Kevin Ming-Jiang Ho

The Search for a Reliable MEMS Switch

The RF community has long been searching for the ideal switch since the birth of electronics, and it is defined as a device having virtually no insertion loss (Ron = 0 Ω) over a wide frequency range, very high isolation [off-state capacitance (Coff)] = 0 fF), extremely high linearity (IIP2 and IIP3 → infinite), medium- to high-power handling (100 mW to 1 kW), and no dc power consumption. Our entire RF infrastructure ecosystem, from communication system networks, to satellite systems, to wideband spectral analysis, to instrumentation and radar systems, uses a variety of switches for signal routing and control (attenuation, phase shifting, etc.). The ideal switch was achieved long time ago using electromechanical relays, and even after nearly 100 years, it is still the best RF switch ever made from an electrical perspective [1]. It has very low insertion loss (Ron <;1 Ω), very high isolation (Coff of few fF), very high linearity and high power handling (100 mW to 50 W). However, it is bulky, expensive, and has an average lifetime of few million cycles.

An Electronically-Scanned 1.8–2.1 GHz Base-Station Antenna Using Packaged High-Reliability RF MEMS Phase Shifters

This paper presents the first 4-element base-station antenna that is passively scanned using low-loss RF MEMS phase shifters. The design is based on packaged RF MEMS SPDT switches, which are capable of handling Watts of RF power with high reliability. The results agree very well with simulations and show pattern scanning to 9° with a measured gain of 8.6-8.3 dB at 2 GHz. The array is capable of handling 5-10 W of power with no distortion.

A Two-Channel 8–20-GHz SiGe BiCMOS Receiver With Selectable IFs for Multibeam Phased-Array Digital Beamforming Applications

An 8-20-GHz two-channel SiGe BiCMOS receiver is presented for digital beam-forming applications. The receiver is based on a dual-down-conversion architecture with selectable IF for interference mitigation and results in a channel gain (in-phase and quadrature paths) of 46-47 dB at 11-15 GHz and >;36 dB at 8-20 GHz with an instantaneous bandwidth of 150 MHz. A 2-bit gain control (0-16 dB) is also provided at baseband. The mea sured noise figure (NF) is <;4.1 dB (3.1 dB at 15-16 GHz) and is independent of the gain state. The measured OPldB is -10 dBm and the input PldB is -56 to -40 dBm at 15 GHz depending on the gain, which is sufficient for satellite applications. The on-chip channel-to-channel coupling is <; -48 dB. The measured evanescent mode is <;3% for a 1-Ms/s quadrature phase-shift keying (QPSK) modulation at 8-20 GHz, and <;1.8% for a 0.1-, 1-, and 10-Ms/s QPSK, 16 quadrature amplitude modulation (QAM), and 64-QAM modulations at 15 GHz. The chip is fabricated using a 0.18-μm SiGe BiCMOS process, has electrostatic discharge protection on the RF and dc pads, consumes 70 mA per channel from a 3.0-V power supply, and is 2.6 × 2.2 mm2, including all pads. A 15-GHz eight-element phased array with an NF <;3.8 dB is also demonstrated with multiple simultaneous beam performance. To our knowledge, this is the first two-channel 8-20-GHz beam-forming chip in SiGe BiCMOS technology.

A 1.5–2.4 GHz tunable 4-pole filter using commercial high-reliability 5-bit RF MEMS capacitors

This paper presents a 1.5-2.4 GHz 4-pole tunable filter using the Cavendish Kinetics RF MEMS capacitors. The MEMS capacitors are fabricated and fully packaged using a 0.18 μm CMOS standard process with integrated high voltage drivers and SPI control logic and with reliability in the billions of cycles. The filter results in a power handling of at least 20 dBm, a second and third harmonic generation of <; -125 dBc at 20 dBm, and an OIP3 of 33-35 dBm. The measured ACPR (adjacent channel power ratio) for a 5-MHz Wideband CDMA signal is ~45-48 dBm at 20 dBm input power. The paper also discusses the requirements on RF MEMS capacitors in order to achieve high performance filters for wireless systems.

Compact Self-Shielded 2–3 GHz High-Q Coaxial Fixed and Tunable Filters

A novel coaxial stepped-impedance resonator (SIR) filter is proposed based on conventional multi-layer printed-circuit board (PCB) technology. The resonator results in a measured unloaded quality factor (Qu) of 185 at 3.7 GHz, has compact size, is self-shielded and has very low electromagnetic (EM) coupling to nearby RF circuits. The 3-D filter topology easily lends to advanced filter design with multiple transmission zeroes using cross coupling and source-to-load coupling on the top printed-circuit board layer. Two third-order fixed-band bandpass filters, and two fourth-order tunable bandpass filters are demonstrated in this technology. The fixed-band filters have an insertion loss of 1.6 dB with a fractional bandwidth of 6.5% at 3.6 GHz and occupy a size of 9 × 12 mm2. The tunable filter covers 2.1-2.9 GHz with a fractional bandwidth of 3.5%, and an insertion loss of 4.2-9.2 dB, limited by the silicon varactors. Multiple transmission zeroes are used in these designs to significantly improve the filter selectivity. Application areas are in fixed and tunable filters with very compact size and high shielding from nearby circuits for advanced communication systems.

Tunable microstrip antenna with circular polarization across 1.4∶1 frequency span

A tunable microstrip antenna with circular polarization across a frequency span of 1.4:1 is presented. A dual mode microstrip antenna element with independent frequency control for each polarization is designed. Circular polarization is then achieved with both modes tuned to resonate slightly offset from the intended operating frequency. Measured return loss and patterns are presented.

Microstrip antennas with full polarization diversity using packaged RF MEMS switches

The design of a 1.32 GHz microstrip antenna with polarization diversity using commercially available low-loss packaged RF-MEMS switches is presented. Two OMRON single-pole double-throw (SPDT) switches are used in a novel re-configurable feed network which is able to provide four polarization states; vertical, horizontal, left-hand circular and right-hand circular polarizations. A hardware demonstrator with measured return loss in the polarization states is presented.

Highly dense microwave and millimeter-wave phased array T/R modules using CMOS and SiGe RFICs

We have used silicon technologies to build highly dense phased array for X to W-band applications. Typical designs include an 8-element 8–16 GHz SiGe phased array receiver, a 16-element 30–50 GHz SiGe transmit phased array, a miniature (&#60; 3mm2) and low power (&#60;100 mW) CMOS phased array receiver at 24 GHz, and a 4-element SiGe/CMOS Tx/Rx phased array at 34–38 GHz with 5-bit amplitude and phase control, a 2-antenna 4-simultaneous beam phased array chip at 15 GHz. Also, a miniature 8×8 Butler Matrix with &#60; 3 dB loss in 0.13 um CMOS has been developed for multibeam applications. It is shown that silicon chips can be used to lower the cost of phased arrays with a significant impact at Ku, K and W-band applications where there is so little available space behind each antenna element due to the very small element area.

X-band phased array development on teflon laminates with CMOS RFIC receivers

We present the development of an 8-channel X-band microstrip phased array receiver with beam-scan capability of +/−45 degrees in the azimuth plane. Two 0.13 µm CMOS RFIC chips are integrated directly on the laminates for the array feed network, with each chip comprising of a 4-way power combiner network and 4 channels of RF front-end. Each RF-front-end consists of an LNA, a VGA and a phase shifter, and the total chip size is 2.9 by 2.5 mm2. The design center frequency and bandwidth is 9.2 GHz and 75 MHz, respectively. An aperture coupled microstrip antenna is used for the basic radiating element, and measured response for the microstrip element deviates from the simulated response by 1.2 %.

Improving 3G/4G receiver sensitivity (TIS) using antenna impedance matching networks

This paper explores new applications for antenna impedance matching networks. It is seen that a tunable matching network can improve the cell phone system noise figure and total integrated sensitivity (TIS) by at ~ 1 dB at 700 MHz - 3 GHz. The reason is that a mismatched low-noise amplifier has a higher noise figure and a lower gain than a noise-matched LNA, and therefore, a tunable matching network is important for noise matching in receiver applications. This would lead to shorter download times and more efficient 3G and 4G mobile networks.