2022/1
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Recent Submissions
- ItemTransmitter IQ Imbalance Mitigation and PA Linearization in Software Defined Radios(Společnost pro radioelektronické inženýrství, 2022-04) Jovanovic, Borisav; Milenkovic, SrdanRadio frequency (RF) power amplifiers (PA) are efficiently linearized by adaptive digital predistortion (DPD). However, performance of DPD is severely degraded in presence of transmitter’s frequency-selective in-phase/quadrature (I/Q) imbalance. We propose DPD/IQ method that compensates the effects of transmitter I/Q imbalance and PA nonlinearity, which is dedicated for implementation in low-cost software radio defined (SDR) cellular base stations. The advantage of DPD/IQ is low complexity in terms of reduced number of DPD coefficients which provides significant savings of FPGA resources. The DPD/IQ has been evaluated after method has been implemented in SDR board. Measured results clearly demonstrate efficient compensation of PA and transceiver impairments enabling transmission of wide bandwidth waveforms and realization of sophisticated modulation schemes. Improvement in image rejection ratio of 10-15dB is achieved. Considering compensation of PA nonlinearities, the ACPR at PA output is decreased by 15dBc.
- ItemA Dual Band CRLH Metamaterial-Inspired Planar Antenna for Wireless Applications(Společnost pro radioelektronické inženýrství, 2022-04) Ashish, Junuthula; Rao, Amara PrakasaThis paper presents the design of a metamaterial based dual band dual-polarized monopole antenna applicable for wireless applications. A monopole antenna is designed and loaded with a CRLH MTM inspired unit cell on either side of the substrate to operate as a dual band antenna with an improved impedance matching and circular polarization in one of the bands. The overall size of the antenna is 24 mm x 17 mm x 1.6 mm, operating at centre frequencies of 3.5 GHz and 5.5 GHz. Measurements were carried out and the impedance bandwidths obtained in the two bands are 940 MHz (26.8%) and 490 MHz (8.9%) with linear polarization in the first band and circular polarization with an axial ratio bandwidth of 150 MHz in the second band of operation. The obtained peak gains of the antenna in the two bands are 4 dBi and 5.1 dBi respectively, with a considerable agreement between the simulated and measured results.
- ItemRadome Enclosed Circularly Polarized Antenna System with Enhanced Beamwidth(Společnost pro radioelektronické inženýrství, 2022-04) Pradhan, Suman; Gupta, BhaskarThis paper presents a circularly polarized (CP) patch antenna system enclosed by a nosecone radome which has a wide beam response. A U-slot loaded corner truncated patch antenna is mounted upon a conical ground structure for achieving the wide beam response. When two such antennas, one Right Handed CP (RHCP) and another Left Handed CP (LHCP) are placed inside a nosecone radome, a drastic reduction in the antenna beamwidth is observed. Finally a metallic conical ring is added to the structure which improves the beamwidth of the antenna and we achieve a beamwidth of 74° and 120° in the ϕ=0° and ϕ=90° planes respectively. The antenna system also provides a good axial ratio bandwidth performance.
- ItemTwo-Propagation-Modes and Dual-Band Antenna for Circular Polarized TX/RX Systems at C-Band(Společnost pro radioelektronické inženýrství, 2022-04) Herrero-Sebastian, Ivan; Benavente-Peces, CesarThis paper presents a novel slotted array for dual-band and circular-polarized applications. Two different propagation modes within a Substrate Integrated Waveguide (SIW), TE10 and TE20, feed at the same time two pairs of slots, aimed at different frequency bands. The pairs are properly placed to be illuminated by an only propagation mode, whereas the magnetic field of the other propagation mode presents a null. Unlike many dual-band slot arrays, this novel antenna holds the same beam tilt for both frequency bands by a new method, which is only feasible through the use of two propagation modes. A dual-mode transition, based on a double microstrip input, allows to excite both propagation modes within the SIW, and it can be fed by a novel single layer dual-band phase shifter with a different shift at each frequency. A square patch is placed over each pair of slots to increase the coupled energy per element, resulting in a low polarization loss and high performance compact antenna at 3.5GHz and 6GHz for dual-band TX/RX systems at C-Band.
- ItemNew Reflector Shaping Methods for Dual-Reflector Antenna(Společnost pro radioelektronické inženýrství, 2022-04) Quzwain, Kamelia; Yamada, Yoshihide; Kamardin, Kamilia; Abd Rahman, Nurul Huda; Ismail, AlyaniIn the fifth-generation (5G) mobile system, new millimeter-wave technologies such as small cell size and multibeam operation are introduced at the base station. Currently, linear array antennas are used at base stations, however higher design complexity and increased losses in feeding network are expected when the same technology is used to produce multibeams in 5G operation. Through a suitable configuration, a dual-reflector antenna system seems to be a promising candidate to replace the currently used array antennas due to the feasibility of achieving high gain and good multibeam characteristics. In the previous authors’ work, in order to increase the antenna gain at on-focus beams, a reflector shaping method was applied to the dual-reflector antenna, and constant phase and adequate amplitude distribution were achieved on the aperture plane. Furthermore, a good multibeam performance was validated through the consistency of multiple off-focus beam patterns, where a shaped spherical reflector antenna has been used. However, during off-focus conditions, spherical aberration has degraded the phase distribution on the aperture plane and caused reduction in the antenna gain. In this paper, modification to the reflector shaping method using equivalent parabola and equivalent circle method is performed to achieve a reflector antenna system having a constant phase distribution on the aperture plane. The idea of modifying the reflector shaping method comes from the equivalent parabola concept in the Cassegrain dual reflector antenna. During modification, first, the equivalent parabola and circle equation is implemented in the reflector shaping algorithms. Second, a Matrix Laboratory (MATLAB) program is developed in order to solve the reflector design equations and to obtain the main and sub reflector shapes. The MATLAB program is able to generate ray path, aperture illumination distribution and radiation pattern to estimate the adequacy of the reflector shaping results. In the final step, multibeam performance is validated using an electromagnetic simulator, FEKO. Through comparison of the equivalent parabola with the equivalent circle reflectors, an antenna efficiency of 67.6% is obtained and better multibeam radiation patterns are demonstrated using the equivalent circle reflector. Therefore, the usefulness of the newly developed shaping method employing equivalent circle reflector is ensured.