Quadrature feeding is an essential in magnetic resonance imaging radio frequency (MRI-RF) coils, to improve the homogeneity of the magnetic field of surface coil, the signal to noise ratio (SNR) of the image by a factor of √2 , and to create a circularly polarized magnetic field inside the volume coil. The quadrature feeding is incorporated, using hybrid coupler. However, at 63.87MHz the Larmor frequency of hydrogen proton, corresponding to 1.5 Tesla, the size of the hybrid coupler and other microwave circuits become large. So, to minimize its physical size, a coaxial cable transmission line with lumped capacitive loading has been proposed. The size of the proposed hybrid coupler is reduced by 68%, as compared to the conventional hybrid coupler. The proposed device is then fabricated as a both rigid and flexible structure, which provides isolation (S41) of around 19 dB and a 900phase difference between coupled and the through ports. Both structures provide return loss S11 > -15 dB and coupling at output ports S21, S31 around 3 dB.
Microwave testing is an area of research where material characterization is done using interrogating microwaves over a frequency band, and this technique can provide excellent diagnostic engineering, geophysical prospecting. Every material has a unique set of electrical characteristics that are dependent on its dielectric properties. Accurate measurements of these properties can provide valuable information about the material. This work presents a non-destructive technique for the detection of adulterants in food using the proposed RF sensor. The proposed RF sensor is operational at C-band with its resonant frequency at 5.7 GHz. The structure is designed using Ansys HFSS, and a predicted model of the proposed sensor is developed and fabricated. Some common food samples are tested using the fabricated sensor, and a shift in resonant frequency is obtained, which indicates the rate of adulteration. From the obtained results, a general conclusion is obtained on the dependency of the rate of adulteration and permittivity of the food sample. A precise correlation of permittivity of common food samples and its resonant frequency is obtained. The predicted model and the experimental results harmonize, which indicates that the model is proficient in real time testing.
A new wideband 3-dB tandem coupler is presented that has wide bandwidth using four 90° short stubs. The proposed tandem coupler does not require a higher transmission line impedance or a narrower coupling gap than conventional couplers. Measurements of the fabricated tandem coupler operated at a center frequency of f0 = 1 GHz are presented as verification of the design concept. The fractional bandwidth (FBW) at which the return loss is suppressed to a level better than 15 dB was 71%. Theoretical calculations and measurements of the tandem coupler were in good agreement
On the basis of serious electromagnetic interference (EMI) produced by power electronic equipment,coupling capacitance existing between transistor and transistor is considered as the main factor disturbing differential-mode(DM) loop. Calculation model of coupling capacitance is established by using FEM (Finite Element Method)and Moment method, and computing method is also derived.EMI improvement method for converter system is proposed by controlling the coupling capacitance impedance. Experimental results show that changing the placement distance and position of the transistor can reduce the conducted interference.
In this paper, the miniaturization of the slot antenna is presented for the first time with the use of high refractive index metamaterial. Based on the effective parameter extraction, the studies conducted on Single Ring Split Ring Resonator (SR-SRR) reveal that the unit cell can produce high values of positive refractive index. By taking the advantage of the principle of duality, the slot is loaded with two Complementary SR-SRRs (CSR-SRRs) on either side of it to create an effective HRI medium. With the partial loading of HRI metamaterial medium, the resonance frequency of the slot is brought down from 4.225 GHz to 2.5 GHz. The radiation characteristics of the loaded slot antenna were found to be almost similar to that of the conventional slot antenna. The simulated and measurement results were found in good agreement.
Electromagnetic interference (EMI) is a crucial problem, and for solving this problem, absorbers especially very thin absorbers are used. Factors like frequency increasing in a device, high integration in electronic systems, higher power densities, and decreasing the size and thickness of PCB make it crucial. So, a novel ultra-wideband and thin metamaterial absorber is proposed in this paper. The absorber consists of metamaterial unit cells, which have a single FR4 layer, metallic ground, and four metallic spirals. A one hundred ohms SMD resistor is placed between two of the spirals. The size of the unit cell is 5.85×5.85×3.2 mm3. The proposed absorber is ultra-thin (λ0/10), and the absorption occurs over a wide incident angle [0°-40°]. The reflection is less than -12dB in [6.5 GHz -12 GHz], and the absorption is more than 94% in this bandwidth. The structure is fabricated, and the outcomes of simulation and measurement are compared with each other. The values of front to back ratio of the fabricated measurements are -12.8, -7.31, and -15.36 dB at 8, 10, and 12 GHz, respectively. The values obtained from simulation are -13, -9.4, and -14 dB, respectively. There is a good agreement(accordance) between the simulation and measurement results of this absorber.
An eight-element ultra-wideband multiple-input multiple-output antenna system is proposed for the 5G mobile terminals. Each radiating branch is composed of a Loop and a monopole antenna. The ultra-wideband characteristics of the antenna are obtained by a T-shaped feed branch coupling a radiation branch. Furthermore, the isolation is lower than -15 dB by introducing a T-shaped neutralization line structure. The results of simulation and measurement show that the antenna system can cover 3.3-5.6 GHz, and the antenna efficiency is 45%-80%. At the same time, the envelope correlation coefficient between any two elements is lower than 0.03. Therefore,the proposed antenna in this study is very suitable for the eight-element MIMO antenna system as a reference.
This study presents a triple resonance microstrip slotted antenna element for 5G (5.15-5.875 Wi-Fi band) applications. This antenna constitutes a rectangular patch stimulated with an I-shaped slot and two shorted metallic vias. This arrangement results in an enhancement of the bandwidth. The antenna features a wide impedance bandwidth (IBW) matching due to triple resonances when being properly excited by coax-probe feed. The IBW of the antenna ranges from 5-6 GHz band with three resonances at around 5.2, 5.5, and 5.8 GHz. Finally, the antenna is fabricated and measured, which displays a -10 dB IBW of 5.04-6.05 GHz (18.2%) featuring stable radiation and gain (around 7 dBi). Moreover, the measurements are in good agreement with simulations. On the account of the single-layered dielectric, this antenna can be easily mounted with active electronics.
A new ring wideband bandstop filter (BSF) and its exact design method is proposed and investigated in this letter. The BSF is devised by introducing an additional transmission line to a traditional hairpin bandstop filter in parallel, hence giving enhanced selectivity and attenuation performance. A lumped lowpass equivalent circuit is introduced to explain the mechanism of the filter. Rigorous correspondence between the BSF and its equivalent circuit is established by comparing their even- and odd-mode input admittances. This enables the BSF to be synthesized the same way as lumped filters. Both the BSF and the method have been documented by a design example.
In this paper, a novel zeroth-order resonator (ZOR) antenna by exciting two asymmetric coplanar strips (ACS) is reported. In order to attain ZOR resonance, the antenna has resorted to two annular ring resonators (ARRs) which control antenna characteristics at 2.7 GHz. In this frequency, antenna treats such as a planar dipole antenna with omnidirectional patterns and linear polarization. The proposed antenna by utilizing two ports can change circular polarization diversity at the second band region. The proposed miniaturized antenna covering more than 80% bandwidth overall two bands and a more than -15 dB isolation between two input ports can be used in portable systems.
A novel, miniature multiple input multiple output (MIMO) ultra wide band (UWB) antenna with dual notched characteristics is proposed. The antenna incorporates a tapered microstrip feed line with two radiating patch structures procured by the incorporation of two ellipses with a circle and a reduced ground structure. The proposed antenna is printed on an FR-4 substrate having a concise size of 40 x 22 mm2 to cover -10 dB bandwidth of 3.18-11.26 GHz with fractional bandwidth of 112%. The two notched bands 3.31-3.99 GHz for WiMAX and 4.97-5.93 GHz for WLAN accomplished by two T-shaped parasitic structures are etched above ground plane and inverted U- shaped slots etched on radiating patch, respectively. The isolation of < -15 dB is realized by inserting a T-shaped stub in between two patch elements. The measured MIMO diversity characteristics are the evidence of that the proposed antenna is appropriate for portable wireless applications.
The paper is devoted to the investigation of radiation frequencies characteristics of a modified waveguide aperture by wire media (WM). Such construction allows radiating weak electromagnetic (EM) waves --- the frequencies of which are non-corresponding to the resonant ones of the modified radiator. It is possible due to the unusual properties of metamaterials, namely the negative value of permittivity of WM. The simulation studying shows that the changing of value of wires radius and at the same time the value of filling factor impacts on the radiation frequency. Therefore, the increase of filling factor leads to the increase of the resonance frequency. The radiation is narrowband with S11-parameter less than -20 dB. The experimental investigation shows that the decrease of the value of lattice period allows increase of the width of radiation frequency range from 30-40 MHz up to approximately 80 MHz at the level of 0.3 (≈ -10 dB). At the same time, the increase of wires' radius values leads to the increase of the value of resonant frequency. Finally, the experimental study demonstrates that the value of overlap between waveguide port (source of EM waves) and wire media sample negligibly impacts on the resonance frequency values and operational range for D/L = 0...0.3.
This paper proposes a novel miniaturized UWB bandpass filter by cascading two miniaturized low-pass and high-pass modules. On account of the slow wave and stopband characteristic of defected microstrip structure (DMS), an E-shaped DMS with low-pass characteristic is presented, and an RLC equivalent circuit is utilized to analyze it. By three-dimensional electromagnetic modeling , the S parameters can be obtained to extract the initial parameter values of the RLC equivalent circuit and verify the validity of equivalent circuit in Advanced Design System. The high-pass module uses a lump element to reduce the circuit dimension. The high frequency selectivity can be achieved by loading L-shaped stubs, which produces one transmission zero at the upper band of passband and has a good rectangle coefficient of 1.2 (25 dB-bandwidth/3 dB-bandwidth). To verify the idea, a compact UWB bandpass filter is simulated and fabricated. The result shows that the passband range is 3.1-10.6 GHz with 1 dB loss, and the measurement has a good agreement with the simulation. Besides, a notched wave working in X wave band can also be generated. Compared with the previous works, this UWB bandpass filter has the advantages of miniature and high selectivity.
A wide locking range injection locked frequency divider (ILFD) with a low power consumption for 60GHz applications is presented. The locking range of the ILFD is enhanced by reducing the parasitic capacitances of the transistors. The cross-coupled transistor and injected transistors are integrated to become a compact structure, which exhibits simple routing and induces less parasitic capacitances. To verify the proposed structure, the ILFD was fabricated using 65 nm CMOS technology. It has a measured locking range of 55.3 GHz to 67 GHz (19%) with 0 dBm input power. The circuit dissipates 1.98 mW at 0.5 V supply voltage without the output buffers.
This letter presents a uniplanar two-port UWB-MIMO antenna with high isolation for wireless communication applications. The designed antenna is composed of a single metal layer and a thin substrate. The single metal layer acts as radiators and a ground plane. The radiator of each element consists of a modified dual-L-shaped feeding structure and a defected rectangular patch, which is shared by the ground plane. The modified dual-L-shaped feeding structure is introduced to broaden the bandwidth. Furthermore, two fork-shaped slots and bent slots are embedded in the rectangular shared structure for further improving the bandwidth and decreasing the mutual couplings without any other additional decoupling structures. The experimental results show that the proposed antenna achieves the ultra-wide impedance bandwidth (3.0-12.4 GHz), high isolation ( > 20 dB at entire impedance bandwidth), very small ECC (< 0.01), high multiplexing efficiency (> -1.9 dB), stable realized gain and radiation patterns. Therefore, the designed antenna is suitable for most wireless UWB communication applications.
A single-layer single-feed wideband omnidirectional microstrip antenna with rotating square patches is investigated in this paper. To obtain wide impedance band, the proximity-fed structure are introduced to the antenna to generate dual resonating modes. Two square patches with rotating angle of 90 degrees are used as the main radiator to improve the omnidirectional feature of the radiation pattern. For verifying the design, an antenna prototype with wide operation bandwidth is designed, simulated, fabricated, and measured. The results indicate that the impedance bandwidth (|S11| < -10 dB) as high as 48.6% (3.02-4.96 GHz) is obtained. Meanwhile, the height of the antenna is only 0.11λ0 (λ0 is the free space wavelength corresponding the lowest frequency). What's more, omnidirectional radiation pattern is obtained over the operation band. The advantages ofwideband, low-profile and simple feed structure make the antenna good candidate in modern communication systems.
In this paper an oscillator-type GaN HEMT based active integrated antenna is proposed where the active part of the circuit and patch antenna are in series. The patch antenna is designed to offer optimum impedance at second harmonic to generate maximum power at second harmonic and overall negative resistance at fundamental frequency for sustained oscillation. The circuit has been designed, fabricated and characterized. The fundamental frequency of oscillation of this circuit is 1.5 GHz. This circuit has Effective Isotropic Radiated Power (EIRP) of 32.1 dBm at 3 GHz. Power at fundamental frequency is suppressed due to mismatch of input impedance of patch antenna and deviation from optimum load required for maximum radiation at fundamental frequency. The power radiated at fundamental frequency is 15.7 dB lower than the power radiated at second harmonic. This design technique can be used for radiating useful high power much beyond the cutoff frequency of the transition of active device.
A narrowband low temperature co-fired ceramic (LTCC) bandpass filter (BPF) with five cascaded physical length-reduced resonators is proposed. Each resonator is built with cascaded horizontal and vertical microstrip lines to produce slow-wave effect, which reduces the physical length of resonators for miniaturization. The entire size of the proposed BPF is only 15 x 2 x 0.3 mm, and a size reduction of 60% is achieved compared with a traditional implementation. A narrowband fractional bandwidth (FBW) of 4% and an average passband insertion loss of only 2.4 dB are achieved. Comparison and discussion are implemented as well.
A new compact ultra-wideband (UWB) bandstop ﬁlter with good performance is proposed. The proposed UWB bandstop ﬁlter is composed of two pairs of quarter-wavelength resonators, a high impedance main transmission line, a half-wavelength resonator, and an H-shaped multiple-mode ring resonator. The proposed H-shaped multiple-mode ring resonator is introduced to achieve three transmission poles appearing in the lower and upper passbands thus to improve the characteristics of selectivity. The proposed quarter-wavelength resonators and half-wavelength resonator are used to obtain four transmission poles showing up in stopband thus to improve the in-band suppression characteristics. To validate the design concept, a new compact UWB bandstop ﬁlter with high selectivity and good suppression is designed and fabricated. UWB stopband, low insertion losses, and good selectivity are achieved as demonstrated in both simulation and experiment.
Lenses can be used to focus and disperse the electric field emitted by the antenna. Sustainable and environmentally friendly lenses were made from lithium molybdenum oxide (LMO) glass composite. Half spherical lenses with a diameter of a 30 mm were fabricated from LMO composite, and the antenna properties were measured with a waveguide feed. The lens enhanced radiation pattern was measured at Ku band, and the improvement in the gain was found to be 2 dB.