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This communication presents an ultra-miniaturized two-way frequency tunable antenna diplexer based on cavity-backed slots and dielectric fluids. The proposed antenna utilizes two half-mode substrate-integrated rectangular cavities loaded with slots and fluidic pockets. The conventional size reduction is achieved by employing half-mode cavities, whereas ultra-miniaturization is obtained by applying the slots, which provides additional capacitive loading. As the cavities are of unequal sizes, a weak cross-coupling path is created between the ports to obtain high isolation (> 30 dB). The isolation is further enhanced by loading the slots. Two mechanisms are analyzed to tune the frequency bands individually or simultaneously. Firstly, the width of the slots can be altered to tune the frequency bands. However, this method involves modification of the physical dimensions of the antenna. Secondly, fluidic vias are created on the bottom plane of the cavities. These can be filled with various dielectric liquids to achieve frequency reconfigurability without altering the physical dimensions of the antenna. To demonstrate the concepts considered, the prototype of the proposed antenna was fabricated and experimentally validated. The structure has a footprint of 0.045λg2 and an isolation exceeding 33.4 dB. The operating frequencies are tunable in the range from 3.08 to 3.84 GHz (lower band) and from 4.97 to 6.33 GHz (upper band) by varying the dimensions of the slots whereas the operating frequencies are reconfigurable in the range from 2.74 to 3.38 GHz (lower band) and from 4.54 to 5.58 GHz (upper band), by employing microfluidic approach. As a result, the working frequencies may be varied in the range from 2.74 to 3.84 GHz (lower band) and from 4.54 to 6.33 GHz (upper band), making this antenna diplexer a competitive candidate for several communication systems. The cross-polarization levels, front-to-back ratio, and realized gain are greater than 19 dB, 18 dB, and 2. dBi, respectively. Excellent consistency is observed between full-wave simulation results and the measurement data. [ABSTRACT FROM AUTHOR]

A highly miniaturized bandpass filter with quad-band response is demonstrated in this article. The proposed quad-band bandpass filter has a novel topology comprising series quarter wavelength transmission lines loaded with tri-stepped impedance openended resonators and a dual-stepped impedance short-ended resonator. The proposed quad-band bandpass filter configuration is validated by theoretically verifying the transmission zeros and pole frequencies using even-odd mode analysis. A prototype operating at 0.475 GHz, 1.695 GHz, 3.48 GHz, and 4.53 GHz is designed, implemented, and experimented. The tested insertion losses at these center frequencies are 0.38 dB, 0.71 dB, 1.03 dB, and 1.22 dB, and the return loss is better than 10 dB in each passband. Each passband is isolated by a transmission zero with a rejection better than 40 dB. The proposed quad-band filter occupies a compact size of 0.146 × 0.087λ²g and is distinguished by its high compactness, wide bandwidth, multiple transmission zeros and poles, and high performance compared to benchmark designs making it more suitable for multi-band wireless applications. [ABSTRACT FROM AUTHOR]

This paper presents high-sensitivity sensors based on an open complementary square split-ring resonator and a modified open complementary split-ring resonator operating at 4.5 GHz and 3.4 GHz, respectively. The sensors are designed for the detection of multiple liquid materials, including distilled water, methanol, and ethanol. The liquid under test is filled in a glass container loaded using a pipette. Compared to the conventional OCSSRR, the modified OCSSRR with multiple rings exhibits a higher frequency shift of 1200 MHz, 1270 MHz, and 1520 MHz for ethanol, methanol, and distilled water, respectively. The modified sensor also demonstrates a high sensitivity of 308 MHz/RIU for ethanol concentration which is the highest among the existing microwave sensors. The sensors in this manuscript are suitable for multiple liquid-material-sensing applications. [ABSTRACT FROM AUTHOR]

This communication presents a novel concept of microfluidically frequency-reconfigurable self-quadruplexing tunable antenna for quad-band applications. At the initial design stage, a substrate-integrated square cavity is divided into four unequal quarter-mode cavity resonators by inserting an X-shaped slot on the top surface of the cavity. Applying four 50-Ω microstrip feed-lines to these four quarter-mode cavity resonators enables quad-band operation with self-quadruplexing capabilities. The feed lines are organized orthogonally and off-center, which leads to port isolation greater than 32.3 dB. An equivalent network model is developed to validate the proposed antenna. To realize frequency reconfigurability, two microfluidic channels corresponding to each port are created by engraving the bottom surface of the cavity. To create a reconfigurable self-quadruplexing antenna, the channels are either filled with air or dielectric liquids of higher permittivity, so that the design offers independent tunability of the operating frequencies. As a proof of concept, the prototype of a self-quadruplexing tunable antenna is fabricated and validated through measurements. The antenna prototype occupies a footprint area of 0.37λg2. The design exhibits frequency tuning ranges of 350 MHz (8.3%), 500 MHz (10.3%), 610 MHz (11.2%), and 845 MHz (14.1%) for the first, second, third, and fourth operating bands, respectively. In all bands and across the entire tuning range, the realized gains of the designed antenna exceed 4.05 dBi. The electromagnetic modeling responses agree extremely well with the measured characteristics. [ABSTRACT FROM AUTHOR]

This article presents two novel architectures of dual-band substrate-integrated waveguide (SIW) bandpass filters (BPFs). Initially, two identical open-loop ring resonators (OLRRs) were coupled face-to-face on the top of the SIW cavity to realize a dual-band single-pole BPF. To obtain two-pole dual-band characteristics, two OLRRs resonant units were assembled horizontally within the top metal layer of the SIW, which is a technique used for the first time in the literature. For demonstration purposes, two types of SIW filters loaded with OLRRs were designed and fabricated. The proposed filters feature an extremely compact size, a low insertion loss, and good selectivity. The single- and two-pole filters have an overall size of 0.012 λ g 2 and 0.041 λ g 2 , respectively. The simulated and measured circuit responses are in good agreement. [ABSTRACT FROM AUTHOR]

In this investigation, an ultra-compact dual-mode bandpass filter (BPF) with a wide stopband response is realized by using a half-mode substrate-integrated rectangular cavity (HMSIRC). The HMSIRC resonator is designed with a cavity that is rectangular in shape and has metallic vias along three of the sides. The fourth side is open-ended and contains microstrip feed lines. For the purpose of constructing a magnetic wall, a rectangular slot is cut into each of the HMSIRC's three edges. In order to produce an electrical wall that may generate a variety of resonances, the side with the open edges is provided with a single metallic via in the center. After that, a second-order BPF is generated by loading a transverse slot in the middle of the BPF, which enables independent frequency regulation of the mode frequencies. The eigen-mode analysis; field distributions; coupling matrix; and full-wave simulation of the proposed HMSIRC filter topology are used to develop the working principle of the filter. A second-order BPF is realized, constructed, and experimentally validated in order to provide evidence that the theory is correct. The BPF prototype achieves satisfactory performance thanks to its compact footprint of 0.028 λg2; its broad passband of 15.9%; its low insertion loss of 0.41 dB; and its wide stopband of 4.36 f0 with a rejection level greater than 20 dB. Both the measured and EM-simulated responses of the BPF are very consistent with one another. [ABSTRACT FROM AUTHOR]

The article presents a novel circular substrate-integrated waveguide (SIW) bandpass filter (BPF) with controllable bandwidth. The proposed BPF was configured using two microstrip feed lines, semi-circular SIW cavities, capacitive slots, and inductive vias. The circular cavity was divided into two halves, and the two copies were cascaded. The resulting bisected and cascaded structures were then connected back-to-back. Finally, by introducing two inductive vias to the circular center cavity, a transmission zero was generated. In order to examine the design concept, a coupling matrix was generated. To demonstrate the theory, a third-order BPF was realized, fabricated, and experimentally validated. The BPF prototype features a wide passband of 8.7%, a low insertion loss of 1.1 dB, and a stopband of 1.5 f 0 with a rejection level better than 20 dB, which makes it a potential candidate for microwave sensing and communication industries. [ABSTRACT FROM AUTHOR]

An ultracompact self-triplexing antenna realized on a substrate-integrated rectangular cavity (SIRC) is discussed in this study. The proposed structure employs two L-shaped slots and an inverted U-shaped slot to radiate at three independent operating frequency bands. Three 50-ohm microstrip feed lines were used to excite the radiation in these slots. The operating frequency was individually tuned using the slot size. The slot placement and size were designed having in mind considering obtaining one or more frequency bands below the SIRC cutoff frequency, which had the advantage of enabling an ultracompact size. High port isolation was achieved by applying one of the ports orthogonally to the two remaining ones, which created a weak cross-coupling channel. A lumped-circuit model was created to examine the antenna operation. The presented design has been prototyped and experimentally validated with the measured operating frequencies of 1.92 GHz, 4.43 GHz, and 5.25 GHz for GSM, 5G, and WLAN applications, respectively. The port isolations are better than 32.4 dB according to both EM simulations and measurements. Meanwhile, the measured realized gain of the antenna is better than 4.3 dBi at all bands. [ABSTRACT FROM AUTHOR]

This paper presents a miniaturized tri- and quad-band power divider (PD)based on substrate integrated waveguide (SIW). By adopting different types of modified circular complementary split-ring resonators on the top surface of SIW, multiple passbands are generated propagating below the SIW cut-off frequency. The working principle is based on evanescent mode propagation that decreases the operating frequency of the PD and helps in the miniaturization of the proposed structure. The operating frequency of the proposed PD can be individually controlled by changing the dimensions of the resonator. To verify the proposed concept, a tri-band and a quad-band PD exhibiting 3 dB equal power division at 2.41/3.46/4.65 GHz and 2.42/3.78/4.74/5.8 GHz are designed using the full-wave simulator, validated through circuit model, fabricated and experimentally verified. The measured results agree well with the simulations. The proposed PDs have good performance in terms of reasonable insertion loss, isolation, minimum amplitude and phase imbalance, smaller footprint, easy fabrication and integration. The size of the fabricated prototype is 18.3 mm × 8.4 mm, which corresponds to 0.205λ g × 0.094λ g , λ g being the guided wavelength at the first operating frequency. [ABSTRACT FROM AUTHOR]

This brief introduces novel architectures of bandpass filters (BPFs) using a substrate integrated waveguide (SIW) cavity with a rectangular ring slot (RRS) for compact size, extensible order, and broad stopband responses. Two bandpass filters, which demonstrate a second-and a fourth-order Chebyshev response, respectively, are realized by employing identical cavities with RRS, without increasing the physical size of the circuit. A rectangular ring slot is etched along the perimeter and a metallic via is allocated towards the bottom edge of the cavity to realize the resonances. The resonant frequencies of different modes are controlled by introducing one or three slots, which enable the realization of the second and fourth-order BPFs with wide stopbands, respectively. The working principles of the filters are illustrated by applying the eigen-mode analysis, field distribution, and the coupling matrix. Finally, a second-order BPF centered at 0.87 GHz, and a fourth-order BPF centered at 0.92 GHz are synthesized, fabricated, and experimentally validated. As compared to the earlier works, the proposed fourth-order BPF offers competitive performance with a low insertion-loss of 0.7 dB, compact size of $0.036\mathbf {\lambda } ^{2}$ , and a wide passband of 22.1%. Additionally, the second- and the fourth-order BPFs achieve wide upper stopband responses of $3.86{f} _{0}$ at a level greater than 20dB and $3.98{f} _{0}$ at a level greater than 30dB, respectively. [ABSTRACT FROM AUTHOR]

In this contribution, novel design is presented for a very compact shielded quarter-mode substrate-integrated waveguide (S-QMSIW) based self-diplexing antenna (SDA) for WiMAX/WLAN applications. In order to achieve dual-band features, a slot is etched onto the top of the metal. Two orthogonal microstrip feed lines in the full-wave EM-simulator (HFSS) simulate the S-QMSIW resonator at two different frequencies (3.45 and 5.45 GHz). The proposed antenna pattern is extremely adaptable, allowing for simple frequency adjustments for each resonant frequency. A lumped circuit model is expected to be used to assess the antenna structure. A self-diplexing antenna based on S-QMSIW was designed, fabricated and tested to claim the proposed concept. At 3.45 and 5.45 GHz, the proposed antenna peak gains are 4.7 and 5.6 dBi, respectively. It offered port isolation better than 38 dB. The antenna front-to-back ratio was greater than 19.5 dB in each band. The proposed antenna circuit size was very compact ( 0.08 λ g 2 ). [ABSTRACT FROM AUTHOR]

In this communication a compact planar-fed substrate integrated waveguide (SIW)-based self-multiplexing (SM) antenna for hexa-band operation is proposed for the first time. Six different patches with planar $50~\Omega $ feed lines are designed and attached to the top side of the rectangular SIW cavity. The antenna operates at six different frequencies (5.33, 5.76, 6.31, 6.86, 7.34, and 7.8 GHz) simultaneously. The antenna attains 4.5, 4.94, 4.9, 5.12, 6.12, and 6.6 dBi peak gain at respective resonant frequencies. Port relocation, stepped patches, and additional vias are exploited to maintain isolation (>23 dB) between any two ports. The front-to-back ratios (FTBRs) are between 10 and 20 dB and Co-pol to Cross-pol ratios are between 10 and 29 dB. The design supports single-variable independent frequency tuning for all six patches and eligible for wide range of applications. The proposed design is fabricated and results are validated through measurement. The antenna is suitable for planar microwave devices. [ABSTRACT FROM AUTHOR]

In this letter, a shielded quarter-mode substrate integrated waveguide (S-QMSIW)-based self-diplexing antenna for closely spaced bands and high isolation is proposed. A ${\rm Y}$ -shaped slot is engraved on the top of the metal to enhance the extra capacitance of the QMSIW cavity resonator; thus, it helps to reduce its size as well as achieve dual-band characteristics. The S-QMSIW resonator is then excited by two orthogonal microstrip feed lines in the full-wave electromagnetic simulator (high-frequency structure simulator) to operate at two distinct frequencies (3.47 and 3.84 GHz). A transmission zero is generated at 3.56 GHz to provide port isolation better than 47 dB. In addition, a lumped circuit model is predicted to validate the antenna structure. To demonstrate the proposed concept, an S-QMSIW-based self-diplexing antenna is designed, fabricated, and tested. The recorded peak gains of the antenna are 4.8 and 5.7 dBi at 3.47 and 3.84 GHz, respectively. At each band, the antenna front-to-back ratio is greater than 20 dB. The circuit size of the proposed antenna is very compact (0.15 $\lambda _g^{2}$). [ABSTRACT FROM AUTHOR]

This paper communicates the design and experimental validation of dual-band SIW power dividers (single-stage and double-stage) with arbitrary power division. The dual-band power dividers are developed for WiMAX (3.5 GHz) and WLAN (5 GHz) applications. The proposed SIW power dividers are realized by a rectangular cavity, two rows of metallic-vias and one pair of unequal complementary split-ring resonators (CSRRs). Two resonating frequencies are produced below the waveguide cut-off frequency due to the unequal CSRRs etched-out on the top-surface of the cavity, which results in size reduction. To realize arbitrary power division, two output-ports are configured asymmetric with respect to input-port. The power division is varied by altering the distance between the two output-ports. Finally, two compact dual-frequency power dividers (single-stage and double-stage) working at 3.5 and 5 GHz are designed and validated through fabrication and measurement. The fabricated prototype exhibits dual-band operation, compact size (0.027 λ g 2 ${\lambda }_{g}^{2}$), good magnitude imbalance, return loss and isolation. [ABSTRACT FROM AUTHOR]

This letter presents the design of compact triple- and quad-band power dividers (PDs) based on substrate integrated waveguide (SIW) technology. The proposed PDs are designed as a rectangular cavity, one pair of unequal complementary split-ring resonators (CSRRs) and U-shaped slots (USSs). Initially, a dual-frequency SIW PD is implemented using unequal CSRRs on the top surface of the SIW cavity. This dual-frequency PD is converted into triple-band and quad-band operations by employing USSs on the bottom surface of the cavity. The center frequencies of the proposed PDs are controlled by varying the dimensions of CSRRs and USS. To demonstrate the proposed concept, triple- and quad-band PDs are designed, fabricated, and tested. The measured responses are very much consistent with the simulated one. The overall sizes of the proposed triple- and quad-band PDs are 0.03λg2 and 0.02λg2, respectively. The proposed PDs feature compact size, triple- and quad-band operation, good return loss, and isolation. [ABSTRACT FROM AUTHOR]

In this article, substrate integrated waveguide (SIW) filter with compact size and wide out-of-band rejection is designed for 5G (sub-6 GHz) applications. To achieve the proposed filter responses, D-shaped resonators oriented face-to-face are etched out on the top layer of SIW. Due to the resonators loading, the filter provides a passband below the cut-off frequency of SIW. This decrease in the operating frequency of the filter allows us to achieve size miniaturization. To enhance the frequency responses, a double-stage SIW filter is proposed and investigated. The equivalent electrical-circuits are developed to validate the transmission responses. To support our claim, single- and double-stage SIW filters are designed, fabricated and tested. The filter prototypes achieve size miniaturization, low insertion loss and wide out-of-band responses. The measured responses are very similar to the full-wave simulation responses. [ABSTRACT FROM AUTHOR]

This article presents a simple, compact, and lightweight substrate integrated waveguide (SIW) backed self‐quadruplexing antenna for quad‐band applications. The design procedure is straightforward. Topside of the SIW cavity is modified to form four patches of different lengths which are fed separately by four 50‐Ω microstrip feed lines and operate at 5.14, 5.78, 6.74, and 7.74. It attains 4.1, 4.96, 6.2, and 6.1 peak gain at the above frequencies, respectively. The observed front‐to‐back‐ratio is more than 17.5 dB and the isolation level is above 28 dB. This antenna topology allows to redesign each resonant frequencies as per application requirement using a single parameter and without disturbing other performances. Design guidelines for developing the proposed antenna are provided. A prototype antenna is fabricated using RT‐Duroid (5870) substrate and characterized for validation. The proposed antenna is suitable for handheld microwave devices for C‐band communication. [ABSTRACT FROM AUTHOR]

A novel and compact all planer-fed self-triplexing patch antenna is designed and demonstrated for triple-band operation simultaneously. The model is comprised of one substrate-integrated waveguide (SIW) cavity, three planar ports, and one modified I-shaped slot. The proposed antenna is designed in a simple three-step method to achieve improved self-triplexing property. In the first step, a rectangular slot is created and its position is altered to obtain initial isolation (>20 dB) between any two ports. Secondly, the same slot is modified to an I-shape, which creates three patches facing three different ports and radiates at three different frequencies (4.14, 6.1, and 8.32 GHz) with minimum isolations above 28.4 dB. In the third step, one input-port is off-centered to obtain port isolation tradeoff so that isolation between any two ports is better than 30.8 dB. Importantly, the proposed design also supports easy individual frequency tuning using single variable. For demonstration purpose, the antenna is fabricated and characterized. The proposed planar antenna is very simple, compact, and feasible for handheld microwave devices. [ABSTRACT FROM AUTHOR]

This article presents a novel design of substrate integrated waveguide (SIW) dual‐band power divider loaded with double‐circular complementary split‐ring resonators (CSRRs). The double‐circular CSRRs are etched on the top layer of the proposed structure to obtain the dual‐band characteristic. The proposed geometry provides a passband frequency below the cut‐off frequency of the SIW due to the electric dipole nature of the CSRRs. By changing the dimensions of the CSRRs, various passband characteristics are studied. To validate the design idea, a compact dual band power divider with equal power division operating at 8.4 and 11.7 GHz is designed, fabricated, and tested. A good steadiness is found between simulated and tested results. The proposed idea provides features of compact size, dual‐band operation, and good isolation. The size of the fabricated prototype excluding microstrip transition is 0.473λg × 0.284λg, where λg is the guided wave length at the center frequency of first band. [ABSTRACT FROM AUTHOR]

Abstract: In this article, an equal split triple‐band Wilkinson power divider is reported. The triple‐frequency operation is obtained by employing an extended cross‐shaped microstrip line. This proposed geometry is constructed using a cross‐shaped structure attached with two series microstrip lines at two ports. The circuit parameters are computed from the graphical solutions plotted based on the derived formulas. To validate the synthesis approach, a triple‐band power divider intended to operate at 0.9/3.15/5.4 GHz is developed, fabricated and tested. A good consistency is observed on the tested and simulated performances. The measured isolation and return loss are greater than 28 dB at all the operating frequencies. The prototype provides a good insertion loss of 3 ± 0.3 dB at the center of each frequency band. Considering minimum 15 dB return loss and maximum 0.5 dB amplitude imbalance, the bandwidths at 0.9, 3.15, and 5.4 GHz are obtained as 140, 130, and 110 MHz, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this article, a tri‐band 180‐degree directional coupler with spurious suppression is proposed. This coupler is realized using the extended π‐shaped Microstrip operating at 3 different frequencies. The design equations of the extended π‐shaped structure are obtained through the ABCD matrix method. The designed coupler provides tri‐frequency response at 1.8, 3.5, and 5.2 GHz corresponding to Global System for Mobile communication, Worldwide Interoperability for Microwave Access, and wireless local area network applications, respectively. The fractional bandwidth variations of the isolation, matching, phase and amplitude imbalance at sum and difference ports are discussed in detail. In addition, the spurious bands beyond the operating frequencies are also suppressed. To validate the performances, the proposed tri‐band coupler is fabricated and tested. [ABSTRACT FROM AUTHOR]

In this article, the design of a new dual-band impedance transformer with ultra-high transforming ratio (UHTR) is presented. The closed-form expressions are derived analytically using a lossless transmission-line theory. To practically validate the proposed design concept, two examples of dual-band transformer working at smaller and larger frequency ratios are designed for different load impedance of 500, 1000, and 1500 V. Finally, three prototypes of dual-band transformer with UHTR are designed, fabricated, and tested. For all these prototypes, different frequency ratios (two operating frequencies can be chosen arbitrarily) are considered. The measured return loss of the prototypes is better than 15 dB at all the operating frequencies. The measured results are matched very closely with the simulated results. This design is then extended to match a complex load at two different frequencies. The multi-band characteristic is obtained by decomposing a shorted stub into a stepped impedance section of the proposed structure. With the necessary derivation and analysis, a tri-frequency matching network is designed for a transforming ratio of 10. [ABSTRACT FROM AUTHOR]

A novel design of planar dual-band microstrip crossover operating at small and large frequency ratios is presented. These features of the proposed dual-band crossover are achieved by a cross-shaped transmission line. To obtain the dual-band characteristics, the required closed form design formulas are computed using the ABCD matrix method. Based on the design formulas, the realizable small and large band ratios are calculated as 1.65–2.14 and 4.1–8.76, respectively. To validate the computed band ratios, three examples of dual-band crossovers are presented. Finally, two prototypes of dual-band crossover working at smaller and larger frequency ratios are fabricated and tested. The fabricated dual-band crossovers exhibit good return loss and isolation of over 20 dB with minimal insertion loss. [ABSTRACT FROM PUBLISHER]

In this article, a novel design of quad-band matching network (QBMN) with ultra-high impedance transforming ratios (UHTRs) is proposed and designed based on ABCD matrix method. The QBMN is capable of matching a very large real load impedance at four different frequencies simultaneously. The quad-band structure is composed of π-section with series connected coupled lines at each port. The design formulas of QBMN are derived analytically to obtain the quad-band operation. In order to validate the proposed idea, three examples of QBMN for different load impedances (500, 1000, and 1500 Ω) are considered. Finally, two QBMNs with transforming ratios of 10 and 20 are fabricated and demonstrated. For both the prototypes, the measured S11 is better than 15 dB at all working frequencies. The experimental performances are consistent with the simulated results. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents the development of a novel dual-band branch line balun with design flexibility. The T-shaped coupled line structure is constructed by two series short-ended coupled lines and one open-ended stub to obtain the dual-band characteristics. The proposed dual-band structure has the capability to design a conventional microstrip line with arbitrary impedances and electrical lengths at two different operating frequencies. In addition to this, different range of frequency ratios is obtained by varying the length of the stub. The required explicit design equations are derived analytically to compute the physical dimensions of the coupled lines and stub. Based on these equations, closely and widely spaced frequency bands useful for many wireless communication systems are devised. To prove better agility, three examples of dual-band branch line baluns are designed. Finally, a prototype of dual-band balun is demonstrated for GSM and WiMAX applications at 0.9 and 3.5 GHz, respectively. Good agreement is found between the theoretical predictions and experimental results. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1197-1202, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT The design of a compact size harmonic suppressed 3 dB branch line coupler using H-shaped transmission line is presented. The circuit parameters of the proposed coupler are evaluated from the closed form equations. In order to validate the theoretical analysis, a prototype of proposed coupler operating at 0.9 GHz is fabricated and demonstrated. The size of the fabricated coupler is reduced by 64% of the conventional coupler with a comparable performance. The measured result not only shows the return loss and isolation better than 28 dB but also suppresses the unwanted spurious passband response up to third harmonic of the operating frequency. The measurement result shows good matching with the simulation result. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:913-918, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents the size-miniaturized, wide-bandwidth, and harmonic-suppressed 10 dB branch line coupler (BLC) using cascaded symmetric PI sections. The complete design equations are derived to obtain the physical parameters of cascaded PI sections. To validate the proposed design, a 10 dB BLC operating at 0.9 GHz is designed, fabricated, and tested. The reported BLC is having dimensions of 0.175 λg × 0.25 λg and is 76.6% smaller than the conventional coupler. The measured results show that the designed coupler fractional bandwidth is >52% and up to 4th harmonic is suppressed with a level better than 20 dB. Good agreement is found between the theoretical predictions and experimental results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1610-1613, 2016 [ABSTRACT FROM AUTHOR]

In this letter, a quad-band balun employing Pi-shaped and series connected coupled lines is proposed. The closed form design equations are derived analytically. Based on these equations, a quad-band balun operating at 1.8/3.6/5.8/7.8 GHz is designed, fabricated and tested. The measurement result shows that, the return loss and isolation are better than 18 dB and the bandwidth obtained is more than 150 MHz at each operating frequency band, which is feasible for most applications. Good agreement is found between the theoretical predictions and experimental results. [ABSTRACT FROM PUBLISHER]