Design and Implementation of a Low Noise Block for Extended C-Band Earth Station

Transcription

1 THE INSTITUTE OF ELECTRONICS, VJMW 2015 INFORMATION AND COMMUNICATION ENGINEERS Design and Implementation of a Low Noise Block for Extended C-Band Earth Station Khanh Duy NGUYEN 1, Doai Van NGUYEN 2, Duc Trong NGUYEN 3, Luan Thanh VU 1 and Yem Van VU 1 1 : School of Electronics and Telecommunication, Hanoi University of Science and Technology 2 : National Institute of Education Management 3 : Vietnam Maritime University 1 khanhndk91@gmail.com, 1 yem.vuvan@hust.edu.vn Abstract In this paper, we design and implement a compact low noise block (LNB) for extended C-band Earth Station in satellite communication systems which converts the radio frequency (RF) signal from extended C-band ( GHz) to a fixed 70 MHz intermediate frequency (IF) signal. The LNB consists of a three-stage low noise amplifier, a band pass filter, a frequency mixer, a local oscillator, IF amplifiers and IF filters. It is fabricated by Rogers RO4350B substrate (ε r = 3.48, h sub = 0.762mm, tan δ = ). With power supply of +12V and 300mA, the LNB yields overall conversion gain of 80 db, noise figure of less than 1.1 db, and output power at 1 db compression of +18dBm. The power sensitivity of the LNB is lower than -80dBm. Simulated and measured results are described to show the performances of the proposed LNB. Keyword: Low Noise Block (LNB), Low Noise Amplifier (LNA), Mixer, Local Oscillator (LO), C-band 1. Introduction Satellite communication systems have spread all over the world, becoming one of the most popular communication systems. In Vietnam, satellite technology is gaining investments with the launches of VINASAT-1 and VINASAT-2 satellites and a wide range of satellite-related services offered. Demand for Earth Stations is increasing as the satellite broadcast industry grows and new research has been carried out in this field in Vietnam [1]. A LNB is the receiving device that receives the very low level microwave signal from the satellite collected by the dish, amplifies it and converts the signals to a lower frequency band [2]. The functional block diagram of the proposed LNB is described in Fig.1. The LNA section of the LNB amplifies the weak signal received from the antenna while adding the minimum possible amount of noise to the signal. The signal is then sent through a band pass filter (BPF) to the mixer which performs the frequency conversion by mixing a fixed frequency produced by the local oscillator with the incoming signal. The frequency sum signal is filtered out and the frequency difference signal (the IF one) is amplified and sent to the indoor receiver. Although there have been many studies on LNB modules [3]-[4], they are implemented by MIC technology and concentrated on Ku and K band satellite receivers. In order to exploit satellite services of VINASAT-1 in Vietnam, it is required to develop integrated receivers operating at extended C-band frequency. This paper presents the design features of the LNB using commercial microwave components and dielectric materials. The purpose of this work is to develop a product that offers not only high performance but also low cost and contribute to the new microwave industry in Vietnam. Fig.1. Functional block diagram of the LNB. 2. Downconverter Design In this paper, the authors present an approach to design and implement a LNB with the following specifications: - Frequency band: GHz - IF frequency: 70 MHz - LO frequency: 3.57 GHz - Noise figure: < 1.5 db - Conversion gain: 80 db - Output power at 1-dB compression point: 19 dbm - Power sensitivity: -80 dbm Copyright 2015 by IEICE

2 2.1. Low Noise Amplifier The LNA employs E-PHEMT SAV-581+ for the first two stages optimized for minimum noise figure with a moderate power gain and monolithic amplifier Gali-39+ for the third stage designed for high power gain. The development of LNA is based on S parameters which can be used to design matching networks, bias networks and calculate noise factor F, stability factor K and stability measure b [5]. A single stage transistor amplifier can be modeled by the circuit shown in Fig.2, where input and output matching networks are employed to transform the input and output impedance Z 0 to the source and load impedance Z S and Z L [6]. Fig.2. The general transistor amplifier circuit. LNA specifications: - Frequency band: GHz - Noise figure: < 1.5dB - Gain: 40dB - Input/output return loss: < -10dB The stability of an amplifier or its resistance to oscillate is an important consideration in a design and can be determined from S-parameters, the matching networks, and the terminations. The necessary and sufficient conditions for unconditional stability are that the stability factor is greater than unity and the stability measure is positive S S S * S S * S K. (1) 2 S * S b 1 S S S * S S * S. (2) Bias networks for amplifiers at microwave frequencies are carried out by using high-impedance quarter wavelength line (λ/4) at center frequency, immediately followed by a radial stub [7]. For the design of the input and output matching networks, to achieve minimum noise figure over a band of frequencies requires that particular source impedance be presented to the input of the transistor [8]. The noise optimizing source impedance is called as Г opt, and is obtained from the manufacturer s data sheet. The corresponding load impedance is obtained from the cascade load impedance formula (3) and the noise figure can be calculated by (4). S22 opt ( S11 * S22 S21 * S12 ) L. (3) 1 opts 11 F F 4R N S opt min 2 2 Z0 opt S 1 (1 ) 2 *. (4) 2.2. Band Pass Filter The BPF is designed using microstrip parrallel coupled-line structure [9] to achieve the following requirements: - Cutoff frequency: 3.5 GHz - Bandwidth: 300 MHz - Ripple in passband: 0.01 db - Order of the filter: 5 - Type of approximation: Chebyshev The BPF is fabricated using Rogers RO4350B substrate (ε r = 3.48, h sub = 0.762mm, tan δ = ) Local Oscillator For the reception of carriers using advanced modulation techniques, such as QPSK, 16-QAM, highly stable and low phase noise local oscillators are required. These use an internal crystal oscillator and a phase-locked loop (PLL) oscillator. The block diagram of a phase-locked loop is depicted in Fig.3 [10]. A phase detector compares the reference signal and the feedback output signal and produces an error signal which is proportional to their phase difference. The error signal is then low-pass filtered and used to drive a voltage controlled oscillator (VCO) which creates an output phase. The output is fed through an optional divider back to the input of the system, producing a negative feedback loop. If the output phase drifts, the error signal will increase, driving the VCO phase in the opposite direction so as to reduce the error. Thus the output phase is locked to the phase at the other input. The output frequency can be calculated by (5). N fout f. (5) REF R f ref R PFD LPF VCO PLL N f out

3 Fig.3. Block diagram of a phase-locked loop. To generate a 3.57-GHz signal for the local oscillator, the device chosen for this study is ADF4350 PLL frequency synthesizer with integrated VCO, which is commonly used for frequency synthesis design [11]-[12]. The low-pass filter was designed for a channel spacing of 200 khz and a closed-loop bandwidth of 35 khz. ADF4350 circuit is revealed in Fig.4. The IC is programed through a three-wire interface to generate a RF output signal at 3.57 GHz with output power level of -6 dbm and phase noise of -83 dbc/hz at 10 khz offset from carrier. To meet the demand of +7-dBm LO drive level of the mixer, the LO signal is amplified by a Gali-39+ amplifier before being sent to the mixer. - Type of approximation: Chebyshev Fig.5. describes the simulation schematic of IF filters. Fig.5. Schematic of the IF filter. For IF amplifiers, we employ the first two stages of Gali-39+ amplifiers and the last one of Gali-74+ amplifier. They acquire a gain of 50 db over MHz range. 3. Simulated and measured Results The components demonstrated above are integrated into a LNB. Fig.6 shows the internal view of it and Fig.7-Fig.10 illustrate its performance. Fig.6. Internal view of the LNB. Fig.4. Schematic of ADF4350 circuit Mixer The frequency mixer is SIM-83+ double balanced mixer which has typical 5.8 db conversion loss, 31 db LO-RF isolation, 24 db LO-IF isolation and 13 dbm IP3 at GHz band IF Filters and Amplifiers The IF filters are required to attenuate LO leakage signal and the frequency sum signal produced by the mixer. They only allow the frequency difference signal at 70 MHz to pass through and are implemented using lumped components to obtain: - Cutoff frequency: 70 MHz - Bandwidth: 14 MHz - Ripple in passband: 0.01 db - Order of the filter: 3 Fig.7. Gain and noise figure of the LNA and BPF. The LNA obtains a gain of 40 db over the GHz range. The absolute gain variation over the operating frequency band is ±1 db. The simulation noise figure of the LNA is 1 db from 3.4 to GHz.

4 output power of +8 dbm when applying input signal frequency at 3.5 GHz and input power of -70 dbm. The output 1dB compression point is obtained at 18dBm when input power is -60 dbm. The power sensitivity is lower than -80 dbm. Fig.8. Gain of IF filters and amplifiers. The measured forward gain of the IF amplifiers achieves 50 db at 70 MHz center frequency. Fig.8 shows that gain flatness is obtained over 14-MHz bandwidth. 4. Conclusion An extended C-band LNB for Earth Station has been successfully developed. It achieves a conversion gain of 80 db and a noise figure of around 1 db over the GHz band. The output 1-dB compression point is 18 dbm. The product consumes total 300 ma from a 12V supply. Acknowledgment This research is carried out in the framework of the project titled Design and Implementation of an Earth Station based on Software Defined Radio in the satellite communication system in the national program on space technology under the grant number VT/CN-02/ This research is funded by the Vietnam Academy of Science and Technology. The authors would like to thank the Vietnam Academy of Science and Technology and the Ministry of Science and Technology, Vietnam for their financial support. Fig.9. Spectrum of LO signal. The LO signal shows its center frequency at GHz with output power of -6 dbm. It is necessary to amplify it before applying to the mixer. Fig.10. Spectrum of output signal. Fig.10 describes IF output signal at 70 MHz with References [1] Tran Van Hoi, Bach Gia Duong, Study and design of wide band low noise amplifier operating at C band, VNU Journal of Mathematics Physics, vol.29, no.2, pp.16-24, [2] D. Roddy, Satellite Communications, third edition, McGraw-Hill, [3] T. Sekiguchi, Ultra small sized low noise block downconverter module, IEEE MTT-S Int. Microwave Symp. Dig., vol.3, pp , June [4] K. Imai and H. Nakakita, A 22 GHz band low noise down converter for satellite broadcast receivers, IEEE transactions on microwave theory and techniques, vol.39, No.6, pp , June [5] G. Gonzales, Microwave Transistor Amplifiers, second edition, Prentice-Hall, [6] A.P. Kulkarni, S. Ananthakrishnan, 1 to 3 GHz wideband low noise amplifier design, th International Conference on computers and devices for communication (CODEC), pp.1-4, Kolkata, India, Dec [7] M.Z.A.A. Aziz, J.B. Din, M.K.A. Rahim, Low noise amplifier circuit design for 5 GHz to 6 GHz, Proc. RF and Microwave Conference, pp.5-8, Malaysia, Oct [8] M.H.C. Halim, A. Othman, S.A. Sahingan, M.F. Selamat, A.A.A Aziz, 5 6 GHz front end Low Noise Amplifier, 2007 Asia-Pacific Conference on Applied Electromagnetics, pp.1-5, Melaka, Malaysia,

5 Dec [9] Jia-Sheng Hong, M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, John Wiley and Sons, [10] Roland E. Best, Phase-locked Loops: Design, Simulation and Applications, McGraw-Hill, [11] Song Qingping, Qi Jianzhong, ADF4350-based Frequency Modulation transmitter design, International Conference on Cyberspace Technology (CCT 2014), pp.1-3, Beijing, China, Nov [12] Hui Xu, Liang Peng, Design of Ultra-broadband microwave sources based on ADF4350, nd International Conference on Advanced Computer Control (ICACC), pp , Shenyang, China, March.2010.

6