Design of Dielectric Lens Loaded Double Ridged Horn Antenna for Millimetre Wave Application

Salih Demirel, Alper Çalışkan, Mücahid T. Mersin Department of Electronics and Communication Engineering

Yıldız Technical University Istanbul, Turkey

salihd@yildiz.edu.tr, acaliskan@yildiz.edu.tr, taha.mersin@gmail.com

Ahmet S. Türk, Mehmet A. Belen, Peyman Mahouti Department of Electronics and Communication Engineering

Yıldız Technical University Istanbul, Turkey

asturk@yildiz.edu.tr, mbelen@yildiz.edu.tr, pmahouti@gmail.com

Abstract— In this paper, designs of Dielectric Lens Loaded Double Ridged Horn Antenna for Millimetre Wave Applications is investigated. Firstly a double ridged horn antenna is designed and simulated in CST environment. After that, 2 dielectric lens architecture are designed and placed at the aperture of the antenna. It is seen that by placing spherical shaped dielectric lens, it is possible to achieve improvement in return loss and far-field gain of the antennas design in a 20-40 GHz bandwidth.

Keywords—dielectric loaded antenna, millimetre band, ridged horn antenna

I. INTRODUCTION

Horn antennas are widely used in many fields, such as electromagnetic compatibility testing, standard gain testing, satellite tracking systems, launching feeds, radars, etc. [1-4]. The reasons of popularity of horn antennas in these applications are can be named as: easy feeding, relatively simple construction, high gain and excellent peak power handling capability [5-9]. In order to increase the maximum practical bandwidth of horns, ridges are introduced in the flared part of the antenna. This is commonly done in waveguides to decrease the cut-off frequency of the dominant propagating mode (TE10) and thus expands the single-mode range before higher order [10]. Although Horn and Ridged horn antennas have the mentioned advantages, these structures have a disadvantages for their own. Radiation pattern distortion increases in the high frequency band in conventional ridged horn antennas, caused by greater phase error at the antenna aperture when the frequency gets higher. To over-come the problem, according to [11-14] dielectric lens loading is investigated in this, work. By adding dielectric lens at the aperture of the antenna design it is aimed to make improvements in the return loss and far field gain performance of the antenna design. In the next section a brief explanation about the antenna and lens designs are explained with detailed layout information’s. In section III, simulation results of all antenna design are studied. And finally the paper ends with conclusion section.

II. DESIGN OF ANTENNA AND DIELECTRIC LENSES

In order to be operational in mm Wave bands, the Cavity back gap of the Double Ridged Horn Antenna is optimized via trial and error. . In order to have a fine simulation model the 50 ohm port of the design is also modelled. Diameter of the connector is modelled based on a standard K-type connectors. Square cavity back dimensions has been optimized for reducing reflections. The layout of the antenna and lens structures are given in Fig. 1. For performance improvement of the DRHA two dielectric lens structures, a square shape and a spherical shaped dielectric lens structures is proposed and modelled in CST microwave environment. The course values of design parameters are obtained via trial and error, then Trust Region algorithm of CST suit is used to obtain optimal value for antenna and lens designs. The material of the lens designs are Teflon (PTFE) with permittivity ε = 2.1. For a better impedance matching, the upper sides of the spherical lens are cut away. Thus, the proposed spherical shape provides a preferable main lobe focusing at the propagation direction.

978-1-5090-2214-4/16/$31.00 ©2016 IEEE

Fig. 1. Layout of the antenna and lenses.

In the next section three simulation cases are taking into the account for studying the effect of dielectric lenses for the designed DRHA. First case is the sole DRHA which is simulated to obtain a reference point for benchmarking purposes. Second case, is the antenna model with square shaped dielectric structures and the third case is the antenna model with spherical dielectric lens structure. There are no changes in the height and width of the antenna design after the placement of dielectric lenses, only in case 3, after the placement the total lengths of the design is increased with 50 mm.

(a) (b)

(c)

Fig. 2. 3D view of the (a) Case 1, (b) Case 2, (c) Case3.

III. SIMULATION RESULTS

In this section, the simulated return loss and far field gain results belong to the mentioned cases are presented. In Fig. 3, the simulation result of return loss is given where one can see that by placing the spherical shaped dielectric lens to the aperture of antenna design a significant improvement to return loss had been achieved for lower and middle band, 20-24 GHz, 28-33 GHz, of the design.

Fig. 3. Simulated return loss.

Fig. 4 gives the simulated maximum far field gain of the cases, as it seen with the placement of the dielectric lenses to the antenna the maximum gain performance have been enhanced significantly over the whole bandwidth especially the performance of the spherical lens design is salient compare to the performance of the square shaped design. Similarly the same improvement can be seen if Figs. 5, where the simulated radiation pattern of the antenna is given. The proposed method increases the gain at main beam direction and decreases the half power beam widths 17-21 degrees.

Fig. 4. Simulated maximum gain over frequency bandwidth.

(a)

(b)

(c)

(d)

(e)

Fig. 5. Simulated H-plane radiation pattern at (a) 20 GHz, (b) 25 GHz, (c) 30 GHz, (d) 35 GHz, (e) 40 GHz..

IV. CONCLUSION

In this work, Design of Dielectric Lens loaded Double Ridged Horn Antenna for Millimetre Wave Applications is presented. Radiation pattern is the key issue on the design. It has a superior pattern behaviour than the traditional DRHA. As it seen from simulation results by placing a properly designed dielectric lens to the aperture of the antenna it is possible to enhance the performance of the antenna design. Especially by adding a spherical shaped dielectric lens to the aperture of the DRHA a gain enhancement of 4.5-6 dB over the 20-40GHz frequency bandwidth is obtained. In future works, it is possible to achieve higher enhancement by using more complex structures such Meta-material, or frequency selective surface based dielectric lens structures.

ACKNOWLEDGMENT

We would like to express our special thanks of gratitude to the Scientific and Technological Research Council of Turkey (TÜBİTAK) for founding our researches under project number

of 114E241 “Millimeter Wave Short Range Active and Passive Sensors for Intelligent Alarm Systems”.

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