Joshua W. Shehan

Measurement of a CMOS negative inductor for wideband non-foster metamaterials

There is increasing interest in impedance-matching methods that use non-Foster circuits to provide wideband operation in a variety of microwave devices such as antennas and metamaterials. In addition, many of these prior non-Foster circuits employ bipolar negative impedance converter designs, and it is advantageous to move such designs into CMOS. Therefore, the present work provides new measured results building upon an earlier proposed design of a negative inductor in a 0.5 micron CMOS process. The proposed circuit eliminates a resistor from a common negative impedance converter topology, and the prototype performs well at high frequency. Measured results show a low-frequency inductance of -95 nH falling to -85 nH at 750 MHz and -63 nH at 1 GHz. Finally, simulation results are presented for the performance of the circuit in a metamaterial application.

A DC-coupled negative inductance circuit with integrated bias

Negative inductance circuits offer the potential for increased bandwidth in a variety of applications such as artificial magnetic conductors and metamaterials with negative permeability. To address such applications, a CMOS dc-coupled negative inductance circuit with integrated presented. The dc-coupled input is tailored voltages and accommodate applications having an inductive load in series with a low resistance. An integrated bias circuit is used to allow operation with a single power supply and to eliminate the need for a separate input bias. In addition, the parasitic capacitance of the CMOS transistors in the basic negative impedance inverter is used to set the negative inductance of the overall circuit. Results are presented that show a negative inductance of -11 0 nH in a 0.5 micron CMOS process.

Comparison of CMOS current conveyor circuits for non-Foster applications

Current conveyors are an important component implementing non-Foster circuits such as negative capacitors negative resistors. However, different topologies exist for implementing negative capacitance using a current conveyor, and the performance of such topologies can vary greatly. Therefore, this paper considers two competing realizations of negative capacitance using a current conveyor, where both circuits are designed for -5 pF in a 0.5 micron CMOS process. Simulation results are presented that show significant bandwidth differences for the two -5 pF designs, where one approach has more than twice the bandwidth of the second approach.

Metamaterial measurement in a cylindrical coaxial fixture with consideration for inter-element coupling

Summary form given only: A great deal of research has been dedicated to the design and synthesis of metamaterials to acheive interesting electromagnetic properties such as very high, sub-unity, and even negative effective relative permeabilities and permittivities. While the design and fabrication of various metamaterial structures can be a challenge, it can be equally demanding in some cases to make accurate measurements that properly characterize the metamaterial. It has been shown that coaxial measurements of metamaterial structures can provide appealing advantages over other approaches although in some cases, it may be necessary to modify the metamaterial depending on its structure or mode of excitation. Fortunately, for planar metamaterials designed to operate under approximately TEM wave excitation, a coaxial cell can work quite nicely. It has, however, been discussed that inter-element coupling along with coupling to the waveguide walls can cause discrepancies between the behavior of the metamaterial in a waveguide and its behavior in an intended application. The Lagrangian formalism for metamaterials has been used extensively in recent years to describe the coupling effects between resonant metamaterial structures and predict the shift of the resonant frequency in the presence of coupling. The Lagrangian formulation is modified here and used to describe the coupling effects of metamaterials near curved conductors such as in the coaxial case. Thus we are able to account for the coupling effects due the curved waveguide walls and predict the shift in the resonant frequency between measurements in a coaxial fixture and other scenarios, such as free space for example. To measure metamaterial parameters, a coaxial fixture along with a complete TRL fabrication kit was fabricated with 3d printing technology. The fixture was made of solid ABS plastic with an inner radius of a = 3.175mm, an outer radius of b = 26.675mm, a dielectric constant of Er ≈ 3 and a loss tangent of tan δ ≈ 0.05 at 1.5 GHz. To transition from the 50Ω SMA measurement cables to the fixture with a characteristic impedance of approximately Z0 ≈ 76Ω, tapered clam-shell transition sections were used. Through measurements of the unloaded fixture, it was apparent that higher order modes began to propagate at approximately 1.5 GHz indicating the limit of the useful bandwidth. To validate the fixture, a metamaterial sample composed of a set of 3 split ring resonators were measured. After calibration, measured data matched very well with simulated data from HFSS with ideal waveports.

A cross-coupled cmos negative capacitor for wideband metamaterial applications

Non-Foster circuits can be used to provide broadband impedance matching for antennas and metamaterials. These circuits allow effective matching over a much wider bandwidth than is expected from traditional passive components. Therefore, this paper considers the design and test of a negative capacitor in a 0.5 micron CMOS process. The proposed circuit uses a cross-coupled design to allow for floating operation, and the designs simulated performance works well at high frequency. Measured results show a low-frequency capacitance of -1.7 pF and within 10% to 200 MHz, and falling to -4 pF at 230 MHz. Although the selected CMOS process is adequate to demonstrate the basic design approach, more advanced process nodes would be expected to extend performance to even higher frequencies. Results are also presented showing performance of the circuit in a metamaterial.

Measurement and simulation of a CMOS current conveyor negative capacitor for metamaterials

Current conveyors can be used as building blocks for implementing non-Foster circuits such as negative capacitors and negative inductors that are useful in extending bandwidth in metamaterials. In the present paper, measured results are presented for a prototype integrated circuit current conveyor negative capacitor. This circuit has been fabricated in a 0.5 micron CMOS process following previous results. Although CMOS is a desirable technology for circuit implementation, it is accompanied by design challenges of associated parasitic resistance. To investigate these issues, a prototype second generation current conveyor (CCII) is designed and tested in a negative capacitance circuit. In addition, full-wave electromagnetic simulation results are also presented showing the effects of observed resistance on overall metamaterial performance.

Capacitance and bandwidth tradeoffs in a cross-coupled CMOS negative capacitor

Recent advances in technology have driven renewed interest in the design of CMOS negative capacitance circuits for diverse applications such as wideband metamaterials and radio frequency integrated circuits. In practice, the particular CMOS fabrication process generally limits the practical range of capacitance values and bandwidths that can be achieved. In addition, the reactive component of the desired impedance is often accompanied by a parasitic resistive component. To address these issues, a CMOS cross-coupled negative capacitance circuit is designed and simulated in a 0.5 micron CMOS process. Results are presented for -5 pF, -10 pF, and -20 pF designs with ten-percent bandwidths of approximately 140 MHz, 100 MHz, and 80 MHz respectively.

Permeability and permittivity extraction issues for non-Foster and active metamaterials

Although a variety of methods have been proposed for the extraction of effective permittivity and permeability of metamaterials, certain underlying passivity constraints and assumptions would not be suitable for non-Foster metamaterials that incorporate active devices and power sources. Moreover, recent arguments suggest that a common passivity constraint in extraction methods does not resolve solution branch ambiguities. To address these issues, the fundamental principles of parameter extraction are revisited for the case of active materials where passivity cannot be assumed. The analysis follows along the lines of Nicolson-Ross-Weir approaches, where parameters are extracted from measured two-port S-parameters. It is shown that a convergence constraint for active materials requires that the magnitude of the product of the transmission coefficient and reflection coefficient must be less than unity. This allows metamaterials with gain, and simulation results are provided for a slab of active material that exhibits gain and satisfies the constraint.

Sleeve monopole antenna with integrated filter for base station applications

The sleeve monopole antenna with an integrated broadband filter is presented for base station applications. The antenna is designed to radiate from 698–960 MHz (low band) and provide band rejection from 1695–2690 MHz (high band). The antenna exhibits return loss better than −15 dB in the low band. The filter exhibits excellent rejection where the worst-case return loss is approximately −0.3 dB in the high band. The filter also reduces peak gain by as much as 50 dBi in the high band.

Dual band, dual polarized, rail mount MIMO stadium antenna

This paper presents a dual band, dual polarized rail mount MIMO antenna designed to provide mobile wireless coverage in the stadium environment. The high band (1695–2690 MHz) antenna is a dual polarized vertical printed dipole array with dual slant linear polarization. The low band (698–960 MHz) elements are vertically and horizontally polarized omnidirectional sleeve monopole antennas.