| 1. |
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3-D band-stop FSS for X-band and Ku-band
- 2017
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Ingår i: 2017 Progress In Electromagnetics Research Symposium - Fall (PIERS - FALL). - : Electromagnetics Academy. - 9781538612118 - 9781538612125 ; , s. 671-675
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Konferensbidrag (refereegranskat)abstract
- A 3-D Frequency Selective Surface (FSS) with band-stop characteristics for X-band and Ku-band is proposed. A 3-D FSS unit cell is constructed by analyzing two 2-D FSS's. The size of the 3-D FSS unit cell is 5 mm × 5 mm wherein two layers of FR4 substrate with respective widths of 0.762 mm and 0.5 mm are used. Dual stop bands are obtained with this FSS unit cell around 10 GHz and 17.4 GHz; where a wide stop-band of 5.2 GHz is obtained. The parametric study carried out on the proposed design in terms change in nature of substrate, alternate use of different substrates and variation in angle of incidence. The 3-D FSS shows its band rejection property X-band and Ku-band respectively. Ansoft HFSS commercial EM solver software is used to carry out the simulation work.
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| 2. |
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A wideband frequency selective surface reflector for 4G/X-Band/Ku-Band
- 2018
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Ingår i: Progress In Electromagnetics Research C. - : Electromagnetics Academy. - 1937-8718. ; 81, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- A Frequency Selective Surface (FSS) reflector with wideband response for 4G/X-band/Ku-band is proposed. The wideband FSS reflector consists of cascaded dual-layer patch FSS which is etched on separate layers of FR4 substrate. The targeted frequency range is 5–16 GHz. A wide stopband of 10.4 GHz (100% percent bandwidth) is obtained with two layers in cascade. The Equivalent Circuit (EC) method is used to approximate the simulated results. An extensive parametric study is also carried out to understand the effect of various combinations of FSS layers and their disposition. A panel of final FSS is fabricated where measured and simulated results agree well.
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| 3. |
- Alizadeh, Mahmoud, et al.
(författare)
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A new Block-Structure Modeling Technique for RF Power Amplifiers in a 2×2 MIMO System
- 2017
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Ingår i: 2017 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications, TELSIKS 2017 - Proceeding. - Nis, Serbia : IEEE. - 9781538618004 ; , s. 224-227
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Konferensbidrag (refereegranskat)abstract
- A new block-structure behavioral model is proposed for radio frequency power amplifiers in a 2×2 multiple-input multiple-output system including input cross-talk. The proposed model forms kernels of blocks of different nonlinear order that correspond to the significant frequency response of measured frequency domain Volterra kernels. The model can therefore well describe the input-output relationships of the nonlinear dynamic behavior of PAs. The proposed model outperforms conventional models in terms of model errors.
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| 4. |
- Alizadeh, Mahmoud, et al.
(författare)
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A two-tone test for characterizing nonlinear dynamic effects of radio frequency amplifiers in different amplitude regions
- 2016
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Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 89, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- A new two-tone test method for radio frequency power amplifiers is presented. The test signal is a two-tone probing-signal superimposed on large-signals of different amplitude. The amplifier is, thus, excited in different amplitude regions. The amplitude and phase of the 3rd order intermodulation (IM) products are measured vs. frequency spacing and probing-signal amplitude in each region. The IM magnitude is a measure of the nonlinearity, while the frequency dependence and asymmetry are measures of the memory effects in the different regions. A Doherty and a class-AB amplifier were tested. For both amplifiers the IM magnitude increased by ∼15 dB from the lowest to the highest amplitude region. For the Doherty amplifier the behavior of the IM products vs. frequency spacing was similar in all regions, indicating similar memory effects. For the class-AB amplifier the IM vs. frequency spacing was significantly different in the different regions, which indicates different memory effects.
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| 5. |
- Alizadeh, Mahmoud, et al.
(författare)
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Basis Function Decomposition Approach in Piece-Wise Modeling for RF Power Amplifiers
- 2018
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Ingår i: 6th Telecommunications forum TELFOR 2018. - Belgrade, Serbia : Telecommunications society. - 9781538671719 - 9781538671726 - 9781538671702
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Konferensbidrag (refereegranskat)abstract
- In this paper, a new approach is proposed to decompose the basis functions in a piece-wise modeling technique for nonlinear radio frequency (RF) power amplifiers. The proposed technique treats the discontinuity problem of the model output at the joint points between different operating points, whereas preserves the linear and nonlinear properties of the original model within each region. Experimental results show that the proposed technique outperforms the conventional piece-wise model in terms of model errors.
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| 6. |
- Alizadeh, Mahmoud, et al.
(författare)
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Behavioral modeling and digital pre-distortion techniques for RF PAs in a 3 x 3 MIMO system
- 2019
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Ingår i: International journal of microwave and wireless technologies. - : Cambridge University Press. - 1759-0795 .- 1759-0787. ; 11:10, s. 989-999
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Tidskriftsartikel (refereegranskat)abstract
- Modern telecommunications are moving towards (massive) multi-input multi-output (MIMO) systems in 5th generation (5G) technology, increasing the dimensionality of the systems dramatically. In this paper, the impairments of radio frequency (RF) power amplifiers (PAs) in a 3 x 3 MIMO system are compensated in both the time and the frequency domains. A three-dimensional (3D) time-domain memory polynomial-type model is proposed as an extension of conventional 2D models. Furthermore, a 3D frequency-domain technique is formulated based on the proposed time-domain model to reduce the dimensionality of the model, while preserving the performance in terms of model errors. In the 3D frequency-domain technique, the bandwidth of the system is split into several narrow sub-bands, and the parameters of the model are estimated for each sub-band. This approach requires less computational complexity, and also the procedure of the parameters estimation for each sub-band can be implemented independently. The device-under-test consists of three RF PAs including input and output cross-talk channels. The proposed techniques are evaluated in both behavioral modeling and digital pre-distortion (DPD) perspectives. The experimental results show that the proposed DPD technique can compensate the errors of non-linearity and memory effects in the both time and frequency domains.
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| 7. |
- Alizadeh, Mahmoud
(författare)
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Characterisation, Modelling and Digital Pre-DistortionTechniques for RF Transmitters in Wireless Systems
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless systems have become an inevitable part of modern technologies serving humankind. The rapid growth towards large dimensional systems, e.g. 5th generation (5G) technologies, incurs needs for improving the performance of the systems and considering aspects to make them as far as possible environmentally friendly in terms of power efficiency, cost, and so on. One of the key parts of every wireless communication system is the radio frequency (RF) power amplifier (PA), which consumes the largest percentage of the total energy. Hence, accurate models of RF PAs can be used to optimize their design and to compensate for signal distortions. This thesis starts with two methods for frequency-domain characterisation to analyse the dynamic behaviour of PAs in 3rd-order non-linear systems. Firstly, two-tone signals superimposed on large-signals are used to analyse the frequency-domain symmetry properties of inter-modulation (IM) distortions and Volterra kernels in different dynamic regions of RF PAs in a single-input single-output (SISO) system. Secondly, three-tone signals are used to characterise the 3rd-order self- and cross-Volterra kernels of RF PAs in a 3 × 3 multiple-input multiple-output (MIMO) system. The main block structures of the models are determined by analysing the frequency-domain symmetry properties of the Volterra kernels in different three-dimensional (3D) frequency spaces. This approach significantly simplifies the structure of the 3rd-order non-linear MIMO model.The following parts of the thesis investigate techniques for behavioural modelling and linearising RF PAs. A piece-wise modelling technique is proposed to characterise the dynamic behaviour and to mitigate the impairments of non-linear RF PAs at different operating points (regions). A set of thresholds decompose the input signal into several sub-signals that drive the RF PAs at different operating points. At each operating point, the PAs are modelled by one sub-model, and hence, the complete model consists of several sub-models. The proposed technique reduces the model errors compared to conventional piece-wise modelling techniques.A block structure modelling technique is proposed for RF PAs in a MIMO system based on the results of the three-tone characterisation technique. The main structures of the 3rd- and higher-order systems are formulated based on the frequency dependence of each block. Hence, the model can describe more relevant interconnections between the inputs and outputs than conventional polynomial-type models.This thesis studies the behavioural modelling and compensation techniques in both the time and the frequency domains for RF PAs in a 3 × 3MIMO system. The 3D time-domain technique is an extension of conventional 2D generalised memory polynomial (GMP) techniques. To reduce the computational complexity, a frequency-domain technique is proposed that is efficient and feasible for systems with long memory effects. In this technique, the parameters of the model are estimated within narrow sub-bands. Each sub-band requires only a few parameters, and hence the size of the model for each sub-band is reduced.
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| 8. |
- Alizadeh, Mahmoud, et al.
(författare)
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Characterization of Volterra Kernels for RF Power Amplifiers Using a Two-Tone Signal and a Large-Signal
- 2018
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Ingår i: 2018 International Conference on Communications, COMM 2018 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538623510 - 9781538623503 - 9781538623497 ; , s. 351-356
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Konferensbidrag (refereegranskat)abstract
- The 3rd-order Volterra kernels of a radio frequency (RF) power amplifier (PA) are characterized using a large-signal and a two-tone probing-signal. In this technique, the magnitude and phase asymmetries of the kernels of the PA excited by the probing-signal are analyzed in different amplitude regions of the large-signal. The device under test is a class-AB PA operating at 2.14 GHz. The maximum sweeping frequency space of the probing-signal is 20 MHz. The results indicate that the Volterra kernels of the PA show different behaviors (frequency dependency and asymmetry) in different regions.
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| 9. |
- Alizadeh, Mahmoud, et al.
(författare)
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Measurement and Analysis of Frequency-Domain Volterra Kernels of Nonlinear Dynamic 3 x 3 MIMO Systems
- 2017
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9456 .- 1557-9662. ; 66:7, s. 1893-1905
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Tidskriftsartikel (refereegranskat)abstract
- Multiple-input multiple-output (MIMO) frequencydomain Volterra kernels of nonlinear order 3 are experimentally determined in bandwidth-limited frequency regions. How the effect of higher nonlinear orders can be reduced and how this affects the estimated errors are discussed. The magnitude and the phase of the kernels are Kramers-Kronig consistent. The self-kernels and cross-kernels have different symmetries, and the kernels are therefore determined and analyzed in different regions in the 3-D frequency space. By analyzing the properties along certain paths in the 3-D frequency space, the block structures for the respective kernels are determined. These block structures contain the significant blocks of the general block structures for the third-order kernels. The device under test is an MIMO transmitter for radio frequency signals.
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| 10. |
- Amin, Shoaib, et al.
(författare)
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2D Extended envelope memory polynomial model for concurrent dual-band RF transmitters
- 2017
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Ingår i: International journal of microwave and wireless technologies. - : Cambridge University Press. - 1759-0795 .- 1759-0787. ; 9:8, s. 1619-1627
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a 2D extended envelope memory polynomial (2D-EEMP) model for concurrent dual-band radio frequency (RF) power amplifiers (PAs). The model is derived based on the physical knowledge of a dual-band RF PA. The derived model contains cross-modulation terms not included in previously published models; these terms are found to be of importance for both behavioral modeling and digital pre-distortion (DPD). The performance of the derived model is evaluated both as the behavioral model and DPD, and the performance is compared with state-of-the-art2D-DPD and dual-band generalized memory polynomial (DB-GMP) models. Experimental result shows that the proposed model resulted in normalized mean square error (NMSE) of -51.7/-51.6dB and adjacent channel error power ratio (ACEPR) of -63.1/-63.4 dB, for channel 1/2, whereas the 2D-DPD resulted in the largest model error and DB-GMP resulted in model parameters that are 3 times more than those resulted with the proposed model with the same performance. As pre-distorter, the proposed model resulted in adjacent channel power ratio (ACPR) of -55.8/ -54.6 dB for channel 1/2 and is 7-10 dB lower than those resulted with the 2D-DPD model and2-4 dB lower compared to the DB-GMP model.
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