# A Low-Cost Microwave Filter with Improved Passband and Stopband Characteristics Using Stub Loaded Multiple Mode Resonator for 5G Mid-Band Applications

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## Abstract

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## 1. Introduction

_{r}= 4.4, thickness h = 1.6 mm and tangent loss of 0.0265. In addition, a folded stepped impedance resonator technique was employed to reduce the filter size by up to 46% compared with the other presented designs. The presented filter using a new configuration has achieved transmission coefficients/fractional bandwidths of 0.60 dB/49.3%, 1.49 dB/18.7% and 1.93 dB/ 13.9% at 0.81 GHz, 1.71 GHz and 2.58 GHz, respectively.

## 2. Filter Structure

## 3. Filter Analysis and Modeling

#### 3.1. SL-MMR Modeling

#### 3.1.1. Odd-Mode Resonant Frequency

#### 3.1.2. Even-Mode Resonant Frequency

#### 3.2. Parasitic Elements Modeling

## 4. Parametric Study

- The dual narrowband mode can be obtained when a short central stub (or no central stub) is attached to the filter. This design is beneficial for only specific applications within this 5G sub-band, but with an improved quality factor.
- The second mode (the main concern of this work) is obtained when a longer central stub is used. In this case, the even and odd resonant frequencies are getting closer to each other to cover wider bandwidth. The advantage of this mode is concluded by covering the entire 5G sub-band with good matching characteristics to make the device, to which the filter is attached, compatible with the entire band of interest.

## 5. Measured Results

- Shielding the fabricated filter to provide a noticeable immunity against the electromagnetic interference;
- Controlling the electrical length of the central stub with the aid of varactor or PIN diode to present a controllable even mode resonant frequency, so that the filter can be used as a wideband 5G filter and dual-band narrow band filter.

## 6. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Geometry of the proposed filter: (

**a**) dimensions of the overall structure and; (

**b**) dimensions of the parallel line coupler (all dimensions are in mm).

**Figure 2.**The structure of the proposed Stub Loaded Multiple Mode Resonator (SL-MMR): (

**a**) the entire SL-MMR; (

**b**) odd mode; and (

**c**) even mode (all dimensions are in mm).

**Figure 3.**A comparison between the SL-MMR estimated and the CST Micriwave Studio simulated resonant frequencies for: (

**a**) odd mode (variable L′); and (

**b**) even mode (variable L).

**Figure 4.**The current distribution of the SL-MMR at L = 8.8 mm and L′ = 5.5 mm: (

**a**) odd mode (f = 3.87 GHz) and (

**b**) even mode (f = 4.1 GHz).

**Figure 6.**The current distribution of the proposed filter: (

**a**) outside the transmission zero (f = 3.9 GHz); and (

**b**) at the created transmission zero (f = 3.24 GHz).

**Figure 7.**Simulated scattering parameters of the proposed SL-MMR-based microwave filter without the parasitic elements at L = 8.8 mm and different values of parallel lines separation: (

**a**) reflection coefficient; and (

**b**) the transmission coefficient.

**Figure 8.**Simulated scattering parameters of the proposed SL-MMR based microwave filter without the parasitic elements at s = 0.2 mm and different values stub length: (

**a**) reflection coefficient; and (

**b**) the transmission coefficient.

**Figure 9.**Simulated scattering parameters of the proposed SL-MMR based microwave filter with the parasitic elements at different values of parasitic element arm length d: (

**a**) reflection coefficient; and (

**b**) the transmission coefficient.

**Figure 11.**Measured versus simulation scattering parameters of the proposed microwave filter: (

**a**) reflection coefficient; and (

**b**) transmission coefficient.

**Figure 12.**A wide window of the measured versus simulation scattering parameters of the proposed microwave filter: (

**a**) reflection coefficient; and (

**b**) transmission coefficient.

Results | RL(dB) @ f_{0}(GHz) | −10 dB Impedance Bandwidth (MHz) | IL(dB) @ f(GHz) | Rejection(dB) @ f(GHz) | |
---|---|---|---|---|---|

Lower Band | Upper Band | ||||

Simulated | 22 @ 3.95 | 550 | 21 @ 3.2 3.0 @ 3.7 2.3 @ 3.95 (f _{0})4.0 @ 4.2 17.7 @ 4.6 | 15 @ 3.0 21 @ 3.2 25 @ 3.24 (f _{TZs})14 @ 3.4 | 17.5 @ 5.0 14.6 @ 4.4 22 @ 4.52 (f _{TZs})18 @ 4.6 |

Measured | 19 @ 3.95 | 490 | 18.4 @ 3.2 3.1 @ 3.7 2.4 @ 3.95 (f _{0})4.2 @ 4.2 19.5 @ 4.6 | 17 @ 3.0 18.4 @ 3.2 25 @ 3.31 (f _{TZs})20 @ 3.4 | −@ 5.0 23 @ 4.4 24.9 @ 4.45 (f _{TZs})19.5 @ 4.6 |

_{0}: center frequency; IL: insertion loss; RL: return loss; TZs: transmission zeros.

Ref. | Technique | Freq. (GHz) | −10 dB FBW (%) | RL (dB) | IL (dB) | Via Holes | Size (mm^{2}) |
---|---|---|---|---|---|---|---|

[16] | MMSRR | 3.5 | 5.7 | 27 | 1.7 | 0 | 45 × 45 |

[17] | MMSIW | 2.2 | 5.4 | 12 | 3.3 | SIW | 89 × 36 |

[18] | MMR | 2.8/3.5/4.2 | 6.8/9.4/3.0 | 13/17/12 | 1.2/1.0/1.9 | 5 | 40 × 65 |

[23] | SLR | 1.8/3.5 | 14/10 | 24/18 | 0.8/0.9 | 1 | 25 × 25 |

[26] | FQC-SSIR | 0.8/1.8/2.62 | 25/10/7 | 15/10/14 | - | 0 | 97 × 129 |

[27] | IPD | 3.75 | 24 | >10 | 1.52 | IPD | 2.0 × 1.25 |

[29] | LTCC | 2.45 | 10.8 | >15 | 2.5 | 0 | 2.48 × 2.02 |

[30] | HTCC | 2.25 | 5.5 | >17 | 1.8 | 0 | 7.0 × 4.8 |

[31] | Acoustic Wave | 4.5 | 8.5 | >14 | 2.7 | 0 | 0.64 × 1.4 |

[34] | Hybrid (IPD & Acoustic) | 3.8 | 22 | - | 2.5 | IPD | 2.0 × 1.8 |

Prop. | SIR/SLR | 3.95 | 14 | 19 | 2.4 | 0 | 25 × 50 |

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**MDPI and ACS Style**

Alnahwi, F.M.; Al-Yasir, Y.I.A.; Abdulhameed, A.A.; Abdullah, A.S.; Abd-Alhameed, R.A.
A Low-Cost Microwave Filter with Improved Passband and Stopband Characteristics Using Stub Loaded Multiple Mode Resonator for 5G Mid-Band Applications. *Electronics* **2021**, *10*, 450.
https://doi.org/10.3390/electronics10040450

**AMA Style**

Alnahwi FM, Al-Yasir YIA, Abdulhameed AA, Abdullah AS, Abd-Alhameed RA.
A Low-Cost Microwave Filter with Improved Passband and Stopband Characteristics Using Stub Loaded Multiple Mode Resonator for 5G Mid-Band Applications. *Electronics*. 2021; 10(4):450.
https://doi.org/10.3390/electronics10040450

**Chicago/Turabian Style**

Alnahwi, Falih M., Yasir I. A. Al-Yasir, Abdulghafor A. Abdulhameed, Abdulkareem S. Abdullah, and Raed A. Abd-Alhameed.
2021. "A Low-Cost Microwave Filter with Improved Passband and Stopband Characteristics Using Stub Loaded Multiple Mode Resonator for 5G Mid-Band Applications" *Electronics* 10, no. 4: 450.
https://doi.org/10.3390/electronics10040450