In this letter, a novel dual-band and polarization-flexible substrate integrated waveguide (SIW) cavity antenna is proposed. The SIW cavity used for the antenna is excited by a conventional TE 120 mode for its first resonance. With the intervention of the slot, a second resonance excited by a modified-TE 120 mode is also generated thereby providing a broadside radiation pattern at two resonant frequencies. In addition, the proposed antenna has two orthogonal feeding lines. Therefore, it is possible to provide any six major polarization states. In this letter, three major polarization cases are simulated and compared with measured results. Since modern communication systems require multifunctional antennas, the proposed antenna concept is a promising candidate.Index Terms-Dual band, polarization, slot antennas, substrate integrated waveguide.

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This paper presents a GaAs double-balanced mixer (DBM) applying an improved Marchand balun. This structure is achieved by adding a frequency-tuning tail capacitor to the end of the imbalanced coil. By using this tail capacitor, the size of balun is greatly reduced and the IF bandwidth is largely extended. The equivalent circuit modeling and working principle of this structure are described in this paper. The RF bandwidth of the proposed mixer is from 6 GHz to 18 GHz. The measurement result shows that the mixer's IF bandwidth ranges from DC to 8 GHz with the conversion loss less than 10 dB. Because of the good amplitude and phase performance of the proposed balun, the LO to IF isolation is also improved. The total chip area is 950 × 600 µm 2 .