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The contribution of this work is to propose miniaturized trisection bandpass filters (BPFs) using size-reduced substrate integrated coaxial resonators (SICRs). The applied SICRs are operated under a coaxial mode. The occupied circuit area of the SICR developed from its structurally similar one, the substrate integrated waveguide (SIW) cavity, is only 6.2% that of the latter, corresponding to a circuit-area reduction rate of 93.8%. The cross-coupling between the input and output resonators can be either a magnetic or electric coupling for locating the transmission zero near either the upper or lower passband edge, respectively. Sample trisection BPFs with magnetic/electric cross-couplings are built for experimental verification. Agreements between measured and simulated data are observed. These miniaturized trisection BPFs with a freely switchable transmission zero are endowed with the advantage of an excellent circuit-area efficiency in the category of SICR and SIW cavity trisection BPFs.

A compact planar inverted-F antenna (PIFA) placed on one of the two hinges of a laptop computer is proposed for wireless local-area network (WLAN) operation. The aim of this design is to integrate ...

The contribution of this study is to develop a miniaturised substrate integrated waveguide (SIW) cavity resonator with two evanescent-mode resonances. The circuit area of the developed dual-frequency SIW cavity is only 9.2% that of its conventional SIW cavity counterpart. A dual-band filter is implemented from using two miniaturised SIW cavity resonators. The two-passband frequencies can be independently controlled. Two transmission zeros are created by the two sides of each passband for enhancing the signal selectivity. A diplexer is also designed from using the proposed SIW cavities. A dual-band filter and a diplexer are built for experimental verification. Agreements between measured and simulated data are observed. To the best of the authors' knowledge, the designed dual-band filter and diplexer have achieved the best circuit area efficiency in the categories of dual-band SIW cavity filters and diplexers.

This paper proposes a low-profile two-element wireless local-area network (WLAN) multi-input multi-output (MIMO) antenna system designed for laptops. The primary and secondary elements are ...

This communication presents a novel design of a differentially fed wideband circularly polarized (CP) slot antenna. The CP antenna consists of two opposite-fed C-shaped radiating patches and a stub-loaded corner-truncated rectangular slot. With the slot designed to be antisymmetric with respect to the bisection plane and oppositely fed by two microstrip lines, good differential-mode (DM) performance was obtained. On the other hand, the radiations contributed by the corresponding parts of the antisymmetric CP antenna will be destructive when in common-mode (CM) operation. This results in high CM suppression without a preceding CM-rejection bandpass filter. Also, low DM axial ratios (ARs) were achieved by tuning the truncated corner length, the protruded stub length, and the coupling length and gap of the C-shaped radiating patches. The measurement shows that the designed CP antenna has a wide 10 dB DM impedance band of 5–6.49 GHz and a 3 dB DM AR band of 4.94–6.03 GHz, corresponding to a CP fractional bandwidth of 18.7%. Also, in 4.5–6.5 GHz, the proposed antenna can effectively reject CM input signals because the measured CM return loss is smaller than 2.91 dB, and can convert only very little DM input power into CM reflected power since the DM-to-CM conversion is less than −50 dB.

A sub-6-GHz multi-input multi-output (MIMO) slot antenna system was proposed in this study, where each antenna element was constructed using a slot structure. To effectively use the available space in a tablet and maximize the screen, we have deployed the MIMO antenna system on the left side-edge frame of the tablet. The MIMO antenna system consists of two identical dual-slot-antenna units that are separated by 10 mm. The two closely spaced slot antennas in the same dual-slot-antenna unit are arranged asymmetrically mirrored of each other with respect to the system ground plane. The isolation between its two slot antennas can be enhanced by 5 dB to meet the design requirement by using an ungrounded full-wavelength microstrip resonator.

This study proposes a low-profile switchable LTE/WWAN multi-input and multi-output (MIMO) antenna system for laptops. The main and auxiliary antennas, mirror-imaged of each other, are confi...

The contribution of this work is to propose a compact balanced bandpass filter design using the miniaturised full/half-mode substrate integrated waveguide cavities (SIWCs) together with the microstrip coupling slot feed. The circuit area of the proposed full-mode SIWC is only 4.64% of its conventional SIWC counterpart, and the half-mode SIWC further reduces the circuit area by half. Besides the circuit compactness, the non-coupling of the microstrip and the slot in the common-mode (CM) operation provides an excellent CM signal rejection. Prototypes of two-pole full/half-mode balanced SIWC BPFs are fabricated and measured to validate the circuit design. Agreements between measured and simulated data are observed. The CM signal rejection levels are larger than 45 dB over a wide-frequency range with the passband's differential-mode insertion losses around 1.6 and 0.8 dB for the full- and half-mode designs, respectively.

This paper proposes a two-element multi-input multi-output (MIMO) open-slot antenna implemented on the display ground plane of a laptop computer for eight-band long-term evolution/wireless wide-area network operations. The metal surroundings of the antennas have been well integrated as a part of the radiation structure. In the single-element open-slot antenna, the nearby hinge slot (which is bounded by two ground planes and two hinges) is relatively large as compared with the open slot itself and acts as a good radiator. In the MIMO antenna consisting of two open-slot elements, a T slot is embedded in the display ground plane and is connected to the hinge slot. The T and hinge slots when connected behave as a radiator; whereas, the T slot itself functions as an isolation element. With the isolation element, simulated isolations between the two elements of the MIMO antenna are raised from 8.3–11.2 to 15–17.1 dB in 698–960 MHz and from 12.1–21 to 15.9–26.7 dB in 1710–2690 MHz. Measured isolations with the isolation element in the desired low- and high-frequency ranges are 17.6–18.8 and 15.2–23.5 dB, respectively. Measured and simulated efficiencies for the two-element MIMO antenna with either element excited are both larger than 50% in the desired operating frequency bands.

A balanced wideband (WB) planar inverted-F antenna (PIFA) integrated with a balanced WB bandpass filter (BPF) is presented in this letter. Due to circuit symmetry, the balanced patch PIFA does not need a grounded via hole for its shorting strip, rendering the PIFA easy to fabricate. The balanced WB BPF that is added in front of the balanced PIFA serves to improve the differential-mode (DM) passband selectivity and upper stopband rejection and meanwhile to increase the common-mode (CM) rejection. In terms of the passband selectivity defined by the ratio of 20-dB bandwidth to the 3-dB bandwidth in the DM return-loss response, the simulated WB filtering PIFA's selectivity is increased from 0.6 to 0.86 after the WB BPF is integrated. In addition, high CM suppression was observed with a maximum return loss of 2.37 dB within the DM passband.

A balanced quad-band diplexer is proposed with wide common-mode (CM) suppression and high differential-mode (DM) isolation in this study. The six-port balanced diplexer was formed by combining two dual-band bandpass filters operating at 1.92/5.25 and 2.45/5.8 GHz through two stepped-impedance resonator (SIR) inserted T-junctions. By carefully designing the section length of the T-junction and the SIR length from its open-end to the joint-point with the T-junction, high isolation between diplexer channels can be attained. A prototype of the proposed balanced quad-band diplexer was implemented and measured with a DM isolation of higher than 51.8 dB and a CM suppression of larger than 47.9 dB in the four DM passbands. Good agreement was observed between the simulated and the measured results.

This paper presents balanced diplexer design using multi-layered substrate integrated waveguide cavities (SIWCs). Four SIWCs are employed in the diplexer design, and each of the two duplexing bands is created by two vertically stacked SIWCs. Two types of the diplexers are proposed, one is the single mode resonance of the SIWC, and the other is the dual-mode resonance. The former has its SIWC either an $\mathbf{TE}_{\mathbf{102}}$ or $\mathbf{TE}_{\mathbf{201}}$ mode resonance and the latter is under the dual-mode (both $\mathbf{TE}_{\mathbf{102}}$ and $\mathbf{TE}_{\mathbf{201}}$ ) operation. A paired CPW is used to form the balanced common port and the SMAs are applied in the balanced duplexing ports. The dual-mode diplexer exhibits a wider bandwidth and sharper band-edges than those of the single-mode due to the dual-mode's double circuit order effect. Experiments are conducted to verify the circuit design and reasonable agreements are observed between the measured and simulated data.

In this paper, a balanced wideband filtering circularly polarized (CP) antenna designed using rectangular quasi-self-complementary structure is proposed. The antenna is fed by a differential microstrip line, and consists of a strip-loaded rectangular slot radiator and its complementary slot-loaded patch counterpart. The fields radiated by the two complementary parts of the antenna are expected to be orthogonal if properly excited. To achieve a CP radiation pattern, a 90° delay line section is embedded in one of the two feedlines to provide 90° phase difference between signals fed to the two antenna input ports. In addition, to suppress the wideband common-mode signals, two half-wavelength microstrip line sections that share part of their structures are connected between the two feedlines for producing two transmission zeros in the DM passband under CM operation. For the designed balanced wideband filtering CP antenna, measurement shows that the |Sdd 11 |≤ −10 dB DM operating band covers a frequency range of 3.16–4.63 GHz. Very good CM suppression was observed with the measured CM reflection coefficient greater than −1 dB over most of the DM passband. The simulated 3-dB axial ratio band is 3.04–5.09 GHz.

In this letter, a new balanced ultrawideband (UWB) bandpass filter (BPF) is proposed and designed using a slotline resonator (SLR) with radial end-sections for better wideband response. The SLR is fed by microstrip lines, and the whole BPF circuit is deployed symmetrically across the plane of symmetry to provide balanced operation. When the BPF is excited differentially, the SLR half circuit behaves as a similar resonator of half width, and by locating its first three resonant modes in the passband, the desired UWB response can be achieved. Conversely, while the BPF is in common-mode (CM) operation, the symmetry plane is virtually open-circuited, and the SLR is incomplete in structure, rendering CM signal suppression very effective. In this design, bandstop filters are embedded in the feeding lines to increase the upper stopband bandwidth. The achieved performances for this proposed balanced UWB BPF are a 3-dB fractional bandwidth of 114% and a minimum measured (simulated) in-band insertion loss of 1.17 (0.92) dB for differential-mode operation and very good CM rejection with an insertion loss of larger than 25 dB over 1–20 GHz frequency range. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2461–2464, 2015

This article proposes a balanced band-pass filter (BPF) designed using a folded half-mode substrate integrated waveguide (FHMSIW) and a hybrid microstrip/slot feed structure for enhancing the common-mode (CM) suppression. The proposed FHMSIW possesses a relatively higher Q factor than other planar structures, such as the microstrip line, coplanar waveguide, coplanar stripline, and slotline, resulting in sharper band edge skirts for the designed filter. The in-band insertion losses of the FHMSIW BPF are reasonably low under differential-mode operation, and the CM rejection level is more than 50 dB over a wide frequency band. The circuit design is experimentally validated. Comparison of the measured and simulated data is presented in this article. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:591–594, 2015

This article proposes a new broadband circularly polarized (CP) printed monopole antenna (PMA) with unidirectional radiation patterns. The simple structure consists of only a circular patch, a tuning rectangular patch, and an inverted-L strip protruded from the signal line of a feeding asymmetric coplanar waveguide (CPW). Through simple design procedures, a CP PMA with bidirectional radiation patterns and with a fractional CP bandwidth (CPBW) of larger than 35% can be obtained. By placing an open metal cavity underneath the bidirectional PMA without changing the PMA's structural dimensions, one can obtain unidirectional radiation patterns without downgrading the CPBW. In addition, the peak antenna gain can be raised by about 6 dB. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1535–1540, 2014

A balanced diplexer and a balun diplexer, both designed for the two channels of 2.45-GHz WLAN and 3.55-GHz WiMAX, are proposed with high common-mode (CM) suppression and differential-mode (DM) isolation in this paper. For the balanced diplexer, balanced BPFs for the two desired channels were first designed using stepped-impedance slot-line resonators (SISLRs). Through two T-junctions, the two BPFs were subsequently combined to form a three-balanced-port diplexer having six single-ended ports. Such a balanced diplexer can be easily converted into a balun diplexer with one single-ended and two balanced ports. For that purpose, one of the T-junctions and its associated two feeding lines are removed, and the feeding lines connected to the other T-junction are modified. For both diplexers, the measured CM suppressions (DM isolations) are larger than 54.3 (39.5), 52.2 (44.5), and 40.7 (38.7) dB, respectively, in the lower channel, the upper channel, and the displayed frequency range of 1–6 GHz. A satisfactory a...

A balanced diplexer and a balun diplexer, both with high isolation, are proposed in this article. First, a balanced bandpass filter (BPF) operating in GSM (with a center frequency of 1.92 GHz) and the other in WLAN (with a center frequency of 2.45 GHz) were designed using ordinary uniform-impedance resonators (UIRs) and center-grounded UIRs. Next, the two balanced BPFs were combined through two T-junctions to form a six-port balanced diplexer. Finally, a five-port balun diplexer was obtained by removing from the balanced diplexer one of the two T-junctions along with the microstrip feeding lines connected to it and by carefully adjusting the structural dimensions of the other T-junction. A satisfactory agreement is validated between simulated and measured results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:555–559, 2014

This paper presents a new balanced wideband band-pass filter (BPF) that is designed using a multi-mode slot-line resonator (MMSLR) with microstrip feed-lines. To obtain good differential operation and meanwhile reject unwanted common-mode (CM) noises, the balanced BPF is arranged in a symmetric fashion. For differential-mode (DM) operation, by locating the first three resonant modes of the MMSLR in the desired passband and feeding the MMSLR with tightly coupled microstrip feed-lines, we obtained a wideband response that meets the requirement of the OFDM group-B bandwidth specification (4.752–6.336 GHz). For CM operation, an open-circuited stub is effectively added to the feeding lines at the output port so that the transmitted CM signals can be attenuated. The measurement agrees well with the simulation. For the designed balanced wideband BPF, the measured minimum DM insertion loss is 0.63 dB in the DM passband, in which the CM suppression is larger than 17.6 dB.

In this article, a new balanced wideband bandpass filter (BPF) is designed using a stub-loaded multimode resonator (SLMMR) with tightly coupled feeding lines. The wideband response is achieved by designing the first three differential resonant modes of the SLMMR to locate evenly in the designated passband. Good common-mode (CM) suppression over the passband is obtained by positioning the transmission zero produced by one half of the low-impedance section (which serves as a shunt open-circuited stub while the BPF is in CM operation) of the SLMMR close to the in-band common modes. A prototype of the proposed BPF is fabricated and measured; the measured (simulated) minimum differential-mode insertion loss (IL) is 0.7 (0.3) dB and the measured (simulated) CM IL is greater than 20.3 (20.1) dB in 1–10 GHz. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2629–2633, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27110

A strategy for enhancing the common-mode (CM) suppression of a band-notched UWB closed-aperture antenna is proposed. The antenna circuit consists of a differentially coplanar-waveguide-fed hexagonal-aperture antenna and a pair of wave-trapping slotline resonators for producing a 5.5 GHz notch band. The enhancement of the CM suppression was achieved by setting the dimension of the aperture along the longitudinal direction (i.e. the direction parallel to the feedlines) small enough, so that the first resonant mode of the CM half-circuit of the aperture antenna can be pushed beyond the differential-mode (DM) UWB passband. A fabricated balanced band-notched UWB antenna was measured to have a 10 dB DM passband of 3–11.2 GHz with a notch band of 5.1–6.1 GHz. Good measured CM suppression was observed with a maximum return loss of 2.9 dB in the DM UWB passband.

This paper presents new balanced single- and dual-band bandpass fllters (BPFs), both of which are constructed using two ring resonators. For each BPF, open-circuited stubs are added to one of the two resonators so that the transmitted common-mode (CM) signals can be attenuated, and source-load coupling is established so that two transmission zeros are generated near the edges of each desired difierential-mode (DM) passband to sharpen the passband selectivity. The measurement agrees well with the simulation. For the single-band BPF, the measured minimum DM insertion loss is 1.4dB in the DM passband, in which the CM suppression is larger than 41.6dB. For the dual-band BPF, the minimum DM insertion losses are 1 and 1.35dB in the flrst and second passbands, respectively, in which the CM rejections are larger than 29 and 22dB.

A novel design is described for a circularly polarized square slot antenna (CPSSA). Circular polarization (CP) operations can be attained using a lightening-shaped feedline protruded from the signal line of the feeding coplanar waveguide (CPW). The CP bandwidth can be significantly enhanced by implanting a pair of inverted-L grounded strips into the slot and adjusting the dimensions of the lightening-shaped feedline, whereas the impedance bandwidth can be greatly enlarged through tuning embedded vertical and horizontal stubs. The designed antenna was measured to exhibit a CP bandwidth of as high as 48.8%.

This paper presents a new balanced dual-band bandpass filter (BPF) designed for 2.4/5.2 GHz wireless local area networks (WLANs). Because adopted in the BPF are only bi-section equal-electric-length stepped-impedance resonators (SIRs), whose dimensions can be determined using analytic formulas, the BPF can be easily and efficiently designed. The inner SIRs are designed to resonate only at the odd-mode resonant frequencies of the input and output SIRs but not at the even-mode ones. This leads to well-behaved differential-mode (DM) transmission and excellent common-mode (CM) suppression for the BPF. Simulated and measured results are found to agree quite well to each other. The measured minimum DM insertion losses in the two passbands are 2.1 and 2.54 dB, whereas the measured CM rejections are higher than 33 dB in the frequency range from 1 to 7 GHz.

This article presents a multimode-resonator (MMR)-based ultra-wideband (UWB) bandpass filter (BPF) fed by modified coplanar waveguides (CPWs). The MMR employed in the UWB BPF is formed by combining two quarter-wavelength (λ/4) microstrip stepped-impedance resonators (SIRs) in a structure-shared fashion. The first two resonant frequencies of the inherent λ/4 SIRs and the fundamental one of the embedded half-wavelength (λ/2) resonator were designed and located inside the UWB passband. Experiments on a prototype UWB BPF were carried out for validating the filter design. The measured frequency responses show an insertion loss of less than 1 dB between the first and the last |S11| null frequencies in the UWB passband and an upper −20-dB stopband bandwidth of about 6.14 GHz. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 918–921, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24199

A square slot antenna fed by a coplanar waveguide for dual-band multistandard applications is presented. Printed on the back of the square slot is a composite patch formed by an annular metal ring inscribed by a circular patch. Appropriate design of the composite back-patch resulted in five resonant bands, the first (last) two of which were combined to form a lower (upper) operating band. The ratio of the two operating band centre frequencies can be tuned larger than 2.5. A pair of notches was embedded in the annular metal ring to further broaden the lower (upper) operating band up to a fractional bandwidth of 37% (20%). The measured results indicate that the proposed antenna can cover the frequency bands of the following wireless communication standards: digital communication system, personal communication services, universal mobile telecommunications system and 2.4/5-GHz wireless local-area networks.

This article presents the design of a compact fourth-order cross-coupled dual-band bandpass filter (BPF) having a wide upper-end stopband. Quarter-wavelength (λ/4) stepped-impedance resonators (SIRs) were employed to construct the BPF to have a relatively small circuit size and high spurious harmonics, as compared with the BPF using half-wavelength (λ/2) SIRs. The resonators tapped by the input and output feeding lines were loaded by a spur-line to suppress the first spurious passband so as to further broaden the upper-end stopband. BPFs with and without the embedded spur-lines were both simulated to compare their frequency responses. Very good agreement between the simulated and measured results was observed. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 691–694, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23186

A novel design of a circularly polarized annular-ring slot antenna is discussed. The circular polarization is attained through a newly proposed double-bent microstripline that feeds the antenna at two different positions. Several structural parameters were experimentally studied with care to establish a design procedure, which was subsequently drawn into a design flow chart. Validation was carried out using the antennas designed at 3.5 and 1.59 GHz. The measured 3-dB axial-ratio bandwidth (ARBW) for the former is 10.5% and for the latter, 10.0%, which is larger than the 8.5% 3-dB ARBW required by an Inmarsat application.

In this article, a compact annular-ring slot antenna for dualband operations is proposed and studied. A pair of spur-like slits was implanted in the center patch of an annular-ring slot antenna to excite two resonant modes with their resonant frequencies easily adjusted by changing the dimensions of these slits, resulting in a large range of dual-frequency ratios (1.07–2.2). For the first excited resonant mode, the routes of the equivalent magnetic current distribution in the slot region can be lengthened by these slits. The resultant lowered first resonant-band center frequency (from that of the unperturbed annular-ring slot antenna) thus made the proposed antenna effectively miniaturized. The proposed antenna was found to have very good linearly polarized broadside radiation patterns and very low cross polarization levels in both operating bands.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1578–1581, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22536

The dispersion properties of a circular dielectric waveguides loaded at the center with periodic center-protruded metal disks were investigated using a mode-matching technique in conjunction with the Floquet theorem. The metal disks with rectangular and crisscrossed cross-sectional shapes in the longitudinal direction were considered. The effects of the cylinder radius, disk size, and disk spacing on the dispersion curves plotted in the form of the Brillouin diagram were studied. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2057–2061, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22645