Direct Conversion EHM Transceivers Design for Millimeter-Wave Wireless Applications
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Research Article Direct Conversion EHM Transceivers Design for Millimeter-Wave Wireless Applications Abbas Mohammadi,1 Farnaz Shayegh,2 Abdolali Abdipour,1 and Rashid Mirzavand1 1 Microwave
and Wireless Communication Research Labratory, Electrical Engineering Department, Amirkabir University of Technology (Polytechnic), Tehran 1587-4413, Iran 2 Electrical and Computer Engineering Department, Concordia University, Montreal, QC, Canada H4G2W1 Received 29 March 2006; Revised 14 November 2006; Accepted 15 November 2006 Recommended by Kiyoshi Hamaguchi A direct conversion modulator-demodulator with even harmonic mixers for fixed wireless applications is presented. The circuits consist of even harmonic mixers (EHMs) realized with antiparallel diode pairs (APDPs). A communication link is set up to examine the overall performance of proposed modulator-demodulator. The transmission of 16-QAM signal with 110 Mbps data rate over fixed wireless link has been examined. We also evaluate the different levels of I/Q imbalances and DC offsets and use signal space concepts to analyze the bit error rate (BER) of the proposed transceiver using M-ary QAM schemes. The results show that this structure can be efficiently used for fixed wireless applications in Ka band. Copyright © 2007 Abbas Mohammadi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Local multipoint distribution system (LMDS) is a broadband wireless point-to-multipoint communication system operating above 20 GHz and provide high-data-rate voice, TV, and internet services. It is desirable to increase the spectral efficiency or the transmission capacity of LMDS services by using sophisticated amplitude and phase modulation techniques (QPSK and QAM). The cost reduction in LMDS transceiver design is a key issue to increase the deployment of this system. Among various realization techniques, the direct conversion implementation reduces the size and cost of LMDS transceiver. A direct conversion modulatordemodulator using even harmonic mixers (EHMs) is designed at 28 GHz for LMDS applications. The EHM is based on antiparallel diode pair (APDP). The APDP has a balanced structure that suppresses the fundamental mixing products (m fLO ± n fIF where m + n = even). These products flow only within the APDP loop [1]. The EHM with APDP has some advantages that make it very attractive for millimeter-wave transceivers. These advantages are: (1) it can operate with halved LO frequency; (2) in direct conversion transmitter, it can suppress the virtual LO leakage (2 fLO ) that locates nearby a desired RF signal; (3) it suppresses DC offset in direct conversion receivers.
The paper is organized as follows: the even harmonic mixer structure and three methods to improve its behavior are introduced. Then, a direct conversion modulator is designed using even harmonic mixers. The modulator structure is reciprocal
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