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In recent years, human motion recognition, as an important application of the intelligent perception of the Internet of Things, has received extensive attention. Many applications benefit from motion recognition, such as motion monitoring, elderly fall detection, and somatosensory games. Several existing RF-based motion recognition systems are susceptible to multipath effects in complex environments, resulting in lower recognition accuracy and difficulty in extending to other scenarios. To address this challenge, we propose RF-Motion, a device-free commercial off-the-shelf (COTS) RFID-based human motion recognition system that can detect human motion in complex multipath environments such as indoor environments. And when the environment changes, RF-Motion still has high recognition accuracy, even without retraining. In addition, we use data slicing to solve the problem of discontinuity in the time domain of RFID communication and then use the synthetic aperture (SAR) algorithm to obtain the fingerprint feature matrix corresponding to each motion. Finally, the dynamic time warping (DTW) algorithm is used to match the prior motion fingerprint database to complete the motion recognition. Experiments show that RF-Motion can achieve up to 90% accuracy for human motion recognition in an indoor environment, and when the environment changes, it can still reach a minimum accuracy of 87%.

This letter reports a strategy of full-digital arrays with nonreciprocal transmitting (Tx) and receiving (Rx) beam patterns, for the first time, for 5G/6G wireless communications. The proposed full-digital array contains a smaller number of Rx channels than that of the Tx channels. The unequal number of Tx and Rx channels makes the transmitting and receiving patterns asymmetrical, which would not only release the burden of data processing but also reduce the hardware cost and power consumption of the entire system. Importantly, as compared with conventional large-scale beamforming arrays, the proposed strategy will not deteriorate the range of coverage at an instantaneous time. A 64-element full-digital beamforming array prototype was designed, fabricated, and characterized for a proof-of-concept demonstration.

A novel wideband magnetoelectric (ME) dipole antenna with dual circular polarization and unidirectional radiation is proposed in this letter. The proposed antenna is based on two perpendicular sub-ME dipoles realized by four V-shaped patches and four V-section columns, and each of them is composed of an electric dipole and a magnetic dipole in parallel. Fed by two simple Γ-shaped feeds, 90° phase difference between the electric dipole and the magnetic dipole in each of the sub-ME dipoles is achieved, hence the dual-circularly polarized radiation is generated. Wide impedance bandwidth is obtained in virtue of the two kinds of dipoles being excited simultaneously. The 3 dB axial-ratio (AR) bandwidth is enlarged by optimizing the V-section columns and a circular cavity. Besides, the port isolation is apparently enhanced by adding slits on the patches and elaborating different spacings between each feed and its two-sided columns. Measured results show that the proposed antenna has many appealing properties, such as a unidirectional radiation pattern, an impedance bandwidth (reflection coefficients ≤–10 dB and port isolation ≥ 10 dB) of 51.1% and a 3 dB AR bandwidth of 41.9%.

A 2-D simplified memory polynomial (2D-SMP) model is proposed for concurrent dual-band power amplifiers (PAs) in this letter. The derivation of the proposed model is similar to that of the 2-D modified memory polynomial (2D-MMP) model. The 2D-SMP model consists of an in-band part and a cross-band modulation part without the envelope factors, which exist in the 2D-MMP model. Theoretical analysis shows that it has moderate complexity but higher modeling accuracy than the 2D-MMP model. The simple least square algorithm can be used to extract the model coefficients, and the additional binary search algorithm for the best envelope factor is not needed. The experimental results show that the 2D-SMP model can achieve higher model accuracy and better digital predistortion (DPD) performance than the 2D-MMP model when a dual-band PA is excited by a combined dual-band long-term evolution signal.

In this paper, a simple fast electromagnetic (EM) optimization method for substrate integrated waveguide (SIW) filters is presented. The feature parameter deviations are estimated by direct response approximation based on the feature parameter model with few times quasi-Newton method. The parameter extraction process is more concise than the parameter identification techniques based on the rational polynomial model and can be used for lossless networks as well as lossy networks. The dimension correction is based on the Jacobian matrix which relates the physical dimensions and the feature parameters. An analytical general mapping model for SIW filters is extracted and applied to generate and update the Jacobian matrix for the first time. The extracted model can be directly used for SIW filter design without repeated extraction. This helps to minimize the number of EM simulations and avoid extra work for model extraction. Using general mapping model can overcome the robustness issue introduced by Broyden update methods. The number of EM simulations required to meet the specifications can be significantly reduced. The effectivity and robustness of the proposed method is validated by two design examples: a 10-order SIW Chebyshev filter and a 5-order SIW cross-coupled filter. The proposed method exhibits low complexity, good stability, good convergence speed and the ability to avoid being trapped in local minimum.

In this talk, a brief review on the newly proposed concept of asymmetric millimeter wave (mmWave) massive multi-input and multi-output (MIMO) system for beyond 5G(B5G) and 6G mobile communications is presented, including the system architecture, requirements for integrated circuits (ICs) design etc., and some research advances.

A fast electromagnetic optimization method for hairpin filters using model-based deviation estimation is presented in this paper. An analytical mapping model between the feature parameters and the physical dimensions of the hairpin filters is established. The design dimension errors are converted from the feature parameter deviations by using the Jacobian matrix of the general model. A five order hairpin filter is demonstrated, which converges after six iterations.

This paper presents a large-frequency-ratio shared-aperture antenna with enhanced suppression of cross-polarization. Based on the previously reported topology, the antenna integrates a 3.5 GHz dipole antenna with a 28 GHz 4-element array. The array employs a double-layer dipole element fed by a stripline to counteract the cross-polarization components. Combined with the separate feeding network of the substrate integrated coaxial line, the array can generate a steerable millimeter-wave beam. The experimental results indicate that the antenna has good performances in both frequency bands, including a cross-polarization lower than −24.5 dB.

In this paper, the development of a millimeter-wave hybrid beamforming (HBF) transceiver system for 5G millimeter-wave multiple-input-multiple-output (MIMO) communication is presented. The developed transceiver system is operated at 28-GHz band in the time division duplex (TDD) mode, with 500-MHz signal bandwidth. To implement high beamforming accuracy, a phased-array-based HBF transceiver with high-precision phase shifting network (PSN) at intermediate-frequency (IF)-paths is proposed. The designed PSN has 8-bit phase resolution within 360° range and 0.13-dB amplitude variation. With the use of such low-cost 8-bit PSN, this HBF transceiver system achieves 0.6° beam resolution and a good RF transceiver performance. In addition, under the over-the-air MIMO communication test with two data streams, the error vector magnitude (EVM) of the received signals at two user equipment (UE) is 2.58% and 2.34%. The high-data rate millimeter-wave communication and MIMO performance of this HBF are verified.

A planar circularly polarized substrate integrated waveguide (SIW) stacked patch antenna array consisting of four sequential-rotation (SR) subarrays is presented for $Ka$ -band applications. Antenna element is realized based on a pair of stacked cavities by the combination of a driven patch layer and a parasitic patch layer, which are formed by a shorted square patch and multiple identical stacked square patches, respectively. Each subarray consisting of two pairs of elements, excited by a coplanar waveguide (CPW) network with four metallic vias, is well matched to a novel SIW SR feeding network. A narrow transverse coupling slot, a semiopening resonant cavity, two pairs of inductive vias, and an inductive window are introduced in the SIW-based feeding network to implement functions of phase shifter, impedance matching, and power divider in the two layers. By employing the proposed SR feeding network, the CPW network, and the four subarrays, the excellent performance of the array is realized. To verify the design, a prototype is fabricated and measured, which demonstrates a −10 dB impedance bandwidth of 29.6%, a 3 dB axial ratio bandwidth of 25.4%, and a peak gain of 20.32 dBic.

A 64-channel massive multiple-input multiple-output (MIMO) transceiver with a fully digital beamforming (DBF) architecture for fifth-generation millimeter-wave communications is presented in this paper. The DBF-based massive MIMO transceiver is operated at 28-GHz band with a 500-MHz signal bandwidth and the time division duplex mode. The antenna elements are arranged as a 2-D array, which has 16 columns (horizontal direction) and 4 rows (vertical direction) for a better beamforming resolution in the horizontal plane. To achieve half-wavelength element spacing in the horizontal direction, a new sectorial transceiver array design with a bent substrate-integrated waveguide is proposed. The measured results show that an excellent RF performance is achieved. The system performance is tested with the over-the-air technique to verify the feasibility of the proposed DBF-based massive MIMO transceiver for high data rate millimeter-wave communications. Using the beam-tracking technique and two streams of QAM-64 signals, the proposed millimeter-wave MIMO transceiver can achieve a steady 5.3-Gb/s throughput for a single user in fast mobile environments. In the multiple-user MIMO scenario, by delivering 20 noncoherent data streams to eight four-channel user terminals, it achieves a downlink peak data rate of 50.73 Gb/s with the spectral efficiency of 101.5 b/s/Hz.

A low-profile circularly polarised (CP) antenna with conical-beam radiation pattern is presented. The proposed antenna consists of a monopolar patch antenna fed by a probe in the centre and a ring-shaped array formed by eight modified parasitic patch elements. Two resonant modes of the monopolar patch which connects to a ground plane by a set of conductive shorting vias are utilised to achieve wide impedance bandwidth. A CP conical-beam radiation pattern is formed by loading the designed array. Loop current and slot resonant mode are employed to discuss the operating principle. A parametric study is carried out for the detailed design concept illustration. To verify the design, a prototype has been fabricated and measured, which shows a low profile of 0.059 λ 0 , a maximum gain of 7.45 dBic, a 10-dB impedance bandwidth of 23.1%, a 3-dB axial ratio bandwidth of 9.6% and a good conical-beam radiation pattern.

A low-profile substrate-integrated waveguide (SIW) cavity-based antenna with conical-beam circularly polarized (CP) radiation is presented. Conical-beam CP radiation is obtained by the combination of a radial current source and a loop current source, which are produced by a shorted monopole patch and an annular array, respectively. The proposed annular array configuration is designed by combining multiple identical customized parasitic patch elements arranged around the monopole. Phase compensatory lines and shorted annular ring slots are introduced in the array to tune phase difference of two current sources and to generate in-phase currents on the elements, respectively. All antenna elements are simultaneously excited within a center-fed SIW cavity. In order to fully picture the operating mechanism, we analyze the wide impedance and axial-ratio (AR) bandwidths based on an equivalent circuit model and an electromagnetic theory. Then, parametric studies are carried out for a detailed design illustration. To verify the design, a prototype has been fabricated and measured, which shows a stable conical-beam radiation and good performance including: a low profile of $0.062\lambda _{0}$ , a 10 dB impedance bandwidth of 20.4%, a 3 dB AR bandwidth of 17%, a maximum gain of 8.25 dBic, and an advantage of large ground compatibility.

With the demanding system requirements for the fifth-generation (5G) wireless communications and the severe spectrum shortage at conventional cellular frequencies, multibeam antenna systems operating in the millimeter-wave frequency bands have attracted a lot of research interest and have been actively investigated. They represent the key antenna technology for supporting a high data transmission rate, an improved signal-to-interference-plus-noise ratio, an increased spectral and energy efficiency, and versatile beam shaping, thereby holding a great promise in serving as the critical infrastructure for enabling beamforming and massive multiple-input multiple-output (MIMO) that boost the 5G. This paper provides an overview of the existing multibeam antenna technologies which include the passive multibeam antennas (MBAs) based on quasi-optical components and beamforming circuits, multibeam phased-array antennas enabled by various phase-shifting methods, and digital MBAs with different system architectures. Specifically, their principles of operation, design, and implementation, as well as a number of illustrative application examples are reviewed. Finally, the suitability of these MBAs for the future 5G massive MIMO wireless systems as well as the associated challenges is discussed.

A low-complexity metallic tapered slot antenna (TSA) array for millimeter-wave multibeam massive multiple-input multiple-output communication is proposed in this paper. Good beamforming performance can be achieved by the developed antenna array because the element spacing can easily meet the requirement of half-wavelength in the H-plane. The antenna element is fed by a substrate-integrated waveguide, which can be directly integrated with the millimeter-wave circuits. The proposed TSA is fabricated and measured. Measured results show that the reflection coefficient is lower than −15 dB Voltage Standing Wave Ratio ((VSWR) ≤ 1.45) within the frequency range from 22.5 to 32 GHz, which covers the 24.25–27.5-GHz band proposed by International Telecommunications Union (ITU) and the 27.5–28.35-GHz band proposed by Federal Communications Commission (FCC) for 5G. The gain of the antenna element varies from 8.2 to 9.6 dBi over the frequency range of 24–32 GHz. The simulated and measured results also illustrate good radiation patterns across the wide frequency band (24–32 GHz). A $1\times 4$ H-plane array integrated with the multichannel millimeter-wave transceivers on one PCB is demonstrated and excellent performance is achieved.

A low-profile broadband circularly polarised patch antenna with four parasitic patches (PPAs) is presented. The proposed antenna has the advantages of broadband reflection coefficient, broadband axial-ratio (AR) performance and low-profile structure. First, a broadband feed network is employed to realise wide reflection coefficient and AR bandwidths. To enhance the gain performance, two types of PPAs employing parasitic technique scheme are designed and compared. Then, resonance mode theories and simulated current distributions are utilised to explain the gain enhancement issue within the operating frequency. Furthermore, the designed antenna is optimised carefully by adopting parametric analysis before fabricating and measuring. Finally, the gain enhancement is verified by the measured results of designed antenna possessing the characteristic of both high-gain and low-profile structure. The results indicate that the adding PPAs scheme and the resonance mode analysis are helpful on research of this type of patch antenna.

This study describes a new low-profile broadband circularly polarised (CP) antenna. The antenna comprises a directly fed CP patch of new configuration that excites four square parasitic patches in an upper layer and an L-shaped parasite alongside the excited patch. This arrangement provides an improvement in axial ratio (AR) bandwidth over existing configurations, having an impedance bandwidth of 38% (return loss > 10 dB), with an AR bandwidth of 28.1% (AR

A 2-D-canonical piecewise linear (2-D-CPWL) function-based behavioral model is proposed for concurrent dual-band power amplifiers (PAs) in this letter. The model is derived from the Volterra-based 2-D-modified memory polynomial (2-D-MMP) model by replacing the high-order terms with CPWL and it can provide a lower complexity than the 2-D-MMP model and some existing CPWL-based dual-band models. The least-square algorithm can be used to extract the model coefficients. Experimental results show that the proposed 2-D-CPWL model can achieve nearly the same model accuracy and digital predistortion performance compared with the 2-D-MMP model, when a dual-band PA is excited by a combined dual-band long-term evolution signals.

A low phase noise X-band oscillator based on the bandpass response power divider in single-layer substrate integrated waveguide (SIW) technology is presented in this letter. The power divider is embedded in the SIW filter; therefore, lower insertion loss and more compact area size can be realized than those using the independent design of both components. To achieve better phase noise performance, transmission zeros are introduced by cross coupling through the resonant cavities to increase peak group delay. In addition, by placing external feeding at the center of cavity edge, the second harmonic can be suppressed efficiently. The measured results verify the performance of the proposed bandpass response power divider and show that the phase noise of the oscillator can achieve −143.3 dBc/Hz at 1-MHz offset frequency.

In this paper, an 8-element linear antenna array with substrate integrated waveguide (SIW) feeding network is proposed. The operating frequency is 28 GHz, and the bandwidth is 2 GHz. The antenna array element contains 8 printed dipoles in half-wavelength spacing, and the feeding network is composed of a 1-to-8 SIW power splitter and a SIW filter. The connection between the feeding network and the feeding source is implemented by coplanar waveguide-SIW (CPWG-SIW) transition. The measurement results show that the proposed antenna array has an impedance bandwidth of more than 2 GHz, with the reflection coefficient lower than −14 dB in the frequency band of 27–29 GHz, and the half power beam width (HPBW) of H-plane and E-plane are about 108.8 ° and 14.5°, respectively. The proposed antenna array is suitable for 5G millimeter-wave systems.

A novel coupling topology of substrate integrated waveguide filter with unequal-length slots is proposed. This filter consists of two resonators and a pair of unequal-length slots, which can be considered as two-stage bypass coupling resonators. There exist two resonant modes (TE101 and TE102) in each resonator. TE101 mode is coupled by the long slot, and TE102 mode is coupled by the short slot, which can achieve two resonant modes couplings between adjacent cavities. This structure uses TE102 mode to design the centre frequency of the passband and regards TE101 mode as spurious response. As a result, this filter leads to three transmission zeros (TZs), two TZs locate above the passband and one TZ is below the passband. The filter is fabricated and measured, the measured results agree well with simulated ones.

This letter proposes a broadband high isolation and high power compact single pole double throw (SPDT) switch. In contrast to the traditional structure of grounded source pad, the source pad of the shunt-stacked FET is absorbed into the transmission line, and the drain of the shunt-stacked FET is grounded to a via-hole. This structure helps to extend the operation bandwidth and reduce the chip size. The proposed SPDT switch is composed of six shunt-stacked FET units on each branch with this novel structure. Stacked FETs technique increases the voltage handling by placing two FETs in series. It has been fabricated using a commercial $0.1~\boldsymbol {\mu }\text{m}$ GaAs pseudomorphic high-electron-mobility transistor (PHEMT) process. The chip size is $1.2\times 0.8$ mm2. The switch operates at the frequency range of 35–70 GHz with less than 3 dB insertion loss and more than 40-dB isolation. The switch demonstrates a 1 dB insertion loss compression with a 20.2 dBm input power at 31 GHz. The isolation is larger than 30 dB from 10 to 95 GHz. To the best of the authors’ knowledge, this broadband isolation performance is among the best of the reported SPDT switches.

This study presents a 1 × 8 active transmitting array based on frequency shiftable vector modulator (FSVM) module. The FSVM module, which should be treated as a separate module, is capable of flexibly shifting the operating band of the vector modulator (VM) while not deteriorating the passing signal. By employing this module, a 1 × 8 active transmitting array with a radio frequency (RF) path beamforming structure is developed and fabricated. Measured results validate the concept of the proposed FSVM module and demonstrate the high-precision beam scanning capability of the active array.

This letter presents a simple and efficient multibeam radio-frequency (RF) beamformer for wideband linear frequency modulation waveform transmission. A time-varying weighting method instead of the true time delay technique is proposed. The process of beamforming weighting is implemented by quadrature modulators in the transmit (TX) path. As the RF operation frequency changes, the modulating phase-shift coefficients in baseband vary in time series. Since this beamformer is easy to perform at the element level, the simultaneous and independent TX multiple beamforming has become achievable. Moreover, the quality of the output signal and the process of wideband equalization among multiple channels are considered. The channel imbalances over a broad frequency range are compensated by time-varying predistortion coefficients. To validate the practical feasibility of this method, a prototype system with four-element antenna array is designed and tested. Single-beam and simultaneous two-beam patterns steering between ± 30° over 500 MHz at the center frequency 2.45 GHz have been demonstrated experimentally.

This letter introduces a Ku band continuously tunable filter with one parameter. The proposed filter is implemented using substrate integrated waveguide (SIW) technology and has a simple and symmetrical structure. The tunability of the circular resonator is a kind of mechanical tuning, achieved by the different distance between moving copper column and the center of the circular cavity. Location of moving distance has an approximately linear relation with the dominant cavity resonance frequency. The single circular cavity has a tuning range of 12.6–15.0 GHz. The fabricated filter is made up of two cavities and has a frequency tuning ratio percentage of 19.2% compared with the center frequency 13.825 GHz. The insertion loss is between 1.7 and 2.8 dB.

A band-limited canonical piecewise-linear function (CPWL)-based model is proposed for wideband power amplifiers (PAs). The model has a similar structure of the band-limited dynamic deviation reduction (DDR) Volterra series model but without high-order terms and long finite impulse response filters, which are replaced by CPWL. The model has lower complexity and more flexibility than the band-limited DDR Volterra series model and the model parameters can be estimated by the least-square method. Experimental results show that the proposed model nearly gives the same normalized mean square error and digital predistortion performance as the band-limited Volterra series when a wideband PA is excited by a 5-carrier long-term evolution advanced signal of 100-MHz bandwidth.

In this paper, we discuss the limitations of phased arrays for 5G massive MIMO systems. The multibeam radiation patterns produced by a full phased array, a phased array with fixed sub-arrays, and a phased array with segmented phased sub-arrays are compared via illustrative examples. In fact, conventional phased array can only improve the link gain or the coverage, but couldn't enhance the capacity. Besides, the requirement of a huge amount of phase shifters makes the phased array not an ideal candidate for 5G massive MIMO base stations. Instead, the digital multibeam antennas would be more appropriate which are able to overcome these shortcomings.

A design of broadband multiple-input and multiple-output(MIMO) millimeter wave transceiver system is developed in this paper. The millimeter wave(mm-wave) transceiver system includes the ultra-wide bandwidth baseband data processing unit (BAP), intermediate frequency module (IF), mm-wave frontend and the power module. The developed system can support 4×4 MIMO configuration. The mm-wave frequency of the transceiver is 28 GHz and the channel bandwidth is up to 500 MHz. The architecture adopts an intermediate frequency of 2.75 GHz, and the receiving link adopts digital intermediate frequency sampling. Meantime, the launch link uses a secondary frequency conversion structure. Link tests and system tests with the antenna arrays are conducted. The experiment results show that the developed system works well and provides hardware basis for future mm-wave broadband access applications.

Implementation of a wideband RF transmitter is reported in this paper. In order to achieve the best performance, a super heterodyne architecture with RF of 14GHz and IF of 1.6GHz is employed, and the signal bandwidth is 1000MHz. Finally, measurement results of the transmitter are provided and the overall system performance indicated by EVM (Error Vector Magnitude) with 100MHz signal bandwidth (maximum digital modulation bandwidth available from Agilent with up to date measurement method) is reported.

This paper presents the design of RF receiver operating in 5.0GHz to 6.0GHz band for high throughput IEEE 802.11ac system. A double-conversion super-heterodyne architecture with IF of 1.05GHz is employed and the maximum bandwidth is 80MHz. Measurement results show that the receiver has excellent performance. The noise figure is about 4.6dB and the gain flatness over any 80MHz bandwidth is less than 1.8dB. In addition, it achieves a wide dynamic range from −80dBm to 5dBm. For 80MHz 256-QAM 802.11ac signal, the EVMs at 5.15GHz, 5.45GHz and 5.85GHz are 1.02%, 0.86% and 0.86% respectively.

This paper describes a 4-element dual-polarized aperture-coupled microstrip patch antenna array with wide bandwidth, high isolation and low cross-polarization levels for a radar and communication integration system. This antenna is composed of two substrate layers and the air layer. The radiation patch is fed by two H shaped apertures. The measured impedance bandwidth is over 20.4% at S-band. The isolation between two polarization ports is better than 45dB and the cross-polarization levels in E and H planes are better than −23dB.

This paper designed and fabricated a 1×4 ultra-wideband (UWB) Vivaldi antenna array for a phased-array radar system. Vivaldi antenna array is a common solution in applications which require broad bandwidth over several octaves and wide scan volume. The measured impedance bandwidth of the four antenna elements are over 2.25:1 with voltage standing wave ratio (VSWR)

These paper proposes a Ka-band quadruple filter with coplanar waveguide (CPW) line to implement negative cross-coupling structure, which can obtain a single pair of transmission zeros (TZs) to improve stopband performance. Position of TZs can be adjustable according to the length of the CPW line, which decides the negative cross-coupling coefficient between the nonadjacent cavities. Compared to the quadruple filter without CPW line, this structure shows steeper attenuation characteristic. The two SIW filters are designed at the same center frequency of 28GHz with the same bandwidth of 2GHz. The measured frequency responses agree well with the simulated results.

In this paper, a wideband circularly-polarized patch antenna is presented. The patch is fed by four probes arranged by sequential rotation arrays, the four probes are connected to a feed network comprising of a pair of broadband 90° phase shifter and Wilkinson power divider. The proposed antenna shows a compact low profile, wide axial-ratio (AR) bandwidth, wide reflection coefficient bandwidth, as well as easiness of integration. To verify the simulation performance of the design, the antenna has been fabricated and measured. The measured results show that the impedance bandwidth S11< −10 dB of 70.2%, the 3-dB AR bandwidth of 63.1%, the gain is 6.65 dBi at 5.8 GHz, and the 3-dB gain bandwidth is 39.3% from 4.9 to 7.3 GHz. Good agreement is observed between simulation and measurement by comparison.

The design of a Q-band superheterodyne transceiver for millimeter wave (mm Wave) communication is presented in this paper. The center frequency is 44.82 GHz with the channel bandwidth of 500 MHz. The overall system is divided into mm Wave frontend, the immediate frequency (IF) module and the local oscillator (LO) for IF. These three parts are implemented and tested respectively to ensure the performance. In order to evaluate the system performance in practical wireless communication, a testing platform constituted of a transmitter and a receiver is established. A 16QAM signal and a QPSK signal with the data rate of 400 Ms/s are transmitted by the transmitter, through 2-meter space attenuation, received and converted to baseband by the receiver. The demodulated baseband signals have the signal-to-noise ratio (SNR) of about 20 dB. The experimental results are satisfactory for such wide bandwidth and such high frequency.

The design of a cross-coupled substrate integrated waveguide (SIW) filter with three transmission zeros (TZs) for 28 GHz millimeter wave application is presented in this paper. The filter consists of an oversized cavity and a cascaded triplet (CT). The oversized cavity introduces a TZ in the lower stopband by the cross-coupling between higher/lower order modes. The location of this TZ can be adjusted by changing the offset distance of input/output ports to the center of the cavity. The CT section consist of three cavities. By analyzing the phase model, two TZs in the upper stopband are predicted, which is verified by the simulation. Measured results show that the filter has a center frequency of 28 GHz with the bandwidth of 600 MHz. The minimum insertion loss in the passband is 2.7 dB, and the return loss is better than 15 dB. Due to the TZs, the SIW filter has sharper transition performance at both lower and upper sidebands, good selectivity is achieved.