h

h = 0.225 λ

Hexagon perimeter = λ

Figure 4: A single helix winding. The hexagon perimeter equals wavelength. For center frequency of 1 THz, λ = 300

micron. Spacing h between turns is 0.225λ (67.50 micron) for optimal design.

As successive layers are stacked, the aggregate structure approximates a helical geometry. This geometry is modeled in

Remcom XFDTD to establish that the electrical behavior is that of a circular helix. Figure 5 depicts the THz antenna in

the XFDTD environment.

Figure 5: Antenna designed for 1 THz. Helix diameter is 95.49 micron, and total height (six turns) is 405 micron.

Ground plane in blue, with center-conductor rod extending ground.

As shown in the figure, a center ground rod is added to extend the ground plane through the structure, for enhanced

guiding and focusing of the field. Gain and spatial field plots for this geometry are presented with simulation results in

following sections.

2.4. Fabrication method

The THz antenna in figure 5 is fabricated in twelve layers, alternating the hexagonal trace layer with contact.

For 1 THz, the contact lead is set to a length of 67.50 micron to achieve the 0.225λ spacing in Kraus' design rule.

Fabrication of this structure may be implemented in several ways. One method follows a traditional manufacturing

sequence--metal deposition, patterning, etch, and film deposition. An alternative process is based on a sol-gel

technique. In this method, a hybrid organic-inorganic glass sol-gel is exposed with UV to combine organic polymers

with silica by way of polymer lithography [17]. The sol-gel is prepared with photoactive organic polymers containing

metallic inclusions for the formation of conductive traces. A second sol-gel of organic-inorganic glass compound forms

the substrate. The planar structure in figure 4 is inscribed into the material by exposure through a photomask. Exposure

and post-exposure bake produce polymerization in the exposed material to reproduce the photomask geometries.