This paper discusses the development of a monolithic image-rejection mixer with very wide-band (about 60% of the center frequency) image rejection characteristics for 16-QAM digital microwave radio communication receivers. The mixer can be commonly used in 4-, 5-, and 6-GHz bands, which reduces the cost. The mixer consists of a wide-band 90splitter, in-phase divider and drain LO injection mixers. They are designed on a single 2.81.8 mm2 GaAs chip based on a uniplanar MMIC lumped-constant element technique. The mixer achieved an image rejection ratio of greater than 25 dB and a conversion loss of less than 2 dB at a wide LO frequency range from 3.5 to 6.5 GHz, without consuming any DC power.

A novel ultra-broad-band bridge-type switch is proposed, which employs a bridge circuit consisting of four common-gate FETs. The isolation of conventional series- and shunt-type switches is limited by the switching device's performance, namely, the ON resistance (Ron) and the OFF capacitance (Coff). Some methods have been proposed to overcome this problem. However, most of them are band-limited. A feature of the newly-developed bridge-type switch is that its isolation characteristics do not depend on the Ron and Coff of the switching devices, but instead on the accuracy of the balancing bridge circuit, and thus ultra-broad-band characteristics can be obtained. The isolation for deviation of the bridge circuit elements and ON-state characteristics are calculated using a simple FET model. The fabricated bridge-type MMIC switch achieves less than 3.0 dB insertion loss and greater than 28 dB isolation in the broad frequency band up to 40 GHz.

A very low spurious frequency doubler for wireless communication systems is proposed. The key to this technique is to change the input signal into a rectangular wave, which effectively suppresses the fundamental frequency and the odd harmonic components. The desired to undesired signal ratio (D/U) is better than 50 dBc at the desired output frequency of 1.1 GHz. The proposed doubler eliminates the need for the band-pass filters which occupy a large part of the radio frequency (RF) module. High order multipliers easily are fabricated with this method. In this paper, a quadrupler is also described.