We investigate the frequency diverse array (FDA) for joint radar and communication systems. The basic idea is to use the transmitter/receiver modules of the radar system for communication purpose during listening mode as a secondary function. The radar will be performing its routine functions during the active mode as a primary function. An FDA at the transmitter side will be used to produce an orthogonal frequency division multiplexed signal, which is proposed for the communication system. The directivity of the radar antenna, FDA in this case, provides an additional advantage to mitigate the interferences other than the Direction of Interest (DoI). The proposed technique allows two beampatterns to be transmitted sequentially from the same FDA structure. Due to the communication signal transmission in the mainlobe of the second beampattern, the bit error rate achieved in the mainlobe is better than the existing techniques using the sidelobe transmission for communications. At the receiver, both incoming signals of radar and communication will share a different spatial angle. Simulation results indicate the novelty of the idea to suppress the interferences in terms of DoI. Furthermore, we analyzed the signal-to-interference ratio and Cramer–Rao lower bounds for angle and range estimation for the proposed technique.

In this paper, a completely reconfigurable comb-line bandpass filter is presented. Due to the modularity, different standard coupling matrix topologies like the folded form, cascaded triplets, and the cul-de-sac form can be implemented and tested. Circuit-based coupling matrices like the extracted pole topology can easily be realized as well. Different types of input-/output- and cross-couplings can be examined before fabrication of a fixed filter set-up takes place. Furthermore, the proposed filter platform can be used to construct a diplexer. By using different heights of the inner and outer conductor of the coaxial resonators, arbitrary center frequencies in the range between 1 and 4 GHz can be realized. Various types of input couplings are available and proposed here to achieve bandwidths between 10 and 110 MHz. A variety of cross-coupling apertures able to realize transmission zeros are presented as well.

In this paper, a microstrip lowpass filter adopting two main resonators with steep transition band and wide rejection band has been introduced. The first main resonance cell consists of meandered transmission lines which are loaded by modified T-shaped patches. The second main resonator is composed of high-impedance lines loaded by polygon patches. To obtain a steep skirt performance, the first and second resonators have been combined. Moreover, employing eight high–low impedance folded stubs and two rectangular open-stubs as suppressing cells has resulted in improving the stopband features. To comprehend the frequency behavior of the employed resonators and also their combination, the formulas of the transmission coefficient, reflection coefficient, and the transmission zeros of their equivalent LC circuits have been extracted, separately. According to the measurement results, the −3 dB operating frequency of this filter is 1.65 GHz. Moreover, a relative stopband bandwidth equal to 166% with a corresponding attenuation level of 23 dB and a sharp roll-off rate (393.61 dB/GHz) have been achieved. In the passband region from DC to 1.632 GHz, the insertion loss and return loss are better than 0.0763 and 15.85 dB, respectively, proving an acceptable in-band performance. Finally, the implemented structure brings about a high figure-of-merit equal to 81 672.

This article proposes a bandpass filter with three controllable transmission zeros (TZs) using three inductive-coupled stub-loaded resonators (SLRs). Different from other works, the proposed SLR can create one transmission pole and one TZ. With the TZs above the passband, high stopband rejection level is achieved. Moreover, the K-inverters are realized by short-circuit stubs between two adjacent SLRs. A general synthesis method for this kind of filter is described. For verification, a filter centered at 2.44 GHz with 0.18 GHz bandwidth is designed. The measured results show that the filter has three TZs at 3.1, 3.9, and 5 GHz. With those TZs, the filter's stopband rejection level is greatly improved.

This paper investigates the generation of passive intermodulation (PIM) in coaxial connectors during vibration. A series of experiments were designed and the simulation model and method were proposed for understanding these phenomena. We found that PIM is mainly influenced by the contact stress and contact surface roughness during vibration. Thus, a power spectral density method is presented to identify the roughness parameter of contact surface based on the Weierstrass–Mandelbrot model, and the simulation model and method were verified by the relative experiments. Eventually, some suggestions for engineering application were provided.

This paper presents a novel assessment method that minimizes test-fixture-induced errors in non-coaxial power combiner measurement by extending the port reduction method. This method involves terminating certain ports to acquire the scattering matrix of an N-port network from the scattering matrix measured at a reduced port order. The entire DUT scattering matrix is obtained from multiple scanning measurements, which are taken from partial coaxial accessible ports, based on a set of configurable terminating states. This advantage is leveraged to exclude a major portion of coaxial launch structures that would otherwise be incorporated in the conventional multiport test fixture. An analogous concept here is applied to measure a waveguide traveling-wave power combiner. A sandwiched twin structure, containing a divider/combiner pair with certain auxiliary through-type components cushioned between them, is utilized to assess the combiner characteristics. A theoretical framework of the proposed method was established to test its potential precision. Thereafter, an in-situ implementation was conducted to test its practical application on a traveling-wave combined amplifier prototype operating at the Q-band (33–39 GHz).

The surface impedance characteristics of a wire grid composed of infinitely long parallel conducting wires embedded in lossless and lossy frequency-dispersive chiral background media have been investigated. Using wavefield decomposition approach for a chiral background and with the application of impedance boundary conditions for a wire grid, an analytic expression for the surface impedance of a wire grid with a chiral background has been derived. It is shown that the surface impedance magnitude of a wire grid with chiral nihility background is close to zero and almost independent of incident polar angles. A strong chiral background significantly enhances the surface impedance magnitude of a wire grid for incident polar angles closer to right angle as compared to the free space background. The same electromagnetic appearance of a wire grid with frequency-dispersive chiral and free space background media at some critical frequency has also been discussed which may find applications in electromagnetic illusions. It is also shown that if the value of incident polar angles are closer to right angle then the impedance magnitude of a wire grid embedded in the realistic chiral background is smaller as compared to the same wire grid when placed in the free space background.

Spatial telemetry links on nanosatellites require more and more reconfigurable beam antennas to improve the Earth coverage. The bi-mode Agile Radiating Matrix Antenna (8.0–8.4 GHz) was successfully designed to solve such kind of problems by using an isoflux mode associated with a switchable directive one. However, such an antenna introduces some manufacturing problems for the isoflux mode, mainly due to the small available volume on the nanosatellite platform. This paper describes a solution to this problem thanks to the ARMA concept. A comparison between theoretical and experimental results for the isoflux mode in circular polarization is presented to validate the results.

A new design method of an ultra-wideband circularly-polarized planar multiple-input-multiple-output (MIMO) antenna is presented in this paper. The proposed MIMO antenna consists of four unit cell antennas, being comprised of a microstrip feed line and a square slotted ground plane. In the proposed unit cell design, a circular stub is protruded from the ground plane strip for achieving circular polarization. The unit cell of the MIMO antenna is optimized by adjusting design parameters. The compact four-port MIMO antenna prototype is designed on the FR4 substrate with the overall dimensions of 45 × 45 × 1.6 mm3. The proposed four-port MIMO antenna design provides an impedance bandwidth (S11 < −10 dB) of 112% (3.1–11 GHz) and a 3 dB axial ratio bandwidth of 36% (4.8–6.9 GHz). The performance of the fabricated MIMO antenna shows good agreement between the EM simulation and measurement results.

In this article, we propose three-dimensional antenna systems for determining the position of electromagnetic radiation source at an unknown location. Received signal power at different antennas and position of radiation source are used as training data for Artificial Neural Network (ANN). It is found that, a well-trained ANN is computationally efficient and capable of predicting the unknown location of the source, from the received power pattern. Two multi-antenna systems with geometry in three dimensions, namely the cube and frustum, are considered in this paper. Further, test results of the proposed method for random positions of electromagnetic source, spanning a hemisphere, are presented for the geometries considered.

This paper presents the design and analysis of a miniaturized, coplanar waveguide-fed ultra-wideband monopole on-chip antenna with band-notch characteristics. By incorporating a “U”-shaped slot in the feedline, a band-notch is realized in the frequency range of 7.9–8.4 GHz to avoid interference from the X-band uplink satellite communication system. The proposed antenna achieved good voltage standing wave ratio (VSWR) characteristics with VSWR value <2 for the frequency range of 2.5–20.1 GHz excluding the band-notched frequencies. The fractional bandwidth and bandwidth ratio are obtained as 156% and 8.04:1, respectively. Dominant factors that affect the center frequency and bandwidth of the notched band are thoroughly investigated. This paper addresses both frequency as well as time domain behavior of the proposed structure. Standard 675 µm thick, high resistive silicon substrate (ρ≥8 kΩ-cm, εr = 11.8, and tan δ = 0.01) is used to design the proposed compact antenna structure with a layout area of 8.5 × 11.5 mm2. Fabrication process steps along with simulated and measured data are presented here. A close analogy between simulated and measured data is observed.