and phase after the preliminary design, the width of each section as well as the average length of a section of the subarray is optimized.
SIMULATED AND MEASURED RESULTSA 4 ϫ 3 array antenna with optimized parameters was fabricated on a 300 mm ϫ200 mm substrate with relative permittivity of 3.5 and thickness of 2 mm. Its return loss was measured by the network analyzer Agilent 8722ES. Figure 2 shows both the simulated and the measured return loss. The simulated results are in good agreement with the measured ones, showing an impedance bandwidth for S11 Յ Ϫ10 dB of 40 MHz.The far field measurement was performed in an anechoic chamber. Figure 3 shows the simulated and measured radiation patterns. The array antenna was designed according to Ϫ27 dB Chebyshev pattern for the horizontal plane with the current ratio 1:2.183: 2.183:1 of a horizontal subarray; however, the simulated horizontal pattern is not the exact Chebyshev one due to errors in the theoretical model, as shown in Figure 3 (b). A SLL of Ϫ21 dB in the horizontal plane and Ϫ14.2 dB in the vertical plane was measured at the frequency of 2.555 GHz. The HPBW for both planes is 27°. The measured polarization radiation patterns for two main planes are shown in Figure 4, showing the axial ratio of below 3 dB within the main beam. The axial ratio of 1.1 dB was measured at 2.56 GHz for the broadside direction. A peak gain of 13.9 dB at 2.55 GHz has been measured by means of the comparison with that of a standard horn.
CONCLUSIONThis work describes a low-sidelobe CP microstrip patch array with a symmetric main beam. Measured results show that the array has a SLL of Ϫ21 dB in the horizontal plane and the HPBW of 27°for horizontal and vertical planes both. Its axial ratio is below 3 dB within the main lobe and the peak gain reaches 13.9 dB. Its return loss is less than Ϫ10 dB for the impedance bandwidth of 40 MHz. The antenna has advantages such as thin profile, simple structure, low cost, low SLL, CP performance, and symmetric main beam. Thus, it is promising for the application of RFID readers and other wireless systems. narrow-band light can go though the FFPF. However, in the Fabry-Perot cavity, the light from an optical fiber tends to diverge, degrading the finesse of the FFPF. For example, the finesses of the resonators in references [4] and [5], which are constructed with two plain mirrors, are 11 and 17, respectively. To improve the finesse of the FFPF, a short piece of optical fiber [6] or hollow-core waveguide [7] was suggested to insert inside the Fabry-Perot cavity. However, it is very difficult and costly to prepare a short piece of fiber or hollow-core waveguide for use inside the resonator, because the resonator is only about 10 m for a practical filter. This letter presents a microlens Fabry-Perot resonator, suitable for optical networks, fiber-optic sensors, filters, and spectrometers. The resonator is easy to construct at low cost, and the finesse is much larger than that of an EFPI with two plain mirrors. It is anticipated that such high-finess...