antenna elements. The basic element is the parametric amplifier design from microwave devices--the familiar LC tank

circuit with resonant frequency f0 = 1 2π LC in figure 1.

···

Vin

Vout

f1 - f2

mf1 + nf2

f1+f2

f1

f2

·

R

·

···

L

C

+

+

f2

f1

V

V

·

-

-

···

(a)

(b)

Figure 1. Parametric amplifiers (a) Tank circuit (b) Manley-Rowe circuit

Because the tank circuit is a resonant device, it operates at center frequency f0 and rejects other frequencies. The driver

circuit is formed by a cascade of LC tank circuits. The front end operates at microwave frequencies and sources the

higher frequency cascades to obtain the THz input required to excite the active element. Connecting tanks in parallel is a

means to achieve frequency conversion [8, 9]. The Manley-Row cascade (MRC) in figure 1(b) consists of a number of

tank circuits in parallel to obtain multiples of the input frequency. In this manner a low frequency is up-converted to a

high frequency. The front end of the MRC is constructed with standard microwave components. Once conversion

extends beyond the limits of COTS components, the signal is coupled to an MRC of SRR elements which are fabricated

in decreasing geometries to achieve higher frequency operation. The SRR's are initially fabricated on a printed circuit

board then patterned on a silicon substrate once PCB dimensional limits are reached.

2.2. Split Ring Resonator

The split ring resonator in figure 2 is formed by concentric geometries fabricated by patterning and etching

metal on dielectric to produce another manifestation of the tank circuit. This geometry has been successfully exploited by

numerous THz workers and is notable for its high Q (e.g. thousands), wide fee spectral range (e.g. 6 THz), and

straightforward fabrication. The behavior of the SRR as a THz metamaterial has been characterized by numerous

researchers [10,11,12,13,14]. Frequencies in the neighborhood of 100 THz are reported from structures on the order of

micron to submicron that are fabricated through electron beam lithography. Frequencies in the range of 10's of THz are

generated by larger geometries and may be fabricated by standard optical lithography. Use of the SRR in the THz has

progressed to the point where design guidelines have been defined, notably in [14]. Marqués et al formulate the

geometry in terms of the dimensions and material parameters necessary to achieve the inductance and capacitance to

obtain a specific resonant frequency.

The circuitry of the SRR array in this paper is designed to synchronously distribute the input signal to each

element, so that array elements oscillate in-phase in order to achieve a high degree of partial coherence across the array.

Signal timing is achieved by sourcing and grounding each element with traces of near-identical impedance and length to

attain uniform delay throughout the array. To verify operation, Remcom XFDTD is used to simulate the device and

effects of variation in critical dimensions. The SRR and results are shown in figure 2.