The aim of this research is to assess feasibility of technology demonstration in developing digital resolution direction finding integrating with theta-theta position fixing method. The proposal is to build an integrated architecture which will simultaneously provide both position and direction of an aircraft in even most adverse situations. Theta-theta is one of the methods of positioning an aircraft in flight. Without the help of 'range' information this method uses only the angles generated from two different VOR transmitters to aircraft; it is possible to find the exact location of the aircraft whereas in proposed digital radio direction finding (DRDF), it is possible to find out aircrafts' direction with respect to runway by simulating the codes containing 'bearing' information generated from VOR transmitters. This integrated architecture will reduce the complexity and cost associated with aviation industry.

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A Proposed Model of Aircraft Direction Finding And

Integrated Architecture of Theta-Theta-DRDF

Md E A Papon1

Lecturer, Aeronautical Engineering Department

Military Institute of Science and Technology

Dhaka, Bangladesh

a.easir@ae.mist.ac.bd*

S W Tanveer2 , A M Nafi3 , S Ferdous4 , U Umaima5

Aeronautical Engineering Department

Military Institute of Science and Technology

Dhaka, Bangladesh

Abstract— The aim of this research is to assess feasibility of

technology demonstration in developing digital resolution

direction finding integrating with theta-theta position fixing

method. The proposal is to build an integrated architecture

which will simultaneously provide both position and direction of

an aircraft in even most adverse situations. Theta-theta is one of

the methods of positioning an aircraft in flight. Without the help

of 'range' information this method uses only the angles generated

from two different VOR transmitters to aircraft; it is possible to

find the exact location of the aircraft whereas in proposed digital

radio direction finding (DRDF), it is possible to find out aircrafts'

direction with respect to runway by simulating the codes

containing 'bearing' information generated from VOR

transmitters. This integrated architecture will reduce the

complexity and cost associated with aviation industry.

Keywords—Position fixing; direction finding, theta-theta,

DRDF, integrated architecture

I. INTRODUCTION

Aircraft navigation is the process of controlling and

monitoring the movement of an aircraft. All navigational

techniques involve locating the navigator's position compared

to known locations or patterns. Position fixing and direction

finding are the two important issues in navigating an aircraft

from one place to another. For monitoring purpose it is a must

to specify the position and direction of aircraft in every stages

of flight. Although the term direction finding refers to

determining which way to travel but this also involves

estimating the direction from which information is coming and

the exact location of the aircraft at that point of time. There are

different techniques involved in position fixing like rho-rho,

rho-theta, theta-theta methods etc. and direction finding like

radio direction finding, automatic direction finding, digital

resolution direction finding etc. Each specific systems

performs specific jobs either position fixing or direction

finding. An integrated system of position fixing and direction

finding which would provide both the two information at a

time would be a cost effective and efficient way of aircraft

navigation.

II. POSITION F IXING AND D IRECTION F INDING

A. Position Fixing with theta-theta principle

The earliest method of electronic navigation was by

direction finding, the determination of direction of arrival of

electromagnetic waves at the receiving station. Being the

oldest form of electronic navigation, this method is still in

wide use both on ships and aircrafts. Position fixing is the

branch of navigation concerned with the use of a variety of

electronic methods to determine the position of an aircraft on

the surface of the earth. This might be expressed as bearing

and range from a known landmark or as angles of latitude and

longitude relative to a map datum. Different navigation

equipment provides different information. Based on those

position can be fixed. Distance Measuring Equipment (DME)

provides range (rho) information whereas VHF

Omnidirectional Directional Range (VOR) provides bearing

(theta). From these range (rho) and bearing (theta) position

can be fixed in rho-rho, theta-theta and theta-theta method.

Among this theta-theta method is the concern of the research

where two VOR stations provide two bearing information

from respective transmitters to find a locked position of

aircraft in flight conditions. In theta-theta method, two VOR

stations are required. One station will provide bearing

informationߠଵ Ç¡ which gives the decision that aircraft must be

any position on the line in the direction ofߠଵ . Similarly

another VOR station will provideߠଶ which gives the decision

that aircraft must be any position on the line in the direction

ofߠଶ . If only ß  ଵ is known in figure-1 then the aircraft can be

anywhere on the line AB.

Fig-1: Position of aircraft with one VOR-1 Txr

If only ߠଶ is known shown in figure-2, the same thing

happens like in figure-1; aircraft can be anywhere in the line

CD.

ß 

ଵ

VOR-1

True North

A

B

International Conference on Electrical Engineering and Information & Communication Technology (ICEEICT) 2014

978-1-4799-4819-2/14/$31.00 ©2014 IEEE

Fig-2: Position of aircraft with VOR-2

When both ß  ଵ and ß  ଶ angles are known, then these lines AB

and CD intersect at a point and pilot can easily get a fix,

shown in figure-3.

Fig-3: Aircraft fixed position with two VOR

Using the bearing data generated from the VOR

transmitters, a system called Digital Resolution Direction

Finding (DRDF) can be developed which would use the

"bearing" information generated from "theta-theta" method

and provide the information of distance and direction of

aircraft from runway center line to pilot and Air Traffic

Controller (ATC) as well [2-4].

B. Proposed Digital Direction Finding Model

DRDF provides the controller with information on bearings of

aircraft in the following forms:

a. Digital pulses are used to give a digital read-out and a

vector display.

b. Direct Current (DC) voltage is proportional to the

angle of the bearing. This is simulated and displayed

on the operator's console.

c. Digital pulses are combined with information from

other installations to provide an exact aircraft

position on a large scale map that is situated at one of

the UK's two main control centers. This is simulated

on the model as well.

d. The DRDF is proposed primarily for aircraft in

distress, and it helps air traffic controllers pinpoint an

aircraft accurately. The 'distressed' aircraft will

transmit a code which is detected by a DRDF station

and used to determine a directional bearing of the

aircraft. This information is passed to a main control

center, which uses similar information from other

installations to triangulate the aircraft's position

(theta-theta method) [1 & 4-7].

The job is to design a system that can show the radial and

bearing data of an aircraft with reference to ground based

infrared transmitter. The concept of the areal navigation is

different to imagine and comprehend. The navigation data

of radio and bearing which is in polar co-ordinate system

is difficult to comprehend. The electronic circuit designed

to replicate the same is named as Digital Resolution

Direction Finder. It works on the principle of ADF to

show the direction of runway. The circuit consists of three

displays indicating relative bearing, compass heading as

shown in figure-4. Relative bearing and radial indication

are shown by LEDs whereas for heading magnetic

compass is used.

Fig-4: DRDF display (4 directional 90º apart)

It will show the relative bearing of the aircraft with respect

to runway. User will easily come to know at which direction

of aircraft the runway is located. There will be eight receivers

faced at eight directions (each 45º apart) of the aircraft. Signal

received through one receiver will let the LED glow at that

end in display.

Eight unique codes will be transmitted by eight

unidirectional ground based transmitter. Particular code

modulated signal will be received. Code will be detected by

detector IC and corresponding LED will glow on the radial

display. It will show the angular position around the

transmitter taking magnetic north as reference of measurement

moving in clockwise direction. Magnetic compass will show

the heading of the aircraft.

ß 

ଶ

VOR-2

True North

C

D

ß 

ଵ

VOR-1

True North

A

B

ß 

ଶ

VOR-2

True North

C

D

Position

of aircraft

Magnetic Direction

Runway Position

Processing Unit

Aircraft Bearing

Receive

C. Working Principle of proposed DRDF Model

DRDF system consists of eight unidirectional ground

based transmitters and eight unidirectional airborne receivers.

Each of the eight infrared transmitters has a unique code

sequence and having radial sector of 45º each. As the code in

each sector is unique, the receiver will interpret the code and

respective LED corresponding to unique code will glow on the

radial display. Each unidirectional receiver is connected with a

signal detector circuit. When signal is received, detector

circuit will glow the corresponding LED on the relative

bearing display. The signal coverage area for eight

transmitters each of covering 450 is 3600 as a whole. This is

been illustrated as follows in figure-5.

Fig-5: Signal coverage Sector

The block diagram of proposed model is as follows in figure-

6.

Fig-6: Block diagram of proposed DRDF Model

Ground based transmitter will transmit 8 different

codes at 8 unique direction (45º Apart), where each direction

is covered by a narrow beam width of 45 degree. Signal

received by one of the eight directional airborne receivers will

indicate a particular display panel at relative bearing indicator.

Simple principle of Infrared signal detection circuit is applied

here. Ground transmitter will transmit particular code for

unique direction. The code starts from the direction of

magnetic north and starting from 000. Respective codes

relative to angular direction are shown in table-1.

TABLE -1: PARTICULAR CODE S FOR D IFFERENT ANGLES

Code Angular Direction in degrees

000 Magnetic North(0/360)

001 45

010 90

011 135

100 180

101 225

110 270

111 315

For the Radial indicator, the modulated signal will be

demodulated by receiver and for particular code received the

receiver will show the radial information on display. For

different situations, the display will perform simultaneously.

As example, two situations are taken into account.

Situation 1: In case-1, aircraft bearing is 225º and relative

bearing is same as aircraft heading is 0º to Magnetic North.

The radial is 45º of the ground station. Over the display in

aircraft, magnetic compass shows magnetic heading which is

0º. Relative bearing display is indicating 225º from the

display. Radial data display indicates 45º by powering up

respective display panel and the LED on the indicator scale.

As here magnetic heading is 0º so relative bearing and bearing

of aircraft are the same.

Situation 2: In case-2, aircraft bearing is 0º and relative

bearing is same as aircraft heading is 45º to magnetic north.

The radial is 225º of the ground station. Over the display in

aircraft, magnetic compass shows magnetic heading as 45º.

Relative bearing display indicates 0º by indicating the LED on

the display. Radial data display indicates 225º using the

similar principle.

III. THETA-THETA-DRDF I NTEGRATED A RCHITECTURE

The proposed integrated architecture works on using the

data provided by VOR station in any specific runway. The

bearing information which is received from VOR transmitter

is used by DRDF processor to calculate and send required

information to pilot and ATC. The integrated architecture is

shown in figure-7.

Fig-7: Theta-Theta-DRDF integrated Block Diagram

8 uni

ue Code

IR Signal Detector for

Relative bearing

IR Code Detector

TC 9149 IC for

Radial data

Display

450

Txr

VOR Transmitter

DRDF Processing

Unit 3 bit code generation

8 x1 Multiplexer

Display in ATC

Display in Cockpit

Bearing from theta-

theta position fixing

method

DRDF

The combined architecture performs both position

fixing and direction finding principles where using the angular

position of aircraft a central processing unit of DRDF

generates 8 different codes each of 3 bit. This 3 bit code is

then sent to a multiplexer who selects which receiver is

supposed to receive the code. When both transmitter and

receiver codes match, then the specific signal is sent to 2

different locations, one in cockpit from where pilot could

visualize the actual position and direction of runway and

another to ATC which is situated near the runway. From this

two, ATC informs and alerts pilot about its position co-

ordinates.

This combined architecture can be a standby system for

guiding and piloting the aircraft in adverse conditions when

visual navigation is not possible. In such a situation theta-

theta-DRDF system would provide an easy understanding

about direction and position of nearby airport. This is an

advantageous system in different aspects as well. As DRDF

can be used for finding bearing of an aircraft, it is also used

for making a course for the aircraft to reach to the destination.

Approach controller uses this equipment to direct an aircraft to

a point above the airfield and from there he controls the

aircraft's CDTC (Control Descent through Cloud) to a

position with height from where the pilot can land visually.

IV. CONCLUSION

The needs for reliable standby navigation techniques are

always being felt. So, the proposed DRDF system and

integrated architecture with theta-theta position fixing method

might be a good approach in obtaining redundancy and safety

in electronic navigation. The work has been done in

theoretical calculations only and proposed model is yet to be

demonstrated which is under research right at this moment.

More analysis and practical workout is needed to achieve

desired output. Further study on Digital Direction Finding and

synchronization between transmitter and receivers are to be

done. The design and projection of the avionics aid is not only

for the purpose of modification, rather this can be considered

as a very effective teaching aid for avionics studies as hands-

on teaching aid is a big impediment in aviation engineering in

any developing country.

REFERENCES

[1] W. Read, "Review of conventional tectical radio direction finding

systems communications" Electronic Warfare Section. Electronic

Warfare Division, Defence Research established Ottawa, May 1989.

[2] N S Nagaraja, "Elements of Electronic Navigation", ISBN: 0-07-

462301-X, Second Edition, pq- 35-43.

[3] Jeppesen, "Avionics Fundamentals", ISBN: 13: 978-0-88487-432-4, pq-

146-160

[4] Mayron Kayton, Walter R Fried, "Avionics Navigation System", Second

Edition, ISBN: 978-81-265-2400-6, pq 122-127, 138

[5] Rohde and Schwarz, "Introduction into Theory of Direction Finding",

Radiomonitoring and Radiolocation, Catalogue 2011/2012.

[6] Dr. David Sadler, "HF Radio Direction Finding", 25th February, 2010.

[7] Sthephan V. Schall, William A. Garner, "High Resolution Direction

Finding", N. K. Bose and C. R. Rao, eds., Handbook of Statistics, Vol.

10.

[8] Nathan M. Harter, "Developmenmt of a Single-Channel Direction

Finding Algorithm", Blacksburg, VA, April 13, 2007.

ResearchGate has not been able to resolve any citations for this publication.

  • Myron Kayton
  • Walter R. Fried

An indispensable resource for all those who design, build, manage, and operate electronic navigation systems Avionics Navigation Systems, Second Edition, is a complete guide to the art and science of modern electronic navigation, focusing on aircraft. It covers electronic navigation systems in civil and military aircraft, helicopters, unmanned aerial vehicles, and manned spacecraft. It has been thoroughly updated and expanded to include all of the major advances that have occurred since the publication of the classic first edition. It covers the entire field from basic navigation principles, equations, and state-of-the-art hardware to emerging technologies. Each chapter is devoted to a different system or technology and provides detailed information about its functions, design characteristics, equipment configurations, performance limitations, and directions for the future. You'll find everything you need to know about: * Traditional ground-based radio navigation * Satellite systems: GPS, GLONASS, and their augmentations * New inertial systems, including optical rate sensors, micromechanical accelerometers, and high-accuracy stellar-inertial navigators Instrument Landing System and its successors * Integrated communication-navigation systems used on battlefields * Airborne mapping, Doppler, and multimode radars * Terrain matching * Special needs of military aircraft * And much more.

  • Stephan V. Schell
  • William A. Gardner

Sensor arrays can be used to obtain high-resolution estimates of the directions of arrival of propagating signals. Several recent direction-finding methods are described in terms of how they use spatial filters (linear combiners) to enhance the contribution of some signals and/or attenuate others in the process of estimating the directions of arrival. It is shown that this physically motivated interpretaion can be used to derive some of the methods, explain their behavior in different signal environments, and lead smoothly to the more abstract framework of subspace fitting which is prevalent in the research literature. Included in this discussion are descriptions of recent advances in unifying apparently diverse methods and exploiting cyclostationarity properties of signals to obtain better performance. Statistical bounds on the errors of the estimates are briefly described, and several departures from ideality are considered. Future research is likely to continue to focus on accommodating multipath and jamming signals, wideband singals, and array calibration errors, and on achieving even better performance at less computational expense.

  • W. Read

This report discusses land based conventional tactical radio direction finding systems used in determining the direction of origin of narrowband (100kHz or less) radio signals (AM, FM, CW, and SSB) in the 30 to 1000 MHz frequency band. These systems are examined from both the theoretical and practical points of view. Examples of actual systems and the problems encountered (and solutions where appropriate) under operational conditions are also given. Finally manufacturers specifications and how they relate to actual system operation and system operation and systems comparisons are also discussed.

  • Nathan M. Harter

A radio direction finding (DF) system uses a multiple-element antenna array coupled with one or more receivers to estimate the direction-of-arrival (DOA) of a targeted emitter using characteristics of the signal received at each of the antennas in the array. In general, DF systems can be classified both by the number of receivers employed as well as which characteristics of the received signal are used to produce the DOA estimate, such as the signal's amplitude, phase, or time of arrival. This work centers on the development and implementation of a novel single-channel direction finding system based on the differential phase of the target signal received by a uniform circular antenna array with a commutative switch. The algorithm is called the PLL DF Method and differs from older single-channel DF techniques in that it is a digital algorithm intended for implementation on a software-defined radio (SDR) platform with a custom-designed antenna array and RF switching network. It uses a bank of parallel software PLLs to estimate the phase of the signal received at each element of the multi-antenna array. Theses estimated phase values are then fed to a specialized signal processing block that estimates the DOA of the received signal. This thesis presents the details of the initial version of the PLL algorithm which was used to produce a proof-of-concept system with an eight-element circular array. It then discusses various technical challenges uncovered in the initial implementation and presents numerous enhancements to the algorithm to overcome these challenges, such as a modification to the PLL model to offer increased estimator robustness in the presence of a frequency offset between the transmitter and receiver, revisions of the software implementation to reduce the algorithm's processing requirements, and the adaptation of the DF algorithm for use with a 16-element circular array. The performance of the algorithm with these modifications under various conditions are simulated to investigate their impact on the DOA estimation process and the results of their implementation on an SDR are considered. System requirements: PC, World Wide Web browser, and PDF reader. Available electronically via the Internet. Title from electronic submission form. Thesis (M.S.)--Virginia Polytechnic Institute and State University, 2007. Vita. Abstract. Includes bibliographical references.

Elements of Electronic Navigation

  • N S Nagaraja

N S Nagaraja, "Elements of Electronic Navigation", ISBN: 0-07-462301-X, Second Edition, pq-35-43.

Introduction into Theory of Direction Finding

  • Schwarz Rohde

Rohde and Schwarz, "Introduction into Theory of Direction Finding", Radiomonitoring and Radiolocation, Catalogue 2011/2012.

  • Jeppesen

Jeppesen, "Avionics Fundamentals", ISBN: 13: 978-0-88487-432-4, pq-146-160

Review of conventional tectical radio direction finding systems communications" Electronic Warfare Section. Electronic Warfare Division, Defence Research established Ottawa

  • W Read

W. Read, "Review of conventional tectical radio direction finding systems communications" Electronic Warfare Section. Electronic Warfare Division, Defence Research established Ottawa, May 1989.