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transformers are used in both designs, which provide even mode impedances of 70.7 X with a line spacing of 0.56 mm [8]. The area of the folded layout is 30% less than the unfolded layout. The simulated and the measured results are compared in Figures 8-10.In Figure 8, the insertion loss for both designs is shown. Because the layouts are symmetrical, only |S 21 | is compared with the simulation. It is found that the measured data fits the simulations well. The insertion loss at the center frequency is 3.2 and 15 dB at 1 and 4 GHz. The one section filter response is clearly observed. The measured 3-dB bandwidth is 60%, which fits the prediction of Figure 6. The return losses for input and output ports are shown in Figure 9. The measured 10-dB input return loss bandwidths are around 33%. The isolation between the two output ports is shown in Figure 10. CONCLUSIONA one section filter is integrated into the PD. The concept can be realized using open-ended coupled lines and shorted-end coupled. The relations between even mode and odd mode impedance are shown. However, fabrication limits restrict the practical implementation. Therefore, an alternative loaded line circuit without coupled lines is used, which provides more flexibility in choosing the bandwidth. Two designs with a center frequency of 2.4 GHz are fabricated and measured to validate the concept. A 3-dB insertion loss bandwidth of 60% and a 10-dB return loss bandwidth of 33% are measured. ABSTRACT: This paper describes a new low-profile X antenna array separated 0.1-0.15 wavelengths from a flat or rimmed square reflector of 0.6 wavelengths in size. The array consists of two closely spaced elements: an active two-port folded-wire X antenna, which radiates two cross-polarized fields and a passive X element. This very compact double X reflector antenna has around 8-9 dBi peak directive gain, 12.5% bandwidth on average around the design frequency of 1800 MHz, a high interport isolation (about 25-30 dB) and low cross-polarization in the whole input-match frequency range. The practical applications of the properly designed and tuned double X reflector antenna may include among others, base station antennas with polarization diversity for GSM PCS or DCS bands, or for the whole UMTS band.