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'''RFID System<ref>S. Gupta, B. Nikfal and C. Caloz, "Chipless RFID System Based on Group Delay Engineered Dispersive Delay Structures," in ''IEEE Antennas and Wireless Propagation Letters'', vol. 10, pp. 1366-1368, 2011, doi: 10.1109/LAWP.2011.2178058. keywords: {Radiofrequency identification;Delay;Dispersion;Time ___domain analysis;Microwave circuits;Encoding;All-pass networks;analog signal processing;dispersive delay structures (DDSs);group delay engineering;radio frequency identification (RFID)},</ref>:'''
Over the past few years, [[RFID]] systems have gained significant attention in the microwave community due to their applications in areas like communications, logistics, transportation, and security. A typical RFID system consists of a reader (interrogator) and multiple tags, which can operate over both long and short distances. RFID tags are either active or passive, with passive tags further divided into chip-based and chipless types. Chipless tags are particularly attractive due to their low cost, as they lack integrated circuits. Conventional time-___domain RFIDs rely on pulse-position modulation (PPM) coding but are prone to interference from reflections. A new approach addresses this by using transmission-type all-pass dispersive delay structures (DDS/Phaser) to generate PPM codes, offering a simple, passive, and frequency-scalable RFID solution.
'''Frequency
A dispersive delay structure (DDS) with a linear group delay response can be utilized in frequency meter applications by mapping the frequency of an incoming signal to a time delay. As the input signal travels through the DDS, each frequency component experiences a different delay, allowing the system to distinguish between frequencies based on their time delays. By increasing the slope of the group delay versus frequency (i.e., enhancing the rate of change of delay with frequency), the time delay difference between two closely spaced frequencies becomes larger. This increased time separation allows for finer resolution in distinguishing closely spaced frequencies, thus improving the frequency resolution of the meter.
'''FDM
keywords: {Frequency division multiplexing;Receivers;Delay;Frequency modulation;Transmitters;Transceivers;Real time systems},</ref>:'''
A dispersive delay structure (DDS) also called Phaser with a linear group delay response can simplify [[frequency division multiplexing]] (FDM) by mapping each frequency component of the multiplexed signal to a specific time delay. In such an FDM system, a C-section all-pass DDS separates the signal's frequencies in the time ___domain, eliminating the need for complex analog and digital circuits typically used in conventional FDM receivers. This purely analog approach not only reduces system complexity but also avoids the limitations of digital circuits, such as high power consumption, low speed, and increased cost at high frequencies, while offering scalability across different frequency ranges.
'''Pulse Compression<ref>B. Nikfal, S. Gupta and C. Caloz, "Low-Cost Analog Pulse Compression Technique Based on Mixing With an Auxiliary Pulse," in ''IEEE Microwave and Wireless Components Letters'', vol. 22, no. 3, pp. 150-152, March 2012, doi: 10.1109/LMWC.2012.2184274. keywords: {Mixers;Baseband;Microwave theory and techniques;Radar;Delay;Bandwidth;Isolators;Dispersive delay structures (DDS);loop systems;pulse compression;pulse generation;ultra-wideband (UWB) technology},</ref>:'''
Microwave analog signal processing can
'''Spectrum Sniffing<ref name="Fsniffer" />:'''
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keywords: {Silicon;Antennas;Real-time systems;Distortion measurement;Leaky-wave antenna (LWA);frequency sniffing;direction of arrival detection;cognitive radio},</ref>:'''
The [[Leaky wave antenna|leaky-wave antenna]] (LWA), as a type of dispersive structure, can be effectively utilized for real-time signal processing to create a system for incoming frequency sector detection. Its unique design allows it to radiate energy continuously along its length, making it sensitive to incoming signals from different directions and frequencies. By reconfiguring the LWA, the system can dynamically steer its detection capabilities to focus on specific angles of arrival. This enables the identification of the direction and frequency of incoming signals in real time, facilitating enhanced spectrum awareness. Coupled with a tunable bandpass filter, the LWA can isolate and analyze specific frequency bands, thereby providing valuable information about spectrum occupancy and enabling cognitive radio systems to opportunistically exploit available channels for improved efficiency and reliability in wireless communications.
'''Enhanced-SNR Impulse Radio Transceiver:<ref>B. Nikfal, Q. Zhang and C. Caloz, "Enhanced-SNR Impulse Radio Transceiver Based on Phasers," in ''IEEE Microwave and Wireless Components Letters'', vol. 24, no. 11, pp. 778-780, Nov. 2014, doi: 10.1109/LMWC.2014.2348792. keywords: {Gaussian noise;Signal to noise ratio;Dispersion;Receivers;Radio transceivers;Dispersion engineering;impulse radio;phaser;radio analog signal processing;signal-to-noise ratio},</ref>'''
Dispersive delay structures (DDS), specifically phasers with opposite chirping slopes, can significantly enhance the signal-to-noise ratio ([[Signal-to-noise ratio|SNR]]) of wideband impulse radio transceivers. In this approach, the transmitted impulse is up-chirped using an up-chirp phaser, which stretches the pulse duration while reducing its peak power, allowing for a more efficient transmission with less risk of exceeding power spectral density limits. Upon reception, the incoming signal, which contains both the desired impulse and noise, is processed through a down-chirp phaser. This phaser effectively compresses the received chirped signal back into a sharper impulse while spreading out the burst noise, which had not been pre-chirped, thus mitigating its impact. Meanwhile, Gaussian noise remains unaffected in its spectral characteristics. As a result, the desired signal is enhanced relative to the noise, achieving SNR improvements of several factors for burst and Gaussian noise types. This simple and low-cost system benefits from the broadband nature of phasers, making it suitable for applications in impulse radio ranging and communications.
'''Dispersion
The present disclosure relates to a method of encoding a data signal, a transmitter and a receiver. The method receives the data signal and encodes the data signal by applying a dispersive delay response to the data signal thereby generating an encoded data signal. The transmitter comprises at least one phaser for applying a dispersive delay response to the signal thereby generating an encoded data signal. The receiver comprises at least one phaser for decoding the received encoded data signal by applying an inverse dispersive delay response to the received encoded data signal.
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