Microwave Engineering Europe - April 2009 - (Page 18)

18 MMICs/RFICs The measured conversion gain versus RF frequency of the downconverter is plotted in Figure 40. Three traces are shown, representing LO drive levels of -3, 0 and +3 dBm with LO frequency ﬁxed at 21.5 GHz. The shaping of the gain response is caused by the IF balun, Figure 38: Photograph of downconverter IC. which had an upper operating frequency of 1 GHz. Gain is slightly higher than simulated at 5 dB, including all PCB tracking losses and the losses of the IF balun. The measured 1 dB gain compressed output power was +1 dBm for an LO drive of 0 dBm. Conclusions (Downconverter) The downconverter IC is designed to be used following the upconverter. It translates the RF output down to an IF suitable for digitisation. The design, fabrication and evaluation have been described. The MMIC operates over a wider band than required with an RF frequency range of 20 to 25 GHz. Evaluation was carried out on a die assembled onto an MIC carrier. The measured conversion gain is 5 dB and varies little with LO drive levels of between -3 and +3 dBm. The measured 1 dB gain compressed output power is +1 dBm for an LO drive of 0 dBm. Broadband receiver MCM A broadband receiver Multi-Chip Module (MCM) was designed, fabricated and evaluated, using the MMICs described above. The module converts signals from anywhere in the 2 to 18GHz frequency range to an IF suitable for digitisation, and includes low noise ampliﬁcation, ﬁltering and limiter protection. A block diagram depicting the module architecture is shown in Figure 41. The input of the receiver is split into two bands, 2 to 6 GHz and 6 to 18 GHz. This reﬂects the antenna bandwidth in the broadband ECM system for which the module was developed [12]. The bandwidth of all Figure 39: Photograph of downconverter evaluation tile. Figure 40: Measured conversion gain of downconverter. MMICs was adequate to cover the entire 2 to 18 GHz band. Front-end ﬁlters remove out of band signals, then the limiter ICs are used to provide protection of the receiver. Two cascaded LNA ICs are used in each channel to improve sensitivity. Following the LNAs, RF switches route either the pair of 2 to 6 GHz inputs or the pair of 6 to 18 GHz inputs to a dual channel frequency converter. (At the time the module was developed the dual channel switch ICs described above were not yet available and commercially available parts were used). Frequency conversion is realised by upconverting, using a broadband swept LO, to an intermediate frequency at around 22 GHz. Coupled line bandpass ﬁlters are then used to reject out of band signals before the wanted band is downconverted to IF using a ﬁxed frequency second LO. The differential IF output of the downconverter IC is transformed to single-ended using a surface mount balun. Low pass IF ﬁltering is also included. The module housed two boards; a microwave board containing the GaAs MMICs and ﬁlters and an FR4 board containing the bias conditioning and control circuitry. Great care was taken with the layout of the microwave board to preserve amplitude and phase symmetry throughout, so that good amplitude and phase balance was obtained between the two channels. A photograph showing the two boards, with the microwave board mounted in the module housing, is shown in Figure 42. The module housing is gold plated aluminium and measures approximately 180 mm x 100 mm x 23 mm, including a separate 3 mm ﬂat lid. The bias conditioning and control board sits above the microwave board in the housing. Interconnection between the two boards is made using spring-loaded probes. An exploded view of the complete assembly is shown in Figure 43. The measured conversion gain of the complete receiver MCM is 10 dB, and the noise ﬁgure 7 dB. More detail on the design and measured performance of the receiver MCM is available in [12]. Conclusions and Summary This paper has described the design, realisation and evaluation of ﬁve different MMICs all designed for broadband receiver applications. Measured performance of all MMICs is in good agreement with the simulated performance, across the full operating bandwidth. Figure 41: Block diagram of receiver MCM. Microwave Engineering Europe ● April 2009 ● www.mwee.com http://www.mwee.com

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Microwave Engineering Europe - April 2009 News Contents Comment MMICs/RFICs: MMICs for Broadband Receiver Applications Antennas: Mutual Coupling Reduction in Compact Arrays for Wireless Sensors via a Pre-fractal Defected Ground Structure Repeatable Characterization of Distortion Caused by Nonlinearities in Wideband Communication Systems Products Calendar

Microwave Engineering Europe - April 2009

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