Jonathan B. Hacker

MEM relay for reconfigurable RF circuits

We describe a microelectromechanical (MEM) relay technology for high-performance reconfigurable RF circuits. This microrelay, fabricated using surface micromachining, is a metal contact relay with electrical isolation between signal and drive lines. This relay provides excellent switching performance over a broad frequency band (insertion loss of 0.1 dB and isolation of 30 dB at 40 GHz), versatility in switch circuit configurations (microstrip and coplanar, shunt and series), and the capability for monolithic integration with high-frequency electronics. In addition, this MEM relay technology has demonstrated yields and lifetimes that are promising for RF circuit implementation.

Low-loss 2- and 4-bit TTD MEMS phase shifters based on SP4T switches

2- and 4-bit microelectromechanical system (MEMS) X- to K/sub u/-band true-time-delay phase shifters with a very low insertion loss are described. The phase shifters are fabricated on 200-/spl mu/m GaAs substrates and the low loss is achieved using MEMS SP4T switches, which reduce the number of switches in the signal path by half when compared to conventional designs with SP2T switches. Measurements indicate an insertion loss of -0.6/spl plusmn/0.3 and -1.2/spl plusmn/0.5 dB at 10 GHz for the 2- and 4-bit designs, respectively. The measured losses agreed very well with Momentum simulations and are the lowest reported to date. The 2-bit phase shifter performed well from dc-18 GHz, with -0.8/spl plusmn/0.3-dB insertion loss at 18 GHz and a return loss of <-10.5 dB over dc-18 GHz.

A DC-to-40 GHz four-bit RF MEMS true-time delay network

A monolithic true-time delay (TTD) network containing sixteen metal-to-metal contact RF microelectromechanical systems (MEMS) switches has been successfully fabricated and characterized. The TTD network was designed to produce flat delay time over a dc-to-40 GHz bandwidth with full 360-degree phase control at 22.5-degree intervals at 10.8 GHz. Measurements show a close match to the designed delay times for all sixteen switch states with 2.2 to 2.6 dB of insertion loss at 10 GHz. The worst group delay ripple in the dc-to-30 GHz range was 3 ps, well within the single bit delay time of 5.8 ps.

A monolithic MEMS switched dual-path power amplifier

RF MEMS switches have been successfully integrated with HEMT MMIC circuits on a GaAs substrate to construct a dual-path power amplifier at X-band. The amplifier uses two MEMS switches at the input to guide the RF signal between two paths. Each path provides single-stage amplification using different size HEMT devices, one with 80-/spl mu/m width and the other with 640-/spl mu/m. Depending on the required output power level, one of the two paths is selected to minimize the dc power consumption. Measurements showed the amplifier producing similar small signal gains of 13.2 and 11.5 dB at 10 GHz for the small and the large devices, respectively. The best PAE was 28.1 percent with 8.5 dBm of output power for the small device, and 15.3 percent with 14.6 dBm for the large device.

A rectangular tem waveguide with photonic crystal walls for excitation of quasi-optical amplifiers

Thin photonic crystal substrates are used to produce a TEM mode in a rectangular waveguide. Hexagonal pads arranged in honeycomb lattice and connected to the ground plane by substrate vias form the photonic crystal waveguide walls. Measurements on a Ku-band waveguide with two photonic crystal sidewalls showed a Field Flatness Efficiency (FFE) of better than 80% between 14.9 and 15.4 GHz, a substantial increase compared to the 50% of conventional rectangular waveguide. Simulations of a striped photonic crystal show similar behavior with additional property that it is also possible to use the crystal on top and bottom walls. Such a waveguide could support dual cross-polarized TEM modes by preventing only the longitudinal magnetic fields at the crystal surface.

A 2-bit miniature X-band MEMS phase shifter

The design and performance of a compact low-loss X-band true-time-delay (TTD) MEMS phase shifter fabricated on 8-mil GaAs substrate is described. A semi-lumped approach using microstrip transmission lines and metal-insulator-metal (MIM) capacitors is employed for the delay lines in order to both reduce circuit size as well as avoid the high insertion loss found in typical miniaturized designs. The 2-bit phase shifter achieved an average insertion loss of -0.70 dB at 9.45 GHz, and an associated phase accuracy of /spl plusmn/1.3/spl deg/. It occupies an area of only 5 mm/sup 2/, which is 44% the area of the smallest known X-band MEMS phase shifter . The phase shifter operates over 6-14 GHz with a return loss of better than -14 dB.

The application of photonic crystals to quasi-optic amplifiers

Quasi-optical spatial power combining provides the high combining efficiency required of solid-state power amplifiers for millimeter-wave frequencies. Photonic crystals (PXTs) are used to implement this type of power combining, as shown by two examples in this paper. The first example describes an all-dielectric structure that provides a carrier for the amplifier array chip satisfying the requirements concerning unilateral transmission and thermal management. The second example describes the use of a high impedance ground plane, based on PXTs, to make the power density incident on the array chip as uniform as possible in order to maximize power and efficiency.

MEMS true-time delay circuit for broadband antennas

A monolithic true-time delay (TTD) circuit based on metal-contact RF MEMS microrelays has been successfully fabricated and characterized. The TTD circuit was designed to produce flat delay time over a DC-to-40 GHz bandwidth with full 360-degree phase control at 22.5-degree intervals at 10.8 GHz. Measurements show a close match to the designed delay times for all sixteen delay states with 2.2 to 2.6 dB of insertion loss at 10 GHz. The worst group delay ripple in the DC-to-30 GHz range was 3 ps, well within the single bit delay time of 5.8 ps.