Phase tracking electronically variable attenuators with receiver protection

Stofberg, Anneke (2018-12)

Thesis (PhD)--Stellenbosch University, 2018.


ENGLISH ABSTRACT: This dissertation presents the development of a set of optimal phase tracking electronically variable attenuators. Secondly, a compact high power PIN diode limiter is developed and its minimum attainable resistance is extracted through high power measurements. Close range reflections cause the receiver of a multi-channel digital beamforming radar to saturate. Controlled attenuation over time, implemented with electronically variable attenuators, is used to prevent receiver saturation (sensitivity time control). An electronically variable attenuator is placed in front of the first low noise amplifier in each channel; its insertion loss directly adds to the receiver’s noise figure. A multi-channel digital beamforming radar receiver requires good phase tracking between its receiver channels to minimise direction of arrival estimation errors. The set of electronically variable attenuators used for sensitivity time control need to track in phase over the control range. In this dissertation, sensitivity analysis is used to identify a set of optimal phase tracking electronically variable attenuators. A root sum square error measure is derived from the multiple output sensitivities of an electronic network. The error measure gives the expected RMS phase error within a set of networks. Applying the error measure to several electronically variable attenuators over the control range, the cascaded parallel quarter-wave attenuator is identified as having optimal phase tracking within a set of attenuators over control range. The cascade parallel quarter-wave attenuator is developed further and optimised through the application of sensitivity analysis. The final attenuator has excellent attenuation flatness, attenuation range, phase tracking and a simple biasing scheme. A multi-channel digital beamforming radar receiver also has to be protected against large signals. These large potentially damaging signals are either due to the radar’s own transmitted signal, or from other radars transmitting large amounts of power in the same frequency band. A receiver protector (e.g. a limiter) typically supplies this function. In a multi-channel digital beamforming radar, a compact circuit based high power limiter has many advantages in terms of space and cost when it is compared to a waveguide limiter. The compact high power limiter developed in this dissertation consists of PIN diodes implemented on a multi-layer printed circuit board. The circuit is referred to as an active PIN-Schottky limiter. The maximum power handling capability of the active PIN-Schottky limiter is determined by the PIN diode at the limiter’s input. The minimum attainable resistance is not given by the manufacturers, so that the diode’s minimum attainable resistance can not be found from the datasheet information. It is difficult to estimate how much power is dissipated in the diode when a large signal is incident. Through a temperature controlled measurement, the PIN diode’s voltage decrease as a function of junction temperature increase is measured. By fitting the PIN diode’s measured and simulated junction temperature increase, it is possible to extract the resistance of the diode when large forward bias is applied. Once the resistance is known, the power dissipated in the PIN diode can be calculated for different operating conditions.

AFRIKAANSE OPSOMMING: In hierdie proefskrif word ’n stel van optimale fasesporende elektronies verstelbare verswakkers ontwikkel. Tweedens word ’n kompakte hoëdrywing PIN diode beperker ontwikkel. Die beperker se maksimum drywing hanteringsvermoë word bepaal deur die PIN diode se minimum haalbare weerstand te onttrek met hoëdrywing metings. Naby teikens veroorsaak onvanger versadiging in ’n multi-kanaal digitale bundelvormende radar. Beheerde verswakking oor tyd, geïmplementeer deur elektronies verstelbare verswakkers, voorkom ontvanger versadiging (sensitiwiteits tyd beheer). ’n Elektronies verstelbare verswakker word voor die eerste lae ruis versterker in elke ontvanger kanaal geplaas; die inset verlies word direk by die ontvanger se ruissyfer getel. Multi-kanaal digitale bundelvormende radar ontvangers benodig goeie fasesporing tussen die verskillende kanale om foute in die teiken rigting skatting te voorkom. As ’n stel van elektronies verstelbare verswakkers gebruik word om sensitiwiteits tyd beheer toe te pas, moet die stel van verswakkers ook spoor in fase oor die verswakking bereik. In hierdie proefskrif word sensitiwiteitsanalise gebruik om ’n stel van fasesporende elektronies verstelbare verswakkers te identifiseer. ’n Wortel kwadraat som foutmaatstaf word afgelei van ’n elektroniese netwerk se veelvuldige uittree sensitiwiteite. Die foutmaatstaf gee die verwagte wortel gemiddelde kwadraat (WGK) fasefout binne ’n stel van elektoniese netwerke. Die fasefout van verskeie aangepaste elektronies verstelbare verswakkers word bereken en die kaskade parallel kwartgolf-lengte verswakker word geïdentifiseer as die topologie met optimale fasesporing binne ’n stel van verswakkers oor die verswakkingsbereik. Deur die toepassing van sensitiwiteitsanalise word die kaskade parallel kwartgolf-lengte verswakker se werksverrigting verder ontwikkel en geoptimiseer. Die kaskade kwartgolf-lengte verswakker het uitstekende verswakking platheid, verswakking bereik, fasesporing en ’n eenvoudige voorspanningskema. ’n Multi-kanaal digitale bundelvormende radar benodig ook beskerming teen skadelike seine afkomstig van die radar se eie sender, sowel as drywing wat uitgesaai word deur ander radars in dieselfde frekwensieband. ’n Ontvanger beskermer (bv. ’n beperker) word tipies vir hierdie toepassing gebruik. Dit is baie meer voordelig om ’n kompakte beperker te gebruik in plaas van ’n golfleier beperker in ’n multi-kanaal digitale bundelvormende radar in terme van prys en spasie in die ontvanger. Die kompakte hoëdrywing beperker wat hier bespreek word bestaan uit PIN diodes wat geïmplementeer is op ’n multi-laag gedrukte stroombaanbord. Die PIN diode beperker beskerm die ontvanger teen beide sy eie sender drywing (aktief) en ander radars se seine (passief). Die maksimum drywing hanteringsvermoë van die beperker word bepaal deur die minimum haalbare weerstand van die eerste PIN diode. Verskaffers gee nie die PIN diode se minimum weerstand nie, sodat die minimum haalbare diode weerstand nie gevind kan word uit datablad inligting nie. Dit maak dit moeilik om die maksimum intreedrywing van ’n spesifieke beperker opstelling te bepaal. ’n Temperatuur beheerde toetsopstelling word gebruik om die afname in PIN diode spanning te meet vir toenemende vlaktemperatuur. Die gemete vlaktemperatuur word vergelyk met ’n termiese model van die PIN diode. Die PIN diode se minimum haalbare weerstand word onttrek deur die gemete en gesimuleerde vlaktemperatuur te pas. As die PIN diode se minimum haalbare weerstand bekend is, kan die drywing wat die diode verkwis bereken word vir verskillende werkstoestande.

Please refer to this item in SUNScholar by using the following persistent URL:
This item appears in the following collections: