Transponder, including transponder system

Abstract

In a transponder (19) for amplification of a received signal (60) into an antenna (1), to a signal (61) for retransmission, and where the retransmitted signal (61) possibly may have information superimposed, a quenched oscillator (5) is incorporated as amplifying element. The oscillator (5) is preferably of superregenerative type and exhibits negative resistance (30) for the received signal (60). Transponders according to the present invention may be introduced as system elements in a wireless or wire based network to work as intelligent or unintelligent connections in the network. The transponders can also be used in positioning systems.

Description

[0001] The present invention concerns transponders of the general type as explained in the preamble of the appended claim 1, the application of such transponders in networks, as well as transponder systems in networks as given in the preamble of the appended claim 33. BACKGROUND [0002] In a transponder a radio frequency signal is transmitted to a transponder, which in turn retransmits the signal, often in modulated form, that is to say with superimposed information from the transponder. The purpose of a transponder may thereby be partly to act as a signal repeater, partly exchanging information with the transponder. Some transponders work indirectly, others directly, in indirect retransmission, the signal is received and retransmitted in sequence. Retransmission may be desired to take place in a frequency band different from the band for received signal. One example is aircraft transponders for DME. In direct retransmission the signal is transmitted simultaneously as it is received,...

AI Technical Summary

Benefits of technology

"The present invention provides a new and improved transponder system that overcomes the disadvantages of existing transponder systems. The invention is a quenched oscillator that has high conversion gain, is easy to install and power, and can be used for both direct and indirect repetition of signals. The invention can be used for interrogation and is applicable to a wide range of communication technologies and infrastructures. The invention also provides a new and improved super regenerative oscillator that does not have CW self-oscillation, but instead has diffuse oscillations that achieve efficient amplification. Overall, the invention provides a simple and effective solution for improving the performance and applicability of transponder systems."

Problems solved by technology

Such transponders therefore, serve few applications within the various areas of wireless communication and radio navigation.

It is frequently required that the transponder is portable, lightweight, compact, simple and carries few components, is inexpensive to manufacture and has several years of battery life, at the same time as available performance margins become inadequate, especially with respect to communication range.

High frequency amplification is not used, mostly on account of power consumption.

The disadvantage with the reflective principle is that the retransmitted signal level only can be amplified by the help of antenna gain.

Too much antenna gain is unwanted, because high antenna gain gives too narrow antenna lobes and consequently pointing errors, and the result may therefore become losses in stead of gain.

With conventional technology this comes with high costs in the form of high power consumption and costly products.

Power consumption becomes high because unconditionally stable amplifiers are required.

Cost becomes high because this, on microwave frequencies, usually is accomplished with microstrip technology and expensive circuit board laminates.

The amplification achievable is very limited due to current draw and because it is difficult to sustain sufficient isolation between transmitter and receiver in low cost products.

Benefits of such solutions are usually not worth the increased cost, and the majority of such products today therefore have passive microwave modules, that is just one diode or a transistor switch.

Harmonics of the RF carrier are often very difficult to suppress sufficiently to meet standard requirements.

Transponder range for the transponder solutions mentioned is very limited, because the outgoing signal amplitude is nearly proportional to the incoming signal amplitude as a consequence of no or little active high frequency amplification in the circuit.

Such amplifying transponders therefore have seen few applications within the various areas of wireless communication and radio navigation concerned.

A significant disadvantage with this solution is that it will require a crystal oscillator for the transmitter if the purpose is not served by the poor frequency stability and calibration otherwise resulting.

Such a transponder is not usable in a homodyne system unless it carries a phase locked loop (PLL) frequency locked to the interrogator.

These have specifications that seriously limit their applications.

As mentioned, the largest disadvantage of the injection locked oscillator is a very narrow lock frequency band and a very low sensitivity.

One example of injection locked oscillator application is in phased antenna arrays, but there, as well, the usefulness is limited on account of narrow locking bandwidth which typically will be some ten thousandths of the carrier frequency, and in addition a CW signal is required.

Still, the locking bandwidth is narrow, typically some thousandths of the carrier wave frequency, and still a CW signal is required, often limited to FM modulated CW, to allow signal repetition to work satisfactorily.

Besides, the locking is heavily dependent on the signal dynamics and will generally only work for strong CW signals.

Another reason is that it is a far more difficult challenge to make a quenched oscillator work according to the intention in superregenerative mode than in injection locked mode, due to added component requirements besides design challenges.

In addition, the quench frequency is often injected in such a way that the superregenerative dynamic range is severely limited, which again shows how poorly the circuit was analysed.

The quenched, injection locked (=locked) oscillator has, as explained herewith, specifications that imply large limitations with respect to signal dynamics and bandwidth and further disadvantages like reliability, that reduce possible applications.

This is proven by the fact that earlier publicised and patent text technologies having failed to succeed in applications (i.e. see U.S. Pat. No. 3,705,385), which is due to several factors, some of the more important ones being unreliable frequency locking and narrow useful information bandwidth in the kilobaud range.

Such bandwidth is mostly rather uninteresting for today's communication technologies.

One application for simple transponders in RFID which include long range, is radio tagging of animals, where limited range for today's transponders makes them less suitable and therefore other technologies are used like pulsed beacons that renders less service per carried energy unit because continues transmission is required.

The evolution of radio based, wireless networks for large bandwidths that is required to use very high frequencies (10-200 GHz) have been hampered by the fact that it is still too expensive to implement transmitters, receivers and transceivers.

Up to now, it has not been possible to realise a simple transponder with large dynamics for such frequencies.

Line amplifiers are expensive to realise and often they can amplify the signal in one direction only.

Examples of line amplifiers that have high amplification, but are unidirectional are cable TV amplifiers used for data communication.

For high frequency it has been possible to make line amplifiers with limited isolation between the amplifier input and output, with resulting low useful amplification and therefore applications are very limited.

This puts strict requirements on real time processing and filtering, and often reduces the update rate of the system.

Until now, such transponders have been too expensive to make or have not been realisable.

This has been excessively expensive and may cost tens of thousands of US dollars per connected unit.

It follows that there can be only a small number of amplifiers along the lines, resulting in a very low communication bandwidth.

Likewise, it is expensive and complicated to bypass transformers and other infrastructure in the power network for communication signals.

With known technology it is not possible to have distributed surveillance along a power line and existing solutions therefore use expensive, widely spaced installations that use radio communication There is therefore a need for a new technology which integrates all types of surveillance and control in any position in the power line network, with two way communication along the power lines.

Line amplifiers are very expensive to realise and install and indirect repeaters reduce the data bandwidth.

Consequently it is often difficult to transmit signals between clients and other units like routers, masters and hubs.

Here, it has until now been impractical to realise inexpensive transponders or repeater systems to amplify the signals in a simple manner and in such a way fill in coverage holes or shadow zones.

Known technology did not achieve the necessary signal amplification and one therefore was obliged to install an additional base station to serve a coverage hole area.

Such insufficient coverage therefore had to be accepted as along roads, within buildings, ships, ferries and so on.

With known technology, it is neither easy nor cost effective to couple shielding rooms in buildings, ships a.s.o. to the outside world to achieve radio coverage.

In other communication systems where passive RF technology or low transmitting power is used, like in RFID tags, the margins often are small giving communication problems from changing conditions of various kinds.

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