Carson R. White

Single- and Dual-Polarized Tunable Slot-Ring 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.

A Variable Negative-Inductance Integrated Circuit at UHF Frequencies

A floating variable Negative Impedance Inverter (NIl) circuit is proposed that is derived from Linvills 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.

Wideband Artificial Magnetic Conductors Loaded With Non-Foster Negative Inductors

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.

A Non-Foster VHF Monopole Antenna

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 Linvills 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.

Stability Analysis of Superluminal Waveguides Periodically Loaded With Non-Foster Circuits

Transmission lines periodically loaded with non-Foster circuits have been shown to have superluminal propagation in the prior literature. They were proposed for applications such as broadband leaky-wave antennas and true-time-delay lines for series feeds of antenna arrays. This letter presents results of an investigation on superluminal waveguides with periodic non-Foster loads. Such waveguides are found to be stable for small line lengths, but have stability problems for practical line lengths containing many unit cells.

A Coaxial TEM Cell for Direct Measurement of UHF Artificial Magnetic Conductors [AMTA Corner]

We have demonstrated a coaxial TEM (transverse electromagnetic wave) cell for direct measurement of artificial magnetic conductors (AMCs) in the VHF-UHF range. The advantages of the coaxial TEM cell are 1) it is a compact, bench-top device; and 2) it provides rapid, direct measurement of artificial-magnetic-conductor reflection response over a broad frequency range. We present measurements of various artificial-magnetic-conductor structures measured in the coaxial TEM cell, including 1) fixed-response, capacitor-loaded artificial magnetic conductors; 2) tunable varactor-loaded artificial magnetic conductors; and 3) wideband, tunable artificial magnetic conductors loaded with non-Foster, negative-inductance circuits. The measurements of the various artificial magnetic conductors were consistent with simulations. The coaxial TEM cell detailed here was 50 cm long with a 10.4 in diameter at the DUT, tapering to an N connector at the feed port. It was single-moded below 500 MHz. The design can be scaled to extend to other frequencies and other artificial-magnetic-conductor geometries.

Two-dimensional pseudo-random optical phased array based on tandem optical injection locking of vertical cavity surface emitting lasers.

We demonstrate, both theoretically and experimentally, a pseudo-random, two-dimensional optical phased array (OPA) concept based on tandem injection locking of 64-element vertical cavity surface emitting laser (VCSEL) arrays. A low cavity-Q VCSEL design resulted in an injection locking optical power of less than 1 μW per VCSEL, providing large OPA scaling potential. Tandem injection locking of two VCSEL arrays resulted in measured controllable optical phase change of 0-1.6π. A high quality beam formed with suppressed grating lobes due to the pseudo-random array design was demonstrated with performance close to simulated results. A preliminary 2.2° x 1.2° beam steering example using the tandem arrays was also demonstrated.

Non-Foster Circuit Adaptation for Stable Broadband Operation

A non-Foster circuit adaptation algorithm has been developed and demonstrated in a printed circuit board by using commercial off-the-shelf components. This algorithm enables adaptive stabilization of non-Foster circuits (NFCs) to achieve broadband operation, such as matching of electrically small receive antennas, hence avoiding potential oscillation and undesirable signal emission. The demonstrated system has been fabricated in a 6.4 ×8.9 cm2 4 layer FR4 PCB. Together with a fabricated NFC board, it achieves stable wideband matching for a 15 cm long monopole antenna under different environment conditions, such as an additional loading of a Cu metallic sheet in a proximate location to the antenna. The demonstration indicates the effectiveness of the proposed NFC adaptation algorithm and paves the way for broad applications of NFCs without stability concerns.

Wideband artificial magnetic conductors loaded with Non-Foster negative inductors

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.

A non-foster monopole array

Antenna arrays enable beamforming and multiple-input multiple output (MIMO) communication schemes, but performance suffers as the element size and spacing is reduced. A non-Foster matching network for an electrically-small 2-element monopole array is proposed to overcome the performance limitations of passive matching. Full-wave simulation and stability analysis show that the proposed network is stable and the reactance of both the even and odd modes can be cancelled simultaneously over a wide bandwidth using ideal negative capacitors and negative resistors.