Manual No. 01XX	Copy No. ____

Instruction Manual

Active Radar Filter

Designed by Mike Sulzer - Project 671

Later version by Jon Hagen - Project TM817

Manual written by Jon Hagen

August 2001

ARECIBO OBSERVATORY

NATIONAL ASTRONOMY AND IONOSPHERE CENTER

ELECTRONICS DEPT.

ARECIBO, PUERTO RICO 00612

Table of Contents

1 Introduction	page 3

2 Specifications	page 3

3 Single-chip Implementation	page 5

schematic diagram	page 6

4 Original Implementation	page 7

schematic diagram	page 7

Attachments:

5.0 Electronics Project 671 Active Radar filter: Design Proposal (Mike Sulzer)

6.0 Linear Technology LTC 156202 Active Quad Universal Filter data sheets

7.0 Linear Technology Demonstration Board DC266A

1.0 Introduction

This manual describes the active filter designed by Mike Sulzer for multifrequency incoherent scatter measurements. Though originally designated as Electronics Project 671, no instruction manual was written. Mike's original notes are included at the end of this manual.

Mike wrote " The purpose of this project is to provide a pair of baseband filters for a new incoherent backscatter technique which uses the radar in a mode where several frequencies are transmitted at once. Other filters distort the data in ways which can be almost eliminated by proper filter design". Basically the filters must have uniform response from dc to 100 kHz and then a fairly rapid fall off. Two additional filters have been built for the newly implemented Gregorian 430 MHz radar capability. These new filters use a single-chip design.

2.0 Specifications:

The filter uses a single-order section followed by three second-order sections. Mike wrote an optimization program and used it to determine the location of the poles (one pole for the first section and two poles for each of the three second-order sections). A block diagram of the filter is shown below in Figure 1

Figure 1. Filter Block Diagram

Each active filter block is assumed to have an infinite input impedance and a zero output impedance. The voltage transfer function of each active block is given in terms of its Q and its natural frequency ( 0 = 2 f0) by the following formula:

The transfer function of the input network is given by

deThe transfer function of the filter is calculated and plotted below.

3.0 Single-chip Implementation

The original filters used three op amps for each 2nd-order section The new filters use a single chip which contains four 2nd-order sections. The basic active filter section is shown below, together with the block schematic of the complete filter.

For each section, the filter parameters are given by

.

Unity gain op amp followers are included to provide a 50 Ohm output impedance and to provide a high impedance termination to the input section. The dc gain of each filter section is given

by R2/Rin and the dc gain of the input section is 22/(150+22)= 1.28 so the dc gain of the overall filter is given by 55696/27k x 27964/ 15k x 19434/10k x 1.28 = 0.955.

The complete schematic of each filter is shown on the next page. Except for the input section and the op amp buffers, everything is contained on an evaluation board, Model DC2661 from Linear Technology. The resistors with heavy outlines are present on the board; light outlines indicate components not installed.

4.0 Original Implementation

The two original filters use three op amps to implement each 2nd order section. The schematic for the first filters is shown below.