ABSTRACT. This paper describes a generalized multi-frequency impedance transformer capable of providing concurrent matching at arbitrary number of frequencies. A frequency dependent complex load (FDCL) has been considered but the scheme is applicable for real loads as well. The exact analysis of the proposed design results in closed form equations with many independent free variables to cater to the wide range of FDCLs. The proposed theory is validated through a prototype fabricated on Rogers RO5880, with permittivity of 2.2, and working at 0.9/1.8/2.1/2.9 GHz. The good agreement between measured and the EM simulated results validate the proposed technique.

ABSTRACT. In this work, two different types of tunable attenuators based on graphene are presented and a comparative analysis of their design and functionality is performed. A preliminary solution of the tunable attenuator has been recently proposed, based on a graphene patch deposited in the gap of a microstrip line: it results in wide band functionality from DC to 20 GHz, with a tunability of 7 dB and minimum insertion loss of 5 dB. A novel enhanced design is proposed, with two graphene patches located between the main microstrip line and two metal vias, located at the two sides of the microstrip line. This solution operates in a frequency band of DC to 5 GHz, with 14 dB tunability and minimum insertion loss of 0.3 dB.

ABSTRACT. A thermally stable L-band switch module containing two very low noise amplifiers, high gain, low insertion loss, and high isolation between the amplifiers input ports is proposed for radiometric medical applications. The modified second stage of a Dicke radiometer front end consists of two low noise amplifiers followed by an SPDT switch. Grounded coplanar waveguides are used as transmission lines between the inputs and output. Negative image modeling technique was employed to design the impedance matching networks of the two low noise amplifiers. At room temperature, the integrated two-LNAs-switch-module has a noise figure below 0.58dB, an input return loss of less than -10dB and 20.5±0.6dB gain between 1.1GHz to 1.6GHz. The switching circuit has an insertion loss below 0.6dB and the measured isolation between input RF ports is less than -60dB. The noise figure of the module was validated at different temperatures. The results show 0.12dB increase in the noise figure when temperature is increased from 25°C to 60°C.

ABSTRACT. The effect of inserting a magnetic layer beneath the semiconductor layer in a Metal-Insulator-Semiconductor (MIS) structure is studied. The proposed structure is called “Metal-Insulator-Semiconductor-Ferrite” (MISF). A closed form expression for the resonance frequency of the MISF structure is derived. This new resonance appears due to the insertion of the magnetic layer in addition to the already existing dielectric insulating material. That resonance will cause an increase in the slow wave factor at high frequencies which was never achieved in conventional MIS structures. The analytical results derived in this paper are in perfect agreement with full-wave simulations. Practical considerations of using the proposed structure are investigated, with special regards to wave attenuation and losses.

ABSTRACT. We introduce a new approach to measure spin waves on-chip and describe the design of an ultra-wideband Low-Noise Amplifier (LNA) implemented in a readout circuitry for characterization of the spin wave devices. The LNA shows a gain of 22.6 dB in the frequency range between 9.7 GHz and 43.3 GHz. The minimum Noise Figure (NF) is 5.3 dB at 22.75 GHz. Simulations were performed with 65nm CMOS technology node in Cadence Virtuoso. Estimated power consumption and chip area are 41.62 mW and 0.172 mm², respectively.

ABSTRACT. This paper presents a substrate integrated waveguide (SIW) Chebyshev bandpass filter using the low cost, commercially available printed circuit board (PCB) technology. The detailed design procedure beginning from the normalized Chebyshev lowpass filter, to the final optimized SIW bandpass filter is presented. The test filter having a 4% fractional bandwidth centered at 1.684 GHz was fabricated on a 1.27 mm thick, Rogers RT/Duroid 6010LM substrate with a 10.8 dielectric constant. The design has also been experimentally validated and results presented. The simulation and measurement responses of the filter show good agreement with a low insertion loss of 1.3 dB. The simulated and the measured return losses of about 15 dB and 16 dB respectively, were achieved across the filter passband.

ABSTRACT. This paper presents the first implementation of hybrid 9-9.8 GHz X-band class J power amplifier (PA) designed with a GaN HEMT power transistor. High efficiency power amplifiers suffer from nonlinear performance and relatively low bandwidth. The proposed high efficiency class J power amplifier provides larger bandwidth and more convenient linearity performance. The class J PAs should have appropriate matching networks at second harmonic of fundamental frequency which cannot easily realize for high frequency hybrid PAs. In the proposed Class J PA, second harmonic matching network was achieved by using low parasitic GaN HEMT power transistor and precise modeling of transmission lines and passive elements up to 20 GHz. The optimum dimensions of matching networks are determined by employing optimizing algorithm. This PA achieves 14 dB power gain over the frequency range of 8.8-9.6 GHz. Input and output return losses are less than -10 dB. Drain efficiency and power added efficiency are about 67% and 58% at 9.3 GHZ, respectively that is about 5% higher than class AB X-band power amplifier.

ABSTRACT. In this work, a simple microwave resonant sensor is proposed for detection of small amount of oil spill in sea water. The sensor is realized using the microstrip technology, and the geometry of the resonant structure is optimized in order to improve the sensitivity. The proposed sensor is designed to operate at 5.85 GHz in the industrial, scientific and medical (ISM) band. The structure of the sensor is modeled in full wave electromagnetic solver, CST Microwave Studio and the dimensions of the sensor are chosen to get the desired operating frequency. The designed sensor is finally fabricated, and is employed for detection of small amount of petroleum products present in the water. The measured results show that the proposed sensor is capable of detecting up to 5 % of petrol in water.

ABSTRACT. In this paper, the design and characterization of a GaN HEMT based class-AB power amplifier (PA) operating in LTE communication band (1.9 - 2.5 GHz) are presented. A model-based design procedure is adopted. Source and load impedances for optimum linearity, power and efficiency are extracted through source- and load-pull simulation. The implemented PA shows excellent performance on the whole frequency band from both the efficiency and linearity points of view. It provides a saturated output power of 36.9 dBm and a gain of 19 dB at the design frequency of 2.3 GHz, over a 600 MHz bandwidth. Measurements report a saturated power-added efficiency (PAE) of 68% and a PAE at 1dB compression of 54.3%. System level characterization with a 7MHz-bandwidth QAM-256 input signal is also carried out on the fabricated PA.

ABSTRACT. In this paper a practical approach for calibrating coax-to-microstrip transitions for narrowband applications, is presented. The method is an in-fixture measurement technique, which uses afterward de-embedding procedure to achieve the target S-parameter results. It is performed by extracting the equivalent circuit models of both measurement fixture-halves. Compared to the other in-fixture measurement approaches, the proposed method requires only the SOLT calibration procedure, which makes the measurement procedure much less complicated. Hence, by using this method, the complex calibration methods could be avoided to measure narrowband microwave circuits. Finally, the sub-circuits of a designed power amplifier are measured using the proposed approach successfully.

ABSTRACT. Tunable filters are reported using low coercivity ferromagnetic nanoparticles or ferroelectric thin films, which are attractive at RF frequencies due to their tunable capabilities using magnetic and electric control fields. This paper employs the soft ferromagnetic Fe60Co40 nanoparticles with relative permeability of larger than 8 and loss tangent smaller than 0.1 to realize tunable RF filters for IEEE802.11g frequency band applications. This nanoparticle material was employed in design of 3rd order annular ring at 2.4GHz that resulted in about 200MHz tuning, when 0.15T external magnetic flux is applied. A 5th order annular ring filter design was also employed for comparison. A similar approach is also extended to design and predicted performance of manganese-doped Ba0.8Sr0.2TiO3 (BST) soft ferroelectric thin films based filters, whereby a high relative permittivity of larger than 140 and loss tangent smaller than 0.02 is reported for the BST thin film. The simulated performance of the BST thin film resulted in 860MHz tuning using a 40V/um applied electric field intensity.

ABSTRACT. Envelope tracking power amplifiers represent an attractive alternative for future high efficiency base station amplifiers. This paper proposes a suitable design alternative customized to envelope tracking power amplifiers. This consists of performing a multi-dimensional load-pull and selecting the reflection coefficients to be presented to the transistor while taking into account the system level architecture of the power amplifier. It is shown that adopting the proposed load reflection coefficient selection algorithm leads to an additional efficiency enhancement of approximately 3% from 44.2% to 47.3%. This extra performance is achieved without additional circuitry or cost.

ABSTRACT. In this work, a new Broadband RF energy harvesting system is introduced, employing an Archimedean spiral antenna, a 6-stage voltage doubler, and a DC-DC converter. The proposed system operates over a frequency range from 0.9 GHz to 4 GHz. A balun is used to feed the antenna and is connected to the rectifying circuit via an SMA connector. The spiral antenna is fabricated using Conductive shieldit super and Felt for the substrate. Also, other textile materials were used such as: Stainless steel threads for the conductive layer and Fleece for the substrate. The measured rectified DC voltage had a peak of 1.5V when testing outdoors, and was 0.5 V when testing indoors. The overall system efficiency was approximately 30%.

ABSTRACT. An annular ring based metamaterial absorber for S- and C- microwave bands is presented in this paper. The proposed structure is resonating at two frequencies of 3.06 GHz and 7.65 GHz with 99.40 % and 98.83 % absorptivities, respectively. The unit cell of the proposed absorber fits in a small volume of 12 mm x 12 mm x 1.6 mm. The proposed structure is polarization insensitive and performs well up to an incidence angle of 600 for TE and TM polarized wave. To get an insight into the dependence of absorption response on shape parameters, parametric variation of some key parameters is presented. The absorption phenomenon of the proposed absorber is investigated by dielectric and ohmic power loss density plots on the structure.

ABSTRACT. Notch characteristic is implemented in a wideband four-arm sinuous antenna with a nominal gain of 4.5 dBi over an operational bandwidth of 2-7 GHz. The notch band is introduced at 4.9 GHz with a fractional bandwidth of % 2 at 4.9 GHz, the center frequency of notched band. The sinuous antenna is backed with a metallic cavity having a low profile of 30 mm. The antenna is working with two orthogonal linear polarizations and fed with two linearly tapered microstrip Baluns. The Baluns are placed horizontally parallel to the radiating elements for size utilization.

ABSTRACT. This paper presents, a compact frequency selective surface (FSS) having band-stop characteristics. This FSS achieves at least 35 dB attenuation to provide effective shielding in X-band. The proposed FSS is realized on low profile FR-4 laminate having compact unit-cell dimension 5mm x 5mm. Most importantly, this FSS has polarization independent behavior at normal and oblique angles of incidences for both TE and TM wave modes.

ABSTRACT. This paper presents an insight on the recently developed antenna pattern measurement system at COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan. Microwave Components and Devices (MCAD) research group at CIIT has been involved in antenna focused research activities but unavailability of anechoic chamber to measure radiation patterns has remained a huge handicap. In this regard efforts have been made to indigenously develop a radiation pattern measurement system. The system can measure radiation patterns from 600 MHz up to 26 GHz. The reflections from surroundings are suppressed by filtering the delayed signals in time domain. The system is automated through a Labview program which also provides users with the control and flexibility on various parameters. The system can provide gain at four frequency points simultaneously along with phase information.

ABSTRACT. This letter proposed a 150 MHz C-shaped meander line inverted-L antenna, which can be embedded in land mines. First, a radiation element of monopole antenna has been transformed to an inverted-L form by turning it to be parallel with the ground. Then, it was designed to a size allowing insertion in a land mine by designing the radiating element being parallel with the ground into C-form by using a meander line. Thus-produced antenna return loss has -12.66 dB at the center frequency of 150 MHz, bandwidth of 2.6 MHz (1.73%), and the radiation pattern has a conical form of -15.4 dBi in maximum gain.

ABSTRACT. This paper addresses the millimetre-wave antenna design aspect of the future 5G wireless systems. The paper reviews the objectives and requirements of the millimetre- wave antennas for 5G. Recent advances in mm-wave antenna design are reviewed and design guidelines are discussed.

ABSTRACT. In this article, a frequency reconfigurable fractal patch antenna using pin diodes is proposed and studied. The antenna structure has been designed on FR-4 low-cost substrate material of relative permittivity ԑr = 4.4, with a compact volume of 30×30×0.8 mm3. The bandwidth and resonance frequency of the antenna design will be increased when we exploit the fractal iteration on the patch antenna. This antenna covers some service bands such as: WiMAX, m-WiMAX, WLAN, C-band and X band applications. The simulation of the proposed antenna is carried out using CST microwave studio. The radiation pattern and S parameter are further presented and discussed.

ABSTRACT. Dielectric Resonators are being used as antennas in wireless communication systems presently due to advantages over microstrip like low loss particularly at higher frequencies. Also with ever increasing demand for bandwidth, wide banding has become one of the prime goals of antenna design. DRA wide banding can be done using stacking. Some literature are already available for stacked DRA with simulated results but theoretical analysis of the same is not presented therein. This paper deals with the theoretical analysis of stacked DRA for the first time.

ABSTRACT. The radiation performances of circular, bee-hived and rectangular array configurations are compared. The number of elements and their spacing’s are assumed identical in all the three structures. The excitation of the array elements are determined by the invasive weed optimization algorithm to obtain the desired side lobe levels. Results show that unlike the rectangular array, the bee-hived and circular arrays have omnidirectional patterns in the horizontal plane. Furthermore, a comparison between the circular and bee-hived arrays shows that the bee-hived array has lower side lobe level, while the circular array gives more receptivity.

ABSTRACT. This paper discusses the use of a one arm Archimedean Sinusoidal Spiral Antenna (ASSA) to capture high frequency signals generated by Partial Discharge (PD) in an oil filled transformer. The antenna is designed such that it blocks low frequencies which corresponds to corona and noise in the transformer and allows higher frequencies which result from harmful PD activities. The captured PD signals will be further processed and classified according to the PD type. A simulation using HFSS® is compared with the real data obtained using a Network Analyzer. Results show that the ASSA performs well in the frequency range between 1GHz and 5GHz. Data processing includes labeling, extracting, and finally classifying was performed on the collected PD signals in both online and offline modes to determine the type of the detected PD.

ABSTRACT. A CPW bowtie aperture antenna loaded with metal strips is presented to operate at tri-band frequencies: 8.45, 9.5 and 10.8 GHz. The new frequencies are achieved without increasing the size of the original unloaded antenna. The new antenna is loaded with 16 rectangular strips of different sizes to operate at tri-band frequencies. The antenna is symmetrical to CPW feed. The simulated results using HFSS are obtained for reflection coefficients, radiation patterns and impedances for loaded and unloaded antennas. The results show that new lower operating frequencies can be achieved without increasing antenna size.

ABSTRACT. Multi-turn, multi-stranded, dual layer microfabricated planar spiral coils with interlayer offset are proposed for improved wireless power transfer efficiency and miniaturization of biomedical implants. Multi-stranding coupled with an interlayer offset, enables implanted coils to operate at higher frequencies due to quality factor improvements. This ultimately leads to miniaturization of overall implant size. Simulation results show a quality factor improvement of 72% at 13.56 MHz in a tissue equivalent phantom.

ABSTRACT. A coplanar waveguide (CPW) - fed compact cupcake shaped printed antenna is proposed for UWB applications. Cupcake structure is formed by capping an ellipse (eccentricity = 0.95) over a semicircle (radius = 12mm). The bandwidth is enhanced by loading an ellipse over the semicircular patch and using CPW ground plane. The antenna parameters are simulated and optimized using Ansoft HFSS electromagnetic simulator. The proposed design fabricated by LPKF (S103) prototyping machine on 27 mm × 28 mm FR4 substrate (εr = 4.4, thickness = 1.5 mm) exhibits a large impedance bandwidth (-10dB) from 2.8 GHz to 12.5 GHz. The developed antenna feature ultra-wideband (UWB) behavior with almost omnidirectional and stable radiation patterns over the entire bandwidth with an average peak gain of 4.5dBi. The simulation and experimental results are found to be in good agreement.

ABSTRACT. Radiation characteristics of an axially slotted elliptic antenna coated by conventional dielectric or metamaterial material embedded partially in a ground plane are investigated analytically. The field in each region is expressed in terms of appropriate radial and angular Mathieu functions with unknown field coefficients. The boundary conditions at the conducting, dielectric coating and ground plane surfaces are enforced to obtain the unknown field expansion coefficients numerically. Results are plotted for the radiation pattern to show the effect of the presence of the ground plane and different coatings

ABSTRACT. A tunable liquid antenna is designed and analyzed. The ability of adjustment is realized with the help of a thin post penetrating the solid dielectric and the liquid layers. The influence of the thickness and parameters of the substrate is investigated. The performance of different liquid materials including sea water, oil and distilled water is analyzed. The influence of the distribution of the liquid, the length of the probe, the feeding positions and other relevant factors are studied. The simulation results reveal that changing the distribution of the liquid as well as other relevant parameters can effectively bring forth the performance alternation, which indicates the validity and flexibility of the antenna.

ABSTRACT. This paper presents the design, implementation and inter-port isolation performance evaluation of three dual port, dual polarized 2.4GHz Microstrip patch antennas. Input matching and inter-port isolation (both DC and RF) performance of implemented antennas has been compared by measuring the input return losses (S11,S22) and inter-port isolation (S12) respectively at 2.4GHz. Two implemented single layer antennas provide around 40dB RF inter-port isolation while the multi-layer antenna has 60dB isolation between transmit and receive ports at center frequency with DC isolated ports. The multi-layer antenna provides more than 55dB inter-port isolation for antenna`s 10 dB input impedance bandwidth of 50MHz.

ABSTRACT. In this paper, a wideband microstrip line transition to groove gap waveguide (GGW) is proposed. The designed structure is composed of two parts: a 50-Ohm microstrip line feeding a planar probe and a GGW structure. The transition structure is optimized to work in the V-band from 50 to 70 GHz.

ABSTRACT. When proximity coupling via a coaxial feed probe is employed to excite a planar array antenna, the efficiency of such excitation could be compromised and the consequences could be severe for large arrays. Center-excitation by a single coaxial probe to a planar array could be an inferior excitation mechanism for a large array. We therefore investigate the efficacy of a 2 × 2 excitation source via a four-coaxial feed probe network. We examine the strength of excitation energy of each source and investigate the radiation map based on each source to determine the radiation boundary per source. We then determine the percentage of excitation distribution per source that is scattered using the scattering parameter.