This paper demonstrates the low voltage operation of a doubly balanced Gilbert mixer fabricated in a 0.8-m CMOS process and operating as both a down-converter and an upconverter. As a down-converter with an RF input of 1.9 GHz, the mixer has a single sideband noise figure as low as 7.8 dB and achieved down-conversion gain for supply voltages as low as 1.8 V. As an up-converter, the mixer demonstrates 10 dB of conversion gain at an RF frequency of 2.4 GHz with an applied local oscillator (LO) power of 07 dBm and LO-RF/LO-IF isolation of at least 30 dB. Up-conversion gain was achieved over a 5-GHz bandwidth and at supply voltages as low as 1.5 V. The mixer presented demonstrates the lowest single side band noise figure for a CMOS doubly balanced down-converting mixer and the highest frequency of operation for a mixer fabricated in CMOS technology to date.

In this letter, characterization of circular High-Impedance Surfaces (HIS) is investigated. The reflection phase characterization used for rectangular HIS is here extended to circular lattices. Circular HIS discussed in this letter present a 2D periodicity and consequently the phase diagram is determined for concentric and radial polarizations. The effect of mapping a rectangular HIS into a circular one is investigated in order to give some insights regarding the design of such metasurface. The presented characterization constitutes a useful tool for the design of low-profile antennas using HIS as reflector.