notched band shifts toward the lower-frequency range significantly and has a wider notch bandwidth as the slot length lengthens. It is found that by adjusting the mean length of the slot to be about one half-wavelength at the desired notched frequency, a destructive interference can take place, thus causing the antenna to be nonresponsive at that frequency. Figure 3 shows the slot-width effect on the notched band. By adjusting the width of the embedded slot, the lengths of the outer and inner perimeters of the embedded slot control the lower-and upper-edge frequencies of the notched band, respectively. It is obvious that the notched bandwidth is increased with increasing slot width. Thus, we can have a specific notched band by changing the slot length and width. The corresponding data are also listed in Tables 1 and 2 for comparison. The measured gains in the boresight direction with respect to frequency are shown in Figure 4. This characteristic meets the requirement of the multiband OFDM physical-layer proposal for IEEE 802.15.3a. And, there is a notched-band between 4.799 and 5.999 GHz, suppressed by the loaded slot, which meets the need for interference immunity with HIPERLAN and WLAN. CONCLUSIONA novel microstrip-line-feed elliptical antenna with a bandnotched characteristic has been proposed and investigated. The proposed antenna provides ultra-wideband characteristics in a planar structure using the simple impedance-matching technique. By adjusting the loaded slot, it can obtain the desired band-notched characteristic. This antenna design is a breakthrough for selecting the notched band and can be directly applied to UWB communications where the band-notched characteristic is needed. INTRODUCTIONA reflectarray is a type of antenna that combines the best features of conventional reflectors with those of microstrip phased arrays. In this structure, a horn or small antenna array illuminates a planar array of printed radiators which, by using suitable phasing circuits, converts an incident spherical wave into a plane wave, collimating the reflected field in a desired direction [1]. Their low cost, flatness, and ease of installation and manufacture convert these structures into ideal solutions to be used as narrow-beam antennas in modern communication systems [2]. Moreover, the spatial signal distribution permits to eliminate the complexity and losses associated to the microstrip-feed distribution network. Depending on the phase-shift distribution it is possible to produce a pencil-beam or a shaped-beam radiation pattern. There are different ways to achieve the required phase-shift per cell, in [3], equal-size patches are employed with passive delay lines of different lengths while in [4] the phase of the scattered field is controlled by means of the patch size. Although these methods assure the correct antenna performance in a desired direction do not permit control of the phase shift between the patches and, consequently, to steer the pencil beam. Fig. 3 ( r ‫؍‬ 4.4, h ‫؍‬ 0.8 mm, r a ‫؍‬ 11 mm, r The pos...

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only see one deep zero point at the high stop-band. Meanwhile, the bandwidth of the model-based results is a little larger than that of the measured results in the upper pass-band. The discrepancies are further investigated. It is found that the weak mutual coupling in the space, which is mainly dominant by electrical coupling and can shift down the odd-mode frequency, is not considered in modelbased circuit design or a circuit simulator. So the operating bandwidth of measurement is slightly reduced, as compared to that of simulation. The dominant magnetic coupling and the weak electric coupling in space are canceled out in the upper stop-band. Thus, the additional zero point in upper stop-band is generated. To demonstrate these effects, a small capacitor (cap) with capacitance of 0.013 pF is added between two open ends, as shown in Figure 6. The modeled cap, which represents the weak electronic coupling of two resonators through the space, can shift down the odd-mode frequency, reduce bandwidth, and generate an additional zero point Zp1. SUMMARYIn this paper, the configuration of a two-order band-pass filter has been proposed, designed, and analyzed. A physically-based lump model, which can represent dispersion characteristics and frequency response in both the pass-band and the stop-band was developed and used to fulfill the filter design. The model-based design, which is helpful for understanding the operating mechanism of the filter, has been verified by the experiment results. The designed BPF has achieved good rolloff in the upper stop-band by generating two finite transmission zero points. APPENDIXAt the open end of a microstrip line with width W and substrate thickness h, the fields do not stop abruptly, but extend slightly further due to the effect of the fringing field [8]. This effect can be modeled as an equivalent transmission line with length ⌬l as follows:where The recent allocation of the frequency spectra for ultra-wideband radio applications has presented a myriad of exciting opportunities and challenges for antenna designers. Despite of the advantages of UWB, existing narrowband systems do not like the interference from UWB signal. However, over the designated UWB frequency band, there are existing operating bands such as the HIPERLAN (5150 -5350 MHz) and WLAN (5725-5825 MHz) bands, which may cause interference with UWB operations [1, 2]. Printed antennas are low cost, lightweight, and easy to construct. These features are desirable for both indoor and outdoor handheld UWB antenna applications. In this paper, we present another promising technique for obtaining the band-notched characteristic with immunity of HIPERLAN and WLAN bands by etching a C-shaped slot on an elliptic patch antenna. With the change of the size of the slot, both the notch center frequency and bandwidth can be easily adjusted. Figure 1 shows the proposed slot-loaded elliptic patch antenna for UWB with band-notched characteristics. The elliptic patch antenna with two axes 2r a , 2r b is printed on a FR-4 substrate of thick...