A simple and robust “cell-based” method is presented for the design of variable-gain amplifiers (VGAs). The proposed unit cell utilizes a unique gain compensation method and achieves accurate dB-linear characteristic across a wide tuning range with low power consumption and wide bandwidth. Several such highly dB-linear unit cells can be cascaded to provide the required gain range for a VGA. To prove the concept, single-cell, 5-cell, 10-cell and 15-cell reconfigurable VGAs were fabricated in a standard 0.18 μm CMOS technology. The measurement results show that the 10-cell VGA achieves a gain range of 38.6 dB with less than 0.19 dB gain error. The 15-cell VGA can either be used as reconfigurable VGA for analog control voltage or tunable PGA for digital control stream, with the flexibility of scaling gain range, gain error/step and power consumption. For the VGA at highest gain setting, it consumes 1.12 mW and achieves a gain range of 56 dB, gain error less than 0.3 dB.

An on-chip bandpass filter (BPF) is designed and fabricated in a 0.13-μm SiGe (Bi)-CMOS technology. This BPF consists of a broadside-coupled meander-line resonator (BCMLR) in conjunction with a defected-ground structure (DGS). By simply grounding a BCMLR, the resonator can be converted into a BPF. Further applying a DGS to this BPF, an additional transmission zero can be generated in the high-frequency band. To understand the fundamentals of this design, an LC-equivalent circuit is given for investigation of the transmission zeros and poles. The measured results show that the BPF has a center frequency at 33 GHz with a bandwidth of 18%. The minimum insertion loss is 2.6 dB, while the maximum stopband attenuation is 44 dB. The chip size, excluding the pads, is only 0.038 mm2 (0.126 × 0.3 mm ² ).

An on-chip resonator is designed and fabricated using a standard 0.13-μm SiGe technology for millimeter-wave applications. The designed resonator is based on a unique structure, which consists of two broadside-coupled meander lines with opposite orientation. The equivalent LC circuit of the resonator is given, while the impact of the structure on the resonance frequencies is investigated. Using this structure along with capacitors, a compact bandpass filter (BPF) is also designed and fabricated. The measured results show that the resonator can generate a resonance at 57 GHz with the attenuation better than 13.7 dB, while the BPF has a center frequency at 31 GHz and a insertion loss of 2.4 dB. The chip size of both the resonator and the BPF, excluding the pads, is only 0.024 mm ² (0.09×0.27 mm ² ).

A novel 360° beam steering patch antenna with parasitic elements is presented in this paper. The designed antenna consists of a radiating patch and six parasitic elements, each of which is connected through a group of shorting vias controlled by PIN diode switches. By switching on the desired groups of the shorting vias, the electric field distribution inside substrate cavity appears at the desired beam direction. Rotationally switching on the groups of the shorting vias, the performance of 360° beam-scanning is realized. To further understand operating mechanism, the antenna is modeled with equivalent circuit in terms of the ON and OFF status of a sector of the antenna, which can be used as a design guide for shorting-vias-controlled reconfigurable microstrip patch antennas. The fabricated antenna achieves a bandwidth of 14.5%, a peak gain of 10 dBi and the efficiency of 80.5%. The achieved beamwidths are 42° and 97° in azimuth and elevation planes, respectively. With an ability of being steered around zenith axis at six directions, the scanned beam range covers the entire 360 degrees. The physical dimension is only 2.5 λg for the size and 0.5 λg for the profile. This antenna operates from 5.1 to 5.9 GHz and has significant meaning in IEEE 802.11ac WLAN applications due to its capabilities of generating 360° steered beams.

A compact balanced frequency doubler with more than 35 dB odd-harmonic rejection and fractional bandwidth of 73% is presented in this letter. Wide bandwidth and high odd-harmonic suppression is achieved by adopting a new technique for the transformer balun design, resulting in a very low magnitude imbalance of 0.13 dB and a phase imbalance of 0.4° over 7-15 GHz. The balun performance is improved by offsetting the radius of the primary and secondary coils, which reduces the parasitic coupling capacitance. The input and output frequency ranges for the doubler are 7-15 GHz and 14-30 GHz respectively. The circuit was fabricated in 0.13-μm SiGe technology. The chip size is 0.6 mm × 0.4 mm.