Miniaturized and Bandwidth Improvement of Bandpass Filter using A Quarter Wavelength Resonator

This paper presents a novel capacitively loaded λ/4 shorted meander line resonator (SMLR). The grounded microstrip lines inserted inside the spaces of SMLR can construct the grounded inter-digital capacitors, which leads to a lower fundamental resonance frequency of capacitively loaded λ/4 SMLR than the λ/4 SMLR. Based on the proposed resonator, two compact fourth order Chebychev response bandpass filters (BPFs) centered at 0.9/1.57 GHz with 3 dB fractional bandwidth (FBW) of 12.5%/15% is designed and fabricated firstly. Then, on the basis of these two BPFs, a BPF-based diplexer operating at 0.9/1.57 GHz with 3 dB FBW of 12.5%/15% is exploited. The designed diplexer employs a novel hybrid microstrip line and phase shifter common T-junction. The phase shifter is implemented by quasi-lumped elements. The designed diplexer exhibits a very high isolation up to 73/68 dB at two channels, respectively. The fabricated diplexer also has a compact size of 0.239λg × 0.06λg. Good agreement can be observed between the simulations and the measurements.

A programmable broadband Radio Frequency (RF) filter is designed using a Digital Micromirror Device (DMD), an Acoustooptic Tunable Filter (AOTF), and a Chirped Fiber Bragg grating (CFBG). This hybrid analog-digital optical design enables implementation of RF filters with higher number of taps in comparison with an AOTF-only RF filter design and improved RF tunability in comparison with a DMD-only design. A 3-tap RF filter is theoretically analyzed and experimentally demonstrated using a combination of analog and digital optical tap selection. Filter nulls recorded at 6.90, 6.945, and 6.99 GHz show the tunability improvement with the hybrid design. Implementation of higher tap count filters can lead to similar improvements in filter tunability and pass-band and stop-band characteristics.

In this paper, a compact microstrip varactor-tuned wideband bandpass filter (BPF) is proposed by using mixed coupling lumped dual-mode resonator. The proposed tunable wideband BPF has a pair of transmission zeros around the passband, resulting in high passband selectivity. The measured results show that the passband can be tuned in a frequency range from 1.01 to 2.04 GHz with an almost 3 dB constant fractional bandwidth of 28 ± 1%. Within the tuning range, the insertion loss varies from 2.1 to 1.65 dB and the return loss is better than 10 dB. In addition, the tunability of 3 dB fractional bandwidth at 1.5 GHz is from 23 to 43%.

A new class of compact high selectivity bandpass filter (BPF) is reported in this paper by making use of open-/short-circuited coupled-lines which are connected at the input and output filter stages and a pair of symmetrical parallel-coupled-lines which are connected to a pair of open stepped-impedance resonators (SIRs). As a result six finite transmission zeros (TZs) at both sides of the passband are introduced. To analyze the characteristics of the proposed design, even-, odd-mode and ABCD analysis is used. A prototype BPF covering the entire S-band (2-4 GHz) with 3- dB fractional bandwidth (FBW) of 60% was designed, fabricated and tested. The filter exhibits measured insertion loss less than 0.8 dB in the entire passband, while the measured return loss within the passband is greater than 16 dB. The fabricated filter is very compact, with an appealing circuit size of less than 0.09λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and at the same time it presents upper stopband suppression level greater than 40 dB.

In this brief, we present a novel ultra-wide stopband compact microstrip bandpass filter (BPF) with low insertion loss and compact size. The proposed filter is designed based on two five-stage stepped impedance resonators (SIRs) which are capacitively coupled to each other's. The five-stage SIRs can be used to have miniaturized size as well as suppression of harmonics. In this BPF, by increasing stages of SIRs, multiple transmission zeros are generated. Therefore, a compact BPF with a ultra-wide stopband could be achieved. The bandpass region of the proposed filter is extended from 3.58 GHz up to 10.31 GHz with insertion loss lower than 0.42 dB. The rejection level is better than -26 dB from 11.25 GHz up to 30 GHz and better than -17.5 dB up to 100 GHz. The center frequency of the proposed BPF is located at 6.95 GHz with -3 dB fractional bandwidth (FBW) of 97%. The dimension of the fabricated filter is 0.128 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ×0.378 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> . The simulation results are verified by fabrication and measurement up to 30 GHz that there is a good agreement between them.

A compact reconfigurable CMOS bandpass filter (BPF) with high selectivity is proposed using transformer-type resonators in this article. The transformer-type resonator is constructed by a transformer loaded with parallel varactors for frequency tuning, and two varactors are then added across primary wind and secondary wind for coupling tuning. With the transformer-type structure, one resonator is formed inside another resonator, thus fully utilizing the chip area and resulting in a miniaturized structure. Magnetic and electrical couplings are formed within the transformer-type resonator and facilitate the bandwidth (BW) tuning. The quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) of each resonator is improved by cross-coupled negative resistance structure. Meanwhile, two pairs of transformer-type resonators are placed side-by-side and naturally form a quadruplet structure; as a result, two transmission zeros (TZs) are introduced at each side of the passband thus significantly improving the selectivity and stopband rejection of the BPF. The proposed tunable on-chip BPF is manufactured by a commercial 55 nm bulk CMOS technology with a core area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.48 \times 0.54$ </tex-math></inline-formula> mm2. The filter center frequency (CF) can be tuned from 2.2 to 3.6 GHz, while the 3 dB fractional BW (FBW) can be tuned from 14% to 33%. The shape factor of the proposed filter is 1.4–1.9.

In this paper, a novel compact band pass filter (BPF) is proposed for Global Positioning System (GPS) receivers. The proposed BPF configuration is composed of a low pass filter (LPF) section formed by the coupled line transformer connected with a radial stub and two short circuited stubs embedded within the 50 Ω microstrip line connecting the input/output (I/O) port of LPF. The lumped equivalent model of proposed BPF is also presented and analyzed. Simulation as well as experimental results shows very good in-band (pass-band) and out-of-band (≈ 7fc (centre frequency)) characteristics. The 3 dB fractional bandwidth (FBW) is 3.2% of fc, thus satisfying the GPS receiver requirement and the minimum insertion loss (IL) in pass-band is 1.28 dB.

A novel multistubs loaded resonator (MSLR) is proposed in this article, which is constructed by several open- and short-circuited stubs. The analysis shows that it is characterized by four resonant modes. Then, the MSLR is applied in the design of a compact ultra-wideband (UWB) bandpass filter. The measured results show that its 3dB bandwidth can cover [3.0, 11.5] GHz, that is, 3 dB fractional bandwidth is 117%, and the return loss within the passband is greater than 15 dB. Especially, the roll-off rate is higher than 33 dB/GHz and more than 40 dB harmonic suppression can be achieved up to 17 GHz. In order to suppress the interference of some undesired narrowband signal such as wireless local-area network (WLAN) radio signal, a notched band is created for the UWB bandpass filter, which is realized by forming one stepped slot on each of the feedlines, respectively. The measured results show that a notched band with 2.01% fractional bandwidth at the center frequency of 5.85 GHz can be achieved and its suppression is about −19 dB.

In this article, we present a novel compact dual wideband bandpass filter (BPF) by using a new structure of ladder stub resonator (LSR). The proposed LSR can produce attenuation poles to form low loss and dual‐wideband bandpass response. By tuning the structure parameters of LSR, the dual‐band characteristic can be controlled. The measured 3 dB fractional bandwidth (FBW) at first and second passbands are 41.5% and 25.7%, respectively. The experiment results of the fabricated filter agree well with the electromagnetic (EM) simulation. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1391–1393, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24392

A new and miniature wide-band bandpass filter (BPF) with 2nd harmonic-suppressed characteristic is proposed in this letter. This designed filter consists of two cascading folded fork-shape resonators paralleled with an open-ended stepped impedance stub (SIS). The harmonic-suppressed filter has been designed, fabricated, and measured. The measurement results are in good agreement with the electromagnetic (EM) simulation results. The obtained frequency responses demonstrated the filter with an excellent band-pass property, including −3 dB fractional bandwidth (FBW) 45% at the central frequency 2.2 GHz, less than 1.4 dB insertion loss within the passband, and broad stopband rejection.

The proliferation of the Internet of Things (IoT) propels the continuous demand for compact, low-cost, and high-performance multiband filters. This paper introduces a novel low-profile dual-band bandpass filter (BPF) constructed with a back-to-back coupled pair of shielded folded quarter-mode substrate integrated waveguide (SF-QMSIW) multimode cavities. A hybrid structure is obtained by etching a coplanar waveguide (CPW) coupling line in the folded cavity’s septum layer. It serves multiple functions: generating an additional resonance, providing a separate coupling mechanism for the upper passband, and offering the flexibility to control the passbands’ center frequency ratio. Additionally, the unused second higher-order mode is suppressed by integrating embedded split-ring resonators (ESRRs) with an inter-digital capacitor (IDC) structure into the feed lines. A filter prototype has been fabricated and experimentally tested. The measurements confirmed reliable operation in two passbands having center frequencies 3.6 GHz and 5.8 GHz, and exhibiting 3 dB fractional bandwidths (FBWs) of 6.4% and 5.3%, respectively. Furthermore, the group delay variation within both passbands equals only 0.62 ns and 1.00 ns, respectively. Owing to the second higher-order mode suppression, the filter demonstrated an inter-band rejection exceeding 38 dB, within a compact footprint of 0.71λg2 (with λg being the guided wavelength at the lower passband’s center frequency).

In this paper, design and development of a via-free composite right/left handed transmission line (CRLH TL)-based diplexer for WiMAX and WLAN bands is reported. The diplexer is having two channels, where each channel consists of a separate bandpass filter (BPF). The BPF of both channels are designed on via-free CRLH TLs based on a newly proposed right-angled corner-modified split ring resonator (RAC-MSRR) structure. The RAC-MSRR incorporates meander paths because of which working scope of frequencies is focused for measured center frequencies (f1) 3.5 GHz with −3 dB fractional bandwidth (FBW) of 21.21% (BPF1 channel) and (f2) 5.6 GHz with −3 dB FBW of 13.29% (BPF2 channel). For diplexer design, T-section is used for joining two BPFs which results in very good isolation of more than 32.5 dB over the frequency band of 2.5–8.0 GHz. The designed diplexer has passband insertion loss of −0.87 dB at f1 and −1.25 dB at f2. Overall size of the fabricated diplexer including 50 Ω feed line is 18 × 15 mm2. Equivalent lumped circuit model parameters of the diplexer are obtained from the pseudo-inverse matrix technique. Measured results show good concurrence with simulated results and subsequently approve the proposed model design.

A compact and high-rejection ultra-wideband (UWB) microstrip band-pass filter is proposed by using the multi-mode resonator (MMR) technique. The proposed MMR structure is realized by three open stubs-loaded and two short stubs-loaded and a high impedance microstrip line. Five modes, including two odd modes and three even modes could be designed within the UWB band. By resizing the dimensions of the stubs, the resonant modes of the MMR structure are arranged wider bandpass which the passband selectivity with this configuration significantly improved. By this configuration, the even modes can be flexibly controlled, while the odd modes remain the same. The proposed filter has a passband covers 4.1–10.6 GHz and its measured 3 dB fractional bandwidth is about 89%. In order to validate the performance of the proposed technique, the designed UWB band-pass filter is fabricated and the experimental verification is provided. A good agreement has been found between simulation and measurement’s results. To our knowledge, the size of the proposed UWB filter is small in comparison with known similar filters.

A kind of novel compact wideband bandpass filter (BPF) is investigated in this paper. It is composed of four open-circuited stubs, in which two of them are folded to minimize the whole size of the filter. The new filter has been simulated and the characteristics are analyzed. The calculated results show that the BPF has a wide 3 dB fractional bandwidth which is more than 60% at the center frequency of 24 GHz. Besides, transmission zeros of the filter are very close to both sides of the passband to achieve a high selectivity. The filter is also fabricated and measured to demonstrate the performance, which shows good agreement with theoretical results.

A compact and sharp rejection UWB microstrip bandpass filter is developed using left handed metamaterials. For realizing a backward-wave propagation medium, two split ring resonator (CSRR) in the back substrate side and also one series capacitor etched in the host line, are used to produce a negative effective e and μ, simultaneously. Moreover, in the proposed structure, two doublets parallel coupling gaps is placed at each side of the series capacitor. In comparison with the other similar filters, this structure shows a significantly wider passband due to the introduction of a cross-coupling between the feed lines (input and output) which generate four pairs of attenuation poles in the passband. On top of that, using two CSRRs and series capacitor leads to the addition of two extra transmission poles at the lower and upper edges of the filter. Consequently, a compact six-pole ultra-wide bandpass filter is designed and fabricated which exhibits extremely sharp rejection skirts around the target passband. The passband covers 3.67 to 10.42 GHz and its measured 3 dB fractional bandwidth is about 95.8%. To the best of our knowledge, the size of proposed ultra-wideband filter is more compact in comparison with known similar filters.