [3] for CSRRs).

Compact, harmonic suppressed power divider using open complementary split‐ring resonator

“…OCSRR is a negative image of the open split‐ring resonator (OSRR). It was first proposed by some of the authors in CPW technology [9] and mostly used for the design of size miniaturized filters [9–12]. In our work, OCSRR is first time used for the size miniaturization of power divider using microstrip technology.…”

Dual-Band Frequency Reconfigurable Small Eighth-Mode Substrate-Integrated Waveguide Antenna

“…[16] . 또한, 좁은 대역폭, 높은 Q factor 값을 갖는 특 성이 있어 필터로써도 많이 활용되었다 [17], [18] . 특히 기존 의 많은 CSRR이 SIW와의 결합이 용이하기 때문에 많은 논문들이 발표되었다 [19], [20] .…”

Compact, deep, and wide rejection bandwidth low‐pass filter using open complementary split ring resonator

“…As discussed in [10], the OCSRR‐based filter characteristic does not fall in any standard approximations such as Chebyshev and elliptic. So the low‐pass filter is constructed using the cascaded stages of OCSRR.…”

“…The measured stopband rejection of the filter is better than 30 dB up to 6 GHz, which is nearly six times the cutoff frequency. The length of the filter is 32.6 mm excluding the access line, which is 73% shorter than the Aznar's low‐pass filter reported in [10]. The proposed low‐pass filter result is compared with the some of the efficient and related filters already existing in literature and tabulated in Table 1.…”

“…Even though the performance of filter is good, length is long due to periodic arrangement of CMRC. Recently, open complementary split ring resonator (OCSRR) has been proposed to design a compact low‐pass filter in microstrip technology [10].…”