Low Insertion Loss Research Articles

Exact synthesis of couple‐line based wideband four‐way filtering power divider with unequal power division

AbstractIn this paper, a coupled‐line‐based wideband four‐way filtering power divider (FPD) with unequal power division is presented. It is composed of three groups of coupled lines (CLs), four types of open‐ended stubs, and three kinds of resistors. By setting the CLs in each group with different parameters, unequal power distribution is obtained. Besides, open‐ended stubs with different characteristic impedances are inserted to each output port to generate two extra transmission zeros, at the same time maintaining good impedance matchings. Resistors are inserted to each group of the CLs to improve the isolations. By applying twice parity mode analysis, the exact synthesis of the proposed FPD is first derived. For demonstration, a prototype with power division ratio of 1:1.2:1.5:1.8 is designed and manufactured. Measurement results verified that more than 60% fractional bandwidth (FBW) is obtained under the criterion of 10 dB return loss and 10 dB isolation. Besides, the 3 dB passband FBWs for the four outputs reach 70% with high frequency selectivity and low insertion loss. And more than 15 dB out‐of‐band rejections are achieved for both the lower and upper stopbands.

A magnetically switchable demultiplexer via Terfenol-D in phononic crystal

This study introduces a novel approach for developing a controllable demultiplexer by applying a magnetic field to Terfenol-D cylinders within a solid–solid phononic crystal structure. Dynamic controllable demultiplexers are essential devices in acoustic and optical communication networks, yet adjustable elastic demultiplexers are notably lacking in current sound systems and acoustic communication technologies. The proposed phononic crystal-based demultiplexer features a square lattice (12 × 19) composed of tungsten cylinders embedded in a poly methyl methacrylate (PMMA) substrate. The switchable design consists of two identical, symmetrical parts separated by an input waveguide. In addition, each unit includes an output channel, a common input channel, and a square ring resonator, with the output channel side-coupled to the input bus waveguide. Moreover, Terfenol-D, a magnetostrictive material, is utilized in the hollow cylinders of the output channels. Switchability of the elastic demultiplexer outputs is achieved by dynamically altering the Young’s modulus of the Terfenol-D cylinders through the application of a magnetic field. This magnetic influence modifies the Young’s modulus of the Terfenol-D material in the output waveguides, enabling controllability. By varying the magnetic field applied to the demultiplexer, we find two distinct values of Young’s modulus within the structure. These two values facilitate the high transmission of two desirable peaks with narrow bandwidth through the output channels, allowing for switchable functionality based on the magnetic field’s position. The proposed demultiplexer demonstrates an average crosstalk value of −25.34 dB, indicating strong performance, along with a high average quality factor (Q) of 1773.5 and low average insertion losses of 0.85 dB in the MHz frequency range. The solid–solid elastic controllable demultiplexer is simulated using the finite element method, showcasing its potential for practical applications.

Compact and low‐loss IPD bandpass filter using 3D glass‐based redistribution layer technology

AbstractA low‐loss miniaturized bandpass filter is presented using 3D glass‐based RDL packaging technology. A new topology consisting of one modified Pi‐section and one modified T‐section is introduced to generate three transmission zeros which can achieve the high out‐of‐band rejection. A combination of 2D planar inductors and high‐Q 3D inductors is used to achieve low insertion loss and minimize the filter size. In addition, one grounded resonator at input terminal is introduced to generate an extra transmission zero in the low end. The proposed bandpass filter covering 3.3–4.2 GHz is fabricated with a compact size of 1.6 mm × 0.8 mm × 0.25 mm. It exhibits an insertion loss of less than 1.0 dB at a center frequency of 3.75GHz and a return loss of better than 14 dB. The proposed design has a 3 dB fractional bandwidth of 37.6%. Its out‐of‐band rejection is better than 20 dB at the low frequency band from DC to 2.0 GHz and better than 19 dB at the high frequency band from 5.0 to 9.0 GHz. The simulated and measured results of the proposed BPF are in reasonably good agreement.

Design and application of D‐band bandpass filter based on 0.18 μm complementary metal oxide semiconductor process

AbstractThis paper designs a bandpass filter for D‐band and 0.18 μm complementary metal oxide semiconductor (CMOS) process. The bandpass filter is composed of an inverted L‐shaped coupling microstrip line and a cross‐coupled resonator, and is coupled to produce two controlled transmission zeros. A defected ground structure is used to make a good impedance match. The designed filter has a 3 dB impedance bandwidth of 52 GHz (149–201 GHz) with a center frequency of 175 GHz and an insertion loss of 3.23 dB. The design of this paper is a CMOS 0.18 μm process capable of applying the D‐band bandpass filter with the advantages of lower insertion loss, broadband, and compact size.

A miniaturized on‐chip BPF with low insertion loss and wide stopband based on integrated passive device technology

AbstractIn this study, a novel bandpass filter (BPF) characterized by low insertion loss (IL) and the presence of two transmission zeros (TZs) based on integrated passive device (IPD) technology is introduced. The design incorporates a low‐pass filter and a high‐pass filter which both exhibit strong out‐of‐band suppression performance. The control structure for TZs is constructed by cascading the inductance and capacitance components. The TZ controlling structure primarily generates TZs at high frequencies, resulting in a further bandwidth enhancement in the stopband. The lumped circuit of the proposed BPF is first constructed, and rigorous design formulas are provided to assist in constructing the proposed design. After schematic optimization, the second step involves layout optimization and simulation based on the specific IPD process. Experimental results mounted on a printed circuit board demonstrate that the bandwidth spans from 3.3 to 4.2 GHz with an IL of only 2.0 dB at the center frequency. Additionally, this BPF achieves impressive sideband suppression, exceeding 18 dB in the 0–1.7 GHz range and 30 dB in the 9–15 GHz range. Remarkably, the BPF is exceptionally compact with only 0.5 mm × 1.0 mm (0.006λc × 0.012λc). The proposed BPF exhibits outstanding performance with minimal IL and extensive sideband suppression at such a compact size based on the IPD technology.

Ultra-broadband and high extinction ratio silicon TM-pass polarizer based on grating-assisted antisymmetric multimode waveguide

We propose an all-silicon TM-pass polarizer using a grating-assisted antisymmetric multimode waveguide (GAMW). The GAMW design facilitates the conversion of the undesired TE0 mode into the back-reflected TE1 mode, enabling efficient transmission of the desired TM0 mode with low insertion loss (IL) and high extinction ratio (ER). Furthermore, by cascading multiple GAMW structures, the device can filter TE0 mode over a broader spectral range effectively. The simulation results indicate that the single-GAMW-based polarizer achieves IL < 0.17 dB and ER > 40 dB in the wavelength range from 1480 nm to 1620 nm. When cascaded, the device expands the bandwidth to 275 nm (1435 nm–1710 nm), maintaining IL < 1 dB and ER > 40 dB simultaneously. The bandwidth can be further improved by cascading more GAMW structures working at different central Bragg wavelength. Limited by the measuring equipment, the measured wavelength range is between [1470 nm, 1630 nm]. The results of experiment demonstrate that the fabricated single-GAMW-based polarizer achieves IL < 0.65 dB and ER > 28.4 dB in 144 nm bandwidth ranging from 1470 nm to 1614 nm. For the cascaded-GAMW-based polarizer, IL < 0.83 dB and ER > 28.8 dB is achieved throughout the entire measuring wavelength range.

A compact SIW dual-functional design with integrated filter and self-diplexing antenna

ABSTRACT This paper proposes a compact dual-functional design (DFD) which integrates a bandpass filter (BPF) and self-diplexing antenna in a half-mode substrate-integrated waveguide (HMSIW) cavity. The design consists of four eighth-mode SIW (EMSIW) sub-cavities that are formed by etching three slots on an HMSIW cavity. Two of the sub-cavities are coupled to form a BPF with low insertion loss with a controllable transmission zero and a wide out-of-band rejection > 33 dB. In contrast, the other two sub-cavities are used to create a self-diplexing antenna with wide frequency tunability (2.8–5.0 GHz) with two additional narrow slots and high isolation (>22 dB). Detailed parametric studies confirmed that tuning of self-diplexing antenna has no significant impact on the performance of integrated BPF. An equivalent circuit model of the design is developed and validated with simulation and measurement results. The proposed design has a simple and compact structure, good isolation, and controllability, making it suitable for modern handheld wireless systems.

Asymmetric CMOS switch for Dicke radiometer in millimeter-wave imaging system

An asymmetric Dicke switch implemented in bulk complementary metal-oxide-semiconductor (CMOS) technology is proposed to achieve high isolation and low insertion loss in the D-band. A Dicke switch eliminates the noise in the signal transmitted from the antenna, providing a high signal-to-noise ratio at the receiver front end. The proposed Dicke switch employs an asymmetric configuration for the signal transmission path and the reference noise incidence path, which overcomes the trade-off relationship between the insertion loss and isolation characteristics. The proposed asymmetric structure presents an optimum impedance in the reference component to achieve the same characteristics as those of the noise incident from the antenna port. The Dicke switch is fabricated using the 65-nm RFCMOS process with a chip size of 350 × 490 μm2, including all the pads. The measurement results in the D-band present an insertion loss below 2.8 dB in the on-state and isolation above 22 dB in the off-state. The minimum insertion loss and maximum isolation were measured to be 1.7 dB at 155 GHz and 29 dB at 122 GHz, respectively.

Fabrication of compact substrate integrated waveguide dual band bandpass filter using complementary split-ring resonators for C and X band applications

This article presents a compact dual-band Bandpass Filter(BPF) based substrate integrated waveguide(SIW) used for C and X band applications. Complementary split-ring resonators(CSRR) are loaded into the waveguide surface to obtain more advantages of compactness and good performance. The SIW cavity undergoes initial optimization utilizing the powerful genetic algorithm, renowned for its robustness in solving complex problems, before proceeding to simulation with Ansys HFSS software with loaded CSRRs. The filter displays two passbands: the first has a bandwidth of 2 GHz and resonates at 6.8 GHz, while the second has a bandwidth of 5,55 GHz and resonates at 10.3 GHz. Moreover, with two resonance frequencies, the developed BPF has the benefit of low insertion loss(S21=-1.7dB and -1.9 dB) and improved return loss: (S11=-24dB and -22 dB) respectively. Furthermore, the proposed combination not only allows the implementation of a forward-wave passband propagating below the characteristic cutoff frequency of the waveguide but also exhibits good rejection, demonstrated by the presence of two transmission zeros with rejection of -16 dB and -19 dB, attained at 7.4 GHz and 14.8 GHz respectively. The proposed SIW BPF was designed using a 0.6mm thick FR4 dielectric substrate measuring 13mm × 15mm. The filter is manufactured to validate the concept and the measured results agree well with the simulation. With all these advantages: compact size, high rejection, and good filtering response, the proposed SIW BPF became suitable for microwave applications.

Inverse design of highly-efficient and broadband polarization beam splitter on SOI platform

Polarization beam splitters (PBSs) are essential components in integrated optics, particularly for applications demanding high polarization purity. However, most existing PBS designs rely on complex forward design methods, often constrained by large size and limited performance. In this study, we introduce an inverse design approach based on shape optimization to develop a high-performance PBS on the silicon-on-insulator (SOI) platform. By optimizing the boundary shape, the proposed PBS exhibits low insertion loss (<1.4 dB) and high extinction ratio (>9.2 dB) across a bandwidth range of 65 nm (1500 nm–1565 nm), as confirmed by experimental results. The footprint of the device measures 1.7 × 16 μm2, and the entire structure can be fabricated through a single lithography step. This work holds great promise for the convenient and efficient design of on-chip PBSs.

High‐selectivity wideband four‐way filtering power divider with input absorptive feature

AbstractIn the paper, a high‐selectivity wideband four‐way filtering power divider with input absorptive feature is presented. It consists of two parallel‐coupled lines (CLs), two three‐coupled lines (TCLs), two open‐ended stepped branches, one absorptive branch, and two isolation resistors. The wideband filtering response is achieved by cascading the TCLs and CLs. While high selectivity is obtained by loading the open‐ended stepped branch, where two extra transmission zeros are generated. In addition, wide absorptive bandwidth with good isolations between adjacent output ports are realized by combining the absorptive branch with the isolation resistors. Equations are derived by using the two‐parity mode analysis, and main parameters are investigated in detail. For validation, a prototype was designed and fabricated. Test results show that the 3‐dB FBW can reach 87% with a 10‐dB input absorptive FBW of 200%. Besides, for the output ports with 10‐dB return loss and 10‐dB isolation, the FBWs are 94% and 91.5%, respectively. It also features high frequency selectivity and low insertion loss.

Ultranarrow and multiband perfect absorbers based on dual quasi-bound states in the continuum in near infrared

High quality factor (Q-factor) and multiband perfect absorbers are highly desired in light-harvesting efficiency related optical devices, yet they are always limited by conventional mechanisms like electromagnetically induced transparency, Tamm or plasmonic resonance. In this paper, through constructing the strong coupling between two guided-mode resonances in subwavelength gratings, we propose an ultranarrow and multiband perfect absorber based the dual-band quasi-bound states in the continuum (quasi-BIC) design in near infrared. Benefiting from its angle-dependent characteristic, the device can be straightforwardly utilized for light-switched lamps and optical sensors. Q-factor 8337 and the modulation depth 98.1% are realized while the insertion loss is only 0.07 dB. Compared with its conventional counterparts, the quasi-BIC based absorber enables an excellent hexa-frequency and ultranarrow asynchronous switch function. The quatary-band perfect absorption below 1 nm bandwidth can be applied to the optical sensor to detect four light signals with weak signal strength. This work provides a theoretical basis for multifunctional absorbers with high Q-factor, high modulation depth, and low insertion loss.

Broadband Eight-Way High-Isolation Cavity Power Divider with Low Insertion Loss for MIMO Communication Systems

Broadband Eight-Way High-Isolation Cavity Power Divider with Low Insertion Loss for MIMO Communication Systems

Compact and efficient photonic lanterns through multi-stage tapering.

Photonic lanterns (PLs) have been recently used in mode-division multiplexed systems with a low insertion loss, a low mode-dependent loss (MDL), and a wide bandwidth. However, the cross talk (XT) performance of the PLs requires further enhancement within a short taper length. In this Letter, a multi-stage cascaded scheme for short PLs is proposed to further improve the performance on losses and XT. The XT of the optimized 6-mode 3-stage PL is below -23.4 dB, while the total length is only 6 cm. To the best of our knowledge, this is the first quantitative optimization of a 3-stage tapered PL, resulting in a compact structure and excellent performance. Furthermore, we experimentally validate the feasibility of the 3-stage tapering process.

Analysis and design of compact dual-mode bandpass filter based on modified CSRR with wide stopband for 5G sub-6 GHz mobile communications

In this paper, a dual-mode bandpass filter with a wide stopband based on modified complementary split-ring resonators for 5G sub-6 GHz mobile communications is presented. The non-magnetic resonant particle known as a complimentary split ring resonator is used with a host microstrip line with a series gap in order to obtain a bandpass response. Since a complementary split-ring resonator provides a narrow passband, a T-slot has been introduced in the middle of this resonator to obtain dual-mode behavior with controllable bandwidth. Moreover, a pair of stubs are added to the host microstrip line in order to achieve a wide stopband with good out-of-band rejection. The proposed resonator is analyzed, and a bandpass filter is designed to operate at 3.6 GHz to cover the 5G band from 3.4 to 3.8 GHz. The results show that the filter has a low insertion loss, good return loss, and a wide stopband up to 9 GHz with a compact size since its resonator offers a size of 0.1 λ g × 0.14 λ g where λ g is the guided wavelength at 3.6 GHz.

A novel wideband phase shifter on coupled microstrip line

AbstractIn this paper, a new 180° broadband phase shifter with coupled microstrip line with enhanced coupling by etched slots is proposed, which uses the energy coupling between the parallel‐coupled microstrip lines on the upper layer of the dielectric substrate and the etched rectangular slots (RS) structure on the bottom floor to circumvent the problem for achieving wide operating broadband and low insertion loss with compact size and simple structure. First, the main line and the reference line of the proposed phase shifter are composed of two parallel coupled lines and a uniform transmission line, respectively. Then, its working mechanism is described. Afterward, the phase shifter introduced an RS structure to increase the coupling strength, achieving a broadband of 69.7% and very low insertion loss (0.09 dB) with a phase shift of 180 ± 5°. Finally, a prototype 180° phase shifter with a center frequency of 3.0 GHz was designed, fabricated, and measured, and the measured results are good in agreement with the simulated ones.

A novel design of a Wilkinson power divider based on the circular-shape resonator

Abstract This paper describes the general properties of power dividers, in particular matching and isolation. This original works relates to three different divider structures based on the circular-shaped resonator. These prototypes resemble the Wilkinson power divider due to their geometric configuration. These power dividers provide very good isolation between their output ports of −51.26 dB. In fact, the originality of these new structures stems from the idea of minimizing the size of this classic power divider. The required design parameters for the three proposed dividers came from a simulation study using the Ansoft HFSS tool in addition to a design theory. The experimental prototypes are well presented and operate at 2.4 GHz. They demonstrate excellent performance in adaptation, which refers to impedance matching, ensuring consistent impedance at the component terminations. Additionally, they exhibit low insertion losses and high isolation at 2.4 GHz. The measurement results agree well with those of the simulation. The benefits demonstrated by this study are significant, justifying the preference for these components.

Ultra-compact and polarization-insensitive silicon waveguide 3 × 3 star-crossing based on composite subwavelength grating metamaterials.

We present what we believe is the first report on a polarization-insensitive 3 × 3 silicon star-crossing utilizing a composite subwavelength metamaterial waveguide structure. Two different types of subwavelength grating metamaterials (nanohole grating and fan-shaped bent subwavelength grating) are respectively used to address diffraction issues in the crossing region and mode interference issues caused by a compact non-adiabatic design. This approach results in a device with an ultra-compact footprint of 12.68 × 10.98 µm2 on a standard 220 nm silicon-on-insulator (SOI) platform. Simulation results show low insertion loss (IL) values of <0.2 dB/0.3 dB and suppressed cross talk (CT) levels of <-27.2 dB/-23.6 dB for TE/TM polarizations across a wavelength range of 100 nm (1500-1600 nm). Experimental measurements of the fabricated devices confirm outstanding performance, with IL values of <0.35 dB/0.4 dB and CT levels of <-31.5 dB/-28.6 dB for TE/TM polarization in the C-band.

Multi‐band pass negative group delay circuit with low insertion loss

AbstractA novel multi‐band pass negative group delay circuit has been designed and proposed. The circuit consists of three types of components: capacitance, inductance, and resistance. An n‐order bandpass negative group delay circuit was analyzed and presented, and taking a three‐frequency bandpass negative group delay circuit as an example, the influence of different component values on the circuit group delay and insertion loss was analyzed. The actual test results of this circuit are consistent with the simulation results, and it can achieve the function of a multi‐bandpass circuit. In actual testing, the circuit frequencies with negative group delay are 49, 82, and 102 MHz, with corresponding group delay values of −2.177, −2.058, and −1.903 ns and corresponding insertion loss values of −5.810, −5.835, and −5.866 dB.

Numerical simulation of an in-fiber broadband plasmonic polarization filter using photonic crystal fiber with dual elliptical gold layers

The demand for advanced and compact photonic filters is increasing in today's optical communication systems. This work introduces a new all-fiber broadband polarization filter using photonic crystal fiber with dual elliptical gold layers. The filtering performance is evaluated and analyzed by the finite element method. The simulation results demonstrate that the two elliptical gold layers can effectively induce a significant change in the energy of x-polarized light, leading to a great difference between the two polarized lights. By selecting reasonable structural parameters of the proposed PCF, the 1 mm-long in-fiber filter has a maximum extinction ratio of -108.90 dB, a low insertion loss of 0.64 dB around 1.31 µm and an ultra-broad bandwidth of 1020 nm, covering two common communication windows of 1.31 µm and 1.55 µm. Additionally, the filtering experimental scheme is discussed. This filter is expected to drive the advancement of optical integrated chips and all-optical communication networks.