A novel printed crossed dipole with broad axial ratio (AR) bandwidth is proposed. The proposed dipole consists of two dipoles crossed through a 90 phase delay line, which produces one minimum AR point due to the sequentially rotated configuration and four parasitic loops, which generate one additional minimum AR point. By combining these two minimum AR points, the proposed dipole achieves a broadband circularly polarized (CP) performance. The proposed antenna has not only a broad 3 dB AR bandwidth of 28.6% (0.75 GHz, 2.25-3.0 GHz) with respect to the CP center frequency 2.625 GHz, but also a broad impedance bandwidth for a voltage standing wave ratio (VSWR) 2 of 38.2% (0.93 GHz, 1.97-2.9 GHz) centered at 2.435 GHz and a peak CP gain of 8.34 dBic. Its arrays of 1 2 and 2 2 arrangement yield 3 dB AR bandwidths of 50.7% (1.36 GHz, 2-3.36 GHz) with respect to the CP center frequency, 2.68 GHz, and 56.4% (1.53 GHz, 1.95-3.48 GHz) at the CP center frequency, 2.715 GHz, respectively. This paper deals with the designs and experimental results of the proposed crossed dipole with parasitic loop resonators and its arrays.Index Terms-Broad axial ratio bandwidth, circularly polarized dipole, crossed dipole, dipole array.

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The fifth-generation (5G) cellular mobile communications look promising with features that can help improving consumer experience and satisfaction. To be able to provide these features, more spectrum is required according to the Shannon-Hartley theorem. Spectrum is, however, a finite and scarce resource, and it can be allocated to a new service only when the spectral coexistence with other incumbents is ensured. New waveforms for 5G that differ from the conventional orthogonal frequency-division multiplexing (OFDM) are required in order to have a superior performance in terms of out-of-band emissions and to be able to utilize the fragmented spectrum in different bands. We developed the analytical models for evaluating the out-of-band emissions of the conventional cyclic prefix (CP)-OFDM as well as its alternatives: windowed OFDM and filtered OFDM, using their signal spectral modeling. The resulting expressions for the power spectral density (PSD) and the frequency-dependent rejection (FDR) involve simple closed-form expressions or easily computable integrals. We applied the expressions to the advanced minimum coupling loss model for assessing the feasibility of the spectral coexistence between the potential 5G systems (with linearized or nonlinear power amplifier) and the incumbent radar systems. The numerical simulation results indicate that both the windowed OFDM and filtered OFDM guarantee the coexistence at the low expense of the spectrum utilization and their coexistence performance can be reduced and reversed with nonlinearity distortion of the power amplifier.

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A switchable Yagi‐Uda antenna prototype with radiation pattern reconfiguration is presented in this letter. The proposed reconfigurable antenna is based on the concept of switching between the reflector and director of a Yagi‐Uda antenna using a radio frequency PIN diode. As a result, the minimum/maximum radiation can be steered towards desired signals or away from interfering signals in opposite directions. The measured 10 dB impedance bandwidth and gain are 210 MHz (7%) and 8.02 dBi at 3 GHz, respectively. Details of the antenna design and its performance are described and empirically analyzed.

In this article, a novel square microstrip antenna with a reconfigurable polarization capability is proposed that utilizes a perturbing segment in a defected ground structure (DGS). To verify the perturbing method, DGSs were embedded into either the two diagonal or all four corners of an antenna. The reconfigurable characteristics are produced by independently controlling the states of the biased DGS PIN diodes. The simulated and measured results show good frequency agility and polarization diversity with remarkable radiation performances.ABSTRACT: A novel miniaturized microstrip Wilkinson power divider with capacitor loading is presented in this article. The new divider not only effectively reduces the occupied area to 45% of the conventional one at 1.0 GHz, but also has good harmonic suppression performance. Furthermore, the new structure has only two variable parameters and can be easily designed. The design is validated both by simulation and measurement.

recommended that the manufacturing and measurement process need to be performed carefully. Figure 9 shows the measured radiation patterns including the co-polarization and cross-polarization in the H-plane (x-z plane) and E-plane (y-z plane). It can be seen that the radiation patterns in x-z plane are nearly omnidirectional for the three frequencies. Figure 10 shows the measured maximum gain of the proposed antenna with and without U-shaped slots. A sharp decrease of maximum gain in the notched frequency band at 5.5 GHz is shown. For other frequencies outside the notched frequency band, the antenna gain with the filter is similar to those without it. CONCLUSIONSIn this article, a novel compact printed monopole antenna with variable band-stop characteristics has been proposed for UWB applications. The fabricated antenna has the frequency band of 2.9 to over 14 GHz with a rejection band around 5.01-5.98 GHz. The proposed antenna has a simple configuration and is easy to fabricate. Experimental results show that the proposed antenna could be a good candidate for UWB application.