antenna, the new difficulty is here to integrate GPS antenna and dielectric radome effects. As regards the effects of the only patch GPS, they are rather weak. GPS SMB connector tends to act as one more overhead ground-wire cable. However, by isolating GPS antenna ground plane from upper GSM plate, we manage to decrease the effects of this new ground wire on the GSM antenna behavior, and to correct the variations by slightly modifying the different dimensions. Concerning the radome, due to its special profile, it is better to proceed as in [4], defining the unmatched input impedance locus to reach first for a structure without radome, allowing the radome effects to be taken into account a second time. The final optimized structure was obtained using principally diameters of wires M1, M2, and M3.The GPS antenna is less difficult to optimize because radome the effects can be directly taken into account by computing a GPS structure with a corresponding dielectric cover. Moreover, in spite of the finite small dimensions of the GPS ground plane, the presence of the entire GSM structure is not a problem for the software simulator because the GSM antenna can be approximated by a single additional metallic plate.
CONCLUSIONThis paper has presented an integrated combined GSM/GPS antenna comprised of a wire-stacked plates element having with a GPS printed cut-corner patch on top. The entire structure is protected by a low-cost dielectric radome and is laid on a small ground plane. The active GPS amplifier and filter are located under the GSM ground plane. In the entire GSM frequency band, the antenna exhibits a high-quality dipolar radiation pattern type, VSWR less than 2, and mean gain around 1.4 dB. In the GPS standard, the structure shows an impedance bandwidth of 25 MHz (1.6%) for VSWR Ͻ 1.5, a circular polarization bandwidth of 5.5 MHz (0.3%), and a 4-dB gain, which is sufficient for the GPS communication standard. A lower-cost solution on epoxy substrate is also possible. The entire structure is a very low cost, strong, and low profile, and has small dimensions; thus, this antenna is very suitable for automobile applications.
ACKNOWLEDGMENTSThe authors wish to thank RADIALL-LARSEN Antenna Technologies Company for financial support under the CNRS 96/019 research project and especially Christophe Delaveaud and Claude Brocheton for helpful discussions.
CAD FORMULAS OF THE CAPACITANCE TO GROUND OF SQUARE-SPIRAL INDUCTORS WITH ONE-OR TWO-LAYER SUBSTRATE BY SYNTHETIC ASYMPTOTE
measured results. The filter has a 3-dB passband from DC to 1.5 GHz. The insertion loss is better than 1.15 dB from DC to 1.36 GHz. The stop-band rejection level is larger than 10 dB from 1.71 to 5.14 GHz, and larger than 20 dB from 5.15 to 7.55 GHz. Three attenuation poles are realized at 2.08, 5.51, and 7.46 GHz. Spurious response occurs at about 8 GHz, which is greater than five times the cutoff frequency. The size of the lowpass filter is 12 ϫ 7.4 mm 2 .
CONCLUSIONA novel compact microstrip lowpass filter using an integration of bandstop structure is an open-loop resonator has been proposed. The lowpass filter is not only of compact size, but also has very wide stop-band and the three attenuation poles in order to suppress the harmonics effectively and achieve good selectivity. Its wide rejection, high selectivity, sharp rejection of the harmonics, and compact size are desirable in communication systems.
CAD FORMULA OF A MICROSTRIP ON A GROUNDED SUBSTRATE OF TWO LAYERS BY SYNTHETIC ASYMPTOTE
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