Theory and Application of Dielectric Rod Antennas and Arrays

Dielectric rods have been used for many years as waveguides and radiators. Their low loss as a transmission line and tendency to radiate at discontinuities have proven useful in applications ranging from fiber optic cables to naval fire control radar. Although this technology is well es- tablished, advances in additive manufacturing techniques and associated materials combined with the ubiquity of wireless communications and their shift to higher frequencies have generated re- newed interest in dielectric rods. Dielectric rod antennas have moderate gain and less conductive loss at higher frequencies. Similar to other surface wave antennas, they can achieve broadband performance.This work is the result of an effort to validate a concept for an array with greater than 20 dBi of gain for direct integration with a fully additive manufactured transmit/receive module at w-band. A literature review of high gain w-band antennas suited for this purpose reveals the dielectric rod antenna (DRA) as a suitable candidate. Further literature review examines the history and state of the art of DRAs as well as their underlying theory and accepted design procedures. The DRA field calculations here are generalized for a solid DRA surrounded by an infinite, generic medium. Rather than assume air in the outer medium, the calculations here keep the permittivity and permeability of the material outside the rod. A planar-fed DRA is designed by analogy to the canonical design for high gain surface wave antennas presented in The Antenna Engineering Handbook [1]. Unlike all but one planar-integrated DRA in the literature, this planar-fed DRA does not use hollow metallic waveguide for electrical or mechanical support. The DRA is fed by a coplanar waveguide (CPW) fed folded-dipole slot antenna. The DRA has a −10 dB impedance bandwidth of 22%, radiation efficiency about 95%, 26◦ 3 dB beamwidth, and a gain of 16.5 dBi at 15 GHz. Even though the final application of these designs is intended to be at w-band, Ku-band DRAs are developed for ease of fabrication and measurement while also validating the underlying principles involved in their design. A planar-fed, 2 x 2 square, four element DRA array with corporate feed is designed, simulated, fabricated, and measured using the single planar-fed design mentioned above. The fabricated array achieves a gain 19 dBi with a 3 dB gain bandwidth of 26%. The array is fabricated with 52 mm separation between elements with a radiation efficiency is 80%. The 4-element array is simple, cost-effective to fabricate, being made with standard PCB processes and 3D printed ABS plastic DRAs, and may be scaled into the mm-wave regime. The final array gain of 19 dBi at 15 GHz is just 1 dB under the desired gain of 20 dBi. Future iterations of this design may take advantage of cladding in the dielectric rod antennas to further customize the size, footprint, weight, and robustness of the array by printing high dielectric con- stant rods embedded in lower dielectric, 3D printed cladding. The generic field equations are applied to DRA design in order to explore the design of cladded DRAs and the effect of cladding on DRA size and performance. The results suggest that the use of cladding in this DRA array design should bring the gain over the 20 dBi threshold while also making it possible to reduce the size of the array. The canonical maximum gain surface wave design procedure generally used for DRA design is modified to account for outer materials other than air or vacuum