Metasurfaces: From microwaves to visible

Reconfigurable antennas, with the ability to radiate more than one pattern at different frequencies and polarizations, are necessary in modern telecommunication systems. The requirements for increased functionality (e.g., direction finding, beam steering, radar, control, and command) within a confined volume place a greater burden on today's transmitting and receiving systems. Reconfigurable antennas are a solution to this problem. This paper discusses the different reconfigurable components that can be used in an antenna to modify its structure and function. These reconfiguration techniques are either based on the integration of radio-frequency microelectromechanical systems (RF-MEMS), PIN diodes, varactors, photoconductive elements, or on the physical alteration of the antenna radiating structure, or on the use of smart materials such as ferrites and liquid crystals. Various activation mechanisms that can be used in each different reconfigurable implementation to achieve optimum performance are presented and discussed. Several examples of reconfigurable antennas for both terrestrial and space applications are highlighted, such as cognitive radio, multiple-input-multiple-output (MIMO) systems, and satellite communication.

Reconfigurable Antennas for Wireless and Space Applications

This survey deals with 1/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an /spl alpha/ value with a magnitude in the order of 10/sup -4/. Damaging the crystal has a strong influence on /spl alpha/, /spl alpha/ may increase by orders of magnitude. Some theoretical models are briefly discussed none of them can explain all experimental results. The /spl alpha/ values of several semiconductors are given. These values can be used in calculations of 1/f noise in devices. >

1/f Noise Sources

Many applications, including laser (LIDAR) mapping, free-space optical communications, and spatially resolved optical sensors, demand compact, robust solutions to steering an optical beam. Fine target addressability (high steering resolution) in these systems requires simultaneously achieving a wide steering angle and a small beam divergence, but this is difficult due to the fundamental trade-offs between resolution and steering range. So far, to our knowledge, chip-based two-axis optical phased arrays have achieved a resolution of no more than 23 resolvable spots in the phased-array axis. Here we report, using non-uniform emitter spacing on a large-scale emitter array, a dramatically higher-performance two-axis steerable optical phased array fabricated in a 300 mm CMOS facility with over 500 resolvable spots and 80° steering in the phased-array axis (measurement limited) and a record small divergence in both axes (0.14°). Including the demonstrated steering range in the other (wavelength-controlled) axis, this amounts to two-dimensional beam steering to more than 60,000 resolvable points.

High-resolution aliasing-free optical beam steering

소형 안테나 ( Small Antennas )

Single-and dual-polarized slot-ring antennas with wideband tuning using varactor diodes have been demonstrated. The single-polarized antenna tunes from 0.95 to 1.8 GHz with better than -13 dB return loss. Both polarizations of the dual-polarized antenna tune from 0.93 to 1.6 GHz independently with better than -10 dB return loss and > 20 dB port-to-port isolation over most of the tuning range. The capacitance of the varactor diodes varies from 0.45 to 2.5 pF, and the antennas are printed on 70times70 times0.787 mm3 substrates with epsivr = 2.2. The dual-polarized slot-ring antenna can either be made both frequency- and polarization-agile simultaneously, or can operate at two independent frequencies on two orthogonal polarizations. To our knowledge, this is the first dual-polarized tunable antenna with independent control of both polarizations over a 1.7:1 frequency range.

Single- and Dual-Polarized Tunable Slot-Ring Antennas

Non-Foster matching promises to improve the performance of electrically small antennas by tens of decibels over a decade of bandwidth, but only a few successful demonstrations have been reported in the literature. A 15-cm monopole antenna has been matched using a variable negative capacitance based on Linvill's balanced negative impedance converter. The realized gain is improved by >;10 dB relative to the unmatched case over 30-200 MHz. This letter reports the design, simulation, and measurement data and gives an equivalent circuit that can be used to synthesize future designs.

A Non-Foster VHF Monopole Antenna

A floating variable Negative Impedance Inverter (NIl) circuit is proposed that is derived from Linvill's unbalanced negative impedance converter. A negative-inductance Integrated Circuit (IC) has been realized using the IBM 8 HP BiCMOS process with an inductance that tunes from -64 to -40 nH. The IC is short-circuit-stable (which has been verified by experiment) and is dc coupled at the terminals, making it directly applicable to susceptance cancellation for slot antennas and artificial magnetic conductors. This letter reports the circuit topology, measurement technique, and measured data.

A Variable Negative-Inductance Integrated Circuit at UHF Frequencies

We examine how the bandwidth of artificial magnetic conductors (AMCs) can be greatly increased when loaded with negative-inductance non-Foster circuits. This increase in bandwidth is achieved by enhancing the structural inductance of the AMC by combining it in parallel with a negative inductance, thus achieving a bandwidth that exceeds what is possible with passive approaches. A prototype VHF-UHF active AMC was fabricated and measured, which achieved a bandwidth greater than 80% at a resonant frequency of 263 MHz.

Wideband Artificial Magnetic Conductors Loaded With Non-Foster Negative Inductors

We examine how the bandwidth of artificial magnetic conductors (AMC) can be greatly increased when loaded with negative-inductance Non-Foster circuits. This increase in bandwidth is achieved by enhancing the structural inductance of the AMC by combining it in parallel with a negative inductance, thus achieving a bandwidth that exceeds what is possible with passive approaches. A prototype VHF-UHF active AMC was fabricated and measured which achieved a bandwidth greater than 80% at resonant frequency of 263 MHz.

Carson R. White

Papers

Single- and Dual-Polarized Tunable Slot-Ring Antennas

A Non-Foster VHF Monopole Antenna

A Variable Negative-Inductance Integrated Circuit at UHF Frequencies

Wideband Artificial Magnetic Conductors Loaded With Non-Foster Negative Inductors

Wideband artificial magnetic conductors loaded with Non-Foster negative inductors