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ICEAA 2013
LENS ANTENNA Based on Fresnel Zone Lens of Flat Dielectric Rings Conformal to Conical Surface
H. D. Hristov1, J. M. Rodriguez1*, J. R. Urumov2, and L. P. Kamburov2
1Departamento de Electrónica, Universidad Técnica Federico Santa María, Av. España 1680, Valparaíso, Chile,
2Department of Communication Technique and Technologies, Technical
University of Varna, Varna, 9010, Bulgaria,

2.
ICEAA 2013
I. Introduction
Dielectric lenses/lens antennas are key devices in many millimeter and terahertz systems
Under some size limitations, like the constant aperture size, achieving superior antenna parameters is a very important and challenging task.
The lens antenna with diffraction curvilinear (3D) Fresnel zone (FZ) lens (like the recently proposed cone-shape flat-ring FZ lens, marked as CFZf.α.ν), can be much lighter, and cost-effective antenna compared to the same aperture-size antenna with an ordinary refraction lens or 2D FZP lens.
Low-THz CFZ flat-ring lens antenna with a 229-GHz CFZf.6.75 lens is studied here by use of CST computer-simulation

3. II. Cone Fresnel Zone Lens Focusing II.1 Flat-ring lens design
ICEAA 2013
II. Cone Fresnel Zone Lens Focusing II.1 Flat-ring lens design
Lens consists of half-wave (phase-reversal) flat dielectric rings conformal to a conical surface. A plane wave is illuminating normally the rings.

4. II.2 Difractive cone-ring & flat-ring FZ lenses
ICEAA 2013
II.2 Difractive cone-ring & flat-ring FZ lenses
(a) (b) (c) (d)
In lens CFZc.3.45 (a), the conical rings and conical surface have the same semi-opening angle α=45deg. In all other lenses (cases (b)-(d)) the flat-ring lenses are illuminated normally, while the surface opening semi-angle α varies: for lens CFZf.3.45 α=45deg (b), for lens CFZf.5.30 α=30deg (c), and for lens FZP α=90deg (d).

5. II.3 Constructional note
ICEAA 2013
II.3 Constructional note
For a constant aperture size the main CFZ lens drawback is its increased axial length. But as it is seen from the volume contrast below between the FZP (a) and CFZ (b) lens antennas, the lens configuration does not affect the lens antenna encased volume, which also includes the antenna feed.
(a) (b)

6. II.3 Lens/antenna design data
ICEAA 2013
II.3 Lens/antenna design data
In this work 3 antenna lens configurations with F/D=0.7 are designed for:
frequency f0 =229 GHz (wavelength λ0=1.31mm)
focal length F=30 mm
lens diameter D =42.6 mm.
The dielectric used for each lens is polyethylene with a relative permittivity eps=2.25 and loss tangent=
The lenses are illuminated by an open waveguide (OWG) feed, which radiation pattern is shown in some of the slides below.
The same OWG feed, has been in used for illumination of each of the three studied lenses: cone flat-ring FZ lens, plane FZP lens and ordinary plane-hyperbolic lens.

7. II.4 Lens focusing: numerical results
ICEAA 2013
II.4 Lens focusing: numerical results
CFZf.6.75 PH
Axial lens field distribution for: CFZf.6.75 lens (left) and PH lens (right).
Observation: CFZf.6.75 lens has notoriously better axial resolution, which is due to the specific conical disposition of the phase-shifting rings leading to a reduced axial spherical lens aberration, compared to PH lens. PH

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ICEAA 2013
Focusing field distribution in the transverse focal plane of CFZf.6.75 and PH lenses illuminated by plane wave
CFZf PH
Table I
Lens focusing gain GF (dB), transverse (ΔX/λ & ΔY/λ),
and axial ΔZ/λ resolutions (in wavelengths)
(dB)
Lenses
GF (dB)
ΔX/λ
ΔY/λ
ΔZ/λ
FZP lens
25.4
0.85
0.89
4.31
CFZ.6.75 lens
26.7
0.74
0.79
3.14
PH lens
27.3
1.03
6.18

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ICEAA 2013
III. Lens Antenna with Cone Fresnel Zone Lens III.1 Antenna consisting of CFZf.6.75 lens and OWG feed
Lens antenna configuration (left), OWG feed radiation patterns: E-, H-, and 45-deg plane co-polar patterns, and 45-deg cross-polar pattern (middle), and near-field distribution of the lens antenna (right);

10. III.1 CFZf.6.75-lens antenna radiations patterns
ICEAA 2013
III.1 CFZf.6.75-lens antenna radiations patterns
(left) Radiation patterns of CFZf.6.75-lens antenna
(right) Radiation patterns of PH-lens antenna
E- and H-plane co-polar patterns, and 45-deg cross-polar pattern

11. Table II Radiation parameters of lens antennas
ICEAA 2013
Table II Radiation parameters of lens antennas
Lens antennas GA
(dB)
HPBW
(deg) SL XP
FZP
30.7
1.85
-20.5
-37.0
CFZf.6.75
32.0
-19.8
-33.1
 PH
32.6
1.95
-22.6
-30.3
Observations:
CFZ.f and PH- lens antennas feature c comparable gains and beamwidths;
CFZ.f.6.75-lens antenna is superior by about 3dB in maximum cross-polar level but inferior by 1.8dB in maximum sidelobe level compared to PH-lens antenna

12. III.2 Frequency bandwidth of lens antennas
ICEAA 2013
III.2 Frequency bandwidth of lens antennas PH
CFZ.6.75
FZP
CFZ.6.75-lens antenna has a -3 dB bandwidth of 35 GHz, or about 15% relative to the design frequency. In contrast, the PH-lens antenna bandwidth is much less-around 80%;
The focal spot location of the FZ lenses is highly frequency dependent, and the corresponding lens antennas are narrowband.

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ICEAA 2013
Conclusion
Near to design frequency of 229GHz, the novel mm-wave lens antenna based on the cone-shape lens CFZ.6.75 is similar in gain and radiation pattern in a much narrower frequency band compared to the PH lens antenna of same aperture diameter and focal length.
On the other hand, the flat-ring dielectric CFZ lens/antenna construction is much lighter and has significant structural and technological advantages, especially at the microwave frequencies.
The CFZ-type lens can be easily fabricated from microwave to THz and optical frequency bands as a multilayer package of flat dielectric or metal rings embedded in a low-permittivity solid, fluid or air space.

14. Remark: Current Experimental Work at UTFSM
ICEAA 2013
Remark: Current Experimental Work at UTFSM
We just started experimental work on a lens focusing in the low
THz band ( GHz). The initial results show a good match
between the theoretical and numerical focusing data.
Experimental setup CFZ.3.45 Lens
(Radiometer-Physics + Thorlabs) Prototype

15. THANKS FOR YOUR ATTENTION!
ICEAA 2013
THANKS FOR YOUR ATTENTION!