Despite its popularity, the conventional Vivaldi antenna has long suffered from some design problems, such as tilted beam, low or inconsistent directivity and gain, complicated design and fabrication methods, and limited size reduction. These setbacks make its progress lag on the fast track of technological demand. Thus, the antenna overall performance is anticipated to improve by incorporating negative index metamaterial (NIM) into the design method, plus, it is also tunable. In this study, the design uses linearly-tapered shape-loading structure, as its projected performance crucially depends on the space in between the antenna arms, a prerequisite to further boost its performance when combined with NIM technology. A unique slitting approach synchronizes the integration between the Vivaldi antenna and NIM where a single layer NIM piece is simply snugged into the slit perpendicular to the middle antenna substrate. The major improvement in the spotlight is the capability of NIM to focus the entire beam so that it can radiate to the targeted direction. The measurement results are similar to the simulations in terms of high gain, where the gain and directivity of the antenna are increased up to 4 dB. The contrast of overall performance between the plain modified Vivaldi antenna and the ones with NIM evidently asserts the expected contribution of snug and boost method applied and attests its significant potentials for a broad range of ultra-wideband applications.
The design, fabrication, and characterization of an amulti-section impedance transformer using Klopfenstein tapering method is presented. The transformer is employed in a Ka-band traveling-wave tube (TWT)for radar applications. The Klopfenstein tapering provides the shortest length between the two different impedance levels with continuous tapering sections.
A compact reconfigurable antenna integrated with stepped impedance stub (SIS) loaded stepped impedance resonator (SIR) and SIS loaded hexagon stepped impedance resonator (HSIR) for ultra wideband (UWB) applications is proposed in this paper. The reconfigurable UWB antenna can work as a UWB antenna and a dual notch band UWB antenna by controlling the switches ON and OFF. The proposed two notch bands are obtained by embedding a SIS-HSIR on hexagon radiation patch and a SIS-SIR on coplanar waveguide (CPW) excitation line. The reconfigurable characteristic is achieved by means of two ideal switches. The proposed reconfigurable antenna has been designed, fabricated and measured. The experimental results show that the proposed reconfigurable antenna has a multi-mode function and good omni-directional characteristics.
This paper presents a conical monopole antenna with two C-shaped slots to provide a frequency stopband to suppress interference. Compared to previous work reported in the literature, the antenna provides increased gain suppression to vertically polarised signals within the notch-band of up to 41.5 dB in four specific directions. It also yields omni-directional radiation patterns at frequencies throughout the operating band, outside the rejection band. The four null directions in vertically polarised plane at the notched band frequency are explained by an analysis of simplified equivalent current sources. The effect of different length of slots has been investigated. Two methods to control the stop band directions are also discussed.
A novel 180° hybrid is proposed, based on a modified Gysel power combiner, using phase shifter and ground bridge for the difference output. Also the Defected Microstrip Structure has been used to increase the hybrid's phase matching. All steps of the design are simulated using HFSS 11 and the final design is validated by the fabrication. It has good results between 7 GHz to 10 GHz and can be used between 6 GHz to 11 GHz with less accuracy.
A broadband monolithic image rejection subharmonic mixer using a standard 0.18 μm CMOS technology is proposed. This circuit is composed of a band-pass filter with an intermediate frequency (IF) extraction function that can simplify the block diagram of the image rejection mixer. The entire passive circuit is constructed using a broadside coupling structure to achieve a high level of integration. Based on measured results, the proposed mixer exhibits conversion loss of 15.5-18.5 dB at a local oscillator (LO) power of 13 dBm, whereas the 3 dB bandwidth ranges from 20 to 31 GHz (43.1%) with a miniature chip dimension of 0.77×0.81 mm2. The LO-to-radio frequency (RF), 2LO-to-RF, and RF-to-IF isolation levels are higher than 22.5, 42.9, and 34.5 dB, respectively. The best image rejection ratio of 29 dBc with 20° phase compensation at 24.5 GHz can be achieved.
This paper presents a two-port antenna including a receiving port and a transmitting one in the same volume. These two antennas are physically integrated and electrically isolated. The receiving antenna is a linearly polarized narrowband slot for energy harvesting, whereas the transmitting one is a circularly-polarized ultrawideband (UWB) quasi-spiral for signal radiation. The measurement results show that, the slot resonates at 5.8 GHz, and the quasi-spiral has a 10-dB return loss bandwidth of 2.85-5.16 GHz and a 3-dB axial ratio bandwidth of 3.05-4.43 GHz. The electrical isolation between these two antennas is more than 20 dB covering 1-8 GHz. This two-port antenna is a good candidate for wireless-powered UWB-RFID tags.
In this article, a low cost, simple, and compact printed microstripfed U-shape monopole ultra-wideband antenna with dual band-notched characteristics is proposed and investigated. By introducing a spiral shaped λ/4 open stub in the microstrip feed line and a pair of L-shaped slots on the rectangular ground patch, dual band notched characteristics can be obtained respectively. The proposed antenna is successfully simulated, designed, fabricated and measured. The measured results show that the proposed antenna with dimensions of 24 mm (Wsub) × 34 mm (Lsub) × 1.6 mm (H) has a large bandwidth over the frequency band from 2.75 GHz to 10.6 GHz with VSWR less than 2, except 3.27-4.26 GHz and 5.01-5.99 GHz frequency bands. The proposed antenna exhibits nearly omnidirectional radiation pattern, stable gain, and small group delay variation over the desired frequency bands.
In this paper, a new look at the electromagnetic field in a reverberating chamber (RC) is presented. It follows the fractional Brownian motion (fBm) model and exploits the Hurst parameter as the key parameter to discriminate among various RC configurations. Experiments accomplished at the RC of the Università di Napoli Parthenope, formerly Istituto Universitario Navale (IUN), confirm the physical soundness of the proposed model.
Microstrip patch antenna has been designed and developed for Unmanned Aerial Vehicle based Synthetic Aperture Radar (UAVSAR). This antenna operates in C-Band at the frequency of 5.3 GHz with a bandwidth of 80\,MHz. The radiation patterns of the antenna were specified to provide a desired scanned area for UAVSAR. The UAVSAR antenna was designed in the form of combination of 3 subpanels to allow dual operating mode (single antenna or dual antenna) selection. Two feed points are provided to the feeding network of each subpanel to reduce undesired power loss. The developed antenna prototype meets the performance requirements of UAVSAR system. It shows promising results in the UAVSAR flight mission conducted in Mersing area, Malaysia for both operating modes.
A design of multilayer dielectric resonator antenna transmitarray for fixed radio frequency identification (RFID) reader applications is presented at 5.8 GHz. Three layers square dielectric resonator antenna (DRA) elements are mounted on dielectric substrate and used as a unit cell in the transmitarray. A circularly polarized 9 × 9 square DRA transmitarray is designed at 5.8 GHz for far-field RFID applications. The transmitarray produces maximum gain of 20.2 dB. The right-hand circular polarization level is lower than -31 dB at the designed frequency with SLL of -22 dB. A design of 9 × 9 near-field focused DRA transmitarray for fixed RFID at 5.8 GHz is investigated. The properties of the near field-focused transmitarray are compared with that of the far field transmitarray designed at the same operating frequency.
A new approach to obtain frequency and pattern reconfiguration in Dielectric Resonator Antenna (DRA) has been proposed. The design consists of two identical aperture coupled DRAs separated by a distance of λ0. A switchable feed based frequency reconfiguration is discussed in which the feed acts as an ideal switch. This design operates at two frequencies viz., 3.6 GHz and 5.2 GHz. These frequencies are independently tuned using trimmers. Further, the slot length of both the DRAs can be tuned independently using movable shorting pins driven by miniature motors. The shorting pins form a part of the ground plane. By varying the slot length of the DRA, the resonant frequency is controlled which in turn helps in gaining pattern reconfiguration. The structure has been designed for lower and middle band frequencies of WLAN, operating between 5.15-5.25 GHz and 5.25-5.35 GHz, respectively. These types of antennas can be employed in MIMO systems for increasing the capacity through Pattern diversity.
The direct position determination (DPD) method can improve the location accuracy compared with the traditional two-step location methods due to omitting the intermediate procedure of estimating the measurement parameters. However, the DPD methods presented so far are significantly more complex than the two-step approach. To overcome the shortcomings of the published DPD algorithms, a novel multi-target direct localization approach is firstly proposed by exploiting the jointly sparse property in the discrete spatial domain. The main idea of this paper is that the location estimation can be obtained by finding the sparsest solution according to the predefined overcomplete basis. Furthermore, the locations of targets can be obtained from noisy signals, even if the number of targets is not known a priori. Experimental results demonstrate that the proposed algorithm has superior positioning accuracy to other DPD methods and improves computational efficiency greatly.
This paper presents a complementary metal-oxide-semiconductor (CMOS) differential voltage-controlled oscillator (VCO) implemented with the push-push principle. The push-push VCO uses two frequency doublers stacked in series with an LC quadrature voltage-controlled oscillator (QVCO) to share the dc current with the QVCO for low power consumption. The proposed CMOS VCO has been implemented with the TSMC 0.18 μm CMOS technology, and the die area is 0.822×1.564 mm2. At the supply voltage of 0.9 V, the total power consumption is 3.15 mW. The free-running frequency of VCO is tunable from 10 GHz to 11.15 GHz as the tuning voltage is varied from 0.0 V to 1.2 V. The measured phase noise at 1 MHz frequency offset is -114.93 dBc/Hz at the oscillation frequency of 9.99 GHz, and the figure of merit (FOM) of the proposed VCO is -190.0 dBc/Hz.
This paper proposes parallel-coupled stepped impedance resonators (SIRs) used for wideband bandpass filters with reduced size and improved spurious response suppression in out-of-band. The filter design concept is demonstrated by both two- and four-parallel coupled line resonator structures with the same fundamental frequency (f0) of 6.5 GHz. The first bandpass filter has been designed using two resonators with λg/4 slot and embedded slot feeds for spurious response suppression at 2f0 and 3f0, respectively. The measured insertion loss is around 0.3 dB and the operation band is from 4.4 to 9.2 GHz (FBW = 73.8%). For the second bandpass filter, the embedded slot feeds and additional loaded open-stubs have been utilized to improve the wide spurious response suppression and sharp skirt characteristic in the passband. The measured passband of frequency response is from 4.2 to 8.6 GHz (FBW = 67.7%). The insertion loss of passband is lesser than 0.25 dB and the return loss is better than 15 dB. The filter designs are described in details. The simulated and experimental results are demonstrated and discussed.
This study is designed mainly for dual band antennas of GSM/WiMAX operation in a wireless mobile communication device. This study proposes a matching technology for single path resonance in a basic monopole antenna running in dual-mode  and extends to a wide tuning range. The tuning of each frequency band is complicated under the constraint of the common path of dual-mode due to mutual interaction. This study proposes a refined process and new type of antennas for excellent dual-frequency matching. The incorporation of such a matching mechanism into a tuning monopole antenna enables the flexible operation bands. Moreover, the ground plane size can be shrunk to a reasonable size, and the details will be discussed in Section~6. As a result, antennas can achieve a tuning ratio of 1.6 (from 1825 to 2943 MHz). The total area of such a compact antenna including its ground can be effectively reduced to 0.018λ02.
A printed discone antenna with dual-band notched characteristics is presented for ultra-wideband applications. The proposed antenna consists of a radiation patch which has an outline expressed by binomial function and a trapeziform ground plane. Dual band-stop performance is achieved by etching a pair of Z-shaped slots on the ground plane and protruding a pair of π-shaped strips in the elliptical slot cut in the radiation patch, respectively, which can reject potential interference with the 3.25-3.8 GHz and 5-6 GHz bands. Surface current distributions and input impedance of the antenna are given to analyze the effects of the two resonant structures. The characteristics of the notched bands can be controlled independently by tuning related parameters. Moreover, the performances of the antenna are validated along with simulated and measured results.
This article reports on the design of a wideband compact microstrip-fed tapered slot antenna aimed at microwave imaging of a brain stroke. The antenna is immersed in a carefully designed coupling liquid that is used to facilitate higher signal penetration in the brain and thus increased dynamic range of the imaging system. A parametric analysis is used to find out the required properties of the coupling liquid. A suitable mixture of materials is then used to implement those properties. In order to protect the antenna from the adverse effects of the coupling medium, dielectric sheets are used to cover the radiator and the ground plane. To verify the proposed design in brain imaging, the antenna is tested using a suitable head model. It is shown that the antenna with a compact size (24 mm × 24 mm) on RT6010 substrate (dielectric constant = 10.2) operates efficiently over the band from 1 GHz to more than 4 GHz with more than 10 dB return loss. The time domain performance of the antenna supports its capability to transmit a distortion-less pulse with a high fidelity factor inside the head tissues.
Small size capacitor loaded ground plane slots are used to reduce the mutual coupling between elements in a microstrip antenna array design. The proposed compact slots are inserted between the adjacent E-plane coupled elements in the array to limit the propagation of surface waves between the elements of the array. In order to validate the feasibility of the proposed structure, a two-element array with 0.5λo distance between centers of two patches is designed, fabricated, and measured. The measured results show a reduction in mutual coupling of 17 dB obtained between elements at the operation frequency of the array.
Compact K-Band CMOS baluns are designed, fabricated and characterized in a 130 nm CMOS technology. These baluns include a tunable active balun, a L-C lumped element balun, and two asymmetric planar transformer baluns. The detailed design processes are presented, including the topology selection, the transistor, inductor and transformer sizing, and the layout considerations. These topologies are compared in various aspects such as insertion loss, phase and amplitude imbalance, bandwidth, chip area, power consumption, and the difficulty to design and integration. An impedance tuning approach is implemented to chose the proper balun topology and to simply the balun integration. The baluns are on-wafer characterized and the measurement results compare the state-of-the-art realizations..