A narrow-band band-pass filter for application in a noticeable interference at the receiver input and, non-linear junction detector has been developed. An interdigital therefore, limit the sensitivity of a NLJD. structure has been used in order to achieve 0.5 % bandwidthIn this paper we present the design of a narrow-band and at the same time high rejection of interference signals. The band-pass filter for application in a nonlinear junction goal was to design a narrow-band filter which ensures high sensitivity of the receiver and high rejection of signals having detecr receiver.aTheogal b wasto desig a band-pass frequencies close to the second harmonic and high rejection of filter having fractional bandwidth equal 0.5 00 and high fundamental frequency. Theoretical analysis as well as attenuation in the stop-band which had to be ensured measurement results are shown.both close to the pass-band to reduce interference signals Key words coupled-line filters, interdigital filters, and further away to ensure fundamental frequency narrow-band filters.rejection. Both theoretical analysis and measurement results of the manufactured model are presented. 1. Introduction f~~~~~~~~~~~~-Microwave filters are often used in modem telecommunication systems, among which, one can to distinguish band-pass filters used at the receivers' inputs to ensure high sensitivity (low noise level) and high rejection of the unwanted signals. In mobile X2 : communication narrow band-pass filters having high°. . attenuation in the stop-band near pass-band are used to fM 2f.properly separate uplink and downlink. In such filters additional zeros near pass-band are inserted to achieve higher isolation between uplink and downlink. Although Fig. 1 Basic concept of a nonlinear junction detector such filters are attractive for mobile communication they often suffer from poor attenuation of the signals being 2. Analysis and design further away from the pass-band [1]. In this paper we have focused on realization of a The goal was to design a narrow-band band-pass filter narrow-band band-pass filter for application in a having center frequency fo = 1730 MHz and the nonlinear junction detector (NLJD), a simplified diagram bandwidth B = 0.5 00. Since high attenuation in the of which is shown in Fig. 1 [2], [3]. A microwave stop-band was desired a stripline technique has been signal is generated, amplified and radiated by a chosen. Such a technique allows also for achieving transmitting antenna, whereas, the receiver is tuned to relatively high Q in comparison to competitive the second harmonic of the radiated signal. The presence transmission line techniques. The investigation of of second harmonic indicates the presence of nonlinear attainable Q values in stripline technique are presented in object within the detector's measurement range. As a [4] and the values of Q normalized to b.(f)/2 reach 6000 fundamental frequency fo = 865 MHz is used and, for transmission lines having impedance Z close to 0 Q therefore, the receiver is tuned to the 2fo = 1730 MHz.(...
