In this article, two types of mixed-mode magic-Ts are proposed, which can realize out-of-/in-phase equal power divisions of multiple mixed modes ports with high isolation, common-mode (CM) rejection, and compact size. The first one, which has five ports, consists of a microstrip T-junction as a single-ended-to-single-ended (SETSE) in-phase power division network, and a microstrip/slotline transition as a balanced-to-single-ended (BTSE) out-of-phase power division network. Through the analysis of scattering matrix, a high isolation is obtained in the mixed-mode magic-T. The second one, which consists of a single-ended-to-balanced (SETB) in-phase power division network based on a microstrip T-junction, and a balanced-to-balanced (BTB) out-of-phase power division network based on a slotline T-junction. Taking advantage of the two types of mixed-mode magic-Ts, a BTSE filtering power divider (FPD) and a BTB FPD are investigated, respectively. The characteristics of the mixed-mode magic-Ts make the proposed configurations unique, since most published balanced FPDs based on complex multi-layer structures to achieve miniaturization. The proposed FPDs are integrated with a pair of asymmetric shorted-stub-loaded resonators (ASSLRs). The expected frequencies and bandwidths of the two differential-mode (DM) passbands can be obtained by turning the parameters of ASSLRs. Meanwhile, multiple transmission zeros (TZs) can be generated to improve the passbands selectivity by employing multiple coupling paths. Besides, a high and broadband CM rejection can be generated by introducing U-type balanced port, which simplifies the design process considerably.

A wideband high-gain terahertz dielectric reflectarray working at 220 GHz is investigated both theoretically and experimentally. The reflectarray unit cell consists of a ground plane and a dielectric block. The reflection phase is obtained by adjusting the height of the block. Using the reflection phase computational algorithm, a dielectric reflectarray composed of 40 × 40 unit cells is designed and fabricated through three-dimensional (3-D) printed technology. Four types of 3-D printed material are measured using the THz time-domain spectroscopy system. It is found that the maximum gain and gain bandwidth of the proposed reflectarray is 31.3 dBi and 20.9%, respectively. Measured results are in reasonable agreement with simulated results. This result is an important step toward the 3-D printed THz dielectric reflectarray above 220 GHz.

An approach for the realization of radiofrequency (RF)/microwave balanced filters with simultaneous differential-mode (DM) and common-mode (CM) two-port-reflectionless behavior for bandpass, quasi-bandstop, and dual-passband applications is reported. These RF filtering components exploit as basic constituent circuit block a type of two-layer broadband magic-T, in which its two-side $/$ coplanar arms are designed as the balanced feeding ports at the top layer. Specifically, two replicas of this wideband magic-T on a microstrip-to-slotline transition are back-to-back connected between their $\bm{\Delta}$ terminals by means of a double-complementary-diplexer-based single-ended low-reflection filtering unit inserted at the bottom layer. In addition, their $\bm{\Sigma}$ accesses are loaded with a resistor to perform the CM RF-power-absorption functionality. Thus, balanced symmetrical-absorptive RF filtering devices for both the DM and CM operations are developed. Such distinctive feature makes this family of microwave filters unique since most of related prior-art balanced filters mainly focused on obtaining the RF-power-absorption property only for the DM or the CM. The theoretical operational foundations and RF design principles of the engineered class of balanced filters with double DM and CM symmetrical-absorptive capabilities are described. Furthermore, their two-layer implementations exemplified in second-and fourth-order bandpass filters (BPFs), a second-order quasi-bandstop filter (BSF), and a second-order dual-band BPF are presented. For experimental-validation purposes, three different prototypes centered around 2 GHz corresponding to single-band BPF and quasi-BSF devices, as well as a dual-band BPF circuit with passbands located at 1.75 and 2.25 GHz, are manufactured and tested. For all these prototypes, 10-dB-referred DM and CM two-port-RF-power-absorption relative spectral ranges larger than 3:1 are measured. Their expected RF filtering functionalities and highly suppressed CM transmission at all frequencies are also verified.

In this paper, a balanced-to-balanced in-phase filtering power divider (FPD) is proposed, which can realize a two-way equal power division with high selectivity and isolation. The design of the proposed FPD is primarily based on microstrip/slotline transition structures and slotline T-junction. A U-type microstrip feed line integrated with a stepped-impedance slotline resonator is adopted at the input and output ports, which makes the differential-mode (DM) responses independent of the common-mode (CM) ones. Meanwhile, superior DM transmission and CM suppression are achieved intrinsically, thereby simplifying the design procedure significantly. By employing slotline resonators loaded with resistors, the isolation between the two output ports can be improved greatly. In addition, a DM passband with a sharp filtering performance is realized by introducing the microstrip stub-loaded resonators (SLRs). By changing the electrical length of the open stub of the SLR, the fractional bandwidth is controllable. In order to verify the feasibility of the proposed design method, two prototype circuits of the proposed FPDs with different bandwidths are fabricated and measured. Good agreement between the simulation and measurement results is observed.

A broadband folded reflectarray antenna (FRA) is presented employing a novel single-layer cross-polarization conversion (CPC) subwavelength element in this letter. The proposed element has a very simple structure and consists of only a square ring resonator loaded with two splits, thereby realizing easy fabrication with low cost. By varying the length of the ring and mirroring the element, a 360° phase change range is achieved with low losses at the center frequency. These characteristics make the proposed configuration unique, as most of the reported FRA elements rely on complex and multilayer structures to realize the broadband CPC. Furthermore, an FRA using the proposed elements is designed and measured at 22 GHz. A good agreement between the simulated and measured results is obtained. The measured results demonstrate that the proposed FRA realizes a 1 dB gain bandwidth of 20.9% and a maximum aperture efficiency of 47.8%.

In this letter, a novel elliptical cylinder dielectric resonator (ECDR) is proposed. By combining a square substrate and two symmetrical ECDRs, an ECDR element is formed, which can effectively achieve the transformation from the linearly polarized incident wave to the circularly polarized (CP) transmitted wave. By adjusting the height of the element, a linear transmission phase range over 360° can be obtained, which can reduce the fabrication difficulty and cost through a 3-D printed technology significantly. Meanwhile, the ECDR element has a low conductor loss in high frequency. Additionally, a CP 3-D printed dielectric transmitarray antenna at the millimeter-wave band is designed by employing the ECDR elements. It is found that the aperture efficiency is up to 40.3%, the 3 dB axial ratio bandwidth is 17%, and the 1 dB gain bandwidth is 13.3%, respectively. The measured results are in good agreement with the simulated ones. This may be the first time that a CP 3-D printed dielectric transmitarray antenna has been reported.