The design of the phase management unit needed for extending the scan range of a 24 GHz array antenna system based on Rotman lens beamforming is presented. The developed phase management unit consists of both static and switchable reflective type phase shifters, whose particular arrangement, in combination with a Rotman lens, allows increasing the maximum steering beam angle by 100%. Finally, the proposed concept is validated through simulation including the complete beamforming network and antenna array system

Bruni, Simona

Litschke, Oliver

Tolin, Enrico

Vipiana, Francesca

English

Enrico Tolin

Oliver Litschke

Simona Bruni

Francesca Vipiana

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

04 August 2020POLITECNICO DI TORINORepository ISTITUZIONALEPhase shifters design for Rotman lens based beamforming network scan range extension / Tolin, Enrico; Litschke,Oliver; Bruni, Simona; Vipiana, Francesca. - ELETTRONICO. - (2018). ((Intervento presentato al convegno 2018 IEEEInternational Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting tenutosi a Boston,Massachusetts, USA nel 8-13 July 2018.OriginalPhase shifters design for Rotman lens based beamforming network scan range extensionieeePublisher:PublishedDOI:Terms of use:openAccessPublisher copyrightcopyright 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all otheruses, in any current or future media, including reprinting/republishing this material for advertising or promotionalpurposes, creating .(Article begins on next page)This article is made available under terms and conditions as specified in the  corresponding bibliographic description inthe repositoryAvailability:This version is available at: 11583/2712396 since: 2019-07-05T11:51:29ZIEEE Phase Shifters Design for Scan Range Extension of Rotman Lens Beamforming Based Antenna Arrays   Enrico Tolin, Francesca Vipiana Dept. of Electronics and Telecommunications  Politecnico di Torino Torino, Italy enrico.tolin@polito.it Oliver Litschke, Simona Bruni Dept. of Antennas and EM modeling IMST GmbH  Kamp-Lintfort, Germany oliver.litschke@imst.com   Abstract—The design of the phase management unit needed for extending the scan range of a 24 GHz array antenna system based on Rotman lens beamforming is presented. The developed phase management unit consists of both static and switchable reflective type phase shifters, whose particular arrangement, in combination with a Rotman lens, allows increasing the maximum steering beam angle by 100%. Finally, the proposed concept is validated through simulation including the complete beamforming network and antenna array system. Keywords—Rotman lens, phased array, beamforming network. I. INTRODUCTION  With the continuous development of high performance communication and radar systems toward millimeter-waves, Rotman lens [1] is gaining importance as beamforming network thanks to its broadband and efficient functionality and its cost-effective implementation. However, the design of a large scan angle phased array based on Rotman lenses can be prohibitive due to component dimensions and increasing phase error. Many attempts were made for enhancing the performance of the lens (see e.g. [2]-[3]), based on new technological solutions or by optimizing the design procedure. This paper focus on the concept introduced in [4], where an innovative method for doubling the scan range capability of the Rotman lens beamforming network was proposed and numerically validated. In particular, the scan range extension method is based on the introduction of a phase management unit, initially built by using ideal phase shifters [4]. This work will the develop a planar, compact and accurate phase shifter system for realizing the proposed concept. II. EXTENDED SCAN RANGE CONCEPT This research is based on the concept described in [4], where a method for doubling the scan range of an automotive Short Range Radar (SRR) based on Rotman lens beamforming network was proposed. The extension of the scan range was achieved by placing a special phase management stage between the antenna array and a 24 GHz Rotman lens, characterized by 16 beam ports, 16 array ports and a maximum scan angles of ±30°. By applying this novel concept, the beam steering capability of the beamforming system can be increased up to ±60°. The two essential functions of the phase management stage are called Complete Beams Shifting (CBS) and Beams Mirroring (BM). The CBS is the transfer of all beams to positive (or negative) scan angles, due to the insertion of an appropriate phase distribution after the Rotman lens. In other words, referring to the SRR systems designed in [4], by applying this functionality the cascade of Rotman lens and CBS stage would shift all beam from the conventional ±30° scanning angles to the range 0° to 60°. On the other hand, the BM consists on the application of an additional switchable 0°/180° phase shift at every second antenna array input: the combination of this phase reversal added to the CBS effect is the mirroring of the beam scanning angles toward the negative range. By considering again the example discussed above, the array beams which are pointing in the 0° to 60° range will be moved to the 0° to -60° scanning angles. In Fig. 1 the application of the phase management unit functions to the SRR Rotman lens based beamforming antenna array is depicted. Fig. 1. Combination of “Complete Beam Shifting” and “Beam Mirroring” for scanning range extension of Rotman lenses.  III. PHASE SHIFTER DESIGN The core element of the extended scan range method is the phase management stage, which is placed between the array and the Rotman lens, as illustrated in Fig. 2. Specifically, 16 phase shifters have to be fabricated for generating the required n•90° (with n=1, 2...16 array ports) phase distribution necessary for the CBS procedure. Furthermore, 8 elements of the phase control stage must be able to provide a phase inversion for producing the BM effect. By design considerations, the reflective type phase shifter (RTPS) has been chosen as development technique.   Fig. 2. Extended scan range concept block diagram As shown in Fig. 3, where the simulated basic phase management cell is shown, a hybrid ring coupler topology has been selected for both fixed (RTPS A) and switchable phase shifters (RTPS B). In fact, in the case RTPS B, the phase inversion is obtained by using PIN diodes mounted in opposite direction for terminating to open/short a pair of reflective loads (thus creating a sign inversion). According to RTPS theory, phase shift is determined by the reflection coefficient of the two loads (ideally pure reactance, realized as stubs).   Fig. 3. Empire XPU model of the designed RTPS A for 90° and RTPS B for 180° phase shifting. PIN diodes  that are ON/OFF simultaneusly are represented in green/red (respectively to 180° and 360° phase shifting).  Furthermore, for compensating the error deriving from the line length difference during the ON/OFF state of the diodes, a balanced approach has been used in such a way that 2 diodes (i.e. PIN diodes 1 and 3 for 180°, while 2 and 4 give 360°) are simultaneously conducting in the opposite branches, thus equalizing the path length to ground. In fact, at millimeters-wave frequencies, physical dimensions of components must be included in the design along with the equivalent circuit of the PIN diode. Moreover, non-idealities of the diode influence the effective length of the stubs, therefore dimensions must be tuned for having the correct phase difference among all the phase shifters. The same concept is used in RTPS A for providing the constant phase shift, by simply using open and short stubs with proper length. Phase shift of 270° and 360°/180°, given by configurations RTPS C and RTPS D respectively, are the dual versions of RTPS A and RTPS B. IV. SIMULATED RESULTS The simulated phase management unit S-parameters, shown in Fig. 4, indicate a good return loss over more than 4.5 GHz BW (referring to -10 dB criterion) and low insertion loss of 1.3 dB at the target frequency of 24 GHz (maximum of 1.9 dB at 27 GHz). The phase reversal concept is also providing good results at center frequency, showing a maximum phase error of 2.7° among the 4 RTPS. However, results confirm that the solution is intrinsically narrowband, but adequate for the 24 GHz SRR application. The cause is the loading line length mismatch among the fixed and switchable RTPS.   Fig. 4. Simulated S-parameters of the 4 reflective type phase shifters providing 90° (black), 180° (red), 270° (green) and 360°(blue). Finally, Fig. 5 shows the simulated directivity of the complete extended scan phased array. From the picture it is noticed that maximum is at broadside, with the value of 26.4 dBi, while the lowest value is of 21.3 dBi when the beam is tilted to 60°. Fig. 5. Simulated directivity of the extended scan range SRR system including the proposed phase management unit. V. CONCLUSIONS The design of the phase management unit based on RTPS for the application of the extended scan range concept on a 24 GHz SRR automotive radar system has been presented and numerically validated. The proposed phase adjustment unit fulfills the CBS and BM procedures necessary to double the scan range of the Rotman lens beamforming network. REFERENCES [1] W. Rotman and R. F. Turner, “Wide-angle microwave lens for line source applications,” IEEE Trans. Antennas Propag., vol. AP-11, pp. 623–632, 1963. [2] N.J.G Fonseca, “A Focal Curve Design Method for Rotman Lenses With Wider Angular Scanning Range,” IEEE Antennas. And Wireless Propag. Letters, vol. 16, pp. 57-59, Apr. 2016. [3] E. Sbarra, L. Marcaccioli, R. V. Gatti and R. Sorrentino, “A novel rotman lens in SIW technology,” 2007 European Radar Conference, Munich, 2007, pp. 236-239 [4] E. Tolin, O. Litschke, S. Bruni and F. Vipiana, "Innovative Rotman lens setup for extended scan range array antennas," 2017 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications (APWC), Verona, Italy, 2017, pp. 252-25 

Phase Shifters Design for Scan Range Extension of Rotman Lens Beamforming Based Antenna Arrays

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Phase shifters design for Rotman lens based beamforming network scan range extension

Phase shifters design for Rotman lens based beamforming network scan range extension

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