In this paper, we present the design, analysis, and experimental verification of a $4 \times 4$ integrated sensing and communication (ISAC) multiple-input multiple-output (MIMO) antenna for boresight applications. The main contributions include the derivation of general requirements for ISAC MIMO antennas, realization of an exemplary scalable MIMO array, incorporation of a defected ground structure (DGS) to reduce selfinterference and mutual coupling, and validation through fabrication and measurements. This work addresses the research gap of validated ISAC MIMO antennas meeting both application needs. A detailed comparison of antenna performance with and without DGS is also provided, alongside an evaluation of system-level suitability for future ISAC applications.

Integrated Sensing and Communications (ISAC) will become a service in future mobile communication networks. It enables the detection and recognition of passive objects and environments using radar-like sensing. One promising first application is the protection of critical infrastructure (CI), for example by monitoring the lower airspace above sensitive sites or facilities to prevent unauthorized drone overflights. Our proposal is based on the concept of a distributed multi-sensor (MS)-ISAC. We assume deploying three or more additional passive sniffing sensors near the protected site (PS) of a CI. The sniffers are connected via Downlink (DL) / Uplink (UL) to the distant illumination base station (BS). Multistatic range-Doppler estimation, including synchronization, is performed according to the Cooperative Passive Coherent Location (CPCL) principle. The multistatic architecture has several advantages over the often considered quasi-monostatic architecture where one sniffer is located close to the base station. We discuss the advantages and disadvantages of both approaches and compare their performance for the considered use case in terms of coverage and geometric dilution of precision (GDoP)

This paper presents a comprehensive comparison of all multistatic sensing configurations within Coordinated Multipoint (CoMP) Integrated Sensing and Communication (ISAC) systems for an automotive intersection scenario. An OFDM-based simulation framework is developed to evaluate monostatic, bistatic, and multistatic sensing schemes under binary integration using various $m$-of- $n$ fusion rules. Simulation results demonstrate that full multistatic sensing significantly enhances sensing performance, improving coverage from 20% in the standalone monostatic configuration to 80%, corresponding to a fourfold increase, while the average probability of detection increases from 0.25 to 0.83 over the entire sensing area. These results confirm that cooperative sensing substantially improves detection reliability and coverage without incurring high communication overhead. Furthermore, the results highlight the trade-off inherent in the fusion logic, where smaller values of $m$ favor coverage extension, while larger values of $m$ improve detection robustness.

To enable Integrated Communications and Sensing (ICAS) in a peer-to-peer vehicular network, precise synchronization in frequency and phase among the communicating entities is required. In addition, self-driving cars need accurate position estimates of the surrounding vehicles. In this work, we propose a joint, distributed synchronization and localization scheme for a network of communicating entities. Our proposed scheme is mostly signal-agnostic and therefore can be applied to a wide range of possible ICAS signals. We also mitigate the effect of finite sampling frequencies, which otherwise would degrade the synchronization and localization performance severely.

In recent years, the sub-THz frequency range has become increasingly important for industrial applications. The availability of unused spectrum and the need for high-gain radio interfaces make it possible to build high-resolution systems that are also well-suited for sensing tasks. In this work, we present a measurement setup and results from fully polarimetric scattering experiments carried out at 184.5 GHz to aid the development of integrated sensing and communication systems in the sub-THz range. The experiments compare both empty and filled cardboard boxes, clearly showing that objects hidden in such boxes can create significant multipath components. This allows the conclusion that usually overlooked side items, such as boxes on a shelf in an industrial scenario, can introduce complex clusters of multipath components.

This paper investigates synchronization accuracy and derived synchronization requirements for multi-bistatic Joint Communication and Sensing (JCAS) systems, with a focus on Coordinated MultiPoint (CoMP) architectures. JCAS technology, especially in Vehicle-to-everything (V2X) networks, can enhance road safety by integrating radar detection with communication systems. Multi-bistatic CoMP configurations minimize hardware complexity by distributing transmitters and receivers to remote radio units (RRUs). Using the cooperative passive coherent location (CPCL) technique, we evaluate key synchronization issues, including carrier frequency offset (CFO), timing offset (TO) and sampling frequency offset (SFO), as well as their impact on radar performance. Simulations show how these offsets affect range resolution, Doppler resolution and detection accuracy. We demonstrate that while CFO and TO lead to misestimation of target velocity and position, SFO additionally reduces resolution along both position axes and velocity. These insights provide system designers recommendations on how to adjust multi-bistatic CoMP JCAS performance.

Reconfigurable Intelligent Surfaces (RIS) and Integrated Sensing and Communication (ISAC) enhance network performance by optimizing both sensing and communication. This paper investigates a polarization-modulating RIS to improve sensing diversity and target classification in a distributed Multiple Input Multiple Output (MIMO) ISAC system. The RIS acts as a virtual transmitter, converting a 1×2 distributed Single Input Multiple Output (SIMO) system into a 2×2 distributed MIMO ISAC system, enhancing spatial diversity, detection probability, Doppler robustness, and resolution while reducing noise. Additionally, polarization diversity enables full polarimetric processing, improving target classification. Simulations show that the RIS-aided system improves radar resolution by 40%, reduces noise by 88.6%, and increases detection probability. These findings highlight the potential of polarization-diverse RIS for ISAC applications in vehicular networks and autonomous driving.

Due to its description of a synchronization between oscillators, the Kuramoto model is an ideal choice for a synchronisation algorithm in networked systems. This requires to achieve not only a frequency synchronization but also a phase synchronization - something the standard Kuramoto model can not provide for a finite number of agents. In this case, a remaining phase difference is necessary to offset differences of the natural frequencies. Setting the Kuramoto model into the context of dynamic consensus and making use of the nth order discrete average consensus algorithm, this paper extends the standard Kuramoto model in such a way that frequency and phase synchronization are separated. This in turn leads to an algorithm achieve the required frequency and phase synchronization also for a finite number of agents. Simulations show the viability of this extended Kuramoto model.

Source localization from raw array data by reparameterizing the array steering vector by the source position is a fundamental principle of direct position determination (DPD). In this paper, we propose a DPD method to estimate the position of locally scattered sources using an unsynchronized array sensor network. Here, we use the well-known generalized array manifold (GAM) model which approximates the steering vector using its first-order gradient in order to characterize the local scattering effect. The proposed method is compared with the conventional two-stage bearings-only localization (BOL) approach. Simulation results reveal that the proposed DPD position estimates asymptotically attain the derived Cramier-Rao Bound (CRB) for high SNR values and an improved localization accuracy is achieved by exploiting the local scattering parameters in the localization.

For the validation and verification of automotive radars, datasets of realistic traffic scenarios are required, which, how ever, are laborious to acquire. In this paper, we introduce radar scene synthesis using GANs as an alternative to the real dataset acquisition and simulation-based approaches. We train a PointNet++ based GAN model to generate realistic radar point cloud scenes and use a binary classifier to evaluate the performance of scenes generated using this model against a test set of real scenes. We demonstrate that our GAN model achieves similar performance (~87%) to the real scenes test set.

Future communication and radar sensing systems will require synchronization methods whichare more versatile in terms of the systems involved in the synchronization process. We presentan over-the-air frequency synchronization algorithm based on the standard and the gen-eralized Kuramoto model which uses continuous wave (CW) signals. In contrast to otherapproaches, all nodes of the network participate equally, and synchronization can even beachieved in presence of a non-cooperative node. By changing the parameters of the radaror by modifying the synchronization algorithm, synchronization accuracy can be adjusted aswell. All claims are supported by measurements conducted with CW radars. It will be demon-strated that our algorithm enables synchronization accuracies down to 1.92ppb and thus couldprovide sufficient accuracy for velocity measurements on pedestrians

Radar sensors used in Advanced Driving Assistance Systems (ADAS) need to function properly in dense clutter environments and at low grazing angles which makes multipath wave propagation scenarios a common occurrence. In this paper, a new usage of a Radar Target Simulator (RTS) for emulating multipath effects by synchronizing multiple point reflections to establish direct and indirect reflection paths is proposed. A simplified mathematical model to simulate multipath effects is implemented both in software and on the RTS. Measurements carried out with the RTS and an automotive radar are compared to the simulation and discussed. The measurements show a matching with a characteristic simulated interference pattern and show potential to be utilized for more complex modelling of multipath effects.

This paper introduces a tunable balanced Nonlinear Transmission-Line (NLTL) frequency doubler topology designed using graphene-based Monolithic Microwave Integrated Circuit (MMIC) technology. The frequency doubler chip, operating at a centre frequency of 1.6 GHz, is presented alongside its validation through a proof-of-concept Printed Circuit Board (PCB). The proposed topology offers significant advantages, including high harmonics suppression and exceptional phase noise performance. We employ two measurement setups to evaluate the PCB's performance, showcasing the practical applicability of the design. The frequency doubler design achieved remarkable performance, featuring a conversion gain of -11 dB with high tunability. The circuit exhibited good fundamental suppression below -25 dB, and third and fourth harmonic suppression lower than -35 dB. Moreover, the circuit showcased low-phase noise with a delta carrier-to-noise ratio (CNR) of 6.33 dB.

Integrated communications and sensing systems in the context of automated driving promise increased road safety, especially if the systems are interconnected to form networks. This however places high demands on time and fre-quency synchronization which lie beyond radio network requirements. In this paper, a simulation of a time varying bistatic ICAS channel as well as generation and transmission of an orthogonal frequency division multiplexing frame is presented. The influence of receiver location on the synchronisation quality is analysed. It is found for the investigated scene that synchronization is especially affected if no line-of-sight connection between transmitter and receiver is available.

Integrated sensing and communication (ISAC) qualifies mobile radio systems for detecting and localizing of passive objects by means of radar sensing. Advanced ISAC networks rely on distributed infrastructure, multisensor uplink and downlink, or meshed sidelink access. In this way, ISAC develops into a MS-MIMO (multisensor multiple input multiple output) network which constitutes a distributed MIMO radar network. Multisensor link coordination and synchronization are becoming crucial. Many multisensor access and signaling techniques find their communication counterpart in multiuser MIMO and cooperative multilink communications (CoMP) and can be adopted from there.

Radar networks promise more reliable detection of radar targets compared to monostatic radars, but require a large number of transmitters and receivers. In this paper, the use of intelligent reflective surfaces is proposed to direct the electromagnetic wave emitted from a monostatic radar and reflected at a target back to the radar receiver. To build the structures without electronic phase shifters, beam broadening is used to establish a reliable link to the radar receiver for different target positions. Results of the simulation of a reflect array show that beam broadening can be achieved for an angular range of at least 20° using a quadratic phase distribution.

Future communication and radar sensing systems will require synchronization methods which are more versatile in terms of the systems involved in the synchronization process. We present an over-the-air frequency synchronization algorithm based on self-synchronization which uses continuous wave signals. In contrast to other approaches, all nodes of the network participate equally, and synchronization can even be achieved in presence of a non-cooperative node. These claims are supported by measurements conducted with continuous wave radars. It will be demonstrated that our algorithm enables synchronization accuracies down to 1.92 ppb and thus could provide sufficient accuracy for velocity measurements on pedestrians.

A fully polarimetric calibration method for a partially polarimetric Ka-band radar combined with a frequency selective twist reflector is presented. Such a system enables the capture of the entire scattering matrix by dividing the available bandwidth instead of requiring additional channels. To test this principle, a quasi-monostatic measurement setup is arranged and described in this paper. Various disturbances, among others, occur due to the use of a twist reflector, which must be taken into account and require a novel calibration approach. Therefore, a four step calibration process containing a single 22.5° oriented dihedral reference, electrical length compensation, phase band correction required by the band separation and an application of the monostatic condition is introduced. A selection of corner reflector types is used for a measurement campaign and processed by the proposed signal processing chain. Targets are clearly identified after applying Pauli decomposition to the calibrated measurement data. Eventually, various error effects are analyzed.

Polarization rotating transmitarrays can be used for enabling the detection of polarimetric scattering effects with radar systems. This work presents a compact Ka-band antenna-filter-antenna (AFA) unit cell design containing a 5 th -order planar interdigital diplexer and three patch antennas for orthogonal polarizations. Thus, the linear polarization incident by a frequency modulated radar system can be preserved or rotated by 90° depending on the instantaneous frequency. The proposed transmitarray is developed for multilayer printed-circuit board fabrication with RO3003 layers composed with RO4450T bondply. Simulations are performed that include losses and copper surface roughness. The design exhibits 25 dB polarization separation and sufficiently low input return loss with a relative bandwidth of 11.4% at the radar layer and within two closely spaced bands with a relative bandwidth of 4.9% at the target layer.

This work proposes a polarization and directivity reconfigurable Fabry-Perot cavity antenna. The design uses a grid of reconfigurable PIN didoes, with rows and columns of diodes being turned on/off to control the radiating aperture. The cavity is excited using circularly polarized patch antenna. Overall, the antenna can be reconfigured to radiate either that for a pol, which to control polarization and aperture size. The reconfiguration is controlled by switching rows and columns of PIN diodes that form the grid of Polarization Selective Surface PSS). For the linear polarization, the antenna offers 40 dB of cross polarization level, while the beam width can be altered from 20° to 32°. The antenna preserves 10 dB impedance bandwidth for all investigated configurations, with the exception when all diodes are turned on to block the radiation for all polarizations.