0.02 mm. The simulated and measured result of frequency response and phase response are shown in Figures 10 and 11, respectively. Good agreement is also observed between the simulated and the measurement results. The measured results of the miniaturized coupler are summarized in the Table 1. CONCLUSIONSAn extremely compact dual-band branch-line coupler operating in 0.9 GHz and 2.4 GHz is presented in this study. The size of this miniaturized coupler is reduced by 74% of the circuit dimension compared with the origin design with good circuit performance. Response of the miniaturized dual-band branch-line coupler and its equivalent circuit are in good agreement, and optimizing circuit performance using the circuit model could be implemented. Furthermore, the design is without lumped elements, via-holes, bound wires, and can be easily fabricated by using standard PCB etching processes, making this dual-band coupler suitable for MIC and MMIC applications. pedance bandwidth of microstrip antennas [1][2][3]. Among all the techniques, the aperture coupled feeding technique is simple and more effective as it has the freedom in designing the required feed line to energize the elements in enhancing the impedance bandwidth. Since in the aperture coupling the microstrip line feed and the antenna elements are separated by a ground plane, the effect of the feed line radiation on the antenna radiation characteristics is less, which improves the quality of antenna radiation pattern [4]. Further use of parasitic element in the form of gap-coupled to the radiating elements and use of slots will also effective in enhancing the impedance bandwidth. This concept has been utilized in designing the four-element gap-coupled slot rectangular microstrip array antenna (FGSRMSA). The obtained experimental results are discussed and presented in this letter. DESIGN AND EXPERIMENTAL DETAILSIn the present study, the antennas are fabricated on low cost glass epoxy substrate material of thickness h ϭ 1.66 mm and permittivity r ϭ 4.2. The geometry of conventional corporate fed four-element gap-coupled rectangular microstrip array antenna (FGRMSA) is as shown in Figure 1. The antenna geometry consists of radiating elements of length L R and width W R . A common parasitic element of length L P and width W P is placed between the radiating elements along their widths, which forms the gap coupling. The distance between the parasitic and radiating elements S is optimized and is taken as 0.025 g , where g is the operating wavelength in cm. The spacing between two radiating elements D R is kept at a distance of 1.5 0 /2. Usually in the array configuration the spacing between the two radiating elements is kept at a distance of 0 /2 for minimum side lobes [5]. But in this case, it is difficult to accommodate corporate feed arrangement between the two radiating elements when distance is 0 /2. If this distance is increased, accordingly the feed line has to be extended, which may increase radiation losses in the feed line. Hence, corporate feed arrangement...

between Q avg and Q t can be obtained with only 1024 samples. This scheme is able not only to reduce the required memory size in the monitoring unit but also to provide estimation for the Q-factor faster than the conventional scheme. CONCLUSIONThis article proposes a novel sampling technique for improving the sampling uniformity with a low number of sampling points. The proposed technique can increase the measurement convergency and accuracy of Q avg by adding deterministic jitter to the sampling pulses. This makes the sampled histogram close to the one obtained with a large number of sampling points. Consequently, we can obtain faster Q-factor monitoring by reducing the data points in a histogram. It also reduces the hardware complexity by reducing the required memory size. The monitoring results are quite independent of the difference between the data rate and the sampling rate. ACKNOWLEDGMENTThis work is supported by the National Science Council (NSC) of Taiwan (R.O.C.) under grants NSC94-2213-E002-061 and NSC95-2221-E-002-194. In recent years, the use and interest in microstrip antennas (MSAs) has become widespread because of its significant merits of smallsize, light-weight, low-profile, low-cost, direct integrability with microwave circuitry, and the ability to conform to the surface of a host object. One of the most attractive features of the equilateral triangular microstrip antenna is that, the area necessary for the patch becomes about nearly half when compared wtih rectangular, square, or circular MSAs designed for the same frequency. Such features make MSAs useful for many applications in radar and wireless communication systems [1]. However, one of the principle limitations of MSAs is their narrow impedance bandwidth. Many techniques are available in the literature for the enhancement of impedance bandwidth of MSAs [2, 3]. One such technique is the use of aperture coupling. This technique is simple and more effective as it has the freedom in designing the required feed line to energize the elements for enhancing the impedance bandwidth. Since in the aperture coupling the microstrip-line feed and the antenna elements are separated by a ground plane, the effect of the feed line radiation on the antenna radiation characteristics is less, which improves the quality of antenna radiation pattern [4]. Further, the slot-loading technique is also effective in broadening the impedance bandwidth. Hence in this study, the aperture coupling and slot loading techniques has been used in designing the antennas. The experimental results are presented and discussed. DESIGNING AND EXPERIMENTAL DETAILSThe proposed antennas are designed using low cost glass epoxy substrate material S 1 of thickness h ϭ 1.66 mm and dielectric constant r ϭ 4.2. The use of high dielectric constant substrate material reduces radiation losses because most of the EM-field is concentrated in the dielectric between the conductive strip and the ground plane. Another benefit of having a high-dielectric constant is that the antenna size decreases ...

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Abstract-This paper reports the design and development of rectangular microstrip antenna comprising a novel slot for enhancing the impedance bandwidth and gain. By incorporating a slot of optimum geometry at suitable location on the radiating patch, the antenna provides 78.08% (3.39-7.73 GHz) of impedance bandwidth and 3 dB of gain without changing the nature of broadside radiation characteristics when compared to conventional rectangular microstrip antenna. The proposed antenna may find applications in mobile WiMax, IEEE802.11a, HIPERLAN/2, cordless phones, fixed wireless etc. Design concept of antennas is given, and experimental results are discussed.

A novel design of square microstrip antenna is designed for dual band operation. By embedding unequal length inverted right angle slot at optimum place on the square patch, the upper operating band enhanced from 27.53 to 60.01% with minimum change in the lower operating band retaining the nature of broad side radiation characteristics. The proposed antennas may find application in radar communication. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2578–2582, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24678