Dual‐wideband filtering power divider based on center‐fed three‐line coupled structure

In this article, a dual‐wideband filtering power divider is proposed by using a center‐fed three‐line coupled structure with three open stubs and two isolation resistors. The center‐fed three‐line coupled structure can generate two wide passbands separated by a transmission zero (TZ). The three open stubs can achieve four TZs around the two passbands, which is conducive to the frequency selectivity. Compared with the reported designs, the bandwidth is extended and the performance of isolation, insertion loss and circuit size can reach balance. The proposed design is implemented with size of 0.22 λ_g × 0.39 λ_g (λ_g is the guided wavelength at the center frequency of the lower passband) which exhibits the 3‐dB fractional bandwidths of 56.5%/24.27% and the insertion loss of 0.51/0.68 dB at the center frequency of two passband (f₁/ f₂) of 1.94/4.2 GHz, while the isolation at f₁/f₂ are higher than 22.5/20.1 dB.     

A self‐packaged wideband filtering power divider based on substrate‐integrated suspended line

In this study, a filtering power divider (FPD) is proposed by utilizing one T‐shaped tri‐mode stepped‐impedance resonator with input/output coupling structures based on substrate‐integrated suspended line (SISL). The circuit topology and SISL technology are combined together to reach balance in performances such as compact size, wideband, high frequency selectivity, low loss, good in‐band isolation, wide stopband, and self‐packaging so that there are no obvious flaws. Wide bandwidth and two near‐band transmission zeros are contributed by the proposed circuit topology. Good isolation can be obtained by comparing different coupling schemes with one resistor. An additional transmission zero for extending the upper stopband can be achieved by the two closely placed stubs without increasing the size of the design. Low loss and self‐packaging can be realized by SISL technology. For demonstration, a prototype is implemented with the size of 0.5λ_g × 0.28λ_g, which exhibits the 1‐dB fractional bandwidth of 26.3%, the frequency selectivity of 0.25/0.37 at the lower/upper edges of the passband, and the insertion loss of 1.1 dB (including transition) at the center frequency (f₀) of 3.34 GHz, while the in‐band isolation is higher than 20 dB and the 15‐dB stopband is achieved up to 3.74 f₀.     

Wideband bandpass filtering branch‐line balun with high‐isolation

The wideband bandpass filtering branch‐line balun with high isolation is presented in this paper. The proposed balun can be designed for wideband performances by choosing a proper characteristics impedance of input vertical transmission line and odd‐mode impedance of parallel‐coupled lines. The proposed balun was designed at a center frequency (f₀) of 3.5 GHz for validation. The measured results are in good agreement with the simulations. The measured power divisions are ?3.31 dB and ?3.24 dB at f₀ and ?3 ± 0.17 dB within the bandwidth of 0.95 GHz (3 GHz to 3.95 GHz). The input return loss of 24.09 is measured at f₀ and higher than 20 dB over the same bandwidth. Moreover, the measured output losses are better than 11 dB within a wide bandwidth. The isolation between output ports is 20.32 dB at f₀ and higher than 13.2 dB for a broad bandwidth from 1 GHz to 10 GHz. The phase difference and magnitude imbalance between two output ports are 180° ± 4.5° and ± 0.95 dB, respectively, for the bandwidth of 0.95 GHz.     

Compact dual‐polarized dipole antenna with high isolation using hybrid balun circuit

In this article, a crossed dipole antenna with compact size (43 × 43 mm²) and high isolation (42 dB) is proposed using a hybrid balun circuit. The hybrid balun consists of a tapered balun and a Marchand balun. The tapered balun transforms the microstrip line into the parallel feeding lines for one pair of dipoles, and the Marchand balun transforms the stripline transmission line into a couple of out‐of‐phase feeding lines for the crossed pair of dipoles. Due to the low coupling between two different baluns, a high isolation of the antenna can be achieved when the crossed dipole antenna is cascaded with the hybrid balun. Moreover, these two baluns can improve impedance matching and therefore further miniaturize the size of the crossed dipole antenna. The impedance matching of two baluns can be controlled and adjusted independently. As a result, the proposed dual‐polarized antenna has the bandwidth of 1.7 to 2.8 GHz for S11 < ?15 dB with compact size and high isolation. The proposed antenna with the hybrid balun circuit are fabricated, and the simulated and measured results meet well.     

Compact ultra‐wideband bandpass filter with configurable stopband based on diamond‐shape resonator

An ultra‐wideband compact bandpass filter (BPF) with configurable stopband by tuning transmission zeroes is proposed in this paper. The ultra‐wideband bandpass response is based on a diamond‐shape resonator consisting of a pair of broadside coupled diamond‐shape microstrip lines, within which a diamond shape defected ground structure (DGS) is etched in the middle. Flexible transmission zeros realized by open and short stubs can be easily adjusted to improve band selectivity and harmonic suppression. Measurement result shows that the dedicated device has a 3 dB fractional bandwidth of 148% (0.94‐6.36 GHz) with 20 dB rejection stopband from 6.87 to 9.7 GHz (77.5%) which agrees good with the simulate performance. The overall size of the proposed BPF is 0.27 λ_g × 0.23 λ_g.     

Coupled‐line band‐pass filter with T‐shaped structure for high frequency selectivity and stopband rejection

A coupled‐line band‐pass filter (BPF) with T‐shaped stub structure is presented. Five transmission poles within the passband and eight deep transmission zeros (TZs) from 0 to 2f₀ (f₀ denotes filter's center frequency) are realized through input impedance calculations. With the simple T‐shaped structure, the positions of six TZs can be appropriately adjusted to achieve high frequency selectivity and stopband rejection. For demonstration, a BPF prototype centered at 2.05 GHz is designed and fabricated, whose measured rejection levels are of over 45.5 dB at lower stopband and better than 19.5 dB at upper stopband. The simulation and measurement results are in good agreement, which validates the design idea.     

A broadband quasi‐Yagi array of rectangular loops on LTCC

In this article, a broadband quasi‐Yagi array of rectangular loops using low‐temperature co‐fired ceramic technology is proposed. The antenna is fed by a simple and compact microstrip‐to‐coplanar strip transition, which serves as balun and impedance transformer simultaneously. Four rectangular loops are used to direct the antenna propagation toward the end‐fire direction. Compared with the planar directors in traditional quasi‐Yagi antenna, they can provide better director effect to improve the radiation performance. Furthermore, they act as good impedance matching elements to broaden the bandwidth. The measured results show that the proposed antenna achieves a wide bandwidth of 42% for S₁₁ < ?10 dB (from 26.1 to 40 GHz), better than 12 dB front‐to‐back ratio, smaller than 14 dB cross polarization and an average gain over 6.5 dBi across the operating bandwidth. The antenna occupies a compact size of 8 × 8 × 1 mm³. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:196–203, 2014.     

A compact balun‐diplexer using interdigital line resonators

A novel compact balun‐diplexer applying new interdigital line resonators (ILRs) is presented in this article. It is found that the proposed ILR can not only reduce circuit size and but also realize high common mode rejection in differential mode operation frequency. By properly converting the symmetric four‐port balanced bandpass filter (BPF) to a three‐port device, a balun BPF with high selectivity and compact size are accomplished using ILRs. Then, the balun‐diplexer can be realized by combining two well‐designed balun filters with two 50 Ω transmission lines. The demonstrated balun‐diplexer with operation at 1.8 and 2.45 GHz have been designed, fabricated, and measured. Excellent performances have been observed. Specifically, 0.4 dB in‐band amplitude error, 1.8 in‐band phase error, more than 50 dB selectivity and 45 dB isolation are obtained. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:485–489, 2015.     

Compact wideband microstrip‐to‐microstrip vertical transition with extended upper stopband

In this article, a compact wideband microstrip‐to‐microstrip (MS‐to‐MS) vertical transition designed with a slotline stepped‐impedance resonator (SIR) is first presented. Compared with the existing wideband transitions, this proposed transition centered at f₀ can tremendously extend its upper stopband via two introduced transmission zeros around 3f₀ and 5f₀. With the designed equivalent circuit, the working principle is theoretically discussed. To realize the size compactness of this proposed wideband transition, the slotline SIR is replaced by two back‐to‐back connected slotline Y‐junctions. Finally, a prototype wideband transition is simulated and fabricated. A wideband filtering response with its upper stopband up to 6.06 GHz under attenuation better than 15 dB is experimentally achieved as expected in the simulation.     

Dual‐band bandpass filters with multiple transmission zeros using λ/4 stepped‐impedance resonators

Two novel dual‐band microstrip bandpass filters (BPFs) with multiple transmission zeros are proposed in this article. The dual‐band BPFs with second‐order bandpass responses are due to two λ/4 stepped‐impedance resonators (SIRs). Two passbands (center frequency ratio f _s/f₀ is 2.36) are realized based on the asymmetric SIRs. The transmission zeros near the passbands can be adjusted conveniently using the stopband transmission characteristic of the open/shorted coupled lines. Two planar microstrip dual‐band BPFs (ε _r = 2.65, h = 0.5 mm) with four and six transmission zeros are designed and fabricated. High selectivity and good in‐band performances can be achieved in the proposed filters.     

Design and fabrication of microstrip lowpass filter using asymmetric hairpin resonator

In this letter, a compact microstrip lowpass filter (LPF) is designed using serial connecting of two modified asymmetric hairpin resonators. The proposed design is consists of four open‐circuited stubs that are used to suppress spurious harmonics in the stopband. The proposed filter has wide‐stop band with attenuation level better than ?28 dB from 2.16 up to 26.1 GHz and sharp roll‐off. The proposed LPF has ?3 dB cutoff frequency equal to 2.11 GHz, wide stopband width around 12th harmonic suppression and insertion loss less than 0.1 dB at about 85% of the passband. The excellent agreement is observed between the simulated results and measured values of the fabricated LPF.     

Compact dual‐band single‐ended‐to‐balanced power dividers with open/short‐ended stubs

In this article, two novel topologies of compact‐size dual‐band single‐ended‐to‐balanced power dividers that are loaded with open‐ and short‐ended stubs are presented. Quarter‐wavelength open‐ended stubs and half‐wavelength short‐ended stubs are respectively exploited in the proposed dual‐band power‐divider configurations to incorporate the dual‐band functionality into them for flexibly‐adjustable dual‐frequency‐ratio specifications. Each engineered five‐port power‐divider circuit features high in‐band input/output power‐matching levels, high in‐band power‐isolation levels between the two differential‐mode outputs, and high common‐mode‐rejection levels in a broad spectral range. Two microstrip prototypes designed at 0.9/1.8 GHz (GSM bands) and 1.57/2.45 GHz (GPS and WLAN bands) are constructed and characterized for experimental‐demonstration purposes.     

Wideband planar log‐periodic balun

This paper presents the analysis, design, and performance characteristics of a new planar balun structure. The design is based on the log‐periodic antenna theory. The design guidelines, as well as simulation and measured results, are presented. It is shown that the new balun has greater than one octave bandwidth. A comparison to the half‐wave balun is also included. The log‐periodic balun will find applications in wireless communication circuits or devices such as mixers, amplifiers, and antennas. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 343–353, 2001.     

Compact three‐antenna MIMO system based on triangular half‐mode substrate‐integrated‐waveguide cavity

A compact three‐antenna MIMO system based on a triangular half‐mode SIW cavity is proposed. Two isosceles‐right cavity edges are shorted by metallic vias while a hypotenuse is opened to radiate cavity energy into the air. By etching two T‐shaped slots and adopting coaxial feedings, three antennas are formed. The same operating frequencies are achieved by adjusting the position of these slots and high isolation is obtained by optimizing their length. The proposed design has attractive features of simple configuration and compact size, which is completely printed on a single‐layered substrate without external circuitries. A prototype with the overall size of 0.53λ₀ × 0.53λ₀ has been fabricated. Measured results exhibit the operating frequencies of about 3.51 GHz, high isolation of 16.0 dB, moderate gain of around 4.12 dBi, good radiation efficiency of 81.22%, and low envelope correlation coefficient of 0.16.     

A compact monopolar patch antenna with bandwidth‐enhancement under dual‐mode resonance

A compact monopolar microstrip patch antenna (MPA) with enhanced‐bandwidth is proposed. In order to achieve the miniaturized patch, the zeroth‐order mode of the MPA instead of its higher‐order modes is employed at first by loading the shorting pin around the center of the patch. After that, a L‐shaped microstrip line with a shorting pin is introduced at the periphery of the patch radiator to excite an additional non‐radiative mode for bandwidth enhancement. In final, the proposed MPA is fabricated and measured. The results illustrate that the antenna generates an enhanced‐bandwidth of about 4.1% ranging from 2.39 to 2.49 GHz, which is significantly larger than that of the traditional MPA around 1%. Meanwhile, the dimensions of the radiating patch are obviously decreased down due to the employment of zeroth‐order mode, which are kept as small as about 0.17 λ₀ × 0.22 λ₀ × 0.026 λ₀ (λ₀ is the free‐space wavelength).     

Compact frequency reconfigurable triple band notched monopole antenna for ultrawideband applications

A compact ultra‐wideband (UWB) reconfigurable microstrip fed monopole antenna having size of 0.22 λ₀ × 0.28 λ₀ × 0.005 λ₀ with switchable frequency bands is presented. Triple band notched characteristics are achieved by inserting two stubs at top of radiator and one slot in between the radiator and microstrip feed line. Proposed antenna achieves reconfigurability with three PIN diodes at strategic positions to obtain eight different operational modes. In one of the operational modes, antenna operates in the entire UWB (3‐14 GHz) with fractional bandwidth of 127.5%. Two stubs are used to notch two frequency bands worldwide interoperability for microwave access (3.3‐3.6 GHz/WiMAX) and C‐band (3.7‐4.2 GHz). T‐shaped slot is also inserted to notch wireless local area network (5.725‐5.825 GHz/WLAN) frequency band. Proper biasing of PIN diodes is done by using suitable chip inductors and capacitors. Proposed antenna exhibits stable radiation patterns with average gain of around 3 dBi. Simulation and measurement results are in good agreement. Proposed antenna is suitable for on‐demand band rejection of parasitic bands coexisting in UWB.     

A dual‐polarized cross‐dipole antenna with wide beam and high isolation for base station

In this paper, a dual‐polarized cross‐dipole antenna with wide beam and high isolation is designed and analyzed for base station. The proposed antenna consists of two planar cross dipoles with four square patches, two L‐shaped microstrip lines, two ground plates, four parasitic patches, and a reflector. The square patches are placed between the center of cross dipoles to couple with L‐shaped microstrip lines. By introducing the parasitic patches, the wide beam can be realized. The measured results show that the proposed antenna achieves an impedance bandwidth (|S₁₁| < ?10 dB) of about 18.7% (1.9‐2.35 GHz) and an isolation better than 30 dB. A measured gain of 5.7 dBi and a half‐power beamwidth over 120° at the center frequency are obtained. Furthermore, the size of the proposed antenna is only 0.5λ₀ × 0.5λ₀ × 0.22λ₀ (λ₀ is wavelength at the center frequency).     

Compact sub‐6 GHz 5G‐multiple‐input‐multiple‐output antenna system with enhanced isolation

A compact two‐element multiple‐input‐multiple‐output (MIMO) antenna system with improved impedance matching and isolation is presented for future sub‐6 GHz 5G applications. The two identical tapered microstrip line fed modified rhombus‐shaped radiating elements are placed in the same orientation at a compact substrate area of 0.24λ₀ × 0.42λ₀ (where, λ₀ at 3.6 GHz) on a shared rectangular ground. A remodeled T‐shaped ground stub is placed between a pair of radiating element to achieve improved impedance bandwidth and isolation. Further, a split U‐shaped stub connected to center of each radiating element to achieve the desired resonant frequency of 3.6 GHz. The proposed antenna covers a ?10 dB operating band of 3.34 to 3.87 GHz (530 MHz) with more than 20 dB isolation between a pair of elements. MIMO performances are also analyzed and experimentally validated. The measured performances of a prototype are found in good agreement with simulated performances. Further, the simulation study is carried out to see the effect of housing and extended ground plane on two‐element MIMO antenna for practical application. An idea of realization of 12‐element MIMO is also studied using the proposed two‐element MIMO antenna.     

Compact tri‐notched ultrawideband bandpass filter design using CSRR,DGS, and FMRR configurations

The folded multiple‐mode resonators with complementary split ring resonator (CSRR), and defected ground structures (DGS) are introduced for notched ultrawideband (UWB) bandpass filter (BPF) design in this article. Using the CSRR, FMRR, notched wide‐band BPF, a notch response can exist in the UWB passband for blocking the interference. Adjusting the size factor of CSRR, the wide tuning ranges of notch frequencies included the desired frequencies of 5.2/5.8 GHz are achieved. The lower insertion loss (0.31 dB), higher rejection level (?48.40 dB), wider bandwidth (FBW 75%), and wider stopband (extended to 2.01 f₀ below ?20 dB rejection level) of UWB band at the central frequency f₀ = 4.58 GHz are obtained. Second, design a CSRR, DGS, FMRR, tri‐notched UWB filter, the wider bandwidth (3.1–9.8 GHz) with FBW = 126%, lower insertion loss (0.26 dB), and higher rejection level (?44 dB) of UWB band at central frequency f₀ = 5.6 GHz are presented. Using the CSRR and interdigital couple, three notch responses can exist in the UWB passband for blocking the interference signals. Adjusting the size factor of CSRR and interdigital couple, the wide tuning ranges of notch frequencies included the desired frequencies of 5.18/6.10/8.08 GHz are achieved. The wide tuning ranges of three notched frequencies cover from 5.0 to 8.4 GHz. It is a simple way to control the notch responses. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:571–579, 2014.     

Compact quad‐channel high‐temperature superconducting diplexer based on stub‐loaded square ring resonator

A compact quad‐channel high‐temperature superconducting diplexer based on stub‐loaded square ring resonator (S‐LSRR) is proposed. The proposed resonator consists of a square ring with symmetrically loaded two open‐circuited stubs and provides four resonant modes for quad‐channel applications. Even‐ and odd‐mode methods are applied to analyze the S‐LSRR. Analytical study shows that four resonant modes of one S‐LSRR can be designed in two pairs and applied to construct two of four channels of the designed diplexer. A square patch is added to the resonator for providing an additional parameter to tune the resonant modes. Based on the proposed resonator, a quad‐channel diplexer with center frequencies of 2.4, 3.2, 3.9, and 5.6 GHz is designed. For demonstration, the diplexer is fabricated on 2‐in‐diameter 0.5 mm‐thick MgO wafer with double sided YBa₂Cu₃O_y films and measured at 77 K. Good agreement between the simulation and measurement is obtained. The diplexer has a compact size of 0.25 λ_g × 0.45 λ_g, where λ_g is guided wave length at the center frequency of first channel.