This article presents a 220-GHz four-channel, noncontiguous, and manifold-coupled waveguide multiplexer for future terahertz (THz) multichannel communication application. The multiplexer is composed of four Chebyshev bandpass filters based on metal waveguide technology. Through a unique design in which the tuning dimensional variables are reduced to 14 and a co-design of low-order electromagnetic (EM) distributed models and full-wave EM models, the design optimization is achieved with a good computational efficiency and design accuracy. The proposed multiplexer is fabricated by high-precision computer numerical control (CNC) milling technology, in which the fabrication errors are evaluated to be within ±3 μm. The measured results exhibit 1.7 dB of in-band insertion loss and better than 15 dB of average common-port return loss for each of the channel filter. The measured results are all in good agreement with the simulated ones, thereby validating the complete design procedure.

A new technique to realize miniaturized broadband multiway and polyphase differential phase shifters is proposed and studied in this article. In contrast to existing designs based on coupled-line and loaded stubs, the multiway phase dispersions are controlled by susceptances of multiple resonant tanks in this work, which can well enlarge the operation bandwidth (BW) and avoid the unachievable physical sizes in strip width and coupling gap over a large phase shift range on the universal reference line topology. In addition, its phase-shift range can be highly extended by properly allocating resonant frequencies of resonant tanks in each path to be specified different values. The theoretical analysis and design formula are studied, and the synthesis method is presented to determine all circuit parameters. By virtue of the quasi-lumped element technology, the proposed multiway phase shifter can be flexibly implemented on a single-layer printed circuit board (PCB) substrate with a very compact size. For demonstration, a five-way differential phase shifter in 0°-180° range has been designed, fabricated, and tested. Over a BW of 80.4%, the achieved phase shifts are 45° ± 4°, 90° ± 5°, 135° ± 5°, and 180° ± 6.3° with low insertion loss (IL) (<1.05 dB) and small amplitude imbalance (<0.29 dB). To the best of our knowledge, this is the tested widest multiway differential phase shifter in the 0°-180° range up until now. Meanwhile, the whole circuit size, including the substrate, is less than 0.30 $λ_{{g}} $ x $0.26λ_{{g}}$ .

A terahertz (THz) CMOS detector array based on multiple chips stitched together is reported. The proposed multichip detector is scalable as the total number of subarray chips is flexible and can be controlled as needed with the help of the modular scheme adopted. Based on the presented multichip technique, a 3 x 3 multichip detector array composed of nine subarray chips has been implemented in this work for operation at 300 GHz. With the subarray chips, each with 7 x 7 pixels, the complete multichip array comprises 21 x 21 physical pixels. By employing virtual pixels, which are included to compensate for the chip interface area consumed for interchip wire-bonding in this work, THz real-time images with 23 x 23 pixels have been successfully acquired. The distribution of the responsivity and noise equivalent power (NEP) over the multichip array is presented. The responsivity distribution shows the effect of the series resistance of the long bias lines stretched over the multichip array, while the effect is not apparent for NEP. The distribution due to series resistance, as well as other nonuniformities over the pixels and chips due to various causes, can be suppressed with a proper calibration for the images acquired with the multichip array.

This article reviews the recent advancements in the utilization of over-the-air combining techniques to enhance the efficiency of phased-array transmitters for signals with a high peak-to-average-power ratio. A methodological comparison between three spatial over-the-air combining techniques--Doherty, outphasing, and quadrature combining--is proposed, along with analysis of their spatial properties, such as a beamwidth angle for a given error vector magnitude (EVM) value, directivity, out-of-band emission, and sensitivity to amplitude and phase mismatches between the different streams. The analysis suggests that the Doherty technique has the widest spatial angle range with EVM under -30 dB and the lowest sensitivity to mismatches, while quadrature combining exhibits the lowest adjacent channel power ratio (ACPR). Also, the Doherty technique enables the largest efficiency enhancement and allows to trade off efficiency enhancement for out-of-band emission. The different methods were tested over-the-air at 28 GHz with a four-element integrated phased array fabricated in 65 nm to validate the analysis.

In this article, a novel wideband bandpass power divider (PD) with out-of-band multi-transmission zeros (TZs) is presented. It consists of 2M shunted short-circuited stubs (SCSs), (M + N) cascaded coupled line sections, and ( $M + N - K_{N)$ isolation resistors. There are two types of topologies, and the number of TZs is solely determined by N. Through even- and odd-mode analyses, general simultaneous equations for characteristic impedances, coupling strengths, and isolation resistors are derived with the proposed algorithm. By suitably selecting all the design parameters, all the S-parameters (S₁₁, S₂₁ = S₃₁, S₂₂ = S₃₃, and S₃₂) of the proposed topology could provide an equal-ripple response with controllable ripple level in the passband. For a given fractional bandwidth (FBW), TZs and out-of-band rejection level can be designed independently. For further optimization, several isolation resistors can be omitted with the unchanged performances. For verification, two experimental circuits are fabricated and measured. Good agreement between the measured and simulated results is attained so as to successfully validate the correctness of the proposed design approach.

We study the behavior of 3-D periodic composite media consisting of several types of split-ring resonators. By initially introducing the H-D periodic eigenmode finite element method (FEM) formulation, the dual counterpart of our formerly proposed E-B formulation, we are able to extract accurate dispersion diagrams and field distributions of electromagnetically complex structures and compare the returned characteristics of the supported modes. Using Babinet's principle, we design the corresponding complementary resonators and evaluate their dual characteristics. Particular attention is given to the explanation of the behavior of these composite media under wave incidence perpendicular to the scatterers' plane. Additionally, we perform a cross-check with excitation problem results, to interpret the response predicted by analytical models existing in literature and confirmed by the eigen-analysis of the structures. Useful conclusions are drawn concerning the potential utilization of the studied resonators in more complex structures in the field of microwave applications.

This article discusses a rigorous and straightforward method to synthesize and design a transmission-line-based reflectionless bandstop filter with high performance in terms of reflectionless range. Our design strategy targets to allow a reflectionless bandstop filter to feature three distinguished advantages that are incomparable to others. First, the presented filter structure is capable of producing an exceptional broadband impedance matching performance. Second, it can be designed to have an extended upper passband. Third, an Nth-order filter has N coupling structures and each of them is used twice in design. Hence, it is required to design and tune only N coupling structures, whereas other design approaches use more than N distinct coupling structures. Although reflectionless filters having one of the aforementioned features have been reported, one exhibiting all the characteristics has never been reported to date. Fabricated filter examples fully validate the design theory.

This article introduces a new type of contact-less electromagnetic bandgap (EBG) structure in the form of an embedded bed of nails. Compared with the traditional bed of nails structure, the smooth upper metal plate originally used to provide the perfect electrical conductor (PEC) boundary is replaced by periodic defect grooves, and the metal pins on the base block are embedded in these grooves without any electric contact. One of the advantages of the embedded EBG structure is that it has a robust tolerance for the height of the air gap. Therefore, this structure provides a cost-effective parallel plate mode suppression solution because it allows a low-precision manufacturing process level while maintaining the stability of the bandwidth. On the other hand, the proposed EBG structure can achieve a stopband range of several octaves. This characteristic makes it indeed suitable for wideband gap waveguides (GWs) to provide horizontal open boundaries. To verify the feasibility of the proposed approach, the new ridge gap waveguide (RGW) (with an embedded bed of nails) and the classic RGW (with a traditional bed of nails) with two 90° bends are designed, fabricated, measured, and compared. The experimental and simulation results are quite consistent and indicate that the embedded RGW has prominent advantages in bandwidth and robustness.

This article presents a novel spoofing device capable of injecting false target information into a frequency-modulated continuous-wave (FMCW) radar. The spoofing device uses a radio frequency (RF) single-sideband (SSB) mixer to introduce a frequency shift to the incoming RF signal transmitted by the victim radar and retransmits the modulated RF signal. The modulated RF signal resembles a false target. Upon down-conversion on the receiver chain of the victim radar, the modulated RF signal creates an illusion of a real target in the radar signal processing system. The frequency shift can be adjusted to vary the range of the spoofed target. The theory of the spoofing mechanism was developed, and a 5.8 GHz prototype was built for experimental validation. Experimental results demonstrate the ability of the proposed spoofing device to inject a false target at any arbitrary range. A hybrid-chirp FMCW approach was proposed and verified as a countermeasure to distinguish a real target from a spoofed target to mitigate the RF-spoofing attack.

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.