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The two proposed filters described here satisfy the Federal Communications Commission Ultra-wideband (FCC-UWB) specifications and also control the center frequency and bandwidth of the filters passband. These filters consist of two distinguishing parts, Electromagnetic bandgap (EBG)-embedded multiple- mode resonator (MMR) and interdigital coupled lines to realize high performance in the operation band with a compact size of 14.0 mm × 10.1 mm. The main advantage of the two proposed filters is that three different bands are tuned. The 1st tuned band is from 3.5 GHz to 11.4 GHz for the first filter and from 3.1 GHz to 11.6 GHz for the second proposed filter, respectively. The 2nd tuned band is from 3.5 GHz to 7.5 GHz for the first filter and from 3.1 GHz to 7.8 GHz for the second proposed filter, respectively. While the 3rd tuned band of the first proposed filter is from 3.5 GHz to 5.9 GHz and from 3.1 GHz to 5.8 GHz for the second proposed filter. The bandwidth of the filters can be changed by increasing the length of the outer open circuited stubs which are controlled by using switching matrix equipment (mini circuit, replacement of PIN diodes). To validate the design theory, a reconfigurable UWB bandpass filters (BPFs) with EBG Embedded MMR are designed, fabricated and measured. Good agreement is found between simulated and measured results.

The filters play an important role in effectively transmitting the desired signals in certain passband regions while attenuating all the undesired signals in the remaining bandstop regions [

Tunable bandwidth microwave filters are especially useful for the design of high-frequency multifunction receivers that support multiple information signals with different frequency bands.

Since that the UWB system has become one of the most favorable technologies for short-range low-power indoor wireless communications, and UWB BPF as one of the essential components of UWB systems (3.1 GHz - 10.6 GHz) has obtained much attention in recent years. The reconfigurable UWB bandpass filter (BPF) will be provided, whereas the recent advances in modern wideband radar and wireless communication applications need high performance, reconfigurable, and compact RF subsystems. Therefore, much attention has been devoted for compact reconfigurable microwave devices. An important component for the multifunction receivers is the UWB BPF with passband from 3.1 to 10.6 GHz. So far, various techniques have been recently developed for UWB bandpass filters. Since 2005, various UWB bandpass filters have been designed and reported, including filters of composite lowpass and highpass structure [

In this paper, we present two Reconfigurable Ultra-Wideband Bandpass Filters with Embedded Multi-Mode Resonator and Electromagnetic Bandgap (MMR-EBG). The proposed UWB BPFs consist of two distinguishing parts, EBG-embedded MMR and interdigital coupled lines to realize high performance in the operation band with a compact size of 14.0 mm × 10.1 mm. The MMR of the first proposed filter is formed by connected three open circuited stubs with two high impedance microstrip lines in center, but the MMR of the second proposed filter is formed by connected five open circuited stubs with four high impedance microstrip lines in center. The topology of a periodic structure with shunt capacitive loading is called electromagnetic bandgap (EBG) structures [

The paper is organized as follows: Section 2 provides the analysis of the proposed filter, and Section 3 introduces the design of the proposed filter in terms of the shape of the filter, its dimensions and the simulation results. Section 4 introduces the fabrication and the measurement of the proposed filters together with simulated results. The conclusion is given in Section 5.

Based on article [

The input/output section is composed of two coupled lines with high impedance line as shown in

The ABCD matrix for the coupled line can be expressed as [

M c = [ cos θ 1 j Z o sin θ 1 j sin θ 1 Z o cos θ 1 ] [ 0 − j J − j J 0 ] [ cos θ 1 j Z o sin θ 1 j sin θ 1 Z o cos θ 1 ] (1)

Z_{o} and θ_{1} represent the characteristic impedance and the electrical length of the coupled line, respectively; while J is the admittance inverter. The admittance

inverter J in ABCD matrix M_{c} can be replaced by the even and odd mode characteristic impedances (Z_{oe} & Z_{oo}) of the coupled line [

J Z o + 1 J Z o = Z o e + Z o o Z o e − Z o o (2)

J Z o 2 = 2 Z o e − Z o o (3)

Substituting by Equation (2), and Equation (3) into Equation (1); the ABCD matrix of the coupled line becomes:

M c = [ Z o e + Z o o Z o e − Z o o cos θ 1 − j 2 [ 4 Z o e Z o o Z o e − Z o o cos 2 θ 1 sin θ 1 − ( Z o e − Z o 0 ) sin θ 1 ] j 2 Z o e − Z o o sin θ 1 Z o e + Z o o Z o e − Z o o cos θ 1 ] (4)

Z_{oe} and Z_{oo} can be calculated as in [

The ABCD matrix of the high impedance line can be expressed as [

M H = [ cos β H l H j Z H sin β H l H j Z H sin β H l H cos β H l H ] (5)

where Z_{H} is the highest line impedance, β_{H} is the propagation constant and l_{H} is the length of the high impedance line.

From Equation (4) & Equation (5), the ABCD matrix of the first part of the proposed filter is:

M 1 = M c × M H (6)

The multi-mode resonator section can be considered as cascaded stepped impedance with high and low impedances as shown in

The ABCD matrix of the second part can be expressed as follows [

M I = [ cos β 1 l 1 j Z 1 sin β 1 l 1 j Z c 1 sin β 1 l 1 cos β 1 l 1 ] (7)

M II = [ cos β 2 l 2 j Z 1 sin β 2 l 2 j Z c 2 sin β 2 l 2 cos β 2 l 2 ] (8)

M III = M I (9)

M IV = M II (10)

M V = [ cos β 5 l 5 j Z 5 sin β 5 l 5 j Z c 5 sin β 5 l 5 cos β 5 l 5 ] (11)

M VI = M II = M IV (12)

M VII = M III = M I (13)

M VIII = M II = M IV = M VI (14)

M IX = M I = M III = M VII (15)

From Equation (7) to Equation (15), the ABCD matrix of the second part of the proposed filter is:

M 2 = M I × M II × ⋯ × M IX (16)

The characteristic impedance and propagation constant of each section can be calculated as in [

Therefore, from the above discussion, it is clear that the total ABCD matrix of the proposed filter can be expressed as:

[ A B C D ] = M 1 × M 2 × M 1 (17)

The equations for computing the reflection and transmission coefficients from

the previous set of ABCD-parameter values of the proposed filter can be written as follows [

S 11 = A + B Z 0 − c Z 0 − D A + B Z 0 + c Z 0 + D (18)

S 21 = 2 A + B Z 0 + c Z 0 + D (19)

_{11}, there is frequency shift about 0.6 GHz between the numerical and simulated results in the first resonant frequency. This may be attributed to the different method of analysis used in the CST and Mat-lab program, while this shift decreases with the second and third resonant frequency as illustrated in _{21} shows very good agreement between the simulated and the numerical results especially in the band of operation from 3.1 GHz to 11.6 GHz. Finally, from

The proposed filter is designed based on the example described in Ref. [

Three shapes of the proposed filter are presented, the first one is UWB BPF with MMR formed by three open circuited stubs mutually coupled with two high impedance microstrip lines in center, the second one is MMR formed by five open circuited stubs mutually coupled with four high impedance microstrip lines in center, and third one as same as the second one but with different length of each open circuited stubs.

The first proposed design with its optimized dimensions is shown in _{L}). As W_{L} increases the bandwidth of the filter decreases as shown in _{L} is modified by using diodes switching matrix equipment where the character D refers to the diode and the different diodes states are described as follow:

1) When all the eight diodes (D_{1}, D_{2}, D_{3}, D_{4}, D_{5}, D_{6}, D_{7}, and D_{8}) are in off state, the length W_{L} will be equal to 4.9 mm, so the bandwidth of the filter will be 7.9 GHz with band extends from 3.5 GHz to 11.4 GHz.

2) When D_{1}, D_{2}, D_{3}, and D_{4} are in on state; while D_{5}, D_{6}, D_{7}, and D_{8} are in off state, the length W_{L} will be equal to 7.5 mm, so the bandwidth of the filter will be 4 GHz with band extends from 3.5 GHz to 7.5 GHz.

3) When all diodes (D_{1}, D_{2}, D_{3}, D_{4}, D_{5}, D_{6}, D_{7}, and D_{8}) are on, the length W_{L} will be equal to 10.1 mm, so the bandwidth of the filter will be 2.4 GHz with band extends from 3.5 GHz to 5.9 GHz.

From the above discussion, the length W_{L} can be modified to control the filter operating bandwidth. The above cases are summarized in

_{L}) by using readymade software package (CST MWS version 2014). It is clear that the 3dB bandwidth of the bandpass filter varies according to W_{L}, and thus there are three tuned bands with the three different lengths (W_{L}).

The second proposed design has five open circuited stubs mutually connected with four high impedance microstrip lines in middle as given in

W_{L} (mm) | −3 dB frequency band (GHz) | Minimum and maximum values of S parameters in passband (dB) | Roll off of passband and stop band (dB/GHz) | ||
---|---|---|---|---|---|

S_{11} | S_{21} | Pass band | Stop band | ||

4.9 | 3.5 - 11.4 | −3 to −45.4 | −0.1 to −3 | 12.47 | 11.8 |

7.5 | 3.5 - 7.5 | −3 to −63 | −0.12 to −3 | 35.3 | 7.09 |

10.1 | 3.5 - 5.9 | −3 to −42.6 | −0.12 to −3 | 36.7 | 8.5 |

are given in _{L} = 4.9, 7.5, 10.1 mm) by using CST. It should be noted that

W_{L} (mm) | −3 dB frequency band (GHz) | Minimum and maximum values of S parameters in passband (dB) | Roll off of passband and stop band (dB/GHz) | ||
---|---|---|---|---|---|

S_{11} | S_{21} | Pass band | Stop band | ||

4.9 | 3.1 - 11.6 | −3 to −47.3 | −0.14 to −3 | 27.7 | 10.5 |

7.5 | 3.1 - 7.8 | −3 to −39.8 | −0.12 to −3 | 30.7 | 8.1 |

10.1 | 3.1 - 5.8 | −3 to −36.5 | −0.12 to −3 | 41.9 | 8.9 |

the roll off of the second filter in the passband is better than the first one, and the bandwidth increased to 8.5 GHz instead of 7.9 GHz as shown in _{L} = 4.9 mm.

From the second proposed filter performance, it is noticed that the selectivity and the out of band rejection are bad, so it has been modified to improve them. An optimization procedure was carried out and the length L_{3} was changed from 5 mm to 4 mm, L_{2} changed from 4.9 mm to 3.6 mm, and L_{1} remains the same as shown in

The design procedure of the modified filter is the same as in the second proposed filter. _{L} = 4.9, 7.5, 10.1 mm) by using CST.

It should be noticed that the selectivity is improved and the out of band rejection has become better (S_{21} improved by more than 20 dB from 11.6 to 14 GHz) for the case of W_{L} = 4.9 mm as in

Our proposed designed filter is compared with similar filters as given in

The designed filters are fabricated using thin film technology and photolithographic technique on Rogers RO3006 (lossy) substrate with (ε_{r} = 6.15, h = 1.52 mm, and tan δ = 0.002). The photos for the fabricated filters are shown in

W_{L} (mm) | −3 dB frequency band (GHz) | Minimum and maximum values of S parameters in passband (GHz) | Roll off of passband and stop band (dB/GHz) | ||
---|---|---|---|---|---|

S_{11} (dB) | S_{21} (dB) | Pass band | Stop band | ||

4.9 | 3.1 to 11.6 | −3 to −43.5 | −0.2 to −3 | 27.8 | 15.7 |

7.5 | 3.1 to 7.8 | −3 to −39.2 | −0.1 to −3 | 25.9 | 8.4 |

10.1 | 3.1 to 5.8 | −3 to −36.8 | −0.13 to −3 | 33.8 | 8.5 |

Ref. | Dielectric constant (ε_{r}) | Height (mm) | Size of filter | Center frequency f0 (GHz) | Passband (GHz) | |
---|---|---|---|---|---|---|

Ref. [ | 10.8 | 0.635 | 23.98 mm × 4.96 mm | 6.85 | 3.1 - 10.6 | |

Ref. [ | 3.38 | 0.508 | 20 mm × 15 mm | 7.1 | 3.6 - 10.6 | |

Ref. [ | 2.65 | 1 | 30 mm × 16 mm | 6.85 | 2.8 - 11.0 | |

Ref. [ | 2.55 | 0.8 | 22.51 mm × 13.66 mm | 6.85 | 3.1 - 10.6 | |

Our work | 1st filter | 6.15 | 1.52 | 14.0 mm × 10.1 mm | 7.45 | 3.5 - 11.4 |

2nd filter | 6.15 | 1.52 | 14.0 mm × 10.1 mm | 7.35 | 3.1 - 11.6 | |

modified | 6.15 | 1.52 | 14.0 mm × 10.1 mm | 7.35 | 3.1 - 11.6 |

measured using the vector network analyzer (N9928A FieldFox Handheld Microwave Vector Network Analyzer, 26.5 GHz.).

Figures 16-18 show the measured and simulated results of the three structures. The measured results are consistent with the simulated ones. The measured 3dB passband of the first proposed filter is between 3.5 to 11.4 GHz in the 1st band, while in the second and third proposed filter is from 3.1 GHz to 11.6 GHz, from 3.5 to 7.5 GHz in the 2nd band of the first filter, while in the second and third filter from 3.1 GHz to 7.8 GHz, and from 3.5 to 5.9 GHz in the 3rd band of the first filter, while in the second and third filter from 3.1 GHz to 5.8 GHz. All filters have compact sizes with dimensions 14.0 mm × 10.1 mm.

_{11}l and lS_{21}l of the modified filter with five open circuit stubs with frequency range from 1 GHz to 20 GHz at W_{L} = 4.9 mm. It should be noted that the frequency range is extented up to 20

GHz in order to show that the out of band rejection has been improved due to the modifications that were carried out in the lengths of the open circuit stubs. HFSS software package was also used as another simulation tool to validate and verify the obtained performance of the proposed filters.

the CST MWS software. It should be noted that the maximum variation of group delay within 1 - 14 GHz is 0.4 ns for the modified filter, while the maximum variation of group delay for second proposed filter is 4.35 ns, and for the first proposed filter is 7.68 ns. As can be noted that the reported values for the modified proposed filter is lower than the other two proprosed filters and indicates a very low distortion that can be happened for the modified filter.

From the above figures, one can notice that:

1) There is a difference between the first, second, and third shape of the proposed filter in the frequency band and the center frequency as shown in

No. of filter shape at W_{L} = 4.9 mm | −3 dB frequency band (GHz) | Minimum and maximum values of S parameters in passband (GHz) | Roll off of passband and stop band (dB/GHz) | Impedance matching (dB) | Group delay at (1 - 14 GHz) (ns) | ||
---|---|---|---|---|---|---|---|

S_{11} (dB) | S_{21} (dB) | Pass band | Stop band | ||||

Shape 1 | 3.5 to 11.4 | −3 to −45.4 | −0.1 to −3 | 12.47 | 11.8 | <−15 | 0.15 - 7.68 |

Shape 2 | 3.1 to 11.6 | −3 to −47.3 | −0.14 to −3 | 27.7 | 10.5 | <−20 | 0.15 - 4.35 |

Shape 3 | 3.1 to 11.6 | −3 to −43.5 | −0.2 to −3 | 27.8 | 15.7 | <−15 | 0.15 - 0.4 |

2) The insertion loss within the pass band of the two shapes is the same.

3) The fabrication of the second and third shapes is more difficult than the first shape.

4) The slope of the insertion loss of the third shape is sharper than the first and second shape.

Reconfigurable Ultra-Wideband Bandpass Filters with EBG Embedded Multi-Mode Resonator have been designed, simulated, and fabricated. Two packages of software were used, namely CST MWS 2014 and 3D EM commercial software HFSS version 13.0 to design and simulate the filters. The simulated and measured results are comparable. The measured results were characterized using a N9928A FieldFox Handheld Microwave Vector Network Analyzer, 26.5 GHz. Small size and three different frequency bands add some advantages to these filters. By adjusting the length of the outer open circuit stubs, the center frequency and the 3 dB frequency band can be easily adjusted. The final size of these filters is 14.0 mm × 10.1 mm, which is suitable for modern ultra-wide band wireless communication systems. According to The FCC regulations, the proposed filters in all their structures satisfy the definitions of the UWB filters whether according to the first definition of FCC which is 3.1 - 10.6 GHz bandwidth requirements or according the second definition which is 500 MHz bandwidth requirements. So, the proposed filter can be used in communication systems with UWB application [

The authors declare no conflicts of interest regarding the publication of this paper.

Ouf, E.G., Mohra, A.S., Abdallah, E.A.-F. and Elhennawy, H. (2018) A Reconfigurable UWB Bandpass Filters with Embedded Multi-Mode Resonators. Open Journal of Antennas and Propagation, 6, 43-59. https://doi.org/10.4236/ojapr.2018.63005