We present unconditionally energy-stable second-order time-accurate schemes for diffuse-interface (phase-field) models; in particular, we consider the Cahn-Hilliard equation and a diffuse-interface tumor-growth system consisting of a reactive Cahn-Hilliard equation and a reaction-diffusion equation. The schemes are of the Crank-Nicolson type with a new convex-concave splitting of the free energy and an artificial-diffusivity stabilization. The case of nonconstant mobility is treated using extrapolation. For the tumor-growth system, a semi-implicit treatment of the reactive terms and additional stabilization are discussed. For suitable free energies, all schemes are linear. We present numerical examples that verify the second-order accuracy, unconditional energy-stability, and superiority compared with their first-order accurate variants.

A compact differential filtering quasi-Yagi antenna is proposed for high frequency selectivity and low cross-polarization. The proposed antenna is formed by inserting a double-sided parallel-strip line (DSPSL) filter between the driver and the reflector of the quasi-Yagi antenna. This integration enables the antenna to achieve both high frequency selectivity and compact size. An antenna prototype exhibits a 10-dB return loss bandwidth of 1.77-1.87 GHz, peak gain of 5.6 dBi, and maximum cross-polarization levels of dB in E-/H-planes at 1.81 GHz. The out-of-band suppression is enhanced by 14.4 and 11.8 dB at 1.67 and 1.97 GHz compared to the quasi-Yagi antenna itself, respectively.

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