This paper proposes the development of a two-axis sun tracking solar energy system using fuzzy logic as intelligent quality policy. To achieve maximum efficiency for solar panels, it is necessary to follow the sun's path in the sky. Therefore, the architecture for the two-axis sun tracking solar energy system uses software to control the hardware. The hardware comprises (i) solar cells; (ii) lead-acid batteries; (iii) a gear box; (iv) a stepping motor; and (v) a light detection circuit, while the software comprises (i) a detection system; (ii) a fuzzy tracking controller; and (iii) a database system. A fuzzy logic controller is designed as the software architecture of the system to decide the timing for tracking the sun. The nearest position that results in receiving direct sunlight is obtained from the database. Our system is fully automatic in a changing environment and takes into account meteorological changes and the effects of the external environment arising from a malfunction. This approach reduces the number of starting motors and results in smaller energy loss in cloudy, cloud mask, or unstable weather conditions.

In this article, we propose a dual‐mode bandpass filter (BPF) at 1.575 GHz using periodic meander slotted ground structures (M‐SGSs) which are etched on the ground plane for spurious suppression. First, single M‐SGS is analyzed. Second, the M‐SGSs are used to provide a good stopband‐rejection to the second harmonics of the dual‐mode BPF with level of over −40 dB. Finally, a dual‐mode BPF with improved stopband is designed, fabricated, and measured. The experimental results of the fabricated filter measured by the network analyzer have good agreement with the simulation results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 445–447, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23123

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With symmetric structure added, the reactive parts of two consecutive jointed sections tend to cancel each other and the purely real impedance over the frequency band is provided. SIMULATION AND MEASUREMENT RESULTSThe proposed balun shown in Figure 2 is designed and fabricated on an RT/Duroid 6010 substrate with a thickness h ϭ 25 mil and a relative dielectric constant r ϭ 10.2. The simulation is performed by using IE3D. The simulated and measured results of return loss for all ports are shown in Figure 3. Without extra impedance matching networks, the simulation results for input return loss are from about Ϫ5 dB to Ϫ13 dB and the measured results for input return loss are from about Ϫ5 dB to Ϫ23 dB. Compared with the conventional log-periodic balun as shown in Figure 4, a symmetric log-periodic balun can provide better performance over the entire designed band. Figure 5 shows the simulated and measured results for amplitude and phase imbalances between the two output ports. The measured amplitude imbalance was about Ϯ1.1 dB with a corresponding phase difference about Ϯ4°. The bandwidth of the balun is around 70%. CONCLUSIONThe high performance UWB balun based on symmetric LogPeriodic structure is presented and fabricated in this letter. The novelty of the proposed UWB balun is emphasized on providing solution to the problems associated with the fabrication and measurement of the conventional log-periodic balun operated at higher frequency and keeping excellent magnitude and phase balancing between two output ports over the entire operation band. For illustrated UWB symmetric balun, the measured performance shows good agreement with the simulated results. In this letter, we propose a compact BPF using only two coupled SIRs to create a wide stopband up to 8.16f 0 and provide an average rejection level of 25 dB. The theory and guidelines for selecting the geometric parameters of SIRs are clearly presented in the next section. Two SIRs with different physical dimension are suitably selected and arranged so as to realize a BPF with very wide stopband. By appropriately choosing the impedance ratio (K) and length ratio (␣) of SIRs, the proposed BPF with a wide stopband up to 8.16f 0 is well achieved. The advantages of the proposed structure are suppression of the spurious responses without any extra elements with BPF and a very compact circuit size. The filter is designed, fabricated, and measured, and shows a good agreement with the electromagnetic (EM) simulation. CIRCUIT DESIGN Determining the Resonant Frequencies of SIRThe proposed BPF with a wide stopband, illustrated in Figure 1, is composed of two coupled SIRs with different dimension. The input/output (I/O) tapped lines are set at the one side of each resonator. The basic structure of a microstrip SIR is shown in Figure 2(a). It consists of two different characteristic impedances, constructed by cascading a long-length (2 1 ) high-impedance section (Z 1 ) in the center connected with the two short-length ( 2 ) low-impedance sections (Z 2 ) in the two sides. T...

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