IMPROVEMENT IN BANDWIDTH OF LOW NOISE AMPLIFIER USING ELECTROMAGNETIC BAND GAP STRUCTURES

Abstract

This thesis is concerned with the designing of broadband low noise amplifiers using the properties of Photonic Bandgap (PBG) Structures. One-dimensional microstrip PBG cell also named as Compact Microstrip Resonant Cell (CMRC), exhibit remarkable slowwave and band-stop characteristics within a single unit and are used to enhance the impedance bandwidth of Low Noise Amplifier. PBG structures have also been proposed as replacement of lumped components, in which case PBG structures perform better than lumped components and provide better control over the LNA performance. First an LNA was designed using conventional techniques. The measured small signal parameters show that LNA has an input bandwidth of only 300MHz with a gain of ≥ 15dB and a noise figure of ≤ 1dB. When the CMRC structure was incorporated in the LNA, the measured results show a good improvement in terms of bandwidth which is enhanced up to 1.2GHz (i.e. from 13% to 66%), however gain drops to ≤ 11dB. This can be attributed to feedback generated by CMRC structure. The single tone (CW) measurement results in output power (P1dB) of 19.4dBm whereas two tone measurement results in output third order intercept point (OIP3) of value 28.7dBm. To study the effect of variation in size of CMRC structure, another LNA was designed using CMRC structure which is double in size from standard CMRC structure. From measured results it was found that by increasing the size of PBG structure, there is a rapid drop in gain by 2dB. To verify the idea of replacement of lumped components with PBG structures, another LNA is designed using lumped inductor. The value of lumped inductor is set to 1.2nH after optimization. Measured results of LNA with inductor implementation were found to be identical to measured results of LNA with CMRC, however noise figure significantly degrades in case of lumped inductor usage.