In this letter, a method to enhance the bandwidth of a double dipole quasi-Yagi antenna using a stepped slotline structure is presented. A stepped slotline with different widths is employed in the coplanar strip line connecting the two dipoles in order to improve impedance matching over a wide frequency band. In addition, two parasitic strip directors are appended to the antenna to enhance the gain in the high-frequency region. A detailed design procedure for the proposed antenna is explained, along with a performance comparison of the input impedance, voltage standing wave ratio (VSWR), and broadside gain. To demonstrate the effectiveness of the proposed design method, a prototype antenna operating in the 1.60-3.60 GHz frequency range with a gain > 6 dBi is designed and fabricated on an FR4 substrate. Experiment results show that the proposed antenna has the desired impedance characteristics with a frequency band of 1.59-3.64 GHz (78.4%) for a VSWR < 2, and a stable gain of 6.4-7.4 dBi in the 1.60-3.60 GHz frequency range. Moreover, a measured front-to-back ratio > 10 dB is obtained. Index Terms-bandwidthenhancement, stepped slotline structure, strip directors, double dipole quasi-Yagi antenna (DDQYA), mobile communications 1536-1225 (c)

A coupled‐sectorial‐loop antenna (CSLA) with circular sectors is presented for super wideband (SWB) applications. Conventional CSLA consists of two parallel sectorial loop antennas connected along an axis of symmetry and triangular sectors are used. The average input impedance of the conventional CSLA is over 100 Ω, and a half of the CSLA above a ground plane is used to match with a 50‐Ω feed line. In the proposed antenna, circular sectors are used instead of triangular sectors to directly match with the 50‐Ω feed line, and the full structure of the CSLA is used. A prototype of the proposed antenna is fabricated on an FR4 substrate, and its performance is compared to the conventional CSLA. The experimental results show that the frequency band for a voltage standing wave ratio < 2.15 is 1.0–19.4 GHz (180.4%), which satisfies the requirement of the SWB antenna. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1683–1689, 2014

A slot-loaded microstrip patch sensor antenna is proposed to enhance sensitivity in measuring the permittivity of planar materials. A thin rectangular slot was etched along the radiating edge of a rectangular patch antenna fed by a microstrip transmission line. Two resonant frequencies were created at a lower frequency compared to the single resonant frequency of a conventional ordinary patch antenna. The sensitivity of the proposed slot-loaded patch antenna was measured by the shift in the resonant frequency of the input reflection coefficient when the planar dielectric superstrate was placed above the patch, and was compared with that of a conventional patch antenna without the slot. The two antennas were designed and fabricated on a 0.76 mm-thick RF-35 substrate for the first resonant frequency to resonate at 2.5 GHz under unloaded conditions. Five different standard dielectric samples with dielectric constants ranging from 2.17 to 10.2 were tested for sensitivity comparison. The experiment results showed that the measured sensitivity of the proposed patch antenna were 3.54 to 4.53 times higher, compared to a conventional patch antenna, for the five samples.

A broadband series-fed two dipole array antenna is presented for mobile-base station applications covering the frequency bands for 2G, 3G, and long-term evolution systems. Two printed-strip dipole antennas with different lengths backed by a ground reflector are connected through a coplanar stripline, and an integrated balun consisting of a microstrip line and slot line is used to match the input impedance of the antenna to the 50 X feed line. Experimental results show that for a voltage standing wave ratio < 2, the proposed antenna presents a 49% bandwidth in the range of 1.7-2.8 GHz, a stable gain of 5.5-6.3 dBi, and a front-to-back ratio of 12-17 dB. Thus, the proposed antenna is suitable as a broadband base station element antenna, covering all mobile frequency bands.ABSTRACT: In this article, a novel wireless local area network (WLAN) frequency range monopole antenna is designed and manufactured for multi-input-multi-output (MIMO) applications. The proposed antenna consists of three pairs of folded L-shaped strips are placed side by side and printed on a dielectric substrate to generate triple-band operation which is suitable for WLAN applications. In this structure, each pair of L-shaped strips monopole antenna can create additional resonances within the WLAN range, which the desired resonant frequencies are obtained by adjusting the dimension of the folded L-shaped strips. The operating frequencies of the proposed antenna are 2.4/5.2/5.8 GHz which covers WLAN systems frequency range. Various configurations of array of this meander line structure monopole antenna for MIMO application are also studied. Prototypes of the proposed antenna have been constructed and studied experimentally. Good return loss and radiation pattern characteristics are obtained in the frequency band of interest. Simulated and measured results are presented to validate the usefulness of this proposed small antenna structure for MIMO applications.

This study proposes a high-sensitivity microwave sensor based on an interdigital-capacitor-shaped defected ground structure (IDCS-DGS) in a microstrip transmission line for the dielectric characterization of planar materials. The proposed IDCS-DGS was designed by modifying the straight ridge structure of an H-shaped aperture. The proposed sensor was compared with conventional sensors based on a double-ring complementary split ring resonator (CSRR), a single-ring CSRR, and a rotated single-ring CSRR. All the sensors were designed and fabricated on 0.76-mm-thick RF-35 substrate and operated at 1.5 GHz under unloaded conditions. Five different standard dielectric samples with dielectric constants ranging from 2.17 to 10.2 were tested for the sensitivity comparison. The sensitivity of the proposed sensor was measured by the shift in the resonant frequency of the transmission coefficient, and compared with conventional sensors. The experiment results show that the sensitivity of the proposed sensor was two times higher for a low permittivity of 2.17 and it was 1.42 times higher for a high permittivity of 10.2 when compared with the double-ring CSRR-based sensor.

A planar-printed E-shaped dual-wideband magneto-electric (ME) dipole antenna for WWAN/LTE applications is proposed. Through changing the surface-current distributions, an E-shaped electric-dipole structure is used to provide a dual-wideband. Besides, to reduce the size of the antenna and improve impedance matching, a novel feeding structure designed with inverted U-shaped tapered line and meandering L-shaped line is introduced. Finally, without conventional vertical ground planes, a small-size one is printed on the back side of the substrate to attain stable gains and omnidirectional radiation patterns. The antenna prototype can attain a bandwidth of 31.6% (0.80-1.10 GHz) with a stable gain of 3.1 6 0.5 dBi for the lower band, and a bandwidth of 47.5% (1.67-2.71 GHz) with a gain of 3.9 6 0.7 dBi for the upper band, covering the frequency bands for WWAN/LTE systems. In comparison with the existing ME dipole antennas, the proposed antenna can be easily fabricated at low cost which makes it suitable for WWAN/LTE applications.ABSTRACT: A simple design for solar powered frequency sensors is presented. The design is based on a rectenna composed of a frequency reconfigurable microstrip antenna, a rectifying circuit, and a low pass filter. The operating frequency of the antenna can be tuned in the range between 2 and 2.8 GHz, and, in this frequency range, the rectifier can effectively perform the conversion from RF to DC. By the measured results of the rectenna, the average conversion efficiency within the operating bandwidth of 33% is 73% over a resistive load of 1 kX at a power density of about 0.8 mW/cm 2 . A frequency sensor is successfully implemented by integrating the frequency reconfigurable rectenna with a preprogrammed microprocessor powered by solar cells.

This article presents a method for improving the gain and bandwidth of a microstrip‐fed broadband planar quasi‐Yagi (QY) antenna.To obtain a better and more stable gain with little variation over a broad frequency band, we used a planar QY antenna with strip‐type elements (a driver dipole and two directors) that had unequal widths and unequal spacing between them. First, to achieve a broad bandwidth of over 50%, a wide strip is used as a nearby director placed very close to the driver dipole. Then, to enhance and stabilize gain over a required frequency band, a narrow strip director and a ground reflector are appended to the driver with a nearby parasitic director. We systematically explain the effect of each element on the input impedance and the realized gain. To validate this proposed design, a QY antenna with a frequency band from 1.75 to 2.7 GHz and a gain of over 5 dBi was designed, then fabricated on an FR4 substrate, and tested. The results show that the fabricated antenna performs well, with a broad bandwidth of 60.4% (1.53–2.85 GHz), a stable gain between 5.38 and 6.41 dBi, and a front‐to‐back ratio of over 10 dB. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:406–409, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27325

In this letter, a miniaturized log-periodic dipole array (LPDA) antenna operating from 1 GHz to 6 GHz is proposed for portable direction finding applications. To reduce the lateral size of an LPDA antenna, bow-tie elements and a top-loading technique are utilized and spacing factor is decreased to reduce the spacing between the LPDA elements. The proposed miniaturized LPDA antenna has the measured gain and front-to-back ratio ranging from 1.2 dBi to 3 dBi and from 7 dB to 22 dB, respectively.