Vol. 16

A novel, short-circuited, flat-plate dipole antenna for WLAN operation in the 2.4 GHz band is presented. The dipole antenna is narrow (5 mm in width) and structured to be of an L shape to fit in corners of possible wireless communications devices. The open ends of the two dipole arms are folded and face each other, so as to achieve a compact structure, and short-circuited via a short-circuiting strip, making it possible for the antenna to be cost-effectively fabricated by stamping one single metal plate only. The antenna when unbent into a flat, rectangular structure has dimensions 5 mm×47 mm and can be is easily fed by using a 50-Ω mini-coaxial cable. Details of a design prototype are described and discussed.

A novel wideband rectangular dielectric resonator antenna (DRA) is proposed in this paper. A hybrid structure with an isolated dielectric resonator (DR) and an equivalent air-dielectric DR is introduced by lifting the resonator from the ground plane. The hybrid structure is excited by a slot-fed mechanism to obtain a smooth transition between each resonant mode. The resonant modes of the isolated DR and the equivalent DR are merged together to form a wideband impedance bandwidth. It is found that the bandwidth of the proposed antenna can be greatly enhanced by using the hybrid DRA structure instead of the case mounted on the ground plane. A detailed parametric study is carried out to analyze the characteristics of the proposed antenna. Measured results show that the proposed DRA has a 10 dB impedance bandwidth of 61% from 2.4 GHz to 4.5 GHz and the radiation pattern is stable through the operating frequency.

This paper presents the design and results of a compact Ultra-wideband (UWB) monopole antenna with a dual band-notched characteristic. The antenna consists of a semi-elliptical radiator with two meandered slots on it to produce a deep notch at 3.5 GHz (the center of WiMax band) and another notch at 5.25 GHz (the center of the lower WLAN band). The antenna is fabricated and measured, and the measured impedance bandwidth defined by VSWR<2 is 8.5 GHz (2.5--11 GHz), with the dual notched bands of 3.3--3.7 GHz and 5.12--5.37 GHz are obtained. The computer simulation results of the radiation pattern and peak gain of the antenna also agree well with measurements.

A 54-66 GHz sub-harmonic monolithic passive mixer using the standard 0.15 μm pHEMT process is demonstrated. The proposed mixer is composed of a hairpin diplexer, an open stub, and a low-pass filter. The mixer also utilizes a pair of anti-parallel diodes to achieve a subharmonic mixing mechanism. The hairpin diplexer formed with two parallel-coupled line band-pass filters is used to improve the isolation between the radio frequency (RF) and local oscillation (LO) ports. The low-pass filter supports an intermediate frequency (IF) ranging from dc to 1 GHz. This proposed configuration leads to a die size of less than 1.5 mm². With a conversion loss of 15.2--18.3 dB, the 2LO-to-RF isolation is found to be better than 27.5 dB. A high LO-to-RF isolation of 23.5--45 dB over 54--66 GHz RF bandwidth, as well as 1 dB compression power of 8 dBm, can be achieved.

The paper presents integrated probe for direct coupling to the WR-10 waveguide with the use of metal filled vias on both sides of the microstrip line. Design and optimization of this novel microstrip-to-waveguide transition has been performed using 3-D finite element method based software HFSS (High Frequency Structure Simulator). A back-to-back transition has been fabricated and measured between 75--110 GHz. The measured return loss is higher than 10 dB and the insertion loss for a single microstrip-to-waveguide transition is about 1.15 dB.

A wide open slot antenna with a pair of symmetrical L-strips for dual-band WLAN applications is proposed in this paper. A T-shaped monopole is used to cover 5.15~5.825 GHz. To achieve dual-band characteristic, a pair of symmetrical L-strips is embedded in the wide open U-slot to generate another band covering 2.4~2.48 GHz. The two bands are relatively independent from each other. The proposed antenna has the advantages of simple structure and excellent performance on the WLAN 2.4/5.2/5.8 GHz bands. The measured results of the fabricated antenna show that the impedance bandwidths are 150 MHz from 2.37 to 2.52 GHz and 1270 MHz from 4.83 to 6.10 GHz, which cover all the desired operating bands. Furthermore, the antenna design and some significant parametric studies are also described in detail.

A novel compact fork-shaped ultrawideband (UWB) antenna with triple band-notched characteristics is proposed. By embedding a spade-shaped slot on the radiating patch as well as adding a separated strip and a C-shaped resonating structure on the front side of the reference UWB antenna, the triple notched frequency bands are realized. The measured impedance bandwidth defined by VSWR<2 of 7.8 GHz (3--10.8 GHz), with the triple notched bands of 3.3--3.7 GHz, 5.15--5.4 GHz, and 5.7--5.9 GHz, are obtained. The proposed antenna with an overall dimension of only 24×30 mm² is successfully simulated, designed and measured, showing broadband matched impedance and stable radiation patterns.

A novel Yagi-Uda antenna with dual-band (915-935MHz and 1760-1805MHz) is presented. Branch structures are used to realize dual-band performance. The geometrical parameters for the branch structures are optimized to explore the antenna to operate satisfactorily in the two bands. Prototype is manufactured and measured, and the results are in good agreement with the simulated ones. In the two operating bands, the proposed antenna achieves directional radiation and the performances that VSWR<2, gain 5-6.6 dBi and front-to-back ratio 6-9.1dB, making it suitable for the non-fixed base station backhaul in wireless communications.

In this article，a printed ultra-wideband (UWB) monopole antenna with dual band-notched characteristics of size 26 mm×35 mm is presented. The prototype consists of pincers-shaped radiation element and corner rounded ground plane. By inserting a pair of flexuous slots on the radiation element and a C-shaped slot on the ground plane, the 3.5/5.5 GHz dual band-notched characteristics are achieved, respectively. Moreover, good radiation patterns and gains within the operating band have been obtained. The detailed design and experimental results are discussed in this article.

A compact balanced frequency MMIC doubler using compensated capacitive line in Marchand balun is proposed. With multi-coupled lines technology, the balun is applied to a balanced doubler successfully. Compared with the conventional Marchand balun, more than 55% reduction in the length of coupled line can be achieved. Implemented by a PHEMT process, the compact monolithic balanced frequency doubler with better performance can be obtained. An operation bandwidth from 20 to 44 GHz with the best conversion loss of 8.4 dB at 25GHz can be achieved. In addition, the fundamental frequency suppression is better than 28.9 dB, and the chip dimension is as small as 0.41 × 0.68 mm².

A compact microstrip-line-fed antenna designed by inserting two pairs of strips into a rectangular slot for achieving triple-band operation is proposed. The antenna, which occupies a small size of only 40×32×1.6 mm³, utilizes inserted strips to generate dual band-notched characteristics so that three operating bands are able to be achieved, which range from 2.2 to 2.7, 3.07 to 3.86, and 5.13 to 6.23 GHz, sufficiently covering both the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX bands. In addition, the measured results show good monopole-like radiation patterns and stable antenna gains across the three operating bands.

A novel type of wideband SICC filter using TM₀₁ mode coupling by the circular hole between the SICCs is proposed. Of circular symmetry, the TM₀₁ mode in SICC demonstrates the advantages of compact and high flexibility of the filter's input and output setting. In order to validate the new proposed topology, three filter prototypes with different included angle between input and output have been designed and manufactured. The filters exhibit a low insertion loss of -1 dB in the 12.8 to 20 GHz, a wide relative bandwidth of 54.5% at -3 dB, high flexibility and very good agreement with simulation data.

We investigated the properties of pulse propagation on coupled nonlinear transmission lines to develop a method for doubling repetition rate of incident pulse streams. Coupled nonlinear transmission lines are two transmission lines with regularly spaced Schottky varactors coupled with each other. It is found that both of the modes developed in a coupled line can support soliton-like pulses because of Schottky varactors. We discuss the fundamental properties of each soliton-like pulse, including the width and velocity, and propose a method of doubling repetition rate of incident pulse streams by managing these soliton-like pulses.

A novel tri-band printed monopole antenna with an etched ∩-shaped slot and a parasitic ring resonator is proposed for satisfying wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications simultaneously. The proposed antenna comprises a rectangular radiation patch with an arc-shaped edge and an embedded ∩-shaped slot on the top side and a parasitic ring resonator on the opposite side. The measured results show that the impedance bandwidths of the proposed antenna, defined by voltage standing wave ratio (VSWR)≤1.5, are 350 MHz (2370--2720 MHz), 680 MHz (3390--4070 MHz) and 1080 MHz (4920--6000 MHz), which cover the required band- widths for both WLAN (2400--2480 MHz, 5150--5350 MHz, and 5725--5825 MHz) and WiMAX (2500--2690 MHz, 3400--3690 MHz, 5250--5850 MHz) applications. Furthermore, good monopole-like radiation characteristics with moderate peak gains are obtained over the operating bands.

Applying a sparse constraint on the beam pattern has been suggested to suppress the sidelobe level of a minimum variance distortionless response (MVDR) beamformer. In this letter, we introduce a weighted sparse constraint in the beamformer design to provide a lower sidelobe level and deeper nulls for interference avoidance, as compared with a conventional MVDR beamformer. The proposed beamformer also shows improved robustness against the mismatch between the steering angle and the direction of arrival (DOA) of the desired signal, caused by imperfect estimation of DOA.

This paper presents a novel coplanar waveguide (CPW) dual passband filter using the split-modes of the loaded stub square loop resonators. With the CPW feeding line, two microstrip stub resonators built on the rear sides are used to suppress the first even resonance. The modes splitting characteristics of the proposed structure are analyzed. A dual passband filter covering center frequencies of 4.8 GHz and 6 GHz is fabricated to verify the validity of the methodology. Good agreement between simulated and measured results is demonstrated.

A racket-shaped slot ultra-wideband (UWB) antenna coupled with parasitic strips for band-notched application is proposed in this paper. By attaching a pair of parasitic rectangular strips on the bottom of the substrate, a band-notched characteristic is well realized. Adjusting the length, width of the two strips and the distance between them, a band-rejected filter characteristic at the WLAN operation in 5.15-5.825 GHz frequency band can be obtained. The fabricated antenna has a small size of 20×37.5 mm². Good agreement is achieved between the simulated and measured results, both of which show an ultra-wide impedance bandwidth from 3.1 to 10.6 GHz for VSWR less than 2 except the bandwidths of 5.15-5.825 GHz for WLAN.

A 40 A triode type magnetron injection gun for a 1 MW, 120 GHz gyrotron has been designed. The preliminary design has been obtained by using some trade-off equations. Computer simulation has been performed by using the commercially available code EGUN and the in-house developed code MIGANS. The operating voltages of the modulating anode and the accelerating anode are 60 kV and 80 kV, respectively. The operating mode of the gyrotron is TE_22,6 and it is operated in the fundamental harmonic. The electron beam with a low transverse velocity spread (δβ_⊥max = 3.3%) and velocity ratio, α = 1.38 at beam current = 40 A is obtained. The simulated results of the MIG obtained with the EGUN code have been validated with another trajectory code TRAK. The results obtained from both the codes are in good agreement. The sensitivity study has been carried out by changing the different gun parameters to decide the fabrication tolerance.

A compact tri-band planar monopole antenna suitable for 2.4/5.2/5.8 GHz WLAN and 3.5 GHz WiMAX is presented. The antenna employs a U-shaped parasitic strip and a defect ground-plane structure. By inserting a U-shaped strip as a parasitic strip into a normal monopole which operates at lower band of the WLAN, one more resonance at the higher WLAN band comes out. A defect ground-plane composed of two symmetrical L-shaped slits leads to another resonance operating at WiMAX band. The proposed antenna has a compact size of 22×41×0.8 mm³ and offers good radiation and reflection characteristics in the above frequency bands. The measured VSWR exhibits a good agreement with the simulated one. Detailed design steps, parametric studies and experimental results for the antenna are investigated in this paper.

In this paper, a circular slot antenna fed by an offset microstrip-fed line is proposed. The antenna exhibit dual-band characteristics. The two operating frequency bands are: 1.83--2.73 GHz and 5.36--7.63 GHz, which are of impedance bandwidth 39.5% and 34.9% respectively. The bands are suitable for PCS, UMTS, IMT-2000, ISM, Bluetooth, RFID and WLAN applications. A parametric study has been carried out by varying the location of the feedline to investigate its effect on the resonant frequency. Impedance, radiation and gain characteristics of the proposed antenna are also presented and discussed.