Frequency‐selective rasorber with two low insertion loss transmission bands

A frequency‐selective rasorber (FSR) with two low insertion loss transmission bands is proposed. The FSR is composed of the resistive sheet layer at the top and bandpass FSS layer at the bottom, and separated by air spacer. Full‐wave simulation results show that the FSR realize two transmission bands at frequencies 8.5 GHz and 10.8 GHz with 0.45 dB and 0.77 dB insertion loss. Meanwhile, the band with |S₁₁| < ?10 dB is over 4.2‐8.8 GHz and 9.2‐17.4 GHz. Compared with the reported FSR with two transmission bands, the proposed FSR in this article achieves two transmission bands with lower insertion loss and wide absorption band at high frequencies. To validate the performance of the proposed FSR, the samples are fabricated and measured, reasonable agreement between simulated and measured results is achieved.     

Low‐profile wideband patch antenna using double‐tuned impedance matching

A low‐profile wideband patch antenna utilizing double‐tuned impedance matching technology is investigated in this paper. To extend the operation bandwidth of the antenna, the step‐folded probe is used here to realize the double‐tuned impedance matching. Using equivalent circuit theory, the working principle of the antenna is analyzed and discussed. The full‐wave simulation is carried out to optimize the design while the prototype of the antenna is fabricated and measured. Good agreement between the simulation and measurement can be observed. The measured results show that the antenna has a height of 0.12λ_L (λ_L is the free space wavelength corresponding to lowest frequency) and the ?10 dB impedance bandwidth can cover 1.60‐2.83 GHz (55.5%). The low profile and wide operation bandwidth of the antenna make it a good candidate for wideband wireless communication systems.     

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 compact angularly‐stable frequency selective surface for GSM 900/1800‐MHz shielding using cascaded 2.5‐dimension structure

In this article, a novel compact dual‐band frequency selective surface (FSS) with stable response is proposed for GSM shielding. This FSS is designed using 2‐layer cascaded 2.5‐dimension structure of which element is composed of two via‐based modified swastika unit cells. The proposed structure has created two stop bands around frequency 900 and 1800 MHz, respectively, with maximum attenuation value close to 70 dB. Besides, this FSS performs an excellent miniaturization characteristic with overall size of 0.048λ₀ × 0.048λ₀, where the λ₀ represents the free space wavelength of the lower resonance frequency. More important, this FSS exhibits a very stable frequency response up to 80° for TE and TM polarization. To understand the structure better, the design procedure of this FSS is introduced in detail. Since the proposed FSS has an excellent comprehensive performance, this FSS has great potential in shielding GSM signal for small electronic devices. Finally, a prototype of proposed FSS is fabricated and measured. The measurement results prove the validity of simulation results.     

A substrate integrated cavity‐fed dual‐polarized filtering patch antenna with high isolation

This article presents a dual‐polarized filtering patch antenna, which uses two orthogonal modes (TE₂₁₀/TE₁₂₀) of the substrate integrated cavity (SIC) to couple with two orthogonal modes (TM₁₀/TM₀₁) of the patch by the cross slot, respectively. The second‐order filtering response on dual polarizations can be achieved by using just one SIC resonator and one slotted square patch, which display simple structure of the proposed antenna. The slotted square patch provides a new way to obtain same external quality factor of the radiator on dual polarization, which makes the performances on two polarizations agree well with each other when changing the bandwidth. High isolation can be achieved by controlling the space of the vias of the SIC. Radiation nulls can be produced by connecting the coupled lines with the feeding lines in parallel. A prototype with the entire height of 0.019 λ₀ (λ₀ is the free‐space wavelength at center frequency) achieves a 10‐dB bandwidth of 1.6%, the gain of 4.9 dBi at the center frequency, the port isolation of 43 dB, and the out‐of‐band rejection level of 25 dB.     

A low volume flexible CPW‐fed elliptical‐ring with split‐triangular patch dual‐band antenna

In this article, the intensive investigations are carried out on a low volume compact flexible antenna for wireless applications with a novel structure model. The proposed model has considered as an elliptical‐ring with split‐triangular patch (ERSTP) antenna with the coplanar waveguide feeding to achieve dual‐bands. The ERSTP antenna is designed with polyimide material having the volume (L _a × W _a × h) 99 mm³. The ERSTP antenna resonates with 2.60 GHz and 3.48 GHz frequencies with a reflection coefficient of ?21.92 dB and ?32.14 dB and a gain of 2.39 dBi and 1.75, dBi respectively. The impedance bandwidths are 100 MHz and 330 MHz observed at two frequency bands. The proposed ERSTP antenna has operated on mobile‐worldwide interoperability for microwave access (M‐WiMAX) and worldwide interoperability for microwave access (WiMAX) bands respectively. The simulated and measured results of ERSTP antenna are in good agreement.     

Ultrawideband high‐gain dual‐polarized antenna with anti‐interference capability

In this article, a high‐gain dual‐polarized antenna with band‐rejection capability for ultrawideband (UWB) applications is proposed. Tapered dipoles are chosen as a primary radiator to achieve UWB operation and it is reflected by a metallic cavity reflector for high gain radiation. A notch at WLAN band is realized by etching a set of four bent slots in the radiating elements. The measured results demonstrate that the proposed design with overall dimensions of 0.69λ _L × 0.69λ _L × 0.16λ _L (λ _L is free‐space wavelength at the lowest operating frequency) has operating bandwidth of 95.1% (3.2‐9.0 GHz) and the rejected frequency band from 5.0 to 5.9 GHz. Additionally, good unidirectional radiation patterns with a broadside gain from 8.1 to 11.5 dBi and radiation efficiency of better than 90% are also achieved.     

A high BDR microstrip‐line fed antenna with multiple asymmetric elliptical wide‐slots for wideband applications

In this study, a novel printed wide‐slot antenna for wideband applications is presented. The designed antenna consists of four merged elliptical wide‐slots (EWSs) of different dimensions in the ground plane. An open‐ended microstrip line having a characteristic impedance of 50 Ω is used to excite the EWS. Each EWS corresponds to the different frequency of operation and hence when merged together give a wideband response. The fabricated prototype of the designed antenna shows the 10 dB return loss bandwidth (RLBW) of about 157.72% ranging from 2.21 to 18.7 GHz. The peak gain varies from 0.1 to 6.5 dB within the RLBW is reported. An almost constant group delay, low variation (<?40 dB) in the transfer function S₂₁ and linear phase variation for both side by side and face to face orientations of the designed antenna shows its applicability for wideband applications. The electrical dimensions of about 0.176λ _L × 0.162λ _L (where λ _L is the lowest operating wavelength) give rise to the bandwidth dimension ratio of about 5505 which is highest among the antenna structures reported in the literature. The measured results are found in good concordance with the results obtained from numerical simulations.     

A dipole‐type millimeter‐wave antenna with directional radiation characteristics

A dipole‐type millimeter‐wave (mm‐wave) antenna with directional radiation characteristics is presented. A radiating patch structure composed of a dipole‐type radiation patch and a rectangular‐shaped parasitic patch are initially investigated to achieve a wider bandwidth. To further improve the operating bandwidth and to realize a directional radiation characteristic, this radiating patch structure is top‐loaded above a conducting cavity‐backed ground structure, which has a low profile (thickness of 3 mm). The measured results show that the proposed mm‐wave antenna can achieve a wide 10‐dB bandwidth of 51.3% (29.6‐50.0 GHz) and stable gain across the desired frequency range. Furthermore, good directional characteristics over the entire mm‐wave frequency band with a compact antenna size of 0.64λ_40GHz × 0.91_λ40GHz × 0.43_λ40GHz are also realized. Hence, it is suitable for many small size wireless mm‐wave systems.     

Novel ultra‐compact two‐dimensional waveguide‐based metasurface for electromagnetic coupling reduction of microstrip antenna array

A novel ultracompact two‐dimensional (2D) waveguide‐based metasurface is proposed herein and applied for the first time to reduce mutual coupling in antenna array for multiple‐input multiple‐output applications. The unit cell of the proposed 2D waveguide‐based metasurface is ultracompact (8.6 mm × 4.8 mm, equal to λ₀/14.2 × λ₀/25.5) mainly due to the symmetrical spiral lines etched on the ground. The metasurface exhibits a bandgap with two transmission zeros attributing to the negative permeability in the vicinity of magnetic resonance and the negative permittivity in the vicinity of electric resonance. Taking advantage of these two features, a microstrip antenna array is then designed, fabricated, and measured by embedding an 8 × 1 array of the well‐engineered 2D waveguide‐based metasurface elements between two closely spaced (9.2 mm, equal to λ₀/13.3) H‐plane coupled rectangular patches. There is good agreement between the simulated and measured results, indicating that the metasurface effectively reduces antenna mutual coupling by more than 11.18 dB and improves forward gain. The proposed compact structure has one of the highest reported decoupling efficiencies among similar periodic structures with comparable dimensions. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:789–794, 2015.     

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 low‐profile wideband dual‐polarization patch antenna with antisymmetric feeding network

In this paper, a novel broadband dual‐polarization patch antenna is proposed. Antisymmetric Γ feeding network is applied to excite the radiating patch etched on the upper side of the horizontal substrate, which could minimize the undesired radiation from the probe and extend the impedance bandwidth. For verifying the proposed approach, a prototype is fabricated and measured, the simulated and measured results show the antenna has a wide impedance bandwidth of 48% (1.66‐2.71 GHz) for S11 < ?10 dB, as well as stable radiation gain around 9.5 dBi with low cross‐polarization. In addition, the total height of the antenna is only 0.17 λ₀ ( λ₀ is the free space wavelength of central frequency) and high port‐to‐port isolation is better than 30 dB. The characteristics of the proposed antenna illustrate it can be an indication for a micro base station in the mobile communication system.     

Integrated circular polarized microstrip antenna with dual‐mode‐polarization insensitive characteristics

A dual‐mode circularly polarized compact antenna with integrated left‐hand and right‐hand circular polarization (LHCP and RHCP) is presented in this work. A multilayer arrangement of a square patch and square ring structure with an irregular transmission line is analyzed for dual‐band, dual‐CP operation. To realize dual mode propagation the proposed structure is excited using electromagnetic coupling technique. Succeeding proximity feeding with T‐stub match is analyzed, which conveys impedance bandwidth of 180 and 300 MHz within |S₁₁| < ?10 dB at 3.5 and 5.5 GHz. The designed CP elements is suitably arranged with feed line for generating two orthogonal polarization of equal amplitude and a 90° phase difference at both the resonant modes (TM₁₀ and TM₀₁). Alterable LHCP and RHCP performance is realized by altering the compensated position and peculiar angle. Having both LHCP and RHCP polarization this design shows polarization insensitive characteristic. Each LHCP and RHCP antenna element accomplished a 3‐dB AR of 70 and 120 MHz with a gain up to 6 dBi. With a low profile of 0.27λ₀ × 0.27λ₀ × 0.04λ₀, the CP antenna is fabricated, and the performance is validated through experimental analysis. With all the viable characteristics, the antenna is proposed for Wi‐MAX/WLAN communication.     

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 broadband circularly polarized slot‐patch antenna array

A simple design of circularly polarized slot‐patch antenna array with broadband operation and compact size is presented in this article. The antenna element consists of a circular slot and a semicircular patch, which are etched on both sides of a substrate. For the gain and axial ratio (AR) bandwidth enhancement, its array antennas are implemented in a 2 × 2 arrangement and fed by a sequential‐phase feeding network. The final 2 × 2 antenna array prototype with compact lateral dimension of 0.8λ_L × 0.8λ_L (λ_L is the lowest frequency within AR bandwidth) yielded a measured impedance bandwidth of 103.83% (2.76‐8.72 GHz) and a measured AR bandwidth of 94.62% (2.45‐6.85 GHz). The peak gain values within the AR bandwidth are from 2.85 to 8.71 dBi. A good agreement between the simulated and measured results is achieved. This antenna array is suitable for multiservice wireless systems covering WiMAX, WLAN and C‐band applications such as satellite communications.     

SIW cavity‐backed 24° inclined‐slots antenna for ISM band application

In this article, a novel resonant series slot linearly polarized antenna is realized using substrate integrated waveguide (SIW) technology for industrial scientific medical radio band (ISM) at 5.8 GHz. The proposed antenna consists of two 24° inclined slots and two metallic vias to produce alternate inductive and capacitive loads. The rectangular slots are introduced at the top metallic surface at an angle of 24° from the Y‐axis to excite a hybrid mode (TE₁₁₀ + TE₁₂₀) near to the modified cavity mode TE₁₂₀. The resonant slots are excited with the help of an inset microstrip feedline which retain its planar integrability. The slots are excited to resonate in the TE₁₂₀ mode at 5.8 GHz. To enhance the bandwidth, the location of two shorting vias are optimized in proximity to the slots. These vias help to couple the hybrid mode and the cavity modes in the desired frequency band, which leads to enhancement in the bandwidth significantly. The proposed geometry is fabricated and experimentally verified. The measured and simulated results depict a good co‐relation which show measured ?10 dB fractional bandwidth of 5.2% with a maximum gain of 7.15 dBi and the front to back ratio better than 15 dB at 5.8 GHz.     

A wideband circularly polarized crossed magneto‐electric dipole

A novel wideband crossed magneto‐electric (ME) dipole for circularly polarized (CP) radiation is proposed in this paper. The proposed antenna consists of a crossed dipole, four parasitic elements, and two pairs of folding metal plates (magnetic dipole). The parasitic elements and magnetic dipole are employed to enhance the axial ratio bandwidth (ARBW). The antenna size is 0.51λ₀ × 0.51λ₀ × 0.33λ₀, where λ₀ is the corresponding free‐space wavelength at the center frequency. A prototype antenna is fabricated and tested. The experiment results depict that the impedance bandwidth (IBW) for voltage standing wave ratio < 2 is 79.2% (2.5‐5.78 GHz) and the 3‐dB axial ratio bandwidth (ARBW) is 72.5% (2.7‐5.77 GHz). At the same time, good CP characteristics and stable symmetrical radiation patterns can be obtained across the operation bandwidth.     

Design of miniaturized substrate integrated coaxial line bandpass filters with quarter‐wavelength spiral resonator

In this article, several miniaturized bandpass filters (BPFs) with substrate integrated coaxial line quarter‐wavelength spiral resonators were proposed. The coupling coefficients and external quality factors of proposed structures were examined by using the commercial simulation software. With different combinations of the proposed resonators, three two‐order and two high‐order miniaturized BPFs operating at 1.2 GHz with 3‐dB fractional bandwidth of 8% were designed, fabricated, and measured. The measured results showed that all the return losses were better than 10 dB over the entirely passbands, and the overall circuit sizes of two‐order and high‐order BPFs were only 0.044λ₀ × 0.028λ₀ and 0.047λ₀ × 0.047λ₀, where λ₀ is the wavelength in free space at the center frequency of the passband. Good agreements were observed between the simulated and measured results. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:489–495, 2016.     

A 1‐to‐n way single‐ended‐to‐balanced substrate integrated waveguide filtering power splitter

An approach to 1‐to‐n (n = 3, 4…) way single‐ended‐to‐balanced filtering power splitter (SETBFPS) is proposed. The properly placed balanced ports with 0.5λ_g (λ_g is the substrate integrated waveguide [SIW] guided wavelength at f₀) space make the TE32nd 103 and TE32nd 105 modes of n 32nd‐mode SIW multimode resonators form differential‐mode (DM) passband of the SETBFPS. Compared with the state‐of‐art single‐ended‐to‐balanced power splitters, the proposed approach has all the functions of 1‐to‐n way, filtering, and common‐mode (CM) suppression. A 1‐to‐3 way prototype is exemplified at 3.5 GHz with the minimum insertion loss (IL) of 0.09 dB, a fractional bandwidth (FBW) for a 15‐dB return loss of 35%, and a FBW for 15‐dB CM suppression of 52%. Low IL and wide bandwidth can be observed.     

CSRR‐loaded T‐shaped MIMO antenna for 5G cellular networks and vehicular communications

This article proposes a multiple input multiple output (MIMO) antenna for 5G‐based vehicular communication applications. The designed MIMO antenna consist of two element iterated T‐shape antenna with defected ground structure (DGS) and split ring resonator. The antenna providing reflection coefficient S₁₁ s₁₁ ≤10 dB and bandwidth of 6.3 and 3.96 GHz over the frequency range of 26.83 to 33.13 GHz and 34.17 to 38.13 GHz, respectively. For the suitable future vehicular millimetric wave communications, this antenna achieved resonant frequencies at 28, 33, and 37 GHz. The designed antenna has achieved peak gain of 7.11 dB in operating band. It is fabricated on 12 x 25.4 x 0.8 mm³ Rogers RT duroid 5880 substrate with dielectric constant (ε_r) of 2.2. The antenna is placed on vehicle in virtual environmental using ANSYS SAVANT tool and the simulated results are showing good matching with the measured results of proposed MIMO antenna.