A planar dual-band array with orthogonal circular polarizations (CPs) in the two frequency bands is proposed in this communication. The array is implemented on a single-layer substrate and easy to be extended to the design of a larger array. A new antenna element for such an array is exploited by symmetrically loading stubs on the edges of a square patch. In this communication, two pairs of orthogonal modes of the patch, namely, TM ₁₀ /TM ₀₁ and TM ₃₀ /TM ₀₃ , are excited simultaneously and used to realize different senses of CP radiation in the two bands. An equivalent transmission-line model of this patch is then developed to describe its working principle and design procedure. To validate its effectiveness, a 2 × 2-element array prototype operating at 2.53 and 3.59 GHz is designed and fabricated. Both the left- and right-hand CPs are obtained simultaneously in the dual bands, and the measured results are found to be in good agreement with the simulated ones. The measured radiation gains in the lower and higher bands are 10.8 and 12.5 dBic, respectively.

This article presents an enhanced single-sideband time-modulated phased array (ESTMPA) using modulating pulses with stepped waveforms. Based on the in-phase/quadrature (I/Q) complex modulation technique, this phase-only weighting array generates a scanning beam at the 1st sideband. The proposed modulating pulses realized through a reconfigurable power divider in I/Q time modulator can avoid the power loss from the switches during switch-OFF state and eliminate the maximum undesired sideband-the 5th harmonic in STMPA. As a result, it brings a power spectrum with less undesired sidebands, lower sideband level (-16.9 dB), higher harmonic efficiency (94.96%), and wider allowable signal bandwidth (eight times as wide as that of the conventional time modulated array). To experimentally verify the feasibility of the proposed design, a wideband enhanced I/Q time modulator and its corresponding eight-element ESTMPA are designed and manufactured. A detailed study on the effect of the magnitude and phase deviations in the circuit and the transition period of modulating pulse are presented. The measured results of power spectrum and radiation pattern have a good agreement with the simulated ones.

A novel design concept to enhance the bandwidth of a differential-fed patch antenna using the dual-resonant radiation of a stepped-impedance resonator (SIR) is proposed. The SIR is composed of two distinctive portions: the radiating patch and a pair of open stubs. Initially, based on the transmission line model, the first and second odd-order radiative resonant modes, i.e., TM10 and TM30, of this SIR-typed patch antenna are extensively investigated. It is demonstrated that the frequency ratio between the dual-resonant modes can be fully controlled by the electrical length and the impedance ratios between the open stub and radiating patch. After that, the SIR-typed patch antenna is reshaped with stepped ground plane in order to increase the impedance ratio as highly required for wideband radiation. With this arrangement, these two radiative modes are merged with each other, resulting in a wide impedance bandwidth with a stable radiation pattern under dual-resonant radiation. Finally, the proposed antenna is designed, fabricated, and measured. It is verified in experiment that the impedance bandwidth (|S _dd11 | <; -10 dB) of the proposed antenna has gained tremendous increment up to 10% (0.85-0.94 GHz) with two attenuation poles. Most importantly, the antenna has achieved a stable gain varying from 7.4 to 8.5 dB within the whole operating band, while keeping low-cross polarization.

A low profile differential-fed microstrip patch antenna (MPA) with broad impedance bandwidth is proposed by incorporating a resonant mode of the slot into TM10 and TM12 modes of the patch resonator. Initially, the shorting pins are symmetrically placed underneath the patch so as to push up the resonant frequency of TM10 mode in proximity to that of TM12 mode (f12). After that, the central slot could be employed to excite an additional mode resonating closely to the f12 by increasing the slot length. Additionally, a pair of small circular disks is introduced below the radiating patch for good impedance matching. Finally, the wideband antenna is fabricated and measured to validate the predicted performance. The results illustrate that the antenna has gained a broad impedance bandwidth of about 55% (1.62-2.85 GHz) with three in-band attenuation poles, while maintaining the normal radiation pattern. In particular, a low profile property with the height of about 0.06 free-space wavelength is achieved.

This letter presents a wideband Huygens resonant transmitarray (TA) based on lightweight polyimide (PI) membranes. A three-resonant Huygens structure unit is proposed by introducing additional resonance points for broadening the bandwidth. The unit consisting of two pairs of metal rings and one pair of metal arcs exhibits low transmission loss and covers almost the entire phase range over a wide band from 17.5 GHz to 23 GHz. Moreover, the Huygens units are printed on the PI membranes using screen printing technology. The TA consists of only two layers of flexible PI membranes with a thickness of 0.125 mm. Within the PI membrane, there is an intermediate air layer. A 15×15 TA is designed and fabricated, and experime-ntally demonstrated. The measured 3 dB gain bandwidth of 21.1% from 18.2GHz to 22.5 GHz is achieved. The TA exhibits a peak gain of 24.63 dBi and a maximum aperture efficiency of 39.9% at 20.3 GHz. The weight of the TA is only 5.7 g due to the thin membrane configuration. Therefore, the proposed TA is suitable for the application of satellite antenna and communication systems for its features of wide bandwidth, lightweight, and flexible deployable capability.

Time-modulated array (TMA) antennas, introduce the dimension of time into antenna design to control the radiation patterns and frequency spectral characteristics, thus improve the reconfigurability of array antennas and provide multiple functionalities. They have great application potential in military and civilian fields, such as precision guidance and mobile communication, and are currently a hot spot of academic research. This article provides a review on the fundamentals and applications of TMAs. First, the basic theory and mathematical formulations of TMAs are introduced. Second, the most important applications of TMAs, namely time-modulated phased arrays (TMPA), are discussed from the perspectives of harmonic suppression and harmonic utilization, which are used for single-beam and multibeam radiation. Then, we survey the combination of TMA with various types of novel antenna arrays, such as single-channel digital beamforming (DBF) arrays, frequency diverse arrays (FDAs), and retrodirective arrays, to create new hardware implementation methods and enhance their performance. Next, recent advances in dedicated integrated chips for TMA, which have played a significant role in driving the progress of TMAs from academic research to practical applications, are presented. Finally, the challenges and prospects for TMAs are discussed, including new research directions and emerging application scenarios.