In-band Return Loss Research Articles

Penta‐band antenna for global system for mobile communications/digital cellular system/personal communications service/universal mobile telecommunications system/wireless local area network operation in portable devices

This study presents a planar inverted-F antenna for penta-band operation in portable devices, in accordance with the following wireless communication standards: global system for mobile communications, digital cellular system, personal communications service, universal mobile telecommunications system, and wireless local area network. The proposed antenna consists of a folded planar radiator with two slots – a J-shaped and a rectangular one – suspended above a substrate partially covered with a ground plane, to which a printed radiating strip is connected. Multiple resonances excited in this structure generate the radiation bands of the antenna, covering all required frequency ranges. A parametric analysis is conducted with the aid of electromagnetic simulation in order to evaluate the influence of geometrical dimensions of the antenna on its performance. The fabricated antenna prototype exhibits overall dimensions of 45 mm × 90 mm × 6.6 mm, and the experimental 10 dB return-loss bands of the antenna are 869–966, 1653–2200, and 2390–2505 MHz, with a measured linearly polarised gain of 2.2 dB at 915 MHz, 2.0 dB at 1900 MHz, and 1.0 dB at 2450 MHz, on the principal cut planes. A good agreement is observed between simulated and experimental results.

Analysis and Design of a New Self-Packaged Wideband Balun Bandpass Filter With the Functionality of Impedance Transformation

In this paper, a new self-packaged wideband balun with the high selective bandpass filtering response and impedance transformation characteristic is presented. By virtue of circuit transformations, corresponding two-port equivalent circuit with asymmetrical port impedances is put forward. The analysis results of this two-port network exhibit that the proposed new design is able to achieve a quasi-elliptic equal-ripple response with three transmission poles and four transmission zeros. In addition, the frequency response can be directly determined according to the desired design specifications of impedance transformation ratio k, ripple fractional bandwidth (FBW), and in-band return loss RL. For validation purposes, a demonstrated wideband balun bandpass filter (BPF) working at 2.0 GHz with 50–100- $\Omega $ impedance transformation has been implemented by utilizing the multilayer liquid-crystal polymer (LCP) bonded printed circuit board (PCB) lamination technology. Theoretical, simulated, and measured results are recorded in good agreement, well verifying the design method.

Design and optimization of a planar folded substrate integrated waveguide bandpass filter exploiting aggressive space mapping

Substrate integrated waveguide (SIW) is a new structure for microwave transmission. In this paper, a planar folded sixth-order SIW filter is designed with aggressive space mapping (ASM) algorithm. Its center frequency is 22 GHz, 3 dB bandwidth 1 GHz, and in-band return loss 22 dB. The filter satisfies design specifications after four iterations, and is fabricated using micro-electro-mechanical systems (MEMS) technology with a chip size of 7.5 mm × 8.5 mm × 0.4 mm. Measurement results show that the center frequency of the filter measures at 22.2 GHz, 3 dB bandwidth at 1 GHz, insertion loss at 3.57 dB, return loss at 22 dB and out-of-band rejection at 40 dB.

A size reduced Gysel power divider with simple structure and high design flexibility

AbstractIn this letter, a new simple structure of Gysel power divider (PD) is proposed. Comparing to the conventional Gysel PD, the high‐power handling capability is reserved with size reduction from the nonlinear relationship between the phase delay and the physical dimension of the utilized open‐circuited coupled line. The structure is analyzed according to an open‐end‐stub‐based equivalent circuit, in which procedure the closed‐form design equations are derived simultaneously. Also, the analysis shows a high design freedom in choosing the values of the isolation resistors and the impedances of the utilized transmission lines (TLs), which property can be used to control the bandwidth (isolation and input return loss band) of the proposed structure. Finally, in order to verify the proposed design theory, a Gysel PD with a center frequency of 2.5 GHz is designed, simulated, fabricated, and characterized. Besides good agreement with the simulation data, the experimental results show that the proposed PD features a wide isolation band which is around 89% with the reference of 15‐dB loss.

Coupling-Matrix-Based Systematic Design of Single-DC-Bias-Controlled Microstrip Higher Order Tunable Bandpass Filters With Constant Absolute Bandwidth and Transmission Zeros

This paper presents a systematic design procedure of microstrip higher order tunable bandpass filters (BPFs) that can realize a constant absolute frequency bandwidth (ABW) and transmission zeros (TZs) with the minimum number of varactors and a single controlled dc-bias voltage. To this end, intrinsic frequency dependence of interresonator couplings is employed instead of external controls, but the design has faced a difficulty of realizing ideal frequency curves of coupling coefficients at all the coupling regions, including nonadjacent couplings. To overcome such a difficulty, this paper introduces a frequency-curve shape design approach considering upward- or downward-curved convex that is dependent on the types of interresonator coupling. As illustrative examples, fourth- and sixth-order tunable BPFs are proposed and designed, starting from a coupling-matrix synthesis. Their structural parameters can be efficiently designed with the proposed design method. The frequency agility with keeping a constant ABW, acceptable low insertion loss, a good in-band return loss level, and TZs is numerically and experimentally demonstrated for both fourth- and sixth-order tunable BPFs.

High-Order Planar Bandpass Filters With Electronically-Reconfigurable Passband Width and Flatness Based on Adaptive Multi-Resonator Cascades

A class of quasi-elliptic-type planar bandpass filters (BPFs) with electronically controllable bandwidth between narrow-band and ultra-wideband states and enhanced passband flatness is reported. It consists of the in-series cascade of replicas of an adaptive BPF stage that exhibits three in-band poles and two transmission zeros (TZs). In this manner, BPF transfer functions with 3K poles and multiple TZs-between two K-multiplicity and 2K one-multiplicity TZs-without cross-coupling can be synthesized with a K-stage BPF architecture. Bandwidth reconfiguration is performed through the spectrally agile allocation of these TZs. Passband flattening for all the states is accomplished through the adjustment of the BPF in-band return-loss profile by tuning the external admittance inverters and those between BPF stages. The aforementioned procedures for bandwidth control and passband flattening are theoretically demonstrated with the coupling-routing diagram formalism. Furthermore, a mechanism to avoid the appearance of out-of-band spurious peaks due to the multi-stage in-series-cascade process in the associated transmission line-based BPF implementation is described. For experimental-validation purposes, a 1-GHz sixth-order varactor-tuned BPF microstrip prototype with measured flattened 1-dB referred passband-width states going from 46 to 482 MHz-measured bandwidth tuning ratio of 11.5:1-is developed and characterized. Measurements for various temperature conditions and their in situ compensation are also shown.

Filtering patch antenna on λ /4‐resonator filtering topology: synthesis design and implementation

In this study, a novel filtering patch antenna (FPA) based on quarter-wavelength or λ /4-resonator filtering topology is presented, and its frequency response is efficiently synthesised to achieve the prescribed higher-order frequency selectivity. As the resonant patch radiator is capacitively fed by two inductively coupled λ /4 resonators, three transmission poles are created in the operating band to demonstrate the third-order bandpass filtering property. In design, two adjacent λ /4 resonators are coupled via a shorting pin as the K inverter, while one of them is coupled with the resonant patch via coupled line as the J inverter. As their equivalent parameters are numerically de-embedded, the overall equivalent filtering network of this proposed FPA is constituted and synthesised with the Chebyshev-function filtering response. Next, the relationship between the realisable fractional bandwidth and in-band return loss is thoroughly investigated for a patch radiator with its constant unloaded quality factor. Finally, a prototype FPA at 4.0 GHz is designed, fabricated, and measured. The measured and simulated results are found in good agreement with each other, demonstrating a few attractive features of the proposed FPA, inclusive of wide operating bandwidth, sharp filtering selectivity, and flat radiation gain, as benefited by the three in-band poles.

Design of Optimized Minimum Inductor Bandpass Filters

A design methodology for optimized minimum inductor bandpass filters (BPFs) is presented. Design curves are provided to determine the filter order for a required out-of-band rejection as a function of bandwidth (BW). Coefficients for BWs from 10% to 100% in steps of 10% for different filter orders and two different transmission zero placements are provided. For both cases, the required in-band return loss is larger than 10 dB. Using the derived coefficients, filters with required rejections can be designed for a given center frequency. To validate the design methodology, five discrete element filters with different BWs are designed and fabricated at a center frequency of 1.5 GHz. Furthermore, to show the application of the minimum inductor filters in complementary metal–oxide–semiconductor (CMOS), an S-band BPF in 0.13- $\mu \text{m}$ CMOS, with 60% BW, is designed and fabricated. The out-of-band rejection of the fabricated filter is larger than 50 dB.

Frequency‐reconfigurable circularly polarized antenna for UHF RFID reader

ABSTRACTA frequency‐reconfigurable circularly polarized (CP) monopole antenna is proposed for ultrahigh frequency (UHF) radio frequency identification (RFID) reader applications. This reader antenna can operate in both North America and Europe regions because of the frequency‐reconfigurable characteristic. Two L shaped strips are the major radiating elements which can produce CP radiation. Two short rectangular patches are connected to the L shaped strips via two pin diodes. By switching the pin diodes on and off, the antenna can produce CP at the two desired frequency bands. The measured 3‐dB axial ratio bands of this antenna are 864–887 and 899–913 MHz at the two different states, respectively, and both bands are included in the 10‐dB return loss bands. This antenna can be used for UHF RFID reader in both North America and Europe. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2842–2845, 2016

Wideband Impedance Transformers With Good Frequency Selectivity Based on Multisection Quarter-Wave Lines and Short-Circuited Stubs

In this letter, a class of wideband impedance transformers based on multisection quarter-wave transmission lines and short-circuited stubs are proposed to be incorporated with good passband frequency selectivity. A synthesis approach is then presented to design this two-port asymmetrical transformer with Chebyshev frequency response. For the specified impedance transformation ratio, bandwidth, and in-band return loss, the required impedance parameters can be directly determined. Next, a transformer with two section transmission lines in the middle is characterized, where a set of design curves are given for practical design. Theoretically, the proposed multisection transformer has attained good passband frequency selectivity against the reported counterparts. Finally, a 50–110 $\Omega$ impedance transformer with a fractional bandwidth of 77.8% and 15 dB in-band return loss is designed, fabricated and measured to verify the prediction.

Compact full Ka‐band waveguide directional coupler based on large aperture array

A compact full Ka-band waveguide directional coupler based on novel aperture array is presented. The broadband, good in-band coupling flatness and excellent return loss are achieved by using the proposed novel aperture array in the common broad wall of two paralleled waveguides. For verification purpose, a prototype of the proposed directional coupler has been designed, fabricated and measured. The experimental results show that the return loss and isolation of the proposed coupler are better than 28 and 30 dB, respectively, and coupling strength varies from −20.35 to −19.23 dB over the full waveguide bandwidth. The length of the coupling region is only 8.5 mm.

A Four-Way Microstrip Filtering Power Divider With Frequency-Dependent Couplings

A four-way microstrip power divider is designed with bandpass filtering response. The synthesized inline filter has a generalized Chebyshev response, where frequency-dependent couplings are utilized. All of the critical parameters, including the characteristic impedances and electrical lengths, can be determined by our derived closed-form formulas. By extending the inline filter, the configuration of four-way power divider is obtained. Then, three isolation resistors are properly selected according to the even-/odd-mode analysis. The proposed four-way filtering power divider has low in-band insertion loss and high frequency selectivity. It can provide the in-band return loss and isolation between outputs better than 16.7 and 17.5 dB, respectively .

Compact bandpass filter with wide stop band response based on meandered-line stepped-impedance resonator using IPD process

This letter presents a compact size, wide-band bandpass filter (BPF) with high selectivity using integrated passive device technology. The structure of the proposed BPF consists of electromagnetically coupled stepped-impedance resonators (SIRs). To miniaturize the size of the proposed BPF, the size of the SIR was geometrically reduced significantly by meandering the line widthwise. Additionally, a uniform-impedance stub, which was placed between the SIRs to enhance the level of electromagnetic coupling between them, reduced the size of the BPF and also improved its pass band return loss. To verify the proposed method, a protocol BPF with central frequency of 6.72 GHz was designed, simulated, and fabricated on a Gallium Arsenide substrate. The measured return and insertion loss of 22.7 and 1.58 dB, respectively, indicated the high pass band selectivity of the BPF. Additionally, the presence of a transmission zero at 8 GHz with a measured suppression level of 37 dB in the stop band improved out-of-band selectivity of the BPF. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1466–1470, 2015

A miniaturized quad‐band bandstop filter with high selectivity based on shunt‐connected, T‐shaped stub‐loaded, stepped‐impedance resonators

ABSTRACTThis letter presents a microstrip quad‐band bandstop filter (QBBSF) with a miniaturized size and high selectivity. The structure of the proposed QBBSF consists of two‐folded, shunt‐connected trisection stepped‐impedance resonators (TSSIRs). One of these TSSIRs, which operates on the second and fourth central frequencies, has been embedded inside another TSSIR operating at the first and third central frequencies of the proposed QBBSF. Characterized by equivalent circuit analysis and full‐wave EM simulations, each TSSIR has been miniaturized by a T‐shaped stub load. The main advantage of the proposed QBBSF lies in its central frequencies, which can be adjusted conveniently within a wide range by varying parameters of TSSIRs, the positions, and dimensions of the stub loads. A protocol QBBSF with a compact size of 0.0115 λg2 operating at central frequencies of 1.90, 3.32, 5.77, and 6.75 GHz was designed, simulated, and fabricated to verify the proposed method. The measured minimum stop band return loss of 21.4 dB and maximum pass band insertion loss of 0.66 dB indicated the excellent in‐band and out of band selectivity of the proposed QBBSF. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1129–1132, 2015

Compact Quasi-Elliptic Response Wideband Bandpass Filter With Four Transmission Zeros

This letter presents a novel quasi-elliptic response bandpass filter (BPF) with 3 dB fractional bandwidth of 39.8% for 2.4 GHz WLAN application. Four resonant modes from two stepped-impedance stub loaded shorted stepped-impedance resonators (SISLSSIRs) and one dual-mode shorted stub loaded stepped-impedance resonator (SSLSIR) can constitute an asynchronously tuned coupled-resonator circuit which support a wideband performance. Four transmission zeros (TZs), i.e., one TZ due to the mixed electric and magnetic coupling, one TZ due to the harmonic effects, and another two TZs owing to the cross-couplings, are realized on both sides of the passband, resulting in its quasi-elliptic response performance. The radial stubs and high-impedance open stubs are loaded at the middle position of SISLSSIRs to improve the in-band return loss of BPF. The fabricated filter has a compact size of $0.22\lambda_{\bf g}\times 0.22\lambda_{\bf g}$ and wide upper stopband from 2.62 to 7.69 GHz. Good agreement is shown between the simulated and measured results.

High Frequency Properties of Ferrite/Fe-Si-Al Alloy Soft Magnetic Composites

The inclusion of Fe-Si-Al alloy particles in NiCuZn ferrite matrix was investigated with regard to the high frequency electromagnetic properties (complex permeability and permittivity). The resultant composites of relatively low density exhibit a shift of the permeability spectra to higher frequencies and an increase of dielectric polarization, which finally favour the electromagnetic wave attenuation at microwave frequencies. Thus, wider band return loss peaks are attained at frequencies above 6GHz by thinner composite materials.

Compact Differential Wideband Bandpass Filters With Wide Common-Mode Suppression

A compact differential wideband bandpass filter (WBPF) composed of a coupled full-wavelength loop is presented. The differential-mode circuit of the proposed filter is analyzed, showing that the proposed filter exhibits a three-pole differential-mode (DM) wideband bandpass filtering response. Moreover, both the fractional bandwidth (FBW) and the inband return loss can be adjusted by changing the parameter of the characteristics of coupled-line. Furthermore, the proposed filter provides a wider common-mode (CM) rejection characteristics owing to its multiple periodical transmission zeros. Additionally, the filter has a very compact size occupation. To verify the design concept, one filter example has been designed, fabricated and measured. The fabricated filter demonstrates good differential WBPF performance including a broad 3 dB fractional bandwidth of 66.6% centered at f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 1.62 GHz, a wider 14.5 dB CM rejection from dc to 2.96f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , and a very compact size of 0.163 λ <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> .

Yagi Array of Microstrip Quarter-Wave Patch Antennas with Microstrip Lines Coupling

A new kind of Yagi array of quarter-wave patch antennas is presented. The Yagi array has a low profile, a wide bandwidth, and a high gain. A main beam close to endfire is produced, with a vertical polarization in the horizontal plane. A set of microstrip lines are introduced between the driven element and the first director element to enhance the coupling between them, and therefore the bandwidth could be increased and the back lobes could be suppressed. Measured results show that the Yagi array with 4 elements generates a peak gain of about 9.7 dBi, a front-to-back ratio higher than 10 dB, and a 10 dB return loss band from 4.68 GHz to 5.24 GHz, with a profile of 1.5 mm and an overall size of 80 × 100 mm2. An increase of the number of director elements would enhance the gain and have the main beam pointing closer to endfire.

Design of a Dual-Band High-Gain Antenna Array for WLAN and WiMAX Base Station

A dual-band $3 \times 2$ antenna array with high gain is presented in this letter. A dual-band folded dipole antenna is utilized as the antenna array element. A broadband symmetric feed network is designed to maintain each array element with the identical current magnitude and phase. The antenna array has a low profile of 12 mm (about $0.1{\lambda _{\rm L}}$ ; ${\lambda _{\rm L}}$ is the wavelength in free space at the lowest operating frequency). Dual bands $2.3\!\sim\! 2.56$ and $3\!\sim\! 4.2~\hbox{GHz}$ for return loss (RL) being higher than 10 dB can be obtained in simulation, while two 10-dB RL bands $2.31\!\sim\! 2.51$ and $3.1\!\sim\! 4.15~\hbox{GHz}$ in measurement cover the wireless local area network (WLAN, $2.4\!\sim\! 2.48~\hbox{GHz}$ ) and Worldwide Interoperability for Microwave Access (WiMAX, $3.3\!\sim\! 3.8~\hbox{GHz}$ ). The measured results also show that this planar antenna array has a high gain $14.3\!\sim \!15.1~\hbox{dBi}\;(2.31\!\sim\! 2.51~\hbox{GHz})$ , $16.2\!\sim\! 17.3~\hbox{dBi}$ ( $3.1\!\sim\! 4.15~\hbox{GHz}$ ) in $ + { z}$ -direction and a low cross-polarization level $ .

A novel TRI-band planar inverted-F antenna for GSM/DCS/PCS operation in mobile handsets

In this article, a novel mobile handset planar inverted-F antenna (PIFA) for tri-band operation in GSM, DCS, and PCS bands is presented. This PIFA comprises a rectangular folded planar radiator, which has a J-shaped slot, suspended above a partially grounded substrate. In this antenna, two resonant modes are excited and originate a lower band for GSM and an upper band for DCS and PCS. The influence of several geometrical parameters of the antenna on its performance was investigated to achieve an optimal design. The fabricated prototype of the proposed PIFA has overall dimensions of 45 × 90 × 6.6 mm3. The measured 10 dB return loss bands of the antenna are 880–892 MHz and 1658–2079 MHz. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:821–825, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27441