K. Sarabandi

• Ph.D. Electrical Engineering
• Professor at University of Michigan

There is a growing body of theoretical and experimental evidence that in addition to the biochemical signaling using auto-inducers and ion channels, biological cells and more specifically certain bacterial biofilms can transmit and receive electromagnetic (EM) waves as a means of communication. It was recently hypothesized that certain cellular str...

This paper presents a novel Substrate Integrated Waveguide (SIW) Cavity-Backed Slot Antenna (CBSA) to enable the next generation of communication and sensing infrastructure. The antenna achieves a bandwidth of 40%, with a low profile (<0.1λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub>), high...

The work presents a full-wave investigation of an impedance sphere coated with a rotationally symmetric gyrotropic layer, with both electric and magnetic gyrotropies. A formulation based on the modal decomposition of fields in terms of spherical harmonics is presented. The scattered field is evaluated by matching the tangential field components at...

This paper presents a low-complexity wideband circularly polarized (CP) array in X-band for vehicular satellite communication. The array comprises dual-polarized corner-fed patch elements for achieving wide bandwidth. The active elements are integrated in a modular manner using interposers that enables the scalability of the array and simplicity of...

A state-of-the-art radar system suitable for terahertz (THz) sensing and imaging is presented. The system is composed of a bistatic superheterodyne transmitter–receiver (TX–RX) pair, designed and fabricated in a 65-nm CMOS process, driven by three coherent external sources and measured using a lock-in amplifier. The TX and RX chips each employ a wi...

This article presents an accurate phase calibration technique and a fast time-domain reconstruction algorithm for frequency-modulated continuous wave (FMCW) synthetic aperture radar (SAR) imaging in 3-D. The phase calibration is tailored toward millimeter-wave imaging systems that operate over a wide bandwidth. The first step in the calibration is...

A highly-isolated dual-band full-duplex antenna subsystem operating at 8-18 GHz (X/Ku band) and 32-40 GHz (Ka band) is presented. Each band includes two conical horn antennas which are juxtaposed sideby-side. Dual circular polarization is generated by using a 3-dB coupler in the lower band and a septum polarizer in the upper band. The two pairs of...

This paper presents a model for the statistics of field fluctuations, phase aberration, and field spatial covariance of electromagnetic waves propagating in the rain at millimeter-wave frequencies as a function of range and rain rate. This statistical model is derived based on a full-wave S-matrix approach and using the fact that the fluctuating co...

A coplanar waveguide (CPW) composite resonator for dielectric characterization of thin films at ${W}$ -band is presented in this article. The sample holder is fabricated using gold evaporation on a fused silica wafer to minimize the resonator losses. The composite resonator is composed of two inductively coupled short-circuited CPW resonators to...

Maintaining calibration of phased array antennas in-situ is a challenging problem that is still considered open. A critical step in the array calibration process is characterizing the channel imbalances between elements so that they can be equalized. In this paper we propose a novel method for monitoring channel imbalances at elements in such array...

This paper reports on polarimetric radar backscatter responses of different types of surfaces at high incidence angles (80° - 89°) at J-band frequencies (221-231 GHz). This study is motivated by the desire to understand the radar phenomenology of target scenes for the next-generation automotive radars. Measured data were collected for paved and unp...

This paper presents a fully polarimetric instrumentation radar designed for conducting phenomenological studies in support of autonomous vehicle research at W-band frequencies. The compact radar utilizes a unique single-antenna system with a narrow beamwidth of 1.1° (two-way) and better than 45 dB isolation between the transmit and receive signal p...

Microwave remote sensing offers a powerful tool for monitoring the growth of short, dense vegetation like soybean. As the plants mature, changes in their biomass and 3-D structure impact the electromagnetic (EM) backscatter signal. This backscatter information holds valuable insights into crop health and yield, prompting the need for a comprehensiv...

This article proposes a millimeter-wave inverse circular synthetic aperture radar system and a fast time-domain wavefront reconstruction (TDWR) algorithm for near real-time, low-cost imaging of packages and concealed objects. An 80-GHz frequency-modulated continuous-wave (FMCW) radar illuminates targets on a high-speed rotating turntable driven by...

In this article, an algorithm for calibrating polarimetric radar systems that ensures accurate measurements of complex scattering matrices of point targets in the backscatter direction is presented. In this approach, only a single target, namely, a metallic sphere, is needed as the calibration target, which significantly simplifies the calibration...

The problem of detecting concealed weapons with a low-cost 3-D imaging radar system is addressed. The concept of affine phase center translations to generate a synthetic array is proposed as an alternative to conventional synthetic aperture and multistatic imaging radars. This enables the generation of a synthetic 2-D array with a dynamic dual refl...

In this work, the Green’s function for a dipole in a stratified uniaxial anisotropic spherical configuration is evaluated, with the dipole in the anisotropic layer. The particular part of the Green’s function is computed by matching the electromagnetic fields at the source in the anisotropic layer. The homogeneous part of the Green’s functions is f...

The design and fabrication of a 230 GHz planar and low-mass reflectionless lens antenna are presented. Phase compensation for the feed's spherical phase front to a planar one emerging from the other side of the lens is accomplished locally using a three-layer spatially varying miniaturized-element frequency selective surface (MEFSS) structure. The...

This article describes the design of a planar spatial power divider structure, which splits the energy of a wave incident at 45 degrees to its surface into a transmitted component and an orthogonally directed reflected component. The reflection and transmission coefficients for both TE and TM incident waves are designed to be approximately equal, h...

This article proposes a device for real-time measurement of the complex dielectric constant of liquids at $X$ -band. The device consists of a narrow waveguide channel operating at the cut-off frequency to achieve a large field enhancement based on epsilon-near-zero (ENZ) supercoupling theory. A micro-3-D-printed sample holder is placed inside the...

Detection and localization of buried pipelines is an important problem for oil and water distribution industries as well as for excavation and construction companies. A novel 3D forward scattering model and dynamic grid search-based inversion algorithm of multiple buried pipelines using multistatic synthetic aperture radar (SAR) configuration is de...

A mechanically scanned high-resolution 2-D imaging radar system with full 360° Field-of-View (FoV) is presented. The system is composed of a multi-function 222-228 GHz frequency modulated continuous wave (FMCW) radar and a moment of inertia optimized 3-D printed offset reflector antenna. The reflector geometry is made from an Elliptic Toroidal su...

Precipitation and in particular rain present a random medium with constituent particles having dimensions comparable to the wavelength at millimeter-wave frequencies. Due to considerable scattering of waves from such particles, significant signal attenuation and phase front aberration can take place which are important factors that must be consider...

In this communication, a 1-bit reconfigurable reflectarray antenna (RRA) providing high aperture efficiency is presented for beam scanning applications. Each element is configured as an aperture-coupled patch antenna composed of a radiating patch, a slotted ground for feed of the patch, a microstrip delay line, and a p-i-n diode switch. Unlike conv...

In this letter, a novel 1-bit transmit- and reflect- array (TRA) antenna is presented for B5G beam scanning applications. Each unit includes a patch-ground-patch layered structure with two embedded PIN diodes and delay lines to serve as binary phase shifters. By properly loading the positions of the two PIN diodes, the sandwiched structure can not...

In this article, a dual-polarized 2-bit electronically reconfigurable reflectarray (RRA) is proposed for 5G beam scanning applications. By introducing two parallel transmission lines and a T-junction, only two p-i-n diodes are used to generate 2-bit phase quantization is analyzed and verified. Based on this concept, a novel 2-bit dual-polarized RRA...

The angular resolution of an imaging radar system is limited by the aperture size and its associated cost and complexity. Relaxing the $\lambda /2$ element spacing condition for large arrays introduces sidelobe and grating lobe effects that severely degrade the image quality. In certain imaging applications, such as automotive radars, the targets...

This paper presents a design for a very low-profile passive reflector device, which presents a large radar cross-section to forward looking automotive radar. With a total height of less than 0.25 mm, the reflector can be embedded in the paint of road markings, enabling the markings to be detected and identified with radar. This will allow radar to...

Satellite and airborne radars currently monitor agricultural regions on earth. Corn is a globally important crop that may benefit from radar observations for estimating soil moisture (SM) and other quantities. Estimates of SM could be used to enhance crop yield and aid in weather prediction. A scattering model is needed, however, to accurately esti...

Directivity enhancement for a conducting cylinder coated with a uniaxial dielectric layer and excited with an electric current source is investigated. A detailed investigation is conducted for all source polarizations. A distinct contribution of the current work relative to the literature is the realization of extremely high directivity correspondi...

Electromagnetic (EM) radiation from Staphylococcus aure us ( S. aureus ) biofilms has been recently detected in the 3.16 – 3.2 GHz frequency range. In this work, a regenerative RF sensing system is designed and implemented to enhance the detection of signals generated by biofilms. The system utilizes the concept of regeneration (also known as po...

All existing state-of-the-art high-resolution millimeter-wave imaging systems experience a tradeoff between image acquisition time and transceiver array complexity. The proposed dual-reflector antenna breaks this tradeoff by drastically reducing the array formation time while maintaining the relative simplicity that comes with using a single transc...

Driven by the perpetual demand for higher data rates, extensive research efforts have been devoted to millimeter-wave (mm-wave) 5G technologies in recent years. Highly integrated mm-wave antennas for 5G user equipment are considered one of the key components in the realization of mm-wave-based mobile networks. An accurate characterization of antenn...

In this communication, a reconfigurable 2-bit leaky-wave antenna (LWA) is proposed for low-cost fixed-frequency beam-steering applications. The proposed antenna consists of a microstrip transmission line loaded with several branches, a series of 2-bit phase shifters, and a $1\times 8$ patch array. Each phase shifter is built by selecting the feed...

This paper reports the first successful detection of electromagnetic (EM) radiation from Staphylococcus aureus biofilms in the gigahertz (GHz) frequency range. Two novel sensing systems are deployed for the measurement. A very sensitive wideband near-zone radiative system specifically designed for this application is first used to search for sign...

A numerical integration of the Sommerfeld integral is performed using the Schelkunoff formulation for cylindrical media. The Schelkunoff kernel for cylindrical media involves higher order modified Bessel functions with azimuthal summation over higher order modes. As such, the convergence characteristics of the cylindrical integral kernel are strong...

A compact fully metallic antenna with high endfire gain and vertical polarization is presented for applications that require the antenna to be mounted on large metallic platforms. The proposed structure includes one driven element on a ground plane, in addition to several parasitic directors and reflectors. The antenna behaves like a Yagi array, bu...

Oil pipeline leak detection and localization is an important problem as regards to environmental issues as well as loss of resources in oil transport systems. This paper shows that a 3D subsurface multistatic imaging radar can better detect water or oil leak when more scattered signals from the leaked region is collected from multiple directions an...

This paper presents a new hardware set-up to suppress radio frequency interference (RFI) for a recently developed microwave radiometer technique, known as wideband autocorrelation radiometry (WiBAR). WiBAR is a method that can directly measure the thickness of a low-loss layer like lake ice or dry snow on the ground by finding the lag time that cor...

This paper presents a model that describes a possible mechanism for electromagnetic (EM) signal transmission and reception by bacterial cells within their biofilm communities. Bacterial cells in biofilms are embedded into a complex extracellular matrix containing, among other components, charged helical nanofibrils from amyloid-forming peptides. Ba...

This paper presents a very low-profile ( $0.105\lambda _{0}$ at 28 GHz) dual-band dual-polarized millimeter-wave phased array for 5G smartphones. The array element is based on two distinct dual-band antennas to realize two orthogonal linear polarizations. A planar folded dipole with a parasitic strip is used to produce horizontally polarized radia...

Multistatic subsurface synthetic aperture radar (SAR) is a promising tool capable of providing 3-D high-resolution images of targets buried underground. The high detection capability of the system stems from the fact that the multistatic configuration allows for viewing the targets from many directions. However, a primal limiting factor for such co...

In this article, the merits of impedance matching a small antenna to the receiver’s impedance are investigated. The goal is to demonstrate that a small antenna with low radiation resistance and high input reactance, when directly connected to a high-impedance (high-impd) receiver, can provide significantly better signal-to-noise ratio (SNR) than wh...

Design procedure and experimental validation for a millimeter-wave (MMW) vehicular antenna with simultaneous multi-beam, for 5G V2X application, is presented. The design overcomes the constraint for requiring both wide angular coverage and high gain through a compact multi-array design. Each array is designed to have a fixed beam direction and suff...

This work presents a full-wave Green’s function approach for the rigorous investigation of a probe-coupled dielectric resonator antenna configuration with an imperfect inner conductor. The impedance boundary condition is applied over the imperfect conductor in the formulation to derive the fields in and outside the dielectric region, considering al...

This paper presents a comprehensive technique for calibrating wideband frequency-modulated continuous-wave (FMCW) fully-polarimetric radars employing linear FM signal chirps. A detailed system distortion model is developed that accounts for both polarimetric distortions and distortions caused by nonlinearities in the transmitted and received radar...

Robust, secure, low-power wireless communications and networking are needed to support emerging applications in emergency and disaster response, robotics, autonomous vehicles, and the Internet of Things (IoT) in physically complex environments, such as indoor/outdoor, dense urban, and other challenging scenarios. These applications require a variet...