In this paper, a compact wideband circularly polarized (CP) crossed-dipole antenna with wide half-power beamwidth (HPBW) and broad 3 dB axial ratio beamwidth (ARBW) is proposed. The antenna is composed of crossed bowtie dipoles, four pentagonal parasitic elements and eight vertical metallic plates. A double vacant-quarter printed ring with orthogonal bowtie dipoles is designed for CP radiation and broadband characteristics of impedance and 3 dB axial ratio (AR) bandwidths. Parasitic elements and vertical metallic plates are utilized to increase bandwidth and broaden beamwidth further. The total size of the proposed antenna is 0.4λ×0.4λ×0.16λ. Simulated results are in good agreement with the measured ones which demonstrate an impedance bandwidth 88.4% and a 3 dB AR bandwidth 73.1%. The HPBW of more than 120° is 70.0%. The 3 dB ARBWs of more than 120° in E-plane and H-plane are 63.1% and 37.5%, respectively. With both the excellent CP performance and compact size, the proposed antenna is attractive for modern wireless communications.
A miniature patch antenna for handset mobile communication is studied by loading an H-shaped patch associated with fashionable mushroom structures. The mushroom structures work as effective high index metamaterials while the H-shape can lengthen the current path on the patch. They both contribute to reduce the patch length. To verify the conceptual method, an H-shaped patch meta-antenna is demonstrated in full wave simulations and experiments. Good agreement has been observed. A compact patch is achieved for the antenna with a size of 0.15λ0×0.15λ0. The measured antenna gain is acceptably high as 4.2 dBi.
This paper presents an ultra-wideband (UWB) high temperature superconducting (HTS) bandpass filter (BPF) based on a ring resonator loaded with a pair of symmetrical cross-shaped stepped-impedance open stubs. The main advantages are that two transmission zeros are introduced to improve passband selectivity, and high mode suppression is achieved by adjusting the impedance ratio of the cross-shaped stubs and using a pair of parallel-coupled lines. The filter is designed on double-sided YBCO/MgO/YBCO HTS films with a thickness of 0.5 mm and dielectric constant of 9.8. At 77 K, the measured 3-dB bandwidth of the filter covers 1.63 GHz~6.03 GHz. Due to the use of superconducting material, the insertion loss at the center frequency of 3.83 GHz is 0.12 dB, and the rejection is greater than 36 dB in the lower stopband, and the upper stopband with 20 dB attenuation level is extended to at least 8.5 GHz.
In this paper, a method to miniaturize a stepped open-slot antenna (SOSA) for ultra-wideband (UWB) applications is proposed. The antenna consists of a stepped open slot, J-shaped slots, and two strip directors. A broadband microstrip-to-slotline transition with circular stubs is applied to feed the antenna. J-shaped slots are inserted on the ground plane of the antenna to create a new resonance in the low-frequency region, thereby miniaturizing the size of the antenna. Finally, two strip directors are appended above the stepped open slot in order to increase the gain in the middle- and high-frequency regions, as well as to enhance input impedance matching in the high-frequency region. A prototype of the miniaturized SOSA is fabricated on an FR4 substrate with dimensions of 30 mm×32 mm. It shows a measured frequency band of 2.99-10.87 GHz for a voltage standing wave ratio < 2, which ensures UWB operation, and the measured gain range is 3.2-7.3 dBi in the band with a front-to-back ratio > 8.7 dB.
In this paper, a novel compact ultra-wideband (UWB) power divider with triple-notched bands is investigated. Firstly, the initial UWB power divider is studied using a couple of square ring quad-mode resonators. Then, by embedding a pair of coupled triple-mode stepped impedance resonators (TMSIRs) into the initial UWB power divider, three desired notched bands are achieved. The central frequencies of the notched bands can be easily controlled by the electrical length of the TMSIRs. To validate the design theory, a novel compact UWB power divider with triple notched bands centered at frequencies of 3.7 GHz, 5.2 GHz and 7.8 GHz is designed and measured. The simulated and measured results indicate that it has a low insertion loss and good return loss performance at all the three ports and a high isolation between the two output ports across the UWB bandwidth from 3.1 to 10.6 GHz.
A phase diversity printed-dipole antenna element for patterns selectivity array application is designed in this paper. The antenna element consists of a printed dipole structure and two varactors. By changing the control voltage of each element, various radiation phases in the far field of each element is realized, that is, the peak gain direction of the array is changed. With this method, the structure designed is simple, and only two varactors are loaded. To verify the feasibility, an antenna prototype is experimentally characterized, which validates the proposed concept. The impedance bandwidth of array is 22.2% (3.2~4.0 GHz), in which the peak gain direction can be scanned during angles from -θ to +θ across broadside (θ = 13°~18° at different frequencies). It can be applied to phased antenna system.
A novel and compact triband planar antenna geometry suitable for DCS/WLAN/WiMAX services is reported. The multiple metal strip geometry in dual F shape is printed on a substrate of dielectric permittivity 4.4 and thickness 1.6 mm. A truncated and asymmetrically placed ground structure is used for improved impedance matching. Feed position is also optimized for good antenna radiation performance. The geometry is simulated using High Frequency Structure Simulator. All the radiation characteristics of the antenna are validated experimentally and found in good agreement with simulation results. Performance of the proposed antenna is compared with other triband antennas reported in the literature. Measured radiation patterns and gain are also presented in this paper. The radiation patterns are validated by EMSCAN Corporation's RFxpertTM application tool also.
In this article, a self complementary frequency independent triple band Sinuous Antenna Array (SAA) is designed for wireless applications such as Mobile- Satellite Service (MSS), Global Positioning System (GPS) and Global System for Mobile communications (GSM) application. Four Sinuous elements are connected to the nearest one in such a way to form an array structure. A prototype of a Sinuous Antenna Array (SAA) is embedded into a flame retardant-4 (FR-4) dielectric material. The performance of the proposed antenna array has been analyzed by using Ansys High Frequency Structure Simulator (HFSS). The suggested antenna is fabricated and tested. The measured results are shown that the proposed antenna array operated at the frequencies of 1.5 GHz for GPS, 1.8 GHz for GSM and 2 GHz for MSS with a reflection coefficient of below -10 dB. It has good reflection coefficient characteristics, Voltage Standing Wave Ratio, impedance bandwidth and radiation characteristics.
A fast Root-MUSIC algorithm based on Nystrom method and spectral factorization is proposed. By using Nystrom method, only two sub-matrices of the sample covariance matrix are calculated, which avoids its complete calculation and has the advantage of low computational complexity. At the same time, the polynomial coefficients of the Root-MUSIC based on the Nystrom method are conjugated, and the order of the polynomial is reduced by half when using iterative operations. Finally, the root algorithm is used to estimate the DOA. The performance of the proposed algorithm is demonstrated by simulation results.
In this letter a four-port multi-input-multi-output (MIMO) antenna for 5G applications is proposed. This antenna is compact with a size of 11.3 mm×31 mm excluding feed lines. The radiation patterns of the antenna show pattern diversity in the azimuthal plane, and each antenna element has an end-fire gain about 10 dBi by employing an array of metamaterial unit cells. The isolation between the antenna elements with edge to edge separation <λ0/5.5 at 28 GHz is enhanced by trimming the corners of the rectangular high refractive index metamaterial region along with a ground stub between antennas. The proposed antenna is fabricated, and each antenna element has return loss, Snn<-10 dB with isolation, Snm>21 dB in the frequency range 26 GHz to 31 GHz, which makes this antenna potential candidate for MIMO application at 28 GHz band enabling 5G cellular communications.
In this letter, a new wideband circularly polarized antenna for Radio Frequency Identification (RFID) readers is proposed. A prototype operating in the Ultra-High Frequency (UHF) band is successfully realized and tested using a defected Ground Structure (DGS). This antenna consists of an L-shaped metal strip and a DGS with four tuning stubs. The overall size covers 90*90*1.6 mm3. The measured -10 dB reflection coefficient S11 bandwidth is 27% (800-1020 MHz) and a good radiation pattern and suitable gain coefficient about 3.7 dB have been achieved. Also, an excellent agreement was noticed between simulation and measurement results demonstrating the good performance of the proposed antenna.
A new miniaturized microstrip lowpass filter with compact size and a wide spurious-free stopband is investigated. To achieve compact design and ultra-wide band rejection, both triangular patch resonators and trapezoid patch resonators are introduced in the filter. To further reduce the circuit size of the filter, the meander transmission line is also adopted in the design. A demonstration filter with 3 dB cutoff frequency at 0.76 GHz has been designed, fabricated and measured. Results indicate that the proposed filter is able to suppress the 16th harmonic response referred to a suppression degree of 15 dB. Furthermore, the proposed filter exhibits a small size of 0.080λg×0.072λg, where λg is the guided wavelength at 0.76 GHz.
This paper presents two novel substrate integrated waveguide (SIW) diplexers with transmission zeros placed below and above the passband. Diplexer I is based on two bandpass filters (BPFs) using eighth mode SIW (EMSIW) cavities with Rx and Tx frequencies at 3.68 GHz and 6.09 GHz. The second one is operated at 2.37 GHz and 6.04 GHz using EMSIW and thirty-second SIW (TMSIW) cavity. The diplexers are all combined through a T-junction by carefully choosing the length and width of two branches to allow each filter to match the antenna, while maintaining an open circuit at the middle band of the other. The proposed diplexers possess compact size, because of the EMSIW and TMSIW cavity. The diplexers are fabricated in SIW technology. The minimum insertion losses including SMA connectors are measured to be 1.39/1.61 dB and 0.38/0.85 dB. Meanwhile, the diplexers exhibit 37 dB and 42 dB isolations between the channels, respectively. Good agreement is achieved between simulated and measured results.
This paper presents a direct matrix synthesis for in-line diplexers constructed by general Chebyshev channel filters. The finite transmission zeros of the channel filters are generated and independently controlled by a set of frequency-variant couplings (FVC) sections. The network only involves resonators cascaded one by one without any auxiliary elements (such as cross-coupled or extracted-pole structures), and this paper provides the best synthesis solution in configuration simplicity for narrowband contiguous diplexers. For the channel filters, considering both the couplings and capacitances matrices of a traditional low-pass prototype, a generalized transformation on the admittance matrix is introduced as the basis of the synthesis, which allows more than one cross-coupling to be annihilated in a single step, while generating an FVC section simultaneously. Two examples of diplexer are synthesized to show the validation of the method presented in this paper.
In a recently published report, Sen and Das  proposed a frequency tunable low-cost microwave absorber to obtain tunable absorption spectra. In this paper, we justify that the proposed device is not an absorber. It is observed that the total absorption rates merely reach 2% and 14.85% for the air gaps of 3.5 mm and 7.5 mm, respectively, when the co- and cross-polarization reflections are taken into account in the reported device. Obviously, The original authors erroneously consider a polarization converter as an absorber, and the obvious errors can be found in their paper.
A novel triple-mode bandpass filter (BPF) using half-wavelength-resonator-coupled square-loop resonator is developed in this letter. The half wavelength resonator is applied to add an additional path, which increases a pole in the passband and a transmission zero in the stopband. Furthermore, the coupling scheme is used to accurately predict its desired performance. Compared to the conventional square-loop dual-mode filter, higher frequency selectivity and wider bandwidth are achieved. Finally, this filter is designed, fabricated and measured. Good agreement is achieved among the theoretical, simulated and measured results. All of these results validate our design idea.
In this paper, we propose a novel method for wideband direction of arrival (DOA) estimation. By calculating the largest principal angle between the signal subspace and the subspace spanned by the augmented array manifold, the proposed method can estimate direction of arrival of wideband signals. Unlike conventional wideband methods, it adopts a new augmented array manifold and constructs the augmented matrix entirely by processing the received signals in frequency domain. It does not require any preliminary DOA estimates or focusing matrices. Simulation results show that the proposed method exhibits satisfactory performance at medium and high signal-to-noise ratio (SNR) conditions in comparison to the existing wideband DOA estimation methods.
A simple broadband and wide stopband half-mode substrate integrated waveguide (HMSIW) filter is proposed. Symmetrical complementary split ring resonators (CSRRs) and metallized holes are loaded on the surface of the HMSIW resonator. Metallized holes placed in the center of the CSRRs are used to create two passbands. CSRRs can reduce the return loss of the first passband, and a transmission zero is introduced to suppress the performance of the second passband, thus generating broadband covering the entire X-band. The simulated results show that the center frequency and fractional bandwidth of the filter are 9.26 GHz and 60.7%. There is a transmission zero at 13.18 GHz, and the insertion loss in the range of 12.30 to 21.46 GHz is better than -10 dB, which means that the out-of-band suppression performance is good. The measured results are in good agreement with the simulated ones. This new combination not only obtains broadband frequency, but also makes the filter more compact. The filter has some practical and application significance.
Four wave mixing (FWM) in optical fiber is unwanted effect to an optical transmission system, which can severely limit the wavelength division multiplexing (WDM) and lower the transmission efficiency. In this work, the robustness of normal Non-Return-to-Zero (NRZ), Return-to-Zero (RZ) and Modified-Duobinary-Return-Zero modulation (MDRZ) to FWM have been evaluated. Furthermore, the system performance is evaluated with the effect of fiber length tuning and applying 160 Gb/s data rate. The findings show that the RZ modulation offers a lower FWM power of -44 dBm at 700 km fiber length than -30 and -38 dBm of NRZ and MDRZ respectively at the same fiber length. In terms of system performance at the first channel and 700 km distance, the minimum BER is observed in normal RZ modulation, equal to 1.2×10-23. It is also noticeable that if NRZ and MDRZ modulations are applied, the system performance will be quickly changed and get worse, where the BEARs are increased to 1.3×10-6 and 1.3×10-8 consecutively at same channel and parameters.
A broadband low-profile circularly polarized (CP) antenna with a stepped sequential feeding structure is proposed in this letter. The CP antenna consists of four dipoles and parasitic structures. A novel feeding network using parallel transmission lines is introduced to realize phase difference required for circular polarization. Four dipoles are excited by the feeding structure to achieve CP radiation, and parasitic elements are loaded to broaden 3-dB axial ratio bandwidth (ARBW). To verify this design, the proposed antenna is fabricated and measured. Measured results show that a 10-dB impendence bandwidth of 42% (1.82 to 2.8 GHz) and 3-dB ARBW of 36.4% (1.89 to 2.73 GHz) are achieved, respectively. Moreover, the designed antenna has a low profile of 0.13λ (λ is the free-space wavelength at the center frequency) and a gain of average 9.5 dBi with less than 1.5-dB variation within the 3-dB ARBW.