диафрагмированные волноводные фильтры / 52775b66-7580-45f4-a333-31896d8898e4

RO4350b substrate with thickness of 0.762 mm and relative permittivity of 3.48. The thickness of copper coating on the top side of the substrate is approximately 0.0175 mm. A 50 - CPW feed line, having a metal strip width Wf = 4 mm and a gap distance G = 0:28 mm, is used to excite the proposed antenna.

The dimensions of rectangular patch are optimized to have resonant frequency at 3.7 GHz. By optimizing parameters of L2, W 2, and T 1 a®ecting the length and width of stub and notch attached to the rectangular radiation patch, improved impedance bandwidth performance can be achieved for the proposed antenna. That is largely due to the fact that the two stubs and two notches a®ect the reactive coupling between the rectangular patch and the ground plane and input impedance of main patch. The impedance bandwidth of the antenna covers from 3.0 GHz to 12.1 GHz for the return loss of less than ¡10 dB. The ¯nal design parameters are as follows: W1 = 10 mm, W2 = 1 mm, L1 = 16 mm, L2 = 8:5 mm, T1 = 2 mm, G = 0:32 mm, Wf = 4 mm , and S2 = 1 mm.

3. FILTER DESIGN AND ANALYSIS

Figure 2 shows the geometry and equivalent models of the proposed ¯lter. This ¯lter can be divided into a conventional highpass and a bandstop ¯lter. To realize band-selective characteristic within UWB frequency band, two ¯lters are integrated on both sides of the 50-ohm microstrip line and design parameters are adjusted to obtain superior frequency response throughout the operating frequency band. The ¯lter is printed on 30-mil Rogers RO4350 substrate with dielectric constant ("r) of 3.48.

Figure 2: (a) Geometry of the proposed ¯lter, (b) Equivalent transmission line model of the highpass ¯lter.

All simulations are carried out by using Ansoft High Frequency Structure Simulator (HFSS) [4]. To design highpass ¯lter for wideband application up to 10.6 GHz, the mixed lumped/distributed (L/D) highpass ¯lter scheme is chosen [5]. The ¯lter consists of a cascade of three shunt shortcircuited stubs of electrical length of µc at the cuto® frequency fc, separated by connecting lines of electrical length of 2µc. The transfer function and ¯ltering function can be described by the following equations [6].

where " is the passband ripple constant, µ is the electrical length, and Tn(x) is the Chebyshev function of the ¯rst kind of degree n. The associated characteristic line impedance for the given terminating impedance Z0 are determined by

58:5 ohms, and Z1;2 = 49:1 ohms. To realize the extremely wide passband, the line width is modi¯ed using full-wave EM simulation and determined to have much better performance throughout UWB frequency band. The initially calculated electrical length (µc) of each ¯lter is 40.68±.

The measured return loss characteristic of proposed antenna is shown in Figure 4. The impedance bandwidth of the proposed antenna reaches 9.1 GHz (3.0»12.1 GHz) for the return loss of less than ¡10 dB, which is enough to cover the entire UWB system. By using the ¯lter, the frequency stop band is created while maintaining the wide bandwidth performance.

Figures 5(a) to 5(c) show measured radiation patterns, including E-and H-planes and co-and cross{polariza tions at 3.5, 5, and 9 GHz. Good omni-directional performance at lower frequency band with a cross-polarization level of less than ¡15 dB are assumed.

Figure 5: Measured radiation patterns of E- and H-planes and co-and cross-polarizations at (a) 3.5 GHz, (b) 5 GHz, and (c) 9 GHz. (- - ± - -: co-pol, | * |: x-pol)

Figure 6 illustrates the measured antenna gains of the designed antenna. From the results illustrated above, one can conclude that the suggested antenna system can be readily utilized for UWB application.

Frequency, GHz

Figure 6: Measured antenna gain.

5. CONCLUSION

A novel and compact CPW-fed UWB antenna with a microstrip band-selective ¯lter is proposed. To obtain the wideband characteristic for UWB frequency band, notches and stubs are utilized. Combining an UWB antenna with a ¯lter having notch-function, the antenna with ultra-wideband performance over UWB band and band-rejection characteristic over WLAN band are obtained.

ACKNOWLEDGMENT

This work was supported by HY-SDR Research Center at Han-yang University, Seoul, Korea, under the ITRC Program of IITA, Korea.

REFERENCES

1.Ammann, M. J. and Z. N. Chen, \A wide-band shorted planar monopole with bevel," IEEE Trans. on Antennas and Propagation, Vol. 51, No. 4, 901{903, April 2003.

2.Chung, K., T. Yun, and J. Choi, \Wideband CPW-fed monopole antenna with parasitic elements and slots," Electronic Letters, Vol. 40, No. 17, August 2004.

3.Suh, S. Y., W. L. Stutzman, and W. A. Davis, \A new ultrawideband printed monopole antenna: the Planar Inverted Cone Antenna (PICA)," IEEE Trans. on Antennas and Propagation, Vol. 52, No. 5, May 2004.

4.Ansoft High Frequency Structure Simulator (HFSS), Ver. 9.2, Ansoft Corporation.

5.Levy, R., \A new class of distributed prototype ¯lters with applications to mixed lumped/distributed component design," IEEE Trans., Vol. MTT-18, 1064{1071, December 1970.

6.Hong, J. S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, Wiley, New York, 2001.