380 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 5, 2006 Innovative High-Gain Corrugated Horn Antenna Combining Horizontal and Vertical Corrugations Jorge Teniente, Ramón Gonzalo, Member, IEEE, and Carlos del-Río, Member, IEEE Abstract—An innovative kind of corrugated horn antenna is proposed within this letter, the profile of the horn is based on the combination of horizontal and vertical corrugations. The main advantage of these profiles is the possibility of combining high-gain with short profiles, meanwhile keeping the main performances of the conventional corrugated horns. Besides, this horn results in an easier manufacture process due to their smaller size and elim2 corrugations inates the difficulties to manufacture the deep at the throat of classical profiles. An example of a horn with 24 dB gain, 35 dB maximum crosspolar, and sidelobe levels and 20% bandwidth has been designed, fabricated and characterized. These horns are a very promising alternative for future earth and space applications. Index Terms—Compact size, corrugated horn antennas, Gaussian profiles, horizontal and vertical corrugations. I. INTRODUCTION E XTREMELY low sidelobe horn antennas are often required for many current applications. This type of horn antennas are really important nowadays to avoid interference with other communication systems. The innovative concept consisting on attaching a short choked antenna (horizontal corrugations) to minimize the length at the initial part of the horn together with a vertically corrugated profile to improve the performance is proposed in this letter. Horn antennas that combine horizontal and vertical corrugations were firstly developed four years ago as choked-gaussian antennas with the main goal of achieving very high performances for stringent applications in a very compact antenna. This type of corrugated horn is easier to manufacture than normal corrugated profiles because they avoid deep throat vertical corrugations necessary in usual corrugated horns. An international patent was issued  and commercial exploitation of the idea is now available. Corrugated horns have always offered very broad bandwidth, low crosspolar levels, low sidelobe levels and low return loss making them a very attractive solution for many applications. Over the last few years, the use of optimization simulating tools has become a revolution in the design of compact corrugated horns –. Actually, due to the high development of the optimization tools, the corrugated horns are usually no longer defined by means of a previously predetermined profile, and typi- Manuscript received June 2, 2006; revised July 7, 2006. The authors are with the Antenna Group, Electric and Electronic Engineering Department, Public University of Navarra, Campus de Arrosad́ia, E-31006 Pamplona, Navarra, Spain (e-mail: jorge.tenienteunavarra.es; [email protected]s; [email protected]). Digital Object Identifier 10.1109/LAWP.2006.881919 cally the optimization focuses on inner and outer radius of each corrugation as variables in the design process. However, the overall size of the corrugated horn antennas is becoming the real key issue. In the past, corrugated horns were usually defined by conical profiles. Conventional conical profiles were huge when a horn with narrow beamwidth had to be designed (gain above 20 dB) because they led to narrow flare angles and large apertures, resulting in very long profiles, heavy, difficult to manufacture and expensive; see Fig. 1(a). Olver et al. – proposed several profiles to reduce the length of corrugated horn antennas and have used optimization methods in them to reduce the excitation of higher order modes with certain success; especially they have focused in the reduction of HE and EH modes and maximization of HE mode content at the aperture. However, HE is a mode that naturally couples in a corrugated horn. In fact, as it was said in , HE mode doesn’t contribute to crosspolar level and if its phase is carefully controlled, contributes to improve main beam radiation pattern and reduce sidelobe level. Advanced technology designs should control the excitation of HE and reduce EH modes to improve antenna performances. When a comparison between conical and new profiles –,  is stated, see Fig. 1(a), it can be concluded that nowadays, the length of corrugated horn antennas has reduced a lot compared to old conical profiles. This length reduction opens the design possibilities to higher gain with a reasonable size. In these advanced profiles of corrugated horn antennas –, , the output diameter size remains unchanged, although its width defines the sidelobe level of the radiation pattern, see Fig. 1(b). If required, prototypes with radiation dB or even lower pattern that presents sidelobe level below can be made available. In such low sidelobe level designs, the HE mode has significant amplitude at the aperture, at least comparable to the HE mode . It is also important to remark that size of these new technology corrugated horns is usually determined by the frequency bandwidth. A narrow bandwidth specification can always be designed with a shorter and narrower aperture prototype, while wide bandwidth requirements impose longer and wider profiles. Bandwidth is usually a question of smoother profiles. In Fig. 1, approximate pessimistic size values are given for a 20% bandwidth. The design objectives for the corrugated horn antenna presented in this letter have been selected as typical parameters of corrugated horns for space and earth applications, i.e., downlinks of DBS applications. No comparisons of performances of this design with other advanced designs have been included be- 1536-1225/$20.00 © 2006 IEEE Authorized licensed use limited to: Universitas Indonesia. Downloaded on February 20,2020 at 03:49:43 UTC from IEEE Xplore. Restrictions apply. TENIENTE et al.: INNOVATIVE HIGH-GAIN CORRUGATED HORN ANTENNA 381 or chokes , see Fig. 2(a). This change has several advantages, the first one is an easier manufacturing process because usually ) and difficult throat vertical corrugations are deep (around to machine. Other advantages are a reduction of length maintaining wide bandwidth and a better return loss response because the horizontal corrugations at the throat region are less likely than the vertical corrugations to produce resonances that lead to unwanted return loss spikes. It is important to remark at this point that the rest of radiation parameters that exhibit the usual corrugated horns; circularly symmetric copolar pattern, bandwidth, low crosspolar levels and low sidelobe level remain unchanged in this technology. II. DESIGN AND RESULTS Fig. 1. Size of new technology corrugated horn antennas versus directivity. (a) Length (L). (b) Output aperture diameter (D ). cause at the present moment no other author has presented any high-gain corrugated horn based on other technologies rather than conical technology described in . For that case, the horn length would be above 20 , see Fig. 1, which at 10 GHz leads to a heavy and huge horn above 60-cm long. So, conventional solutions to achieve these high-gain antennas have made use of a reflector antenna or a lens horn antenna to overcome these limitations in microwave bands. On the other hand, for higher frequencies, (mm and sub-mm bands), corrugated horns with a gain above 26 dB have usually been designed to avoid the complexity of reflectors at this short wavelengths. In this case, the size as frequency increases is not the real problem; the problem usually is the increased manufacture complexity. This problem would be also reduced by the use of the proposed antenna configuration. The main difference between the corrugated horn profiles proposed in this letter and the advanced ones proposed by the rest of authors is in the throat region and consists in the substitution of the throat vertical corrugations, which are usually deeper to match the incident mode, with horizontal corrugations To demonstrate the main properties of this innovative type of horn profile, a corrugated horn antenna with 24 dB gain has been designed, manufactured and measured. The design objectives were to obtain in at least a 20% bandwidth a design with dB, crosspolar kevel below a return loss lower than dB, sidelobe level below dB, and 24 dB gain at central frequency. The Mician Wave Wizard software package was used for simulation purposes. This software is an optimization (EM) CAD tool for passive waveguide components and antennas, and uses mode-matching techniques. As it can be seen in Fig. 2(a) and (b), the designed 24 dB gain corrugated horn meets the specification with a size of 10.5 long and 8.7 wide (the aperture width is given for overall aperture diameter, including last corrugation depth and metal thickness, usually other authors give this value for inner diameter so the number we give is usually between 0.4 and bigger and depends on last corrugation depth). Besides, in a 10% bandwidth the specifications are ever better, the sidelobe/shoulder dB and the crosspolar level well below level is around dB. This design was manufactured by a conventional milling machine at a central frequency of 10 GHz and measured in a far field range anechoic chamber. Measurements show excellent agreement, see Fig. 3, in spite of fabrication inaccuracies that destroyed two corrugations in the flare region, (milling machine made a bite during the manufacturing process), see Fig. 4. The error in the machining process was probably the reason of a measured crosspolar level slightly higher than expected, but still close to the specifications. As it is said in , a perfectly constructed special purpose corrugated horn, when measured in a very high performance anechoic chamber, gives exact agreedB. In fact, as ment with theoretical radiation patterns till it is shown in this case, manufacturing errors do not affect considerably to the performance of corrugated horn antennas, reinforcing one of the benefits of corrugated horns, manufacture accuracy is not usually a real problem. In the presented case, a random number generator to vary both the length and the radius of each corrugation was used to test the necessary accuracy in the manufacturing process. The results confirmed that the needed accuracy is similar to any other kind of corrugated horns. Authorized licensed use limited to: Universitas Indonesia. Downloaded on February 20,2020 at 03:49:43 UTC from IEEE Xplore. Restrictions apply. 382 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 5, 2006 Fig. 3. 24-dB gain horn antenna measurements. (a) Measured radiation pattern at f . (b) Measured and simulated return loss response. Fig. 2. 24-dB gain horn antenna simulations. (a) Simulated radiation pattern at f and corrugated horn antenna profile. (b) Simulated radiation properties. Regarding return loss measurement; the horn response presents it below dB in the whole frequency band including a coaxial to rectangular transition (this transition has dB according to manufacturer) a return loss better that and a rectangular to circular transition (no manufacturer data available of its VSWR response), so it is assumed that the return loss meets the specification, no spike responses have been detected. III. CONCLUSION A very compact and high performance 24-dB gain corrugated horn antenna that combines horizontal and vertical corrugations has been designed, manufactured and measured. Measured results meet the proposed specifications. By applying these innovative ideas, moderate to high-gain corrugated horns where stringent requirements must be met; can nowadays be made available in much reduced size than old corrugated technology prototypes. Fig. 4. Manufactured 24 dB gain corrugated horn (f = 10 GHz) and detail of manufactured error in two corrugations (to compare size, 1 Euro coin was photographed). ACKNOWLEDGMENT The authors would like to thank Dr. S. Loredo for the prototype measurement at the Oviedo University anechoic chamber. They would also like to thank the reviewers for their useful comments in improving this manuscript. Authorized licensed use limited to: Universitas Indonesia. Downloaded on February 20,2020 at 03:49:43 UTC from IEEE Xplore. Restrictions apply. TENIENTE et al.: INNOVATIVE HIGH-GAIN CORRUGATED HORN ANTENNA REFERENCES  R. Gonzalo, C. del Rio, D. Goñi, and J. Teniente, “Horn antenna combining horizontal and vertical ridges,” Int. 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