Shulabh Gupta

Group-Delay Engineered Noncommensurate Transmission Line All-Pass Network for Analog Signal Processing

A group-delay engineered noncommensurate transmission line two-port all-pass network for analog signal-processing applications is presented, analytically modeled, and experimentally demonstrated. This network consists of transversally cascaded C-sections, which are distributed implementations of the bridged-T equalizer lumped circuit. It is obtained by interconnecting the alternate ports of adjacent lines of a 2N -port coupled transmission line network with transmission line sections, and it is modeled using multiconductor transmission line theory with per-unit-length capacitance matrix C and inductance matrix L. By allowing the different C-sections of the network to exhibit different lengths, a generalized group-delay engineering procedure is proposed, where quasi-arbitrary group-delay responses are achieved by combining the group-delay responses of C-sections with different lengths. A computer design approach based on genetic algorithms is applied for synthesis, which consists of determining the structural parameters of the different C-section groups. Using this approach, noncommensurate networks are group-delay engineered in edge-coupled stripline technology, and Gaussian, linear and quadratic group-delay responses are realized. The theoretical results are validated by experiment. Finally, two application examples of analog signal processing-a tunable impulse delay line and a real-time frequency discriminator-using the proposed dispersive noncommensurate all-pass networks are presented.

Microwave Analog Real-Time Spectrum Analyzer (RTSA) Based on the Spectral–Spatial Decomposition Property of Leaky-Wave Structures

A novel analog real-time spectrum analyzer (RTSA) for the analysis of complex nonstationary signals (such as radar, security and instrumentation, and electromagnetic interference/compatibility signals) is presented, demonstrated, and characterized. This RTSA exploits the space-frequency mapping (spectral-spatial decomposition) property of the composite right/left-handed (CRLH) leaky-wave antenna (LWA) to generate the real-time spectrograms of arbitrary testing signals. Compared to digital RTSAs, it exhibits the advantages of instantaneous acquisition, low computational cost, frequency scalability, and broadband or ultra-wideband operation. The system is demonstrated both theoretically by a commercial full-wave simulator and an efficient Greens function approach and experimentally by a parallel-waveguide prototype including a metal-insulator-metal CRLH LWA, 16 patch antenna probe detectors circularly arranged around the LWA, and a digital oscilloscope performing analog/digital conversion and time-domain acquisition before the postprocessing and displaying of the spectrogram. The system is tested for a large diversity of nonstationary signals and generates, in all cases, spectrograms that are in excellent agreement with theoretical predictions. The fundamental tradeoff between time and frequency resolutions inherent to all RTSA systems is also discussed, and an interchangeable multi-CRLH LWA solution is proposed to handle signals with different time durations.

Analog Signal Processing: A Possible Alternative or Complement to Dominantly Digital Radio Schemes

Todays exploding demand for faster, more reliable, and ubiquitous radio systems in communication, instrumentation, radar, and sensors poses unprecedented challenges in microwave and millimeter-wave engineering. Recently, the predominant trend has been to place an increasing emphasis on digital signal processing (DSP). However, while offering device compactness and processing flexibility, DSP suffers fundamental drawbacks, such as high-cost analog-digital conversion, high power consumption, and poor performance at high frequencies.

Compressive Receiver Using a CRLH-Based Dispersive Delay Line for Analog Signal Processing

A compressive receiver (CR) is presented utilizing a composite right/left-handed (CRLH) dispersive delay line (DDL) for analog signal processing applications. The CRLH DDL offers advantages such as arbitrary frequency of operation and wide bandwidth, filling a gap with competing DDL technologies. The presented CR system utilizes an impulse-driven CRLH DDL and mixer inversion for chirp generation required for real-time signal processing. At high frequencies, this eliminates frequency ramp generators. The CR is employed as a frequency discriminator and a tunable delay line with dispersion compensation. The simulation and experimental results fully validate the presented systems as proof-of-concept for high-frequency applications such as real-time Fourier transformers and signal analyzers.

Experimental Demonstration and Characterization of a Tunable CRLH Delay Line System for Impulse/Continuous Wave

A new tunable delay system is presented and demonstrated experimentally in this letter. This system, which incorporates a composite right/left-handed (CRLH) transmission line, two mixers, and a low-pass filter, achieves a tunable group delay for impulse and continuous-wave signals, controlled by a local oscillator. This group delay tunability follows from the dispersion property of the CRLH transmission line and is achieved without suffering from the drawbacks of conventional delay lines in terms of matching, frequency of operation, and planar circuit implementation. The realized prototype exhibits measured group delays tunable between 5.1 and 8.54 ns over a frequency range of 2-4.5 GHz.

Chipless RFID System Based on Group Delay Engineered Dispersive Delay Structures

The concept of pulse-position modulation coding based on group delay engineered microwave C-section dispersive delay structures (DDSs) is experimentally demonstrated as a novel chipless radio frequency identification (RFID) system. The tags consist of various DDSs whose group delay responses can be engineered to provide different pulse-position modulation (PPM) codes. A 3-bit system is presented with an RFID reader and various different DDS-based tags. The proposed concept offers system simplicity, frequency scalability, and M-ary coding capability for large ID coding diversity.

Increased Group-Delay Slope Loop System for Enhanced-Resolution Analog Signal Processing

A novel increased group-delay slope loop scheme is proposed to enhance the time-frequency resolution of dispersive delay structure (DDS) components for microwave analog signal processing systems. In this scheme, the signal at the output of the DDS is regenerated by an amplifier and reinjected via a nondispersive delay line toward its input along a loop. At each pass across the DDS, the effective group-delay slope of the system is increased so that, after n turns along the loop, the time-frequency resolution has been enhanced by a factor n. This approach provides a solution to the unpractical approach of cascading n DDS units, which would lead to excessively large device footprint, unacceptably high insertion loss, and severe signal-to-noise reduction. The proposed scheme is implemented in a proof-of-concept circuit using a C-section all-pass network DDS and demonstrated experimentally in a frequency meter and in a frequency discriminator. Possible improvements for higher performance are discussed.

Synthesis of Narrowband Reflection-Type Phasers With Arbitrary Prescribed Group Delay

An exact closed-form synthesis method is proposed for the design of narrowband reflection-type (mono-port) phasers with arbitrary prescribed group-delay responses. The proposed synthesis technique consists in three steps. First, it transforms the phase problem from the bandpass domain to the low-pass domain using a one-port ladder network, where a mathematical synthesis is performed via a Hurwitz polynomial. Second, it transforms the synthesized low-pass network back to the bandpass domain for implementation in a specific technology. Third, it uses an iterative post-distortion correction technique to compensate for distributed effects over the broader bandwidth required. The proposed synthesis method is verified by both full-wave analysis and experiment where the synthesized bandpass network is realized in an iris-coupled waveguide configuration.

Distortion-Less Real-Time Spectrum Sniffing Based on a Stepped Group-Delay Phaser

The concept of real-time spectrum sniffing - featuring a simple and low-cost circuit architecture with straightforward frequency scalability - is introduced for cognitive radio systems. A stepped group-delay phaser is proposed and demonstrated to eliminate the issue of frequency resolution limitation due to the dispersion spreading induced by conventional phasers.

CRLH–CRLH C-Section Dispersive Delay Structures With Enhanced Group-Delay Swing for Higher Analog Signal Processing Resolution

A novel dispersive delay structure (DDS) based on a composite right/left-handed (CRLH)-CRLH coupler is proposed and demonstrated by both full-wave and experimental results. The experimental prototypes are compact and shielded multilayer DDSs implemented in low-temperature co-fired ceramics technology. Compared to the conventional all-pass C-section DDS, the proposed CRLH C-section DDS exhibit a larger group-delay swing, which leads to higher resolution in analog signal processing applications, as a result of their higher coupling capability. Moreover, they feature a larger bandwidth and a smaller size. A generalized wave-interference analysis is presented to both rigorously derive the transfer functions and group-delay characteristics of C-section DDSs and provide deeper insight into their operating mechanisms in both their left- and right-handed regimes.