In this paper, the concept of high-gain multifunctional antenna based on folded reflectarray antenna (FRA) and polarization-sensitive frequency selective surface (FSS) is proposed. Antenna with multiple functions can be realized by using a polarization-sensitive FSS as the subreflector of FRA instead of the traditional polarizing grid. To validate this concept, a high-gain filtering antenna designed at Ka band is presented as a design example. Good filtering performance of the antenna has been achieved due to the frequency selective characteristics of FSS. Besides, the relationship between the focal-length-to-diameter (F/D) ratio of FRA and the size of FSS element has also been discussed.

This article introduces a negative group delay (NGD) analysis of interconnect line coupled with a radial stub terminated line. The NGD topology equivalent model is established by considering the microstrip interconnect line and radial stub circuits. The S-parameter and the group delay are expressed as a function of NGD fully distributed topology parameters. The NGD optimal frequencies and existence condition are originally established as a function of the coupler and the associated RLC-network parameters. It was innovatively shown that the proposed NGD circuit presents a property to generate double NGD center frequency. A proof-of-concept designed and implemented in the microstrip technology was simulated and fabricated to validate the NGD concept. Simulated and measured results are in good correlation with the NGD theoretical prediction. The prototype test results confirm the NGD characteristics as −2.1 ns NGD level at the 1.34-GHz center frequency over 56-MHz bandwidth.

In this paper, a 94 GHz dual-polarization high-isolation cassegrain antenna feed by a diagonal horn antenna is designed. The antenna consists of a D = 540 mm main reflector, sub-reflector, and dual-port dual-polarization diagonal horn feed antenna. To obtain similar feed horn E-H radiation patterns, gain, high polarization, and port isolation, a dual-port diagonal horn was designed in the feed. The measured antenna gains are 50.85 dBi and the side-lobe levels are −24.5 dB at E-H radiation patterns of two ports at 94 GHz, respectively. The VSWRs of port 1 and port 2 are less than 1.5:1 in the range 93.2–95.3 GHz, which meets the working requirements of frequency modulated continuous wave and pulse cloud radars. And the isolation between the two ports is above −50 dB, whereas the polarization isolation of each port is above 40 dB. The proposed W-band antenna is a suitable candidate for the dual-polarization cloud radars.

This paper deals with an innovative design of negative group delay (NGD) topology presenting O=O geometrical shape. This fully distributed NGD topology is composed of a power divider (PWD), power combiner (PWC) and coupled line (CL) built with lossy and delayed transmission lines (TLs). The PWD and PWC are connected via the CL. By using 3-port PWD and PWC, 4-port CL S-matrices, the O=O topology model allowing to determine the group delay (GD) is established. To verify the NGD aspect of the O=O topology, parametric analyses with respect to TL characteristic impedance and delay are performed. In addition, a microstrip circuit prototype is designed, simulated and measured. A good NGD performance with NGD level of approximately -2.8 ns around the center frequencies 1.2 GHz with transmission coefficient of approximately -2.2dB and reflection coefficient better than -15dB. The measured results are in very good agreement with calculated model and simulations.

This paper aims to develop an original circuit theory of inductorless NGD topology. The considered passive cell comprised of resistor and capacitor elements without inductor operates as a bandpass (BP) NGD function. The specifications of NGD functions are defined. Generally, the BP NGD fully lumped circuits available in the literature operate with resonant RLC-network. In the introduced research work, a lumped circuit was first time identified to exhibit the BP behavior without the presence of inductive component. The inductorless BP NGD topology is inspired from the combination of low-pass (LP) and high-pass (HP) NGD passive cells. Therefore, an original LP-HP NGD composite topology is obtained. The identified BP NGD topology is constituted only by passive RC-networks. Then, theoretical development of BP NGD analysis is explored. The inductorless circuit theory starts with the identification of BP NGD canonical form. Then, the expressions of NGD value, center frequency and attenuation in function of RC-network parameters are established. The synthesis equations allowing to determine the resistor and capacitor elements are derived. Proofs-of-concept are designed and prototypes are fabricated to verify the effectiveness of the developed LP-HP NGD composite theory. To validate the developed original circuit theory, two prototypes of RC-network based LP-HP NGD composite were designed, fabricated, simulated and tested. The two prototypes were synthesized with respect to two different NGD center frequencies 13.5 MHz and 22 MHz. As expected, the calculated, simulated and measurement results are in very good agreement with NGD value of about some negative nanoseconds. In the future, the characterized inductorless topology enable to overcome the traditional limitations of RLC-network based BP NGD circuits because of inductance self-effect limitation.