A novel theory is proposed in this article to design a bandpass frequency-selective surface (FSS) with a stable angular response. Based on this theory, the performance of the structure is closely related to its tangential and normal components of permittivity and permeability. Theoretical formulas are derived to realize a high-efficiency transmission response with angular independence. To validate our design concept, an ultrawide-angle bandpass FSS with metallic strips and square patch printed on the dielectric substrate is designed, and it exhibits a characteristic impedance matching for nearly all incident angles from 0° to 80 °. Moreover, varactor diodes are mounted at the center of the square patch, and the transmission window can be tuned by changing the capacitance of the varactors from 6.07 to 6.61 GHz without affecting its ultrawide-angle characteristic. Finally, a prototype of the tunable ultrawide-angle bandpass FSS is fabricated and measured, and the experimental results are in satisfying agreement with the predicted ones.

Orthogonal Frequency Division Multiplexing (OFDM) technique is obtained significant attention in radar applications for its interference resilience property. In this paper, Fractional Fourier Transformation (FRFT) and phase analysis techniques are proposed to enhance ranging accuracy of an OFDM Radar. A proof-of-concept radar is built and tested at 79 GHz and a range accuracy of 20 m at 5 MHz measurement rate was measured. The range accuracy is 500 times higher than using fast Fourier transformation (FFT) method.

This work presents a packaging technique for Monolithic Microwave Integrated Circuits (MMIC) demonstrated in a fully integrated receiver (Rx) module at D-band (110 - 170 GHz). The solution consists of a MMIC-to-waveguide transition realized using an on-chip probe mounted in the E-plane of a split-block waveguide module. An Artificial Magnetic Conductor (AMC) structure is implemented to suppress cavity modes and achieve better coupling from the waveguide to the probe. The transition's performance is experimentally verified using a back-to-back test chip and measurement results show that the proposed packaging solution achieves a low insertion loss of only 0.7 dB and covers a very wide frequency range extending from 105 to 175 GHz. The proposed transition is also integrated with an in-phase/quadrature-phase (I/Q) Rx on the same chip. The Rx is realized in a 250-nm indium phosphide (InP) double heterojunction bipolar transistor (DHBT) technology and consists of a low noise amplifier (LNA), an I/Q mixer and a frequency tripler. Measurement results show that the Rx module achieves an average conversion gain of 23 dB across the frequency range of 110-145 GHz and has an average noise figure (NF) of 10.6 dB. The Rx MMIC has a dc power consumption of 440 mW and occupies an area of $1.6 \times 1.6\;\text{mm}^2$ . This work addresses one of the main challenges in systems operating above 100 GHz and presents a fully integrated packaging solution that suits large integrated circuits and does not require any galvanic contacts nor impose any limitations on MMIC dimensions.

A novel methodology to create metallic waveguides with multilayer integrated vertical-electromagnetic bandgap (EBG) structure is proposed in this article, and the structure realizes low-cost millimeter-wave (mmWave) slot array antennas. A multilayer stack of easy-to-process thin metallic etching plates is introduced to design mmWave waveguide using compression fit instead of diffusion bonding and welding assembly process. The electromagnetic (EM) wave leakage from the gaps between the metallic plates is suppressed using the vertical-EBG structure and antiphasing feeding. The dispersion diagrams of the vertical-EBG unit cell are investigated to illustrate the suppression of leakage. Another leakage wave intercepting methodology is adopted by antiphase feeding to prevent leakage wave from the adjacent slot subarrays. Finally, two examples of 2 $\times $ 8 and 8 $\times $ 8 slot array antennas are presented to verify our design concept. The measured impedance bandwidths of the two antennas are 77.1–84.6 GHz (9.3%) and 78.6–84.9 GHz (7.7%). In addition, the 3 dB broadside gain bandwidths are 73.1–85.3 GHz (15.1%) and 76.8–84.4 GHz (9.4%). The results show the aperture efficiencies up to 56.4%.

This paper proposes a new concept of designing compact high precision millimeter-wave wideband variable phase shifters. The phase shifter is implemented with a stacked shim with extremely short length of 0.9 mm and two waveguide flange adaptors with length of 0.5mm. High precision phase shifting is achieved over entire D-band (110-170 GHz) by rotating the shim 90 degrees from aligned to perpendicular with consistent impedance matching performance. In addition, a glide-symmetric holey electromagnetic bandgap (EBG) structure is adopted to avoid wave leakage from the gap between the shim and the flange adaptors. A proof-of-concept (PoC) demonstrator is designed, manufactured, and tested. The measured results show that the designed stacked shim phase shifter with embedded EBG structure ensures return loss higher than 10 dB across 110-170 GHz with a 75 μm airgap between waveguide flanges. The studied phase shifter provides a 0.88° phase shifting with each degree of mechanical rotation. The fabricated PoC phase shifter has a worst-case insertion loss of 0.92 dB and a return loss of 20 dB across the entire 110-170 GHz band and a maximum phase shift of 30°. At 10° phase shifting, the measured insertion loss is lower than 0.52 dB, and return loss is higher than 23 dB, respectively.

A novel synchronous baseband receiver is presented in this letter. With a pilot tone insertion at the transmitter, the proposed baseband receiver can perform carrier recovery (CR) regardless of modulation scheme and/or baud rate. The synchronous baseband receiver has an analog-digital hybrid structure, where a low-cost digital signal processor controls an analog local oscillator (LO) in frequency and phase to achieve CR. This structure requires only one low-cost analog-to-digital converter (ADC) with a sampling rate of 100 MS/s. A proof-of-concept demonstration at E-band achieves 9-Gb/s 64-quadratic-amplitude modulation (QAM) and 16-Gb/s QPSK transmissions.