Tuning a bandpass filter by optical control of a negative-resistance circuit

Abstract

A novel tunable active bandpass filter is presented in X-band. Basically, this is an end-coupled half-wavelength microstrip bandpass filter coupled by a high-Q value negativeresistance circuit, which is optically tunable. In this filter, one MESFET works both as a tuning element and negative resistance. To increase the tunability of the active MESFET circuit compared with the half-wavelength resonator, the port of the negative resistance is connected to the open stub through one side line in the quarter-wavelength coupler. Tuning range of 123 MHz is achieved by optical tuning. This optically tunable range of the active bandpass filter exceeds 1% of the center frequency.

Microwave Planar Varactor Tuned Bandpass Filters: Historical Overview

“…However, they strongly depend on the active elements used in the circuit B. The active tunable filter using microstrip coupled line [37][38][39][40][41] Fig . 18.…”

“…In this paper, an attempt has been made to describe the advances in passive and active tunable filters. In section II and III, we will discuss the design schemes as well as the performances of the passive and active varactor tunable filters [35][36][37][38][39][40][41][42][43][44][45][46][47][48] realized in various configurations.…”

A Low-Noise Band Pass Filter Using an X-Band Injection-Locked Gunn Oscillator

“…Microwave BPFs can be divided into two categories, viz., passive BPF [9][10][11][12][13] and active BPF [14][15][16][17][18][19][20][21][22][23][24]. Passive BPFs are constructed using passive microwave components.…”

A band-pass filter based on the optically controllable S22 parameter of a MESFET

“…Using this principle, the authors proposed an optically controllable double tuned filter called a "three-terminal MESFET filter with an open stub [7]." In that report, the tuning principle and the equivalent circuit of the filter were shown.…”

“…On the other hand, many authors investigated optically generated currents in a MESFET, and showed that light irradiation caused an increase of the drain current [4,5,6]. The negative resistance circuit in the filter is an injection-locking type MESFET oscillator, therefore, the input reactance of the circuit depends on the S 22 parameter of the MESFET [7]. It can be expected that the increase in the drain current due to the laser irradiation causes a significant change in the imaginary part of the S 22 parameter for the MESFET.…”